Ni-catalyzed undirected and regioselective acceptorless dehydrogenative silylation of primary benzylic C(sp3)–H bonds

Abstract

The dehydrogenative silylation of ubiquitous inactive C–H bonds provides an eco-friendly synthetic protocol for useful organosilicon compounds. Compared with the well-established C(sp²)–H dehydrogenative silylation, C(sp³)–H dehydrogenative silylation is immature and generally requires directing groups such as heterocyclic structures and intramolecular Si–H groups. In particular, the undirected benzylic C(sp³)–H silylation has been hardly reported partly because of the difficult regioselectivity control between benzylic C(sp³)–H and aryl C(sp²)–H bonds. In this work, an undirected acceptorless dehydrogenative silylation with an excellent benzylic C(sp³)–H selectivity was successfully developed using a CeO₂-supported highly dispersed Ni(0) nanocatalyst, which was prepared via reduction with pinacolborane. Surprisingly, the dehydrogenative silylation occurred preferentially at the primary benzylic positions even in the presence of secondary ones, possibly due to the steric hindrance of substrates on the Ni catalyst.