Transition Metal Manganese and Main Group Gallium 
 Complexes as Catalysts for Alkene Epoxidation 
 
by 
 
Wenchan Jiang 
 
 
 
 
A dissertation submitted to the Graduate Faculty of 
Auburn University 
in partial fulfillment of the 
requirements for the Degree of 
Doctor of Philosophy  
 
Auburn, Alabama 
May 04, 2012 
 
 
 
 
Approved by 
 
Christian R. Goldsmith, Assistant Professor 
David M. Stanbury, Professor 
Anne E. V. Gorden, Associate Professor 
Eduardus C. Duin, Associate Professor 
 
Department of Chemistry and Biochemistry 
ii 
Abstract 
 
 
Epoxides are important organic synthesis precursors and widely used in industry. Alkene 
epoxidation has been under extensive investigation over decades. Synthetic models have been 
established for catalytic epoxidations, employing transition and main group metals. 
Epoxidation proceeds either through high valent metal-oxo species and/or a Lewis acid 
mechanism for oxygen transfer to substrate. Specifically, by high valent metal-oxo species, 
Jacobsen?s catalyst (MnIII-salen) and non-porphyrin MnII complexes can catalyze 
enantioselective epoxidation and electron-rich terminal alkene epoxidation respectively. 
Sharpless catalyst (TiIV-tartrate) and Al3+ centered complexes catalyze epoxidation through 
Lewis acid mechanisms. 
Manganese complexes with phenanthroline derivatives ([Mn(R-phen)2Cl2]Cl, R = NH2, 
Me, H, Cl, NO2) as catalysts are reported. The MnII complexes catalyze epoxidation of a 
variety of substrates with electron-rich alkenes being favored. The installation of functional 
groups on the 5-position of phenanthroline ligand plays important roles in influencing 
catalyst reactivity. The more electron-donating the functional group is, the more reactive it is. 
The reactivities with different substituent groups on the ligand have been correlated with 
Hammett constant, which showed a good linear relationship. EPR and spectroscopic studies 
indicated possible involvement of high valent MnIV-oxo species which decays quickly under 
experimental conditions. 
Gallium complexes are effective catalysts as well. [Ga(phen)2Cl2]Cl is reported to be the 
first homogeneous gallium catalyst for alkene epoxidation with peracetic acid. Compared 
with other group 13 metals, the activity of [Ga(phen)2Cl2]Cl is high with low loading of 1%. 
The epoxide is the only product, indicating good selectivity. Furthermore, six gallium(III) 
complexes with N-donor ligands were synthesized to study the mechanism of 
Ga(III)-catalyzed olefin epoxidation by peracetic acid. Although the complexes with 
relatively electron-poor phenanthroline derivatives display faster initial reactivity, the Ga(III) 
complexes with the polydentate pyridylamine ligands appear to be more robust, with less 
noticeable decreases in their catalytic activity over time. The more highly chelating trispicen 
and tpen are associated with markedly decreased activity. 
iii 
Acknowledgement 
 
 
This dissertation is completed under the supervision of Prof. Christian Goldsmith. I am 
very grateful for his help all through these years. As my advisor, he has set up an example for 
me about how to pursue science achievement in a hard working and intellectual way. I leant a 
lot from his expertise in chemistry. I owe thanks to Prof. David Stanbury, who taught me in 
two advanced inorganic courses and shared his profound knowledge in helpful research 
discussion. I extend my thanks to Prof. Anne Gorden, who taught me organic chemistry in my 
first year and gave me suggestions in my oral defense. I also want to thank Dr. John Gorden 
who guided me through all of my crystal data collection and analysis. I am indebted to Prof. 
Evert Duin who taught me biochemistry and helped with EPR experiments and data analysis, 
and Dr. Yonnie Wu for his assistance with MS experiments and interpretation. I am thankful 
to Prof. William Robert Ashurst for spending his precious time serving on the committee and 
providing advice on this dissertation. I appreciate their help and care. I will always remember 
the friendship I got in my lab with all lab mates Roger (Yu) He, Qiao Zhang, and Meng Yu. 
I would like to thank my fianc?e Wenting (Lucia) Wang, who moved from Boston to be 
with me in Auburn and has been supportive all through even during my toughest time. Last 
but not least, I dedicate this dissertation to my parents, without their support and 
encouragement I wouldn?t even have arrived in the United States to pursue my Ph.D. degree. 
iv 
Table of Contents 
 
 
Abstract??????????????????????????????..?ii 
List of Tables ?????????????????????????????vi 
List of Figures???????????????????????????..vii 
List of Schemes????????????????????????????..x 
Chapter 1 Review of Alkene Epoxidation Catalyzed by Main Group and Transition 
Metal Complexes??????????????????????...1 
 1.1 Value and Industrial Production of Epoxides ???????.???2 
 1.2 Development of Alternative Catalysts for Alkene Epoxidation???..2 
     1.2.1 Jacobsen?s Catalyst??????????????..???.3 
     1.2.2 Manganese Complexes with Neutral, Polydentate N-Donors?..9 
 1.2.3 Non-Heme Iron Complexes????????????...?12 
 1.2.4 The Sharpless Catalyst???????????????...15 
 1.2.5 Homogenous Aluminum Catalysts???????...???..18 
 1.3 Summary ???????.????????????????.20 
 References.?????????????????????.???.21 
Chapter 2 Alkene Epoxidation Catalyzed by Manganese Complexes with 
Electronically Modified 1,10-Phenanthroline Ligands ??.???.??25 
 2.1 Introduction ????????????????????.?.....26 
 2.2 Experimental ??.???????????????????...27 
 2.3 Results ??????.??????????????????.30 
 2.4 Discussion ????.??????????????????...32 
iv 
 2.5 Conclusions ????.??????????????????.35 
 References ????????????????????????..37 
Chapter 3 A Homogeneous Gallium(III) Compound Selectively Catalyzes the 
Epoxidation of Alkenes ???????????????????..39 
 3.1 Introduction ??????????.????????????.40 
 3.2 Experimental ?????????????????????....40 
 3.3 Results and Discussion ??????????????????.44 
 3.4 Conclusions ???????????????????.???.55 
 References ????????????????????????..56 
Chapter 4 Selective Epoxidation of Electron-Rich Alkenes Catalyzed by a Series of 
Gallium(III) Compounds ???????????????????58 
 4.1 Introduction ??????????????.????????.59 
 4.2 Experimental ??????????.???????????...60 
 4.3 Results ??????.????????????????.??66 
 4.4 Discussion???????????????????????77 
 4.5 Conclusions ?????????.?????????????.82 
 Appendix?????????????????????????.83 
 References ????..??????????????????...?.99 
 
 
 
vi 
  List of Tables 
 
 
Table 1.1 Asymmetric epoxidation of representative olefins by Jacobsen?s catalyst.........4 
Table 1.2 Epoxidations catalyzed by [MnII(R,R-mcp)(CF3SO3)2] with PAA????.......10 
Table 1.3 Epoxidations catalyzed by [Fe(mep)(CF3SO3)2]????????????..13 
Table 1.4 Summary of epoxidation scope catalyzed by Beller?s in situ FeIII complex ?...14 
Table 1.5 Selected asymmetric epoxidation of allylic alcohols??????????..17 
Table 1.6 Epoxidation of ?, ?-unsaturated ketones by [Al(H2O)6]3+/H2O2 ????...?..19 
Table 2.1 Yields of epoxides for Mn(II)-catalyzed olefin oxidation by PAA ???...?. 29 
Table 3.1 Selected crystallographic data for [Ga(phen)2Cl2]Cl ???...??..???.....43 
Table 3.2 Bond lengths (?) and bond angles (?) for [Ga(phen)2Cl2]+?..??................?46 
Table 3.3 Yields/turnover numbers of gallium(III) catalyzed alkene epoxidation reactions by various grades and amounts of PAA ???.????????????..48 
Table 3.4 Yields of epoxide products (%) in control reactions ????.??????..49 
Table 3.5 Summary of ICP-OES analysis ??????????????.???.?.51 
Table 4.1 Selected crystallographic data for [Ga(bispicen)Cl2]Cl (1) and [Ga(trispicen)Cl](GaCl
4)(Cl) (7)??????????????????..71 
Table 4.2 Alkene Conversions/Yields of Epoxides (%) of Reactions Catalyzed by 1-6?.73 
Table A1 Selected crystallographic data for [Ga(trispicen)Cl]Cl2?????????..83 
  
 
vii 
List of Figures 
 
 
Figure 1.1 Structure of the prototypical Jacobsen catalyst ?????...?.???..4 
Figure 1.2 The molecular structure of the R,R-mcp ligand and the crystal structure of [MnII(R,R-mcp)(CF
3SO3)2]???????????..?????.?..8 
Figure 1.3 Illustration of the mep ligand (left) and the crystal structure of dinuclear [Fe
2(?-O)(?-CH3CO2)(mep)2] cation???????...?????.....12 
Figure 1.4 The dimeric structure of the Sharpless catalyst??????????.16 
Figure 2.1 Epoxidation of cyclooctene by peracetic acid catalyzed by [Mn(NO
2-phen)2Cl2] in MeCN at 0 oC under N2.????.?????31 
Figure 2.2 X-band EPR spectra of a solution of 1.1mM [Mn(NO2-phen)2Cl2] in 3:2 MeCN/CHCl
3 ??????????????????..????.32 
Figure 2.3 Plot of the reaction yields (as assessed at 1 h) for the oxygenation of each alkene as a function of the ?
P value of the 5-substituent on the catalyst?s 
phenanthroline ligands ???..??????????????.?..34 
Figure 3.1 ORTEP representation of the cation [Ga(phen)2Cl2]+ ???????..45 
Figure 3.2 Yield of cyclohexene oxidation by 2 equiv of PAAR as a function of time???????????????????????????52 
Figure 3.3 Mass spectrometric analysis of the reaction between cyclooctene and two equiv. of PAA
R at t = 5 s (top) and t = 60 min (bottom) ????.??.53 
Figure 4.1 ORTEP representation of the cation [Ga(bispicen)Cl2]+?.?..................70 
Figure 4.2 ORTEP representation of the dication [Ga(trispicen)Cl]2+????...?71 
Figure 4.3 Yields of alkene epoxidations by PAAR catalyzed by the bispicen complex 1 as a function of time????????????.???????..75 
Figure 4.4 Yields of alkene epoxidation by PAAR catalyzed by the 1-6 and [Ga(phen)
2Cl2]Cl as a function of time?????????????.76 
Figure 4.2 Yield of epoxides by Ga(bispicen)Cl3 as a function of time ???...?.67 
Figure A1 ORTEP representation of [Ga(trispicen)Cl]Cl2?MeCN?3H2O grown from a solution of [Ga(tpen)Cl
2]Cl in MeCN?????????????82 
viii 
Figure A2 Mass spectrum (ESI) of [Ga(tpen)Cl2]Cl??????????..??83 
Figure A3 1H NMR spectrum of 1 in CD3OD at 294 K???????????.84 
Figure A4 13C NMR spectrum of 1 in CD3OD at 294 K???????????84 
Figure A5 IR spectrum of 1??????????????????????85 
Figure A6 1H NMR spectrum of 2 in CD3OD at 294 K??????????.....85 
Figure A7 13C NMR spectrum of 2 in CD3OD at 294 K???????????86 
Figure A8 IR spectrum of a powder sample of 2????????..?????.86 
Figure A9 IR spectrum of a crystalline sample of 7???????????.?..87 
Figure A10 1H NMR spectrum of 3 in CDCl3 at 294 K?????????...??87 
Figure A11 1H NMR spectrum of 3 in CD3CN at 294 K???????????.88 
Figure A12 13C NMR spectrum of 3 in CDCl3 at 294 K???????????..88 
Figure A13 IR spectrum of a powder sample of 3??????.???????..89 
Figure A14 1H NMR spectrum of 4 in CD3OD at 294 K???????????.89 
Figure A15 13C NMR spectrum of 4 in CD3OD at 294 K?????...?????.90 
Figure A16 IR spectrum of a powder sample of 4???...??????????90 
Figure A17 1H NMR spectrum of 5 in DMSO-d6 at 294 K??????????.91 
Figure A18 1H NMR spectrum of 5 in CD3OD at 294 K???????????.91 
Figure A19 13C NMR spectrum of 5 in DMSO-d6 at 294 K??..???????.92 
Figure A20 IR spectrum of a powder sample of 5???????.??????..92 
Figure A21 1H NMR spectrum of 6 in DMSO-d6 at 294 K?????.?????93 
Figure A22 13C NMR spectrum of 6 in DMSO-d6 at 294 K????????...?.93 
Figure A23 IR spectrum of a powder sample of 6????????...?????94 
ix 
Figure A24 The yields of the organic products of [Ga(bispicen)Cl2]Cl-catalyzed cyclohexene oxidation by PAA
R over time???????.????..94 
Figure A25 Mass spectrum (ESI) of the gallium species present in solution 3 h after 
the beginning of the cyclohexene epoxidation reaction catalyzed by 1?95 
Figure A26 Mass spectrum (ESI) of the gallium species present in solution 3 h after the beginning of the cyclohexene epoxidation reaction catalyzed by 
2??..?????????????????????????.96 
Figure A27 Mass spectrum (ESI) of the gallium species present in solution 3 h after 
the beginning of the cyclohexene epoxidation reaction catalyzed by 3....97 
 
x 
List of Schemes 
 
 
Scheme 1.1 Substituent effects on enantioselectivity ???????????...???.5 
Scheme 1.2 Possible pathways for epoxidation catalyzed by Jacobsen?s compound ?..?.6 
Scheme 1.3 Hammett plots depicting enantiomeric ratios of epoxides generated with catalysts with various electronically modified ligands ???...??.?.??.7 
Scheme 1.4 Parallel Lewis acid and redox pathways for [Mn(salen)]+ catalyzed 
epoxidations?????????????????????????..9 
Scheme 1.5 Possible mechanistic pathways for Mn(II)-catalyzed olefin epoxidation?.....12 
Scheme 1.6 Proposed catalytic cycle for non-heme iron catalyzed epoxidation????..15 
Scheme 1.7 Proposed mechanism for Sharpless epoxidation (E refers to ester group)?...18 
Scheme 1.8 Proposed mechanism for epoxidation catalyzed by [Al(H2O)6]3+???..?..20 
Scheme 2.1 Illustration of Mn(R-phen)2Cl2 complexes ?????????????..27 
Scheme 2.2 Mn(R-phen)2Cl2 catalyzed epoxidation reaction ??????????.?.27 
Scheme 2.3 Substrate used in Mn(R-phen)2Cl2 epoxidation ????????.??..?31 
Scheme 3.1 Illustration of epoxidation catalyzed by [Ga(phen)2Cl2]Cl ????.??.....40 
Scheme 3.2 Proposed Sharpless type mechanism ????.??????????..?54 
Scheme 4.1 Neutral N-donor ligands ????????????????...................59 
Scheme 4.2 Possible solution structures of 2?????????????????....67 
Scheme 4.3 Proposed solution structure of 3??????????..???????.68 
Scheme 4.4 Possible conformations of the phen ligands in complexes 4 and 5????...69 
Scheme 4.5 Illustration of possible mechanism for the epoxidation reactions?????.79 
 
1 
 
 
 
 
 
Chapter 1 
Review of Alkene Epoxidation Catalyzed by Main Group and 
Transition Metal Complexes   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
1.1 Value and Industrial Production of Epoxides 
Epoxides are valuable for their capacity to be converted into a wide range of useful 
functional groups. Ethylene oxide and propylene oxide are particularly vital to industry. 
Ethylene oxide is a key precursor for ethylene glycol and surface-active agents.1 Further 
polymerization of ethylene glycol leads to polyethylene glycol for detergent use.2 Propylene 
oxide is used in the preparation of polyurethane-based plastics. Certain medicinal compounds 
are either prepared via epoxide intermediates or are themselves epoxides. The HIV protease 
inhibitor indinavir is made from 3,4-epoxytetrahydrofuran.3 The antibiotic 
(1R,2S)-(-)-(1,2)-epoxypropyl phosphonic acid is prepared by the epoxidation of 
cis-1-propenylphosphonic acid.4-5  
Industrial epoxidation relies heavily on heterogeneous catalysts to accelerate the oxidation 
of alkenes by dioxygen or other oxidants. In the industrial preparation of ethylene oxide, 
ethylene is directly oxidized with air or pure oxygen at 230-280 oC under 10-35 atm in a 
packed-bed, multitubular reactor.6-7 Generally, these systems use cesium as a promoter and 
silver supported on ?-Al2O3 as a catalyst.8-9 The activity relies on silver?s ability to rapidly 
adsorb and desorb oxygen.10-11 Gold has also been used as a catalyst, albeit on different solid 
supports such as titanium/silicon.12 Propylene oxide is often produced using a gold catalyst 
supported on a titanium-containing silicate mesoporous material, with barium serving as a 
promoter.13 These reactions have several disadvantages, including the cost of the catalysts, 
the necessity of high reaction temperatures and pressures, and substantial side-reactivity. The 
high reaction temperatures, in particular, preclude the use of these systems for the production 
of more thermally sensitive epoxides. 
 
1.2 Development of Alternative Catalysts for Alkene Epoxidation 
Much recent research in the catalysis of olefin epoxidation reactions is directed at 
identifying and developing cheaper alternatives to the aforementioned silver and gold species 
that can speed the oxidation of alkenes under milder conditions. Recently investigated 
3 
catalysts are remarkably diverse and include both main group and transition metal complexes. 
Boron,14 arsenic,15-16 selenium,17-19 silicon,20 and aluminum21 compounds have been reported 
to catalyze the epoxidation of alkenes by H2O2.  
Transition metal complexes have been explored more thoroughly. The successful catalysts 
can be further classified into two categories, based on whether they contain early or late 
transition metal ions. In the catalysts that contain early transition metals, such as 
molybdenum,22-25 vanadium,26-29 zirconium,30 and titanium,31-34 the metal ions are believed to 
remain in their highest possible oxidation states during the alkene epoxidation. The metals are 
believed to accelerate oxygen atom transfer from a metal-oxidant adduct to the substrate by 
acting as Lewis acids. Late transition metal species used to promote the oxidation of alkenes 
to epoxides include manganese35-42 and iron complexes.43-45 The proposed mechanisms for 
alkene epoxidation involving these more redox-active metals generally posit higher valent 
intermediates, such as MnV=O species, as the active oxidant.46 
Although O2 is the most desirable oxygen source due to its ready availability and low cost, 
it isn?t commonly used in specialty epoxidation reactions because of the high free energy 
barrier for its activation and its involvement in autoxidation-related radical side-reactions.47 
Because of these drawbacks, two-electron terminal oxidants, such as hydrogen peroxide 
(H2O2), isodosylbenzene (PhIO), sodium hypochlorite (NaOCl), meta-chloroperoxybenzoic 
acid (m-CPBA), N-methyl-morpholine-N-oxide,38 dimethyldioxirane,48 or peracetic acid 
(PAA),42 are used instead. 
The remainder of this Chapter will focus on five specific classes of homogeneous catalysts 
for alkene epoxidation. These have been chosen due to their relevance to the material 
presented in Chapters 2-4. 
1.2.1 Jacobsen?s Catalyst 
Jacobsen?s catalyst consists of a MnIII-salen compound (Figure 1.1) and promotes the 
enantioselective epoxidation of non-functionalized olefins by either PhIO or NaOCl.49-51 
Sample illustrative reactions are summarized in Table 1.1. 
4 
N N
O O
MnIII
+
 
Figure 1.1 Structure of the prototypical Jacobsen catalyst37 
   
 
Table 1.1 Asymmetric epoxidation of representative olefins by Jacobsen?s catalysta 
entry olefin substrate yield (%)b ee (%)c equiv of catalyst required for complete reaction 
1 Ph Me 84 92 0.04 
2 Mep-ClC6H4  67 92 0.04 
3 
O
 
72 98 0.02 
4 
O
NC  
96 97 0.03 
5 
O
O
 
63 94 0.15 
6d Ph CO2Me 65e 89 0.10 
aReactions were run at 4 ?C in CH2Cl2 with 0.25 mmol catalyst and 12.5 mmol substrate. 
bIsolated yield based on olefin. cEnantiomeric excess. dReaction carried out in the presence of 
0.4 equiv of 4-phenylpyridine N-oxide. eYield determined by GC. All data are from reference 
35. 
   
5 
Several trends were noted in the studies of Jacobsen?s catalyst and its close derivatives. 
First, electron-donating and withdrawing substituents on substrates influence both the 
cis/trans selectivity and the rate of the reaction, as summarized in Scheme 1.1. With the more 
electron-rich alkenes, the cis-epoxide product forms preferentially. It is hypothesized that 
electron-withdrawing groups stabilize radical intermediates that can form when the substrate 
binds to the MnV-oxo center. This facilitates C-C bond rotation necessary for the formation of 
trans-epoxides (Scheme 1.2). 
 
