Nickel-catalysed reactions with trialkylboranes and silacyclobutanes.

Nickel catalysis enables us to develop new reactions with trialkylboranes and silacyclobutanes of modest reactivity. A combination of Ni(cod)(2) and tri-tert-butylphosphine catalyses alkylation reactions of aldehydes and alpha,beta-unsaturated esters with various trialkylboranes of modest reactivity, suppressing conceivable beta-hydride elimination from alkylnickel intermediates. A nickel catalyst is also useful for 1,4-addition of bis(pinacolato)diboron to alpha,beta-unsaturated esters and amides. Nickel-catalysed reaction of silacyclobutanes with aldehydes results in ring opening to afford the corresponding alkoxyallylsilanes. In contrast, the ring expansion reaction of benzosilacyclobutene with aldehydes yields benzoxasilacyclohexenes. A nickel catalyst prepared from Ni(cod)(2) and tricyclohexylphosphine realises direct silylation of terminal alkenes with silacyclobutane furnishing vinylsilanes.