Crystal structures and unusual solution behaviour of diastereomeric aluminium and gallium complexes of chiral amines [Me 3M · RR*NH

Abstract

The highly air sensitive reaction of trimethylaluminium and trimethylgallium with a series of commonly utilised chiral secondary amines (( S)-Ph(Me)CH)(PhCH 2)NH, ( R, R)-Ph(Me)CH 2NH and ( S)-Ph(Me)CH(CH 2CH CH 2)NH afforded the corresponding datively bonded chiral Lewis acid/base adducts. The molecular structures of ( S, R)-[Me 3Al · HN(CHMePh)(CH 2Ph)] ( 1), [( S, R)-Me 3Ga · HN(CHMePh)(CH 2Ph)] ( 2), Me 3Al · HN(CHMePh) 2 ( 3), Me 3Ga · HN(CHMePh) 2 ( 4), ( S, S)-]Me 3Al · HN(CHMePh)(CH 2CH CH 2)] ( 5) and ( S, S)-[Me 3Ga · HN(CHMePh)(CH 2CH CH 2)] ( 6) have been determined by single-crystal X-ray diffraction and found to be isostructural, crystallising in the same space group, P2 12 12 1. NMR studies established that complexes 1, 2, 5 and 6 form as a diasteriomeric mixture however, in contrast to the other complexes, 1 appears to display two distinct structural isomers at low temperature.