 
 
CO2R
5% Jacobsen catalystCH2Cl2, 4?C
O
Ar CO2R
O
Ar CO2R
+
X
 
Scheme 1.1 Substituent effects on stereoselectivity 
 
6 
 
Scheme 1.2 Possible pathways for epoxidation catalyzed by Jacobsen?s compound46 
 
The cis/trans ratios of the stilbene oxides produced by the oxidation to stilbene by various 
iodosylbenzene derivatives were found to be dependent on the terminal oxidant.52 The results 
suggest at least partial coordination of an equiv of terminal oxidant in the active oxidant, as 
opposed to the sole agency of a MnV=O species.  
The counterion also modulates the cis/trans ratio of the epoxide products.53 In the  
epoxidation of cis-stilbene, [Mn(salen)]+ catalysts with strongly coordinating counteranions 
favor trans-stilbene oxide as the major product, whereas non-ligating couteranions are 
associated with the preferential formation of cis-stilbene oxide.54 Computational studies 
suggest the involvement of different MnV=O spin-states, which are stabilized by coordinating 
ligands to varying degrees.55-56   
7 
  The salen ligand in Jacobsen?s first epoxidation catalyst is chiral, opening the possibility 
for chiral epoxide products from prochiral alkenes. The enantioselectivity of 
MnIII(salen)-catalyzed asymmetric epoxidation is directly correlated to the electronic 
character of the ligand, with more strongly electron-donating ligands resulting in higher 
enantiomeric excesses. The ratio of enantiomers for the epoxidation of 2,2-dimethylchromene 
and cis-?-methylstyrene can be fit to a Hammett plot (Scheme 1.3).36 Jacobsen and 
co-workers proposed that the ligand?s electron-withdrawing groups enable the Mn(V) oxo to 
react with the substrate in an earlier transition state, which reduces the selectivity. 
Electron-donating groups, conversely, stabilize the Mn(V) oxidant, allowing a later transition 
state and higher enantioselectivity.57  
Much effort has been spent towards evaluating the mechanism of the Jacobsen epoxidation. 
Four mechanisms have been proposed (Scheme 1.2 and Scheme 1.4). In the first proposed 
mechanism, the olefin substrate reacts directly with the MnV-oxo oxidant, proceeding through 
a transition state resembling a manganese-bound epoxide. Due to the concerted nature of this 
pathway, the oxygen atom transfer results in exclusively cis-epoxides. In the second proposed 
mechanism, metallaoxetane species result from the reaction between the alkene and the 
Mn(V) species. The subsequent release of the product from the organometallic intermediate 
can either occur in a single concerted step, resulting in cis-epoxides, or in two steps, which 
can allow the formation of trans-epoxides. In the third pathway, the MnV-oxo oxidant adds to 
the alkene as a radical species. The alkyl radical can rotate freely around the former C=C 
bond, allowing both cis- and trans-epoxides. The fourth pathway (pathway 2 in Scheme 1.4) 
differs from the previous three in that it does not involve oxidation or reduction of the 
manganese center.54 Instead, the manganese serves as a Lewis acid, analogous to what has 
been proposed for early transition metal-containing catalysts for olefin epoxidation. The 
relevant oxidant in this pathway is a MnIII adduct with the terminal oxidant (OLG in Scheme 
1.4).  
 
8 
 
 
Scheme 1.3 Hammett plots depicting enantiomeric ratios of epoxides generated with catalysts 
with various electronically modified ligands. Data from reference 34. 
   
9 
 
MnIII
 
Scheme 1.4 Parallel Lewis acid and redox pathways for [Mn(salen)]+ catalyzed epoxidations. 
 
1.2.2 Manganese Complexes with Neutral, Polydentate N-Donors 
  Manganese can also catalyze alkene epoxidation when bound to neutral N-donor ligands. 
Unlike the aforementioned salen complexes, the metal starts in the +2, rather than +3, 
oxidation state. Another key difference from the aforementioned salen complexes is that the 
tetradentate ligand does not coordinate the metal in a square planar fashion. 
  Stack et al evaluated the epoxidation performance of a variety of MnII complexes, 
finding [MnII(R,R-mcp)(CF3SO3)2] to be the most active catalyst (Figure 1.2).41 Within 5 min, 
[MnII(R,R-mcp)(CF3SO3)2] efficiently catalyzes the epoxidation of a wide range of terminal 
olefins by PAA (Table 1.2), with turnover frequencies as high as 250 min-1. The reactivity 
proceeds with a catalyst loading as low as 0.1 mol%.41 Although terminal alkenes can be 
oxidize, electron-rich olefins are preferentially oxidized.  
 
10 
 
 
Figure 1.2 The molecular structure of the R,R-mcp ligand and the crystal structure of 
[MnII(R,R-mcp)(CF3SO3)2].41 
   
Table 1.2 Epoxidations catalyzed by [MnII(R,R-mcp)(CF3SO3)2] with PAAa 
 
aGeneral reaction conditions: [olefin]o = 0.50 M, MeCN, 25 oC. Yields measured at 5 min. 
bYields determined by GC. The numbers in parentheses represent a standard deviation of a 
minimum of three experiments. cIsolated yields, 1 g scale. d0.25-mol scale, 88% yield. e98% 
cis-epoxide, 2% trans-epoxide. f97% trans-epoxide, 3% cis-epoxide. gtrans,trans- 
CH3CH2=CH2CH2=CH2-CO2CH2CH3. h4:1 mixture of 4,5-monoepoxide and 
2,3-monoepoxide. i0 oC, diepoxide product, 20% disastereoselectivity. j-20 ?C, 
R-carvone-8,9-monoepoxide, 15% disastereoselectivity. All data are from reference 41. 
11 
In subsequent research, the influence of the solvent?s acidity and the catalyst?s ligand 
structure were further explored.40, 42 The pH greatly impacts the catalyst reactivity, and the 
addition of HClO4 slows the initial reaction rate. Conversely, the use of a less acidic grade of 
PAA results in faster reactivity and higher turnover numbers. The inhibitory effect of acid is 
attributed to the protonation of the N-donor ligand, which promotes its dissociation from the 
metal center. Various MnII salts (e.g. MnCl2, Mn(CF3SO3)2) are not competent catalysts for 
olefin epoxidation in the absence of the N-donor ligand. Neutral, tetradentate N-donor ligands 
capable of binding Mn(II) in a cis-? conformation best support the reactivity. The availability 
of cis vacant coordination sites associated with this conformation is believed to facilitate 
activation of the PAA.40  
Electron paramagnetic resonance (EPR) studies were unable to identify high valent 
manganese species during the catalysis; the EPR spectrum appears unchanged from the Mn(II) 
starting material after the addition of oxidant. However, this does not necessarily preclude the 
possible involvement of such high valent intermediates, which simply may not accumulate to 
detectable levels. The possible contribution of a Lewis acid mechanism was tested by 
analyzing the reactivity of the redox-inactive [ZnII(R,R-mcp)]2+. The Zn(II) complex could 
not catalyze the oxidation of alkenes, suggesting that the manganese is accelerating the 
reactivity through alternative pathways, at least for the R,R-mcp system.41 
As with the manganese-salen complexes, multiple mechanistic pathways have been 
proposed for the Mn(II)-catalyzed olefin epoxidations (Scheme 1.5).58 The leftmost pathway 
has the manganese remaining in the +2 oxidation state, with a Mn(II)-oxidant adduct 
transferring an oxygen atom to the substrate. Here, the Mn(II) is simply acting as a Lewis 
acid. The middle pathway features the Mn(II) being oxidized to a MnIV=oxo intermediate that 
oxidizes the substrate. Upon the oxygen atom transfer, the manganese gets reduced back to 
the +2 oxidation state. The oxygen atom transfer can occur in either a single concerted step or 
in two steps, analogous to that depicted for the manganese salen complexes in Scheme 1.2. In 
the rightmost pathway, the MnIV=oxo intermediate acts as a Lewis acid activator, binding an 
additional equiv of oxidant, which provides the transferred oxygen atom. The high-valent 
manganese oxo species does not change its +4 oxidation state during the actual catalysis. 
12 
 
Scheme 1.5 Possible mechanistic pathways for Mn(II)-catalyzed olefin epoxidation.58 
 
1.2.3 Non-Heme Iron Complexes 
Many non-heme iron complexes have been found to accelerate the epoxidation of alkenes 
by H2O2. White et al., for instance, found that the complex of Fe(II) with the tetradentate 
ligand N,N?-dimethyl-N,N?-bis(2-pyridylmethyl)-ethane-1,2-diamine (mep, Figure 1.3) could 
catalyze the epoxidation of a wide variety of substrates, including terminal olefins, in under 5 
min with isolated yields ranging from 60-90% (Table 1.3).45 They crystallized a ?-oxo, 
carboxylate bridged diiron(III) complex (Figure 1.3) from the reaction between the FeII-mep 
precursor, H2O2, and acetic acid. Whether this species is catalytically relevant remains 
unresolved . 
N N
N N
 
 
Figure 1.3 Illustration of the mep ligand (left) and the crystal structure of dinuclear 
[Fe2(?-O)(?-CH3CO2)(mep)2]3+ cation.45 
13 
 Table 1.3 Epoxidations catalyzed by [Fe(mep)(CF3SO3)2]a 
 
aReaction conditions: olefin (2.0 mmol, 0.16 M in MeCN), mononuclear precursor (3.0 mol 
%), CH3CO2H, H2O2 (aqueous 50 wt %, 3.0 mmol, 1.5 M in MeCN, added dropwise over 2 
min), 4 oC, 5 min. bIsolated yields based on an average of 3 runs. cGC yields were determined 
using nitrobenzene as an internal standard for especially volatile substrates. dReaction carried 
out at [olefin]o = 0.13 M due to poor solubility in MeCN. e5 mol % mononuclear precursor. 
f1.5 mol % mononuclear precursor/1.5 mol % CH3CO2H. g6 mol % CH3CO2H. Data from 
Reference 45. 
   
Beller et al. prepared a catalyst in situ using FeCl3.6H2O as the iron source and a 
protonated pyridine-2,6-dicarboxylate (H2Pydic) ligand which was proposed to mimic the 
carboxylate and histidine groups in the coordination sphere of a non-heme dioxygenase.59 
Their system showed excellent reactivity and selectivity towards terminal and 
1,2-disubstituted aromatic olefins and moderate reactivity towards 1,3-dienes at room 
temperature (Table 1.4). 
14 
Table 1.4 Summary of epoxidation scope catalyzed by Beller?s in situ FeIII complexa  
 
aReaction procedure: in a 25 mL Schlenk tube, FeCl3.6H2O (0.025 mmol), H2pydic (0.025 
mmol), tert-amyl alcohol (9 mL), pyrrolidine (0.05 mmol), olefin (0.5 mmol) and dodecane 
(GC internal standard, 100 mL) were added in sequence at RT in air. To this mixture, a 
solution of 30% H2O2 (114 mL, 1.0 mmol) in tert-amyl alcohol (886 mL) was added over a 
period of 1 h (or 5 min) at RT by a syringe pump. bConversion and yield were determined by 
GC analysis. cSelectivity refers to the ratio of yield to conversion as percentage. dThe oxidant 
was added over a period of 5 min. e19% trans-?-methylstyrene oxide was observed. Data 
from Reference 59. 
   
The coordination geometry of the ligand strongly impacts the activity of iron catalysts. 
Catalysts with pentadentate ligands are found to have inferior stereoselectivity and 
epoxidation efficiency,60 whereas systems containing tetradentate ligands with a proclivity for 
binding metal ions in trans conformations generally lead to better reactivity.61-62 The 
counteranions on the metal salt also influence the activity, similar to what was observed for 
the manganese-salen systems. In a study of iron compounds with tetradentate N-donor 
ligands, increasing the amount of chloride present in solution decreases the alkene 
15 
epoxidation.62 Weakly coordinating anions like triflate and hexafluoroantimonate, conversely, 
lead to enhanced activity. 
  In the epoxidation catalyzed by non-heme Fe(II) catalysts, two high-valent iron-oxo 
oxidants have been proposed: FeV=O and FeIV=O. The agency of FeV=O species was 
suggested as a means to explain how 18O atoms from added H218O were incorporated into the 
epoxide products.62-63 Such species have not, however, been isolated and spectroscopically 
characterized. FeIV=O species, conversely, are stable enough to be structurally and 
spectroscopically studied.64-66 Consequently, Fe(IV) species are currently believed to be more 
plausible intermediates (Scheme 1.6).  
FeII
N
N
X
X
N
N
X: weakly coordinating anion
FeII
N
N
X
O
N
N
O
H H
FeIV
N
N
O
O
N
N
H
H
FeIV
N
N
OH2
O
N
N
H2O2
heterolytic
cleavage
alkene, X
epoxide, H2O
 
Scheme 1.6 Proposed catalytic cycle for non-heme iron catalyzed epoxidation. 
1.2.4 The Sharpless Catalyst 
Sharpless used a mixture of titanium(IV) tetraisopropoxide (Ti(Oi-Pr)4), (+/-)diethyl 
tartrate, and t-BuOOH to catalyze the asymmetric epoxidation of olefins.31-32 The major 
species in the titanium-tartrate mixture is a dimeric species (Figure 1.4), as supported by mass 
spectrometry, NMR, and IR measurements.33  
16 
 
Figure 1.4 The dimeric structure of the Sharpless catalyst.33 
 
The Ti(IV) complex catalyzes the oxidation of a variety of substrates by t-BuOOH. 
(Table 1.5).31 The enantioselectivity is determined by the given tartrate enantiomer and is not 
dependent on the substituents on the allylic alcohol skeleton.     
The proposed mechanism of the Sharpless epoxidation is shown on Scheme 1.7. There 
are several key features about this route: 1) both the substrate and terminal oxidant bind to the 
Ti(IV) as ligands; 2) the tartrates direct the bound oxidant towards the face of the C=C bond, 
accounting for the observed enantioselectivity; 3) the epoxide and t-BuO group dissociate 
from Ti(IV) center to complete the catalytic cycle; 4) the titanium remains in the +4 oxidation 
state, and the redox-activity is limited to the two transiently bound ligands. 
 
 
 
 
 
 
 
17 
Table 1.5 Selected asymmetric epoxidation of allylic alcoholsa 
Allylic Alcohol Epoxyalcohol % yieldb % e.e.c Configuration 
OH
 H
OH
O
2
3
 
77 95 2 (S), 3 (S) 
OH  
H
OH
O
2
3
 
79 94 2 (S), 3 (R) 
OAc
OH 
H
OH
O
7
6
 
70 >95 6 (S), 7 (S) 
Ph
Ph
OH
 
Ph H
Ph
OH
O
 
87 >95 2 (S), 3 (S) 
n-C9H19
OH 
H
H
OH
O
2
3
 
79 >95 2 (S), 3 (S) 
n-C9H19
OH  
H
H
OH
O
2
3
 
82 90 2 (S), 3 (R) 
n-C9H19
OH  
O
2
H
H
OH
3
 
80 90 2 (R), 3 (S) 
OH
 
H H
OH
O
2  
81 >95 2 (S) 
a5%-10% catalyst loading, -20 oC. bIsolated yield. cEnantiomeric excess determined by 1H 
NMR on the corresponding epoxy acetates. Data from Reference 31. 
 
18 
 
Scheme 1.7 Proposed mechanism for Sharpless epoxidation (E refers to ester group).67 
 
1.2.5 Homogenous Aluminum Catalysts 
  Although aluminum is typically not redox-active, it can support modest alkene epoxidation 
catalysis. Valentine used [AlIII(porphyrin)]Cl to promote the epoxidation of stilbene and 
cyclohexene by PhIO, with up to 9.3 turnovers.61 More recently, mixtures of [Al(H2O)6]3+ and 
H2O2 in MeCN-H2O were reported to catalyze the epoxidation of ?, ?-unsaturated ketones 
(Table 1.6).68 Much like the aforementioned Sharpless epoxidation, Al(III) catalysis is 
proposed to proceed through pathways that do not involve metal-centered redox or 
high-valent metal oxo intermediates. 
   
19 
Table 1.6 Epoxidation of ?, ?-unsaturated ketones by [Al(H2O)6]3+/H2O2 
 
C: conversion, S: selectivity. Reaction conditions: substrate (25 mmol), di-n-butylether 
(internal standard, 12.5 mmol), 70 wt.% H2O2 (56 mmol), Al(ClO4)3?9H2O (0.5 mmol), THF 
(solvent), at the temperature indicated in this table. Data from Reference 68. 
 
The reactivity of (R)-carvone (compound 1 in Table 1.6) is used to assess the electronic 
character of the active oxidant. (R)-Carvone has two C=C bond sites. The external C=C bond 
is most nucleophilic, whereas the ring olefin is more electrophilic, as supported by DFT 
calculations. Epoxidation exclusively occurs at the ring C=C bond site, suggesting a 
nucleophilic oxidant, e.g. HOO- derived from H2O2. This differs from most transition 
metal-based systems, which prefer to oxidize more electron-rich olefins.  
A Sharpless-type mechanism is proposed, based on DFT calculations (Scheme 1.8).21 
Much like the aforementioned Ti(IV) catalysis, the oxidant binds to the Al(III) center as a 
ligand, and the Al(III) serves to activate the oxidant through its Lewis acidity. The substrate is 
subsequently oxidized by the bound H2O2, generating the epoxide and H2O as a by-product. 
The [Al(H2O)6]3+/H2O2/MeCN-H2O system requires elevated temperatures and long reaction 
times, particularly relative to the aforementioned transition metal catalysts. Additionally, the 
reactivity becomes less selective as the catalyst degrades, leading to increasingly large 
amounts of side-products such as diols. 
20 
 
 
Scheme 1.8 Proposed mechanism for epoxidation promoted by [Al(H2O)6]3+. 69 
 
1.3 Summary 
In Chapter 2 of this thesis, we use Mn(II) complexes with phenanthroline derivatives to 
assess the influence of the ligand?s electronic character on Mn(II)-catalyzed alkene 
epoxidation. We also study the impact of acidity on the epoxidation reactivity. In Chapters 3 
and 4, we study olefin epoxidation catalyzed by Ga(III) complexes with various N-donor 
ligands. We systematically explore how the ligand influences the reactivity in Chapter 4.  
21 
References 
(1) Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, John Wiley & Sons, Inc., 
2003, Vol 12, Ethylene Glycol, 597. 
(2) Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, John Wiley & Sons, Inc., 
2003, Vol 28, Polyoxalkylenes, 497. 
(3) Senanayake, C. H., Roberts, F. E., DiMichele, L. M., Ryan, K. M., Liu, J., Fredenburgh, L. 
E., Foster, B. S., Douglas, A. W., Larsen, R. D., Verhoeven, T. R. and Reider, P. J., 
Tetrahedron Lett. 1995, 36, 3993-3996. 
(4) Wang, X.-Y., Shi, H.-C., Sun, C. and Zhang, Z.-G., Tetrahedron 2004, 60, 10993-10998. 
(5) Hendlin, D., Stapley, E. O., Jackson, M., Wallick, H., Miller, A. K., Wolf, F. J., Miller, T. 
W., Chaiet, L., Kahan, F. M., Foltz, E. L., Woodruff, H. B., Mata, J. M., Hernandez, S. and 
Mochales, S., Science 1969, 166, 122-123. 
(6) Mao, C.-F. and Albert Vannice, M., Appl. Catal., A 1995, 122, 61-76. 
(7) Ayame, A., Uchida, Y., Ono, H., Miyamoto, M., Sato, T. and Hayasaka, H., Appl. Catal., A 
2003, 244, 59-70. 
(8) Linic, S. and Barteau, M. A., J. Catal. 2003, 214, 200-212. 
(9) Atkins, M., Couves, J., Hague, M., Sakakini, B. H. and Waugh, K. C., J. Catal. 2005, 235, 
103-113. 
(10) Linic, S. and Barteau, M. A., J. Am. Chem. Soc. 2001, 124, 310-317. 
(11) Linic, S. and Barteau, M. A., J. Am. Chem. Soc. 2003, 125, 4034-4035. 
(12) Taylor, B., Lauterbach, J. and Delgass, W. N., Appl. Catal., A 2005, 291, 188-198. 
(13) Lu, J., Zhang, X., Bravo-Su?rez, J. J., Bando, K. K., Fujitani, T. and Oyama, S. T., J. 
Catal. 2007, 250, 350-359. 
(14) Wolf, P. F. and Barnes, R. K., J. Org. Chem. 1969, 34, 3441-3445. 
(15) Tosaki, S.-y., Tsuji, R., Ohshima, T. and Shibasaki, M., J. Am. Chem. Soc. 2005, 127, 
2147-2155. 
(16) van Vliet, M. C. A., Arends, I. W. C. E. and Sheldon, R. A., Tetrahedron Lett. 1999, 40, 
5239-5242. 
22 
(17) Hori, T. and Sharpless, K. B., J. Org. Chem. 1978, 43, 1689-1697. 
(18) Jacobson, S. E., Mares, F. and Zambri, P. M., J. Am. Chem. Soc. 1979, 101, 6946-6950. 
(19) ten Brink, G.-J., Fernandes, B. C. M., van Vliet, M. C. A., Arends, I. W. C. E. and 
Sheldon, R. A., J. Chem. Soc., Perkin Trans. 1 2001, 224-228. 
(20) Rebek, J. and McCready, R., Tetrahedron Lett. 1979, 20, 4337-4338. 
(21) Kuznetsov, M. L., Kozlov, Y. N., Mandelli, D., Pombeiro, A. J. L. and Shul?pin, G. B., 
Inorg. Chem. 2011, 50, 3996-4005. 
(22) Sobczak, J. and Zi??kowski, J. J., J. Mol. Catal. 1977, 3, 165-172. 
(23) Sharpless, K. B., Townsend, J. M. and Williams, D. R., J. Am. Chem. Soc. 1972, 94, 
295-296. 
(24) Ledon, H. J., Durbut, P. and Varescon, F., J. Am. Chem. Soc. 1981, 103, 3601-3603. 
(25) Mitchell, J. M. and Finney, N. S., J. Am. Chem. Soc. 2001, 123, 862-869. 
(26) Chong, A. O. and Sharpless, K. B., J. Org. Chem. 1977, 42, 1587-1590. 
(27) Itoh, T., Jitsukawa, K., Kaneda, K. and Teranishi, S., J. Am. Chem. Soc. 1979, 101, 
159-169. 
(28) Mimoun, H., Mignard, M., Brechot, P. and Saussine, L., J. Am. Chem. Soc. 1986, 108, 
3711-3718. 
(29) Murase, N., Hoshino, Y., Oishi, M. and Yamamoto, H., J. Org. Chem. 1999, 64, 338-339. 
(30) Li, Z. and Yamamoto, H., J. Am. Chem. Soc. 2010, 132, 7878-7880. 
(31) Katsuki, T. and Sharpless, K. B., J. Am. Chem. Soc. 1980, 102, 5974-5976. 
(32) Woodard, S. S., Finn, M. G. and Sharpless, K. B., J. Am. Chem. Soc. 1991, 113, 106-113. 
(33) Finn, M. G. and Sharpless, K. B., J. Am. Chem. Soc. 1991, 113, 113-126. 
(34) Corey, E. J., J. Org. Chem. 1990, 55, 1693-1694. 
(35) Jacobsen, E. N., Deng, L., Furukawa, Y. and Mart?nez, L. E., Tetrahedron 1994, 50, 
4323-4334. 
(36) Jacobsen, E. N., Zhang, W. and Guler, M. L., J. Am. Chem. Soc. 1991, 113, 6703-6704. 
(37) Jacobsen, E. N., Zhang, W., Muci, A. R., Ecker, J. R. and Deng, L., J. Am. Chem. Soc. 
1991, 113, 7063-7064. 
(38) Palucki, M., Pospisil, P. J., Zhang, W. and Jacobsen, E. N., J. Am. Chem. Soc. 1994, 116, 
9333-9334. 
23 
(39) Terry, T. J. and Stack, T. D. P., J. Am. Chem. Soc. 2008, 130, 4945-4953. 
(40) Murphy, A. and Stack, T. D. P., J. Mol. Catal. A: Chem. 2006, 251, 78-88. 
(41) Murphy, A., Dubois, G. and Stack, T. D. P., J. Am. Chem. Soc. 2003, 125, 5250-5251. 
(42) Murphy, A., Pace, A. and Stack, T. D. P., Org. Lett. 2004, 6, 3119-3122. 
(43) Dubois, G., Murphy, A. and Stack, T. D. P., Org. Lett. 2003, 5, 2469-2472. 
(44) Chen, K., Costas, M., Kim, J., Tipton, A. K. and Que, L., J. Am. Chem. Soc. 2002, 124, 
3026-3035. 
(45) White, M. C., Doyle, A. G. and Jacobsen, E. N., J. Am. Chem. Soc. 2001, 123, 
7194-7195. 
(46) Flessner, T. and Doye, S., J. Prakt. Chem. 1999, 341, 436-444. 
(47) Pozzi, G. and Cinato, F., Chem. Commun. 1998, 877-878. 
(48) Kass, S. R. and DePuy, C. H., J. Org. Chem. 1985, 50, 2874-2877. 
(49) Linker, T., Angew. Chem. Int. Ed. 1997, 36, 2060-2062. 
(50) Feichtinger, D. and Plattner, D. A., Angew. Chem. Int. Ed. 1997, 36, 1718-1719. 
(51) Feichtinger, D. and Plattner, D. A., Chem. Eur. J. 2001, 7, 591-599. 
(52) Collman, J. P., Zeng, L. and Brauman, J. I., Inorg. Chem. 2004, 43, 2672-2679. 
(53) Adam, W., Roschmann, Konrad J. and Saha-M?ller, Chantu R., Eur. J. Org. Chem. 2000, 
2000, 3519-3521. 
(54) Adam, W., Roschmann, K. J., Saha-M?ller, C. R. and Seebach, D., J. Am. Chem. Soc. 
2002, 124, 5068-5073. 
(55) Schr?der, D., Shaik, S. and Schwarz, H., Acc. Chem. Res. 2000, 33, 139-145. 
(56) Abashkin, Y. G. and Burt, S. K., Org. Lett. 2003, 6, 59-62. 
(57) Palucki, M., Finney, N. S., Pospisil, P. J., G?ler, M. L., Ishida, T. and Jacobsen, E. N., J. 
Am. Chem. Soc. 1998, 120, 948-954. 
(58) Ottenbacher, R. V., Bryliakov, K. P. and Talsi, E. P., Inorg. Chem. 2010, 49, 8620-8628. 
(59) Anilkumar, G., Bitterlich, B., Gelalcha, F. G., Tse, M. K. and Beller, M., Chem. Commun. 
2007, 0, 289-291. 
(60) Bukowski, M. R., Comba, P., Lienke, A., Limberg, C., Lopez de Laorden, C., 
Mas-Ballest?, R., Merz, M. and Que, L., Angew. Chem. Int. Ed. 2006, 45, 3446-3449. 
(61) Nam, W., Ho, R. and Valentine, J. S., J. Am. Chem. Soc. 1991, 113, 7052-7054. 
24 
(62) Mas-Ballest?, R., Costas, M., van den Berg, T. and Que, L., Chem. Eur. J. 2006, 12, 
7489-7500. 
(63) Oldenburg, P. D., Shteinman, A. A. and Que, L., J. Am. Chem. Soc. 2005, 127, 
15672-15673. 
(64) Rohde, J.-U., In, J.-H., Lim, M. H., Brennessel, W. W., Bukowski, M. R., Stubna, A., 
M?nck, E., Nam, W. and Que, L., Science 2003, 299, 1037-1039. 
(65) Klinker, E. J., Kaizer, J., Brennessel, W. W., Woodrum, N. L., Cramer, C. J. and Que, L., 
Angew. Chem. 2005, 117, 3756-3760. 
(66) Costas, M., Mehn, M. P., Jensen, M. P. and Que, L., Chem. Rev. 2004, 104, 939-986. 
(67) Katsuki, T. and Martin, V. Asymmetric Epoxidation of Allylic Alcohols: the 
Katsuki?Sharpless Epoxidation Reaction, Org. React., 1996, 48, 1-299. 
(68) Rinaldi, R., de Oliveira, H. F. N., Schumann, H. and Schuchardt, U., J. Mol. Catal. A: 
Chem. 2009, 307, 1-8. 
(69) Kuznetsov, M. L., Kozlov, Y. N., Mandelli, D., Pombeiro, A. J. L. and Shul?pin, G. B.,  
Inorg. Chem. 2011, 50, 3996-4005. 
 
