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

The reduction of ((PDI)-P-Ph2PPr)MnCl2 allowed the preparation of the formally zerovalent complex, ((PDI)-P-Ph2PPr)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 ((PDI)-P-Ph2PPr)Mn was found to mediate the atom-efficient utilization of Si-H bonds to form quaternary silane products. ((PDI)-P-Ph2PPr)Mn was also shown to catalyze the dihydrosilylation of esters following cleavage of the substrate acyl C-O bond. Electronic structure investigation of ((PDI)-P-Ph2PPr)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.