Synthesis, Reactivity, and Catalytic Application of a Nickel Pincer Hydride Complex

The nickel(II) hydride complex [((N2N)-N-Me)Ni-H] (2) was synthesized by the reaction of [((N2N)-N-Me)Ni-OMe] (6) with Ph2SiH2 and was characterized by NMR and IR spectroscopy as well as X-ray crystallography. 2 was unstable in solution, and it decomposed via two reaction pathways. The first pathway was intramolecular N-H reductive elimination to give (N2NH)-N-Me and nickel particles. The second pathway was intermolecular, with H-2, nickel particles, and a five-coordinate Ni(II) complex [((N2N)-N-Me)(2)Ni] (8) as the products. 2 reacted with acetone and ethylene, forming [((N2N)-N-Me)Ni-(OPr)-Pr-i] (9) and [((N2N)-N-Me)Ni-Et] (10), respectively. 2 also reacted with alkyl halides, yielding nickel halide complexes and alkanes. The reduction of alkyl halides was rendered catalytically, using [((N2N)-N-Me)Ni-Cl] (1) as catalyst, (NaOPr)-Pr-i or NaOMe as base, and Ph2SiH2 or Me(EtO)(2)SiH as the hydride source. The catalysis appears to operate via a radical mechanism.