25 
 
 
 
 
 
Chapter 2 
Alkene Epoxidation Catalyzed by Manganese Complexes with 
Electronically Modified 1,10-Phenanthroline Ligands* 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
* This chapter is a revision of a published paper: Christian R. Goldsmith, Wenchan Jiang, 
Inorg. Chim. Acta, 2012, 384, 340-344. Reprinted with permission. Copyright? 2012 by 
Elsevier B.V. 
26 
2.1 Introduction  
The epoxidation of terminal and electron-de?cient ole?ns remains a challenging task in 
synthetic chemistry. Although many alkenes react directly with peracids, these uncatalyzed 
reactions often require extended reactions times and/or elevated temperatures, both of which 
can reduce selectivity. The use of transition metal catalysts can enhance the selectivity, reduce 
reaction times, and allow reactivity at ambient temperatures 1-21. Many homogeneous and 
heterogeneous catalysts for epoxidation reactions employ manganese as the active metal.1-13 
Electron-rich ole?ns are generally more reactive, to the extent that the development of 
catalysts capable of activating more electron-de?cient ole?ns, such as terminal alkenes, 
remains an intense area of research.1-4, 21 The terminal oxidant and the acidity of the reaction 
also strongly in?uence the activity.1-2, 13, 22 Systematic studies on the in?uence of the 
electronic nature of the catalyst, as opposed to that of the substrate,23 on alkene epoxidation 
are comparatively rare.24-25 In studies involving manganese?salen catalysts, the addition of 
electron-donating substituents onto the catalyst?s ligand were found to slow the rate and 
improve the stereoselectivity of ole?n oxidation.10, 24 This has been attributed to the ability of 
the electron donors to stabilize the Mn=O bond in the Mn(V) oxo species that is believed to 
be the active oxidant.25  
We report three novel monomeric manganese complexes with electronically modi?ed 
derivatives of 1,10-phenanthroline (phen) that are related to two highly active catalysts 
reported by Murphy and Stack.2 1,10-phenanthroline is chosen as the ligand backbone based 
on the facts that with versatile derivatives it has strong chelating ability and is relatively 
oxidative robust during catalysis. The electronic perturbations are installed on the 5-position 
of the phen ligands in order to minimize the in?uence of steric effects on the alkene 
epoxidation. Scheme 2.1 shows the molecular structure of the phen derivatives and a sketch 
of the anticipated coordination around the Mn(II) ion.26-27 Each of the [Mn(R-phen)2Cl2] 
compounds (R = NH2, CH3, H, NO2) can catalyze the oxygenation of alkenes by peracetic 
acid (Scheme 2.2). The yields of the reactions are correlated with the electron-donating 
capacity of the substituent on the 5-position, with electron-withdrawing groups impeding, not 
hastening, the alkene epoxidation.  
27 
 
Scheme 2.1 Illustration of Mn(R-phen)2Cl2 complexes 
 
 
Scheme 2.2 Mn(R-phen)2Cl2 catalyzed epoxidation reaction 
 
2.2 Experimental  
Materials 
Acetonitrile (MeCN), manganese(II) chloride (MnCl2), 1,10-phenanthroline (phen), 
5-nitro-1,10-phenanthroline (NO2-phen), 5-chloro-1,10-phenanthroline (Cl-phen), 
cyclohexene, cyclohexene oxide, 3-cyclohexenol, 3-cyclohexenone, cyclooctene, 1-octene, 
2,4-hexadienoic acid (sorbic acid), peracetic acid (32% in acetic acid, PAA), and 
1,2-dichlorobenzene were purchased from Sigma?Aldrich and used as received. 
5-Amino-1,10-phenanthroline (NH2-phen) and 5-methyl-1,10-phenanthroline (Me-phen) 
were acquired from Acros. Anhydrous ethanol (EtOH) and anhydrous diethyl ether (ether) 
were bought from Pharmco-Aaper and Fisher Scienti?c, respectively. Deuterated acetonitrile 
(CD3CN) was purchased from Cambridge Isotopes.  
Instrumentation  
All 1H magnetic resonance (NMR) spectra were acquired on a 400 MHz AV Bruker NMR 
spectrometer at 294 K. All NMR resonances were referenced to internal standards. A 
Shimadzu IR Prestige-21 FT-IR spectrophotometer was used to record infrared spectra on 
samples that were prepared as KBr pellets. All samples that were submitted for elemental 
analysis were powdered and dried before shipment; Atlantic Microlabs (Norcross, GA) per-
formed all elemental analysis. The magnetic susceptibilities of solid samples were measured 
28 
on a Johnson Matthey balance (model MK I#7967). The diamagnetic contribution to each 
magnetic susceptibility was estimated using Pascal?s constants.28 Electron paramagnetic 
resonance (EPR) spectra were collected on a Bruker EMX-6/1 X-band EPR spectrometer 
operated in the perpendicular mode. Each EPR sample was run as a frozen 3:2 MeCN/CHCl3 
solution in a quartz tube, and the program EasySpin was used to analyze the acquired EPR 
data. Gas chromatography (GC) was obtained on a ThermoScienti?c Trace GC Ultra 
spectrometer with a ?ame ionization detector (FID). 
Syntheses 
Dichloro(bis(5-nitro-1,10-phenanthroline))manganese(II), [Mn(NO2-phen)2Cl2] 
A solution of NO2-phen (0.105 g, 0.47 mmol) in 10 mL of EtOH was added to 0.046 g of 
MnCl2 (0.23 mmol). The resultant slurry was heated until the residual manganese salt had 
dissolved. The solution was ?ltered and cooled to precipitate the product as a yellow powder 
(0.113 g, 85%). Solid-state magnetic susceptibility (294 K): ?eff = 5.7 ?B. Elemental Anal. 
Calc. for C24H14Cl2MnN6O4: C, 50.02; H, 2.45; N, 14.58. Found: C, 49.80; H, 2.51; N, 
14.54%. FT-IR (KBr, cm-1): 3422 (m), 3325 (m), 3226 (m), 3051 (m), 2951 (m), 2922 (m), 
2852 (m), 2729 (w), 2694 (w), 1634 (s), 1628 (s), 1501 (s), 1480 (s), 1378 (m).  
Dichloro(bis(1,10-phenanthroline))manganese(II), [Mn(phen)2Cl2]  
The synthesis of this compound has been reported previously 17. Solid-state magnetic 
susceptibility (294 K): ?eff = 5.8 ?B. Elemental Anal. Calc. for C24H16Cl2MnN4: C, 59.28; H, 
3.32; N, 11.52. Found: C, 58.41; H, 3.25; N, 11.35.FT-IR% (KBr, cm-1): 2951 (w), 2922 (w), 
2852 (w), 2727 (w), 2673 (w), 1635 (m), 1544 (m), 1494 (m), 1300 (m).  
Dichloro(bis(5-methyl-1,10-phenanthroline))manganese(II), [Mn(Me-phen)2Cl2]  
Me-phen (0.100 g, 0.52 mmol) and MnCl2 (0.051 g, 0.26 mmol) were added to 10 mL of 
EtOH. The resultant slurry was re?uxed until the solids had completely dissolved. The 
solution was ?ltered and cooled to precipitate the product as a yellow powder (0.106 g, 79%). 
Solid-state magnetic susceptibility (294 K): ?eff = 5.6 ?B. Elemental Anal. Calc. for 
C26H20Cl2MnN4.H2O: C, 58.66; H, 4.17; N, 10.53. Found: C, 58.83; H, 3.83; N, 10.52%. 
FT-IR (KBr, cm-1): 3043 (w), 2951 (s), 2922 (s), 2852 (s), 2725 (w), 2673 (w), 1462 (m), 
1377 (m).  
Dichloro(bis(5-amino-1,10-phenanthroline))manganese(II), [Mn(NH2-phen)2Cl2] 
NH2-phen (0.103 g, 0.51 mmol) was dissolved in 10 mL of EtOH. The resultant solution was 
added to 0.051 g of MnCl2 (0.25 mmol) and heated to dissolve as much of the residual 
manganese salt as possible. The hot solution was ?ltered, then cooled to deposit the product 
29 
as a yellow powder (0.112 g, 87%). Solid-state magnetic susceptibility (294 K): ?eff = 5.7 ?B. 
Elemental Anal. Calc. for C24H18Cl2MnN6: C, 55.83; H, 3.51; N, 16.28. Found: C, 55.24; H, 
3.60; N, 15.97%. FT-IR (KBr, cm-1): 3385 (w), 2922 (s), 2854 (s), 2725 (w), 2671 (w), 1529 
(m), 1514 (m), 1462 (m), 1377 (m), 1350 (m).  
Reactivity studies 
All reactions were run in MeCN at 0 oC under N2. The initial concentrations of the catalyst, 
ole?n substrate, and terminal oxidant (PAA) were 0.010, 1.00, and 2.00 mM, respectively. 
The reaction mixtures were stirred for 1 h, at which point excess ether was added to 
precipitate the manganese compounds. With all substrates except sorbic acid, the quenched 
reaction mixtures were sequentially ?ltered through plugs of neutral alumina, basic alumina, 
and silica gel to remove the remaining PAA and metal salts. For these substrates, the 
preceding workup did not remove organic starting materials or products from the reaction 
mixture. For reactions using sorbic acid as the substrate, the reaction mixtures were not run 
through the basic alumina plug; the workup was otherwise identical to that previously 
described. All products were identi?ed by both GC and NMR. The yields of the products 
were quanti?ed relative to both an internal standard of 1,2-dichlorobenzene, which does not 
react under these conditions, and the remaining alkene starting material. All reactions were 
run at least six times to ensure reproducibility; the yields were averaged to provide the values 
listed on Table 2.1.  
 
Table 2.1 Yields of epoxides for Mn(II)-catalyzed olefin oxidation by PAA. 
Substrate R = NH2 R = Me R = H R= NO2 Controla 
Cyclohexene 41 (?7) 40 (?7) 36 (?7) 24 (?5) 5 (?3) 
1-Octene 39 (?4) 36 (?6) 29 (?7) 23 (?7) 0b 
Cyclooctene 87 (?6) 78 (?7) 76 (?7) 69 (?9) 20 (?3) 
Sorbic acid 30 (?3) 25 (?3) 23 (?5) 16 (?5) 0 
Initial concentrations in MeCN: [substrate] = 1.00 mM, [PAA] = 2.00 mM, [Mn(R-phen)2Cl2] 
= 0.010 mM. Reactions ran at 0 oC for 1 h under N2.  
a: Experiments were run in the absence of Mn(II) with identical concentrations of substrate 
and PAA.  
b: No epoxide products were detected above the limit of detection. 
 
30 
2.3 Results  
Syntheses and characterization of the manganese complexes  
All four organic ligands are commercially available (Scheme 2.1), and the syntheses of the 
associated Mn(II) complexes are straightforward. The complex [Mn(phen)2Cl2] had been 
reported previously;29 the other three Mn(II) compounds can prepared through the same 
fundamental procedure. The yields for the metal complex syntheses range from 70% to 83%, 
with no correlation between the yield and the identity of the substituent on the 5 -position of 
the phen. Spectroscopically, the four compounds are typical Mn(II) complexes. Each is pale 
yellow, with no ligand-to-metal charge transfer bands past 300 nm. The magnetic moments of 
the compounds range from 5.6 to 5.8 ?B and are most consistent with high-spin d5 metal 
centers. The electronic modi?cations to the ligand are not great enough to force a change in 
the spin-state. 
Reactivity studies with manganese compounds 
The abilities of the four manganese compounds to act as catalysts for ole?n epoxidation 
were tested with four ole?n substrates: cyclohexene, cyclooctene, 1-octene, and sorbic acid 
(Scheme 2.3, Table 2.1). The latter two are relatively electron-de?cient and resistant to 
epoxidation. In the absence of a metal catalyst, no epoxidation above the detection limit of 
the GC is observed over the course of 1 h for sorbic acid and 1-octene. The more 
electron-rich cyclohexene and cyclooctene, conversely, will react directly with PAA, with 
non-negligible amounts of products observable at 1 h. With all four ole?n substrates, the yield 
of the manganese-catalyzed epoxidation dwarfs that of the uncatalyzed reaction. As shown in 
Figure 2.1, the epoxidation reaction is mostly ?nished at 1 h. The yield continues to increase 
past this point, but this additional activity can be attributed to the uncatalyzed reaction 
between the residual ole?n and the peracid.  
Only epoxides and unreacted alkene starting materials are observed in the product mixtures. 
Cyclohexene is often oxidized at the allylic position to 3-cyclohexenol and 
3-cyclohexenone,11-12, 30 but neither of these side-products is observed. Diols, which have 
been observed as products in some transition metal-catalyzed epoxidation reactions,19-20, 31-33 
are likewise not seen above the limit of detection. The diene sorbic acid is oxygenated at the 
more electron-rich alkene farther from the carboxylic acid functional group, yielding 
4,5-sorbic acid oxide as the sole organic product.  
31 
EPR spectroscopy of [Mn(NO2-phen)2Cl2]  
The reaction between [Mn(NO2-phen)2Cl2] and PAA was followed by EPR (Figure 2.2). 
The addition of PAA to a solution of the Mn(II) compound in 3:2 MeCN/CHCl3 does not 
generate Mn(IV) species above the limit of detection, as had been observed by Ottenbacher et 
al. in a recent study of manganese complexes with neutral N-donor ligands.13 The spectra of 
the solutions with 0, 2, 4, and 8 equiv of PAA are nearly identical, with integrated signal 
intensities that are within error of each other. Although the solvent and the concentrations of 
PAA in these samples are different than those used in the catalytic epoxidation reactions, they 
were suf?cient to generate Mn(IV) species in the aforementioned studies of Mn(II) 
complexes with aminopyridyl ligands.13 When 50 equiv of PAA are added, the integrated 
signal intensity decreases by 15%. This is accompanied by a noticeable browning of the 
solution, which is typical of oxidation to either Mn(III) or Mn(IV) 34. Monitoring the reaction 
by optical spectroscopy reveals that the brown color is due to an absorption band at 365 nm.  
 
Scheme 2.3 Substrates used in this study 
 
Figure 2.1 Epoxidation of cyclooctene by peracetic acid catalyzed by [Mn(NO2-phen)2Cl2] in 
MeCN at 0 oC under N2. The results from four independent kinetic runs are superimposed. 
32 
 
Figure 2.2 X-band EPR spectra of a solution of 1.1 mM [Mn(NO2-phen)2Cl2] in 3:2 
MeCN/CHCl3 (solid). To this solution was added 2, 4, 8, and 50 equiv of peracetic acid. The 
following signal intensities were calculated through the double integration of the 
?rst-derivative spectra with subsequent normalization to the intensity of the 0 Equiv spectrum: 
1.00 (0 Equiv), 0.99 (2 Equiv), 0.97 (4 Equiv), 1.01 (8 Equiv), 0.85 (50 Equiv). The 
temperature of all samples was 77 K. 
 
2.4 Discussion 
Installing electronic modi?cations on organic ligands has been shown to impact the 
reactivity of transition metal catalysts. In the current work, Mn(II) complexes with 
electronically modi?ed phenanthroline (phen) ligands are prepared and used to catalyze the 
epoxidation of alkenes by peracetic acid (PAA). The electronic perturbations are installed on 
the 5-position of the phen heterocycle (Scheme 1); this placement minimizes the ability of the 
added functional groups to modulate the chemistry through steric effects. Previously, it was 
found that Mn(II) complexes with 2-derivatized phen ligands displayed severely curtailed 
oxidative catalysis.2 The functional groups present on the 2-position either block the access of 
substrate and/or terminal oxidant to the metal center or weaken the Mn-N bonds enough to 
promote the dissociation of the ligands from the manganous ions.2 Either of these events 
would account for the diminished reactivity.  
The reactivity was tested using commercially available PAA as the terminal oxidant. 
Commercially available PAA is not as effective as a previously reported, less concentrated 
grade of PAA;35 consequently, the yields (Table 2.1) and reaction times (Figure 2.1) of the 
33 
reported ole?n epoxidations compare poorly to previously reported epoxidation catalyzed by 
Mn(II)-phen species.2 The greatest number of catalytic turnovers is 87, corresponding to the 
epoxidation of cyclooctene to cyclooctene oxide by [Mn(NH2-phen)2Cl2], and 20 of those 
turnovers can be accounted for by the background reactivity (Table 2.1). The oxidative 
ef?ciency, de?ned as the yield with respect to the terminal oxidant, is also inferior, reaching a 
maximum of 44% in the aforementioned cyclooctene reaction. The selectivities of the 
catalyzed reactions for the epoxide, however, are retained,2 and no products corresponding to 
allylic oxidation or dihydroxylation are observed.  
The less extensive reactivity offers an advantage in that it allows us to differentiate the 
oxygenating activities of the four manganese catalysts. Murphy and Stack had previously 
compared the reactivity of manganese complexes with 1,10-phenanthroline and 5-chloro-
-1,10-phenanthroline. With a 5 min reaction time, they did not observe a meaningful 
difference in the epoxidation activity using either commercial or custom-made PAA.2 Using a 
less ef?cient terminal oxidant and extending the reaction times to 1 h reveal the impact of 
such electronic modi?cations. When an electron-withdrawing substituent (NO2) is used, the 
yields of all four alkene epoxidation reactions decrease (Figure 2.3). Conversely, 
electron-donating substituents (NH2, Me) increase the yields of the reactions measured at 1 h. 
The decrease in the yield going from R = NH2 to NO2 is approximately 15% for each 
substrate, with a strong linear correlation between the yield at 1 h and the ?P parameter for 
the substituent on the 5-position of the phen. With cyclohexene, 1-octene, and sorbic acid, the 
reactivity is approximately halved upon switching the ligand from NH2-phen to NO2-phen. 
The R values for the ?ts in Figure 2.3 range from 0.95 (cyclohexene) to 0.98 (cyclooctene). 
These results differ from the manganese?salen chemistry developed by Jacobsen, in which 
electron-withdrawing substituents were found to increase the rate of epoxidation.10, 24-25 As 
with other reported systems, more electron-rich ole?ns (cyclohexene, cyclooctene) are 
oxygenated to a greater extent than more electron-de?cient ones (sorbic acid, 1-octene),1, 13, 24, 
30, 36 and the diene sorbic acid is oxygenated at the more electron-rich 4,5-alkene.  
34 
 
Figure 2.3 Plot of the reaction yields (as assessed at 1 h) for the oxygenation of each alkene 
as a function of the ?P value of the 5-substituent on the catalyst?s phenanthroline ligands.  
 
