Crystal structures and unusual solution behaviour of diastereomeric aluminium and gallium complexes of chiral amines [Me3M · 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 2 NH and ( S )-Ph(Me)CH(CH 2 CH CH 2 )NH afforded the corresponding datively bonded chiral Lewis acid/base adducts. The molecular structures of ( S , R )-[Me 3 Al · HN(CHMePh)(CH 2 Ph)] ( 1 ), [( S , R )-Me 3 Ga · HN(CHMePh)(CH 2 Ph)] ( 2 ), Me 3 Al · HN(CHMePh) 2 ( 3 ), Me 3 Ga · HN(CHMePh) 2 ( 4 ), ( S , S )-]Me 3 Al · HN(CHMePh)(CH 2 CH CH 2 )] ( 5 ) and ( S , S )-[Me 3 Ga · HN(CHMePh)(CH 2 CH CH 2 )] ( 6 ) have been determined by single-crystal X-ray diffraction and found to be isostructural, crystallising in the same space group, P 2 1 2 1 2 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.