Mechanism and origin of the stereoselectivity of manganese-catalyzed hydrosilylation of alkynes: a DFT study

Abstract

The manganese-catalyzed hydrosilylation reaction provides a powerful platform to synthesize organosilicon compounds due to their rich reserves, low toxicity, and promising novel reactivity. In this work, the detailed mechanisms of the manganese-catalyzed hydrosilylation of alkynes using the mononuclear Mn(CO)₅Br and binuclear Mn₂(CO)₁₀ have been systematically investigated and compared by DFT calculations. The mononuclear Mn(CO)₅Br-catalyzed hydrosilylation of alkynes belongs to an organometallic mechanism. The computational results indicate that the proposed organometallic catalytic cycle in the early literature cannot completely explain the experimental results due to the high energy barrier involved. A novel catalytic mechanism, in which the CO firstly dissociates from Mn(CO)₄BrL, provides an explanation to the studied reaction. E-pro is the main product of the mononuclear Mn(CO)₅Br-catalyzed hydrosilylation of alkynes. Meanwhile, the Mn₂(CO)₁₀-catalyzed cycle occurs via radical mechanism, and Z-pro is obtained due to the steric effect. In both mononuclear Mn(CO)₅Br and binuclear Mn₂(CO)₁₀-catalyzed cycles, the substituted alkyne addition process is the rate-determining step. Our calculated results provide deep insight into and amend the mechanistic details for the significant manganese-catalyzed hydrosilylation of alkyne, which is expected to be informative for the effective utilization of Mn catalysts and stereoselective control of alkyne functionalization reactions.