Synthesis of Surface-Analogue Square-Planar Tetranuclear Nickel Hydride Clusters and Bonding to μ 4 -NR, -O and -BH Ligands

Tetranuclear Ni complexes were synthesized with bonding to BH, NR, and O in atypical surface-like geometries. The previously reported electron-deficient cluster [( Pr P)Ni] H (1) reacts with N-methylmorpholine oxide to give [( Pr P)Ni] H (μ -O) (2), which contains O coordinated in the center of a square-plane arrangement of Ni atoms. Reaction of 1 with benzonitrile gave the square-planar tetranuclear Ni cluster [( Pr P)Ni] H (μ -NCH Ph) (3), which contains an imido donor in a square-based-pyramidal geometry. This reaction also gives [( Pr P)Ni(N≡CPh)] (4), with bridging benzonitrile ligands. Trimer 4 was independently synthesized from the reaction of Ni(COD) , Pr P, and PhC≡N. The addition of dihydrogen to a 1:1 mixture of [( Pr P) Ni] (N ) and ( Pr P) NiCl yielded [( Pr P)Ni] (μ -H) (μ -Cl) (5), with a tetrahedral Ni core, in contrast to the square-planar geometries of 2 and 3. The solid-state structure of 5 was determined using both X-ray and neutron diffraction. Reaction of 5 with LiBH gave [( Pr P)Ni] H (μ -BH) ] (6) via loss of LiCl and H .