There is compelling evidence that Jacobsen?s system proceeds through a Mn(V) oxo 
species,10, 37 which installs the oxygen atom onto the alkene through either a single 
two-electron or two one-electron steps.23 A study of Mn(II) complexes with aminopyridyl 
ligands also implicates higher-valent oxidants in epoxidation, speci?cally Mn(IV) oxo 
adducts with the terminal oxidant.13 The presence of electron-withdrawing groups would 
further destabilize these already electron-de?cient metal centers and provide a greater 
thermodynamic impetus for the reduction of the manganese oxidant, with concomitant 
oxidation of the alkene.24-25 That we see the opposite effect may indicate either a different 
rate-determining step or a fundamentally different mechanism.  
The greater negative charge on the salens used in the aforementioned work would be 
anticipated to better stabilize more positively charged metal centers (e.g. Mn(V)) relative to 
neutral ligands. The EPR spectra of [Mn(NO2-phen)2Cl2] and the [Mn (NO2-phen)2Cl2]/PAA 
mixtures differ only slightly, and we observe no unambiguous evidence for Mn(IV) even with 
a 50-fold excess of terminal oxidant. Parallel experiments monitored by NMR did not reveal 
any paramagnetic resonances that would be indicative of Mn(III). The EPR signal intensity of 
the Mn(II), however, does decrease 15% when a 50-fold excess of PAA is added. This loss of 
signal intensity and the concurrent browning of the solution under these circumstances 
suggest that the manganese is being oxidized. The data suggest that [Mn(R-phen)2Cl2] 
35 
complexes may be more difficult to oxidize than related salen and aminopyridyl manganese 
complexes but certainly cannot preclude higher-valent oxidants in the catalytic cycle. One 
mechanistic possibility is that the reactivity proceeds through a Mn(IV) oxo species but with 
the rate-limiting step being the oxidation of the Mn(II) rather than the oxygen atom transfer 
from the oxidized manganese species to the alkene. This would prevent the accumulation of 
Mn(IV) above the detection threshold of EPR and would explain the decreased activity with 
more electron-withdrawing ligands.  
In their analysis of non-porphyrin manganese catalysts, Murphy and Stack proposed that 
the acid in many epoxidation reactions quenches the reactivity by protonating the 
phenanthroline, which facilitates their removal from the manganese ions.1 In their control 
studies, these unbound manganese ions were found to be unproductive as catalysts for 
epoxidation. The more electron-de?cient phen derivatives are anticipated to bind to the metal 
ions less avidly and [Mn(R-phen)2Cl2] complexes with these ligands may be more susceptible 
to acid-induced deactivation. Although we do not observe any of the 1H NMR features 
associated with dissociated phenanthroline ligands in mixtures of the [Mn(R-phen)2Cl2] 
species with either acetic acid or peracetic acid, this remains a plausible alternative 
explanation for the reduced activity of [Mn(NO2-phen)2Cl2].  
Another possibility consistent with the EPR data is that the active oxidant is a Mn(II)?PAA 
adduct and that higher-valent manganese species are not relevant to the hydrocarbon 
oxidation. Similar low-valent metal species have been mentioned as potential oxidants in 
other transition metal-based epoxidations.13, 38 Furthermore, complexes with metals that 
generally do not exhibit much redox activity (e.g. Ti(IV), Al(III), Zn(II)) have been found to 
act as competent catalysts for alkene epoxidation.30, 39-41 If the metal ion were merely acting 
as a Lewis acid, however, more strongly electron-withdrawing ligands would be anticipated 
to amplify the reactivity, which is contrary to what we observe.  
 
2.5 Conclusions  
A series of Mn(II) complexes with electronically modi?ed phenanthroline ligands has been 
prepared. The three novel compounds catalyze the epoxidation of alkenes by commercially 
available peracetic acid. Unexpectedly, the more electron-rich ligands lead to faster reactivity 
with all alkenes investigated, as assessed by the yields of the ole?n oxidations measured at 1 
36 
h. The results may suggest that [Mn(phen)2Cl2] and related complexes may oxidize alkenes to 
epoxides through a fundamentally different free energy pathway than Mn(III)?salen catalysts. 
Further experimental and theoretical work is needed to fully elucidate these differences.  
37 
References 
(1) Murphy, A., Pace, A. and Stack, T. D. P., Org. Lett. 2004, 6, 3119-3122. 
(2) Murphy, A. and Stack, T. D. P., J. Mol. Catal. A: Chem. 2006, 251, 78-88. 
(3) Murphy, A., Dubois, G. and Stack, T. D. P., J. Am. Chem. Soc. 2003, 125, 5250-5251. 
(4) Ho, K.-P., Wong, W.-L., Lam, K.-M., Lai, C.-P., Chan, T. H. and Wong, K.-Y., Chem. Eur. 
J. 2008, 14, 7988-7996. 
(5) Jacobsen, E. N., Zhang, W., Muci, A. R., Ecker, J. R. and Deng, L., J. Am. Chem. Soc. 
1991, 113, 7063-7064. 
(6) Terry, T. J. and Stack, T. D. P., J. Am. Chem. Soc. 2008, 130, 4945-4953. 
(7) Wu, M., Wang, B., Wang, S., Xia, C. and Sun, W., Org. Lett. 2009, 11, 3622-3625. 
(8) Fujii, Y., Ebina, F., Yanagisawa, M., Matsuoka, H. and Kato, T., J. Inorg. Organomet. P. 
1994, 4, 273-288. 
(9) Collman, J. P., Lee, V. J., Kellen-Yuen, C. J., Zhang, X., Ibers, J. A. and Brauman, J. I., J. 
Am. Chem. Soc. 1995, 117, 692-703. 
(10) McGarrigle, E. M. and Gilheany, D. G., Chem. Rev. 2005, 105, 1563-1602. 
(11) Nehru, K., Kim, S. J., Kim, I. Y., Seo, M. S., Kim, Y., Kim, S.-J., Kim, J. and Nam, W., 
Chem. Commun. 2007, 4623-4625. 
(12) Yin, G., Buchalova, M., Danby, A. M., Perkins, C. M., Kitko, D., Carter, J. D., Scheper, 
W. M. and Busch, D. H., J. Am. Chem. Soc. 2005, 127, 17170-17171. 
(13) Ottenbacher, R. V., Bryliakov, K. P. and Talsi, E. P., Inorg. Chem. 2010, 49, 8620-8628. 
(14) Sharpless, K. B. and Michaelson, R. C., J. Am. Chem. Soc. 1973, 95, 6136-6137. 
(15) White, M. C., Doyle, A. G. and Jacobsen, E. N., J. Am. Chem. Soc. 2001, 123, 
7194-7195. 
(16) Kamata, K., Yonehara, K., Sumida, Y., Yamaguchi, K., Hikichi, S. and Mizuno, N., 
Science 2003, 300, 964-966. 
(17) Gelalcha, F. G., Anilkumar, G., Tse, M. K., Br?ckner, A. and Beller, M., Chem. Eur. J. 
2008, 14, 7687-7698. 
(18) B?hl, M., Schurhammer, R. and Imhof, P., J. Am. Chem. Soc. 2004, 126, 3310-3320. 
(19) Chen, K., Costas, M., Kim, J., Tipton, A. K. and Que, L., J. Am. Chem. Soc. 2002, 124, 
3026-3035. 
(20) Mas-Ballest?, R. and Que, L., J. Am. Chem. Soc. 2007, 129, 15964-15972. 
38 
(21) Dubois, G., Murphy, A. and Stack, T. D. P., Org. Lett. 2003, 5, 2469-2472. 
(22) Zhang, J.-L. and Che, C.-M., Chem. Eur. J. 2005, 11, 3899-3914. 
(23) Linde, C., Kolia?, N., Norrby, P.-O. and ?kermark, B., Chem. Eur. J. 2002, 8, 
2568-2573. 
(24) Jacobsen, E. N., Zhang, W. and Guler, M. L., J. Am. Chem. Soc. 1991, 113, 6703-6704. 
(25) Cavallo, L. and Jacobsen, H., J. Org. Chem. 2003, 68, 6202-6207. 
(26) Malinowski, T. J., Kravtsov, V. C., Simonov, Y. A., Lipkowski, J. and Bologa, O. A., J. 
Coord. Chem. 1996, 37, 187-193. 
(27) McCann, M., Casey, M. T., Devereux, M., Curran, M. and McKee, V., Polyhedron 1997, 
16, 2741-2748. 
(28) Bain, G. A. and Berry, J. F., J. Chem. Educ. 2008, 85, 532. 
(29) Morcom, R. E. and Bell, C. F., J. Inorg. Nucl. Chem. 1973, 35, 1865-1874. 
(30) Nam, W. and Valentine, J. S., J. Am. Chem. Soc. 1990, 112, 4977-4979. 
(31) Matsumoto, T., Furutachi, H., Kobino, M., Tomii, M., Nagatomo, S., Tosha, T., Osako, T., 
Fujinami, S., Itoh, S., Kitagawa, T. and Suzuki, M., J. Am. Chem. Soc. 2006, 128, 3874-3875. 
(32) Mas-Ballest?, R., Costas, M., van den Berg, T. and Que, L., Chem. Eur. J. 2006, 12, 
7489-7500. 
(33) Qui?onero, D., Musaev, D. G. and Morokuma, K., Inorg. Chem. 2003, 42, 8449-8455. 
(34) Cotton, F. A., Wilkinson, G., Advanced Inorganic Chemistry, 5th Edition, John Wiley & 
Sons, New York 1988. 
(35) Hawkinson, A.T., Schmitz, W. R., E.I. du Pont de Nemours & Co., US 2910504, 1959. 
(36) Indictor, N., J. Org. Chem. 1965, 30, 2074-2075. 
(37) Hamada, T., Fukuda, T., Imanishi, H. and Katsuki, T., Tetrahedron 1996, 52, 515-530. 
(38) Collman, J. P., Chien, A. S., Eberspacher, T. A. and Brauman, J. I., J. Am. Chem. Soc. 
2000, 122, 11098-11100. 
(39) Katsuki, T. and Sharpless, K. B., J. Am. Chem. Soc. 1980, 102, 5974-5976. 
(40) Kuznetsov, M. L., Kozlov, Y. N., Mandelli, D., Pombeiro, A. J. L. and Shul?pin, G. B., 
Inorg. Chem. 2011, 50, 3996-4005. 
(41) Pescarmona, P. P., Janssen, K. P. F. and Jacobs, P. A., Chem. Eur. J. 2007, 13, 6562-6572. 
 
 
39 
 
 
 
 
 
Chapter 3 
A Homogeneous Gallium(III) Compound Selectively Catalyzes the 
Epoxidation of Alkenes* 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
* This chapter is a revision of a published paper: Wenchan Jiang, John D. Gorden, and 
Christian R. Goldsmith, Inorg. Chem., 2012, 51, 2725-2727. Reprinted with permission. 
Copyright ? 2012 by the American Chemical Society. 
40 
3.1 Introduction 
Group 13 elements have been explored intensively as catalysts for many reactions because 
of their low cost and ability to be readily extracted and recovered from reaction mixtures.1 
The overwhelming majority of their catalytic capability derives from their strong Lewis 
acidity.2-6 Alkyl and hydrido complexes with these elements are also well-known for their 
ability to stoichiometrically reduce various functional groups, with the metal complex 
donating a carbanion or hydride, respectively.2-3, 7-9 Because of the limited redox activity 
exhibited by these elements, there are comparatively few reports of group 13 catalyzed 
oxidation?reduction reactions; notable examples include Meerwein?Verley?Ponndorf 
carbonyl reduction and Oppenauer oxidation.5, 10-19 The hydrocarbon oxidation catalysis that 
has been reported tends to be unselective; the documented olefin epoxidation, for instance, is 
accompanied by substantial allylic oxidation.12-17, 20 
Reported here is the selective epoxidation of olefins by the previously described 
[Ga(phen)2Cl2]Cl (phen = 1,10-phenanthroline).14, 17, 20-22 To the best of our knowledge, this is 
the first instance of a gallium(III) compound serving as a homogeneous catalyst in alkene 
epoxidation (Scheme 3.1), although this metal ion has previously been a component in 
heterogeneous catalysts for such reactions.14, 17 
 
Scheme 3.1 Illustration of epoxidation catalyzed by [Ga(phen)2Cl2]Cl 
3.2 Experimental  
Materials  
Unless stated otherwise, all chemicals were purchased from Sigma-Aldrich and used as 
received. Anhydrous ethanol and diethyl ether (ether) were bought from Pharmco-Aaper and 
41 
Fisher Scientific, respectively. Deuterated acetonitrile (CD3CN) was purchased from 
Cambridge Isotopes. [Ga(phen)2C12]Cl was prepared and characterized as previously 
described.20-22 The Ga(III) complex crystallized upon adding ether to a saturated solution of 
the compound in acetonitrile (MeCN). The identity and purity of the Ga(III) catalyst were 
confirmed by nuclear magnetic resonance (NMR).  
Preparation of Custom-Made Peracetic Acid (PAAR)  
  The more basic grade of peracetic acid (PAAR) was prepared through a slightly modified 
version of a reported procedure.4 17 g of 50% H2O2 (0.25 mol) was slowly added to glacial 
acetic acid (150 g, 2.5 mol), which was stirred in a polyethylene bottle at room temperature. 
After 5 min, 5.0 g of Amberlite IR-120 was added. The resultant mixture was allowed to stir 
behind a blast shield for 24 h. After this duration, the solution was filtered, and the molar 
concentration of PAA was determined by its integrated 13C NMR resonance relative to that of 
acetic acid. The solution was stored in a standard -20 oC freezer when not in use. The content 
of PAA was determined to be 7.1% (molar) by 13C NMR analysis; this molar concentration 
was replicated in multiple batches.  
  CAUTION: Peracids and mixtures of peroxides and organic solvents are potentially 
explosive and should be handled with care. The dangers can be minimized by using minimal 
amounts of these materials, using proper protective equipment including blast shields, and 
working at lower temperatures.  
Instrumentation  
  Proton and carbon-13 nuclear magnetic resonance (1H NMR, 13C NMR) spectra were 
acquired on a 400 MHz AV Bruker NMR spectrometer at 294 K. All resonances were 
referenced to internal standards. Gas chromatography (GC) was obtained on a 
ThermoScientific Trace GC Ultra spectrometer with a flame ionization detector (FID).  
  Mass spectrometry was performed on an Ultra Performance LC System (ACQUITY, 
Waters Corporation, Milford, MA) coupled to a quadrupole time-of-flight mass spectrometer 
(QS2 TOF Premier, Waters Corporation, Milford, MA) via direct probe analysis operated in 
the positive ion mode. All samples were run as MeCN solutions.  
  Inductively coupled plasma optical emission spectrometry (ICP-OES) was performed on a 
42 
SPECTRO CIROS ICP-OES spectrometer in Auburn University?s Department of Agronomy 
and Soils. All samples were prepared and run as solutions in 10% (by volume) aqueous HCl.  
X-Ray Crystallography  
  The crystal was mounted in paratone oil on a glass fiber and aligned on a Bruker SMART 
APEX CCD X-ray diffractometer. Intensity measurements were performed using graphite 
monochromated Mo K? radiation (? = 0.71073 ?) from a sealed tube and monocapillary 
collimator. SMART (v 5.624) was used to determine the preliminary cell constants and 
control the data acquisition. The intensities of reflections of a sphere were collected through 
the compilation of three sets of exposures (frames). Each set had a different ? angle for the 
crystal, with each exposure spanning 0.3o in ?. A total of 1800 frames were collected with 
exposure times of 40 s per frame. After the data were corrected for Lorentz and polarization 
effects, the structure was solved using direct methods and expanded using Fourier techniques. 
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included at 
idealized positions 0.95 ? from their parent atoms prior to the final refinement. Details 
regarding the data acquisition and analysis are included in Table 3.1. 
43 
Table 3.1. Selected crystallographic data for [Ga(phen)2Cl2]Cl. 
Parameter [Ga(phen)2Cl2]Cl.0.5MeCN.H2O 
Formula C50H39Cl6Ga2N9O2 
Mw 1150.04 
Crystal System Orthorhombic 
Space group Pbcn (#60) 
a (?) 12.7377 (11) 
b (?) 23.275 (2) 
c (?) 16.5439 (15) 
? (deg) 90 
? (deg) 90 
? (deg) 90 
V (?3) 4904.8 (8) 
Z 4 
Crystal color Yellow 
T (K) 183 
Reflns collected 47811 
Unique reflns 4661 
R1 (F, I > 2?(I)) 0.0476 
wR2 (F2, all data) 0.121 
R1 = ???Fo?- ?Fc??/??Fo?; wR2 = [?w(Fo2-Fc2)2/?w(Fo2)2]1/2 
Reactivity studies 
All reactions were run in acetonitrile (MeCN) at 0 oC under N2. The reaction mixtures were 
stirred for 1 h, at which point excess ether was added to precipitate the gallium compounds. 
With all substrates, the quenched reaction mixtures were sequentially filtered through plugs 
of neutral alumina, basic alumina, and silica gel to remove the remaining PAA and metal salts. 
The workup did not remove organic starting materials or products from the reaction mixture, 
as assessed by analyzing control mixtures of alkenes and epoxides that were subjected to the 
44 
same protocol. All products were identified by their GC retention times and NMR. The yields 
of the products were quantified relative to an internal standard of 1,2-dichlorobenzene, which 
was found to be unreactive under these conditions. All reactions were run at least four times 
to ensure reproducibility. The results were also found to be reproducible with different 
batches of both [Ga(phen)2Cl2]Cl and PAAR.  
Isolated Yields  
  Isolated yields were obtained for cyclohexene, cyclooctene, and 1-octene.  
  Cyclohexene oxide. [Ga(phen)2C12]Cl (0.054 g, 0.10 mmol) and cyclohexene (0.842 g, 
10.0 mmol) were dissolved in 2 mL of MeCN. After the solution was put under N2 and cooled 
to 0 oC, PAAR solution (11.4 g, 20.0 mmol) was added dropwise. After 1 h, the reaction 
solution was filtered through plugs of silica gel and K2CO3. Cyclohexene oxide was isolated 
from the filtrate through distillation, yielding 0.38 g of product (39% vs. 46% GC yield).  
  Cyclooctene oxide. [Ga(phen)2C12]Cl (0.0540 g, 0.10 mmol) and cyclooctene (1.18 g, 10.0 
mmol) were dissolved in 2 mL of MeCN. The solution was put under N2 through nitrogen 
bubbling and cooled to 0 oC. Subsequently, PAAR solution (11.4 g, 20.0 mmol) was added 
slowly. After 1 h, the reaction mixture was filtered through silica gel and K2CO3. Cyclooctene 
oxide was distilled from the filtrate (0.97 g, 77% vs. 87% GC yield).  
  1-Octene oxide. [Ga(phen)2C12]Cl (0.054 g, 0.10 mmol) and 1-octene (1.14 g, 10.0 mmol) 
were dissolved in 2 mL of MeCN. The reaction mixture was put under N2 and cooled to 0 oC. 
Once the temperature equilibrated, 11.4 g of PAAR solution (20.0 mmol) was added dropwise. 
1 h after the addition was completed, the reaction mixture was filtered through plugs of silica 
gel and K2CO3. 1-Octene oxide was distilled from the filtrate (0.47 g, 37% vs. 41% GC 
yield).  
 
3.3 Results and Discussion 
The [Ga(phen)2Cl2]Cl complex was crystallized from ethanol (Figure 3.1). The structural 
data confirm the compositions of the inner and outer spheres, with the outer-sphere chloride 
45 
located 5.57 ? away from the GaIII ion. The halides are terminal rather than bridging, 
analogous to what is observed in the structure of [Ga(phen)2Br2]Br.23 The structure is a rare 
example of a hexacoordinate dihalide gallium(III) complex.23-25 The chlorides are cis to each 
other, as has been observed in other hexacoordinate dihalide gallium(III) complexes with 
bidentate ligands.23-25  
 
 
Figure 3.1 ORTEP representation of the cation [Ga(phen)2Cl2]+. The counterion, H atoms, 
and outer-sphere solvent molecules have been removed for clarity. All thermal ellipsoids are 
drawn at 50% probability. A fuller description of the structure, including a table of metrical 
parameters, is included in Table 3.2.  
 
