A Mechanism for the Palladium-Catalyzed Regioselective Silaboration of Allene: A Theoretical Study

A mechanism for the regioselective silaboration of terminal allene by a palladium catalyst has been studied theoretically. The overall reaction scheme has been examined in particular to determine the mechanism of the regioselectivity. The present catalytic reaction is exothermic and the rate-determining step is the insertion of allene into the Pd−B bond of the Pd complex. σ-Allylic and π-allylic complexes exist as intermediates and play an important role in the regioselectivity. Selective insertion of the unsubstituted C═C bond into the Pd−B bond produces the most stable σ-allylic complex, which converts to the π-allylic complex while maintaining the Pd−O coordination. The selective formation of the specific σ-allylic complex and the large activation barrier between two isomeric π-allylic complexes dominantly determines the regioselectivity of the present reaction. The major-product complex is less stable than the minor-product complex, and therefore kinetic control is predominant in the present reaction.