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.配体设计是合成化学的核心准则，简单的结构修饰即可引发反应活性的显著差异。本文报道了两种二级配位球中含有八个悬挂式硼烷的双(二膦基)合镍(II)氢化物配合物的制备方法，其通式为[Ni(H)(P2BR4)2]+（R为环己基（Cy）或均三甲苯基（Mes），其中Mes为2,4,6-三甲基苯基）。本文重点考察了该环己基取代衍生物与烟酰胺腺嘌呤二核苷酸（NAD+）模型底物3-乙酰基-N-苄基溴化吡啶鎓([BNAcP]Br)的反应活性差异：当配合物[Ni(H)(P2BCy4)2]+发生快速氢负离子转移反应时，同系列的[Ni(H)(dnppe)2]+（dnppe为1,2-双(二正丙基膦基)乙烷）以及加合物[Ni(H)(P2BCy4)2(DMAP)8]+（DMAP为4-N,N-二甲基氨基吡啶）均未表现出此类反应活性。这种带有悬挂硼烷的镍(II)氢化物与传统的"全烷基"同类配合物表现迥异，为后续设计用于氢负离子转移反应的[Ni(H)(二膦)2]+类试剂提供了新的研究方向。