46 
Table 3.2 Bond lengths (?) and bond angles (?) for [Ga(phen)2Cl2]+. 
Bond Length  Angle  
Ga-N (1) 2.085 (2) N(1)-Ga-Cl(1) 94.19 (6) 
Ga-N (12) 2.127 (2) N(1)-Ga-Cl(2) 95.09 (7) 
Ga-N (15) 2.134 (2) N(12)-Ga-Cl(1) 88.16 (6) 
Ga-N (26) 2.084 (2) N(12)-Ga-Cl(2) 171.58 (6) 
Ga-Cl (1) 2.2849 (7) N(15)-Ga-N(26) 78.57 (9) 
Ga-Cl (2) 2.2642 (8) N(15)-Ga-Cl(1) 169.26 (6) 
Angle  N(15)-Ga-Cl(2) 90.47 (6) 
N(1)-Ga-N(12) 78.73 (8) N(26)-Ga-Cl(1) 94.32 (7) 
N(1)-Ga-N(15) 91.51 (8) N(26)-Ga-Cl(2) 93.61 (7) 
N(1)-Ga-N(26) 166.86 (9) Cl(1)-Ga-Cl(1) 98.07 (3) 
The Ga(III)-N bond distances and the L-Ga(III)-L bond angles are similar to those reported 
for [Ga(phen)2Br2]+.23 The major difference between the two structures is that the bonds 
between the Ga(III) and the nitrogen atoms on the 10-positions of the phenanthroline ligands 
are slightly longer in the chloride structure, averaging 2.13 ? as opposed to the 2.10 ? 
average for the bromide structure. 
The ability of [Ga(phen)2Cl2]Cl to catalyze the epoxidation of alkenes in acetonitrile 
(MeCN) was initially tested using H2O2. Although H2O2 served as a competent terminal 
oxidant in aluminum(III)-catalyzed alkene epoxidation,12, 15 it did not lead to any epoxidation 
with the gallium(III) catalyst. Speculating that the poor binding affinity of H2O2 to GaIII was 
responsible for the lack of activity,26 we investigated two grades of peracetic acid (PAA). In 
addition to commercially available PAA (PAAC, pH ? 1), we prepared and investigated a less 
acidic, custom-made grade (PAAR, pH ? 4)27 that previously led to excellent activity in 
manganese-catalyzed epoxidation.28-29 PAAR was prepared by reacting acetic acid and H2O2 
in the presence of a highly acidic resin (Amberlite IR 120); PAAR lacks the ?1% H2SO4 
additive that is used as the catalyst for the commercial preparation of PAA. The peracids 
should ligate metal ions more readily than H2O2, particularly under more basic conditions.  
Using PAAC as the terminal oxidant led to modest epoxidation at 0 ?C, but PAAR was 
47 
much more effective, particularly with electron-deficient substrates (Table 3.3). As is 
commonly observed, the more electron-deficient olefins tend to react less readily. The two 
substrates with two alkene groups, ethyl sorbate and 4-vinylcyclohexene, are oxidized 
exclusively at the more electron-rich site. These results parallel those found for the 
aforementioned manganese(II)-catalyzed alkene epoxidation.28-29 Although the yields of the 
epoxide do increase when more PAAR is added, the reactions become noticeably less efficient. 
Adding one additional equiv of PAAR to the cyclooctene reaction, for instance, only raises the 
yield of the epoxide from 64% to 87%, with a concomitant drop in the oxidative efficiency 
from 64% to 44%.  
 
 
 
 
48 
Table 3.3 Yields/Turnover Numbers of Gallium(III) Catalyzed Alkene Epoxidation Reactions 
by Various Grades and Amounts of PAAa  
 
a Sandard reaction conditions: MeCN, 0 ?C, initial concentrations of 5.0 mM 
[Ga(phen)2Cl2]Cl and 500 mM alkene. The yields, defined as the percentage of alkene 
converted to the epoxide, were measured at 1 h via gas chromatography. The yields also serve 
as the turnover numbers because the substrate is present in a 100-fold excess relative to the 
gallium(III).  
b The ratio of [Ga(phen)2Cl2]Cl/alkene/PAA was 1:100:200 when 2 equiv of PAA was used 
and 1:100:100 when 1 equiv of terminal oxidant was added.  
c Isolated yields for cyclohexene oxide (39%), cyclooctene oxide (77%), and 1-octene oxide 
(37%).  
 
The control studies confirm that both the phen ligands and the GaIII ions are essential for 
the observed catalysis. GaCl3 by itself does not catalyze epoxidation to an appreciably greater 
extent than the metal-free controls. The summary of control experiments is in Table 3.4. We 
hypothesize that the electron-withdrawing nature of the phen ligands30 amplifies the Lewis 
acidity of the GaIII metal center relative to that in the chloride salt.  
49 
Table 3.4 Yields of Epoxide Products (%) in Control Reactions. 
 
The conditions are identical to those described for the reactions in Table 3.3, with the 
exceptions of the identity and concentration of the catalyst. For the above reactions, the ratio 
of alkene/PAA was 1:2 when 2 equiv. of PAA were used and 1:1 when 1 equiv. of terminal 
oxidant was added, with the concentration of alkene set at 500 mM. All reactions were run in 
MeCN at 0 ?C under N2. The yields, defined here as the percentage of alkene converted to the 
epoxide, were measured at 1 h through a comparison of the GC integration of the epoxide 
peak to that of an internal standard, 1,2-dichlorobenzene. No other organic products were 
observed in the above reactions. 
 
50 
In order to exclude the mechanistic possibility of a highly active transition-metal 
contaminant, we assessed the catalytic activity of 0.1 mM [Mn(phen)2Cl2] and found it to be 
inferior to that of 5.0 mM [Ga(phen)2Cl2]+. The loading of the manganese(II) complex, which 
is known to catalyze olefin epoxidation,29 is meant to mimic an active 2% molar impurity. 
The 2% value is a conservative upper limit, given the high purities of the available 
gallium(III) salts and the crystallinity of the [Ga(phen)2Cl2]+ catalyst (Figure 3.1). The purity 
of the gallium(III) complex is further confirmed by inductively coupled plasma optical 
emission spectrometry (ICP-OES), which found that the iron and manganese contents were 
equal within error to those of a blank sample. The results of ICP-OES are summarized in 
Table 3.5. That the reactivity cannot be fully accounted for by a highly active transition-metal 
contaminant demonstrates that a gallium(III) species is indeed catalyzing olefin epoxidation.  
 
51 
Table 3.5 Summary of ICP-OES Analysis 
 
a The ?<? means the given value is below the limit of accurate detection for that analyte. b 
Corresponds to a 0.01% impurity in the 122 ppm sample. 
52 
 
Figure 3.2 Yield of cyclohexene oxidation by 2 equiv of PAAR as a function of time. The 
blue data points (round dot) correspond to the reactivity observed in the presence of 10 equiv 
of additional phen. Otherwise, the reaction conditions are identical with those in Table 3.3.  
 
Monitoring the yield of several epoxidation reactions over time reveals that the reactivity 
persists for approximately 2 h at 0 ?C (Figure 3.2). Mass spectrometric (MS) analysis of the 
reaction suggests that the chloride ligands are displaced by acetate almost immediately; by 
mass balance, this would generate HCl. MS analysis (Figure 3.3) also reveals that the phen 
ligands dissociate from the GaIII ions over the period of the reaction, with noticeably fewer 
GaIIIphen adducts remaining at 1 h. Because the gallium(III) salts by themselves are not 
competent catalysts for olefin epoxidation, dissociation of the phen ligands is a plausible 
explanation for the loss of activity. The speculation that the resultant greater concentration of 
H+ will more effectively compete with the GaIII ions for the N-donor atoms of the phen 
ligands has been proved to be wrong after a careful calculation. Under current experimental 
conditions, the pH value in the reaction solutions will not change too much even after all 
PAAR have been converted to acetic acid. The lifetime of the catalytic activity and the 
ultimate yield of the epoxide can be increased by adding free phen ligand to the initial 
reaction mixture (Figure 3.2). With the shown cyclohexene epoxidation, the yield at 3 h 
53 
increased from 55% to 79% when 10 equiv of additional phen were present. Attempts to 
further increase the yield by running the reaction in a solution of 50 mM HEPES in H2O 
buffered to pH 7.0 were unsuccessful. The yield measured at 3 h was 68% in the HEPES 
buffer, as opposed to 79% in MeCN. We attribute this lesser activity to the immiscibility of 
the alkene substrate with water.  
 
Figure 3.3. Mass spectrometric analysis of the reaction between cyclooctene and two equiv. 
of PAAR at t = 5 s (top) and t = 60 min (bottom). The reaction conditions are identical to 
those listed under Table 3.3 (0 ?C, MeCN, 5.0 mM [Ga(phen)2Cl2]Cl, 500 mM cyclooctene, 
1000 mM PAAR). The m/z feature at 244.0344 was assigned to [Ga(phen)2(CH3CO2)]2+, 
indicating that the chlorides are displaced almost instantaneously by the acetic acid in 
solution. At t = 60 min, this feature has almost completely disappeared; the major feature of 
this spectrum has m/z = 181.0743, which corresponds to protonated phen. Since the GaCl3 
salt by itself is unable to catalyze significant alkene epoxidation (Table 3.5), we propose that 
the oxidation of the phen ligands by PAAR promotes the dissociation of the ligands from the 
Ga(III), halting the catalytic activity. 
The [Ga(phen)2Cl2]+/PAA mixtures oxidize olefins quickly relative to other group 13 
metal-containing systems. Previously reported homogeneous and heterogeneous 
aluminum(III) and gallium(III) catalysts for these reactions have been reported to turn over 
54 
up to ?50 times.13-15, 17 The most successful of these alkene epoxidations were run at a 
relatively high temperature (80 ?C) and required 4?5 h to reach this level of activity.14-15 In 
contrast, the turnover number of 87 for the best cyclooctene epoxidation in Table 3.3 was 
measured at 1 h and corresponded to reactions run at 0 ?C. Increasing the reaction 
temperature to 25 ?C did not have a substantial impact on the yield. When cyclohexene 
epoxidation (MeCN, 10 equiv of additional phen) was run at this temperature, the yield at 3 h 
only increased from 79% to 82%. Although the time and temperature required for the 
reactions are both lower than those reported for other group 13 mediated epoxidations, it 
should be noted that the gallium(III)-promoted epoxidations proceed much more slowly than 
those catalyzed by MnIIphen complexes and other transition-metal compounds.28-29, 31-32  
Notably, the only oxidized organic products with the 1% catalyst loading are epoxides. 
This again contrasts with other reported group 13 catalyzed alkene epoxidations, which 
produce sizable amounts of alcohols and ketones/aldehydes.12-15 This selectivity is lost as the 
catalyst loading is lowered. With a gallium(III) loading of 0.1%, the major products are 
3-cyclohexenol (39%) and 1,2-cyclohexanediol (51%); the yield of cyclohexene oxide is only 
8%. The new products do not result from further chemical transformation of the epoxide; 
epoxides do not react with the GaIII/PAA mixtures when used as substrates. The inability of 
the system to oxidize epoxides suggests that different oxidation mechanisms, as opposed to 
overoxidation, occur with the higher PAA/GaIII ratio.  
 
Scheme 3.2 Proposed Sharpless type mechanism 
On the basis of our observations, we speculate that the olefin epoxidation proceeds through 
a Sharpless-type mechanism (Scheme 3.2),33 as has been proposed for a [Al(H2O)6]3+/H2O2 
55 
system.12 The competitive C?H activation observed in the aluminum(III) system was 
attributed to the formation of [Al(H2O)4(H2O2)(O2H)]2+ species.12 The bidenticity of the phen 
ligands would be anticipated to hinder similar chemistry in the [Ga(phen)2Cl2]+ reactions by 
better blocking the coordination of a second equiv of terminal oxidant. When the 
concentration of PAA is much higher, the formation of such species should be more likely. 
The higher levels of 2:1 PAA/ adducts associated with the 0.1% catalyst loading would 
account for the observed allylic oxidation.  
3.4 Conclusions 
In summary, we report the first homogeneous gallium(III) catalyst for olefin epoxidation. 
Relative to other group 13 catalysts, the activity of [Ga(phen)2Cl2]+ is both fast and, with a 
1% catalyst loading, exquisitely selective for the epoxide product. We attribute the greater 
activity and selectivity to the presence of the electron-withdrawing and bidentate 1,10 
phenanthroline ligands. Although GaIII is widely perceived to be less Lewis acidic than AlIII, 
the greater affinity of GaIII for these ?-accepting N-donor ligands compensates for this 
deficiency. The results suggest that the full potential of group 13 metals for hydrocarbon 
oxidation reactions has not yet been realized, and the [Ga(phen)2Cl2]+ complex may be a 
promising lead to other homogeneous, non-transition-metal catalysts.  
 
56 
References 
(1) Moskalyk, R. R., Miner. Eng. 2003, 16, 921-929. 
(2) Dagorne, S. and Atwood, D. A., Chem. Rev. 2008, 108, 4037-4071. 
(3) Yamaguchi, M. and Nishimura, Y., Chem. Commun. 2008, 35-48. 
(4) Kilyanek, S. M., Fang, X. and Jordan, R. F., Organometallics. 2008, 28, 300-305. 
(5) Fricke, R., Kosslick, H., Lischke, G. and Richter, M., Chem. Rev. 2000, 100, 2303-2406. 
(6) Balskus, E. P. and Jacobsen, E. N., Science 2007, 317, 1736-1740. 
(7) Tewari, B. B., Shekar, S., Huang, L., Gorrell, C. E., Murphy, T. P., Warren, K., Nesnas, N. 
and Wehmschulte, R. J., Inorg. Chem. 2006, 45, 8807-8811. 
(8) Larock, R. C., Comprehensive Organic Transformations, 2nd ed; Wiley-VCH: New York 
1999. 
(9) Gu, W., Haneline, M. R., Douvris, C. and Ozerov, O. V., J. Am. Chem. Soc. 2009, 131, 
11203-11212. 
(10) Oppenauer, R. V., Recl. Trav. Chim. Pays-Bas 1937, 56, 137-144. 
(11) Meerwein, H. and Schmidt, R., Justus Liebigs Ann. Chem. 1925, 444, 221-238. 
(12) Kuznetsov, M. L., Kozlov, Y. N., Mandelli, D., Pombeiro, A. J. L. and Shul?pin, G. B., 
Inorg. Chem. 2011, 50, 3996-4005. 
(13) Nam, W. and Valentine, J. S., J. Am. Chem. Soc. 1990, 112, 4977-4979. 
(14) Pescarmona, P. P., Janssen, K. P. F. and Jacobs, P. A., Chem. Eur. J. 2007, 13, 6562-6572. 
(15) Rinaldi, R., de Oliveira, H. F. N., Schumann, H. and Schuchardt, U., J. Mol. Catal. A: 
Chem. 2009, 307, 1-8. 
(16) Rinaldi, R. and Schuchardt, U., J. Catal. 2005, 236, 335-345. 
(17) Stoica, G., Santiago, M., Jacobs, P. A., P?rez-Ram?rez, J. and Pescarmona, P. P., Appl. 
Catal., A 2009, 371, 43-53. 
(18) Verley, A., Bull. Soc. Chim. Fr. 1925, 37, 537. 
(19) Ponndorf, W., Angew. Chem. 1926, 39, 138-143. 
(20) Ivanov-Emin, B. N. N. s., L. A.; Rabovik, Ya. I.; Larionova, L. E., Russ. J. Inorg. Chem. 
57 
1961, 6, 1142-1146. 
(21) Carty, A. J., Dymock, K. R. and Boorman, P. M., Can. J. Chem. 1970, 48, 3524-3529. 
(22) McPhail, A. T., Miller, R. W., Pitt, C. G., Gupta, G. and Srivastava, S. C., J. Chem. Soc., 
Dalton Trans. 1976, 1657-1661. 
(23) Junk, P. C., Skelton, B. W. and White, A. H., Aust. J. Chem. 2006, 59, 147-154. 
(24) Restivo, R. and Palenik, G. J., J. Chem. Soc., Dalton Trans. 1972, 341-344. 
(25) Sofetis, A., Raptopoulou, C. P., Terzis, A. and Zafiropoulos, T. F., Inorg. Chim. Acta 
2006, 359, 3389-3395. 
(26) DiPasquale, A. G. and Mayer, J. M., J. Am. Chem. Soc. 2008, 130, 1812-1813. 
(27) E.I. du Pont de Nemours & Co. Hawkinson, U.S. 2,910,504, 1959. 
(28) Murphy, A., Pace, A. and Stack, T. D. P., Org. Lett. 2004, 6, 3119-3122. 
(29) Murphy, A. and Stack, T. D. P., J. Mol. Catal. A: Chem. 2006, 251, 78-88. 
(30) Bencini, A. and Lippolis, V., Coordin. Chem. Rev. 2010, 254, 2096-2180. 
(31) White, M. C., Doyle, A. G. and Jacobsen, E. N., J. Am. Chem. Soc. 2001, 123, 
7194-7195. 
(32) Jacobsen, E. N., Zhang, W., Muci, A. R., Ecker, J. R. and Deng, L., J. Am. Chem. Soc. 
1991, 113, 7063-7064. 
(33) Sharpless, K. B., Townsend, J. M. and Williams, D. R., J. Am. Chem. Soc. 1972, 94, 
295-296. 
 
 
58 
 
 
 
 
 
 
Chapter 4 
Catalysis of Alkene Epoxidation by a Series of Gallium(III) 
Complexes with Neutral N-Donor Ligands* 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
* This chapter derived from a manuscript in preparation to be submitted to a peer-reviewed 
scientific journal, co-authored by Wenchan Jiang, John D. Gorden, and Christian R. 
Goldsmith. 
59 
 
4.1 Introduction 
The coordination chemistry of gallium has been investigated to serve a number of 
applications, including the development of volatile precursors for gallium oxide, nitride, 
selenide, arsenide, and sulfide layers in chemical vapor deposition1-7 as well as 
68Ga-containing radiopharmaceuticals suitable for positron emission tomography.8-11 
Gallium(III) compounds have also garnered attention for their capabilities to act as 
homogeneous Lewis acid catalysts.7, 12-16 One trend observed in the aforementioned catalysis 
is that cationic Ga(III) species tend to promote faster and more extensive reactivity. 
Recently, our group reported that the previously known compound [Ga(phen)2Cl2]Cl (phen 
= 1,10-phenanthroline)17-19 could catalyze the epoxidation of alkenes by peracetic acid.20 This 
is a rare example of gallium accelerating an oxidation-reduction reaction21-24 and to the best 
of our knowledge, represents the first instance of a homogeneous Ga(III) catalyst for olefin 
epoxidation. The reactivity proceeded more quickly and at a lower temperature than 
analogous reactions catalyzed by Al(III) complexes.25-27 We attributed the activity of 
[Ga(phen)2Cl2]+ to the presence of the neutral and relatively electron-poor phen ligands, 
which appear to remain bound to the Ga(III) during the catalysis.20 Without these ligands, the 
oxidation does not proceed; GaCl3 by itself is not a competent catalyst. Neutral N-donor 
ligands do not commonly coordinate to Al(III), which instead prefers to ligate harder bases. 
These ligands? affinities for Ga(III), however, are considerably higher.28 Although the 
complexation of Ga(III) to polydentate neutral N-donor ligands could result in enhanced 
catalytic activity for Group 13 metals, this chemistry has never been systematically studied. 
Here, we report the syntheses and characterizations of six Ga(III) complexes with neutral 
N-donor ligands (Scheme 4.1). The ligands were selected to interrogate the influences of 
ligand denticity and electronics on the catalytic activity. One noted shortcoming with the 
[Ga(phen)2Cl2]+ system is that its catalysis essentially ends after approximately 1 h.20 
Replacing the two bidentate phen ligands with a single more highly coordinating molecule 
extends the lifetime of the catalysis and increases the optimum yield of the epoxides, 
although the activity decreases if the ligand has the capacity to bind in a penta- or 
60 
 
hexadentate fashion. The more electron-poor ligands promote more extensive alkene 
epoxidation, with the best activity being associated with 5-nitro-1,10-phenanthroline 
(NO2-phen). 
 
