Organo-aluminium compounds. IV. Exchange reactions between trialkylaluminiums and triphenylaluminium

Abstract

Dimethylphenylaluminium, diethylphenylaluminium, di-isobutylphenylaluminium, and isobutyldiphenylaluminium have been prepared as solids by reaction of triphenylalurninium with the appropriate amount of trialkylaluminium. Dimethylphenylaluminium is more conveniently prepared from triphenylaluminium etherate and excess trimethylaluminium. All four compounds undergo thermal disproportionation, that of the isobutyldiphenylaluminium occurring in cyclohexane at 40°. Disproportionation of dimethylphenylaluminium occurs in benzene with a half-time of less than 10^-1 sec even in the presence of more than one equivalent of ether or tetrahydrofuran. In the presence of more than two equivalents of ether or tetrahydrofuran, or in either of these two solvents alone, disproportionation is slower; the half-life is then in the range 10^-1-10² sec. It is concluded that exchange of methyl for phenyl groups can occur when at least one of the two participating aluminium atoms is bound to an ether or tetrahydrofuran molecule.