Tris(1,3 -dihydroxy -2 -propyl)amine, a planar trialkylamine: Synthesis, structure, and properties. A potential precursor to hypervalent nitrogen.

摘要

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 A) was shorter than normal. An explanation of this bond contraction is offered. The oxidation potential E 1/2ox 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[3.3.3.0.5]undecane) and a "two-boron" compound, 69 (1,7-dibora-11-aza-2,6,8,14,15,17-hexaoxytetracyclo-[8.4.2.2.7,1204,11]octadecane). The X-ray crystal structure of 67 showed a dative bond between nitrogen and boron (1.6875(13) A). 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).