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.