Reversible substrate activation and catalysis at an intact metal-metal bond using a redox-active supporting ligand

An electron rich Ni(I)-Ni(I) bond supported by a doubly reduced naphthyridine-diimine (NDI) ligand reacts rapidly and reversibly with Ph2SiH2 and Et2SiH2 to form stable adducts. The solid-state structures of these complexes reveal binding modes in which the silanes symmetrically span the Ni-Ni bond and exhibit highly distorted H-Si-H angles and elongated Si-H bonds. This process is facilitated by the release of electron density stored in the π-system of the NDI ligand. Based on this dinuclear mode of activation, [NDI]Ni2 complexes are shown to catalyze the high-yielding hydrosilylation of alkenes, dienes, alkynes, aldehydes, ketones, enones, and amides. In comparative studies of alkyne hydrosilylations, the [NDI]Ni2 catalyst is found to be significantly more active than its mononuclear counterparts for aryl-substituted substrates.