 
Scheme 4.1 Neutral N-donor ligands 
 
4.2 Experimental 
Materials 
Cyclooctene, cyclohexene, styrene, 1-octene, 4-vinylcyclohexene, 1,2-ethanediamine (en), 
5-amino-1,10-phenanthroline (NH2-phen), 5-nitro-1,10-phenanthroline (NO2-phen), and 
gallium trichloride (GaCl3) were purchased from Sigma-Aldrich and used as received. 
Methylene chloride (CH2Cl2) was bought from Macron Chemicals. Anhydrous acetonitrile 
(MeCN) and methanol (MeOH) were procured from Acros. Diethyl ether (ether) was 
obtained from J. T. Baker. Deuterated chloroform (CDCl3), acetonitrile (CD3CN), 
dimethylsulfoxide (DMSO-d6), water (D2O), and methanol (CD3OD) were purchased from 
Cambridge Isotopes. 
61 
 
Peracetic acid (PAAR) was prepared through a previously described procedure that uses an 
acidic resin as the catalyst in place of the more commercially used sulfuric acid.29 50% H2O2 
(17 g, 0.25 mol) was slowly added to 150 g of glacial acetic acid (2.5 mol) in a room 
temperature (RT) polyethylene bottle. After the addition was complete, 5.0 g of Amberlite 
IR-120 was added, and the reaction mixture was stirred behind a blast shield for 24 h at RT. 
After this time, the solution was filtered to remove the resin and yield the 7.5% wt PAAR 
solution used for the reactivity experiments. The solution was stored in a freezer when not in 
use. The concentration of PAAR was determined by comparing the intensities of the 13C NMR 
resonances of CH3CO3H and CH3CO2H. 
CAUTION: Peracids and their mixtures with organic solvents are potentially explosive and 
should be handled judiciously. The potential hazards can be minimized by using minimal 
amounts of these materials at lower temperatures and by using proper protective equipment, 
such as blast shields. 
Instrumentation 
All 1H nuclear magnetic resonance (NMR) spectra were acquired on either a 250, 400, or 
600 MHz AV Bruker NMR spectrometer at 294 K. All resonances were referenced to internal 
standards. Atlantic Microlabs (Norcross, GA) performed all elemental analyses. A Shimadzu 
IR Prestige-21 FT-IR spectrophotometer was used for the described infrared (IR) 
spectroscopy. Gas chromatography (GC) data were obtained using a ThermoScientific Trace 
GC Ultra spectrometer with a flame ionization detector. High-resolution mass spectrometry 
(HR-MS) data were collected at the Mass Spectrometer Center at Auburn University using a 
Bruker microflex LT MALDI-TOF mass spectrometer via direct probe analysis operated in 
the positive ion mode. 
X-ray Crystallography 
 X-ray diffraction data were acquired using a Bruker SMART APEX CCD X-ray 
diffractometer and Mo K? radiation. Crystalline samples were mounted in Paratone-N oil on 
glass fibers. The program SMART (v 5.624) was used for the preliminary determination of 
cell constants and data collection control. Determination of integrated intensities and global 
cell refinement were performed with the Bruker SAINT software package using a 
62 
 
narrow-frame integration algorithm. The program suite SHELXTL (v 5.1) was used for space 
group determination, structure solution, and refinement.30 Refinement was performed against 
F2 by weighted full-matrix least-square, and empirical absorption correction (SADABS) were 
applied.31 Hydrogen atoms were placed at calculated positions using suitable riding models 
with isotropic displacement parameters derived from their carrier atoms. Crystallographic 
data are provided in Table 4.1. 
Syntheses 
The ligands N,N?-bis(2-pyridylmethyl)-1,2-ethanediamine (bispicen), 
N,N,N?-tris(2-pyridylmethyl)-1,2-ethanediamine (trispicen), and 
N,N,N?,N?-tetrakis(2-pyridylmethyl)-1,2-ethanediamine (tpen) were prepared as described 
previously.32-34 The identities and purities of these compounds were confirmed by NMR. 
cis-Dichloro(N,N?-Bis(2-pyridylmethyl)-1,2-ethanediamine)gallium(III) chloride (1). 
GaCl3 (0.164 g, 0.931 mmol) and bispicen (0.227 g, 0.937 mmol) were dissolved in 10 mL of 
CH2Cl2 and stirred at RT under N2. After 2 h, ether was added to the cloudy solution, 
precipitating 0.360 g of the product as a white powder (82%). Colorless crystals were grown 
from the slow diffusion of ether into a saturated solution of the complex in MeOH. 1H NMR 
(CD3OD, 400 MHz): 9.41 (2H, d, J = 5.2 Hz), 8.24 (2H, t, J = 7.6 Hz), 7.77 (2H, t, J = 6.4 
Hz), 7.71 (2H, d, J = 7.6 Hz), 4.88 (2H, d, J = 17.2 Hz), 4.18 (2H, d, J = 17.2 Hz), 2.69 (2H, 
d, J = 9.2 Hz), 2.53 (2H, d, J = 9.2 Hz). 13C NMR (CD3OD, 150 MHz): 153.7, 147.0, 143.0, 
125.8, 124.6, 51.5, 47.0. IR (KBr, cm-1): 3416 (s), 3389 (s), 3100 (s), 3040 (s), 2991 (s), 2914 
(s), 2850 (s), 2482 (w), 2395 (w), 2270 (w), 2166 (w), 1665 (w), 1612 (s), 1578 (m), 1481 (s), 
1440 (s), 1363 (s), 1300 (s) 1262 (m), 1226 (s), 1160 (m), 1099 (s), 1048 (s), 1033 (s), 980 
(m), 906 (w), 849 (m), 821 (w), 777 (s), 723 (m), 649 (m), 567 (m), 506 (m), 480 (m), 425 
(m). Elemental Analysis: Calcd for C14H18N4GaCl3?H2O: C, 38.53%; H, 4.62%; N, 12.84%; 
Found: C, 38.32%; H, 4.53%; N, 12.51%. 
Dichloro(N,N,N?-tris(2-pyridylmethyl)-1,2-ethanediamine)gallium(III) chloride (2). 
GaCl3 (0.189 g, 1.074 mmol) and trispicen (0.359 g, 1.079 mmol) were dissolved in 10 mL of 
CH2Cl2 (2 mL). The resultant solution was stirred for 2 h at RT under N2. The addition of 
ether deposited the product as a pale yellow powder (0.356 g, 65%). 1H NMR (CD3OD, 400 
63 
 
MHz): 9.40 (1H, d, J = 4.4 Hz), 9.17 (1H, d, J = 4.4 Hz), 8.45 (1H, d, J = 5.2 Hz), 8.26 (2H, 
m), 7.96 (2H, m), 7.83 (2H, m), 7.61 (1H, d, J = 5.2 Hz), 7.55 (1H, t, J = 4.4 Hz), 7.16 (1H, d, 
J = 3.6 Hz), 4.56 (1H, d, J = 15.6 Hz), 4.49 (1H, d, J = 15.6 Hz), 4.08 (1H, d, J = 14.4 Hz), 
3.58 (4H, m), 3.20 (1H, m), 2.93 (1H, m), 2.84 (1H, m). 13C NMR (CD3OD, 150 MHz): 
148.5, 147.9, 147.5, 146.0, 144.7, 144.6, 143.5, 128.8, 128.1, 127.9, 127.1, 126.3, 126.2, 
124.7, 61.2, 61.1, 56.8, 53.1, 47.5. IR (KBr, cm-1): 3487 (s), 3387 (s), 3334 (s), 3115 (s), 2850 
(s), 2657 (s), 2476 (m), 2392 (m), 2271 (m), 2157 (m), 2034 (w), 1936 (w), 1882 (w), 1815 
(w), 1747 (w), 1611 (s), 1478 (s), 1438 (s), 1363 (s), 1298 (s), 1230 (s), 1159 (s), 1107 (s), 
1040 (s), 1031 (s), 977 (s), 910 (w), 849 (m), 777 (s), 720 (m), 646 (m), 565 (m), 492 (m), 
424 (m). Elemental Analysis: Calcd for C20H23N5GaCl3: C, 47.15%; H, 4.55%; N, 13.75%; 
Found: C, 47.44%; H, 4.45%; N, 13.36%. 
Dichloro(N,N,N?,N?-tetrakis(2-pyridylmethyl)-1,2-ethanediamine)gallium(III) chloride 
(3). GaCl3 (0.134 g, 0.761 mmol) and tpen (0.324 g, 0.763 mmol) were dissolved in 10 mL of 
CH2Cl2 under N2. The resultant solution stirred for 2 h at RT, after which excess ether was 
added to precipitate 0.388 g of the product as a white powder (85%). 1H NMR (CDCl3, 250 
MHz): 9.61 (2H, d, J = 5.4 Hz), 8.64 (2H, d, J = 4.8 Hz), 8.19 (2H, t, J = 8.2 Hz), 7.85 (2H, 
m), 7.74 (2H, t, J = 6.8 Hz), 7.60 (4H, m), 7.39 (2H, m), 5.09 (2H, d, J = 16.2 Hz), 4.65 (2H, 
d, J = 13.2 Hz), 4.20 (2H, d, J = 11.4 Hz), 3.60 (4H, m), 3.00 (2H, m). 1H NMR (CD3CN, 
400 MHz): 9.52 (2H, d, J = 5.2 Hz), 8.63 (2H, d, J = 5.6 Hz), 8.21 (2H, t, J = 8.0 Hz), 7.83 
(2H, t, J = 5.6 Hz), 7.75 (2H, t, J = 6.4 Hz), 7.62 (4H, d, J = 7.6 Hz), 7.41 (2H, m), 4.93 (2H, 
d, J = 16.0 Hz), 4.56 (2H, d, J = 13.6 Hz), 3.97 (2H, d, J = 16.4 Hz), 3.61 (2H, d, J = 13.6 
Hz), 3.48 (2H, d, J = 5.2 Hz), 3.27 (2H, d, J = 5.2 Hz). 13C NMR (CDCl3, 100 MHz): 151.9, 
151.5, 149.9, 147.0, 142.8, 137.5, 127.5, 126.6, 125.6, 124.2, 56.6, 56.4, 46.3. IR (KBr, cm-1): 
3045 (m), 3008 (s), 2945 (s), 2907 (s), 2863 (s), 2815 (s), 2800 (s), 2764 (s), 2695 (m), 2550 
(w), 2300 (w), 1905 (w), 1859 (w), 1796 (w), 1662 (w), 1588 (s), 1572 (s), 1472 (s), 1433 (s), 
1364 (s), 1345 (s), 1298 (s), 1245 (s), 1209 (m), 1170 (s), 1126 (s), 1085 (m), 1045 (m), 1016 
(w), 989 (s), 902 (m), 864 (m), 839 (m), 786 (s), 765 (s), 732 (m), 687 (w), 662 (w), 617 (m), 
593 (w), 546 (w), 470 (w). MS (ESI): Calcd for [Ga(tpen)Cl2]+, 563.1008; Found, 563.0988. 
Elemental Analysis: Calcd for C26H28N6GaCl3: C, 51.99%; H, 4.70%; N, 13.99%; Found: C, 
64 
 
51.70%; H, 4.65%; N, 14.00%.  
Dichlorobis(5-nitro(1,10-phenanthroline)gallium(III) chloride (4). GaCl3 (0.169 g, 0.959 
mmol) and NO2-phen (0.437 g, 1.94 mmol) were combined in 10 mL of CH2Cl2 under N2. 
After the solution was stirred for 2 h at RT, ether was added, precipitating 0.332 g of the 
product as a pale yellow powder (51%). 1H NMR (CD3OD, 600 MHz): 10.35 (2H, m), 9.82 
(1H, d, J = 12.0 Hz), 9.50 (1H, d, J = 8.4 Hz), 9.44 (1H, s), 9.33 (2H, m), 9.03 (1H, d, J = 8.4 
Hz), 8.67 (2H, m), 8.06 (1H, d, J = 3.6 Hz), 8.02 (1H, d, J = 3.6 Hz), 7.86 (2H, m). 13C NMR 
(CD3OD, 150 MHz): 155.9, 153.4, 151.8, 149.6, 148.0, 147.2, 146.6, 146.3, 146.0, 144.6, 
141.4, 140.0, 139.5, 139.0, 133.2, 131.1, 129.6, 129.3, 129.0, 128.4, 128.1, 127.1, 126.8, 
124.9, 124.5. IR (KBr, cm-1): 3422 (m), 3113 (w), 3071 (m), 3004 (w), 2970 (w), 2934 (w), 
2871 (w), 2337 (w), 1970 (w), 1946 (w), 1841 (w), 1627 (m), 1586 (m), 1540 (s), 1522 (s), 
1507 (s), 1490 (m), 1453 (m), 1421 (s), 1388 (m), 1349 (s), 1335 (s), 1261 (w), 1207 (m), 
1181 (m), 1153 (m), 1117 (m), 1104 (m), 1038 (w), 992 (w), 974 (w), 920 (m), 838 (s), 823 
(s), 810 (m), 751 (m), 734 (s), 721 (s), 652 (m), 619 (w), 541 (w), 507 (w), 429 (w). 
Elemental Analysis: Calcd for C24H14N6GaCl3?3H2O: C, 42.34%; H, 2.96%; N, 12.35%; 
Found: C, 42.56%; H, 2.73%; N, 12.11%. 
Dichlorobis(5-amino(1,10-phenanthroline)gallium(III) chloride (5). GaCl3 (0.104 g, 0.589 
mmol) and NH2-phen (0.228 g, 1.18 mmol) were dissolved in 10 mL of MeCN under N2. The 
solution was allowed to stir for 2 h at RT. After this time, excess ether was added to 
precipitate 0.287 g of the product as a yellow powder (87%). 1H NMR (DMSO-d6, 250 MHz): 
10.00 (1H, t, J = 5.2 Hz), 9.54 (2H, m), 9.06 (1H, d, J = 8.0 Hz), 8.88 (1H, d, J = 8.5 Hz), 
8.55 (1H, m), 8.40 (1H, d, J = 8.2 Hz), 8.28 (1H, m), 7.71 (2H, m), 7.45 (1H, m), 7.25 (2H, 
m), 7.10 (1H, s). 1H NMR (CD3OD, 600 MHz): 10.18 (1H, d, J = 16.5 Hz), 9.74 (1H, d, J = 
16.2 Hz), 9.39 (1H, t, J = 6.9 Hz), 8.91 (1H, d, J = 7.8 Hz), 8.75 (1H, m), 8.46 (1H, m), 8.27 
(1H, d, J = 7.8 Hz), 8.21 (1H, m), 7.66 (2H, m), 7.40 (1H, m), 7.25 (2H, m), 7.14 (1H, s). 13C 
NMR (DMSO-d6, 62.5 MHz): 148.2, 145.1, 144.9, 144.7, 144.5, 142.6, 138.9, 138.3, 137.2, 
136.9, 136.4, 136.0, 132.4, 132.0, 129.6, 128.8, 126.6, 126.3, 125.5, 125.2, 122.8, 122.3, 
101.0, 100.8. IR (KBr, cm-1): 3399 (s), 3339 (s), 3208 (s), 3080 (m), 1640 (s), 1620 (s), 1604 
(s), 1586 (m), 1522 (w), 1494 (s), 1465 (m), 1435 (s), 1350 (w), 1323 (w), 1287 (w), 1226 
65 
 
(w), 1164 (w), 1146 (w), 1122 (w), 1087 (w), 913 (w), 851 (w), 826 (w), 802 (w), 725 (s), 
665 (w), 653 (w), 427 (w). Elemental Analysis: Calcd for C24H18N6GaCl3?H2O: C, 49.31%; H, 
3.45%; N, 14.38%; Found: C, 49.56%; H, 3.43%; N, 14.51%. 
Dichlorobis(1,2-ethanediamine)gallium(III) chloride (6). GaCl3 (0.214 g, 1.22 mmol) and 
ethylenediamine (165 ?L, 2.46 mmol) were dissolved in 10 mL of MeCN under N2. As the 
reaction stirred for 2 h, a white precipitate began to form. The addition of ether deposited 
more solid. 0.320 g of the product was isolated as a white powder (79%). 1H NMR 
(DMSO-d6, 400 MHz): 3.07 (8H, s). 1H NMR (D2O, 600 MHz): 3.14 (8H, s). 13C NMR 
(DMSO-d6, 100 MHz): 36.57. 13C NMR (D2O, 150 MHz): 39.31. IR (KBr, cm-1): 3420 (s), 
3225 (s), 2978 (s), 2912 (s), 2804 (s), 2747 (s), 2711 (s), 2677 (s), 2634 (s), 2575 (m), 2521 
(m), 2420 (m), 2280 (w), 2055 (m), 1624 (m), 1602 (m), 1504 (s), 1342 (w), 1182 (w), 1085 
(m), 1034 (s), 1008 (w), 973 (w), 917 (w), 786 (w), 568 (m), 467 (m), 445 (w), 431 (w). 
Elemental Analysis: Calcd for C8H16N4GaCl3?2H2O: C, 14.46%; H, 6.07%; N, 16.86%; 
Found: C, 14.61%; H, 6.03%; N, 16.71%. 
Reactivity Studies 
All reactions were run in MeCN at 273 K under N2, with the initial concentrations of the 
catalyst, alkene, and PAAR being 5.0 mM, 500 mM, and 1.0 M, respectively. Most reactions 
were allowed to proceed for 1 h. At the end of each reaction, excess ether was added to 
precipitate the Ga(III) compound, effectively quenching the catalysis. For the studies 
focusing on the catalytic activity as a function of time, aliquots were taken at the indicated 
time points. Each portion was quenched with excess ether and filtered through a plug of silica 
gel to remove the remaining peracetic acid and Ga(III) salts. Control studies confirmed that 
this workup removed neither the olefin starting material nor the epoxide product from the 
solution. The remaining alkene and epoxide products were quantified relative to an internal 
standard of 1,2-dichlorobenzene, which is inert under the reaction conditions. All reactions 
were run at least three times to ensure reproducibility. All reported values are the averages of 
the results from these reactions. The errors represent one standard deviation. 
66 
 
4.3 Results 
Synthesis and Characterization 
The syntheses of the Ga(III) complexes proceed in a straightforward manner, and simply 
mixing the GaCl3 salt and ligand in room temperature CH2Cl2 or MeCN is sufficient to 
ensure complexation. The compounds with the polydentate pyridylamine ligands (bispicen, 
trispicen, tpen) can be isolated in high purities and yields (77-85%) through precipitation 
from CH2Cl2/ether mixtures. Compounds 1-3 tend to be hygroscopic and noticeably moisten 
upon prolonged exposure to air. The compounds with the bidentate ligands (NO2-phen, 
NH2-phen, en) are prepared in moderate to high yields (51-87%) through precipitation. The 
en complex 6 is the least soluble of the six Ga(III) compounds in organic solvents. 
Complexes 4-6 appear to be more hygroscopic than compounds 1-3, as we were unable to 
exclude water from the elemental analyses of the former. When the syntheses of 1-6 were run 
under air instead of N2, much lower yields of the desired products were obtained.  
 The Ga(III) complexes are diamagnetic and nearly colorless, as anticipated. The 294 K 
1H NMR spectrum of the bispicen complex 1 has four resonances in the aromatic region, 
indicating that its two pyridine rings are equivalent at this temperature. The doublet at 9.41 
ppm is assigned to the protons on the 6-positions of the pyridine rings. These resonances tend 
to be exquisitely sensitive to metal ion coordination, and their chemical shifts can be used to 
assess whether the affiliated pyridine rings bind to the Ga(III).35 The resonances at 4.88 and 
4.18 ppm indicate that there are two sets of methylene protons. This pattern is inconsistent 
with a trans ligand conformation, which has a sufficiently high symmetry to render all of the 
methylene protons equivalent. The splitting pattern is consistent with each methylene carbon 
bonding to two inequivalent protons and suggests a C2 symmetry for the Ga(III) complex in 
solution. The 13C NMR spectrum features only seven resonances, providing further evidence 
that the two halves of the bispicen ligand are equivalent in solution. The NMR data suggest 
that 1 retains the cis-? ligand conformation observed in its crystal structure (vida infra). 
The 1H NMR spectrum of the trispicen complex 2 has two doublets at 9.40 and 9.17 ppm 
that are comparable in energy to the 9.41 ppm resonance observed for 1. We have therefore 
67 
 
assigned these as corresponding to the protons on the 6-positions of Ga(III)-bound pyridine 
rings. The integrated intensity of each of these doublets corresponds to one proton, 
suggesting that the two associated pyridines are inequivalent at 294 K. The resonance for the 
third pyridine ring?s 6-position proton appears at a significantly lower chemical shift (8.45 
ppm), suggesting that it does not coordinate to the Ga(III). The inequivalence of the two 
coordinated pyridine rings is supported by the acquired 13C NMR spectrum. If the pyridines 
were equivalent, we would observe 14 13C resonances at most; instead, 19 resonances can be 
unambiguously identified. The conformation of the four coordinated N-donors cannot be 
assigned with certainty; Scheme 4.2 shows three possible solution structures in which the two 
chlorides are coordinated cis to each other. 
 
Scheme 4.2 Possible solution structures of 2 
 The tpen complex 3 likewise appears to have the pyridylamine ligand coordinated to the 
metal in a hypodentate fashion. The 1H NMR spectra in CD3CN and CDCl3 strongly 
resemble each other, suggesting that MeCN does not displace the chlorides to an observable 
degree. The NMR spectra are consistent with a structure with two pendant pyridine rings. 
This is again most apparent from consideration of the protons on the 6-position of the 
pyridine moieties, which are evenly split between doublet resonances at ~9.6 (bound) and 
~8.6 ppm (unbound). There are four doublets that can be reasonably assigned to methylene 
protons; as with 1, this pattern is consistent with a C2 symmetry and a cis-? conformation of 
the N-donors. The number of resonances in the 13C NMR data suggests that the two halves of 
the tpen ligand are equivalent in solution, supporting the assignment of a C2 symmetric 
species. High-resolution mass spectrometric analysis of 3 detects a [Ga(tpen)Cl2]+ cation; 
consequently, we believe that the Ga(III) center in 3, like those in 1 and 2, is primarily 
68 
 
coordinated by a N4Cl2 set of donor atoms in solution. The mode of tpen coordination that is 
most consistent with the data is depicted in Scheme 4.3. The exchange between the pendant 
and bound pyridines appears to be slow; we observe neither broadening nor coalescing of the 
1H NMR signals as samples of 3 in CD3CN are heated from 294 K to 324 K. 
 
Scheme 4.3 Proposed solution structure of 3 
 The solution structures of the two Ga(III) complexes with the phen derivatives are more 
difficult to interpret. Potentially, two 5-derivatized phen ligands could coordinate to the metal 
ion to form six isomers of cis-[Ga(R-phen)2Cl2]+; these six are comprised of three pairs of 
enantiomers (Scheme 4.4). Given that the cis conformation is present in the structures of both 
[Ga(phen)2Cl2]+ and [Ga(phen)2Br2]+,20, 36 we suspect that additional trans isomers are not 
present in significant quantities, although the data certainly cannot preclude such a possibility. 
The 1H and 13C NMR spectra of the two Ga(III) complexes with NO2-phen and NH2-phen, 4 
and 5, display more resonance features than would be anticipated from the uncoordinated 
ligands. This demonstrates that the isomers of the Ga(III) complexes, like complex 3, have 
limited fluxionality at room temperature. Rapid isomerization of 4 and 5 would result in 
seven and eight observable 1H NMR resonances, respectively; instead, we observe ten and 
twelve features. As with 3, we do not observe any 1H NMR resonances broaden or shift as 
samples of 4 are heated to 324 K. Given the number of multiplets observed in the 1H NMR 
spectra, we currently believe that 4 and 5 each exist as a mixture of multiple cis isomers in 
solution. 
 
 
 
69 
 
 
Scheme 4.4 ? Possible conformations of the phen ligands in complexes 4 and 5 
 The 1H and 13C NMR spectra of the en complex 6 each contain a single resonance, 
consistent with the presence of a single compound with two chemically equivalent en ligands. 
These NMR spectra are distinct from those of free en in both DMSO-d6 and D2O, indicating 
that the ligand is indeed chelating the metal ion. The data in D2O suggest that the Ga(III)-N 
bonds remain intact in solvents that can potentially ligate the Ga(III) center. 
Infrared Spectroscopy 
 IR measurements provide support for the modes of coordination suggested by the NMR 
data. The IR spectrum of non-coordinated pyridine features a C-N stretch at 1578 cm-1; 
coordination to a metal ion typically shifts this frequency to the 1590-1615 cm-1 range.37 The 
IR spectra of complexes 1-3 display stronger absorbance in the 1560-1580 cm-1 region as the 
number of pyridine rings increases (Figure A5, A8, A13), with complexes 1 and 3 having 
weak and strong bands at 1578 cm-1 and 1572 cm-1, respectively. The presence of this peak 
for 1 is unexpected and may result from either another vibrational mode or from the partial 
dissociation of the ligand during the preparation of the KBr pellet. Complex 2 lacks a distinct 
band in the 1560-1580 cm-1 range, but its 1611 cm-1 feature has a prominent shoulder that 
70 
 
extends into this region. All three complexes have intense bands where the C-N stretches of 
coordinated pyridines are expected (1612, 1611, and 1588 cm-1 for 1, 2, and 3 respectively). 
X-ray Crystallography 
 Crystals of 1 were grown from the slow diffusion of ether into saturated MeOH solutions 
(Table 4.1). The X-ray diffraction data confirm that the composition of 1 is 
[Ga(bispicen)Cl2]Cl (Figure 4.1). The outer-sphere chloride is 3.19 ? from one of the amine 
nitrogens, which may be consistent with a N-H???Cl hydrogen bond.38 In the cation, the 
bispicen ligand is bound to the Ga(III) in a cis-? conformation, which is commonly seen in 
the ligand?s complexes with transition metal ions,39-43 and contributes to an overall distorted 
octahedral coordination geometry around the metal center. In gallium chemistry, cis-? 
conformation of four N-donors has also been observed in complexes with N4O2 coordination 
spheres.11, 28 The Ga-N and Ga-Cl bond lengths observed for 1 are typical for a 
hexacoordinate Ga(III) complex with a N4Cl2 donor atom set.20, 44, 45 The Ga-N bond lengths 
differ only slightly, and the symmetry of the cation is approximately C2. 
 
