|dc.description.abstract||The hindered amine tris(1,3-dihydroxy-2-propyl)amine, 36, is a potential precursor to possible examples of nitrogen hypervalency. There are no simple, effective, and general methods to synthesize hindered tertiary amines. Extending previous work in our laboratory on Rh2(OAc)4-catalyzed insertions of carbenoids into N-H bonds, we achieved a synthesis of 36 in five steps and 49% overall yield. Starting from commercially available dihydroxyacetone dimer, our synthesis makes 36 available in multigram quantities.
Some properties and structure of 36 have been studied. The pKa of 36 was found to be 3.08 ± 0.03, a low value for a tertiary amine. The X-ray crystal structure of 36 showed the nitrogen is essentially planar (sum of C-N-C angles 359.05(7) °), and the average C-N bond length (1.454 Å) was shorter than normal. An explanation of this bond contraction is offered. The oxidation potential E1/2ox of 36 measured by cyclic voltammetry was found to be 0.88 V. The oxidation was reversible; oxidations of ordinary tertiary amines are usually irreversible. The X-ray crystal structure of 36•HCl revealed a severely flattened tetrahedral geometry about nitrogen (average H-N-C angle 102.3 °).
The reaction of 36 with boric acid led to a “one- boron” compound, 67 (2,8,9-tris(hydroxymethyl)-5-bora-1-aza-4,6,11-trioxytricyclo[3.3.3.01,5]undecane) and a “two-boron” compound, 69 (1,7-dibora-11-aza-2,6,8,14,15,17-hexaoxy¬tetra¬cyclo¬[18.104.22.168.7,1204,11]octadecane). The X-ray crystal structure of 67 showed a dative bond between nitrogen and boron (1.6875(13) Å). Compound 69 is very hydrolytically unstable, but the X-ray crystal structure of a complex of 69 with pyridine confirmed the presence in 69 of two borons.
The reaction of 36 with Z-Si(OEt)3 (Z = Me, Ph) led to analogous ""one-silicon"" and ""two-silicon"" compounds. The X-ray crystal structures of both two-silicon compounds revealed a nearly symmetrical SiNSi array (Z = Me) and an unsymmetrical one (Z = Ph).||en_US