Synthesis of Surface-Analogue Square-Planar Tetranuclear Nickel Hydride Clusters and Bonding to μ₄-NR, -O and -BH Ligands

Abstract

Tetranuclear Ni complexes were synthesized with bonding to BH, NR, and O in atypical surface-like geometries. The previously reported electron-deficient cluster [( ⁱPr₃P)Ni]₅H₆ (1) reacts with N-methylmorpholine oxide to give [( ⁱPr₃P)Ni]₄H₄(μ₄-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 [( ⁱPr₃P)Ni]₄H₄(μ₄-NCH₂Ph) (3), which contains an imido donor in a square-based-pyramidal geometry. This reaction also gives [( ⁱPr₃P)Ni(N≡CPh)]₃ (4), with bridging benzonitrile ligands. Trimer 4 was independently synthesized from the reaction of Ni(COD)₂, ⁱPr₃P, and PhC≡N. The addition of dihydrogen to a 1:1 mixture of [( ⁱPr₃P)₂Ni]₂(N₂) and ( ⁱPr₃P)₂NiCl₂ yielded [( ⁱPr₃P)Ni]₄(μ₃-H)₄(μ₂-Cl)₂ (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 LiBH₄ gave [( ⁱPr₃P)Ni]₄H₄(μ₄-BH)₂] (6) via loss of LiCl and H₂.