Figure 4.1. ORTEP representation of the cation [Ga(bispicen)Cl2]+. All hydrogen atoms, the 
Cl- counterion, and three non-coordinated water molecules have been removed for clarity. All 
thermal ellipsoids are drawn at 50% probability. 
 
 
71 
 
 
Figure 4.2. ORTEP representation of the dication [Ga(trispicen)Cl]2+. All hydrogen atoms, 
the Cl- and [GaCl4]- counteranions, and a non-coordinated MeCN molecule have been 
removed for clarity. All thermal ellipsoids are drawn at 50% probability. 
 
Table 4.1. Selected crystallographic data for [Ga(bispicen)Cl2]Cl (1) and 
[Ga(trispicen)Cl](GaCl4)(Cl) (7) 
Parameter [Ga(bispicen)Cl2]Cl?3H2O [Ga(trispicen)Cl](GaCl4)(Cl)?MeCN 
Formula C14H24Cl3GaN4O Ga2H26Cl6Ga2N6 
MW 472.45 727.64 
Crystal system Monoclinic Triclinic 
Space group P21/c(#14) P1(#2) 
a (?) 13.7249(5) 9.2381(7) 
b (?) 7.3885(3) 12.0453(9) 
c (?) 20.7913(8) 14.7889(11) 
? (deg) 90 88.9220(10) 
? (deg) 105.600(1) 79.7160(10) 
? (deg)? 90 69.0670(10) 
V (?3) 2030.70(14) 1510.5(2) 
?? 4 2 
Cryst color Colorless Colorless 
?????? 296 296 
Reflns collected 63556 59468 
Unique reflns 4194 7113 
R1 (F, I > 2?(I)) 0.0302 0.0327 
wR2 (F2, all data) 0.0828 0.0728 
R1 = ???Fo?- ?Fc??/??Fo?; wR2 = [?w(Fo2-Fc2)2/?w(Fo2)2]1/2. 
72 
 
 Crystals were also grown from saturated solutions of 2 in mixtures of MeOH and MeCN 
(Table 4.1). The structural data, however, correspond to the formula 
[Ga(trispicen)Cl](GaCl4)(Cl) (7, Figure 4.2), as opposed to [Ga(trispicen)Cl2]Cl. Given that 
only the latter composition is consistent with the NMR, IR, and elemental analysis data for 
freshly isolated solid samples of 2, we believe that 2 converts to 7 over the prolonged period 
of time required for crystal growth. In the structure of 7, the bound trispicen is ?-5 rather than 
?-4. Two different counteranions are in the outer sphere: [GaCl4]- and Cl-. The presence of the 
tetrachlorogallate(III) anion indicates that some of the Ga(III) in the sample had dissociated 
from the trispicen ligand over the time required for crystallization. 
 Crystals that grew from saturated solutions of 3 were likewise consistent with 
decomposition products rather than the formula anticipated from the NMR and elemental 
analysis of the freshly precipitated product. In some cases, the Ga(III) centers in the crystals 
were coordinated by bispicen, with unit cell parameters that were identical to those of the 
aforementioned crystals of 1. In other cases, Ga(III) complexes with trispicen were isolated 
from the solutions. Both degradation products contain ligands that are missing picolyl arms. 
Water molecules are present in these crystal structures, which may suggest that these portions 
are being lost through hydrolytic processes. Attempts to grow the crystals in the strict absence 
of air and moisture were unsuccessful. 
Short-Term Reactivity 
 The six Ga(III) compounds were tested for their ability to catalyze the epoxidation of 
alkenes by PAAR (Table 4.2). A 1% loading of catalyst and two equiv of PAAR per equiv of 
substrate were used, primarily to facilitate comparison to our previous results with 
[Ga(phen)2Cl2]Cl.20 For each catalyzed oxidation reaction, the epoxide is the sole organic 
product observed at 1 h; no allylic oxidation or dihydroxylation is observed with the 1% mol 
catalytic loading. In all cases, the percentage of the alkene substrate that has been consumed 
is equal within error to the yield of the epoxide product, suggesting that the GC analysis has 
accounted for all organic products. As anticipated, the more electron-deficient terminal 
alkenes react less readily, as evidenced by the lower yields of epoxides. 
73 
 
Table 4.2. Alkene Conversions/Yields of Epoxides (%) of Reactions Catalyzed by 1-6a 
Substrate Product [Ga(phen)2Cl2]Clb 1 2 3 4 5 6 
  
46 (?5) 
46 (?8) 
31 (?4) 
32 (?4) 
27 (?2) 
25 (?2) 
14 (?1) 
15 (?1) 
56 (?4) 
56 (?7) 
43 (?2) 
40 (?3) 
41 (?2) 
40 (?3) 
  
90 (?3) 
87 (?4) 
80 (?3) 
82 (?2) 
66 (?4) 
68 (?5) 
32 (?2) 
31 (?3) 
93 (?3) 
94 (?2) 
87 (?3) 
84 (?2) 
85 (?5) 
83 (?5) 
  
10 (?1) 
11 (?2) 
7 (?0.4) 
7 (?0.6) 
3 (?0.2) 
3 (?0.2) 
0 
0 
13 (?1) 
13 (?1) 
10 (?1) 
9 (?1) 
10 (?1) 
9 (?1) 
 
 38 (?4) 
41 (?3) 
2 (?0.2) 
2 (?0.3) 
2 (?0.2) 
2 (?0.2) 
0 
0 
51 (?3) 
47 (?3) 
34 (?3) 
35 (?3) 
2 (?0.2) 
2 (?0.2) 
  
59 (?8) 
61 (?6) 
40 (?4) 
37 (?3) 
26 (?4) 
28 (?4) 
17 (?2) 
17 (?2) 
70 (?6) 
72 (?4) 
52 (?5) 
50 (?5) 
38 (?2) 
39 (?3) 
aStandard reaction conditions: MeCN, 273 K, N
2, [Ga(III)] = 5.0 mM, [alkene]o = 500 mM, [PAAR]o = 1.0 
M. The alkene conversion, defined as the percentage of alkene that has been consumed by the reaction, 
was measured at 1 h via GC. The alkene conversions are italicized in the above table. The yield of epoxide, 
defined as the percentage of alkene converted to the epoxide, was measured at 1 h via GC. Since the 
substrate is in a 100-fold excess relative to the catalyst, the above yield of epoxides also serve as turnover 
numbers. bFrom reference 20.  
Three trends can be observed in the epoxidation activities. First, the Ga(III) complexes 
with phen derivatives promote alkene epoxidation to much greater extents. In particular, 
compounds 4 and 5 promote the oxidation of 1-octene to 1-octene oxide to much higher 
degrees than any of the other four newly reported Ga(III) complexes. The increases in the 
yields of the other epoxide products are much less pronounced. Second, the use of more 
electron-deficient ligands tends to result in more epoxidation. Comparison of the activities of 
[Ga(phen)2Cl2]Cl, 4, and 5 reveals that the installation of a more electron-withdrawing NO2 
group on the 5-position of the phen ligands increases the turnover rate; the addition of an 
electron-donating NH2 group reduces the yield of the epoxide at 1 h. Third, as the maximum 
denticity of the ligand increases past ?-4, the Ga(III) complexes become less able to quickly 
catalyze olefin epoxidation. Within the series of complexes with pyridylamine ligands, the 
catalytic activity associated with the tetradentate ligand bispicen is fastest; conversely, the 
complex with the potentially hexadentate tpen, 3, is the worst at promoting olefin 
epoxidation. 
74 
 
In the previously studied alkene oxidation catalyzed by [Ga(phen)2Cl2]Cl, the selectivity 
for the epoxide product is lost upon switching to a lower catalyst loading. With a 0.1% 
catalyst loading of the phen complex, the most heavily represented products result from 
allylic C-H oxidation and bishydroxylation.20 A loss of selectivity for the epoxide is also 
observed for the oxidation of cyclohexene catalyzed by 1, but with a substantially different 
product distribution. With a 0.1% loading of 1, 3.0 M cyclohexene is oxidized by 6.0 M 
PAAR to predominantly trans-1,2-cyclohexanediol (49%), with cyclohexene oxide as a minor 
product (6%) and the remainder of the substrate failing to react (45%). Unexpectedly, 
2-cyclohexenol is not observed. Another potential product of allylic C-H oxidation, 
2-cyclohexenone, is not formed in the olefin oxidations catalyzed by low concentrations of 
either 1 or [Ga(phen)2Cl2]Cl.20 
Time-Scale of Reactivity 
 The ability of the Ga(III) complexes to catalyze the epoxidation of olefins by peracetic 
acid was monitored beyond 1 h in order to assess whether a more highly chelating ligand 
could extend the lifetime of the reactivity. Figure 4.3 shows the yields as a function of time 
for the epoxidations of five olefins catalyzed by the bispicen complex 1. There is no 
noticeable initiation period, although this may occur on a much shorter timescale. The data 
show that the catalytic activity of 1 is maintained past 1 h; the observed increases in the 
yields beyond this time point are too large to be attributed to the uncatalyzed reactions 
between the olefins and terminal oxidant.20 The most reactive substrate, cyclooctene, is fully 
converted to cyclooctene oxide by 2 h. Beyond 5 h, diol products consistent with the 
subsequent opening of the epoxide are observed. With cyclohexene as the substrate, 
cyclohexene oxide is the sole organic product until 5 h, forming in 75% yield from the alkene. 
By 6 h, noticeable amounts of trans-1,2-cyclohexanediol are observed in addition to the 
epoxide.  
75 
 
 
Figure 4.3. Yields of alkene epoxidations by PAAR catalyzed by the bispicen complex 1 as a 
function of time. The reaction conditions are identical to those listed for Table 4.2. 
 Mass spectrometry (MS) of the cyclohexene epoxidation at 3 h reveals that the 
bispicen-Ga(III) adduct is still intact. At both 5 min and 3 h, the most intense feature has a 
m/z of 369.0817, consistent with [Ga(bispicen-H)(CH3CO2)]+ (predicted m/z = 369.0842). 
This suggests that the two chlorides in 1 are displaced by acetate shortly after the beginning 
of the reaction. Under the ionization conditions, one of the amine protons is likely lost, 
explaining both the reduced mass and the +1 charge of the observed ion.  
The trispicen and tpen complexes 2 and 3 likewise appear to retain their catalytic activity 
for longer periods of time than [Ga(phen)2Cl2]Cl, as assessed by their abilities to catalyze the 
oxidation of cyclohexene by PAAR. Figure 4.4A compares the longer term reactivities of 
compounds 1-6 and [Ga(phen)2Cl2]Cl, using the oxidation of cyclohexene to cyclohexene 
oxide as a standard.20 The plot shows that the activities of the complexes with the bidentate 
ligands have decreased substantially by 3 h. Catalysts 1-3, though slower, appear to retain 
more of their activity, with the overall catalytic activity of 1 becoming approximately 
equivalent to those of 5 and [Ga(phen)2Cl2]Cl by 3 h. As anticipated, compounds 2 and 3 are 
much less active than 1 throughout the 3 h. MS analyses of 2 and 3 at 3 h do not reveal any 
76 
 
peaks consistent with the ligand hydrolysis observed in the crystals grown from solutions of 3. 
Although 3, for instance, eventually decomposes to 1 and 2 (Figure 4.2), we did not observe 
m/z features for either of these compounds in the 3 h data for reactions using 3 as a catalyst. 
As with 1, the peaks observed at 3 h are consistent with acetate adducts.  
The plots of the cyclohexene oxide yields versus time for catalysts 4-6 are more curved 
than those observed for compounds 1-3, suggesting that the former set is less durable under 
the reaction conditions. Despite this, catalyst 4 remains the best catalyst of the six at the 3 h 
timepoint. Losses of activity for 4 and 5 are also observed over time when 1-octene is used as 
the standard (Figure 4.4B), but with this particular substrate, the durabilities of 1-3 do not 
come close to compensating for their slower activity.  
A. B.  
Figure 4.4. Yields of alkene epoxidation by PAAR catalyzed by the 1-6 and [Ga(phen)2Cl2]Cl 
as a function of time. Panel A shows the oxidation of cyclohexene; whereas, B shows the 
oxidation of 1-octene. The reaction conditions are identical to those listed for Table 4.2. The 
data for [Ga(phen)2Cl2]Cl are from Reference 20. 
4.4 Discussion 
 The syntheses of the Ga(III) complexes are generally straightforward, in that no special 
measures are necessary to form adducts between the N-donor ligands and the metal ion and 
that pure products can be isolated without chromatography. The obtained yields range from 
77 
 
moderate (51%) to high (85%). One complication with the syntheses is that the compounds 
are hygroscopic, and prolonged exposure to moisture appears to degrade the pyridylamine 
ligands, as evidenced by the crystallized decomposition products of 3. The complexes with 
the phen derivatives are likely isolated as mixtures of cis isomers (Scheme 4.4). 
 Three pyridylamine ligands were investigated: bispicen, trispicen, and tpen (Scheme 4.1). 
The bispicen molecule is a well-established tetradentate ligand.32, 46-48 The tpen ligand 
typically coordinates metal ions in a hexadentate fashion, although tetra- and pentadentate 
modes of coordination have been observed.49-53 With respect to previously reported Group 13 
chemistry, there exists a heptacoordinate complex of tpen with In(III), with the tpen itself 
providing six of the donor atoms in the inner sphere.54 The coordination chemistry of 
trispicen is much less established, but a singly methylated derivative, 
N?-methyl-N,N,N?-tris(2-pyridylmethyl)-1,2-ethanediamine, is pentadentate in its structurally 
characterized complexes with Mn(II) and Fe(II).34, 55 NMR analysis of 1, 2, and 3 suggests 
that all three ligands predominantly coordinate Ga(III) through four N-donors, with one or 
two pyridine rings failing to ligate the metal in 2 and 3, respectively. This is supported by IR 
analysis of freshly precipitated powder samples of these compounds. 
 Although the crystal structure of 1 (Figure 4.1) is consistent with its NMR spectra and 
elemental analysis, crystals grown from solutions of 2 are not consistent with the initially 
obtained [Ga(trispicen)Cl2]Cl. The crystal structure of the isolated 7 (Figure 4.2) 
demonstrates that the coordination of trispicen to Ga(III) is not limited to the hypodentate 
mode supported by the NMR data. In one of the complex ions within the asymmetric unit, 
[Ga(trispicen)Cl]2+, the ligand is pentacoordinate; whereas, in the other complex ion, [GaCl4]-, 
the trispicen is entirely absent from the gallium. The [Ga(trispicen)Cl]2+ dication represents 
only the second example of a structurally characterized Ga(III) ion with a N5X coordination 
sphere (X = F, Cl, Br, I).56 
 The capability of the trispicen and tpen ligands to more fully coordinate the Ga(III) may 
explain the decreased epoxidation activities exhibited by 2 and 3 (Table 4.2, Figure 4.4). 
Focusing the analysis on the complexes with the three pyridylamine ligands, the bispicen 
complex 1 promotes the most extensive epoxidation of all substrates except 1-octene, which 
78 
 
essentially doesn?t react with either 1, 2, or 3 present as the catalyst. The tpen-containing 3 is 
the worst catalyst of the three compounds, with 1 h yields that are less than half of those 
measured for 1. Based on the results, we speculate that the pendant pyridine rings in 2 and 3 
may compete with the terminal oxidant for the coordination sites vacated by the initially 
bound chloride anions. Previous work suggests that the affinities of pyridine rings to Ga(III) 
are comparable to those of carboxylate ligands.28 Reducing the number of pendant pyridine 
donors would alleviate the competition between intramolecular and intermolecular binding 
and facilitate the coordination of PAA to the Ga(III) center necessary for catalysis. 
Alternatively, the steric bulk provided by the additional binding arms in 2 and 3 may hinder 
coordination of the terminal oxidant and/or limit the accessibility of the alkene substrate to 
the reactive portion of the active oxidant. 
The results may suggest that two available coordination sites are needed to activate the 
PAA most efficiently, which is reminiscent of the Sharpless type mechanism proposed for the 
epoxidation of alkenes by mixtures of [Al(H2O)6]3+ and H2O2.27, 57 In the mechanistic scheme 
proposed by Shul?pin et al for this Al(III) catalysis, coordination of both oxygen atoms of the 
H2O2 to the metal center precedes a concerted oxygen atom transfer from the bound oxidant 
to an uncoordinated alkene.27 If two coordination sites are likewise needed for the activation 
of PAA by the Ga(III) centers of the current catalysts, 2 would be anticipated to be an inferior 
catalyst to 1, in accordance with our results (Table 4.2). Scheme 4.5 illustrates a possible 
mechanism for the epoxidation reactions that highlights the potential benefit of a second 
coordination site for the PAA. The illustrated mechanism assumes that the N-donor ligands 
remain fully bound during the reaction; this assumption has not been experimentally 
confirmed. We are currently assessing the feasibility of various mechanistic pathways 
through computational analysis and experiments involving Ga(III) complexes with sterically 
encumbered bispicen derivatives. 
79 
 
 
Scheme 4.5 Illustration of possible mechanism for the epoxidation reactions  
The higher catalytic activities of the complexes with the phen derivatives suggest that the 
Ga(III) centers enable catalysis through their abilities to act as Lewis acids. That more 
electron-rich alkenes tend to react more readily would suggest an electrophilic oxidant, which 
would be stabilized and rendered less active by more electron-rich ligands. The 
electrophilicity of the oxidant in the Ga(III) catalysis is also consistent with the inability of 
H2O2 and t-BuOOH to serve as terminal oxidants for the epoxidation reactions. Carbonyl 
groups are widely considered to be electron-withdrawing functional groups. When PAA is 
used as the terminal oxidant, its carbonyl group may reduce the electron density on the 
transferred oxygen atom sufficiently to allow oxygen atom transfer to the alkene substrate. 
The acetate produced upon oxygen atom transfer would also be a better leaving group than 
the hydroxide or t-butyloxide resulting from H2O2 or t-BuOOH. 
1,10-Phenanthroline is widely viewed as being electron-poor relative to amine N-donor 
ligands and should render chelated metal ions more electron-deficient. Complexes 4 and 5 are 
notable for their ability to catalyze the oxidation of 1-octene; the other four Ga(III) 
compounds reported here, conversely, cannot promote this reaction to a significant degree. 
The addition of electron-withdrawing nitro groups onto the phen ligands improves the yields 
of the epoxidation reactions; conversely, the installation of electron-donating amino groups 
decreases the yields (Table 4.1).  
Although the complexes with the phen ligands are more active over shorter durations, the 
compounds with the pyridylamine ligands can potentially achieve superior turnover numbers 
over longer periods of time due to the greater stability provided by chelate effects. One noted 
shortcoming with the [Ga(phen)2Cl2]Cl catalyst is that it decomposed to unreactive Ga(III) 
80 
 
salts and free phen within approximately the first hour of the epoxidation reactions.20 The 
phen appears to slowly dissociate from the Ga(III) center under acidic conditions. The 
stability of the Ga(III) catalyst can be increased by using a single tetradentate ligand in the 
place of two bidentate ligands. The ability of bispicen, trispicen, and tpen to sustain the 
catalysis over longer periods of time confirms that this is a viable strategy for 
Ga(III)-catalyzed olefin epoxidations (Figures 4.3 and 4.4). Compound 1 is an equivalent 
catalyst to [Ga(phen)2Cl2]Cl when the yields of cyclohexene epoxidation are measured at 3 h 
(Figure 4.4). Unlike the phen compound, the Ga(III)-bispicen adduct remains intact at 3 h. 
The observed decomposition of 2 and 3 (Figure 4.2, Figure A1), however, suggest that the 
pyridylamine-containing complexes do have finite catalytic lifetimes. Compounds 1-3 appear 
to retain their intact polydentate ligands through the 3 h necessary for the alkene epoxidation, 
however, suggesting that the ligand degradation is slow relative to the alkene epoxidation.  
The reactivity with the 1% catalyst loading is selective for the epoxide product for short 
durations, with the epoxide accounting for the entirety of the observed organic product. The 
reactions using 1 as the catalyst do start to produce trans-1,2-cyclohexanediol between 5 and 
6 h after the start of the reaction. As with the olefin oxidation catalyzed by 
[Ga(phen)2Cl2]Cl,20 the selectivity for the epoxide product is lost when the catalyst loading of 
1 is reduced to 0.1%. Oddly, the chemistry associated with 1 differs from that promoted by 
the phen compound in that the lower concentration of 1 does not promote allylic C-H 
activation. Instead, bishydroxylation is overwhelmingly favored under such circumstances. 
When cyclohexene oxide is used as a substrate with the standard reaction conditions and a 
1% mol loading of gallium (3.0 mM 1, 6.0 M PAAR, 0 ?C, 7 h), no diol is observed, 
suggesting that cyclohexene may be converted directly to trans-1,2-cyclohexanediol as 
opposed to a two-step reaction involving epoxidation followed by ring-opening. We speculate 
that another Ga(III)-based oxidant is responsible and are continuing to investigate this 
side-reactivity through experimental and computational methods. The mechanism displayed 
on Scheme 4.5 certainly doesn?t explain all of the observed oxidative activity of the Ga(III) 
complexes. 
 
