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

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.