A d~(10) Ni-(H2) Adduct as an Intermediate in H—H Oxidative Addition across a Ni—B Bond

摘要

Bifunctional E—H activation offers a promising approach for the design of two-electron-reduction catalysts with late first-row metals, such as Ni. To this end, we have been pursuing H2 activation reactions at late-metal boratranes and herein describe a diphosphine-borane-supported Ni—(H2) complex, [(~(ph)DPB~(iPr))Ni(H2)], which has been characterized in solution. ~1H NMR spectroscopy confirms the presence of an intact H2 ligand. A range of data, including electronic-structure calculations, suggests a d~(10) configuration for [(~(ph)DPB~(iPr))Ni(H2)] as most appropriate. Such a configuration is highly unusual among transition-metal H2 adducts. The nonclassical H2 adduct is an intermediate in the complete activation of H2 across the Ni-B interaction. Reaction-coordinate analysis suggests synergistic activation of the H2 ligand by both the Ni and B centers of the nickel boratrane subunit, thus highlighting an important role of the borane ligand both in stabilizing the d~(10) Ni—(H2) interaction and in the H—H cleavage step.