Unexpected Role of Zinc Hydride in Catalytic Hydrosilylation
of Ketones and Nitriles
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Abstract
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-NC(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