Unexpected Role of Zinc Hydride in Catalytic Hydrosilylation of Ketones and Nitriles

The hydride compound DippNacNacZnH (<b>1</b>) catalyzes chemoselective hydrosilylation of ketones and aldehydes under mild conditions and chemoselective reduction of nitriles to imines. Mechanistic studies showed that the product of nitrile insertion into the Zn–H bond of <b>1</b>, DippNacNacZn-NC­(H)­(Ph) (<b>2</b>), is not a potent catalyst. Kinetic studies under catalytic conditions suggest a reversible coordination of silane to <b>1</b> to form an intermediate which then reacts with the substrate (nitrile or ketone) via a cyclic transition state to give the silylated product.