Mn-Catalyzed Regioselective Alkene Hydrosilylation: From Mechanism Investigation to the Design of a Pre-Catalyst Candidate

Abstract

The catalytic hydrosilylation of alkenes is a cornerstone process in the large-scale production of organosilicon compounds. As an alternative to precious metal catalysts, manganese-based systems such as Mn(CO)₅Br have gained significant attention due to their low cost and high availability. However, the catalytic mechanism in place is not completely understood, and several propositions have been described in the literature. To clarify this point, we have employed a combined experimental and computational approach to elucidate the activation mechanism of Mn(CO)₅Br in the anti-Markovnikov hydrosilylation of alkenes. Our findings reveal that the initiation involves specific CO ligand dissociation and substrate coordination to generate an active Mn(I) intermediate that catalyzes the desired transformation via concerted 2-electron organometallic pathways. Exploration of reaction mechanisms at the DFT level provided detailed insights into the activation mechanism of Mn(CO)₅Br, enabling the rational design of the Mn–alkyl complex Mn(CO)₅(ⁿOct) as a precatalyst that offers direct access to the active catalytic cycle. This complex promotes anti-Markovnikov hydrosilylation of alkenes at room temperature with loadings as low as 0.5 mol % while retaining high activity and selectivity even in the presence of some contaminants.