Octaboraneyl [Ni(H)(diphosphine)2]+ Complexes: Exploiting Phosphine Ligand Lability for Hydride Transfer to an [NAD]+ Model.

Ligand design represents a central tenet of synthetic chemistry, wherein simple modification can lead to major differences in reactivity. Herein, we describe the preparation of two bis(diphosphino)nickel(II) hydride complexes that contain eight pendant boranes in their secondary coordination sphere, [Ni(H)(P2BR4)2]+ (R = Cy or Mes; Mes = 2,4,6-trimethylphenyl). Divergent reactivity of the cyclohexyl analogue toward the [NAD]+ model, 3-acetyl-N-benzylpyridinium bromide ([BNAcP]Br), is underscored. While [Ni(H)(P2BCy4)2]+ undergoes rapid hydride transfer, the related species [Ni(H)(dnppe)2]+ [dnppe = 1,2-bis(di-n-propylphosphino)ethane] and adduct [Ni(H)(P2BCy4)2(DMAP)8]+ (DMAP = 4-N,N-dimethylaminopyridine) exhibit no such reactivity. This borane-appended nickel(II) hydride distinguishes itself from its "all-alkyl" cousins and provides future opportunities for the design of [Ni(H)(diphosphine)2]+ reagents for hydride transfer.