Visible Light‐Induced Catalytic Hydrosilylation of Ketones Mediated by Manganese NHC Complexes

Manganese catalysis has attracted significant attention in the last few years. In comparison with the extensively studied Mn complexes bearing phosphine-based pincer ligands, catalysis with Mn containing N-heterocyclic carbenes (NHC) is poorly developed. In this work, new manganese(I) complexes bearing an NHC ligand with picolyl wingtip substituents (an N,C,N ligand) have been synthesized and fully characterized. The structure of fac-[Mn(CO)₃(κ²N,C,N)Br] and fac-[Mn(CO)₃(κ³N,C,N)](OTf) complexes with a bidentate and tridentate coordination of the N,C,N ligand, respectively, has been elucidated by single crystal X-ray diffraction studies. These Mn complexes were applied as catalysts for the visible light-induced hydrosilylation of ketones. The mild protocol operated efficiently at room temperature under visible light irradiation (blue LED), enabling the conversion of a wide variety of aromatic ketones to their respective alcohols in high yields. Evidence for radical intermediates and the participation of Mn-H species has been demonstrated by a series of trapping experiments.