Hemi-alkoxides from reactions of trimethylaluminium with aldehydes or ketones

Abstract

One mole of an aldehyde or ketone reacts stoicheiometrically with one mole of trimethylaluminium dimer at ambient temperature in hydrocarbon solvents to form a "hemi-alkoxide" in which an alkoxy group and a methyl group bridge two aluminium atoms. Benzaldehyde, acetone, acetophenone, benzophenone, and cyclohexanone give p-alkoxy-p-methyl-tetramethyldialuminiums (Me₂A1.OR.Me.AlMe₂; R = CHPhMe, Bu^t, CphMea₂ CPh₂Me, and 1-methylcyclohexyl, respectively). Such compounds can also be prepared in low yields starting from alcohols, rather than aldehydes or ketones. The analogous compound, NezAl.N=CPhMe.Me.AlMez, is formed by reaction of benzonitrile with one mole of trimethylaluminium dimer in the absence of solvent at 100º. Exchange of methyl groups between bridge and terminal sites in these new compounds has been studied by proton magnetic resonance spectroscopy.