Hexameric chiral α-amino lithium alkoxides: a solid-state and theoretical structural investigation

Abstract

The nucleophilic reagents lithium N-methylpiperazide, 1-Li, and lithium N,N,N′-trimethylethylenediamide, 2-Li, react with 1 equiv. of 4-methoxybenzaldehyde and 2-methylbenzaldehyde respectively to afford the corresponding chiral α-amino lithium alkoxides, (3)₆·2PhMe·THF and (4)₆·2PhMe, which are hexamers in the solid state. Stabilisation of the metal centres is assisted by dative coordination of the dialkylamine α-N-centres. While for (3)₆·2PhMe·THF this is rationalised in terms of steric constraints imposed by the employment of a heterocyclic dialkylamine, for (4)₆·2PhMe it contrasts starkly with previously observed structural analogues. Abinitio MO calculations are employed to investigate the relationship between structure and ligand chirality.