Kinetics of the reaction of metal-alkyl compounds with alkenes III. Diisobutylaluminium hydride

Abstract

The addition of dissobutylaluminium hydride to 1-butene is investigated and the rate found to exhibit half order in aluminium hydride concentration. A mechanism is given in which the monomeric form of the aluminium hydride is active in the addition reaction. It has been shown that the addition of aluminium alkyls to n-alkenes is limited by the dissociation of the dimer 1,2, i.e.: Al 2Et 6 ←→ 2 AlEt 3 (1) as addition proceeds through the monomer, i.e.: AlEt 3CH 2=CHR → Et 2AlCH 2CH(Et)R (20 Under the conditions of the reaction the β-branched alkyl group is eliminated and in the presence of excess n-alkene an n-alkylaluminium compound is produced. An aluminium hydride intermediate rather than direct group displacement may be involved in this reaction, i.e.: Et 2AlCH 2CH(Et)R → Et 2AlH+CH=C(Et)R (3) Et 2AlH+CH 2=CHR → Et 2AlCH 2CH 2R (4) This overall reaction scheme was substantiated by a study of the reaction products of triethylaluminium and n-1-octene to high conversions. These were 2-ethyl-1-octene-, hexadecene; n-octyl-, 2-ethyloctyl- and hexadecylaluminium compounds. The present paper considers the evidence for the displacement reaction proceeding via a hydride intermediate in the light of the reactivity of diisobytylaluminium hydride to n-1-butene addition, and is compared with the addition reaction with triethylaluminium