81 
 
4.5 Conclusions 
 Six new gallium(III) complexes with N-donor ligands have been prepared and tested as 
catalysts for the epoxidation of alkenes by peracetic acid. Comparison of the compounds? 
activities provides three major insights into Ga(III)-catalyzed alkene epoxidation. First, more 
electron-deficient ligands are found to support more rapid catalytic turnover, with phen 
derivatives leading to superior initial activity over ligands with amine and pyridine chelating 
groups. The Ga(III) complexes with phen derivatives are markedly better at activating the 
electron-deficient substrate 1-octene, and [Ga(NO2-phen)2Cl2]Cl is the best catalyst of the six 
under all characterized reaction conditions. Second, more highly coordinating ligands, such 
as the tetradentate bispicen, can prolong the catalytic activity by stabilizing the ligand-metal 
adduct. Third, it is found that the more highly chelating N-donor ligands, trispicen and tpen, 
decrease the catalytic activity. The additional binding arms may compete with terminal 
oxidant for the coordination sites, or they may impede the reactivity through steric effects. 
 
82 
 
Appendix 
 
 
Figure A1. ORTEP representation of [Ga(trispicen)Cl]Cl2?MeCN?3H2O grown from a 
solution of [Ga(tpen)Cl2]Cl in MeCN. All hydrogen atoms are omitted for clarity. All thermal 
ellipsoids are drawn at 50% probability. 
 
83 
 
Table A1. Selected crystallographic data for [Ga(trispicen)Cl]Cl2. 
Parameter [Ga(trispicen)Cl]Cl2?MeCN?
Formula C22H32Cl3GaN6O3 
MW 602.61 
Crystal system Triclinic 
Space group P1(#2) 
a (?) 9.1540(3) 
b (?) 11.9245(4) 
c (?) 12.8632(4) 
? (deg) 80.3060(10) 
? (deg) 81.8800(10) 
? (deg)? 88.0630(10) 
V (?3) 1370.11(8) 
?? 2 
Cryst color Colorless 
?????? 198 
Reflns 36681 
Unique reflns 3770 
R1 (F, I > 2?(I)) 0.0364 
wR2 (F2, all 0.0943 
R1 = ???Fo?- ?Fc??/??Fo?; wR2 = [?w(Fo2-Fc2)2/?w(Fo2)2]1/2. 
 
Figure A2. Mass spectrum (ESI) of [Ga(tpen)Cl2]Cl. The m/z features at 563.1000 and 
565.0953 are assigned to [Ga(tpen)Cl2]+ (calcd m/z = 563.1008 and 565.0979). The m/z 
feature at 264.0689 is assigned to [Ga(tpen)Cl]2+ (calcd m/z = 264.0650).  
84 
 
 
 
Figure A3. 1H NMR spectrum of 1 in CD3OD at 294 K. The data were acquired on a 400 
MHz instrument. Solvent peaks are present at 4.87 (water) and 3.31 (methanol) ppm; these 
have been truncated for clarity. The doublet centered at 4.88 ppm overlaps with the water 
peak. 
 
 
 
 
Figure A4. 13C NMR spectrum of 1 in CD3OD at 294 K. The solvent peak at 49.86 ppm 
(methanol) has been truncated for clarity. 
 
85 
 
 
 
 
Figure A5. IR spectrum of 1. The sample was prepared as a KBr pellet. The full listing of 
peak frequencies in cm-1 is as follows: 3416 (s), 3389 (s), 3100 (s), 3040 (s), 2991 (s), 2914 
(s), 2850 (s), 2482 (w), 2395 (w), 2270 (w), 2166 (w), 1665 (w), 1612 (s), 1578 (m), 1481 (s), 
1440 (s), 1363 (s), 1300 (s) 1262 (m), 1226 (s), 1160 (m), 1099 (s), 1048 (s), 1033 (s), 980 
(m), 906 (w), 849 (m), 821 (w), 777 (s), 723 (m), 649 (m), 567 (m), 506 (m), 480 (m), 425 
(m).  
 
 
Figure A6. 1H NMR spectrum of 2 in CD3OD at 294 K. The data were acquired on a 400 
MHz instrument. The solvent peaks present at 4.87 (water) and 3.31 (methanol) ppm have 
been truncated for clarity. 
86 
 
 
 
Figure A7. 13C NMR spectrum of 2 in CD3OD at 294 K. The solvent peak at 49.86 ppm 
(methanol) has been truncated for clarity. 
 
 
Figure A8. IR spectrum of a powder sample of 2. The sample was prepared as a KBr pellet. 
The full listing of peak frequencies in cm-1 is as follows: 3487 (s), 3387 (s), 3334 (s), 3115 (s), 
2850 (s), 2657 (s), 2476 (m), 2392 (m), 2271 (m), 2157 (m), 2034 (w), 1936 (w), 1882 (w), 
1815 (w), 1747 (w), 1611 (s), 1478 (s), 1438 (s), 1363 (s), 1298 (s), 1230 (s), 1159 (s), 1107 
(s), 1040 (s), 1031 (s), 977 (s), 910 (w), 849 (m), 777 (s), 720 (m), 646 (m), 565 (m), 492 (m), 
424 (m). Note the shoulder on the feature at 1611 cm-1. 
 
87 
 
 
Figure A9. IR spectrum of a crystalline sample of 7, which was grown from a saturated 
solution of 2. The sample was prepared as a KBr pellet.Note that the peak at 1613 cm-1 lacks 
the shoulder found for the powder sample of 2, which would be consistent with the lack of 
non-coordinated pyridine rings in the solid. 
 
 
Figure A10.1H NMR spectrum of 3 in CDCl3 at 294 K. The data were acquired on a 250 
MHz instrument. The solvent peak present at 7.26 (chloroform) has been truncated for clarity. 
 
 
88 
 
 
 
Figure A11.1H NMR spectrum of 3 in CD3CN at 294 K. The data were acquired on a 400 
MHz instrument. The solvent peak present at 1.94 (acetonitrile) has been truncated for clarity. 
 
 
 
Figure A12. 13C NMR spectrum of 3 in CDCl3 at 294 K. The solvent peak at 77.16 
(chloroform) has been truncated for clarity. 
 
89 
 
 
Figure A13. IR spectrum of a powder sample of 3. The sample was prepared as a KBr pellet. 
The full listing of peak frequencies in cm-1 is as follows: 3045 (m), 3008 (s), 2945 (s), 2907 
(s), 2863 (s), 2815 (s), 2800 (s), 2764 (s), 2695 (m), 2550 (w), 2300 (w), 1905 (w), 1859 (w), 
1796 (w), 1662 (w), 1588 (s), 1572 (s), 1472 (s), 1433 (s), 1364 (s), 1345 (s), 1298 (s), 1245 
(s), 1209 (m), 1170 (s), 1126 (s), 1085 (m), 1045 (m), 1016 (w), 989 (s), 902 (m), 864 (m), 
839 (m), 786 (s), 765 (s), 732 (m), 687 (w), 662 (w), 617 (m), 593 (w), 546 (w), 470 (w).Note 
the intense feature at 1588 cm-1, which is consistent with the presence of two non-coordinated 
pyridine rings in the solid. 
 
 
 
Figure A14. 1H NMR spectrum of 4 in CD3OD at 294 K. The data were acquired on a 600 
MHz instrument. Only solvent resonances were observed outside the shown 7.0-10.5 ppm 
range. 
90 
 
 
Figure A15. 13C NMR spectrum of 4 in CD3OD at 294 K. The feature at 49.00 ppm 
corresponds to solvent and has been truncated for clarity. 
 
 
Figure A16. IR spectrum of a powder sample of 4. The sample was prepared as a KBr pellet. 
The full listing of peak frequencies in cm-1 is as follows: 3422 (m), 3113 (w), 3071 (m), 3004 
(w), 2970 (w), 2934 (w), 2871 (w), 2337 (w), 1970 (w), 1946 (w), 1841 (w), 1627 (m), 1586 
(m), 1540 (s), 1522 (s), 1507 (s), 1490 (m), 1453 (m), 1421 (s), 1388 (m), 1349 (s), 1335 (s), 
1261 (w), 1207 (m), 1181 (m), 1153 (m), 1117 (m), 1104 (m), 1038 (w), 992 (w), 974 (w), 
920 (m), 838 (s), 823 (s), 810 (m), 751 (m), 734 (s), 721 (s), 652 (m), 619 (w), 541 (w), 507 
(w), 429 (w). 
91 
 
 
 
Figure A17. 1H NMR spectrum of 5 in DMSO-d6 at 294 K. The data were acquired on a 250 
MHz instrument. The solvent contributes a resonance feature at 2.50 ppm. 
 
 
Figure A18. 1H NMR spectrum of 5 in CD3OD at 294 K. The data were acquired on a 600 
MHz instrument. Only solvent resonances were observed outside the shown 7.0-10.5 ppm 
range. 
92 
 
 
Figure A19. 13C NMR spectrum of 5 in DMSO-d6 at 294 K. The feature at 39.51 ppm 
corresponds to solvent and has been truncated for clarity. 
 
 
Figure A20. IR spectrum of a powder sample of 5. The sample was prepared as a KBr pellet. 
The full listing of peak frequencies in cm-1 is as follows: 3399 (s), 3339 (s), 3208 (s), 3080 
(m), 1640 (s), 1620 (s), 1604 (s), 1586 (m), 1522 (w), 1494 (s), 1465 (m), 1435 (s), 1350 (w), 
1323 (w), 1287 (w), 1226 (w), 1164 (w), 1146 (w), 1122 (w), 1087 (w), 913 (w), 851 (w), 
826 (w), 802 (w), 725 (s), 665 (w), 653 (w), 427 (w). 
93 
 
 
 
Figure A21. 1H NMR spectrum of 6 in DMSO-d6 at 294 K. The data were acquired on a 400 
MHz instrument. A solvent peak is present at 2.50 ppm. 
 
 
 
 
Figure A22. 13C NMR spectrum of 6 in DMSO-d6 at 294 K. The solvent peak at 39.51 ppm 
has been truncated for clarity. 
94 
 
 
Figure A23. IR spectrum of a powder sample of 6. The sample was prepared as a KBr pellet. 
The full listing of peak frequencies in cm-1 is as follows: 3420 (s), 3225 (s), 2978 (s), 2912 (s), 
2804 (s), 2747 (s), 2711 (s), 2677 (s), 2634 (s), 2575 (m), 2521 (m), 2420 (m), 2280 (w), 
2055 (m), 1624 (m), 1602 (m), 1504 (s), 1342 (w), 1182 (w), 1085 (m), 1034 (s), 1008 (w), 
973 (w), 917 (w), 786 (w), 568 (m), 467 (m), 445 (w), 431 (w). 
 
 
Figure A24.The yields of the organic products of [Ga(bispicen)Cl2]Cl-catalyzed cyclohexene 
oxidation by PAAR over time. The reaction was run at 0 ?C in MeCN with initial 
concentrations of 5.0 mM Ga(III) catalyst, 500 mM cyclohexene, and 1000 mM PAAR.The 
points on the plot are the averages of three separate reactions, with errors of ?2% for the 
yields of cyclohexene oxide and ?1% for the yields of 1,2-cyclohexanediol. The diol is not 
observed until the 6 h time point. 
 
95 
 
 
 
 
Figure A25. Mass spectrum (ESI) of the gallium species present in solution 3 h after the 
beginning of the cyclohexene epoxidation reaction catalyzed by 1. 500 mM cyclohexene, 
1000 mM peracetic acid, and 5.0 mM [Ga(bispicen)Cl2]Cl were mixed in MeCN and allowed 
to stir at 0 ?C for 3 h. The m/z features at 369.0817 and 371.0823 are assigned to 
[Ga(bispicen-H)(CH3CO2)]+ (calcd m/z = 369.0842 and 371.0833). 
96 
 
 
Figure A26. Mass spectrum (ESI) of the gallium species present in solution 3 h after the 
beginning of the cyclohexene epoxidation reaction catalyzed by 2. 500 mM cyclohexene, 
1000 mM peracetic acid, and 5.0 mM [Ga(trispicen)Cl2]Cl were mixed in MeCN and allowed 
to stir at 0 ?C for 3 h. The m/z features at 460.1083 and 462.1095 are assigned to 
[Ga(trispicen-H)(CH3CO2)]+ (calcd m/z = 460.1264 and 462.1255). The peaks at 281.5377 
and 219.5382 are assigned to [Ga(trispicen)Cl]2+ (calcd m/z = 218.5445 and 219.5445). The 
peaks at 200.5546 and 201.5544 are assigned to [Ga(trispicen-H)]2+ (calcd m/z = 200.5566 
and 201.5561). 
97 
 
 
Figure A27. Mass spectrum (ESI) of the gallium species present in solution 3 h after the 
beginning of the cyclohexene epoxidation reaction catalyzed by 3. 500 mM cyclohexene, 
1000 mM peracetic acid, and 5.0 mM [Ga(tpen)Cl2]Cl were mixed in MeCN and allowed to 
stir at 0 ?C for 3 h. The m/z features at 551.1714 and 553.1232 are assigned to 
[Ga(tpen-H)(CH3CO2)]+ (calcd m/z = 551.1686 and 553.1677).  
 
 
 
98 
 
References 
(1) Chi, Y.; Chou, T.-Y.; Wang, Y.-J.; Huang, S.-F.; Carty, A. J.; Scoles, L.; Udachin, K. A.; 
Peng, S.-M.; Lee, G.-H. Organometallics 2003, 23, 95-103. 
(2) Park, J.-H.; Afzaal, M.; Helliwell, M.; Malik, M. A.; O'Brien, P.; Raftery, J. Chem. 
Mater. 2003, 15, 4205-4210. 
(3) Valet, M.; Hoffman, D. M. Chem. Mater. 2001, 13, 2135-2143. 
(4) Suh, S.; Hoffman, D. M. Chem. Mater. 2000, 12, 2794-2797. 
(5) MacInnes, A. N.; Power, M. B.; Barron, A. R. Chem. Mater. 1993, 5, 1344-1351. 
(6) Kouvetakis, J.; Beach, D. B. Chem. Mater. 1989, 1, 476-478. 
(7) Cowley, A. H. J. Organomet. Chem. 2000, 600, 168-173. 
(8) Bartholom?, M. D. Inorg. Chim. Acta 2012, 389, 36-51. 
(9) Wadas, T. J.; Wong, E. H.; Weisman, G. R.; Anderson, C. J. Chem. Rev. 2010, 110, 
2858-2902. 
(10) Bartholom?, M. D.; Louie, A. S.; Valliant, J. F.; Zubieta, J. Chem. Rev. 2010, 110, 
2903-2920. 
(11) Boros, E.; Ferreira, C. L.; Cawthray, J. F.; Price, E. W.; Patrick, B. O.; Wester, D. W.; 
Adam, M. J.; Orvig, C. J. Am. Chem. Soc. 2010, 132, 15726-15733. 
(12) Dagorne, S.; Atwood, D. A. Chem. Rev. 2008, 108, 4037-4071. 
(13) Yamaguchi, M.; Nishimura, Y. Chem. Commun. 2008, 35-48. 
(14) Wehmschulte, R. J.; Steele, J. M.; Young, J. D.; Khan, M. A. J. Am. Chem. Soc. 2003, 
125, 1470-1471. 
(15) Lichtenberg, C.; Spaniol, T. P.; Okuda, J. Inorg. Chem. 2012, 51, 2254-2262. 
(16) Tang, S.; Monot, J.; El-Hellani, A.; Michelet, B.; Guillot, R.; Bour, C.; Gandon, V. 
Chem. Eur. J. 2012, 18, 10239-10243. 
(17) Carty, A. J.; Dymock, K. R.; Boorman, P. M. Can. J. Chem. 1970, 48, 3524-3529. 
(18) Ivanov-Emin, B. N.; Nisel'son, L. A.; Rabovik, Y. I.; Larionova, L. E. Russ. J. Inorg. 
Chem. 1961, 6, 1142-1146. 
99 
 
(19) McPhail, A. T.; Miller, R. W.; Pitt, C. G.; Gupta, G.; Srivastava, S. C. J. Chem. Soc., 
Dalton Trans. 1976, 1657-1661. 
(20) Jiang, W.; Gorden, J. D.; Goldsmith, C. R. Inorg. Chem. 2012, 51, 2725-2727. 
(21) Fricke, R.; Kosslick, H.; Lischke, G.; Richter, M. Chem. Rev. 2000, 100, 2303-2405. 
(22) Pescarmona, P. P.; Janssen, K. P. F.; Jacobs, P. A. Chem. Eur. J. 2007, 13, 6562-6572. 
(23) Stoica, G.; Santiago, M.; Jacobs, P. A.; P?rez-Ram?rez, J.; Pescarmona, P. P. Appl. 
Catal. A 2009, 371, 43-53. 
(24) Cates, C. D.; Myers, T. W.; Berben, L. A. Inorg. Chem. 2012, 51, 11891-11897. 
(25) Nam, W.; Valentine, J. S. J. Am. Chem. Soc. 1990, 112, 4977-4979. 
(26) Rinaldi, R.; de Oliveira, H. F. N.; Schumann, H.; Schuchardt, U. J. Mol. Catal. A 
2009, 307, 1-8. 
(27) Kuznetsov, M. L.; Kozlov, Y. N.; Mandelli, D.; Pombeiro, A. J. L.; Shul'pin, G. B. 
Inorg. Chem. 2011, 50, 3996-4005. 
(28) Caravan, P.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1997, 36, 1306-1315. 
(29) Murphy, A.; Pace, A.; Stack, T. D. P. Org. Lett. 2004, 6, 3119-3122. 
(30) Sheldrick, G. M., 6.12 ed.; Siemens Analytical X-ray Instruments, Inc.: Madison, WI, 
2001. 
(31) Sheldrick, G. M.; Bruker Analytical X-ray Systems: Madison, WI, 1996. 
(32) Toftlund, H.; Pedersen, E.; Yde-Andersen, S. Acta. Chem. Scand. A 1984, 38, 
693-697. 
(33) Anderegg, G.; Wenk, F. Helv. Chim. Acta 1967, 50, 2330-2332. 
(34) Mialane, P.; Nivorojkine, A.; Pratviel, G.; Az?ma, L.; Slany, M.; Godde, F.; Simaan, 
A.; Banse, F.; Kargar-Grisel, T.; Bouchoux, G.; Sainton, J.; Horner, O.; Guilhem, J.; 
Tchertanova, L.; Meunier, B.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1085-1092. 
(35) Goldsmith, C. R.; Jonas, R. T.; Cole, A. P.; Stack, T. D. P. Inorg. Chem. 2002, 41, 
4642-4652. 
(36) Junk, P. C.; Skelton, B. W.; White, A. H. Aust. J. Chem. 2006, 59, 147-154. 
(37) Gill, N. S.; Nuttall, R. H.; Scaife, D. E.; Sharp, D. W. A. J. Inorg. Nucl. Chem. 1961, 
18, 79-87. 
100 
 
(38) Willett, R. D.; G?mez-Garc?a, C. J.; Twamley, B.; G?mez-Coca, S.; Ruiz, E. Inorg. 
Chem. 2012, 51, 5487-5493. 
(39) Goodson, P. A.; Glerup, J.; Hodgson, D. J.; Michelsen, K.; Pedersen, E. Inorg. Chem. 
1990, 29, 503-508. 
(40) Coates, C. M.; Fiedler, S. R.; McCullough, T. L.; Albrecht-Schmitt, T. E.; Shores, M. 
P.; Goldsmith, C. R. Inorg. Chem. 2010, 49, 1481-1486. 
(41) Collins, M. A.; Hodgson, D. J.; Michelsen, K.; Towle, D. K. J. Chem. Soc., Chem. 
Commun. 1987, 1659-1660. 
(42) Arulsamy, N.; Hodgson, D. J.; Glerup, J. Inorg. Chim. Acta 1993, 209, 61-69. 
(43) Ardon, M.; Bino, A.; Michelsen, K.; Pedersen, E.; Thompson, R. C. Inorg. Chem. 
1997, 36, 4147-4150. 
(44) Restivo, R.; Palenik, G. J. J. Chem. Soc., Dalton Trans. 1972, 341-344. 
(45) Sofetis, A.; Raptopoulou, C. P.; Terzis, A.; Zafiropoulos, T. F. Inorg. Chim. Acta 2006, 
359, 3389-3395. 
(46) Glerup, J.; Goodson, P. A.; Hazell, A.; Hazell, R.; Hodgson, D. J.; McKenzie, C. J.; 
Michelsen, K.; Rychlewska, U.; Toftlund, H. Inorg. Chem. 1994, 33, 4105-4111. 
(47) Arulsamy, N.; Goodson, P. A.; Hodgson, D. J.; Glerup, J.; Michelsen, K. Inorg. Chim. 
Acta 1994, 216, 21-29. 
(48) Heinrichs, M. A.; Hodgson, D. J.; Michelsen, K.; Pedersen, E. Inorg. Chem. 1984, 23, 
3174-3180. 
(49) Hureau, C.; Blanchard, S.; Nierlich, M.; Blain, G.; Rivi?re, E.; Girerd, J.-J.; 
Anxolab?h?re-Mallart, E.; Blondin, G. Inorg. Chem. 2004, 43, 4415-4426. 
(50) Musso, S.; Anderegg, G.; Ruegger, H.; Schl?pfer, C. W.; Gramlich, V. Inorg. Chem. 
1995, 34, 3329-3338. 
(51) Chang, H. R.; McCusker, J. K.; Toftlund, H.; Wilson, S. R.; Trautwein, A. X.; Winkler, 
H.; Hendrickson, D. N. J. Am. Chem. Soc. 1990, 112, 6814-6827. 
(52) Yoon, D. C.; Lee, U.; Oh, C. E. Bull. Korean Chem. Soc. 2004, 25, 796-800. 
(53) Dueland, L.; Hazell, R.; McKenzie, C. J.; Nielsen, L. P.; Toftlund, H. J. Chem. Soc., 
Dalton Trans. 2001, 152-156. 
101 
 
(54) Harrington, J. M.; Oscarson, K. A.; Jones, S. B.; Reibenspies, J. H.; Bartolotti, L. J.; 
Hancock, R. D. Z. Naturforsch. 2007, 62b, 386-396. 
(55) Hureau, C.; Groni, S.; Guillot, R.; Blondin, G.; Duboc, C.; Anxolab?h?re-Mallart, E. 
Inorg. Chem. 2008, 47, 9238-9247. 
(56) Radish, K. M.; Cornillon, J. L.; Korp, J. D.; Guilard, R. J. Heterocycl. Chem. 1989, 26, 
1101-1104. 
(57) Sharpless, K. B.; Townsend, J. M.; Williams, D. R. J. Am. Chem. Soc. 1972, 94, 
295-296.