A DFT Study on Palladium and Nickel-Catalyzed Regioselective and Stereoselective Hydrosilylation of 1,3-Disubstituted Allenes

Theoretical calculations have been carried out to illustrate the mechanisms and origins of regio/stereoselective hydrosilylation of 1,3-disubstituted allenes catalyzed by Pd and Ni catalysts. Investigations indicated that the mechanisms are divided into three important steps: coordination of silane and allene to the metal center, concerted oxidative addition, and silyl/hydride migration as well as C–H/C–Si bond reductive elimination. We found that concerted oxidative addition is the rate-limiting and regioselective step for the allene-hydrosilylation reaction. Moreover, the utilization of different palladium and nickel catalysts containing N-heterocyclic carbene (NHC) ligands can lead to switchable regioselectivity in allene hydrosilylations. The reaction with Pd–NHC catalysts favors allylsilane products, whereas the reaction with Ni–NHC catalysts affords alkenylsilane products. Intrinsic electronic effects of Pd or Ni catalysts and steric repulsions between catalysts and substrates (silyl and allene) can significantly affect the regioselectivity. These computations are in accordance with observations from experiments and can help to design new palladium and nickel catalysts for the regio/stereoselectivities of allene-hydrosilylation reactions.