Boryl–Metal Bonds Facilitate Cobalt/Nickel-Catalyzed Olefin Hydrogenation

New approaches toward the generation of late first-row metal catalysts that efficiently facilitate two-electron reductive transformations (e.g., hydrogenation) more typical of noble-metal catalysts is an important goal. Herein we describe the synthesis of a structurally unusual S = 1 bimetallic Co complex, [( Cy PBP)­CoH] 2 (1), supported by bis­(phosphino)­boryl and bis­(phosphino)­hydridoborane ligands. This complex reacts reversibly with a second equivalent of H2 (1 atm) and serves as an olefin hydrogenation catalyst under mild conditions (room temperature, 1 atm H2). A bimetallic Co species is invoked in the rate-determining step of the catalysis according to kinetic studies. A structurally related NiINiI dimer, [( Ph PBP)­Ni] 2 (3), has also been prepared. Like Co catalyst 1, Ni complex 3 displays reversible reactivity toward H2, affording the bimetallic complex [( Ph PBHP)­NiH] 2 (4). This reversible behavior is unprecedented for NiI species and is attributed to the presence of a boryl–Ni bond. Lastly, a series of monomeric ( tBu PBP)­NiX complexes (X = Cl (5), OTf (6), H (7), OC­(H)O (8)) have been prepared. The complex ( tBu PBP)­NiH (7) shows enhanced catalytic olefin hydrogenation activity when directly compared with its isoelectronic/isostructural analogues where the boryl unit is substituted by a phenyl or amine donor, a phenomenon that we posit is related to the strong trans influence exerted by the boryl ligand.