A Highly Active Manganese Precatalyst for the Hydrosilylation of Ketones and Esters

The reduction of (^Ph₂PPrPDI)­MnCl₂ allowed the preparation of the formally zerovalent complex, (^Ph₂PPrPDI)­Mn, which features a pentadentate bis­(imino)­pyridine chelate. This complex is a highly active precatalyst for the hydrosilylation of ketones, exhibiting TOFs of up to 76,800 h^–1 in the absence of solvent. Loadings as low as 0.01 mol % were employed, and (^Ph₂PPrPDI)Mn was found to mediate the atom-efficient utilization of Si–H bonds to form quaternary silane products. (^Ph₂PPrPDI)Mn was also shown to catalyze the dihydrosilylation of esters following cleavage of the substrate acyl C–O bond. Electronic structure investigation of (^Ph₂PPrPDI)Mn revealed that this complex possesses an unpaired electron on the metal center, rendering it likely that catalysis takes place following electron transfer to the incoming carbonyl substituent.