Towards an understanding of the conjugate addition of organolithium reagents to α,β-unsaturated ketones:: the isolation and solid-state structure of a monomeric lithium aluminate with very short agostic Li•••HC interactions

Reaction of methylaluminium bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD), I, with alkyllithium reagents, R'Li (R' = Me, n-Bu or t-Bu), yields the solvent-dependent products lithium bis(2,6-di-tert-butyl-4-methylphenoxide) complex, 2 THF, lithium dimethylbis(2,6-di-tert-butyl-4-methylphenoxide)aluminate 3, a new type of lithium aluminate in which the lithium centre is stabilised by very short agostic Li ... H(t-Bu) interactions, and tris(alkyl)aluminium. The observation of these products suggests an explanation for the tendency of alpha,beta-unsaturated ketones to undergo conjugate (rather than 1,2-) addition in the presence of MAD and organolithium reagents. (C) 1999 Elsevier Science S.A. All rights reserved.