A d^10 Ni–(H_2) Adduct as an Intermediate in H-H Oxidative Addition across a Ni-B Bond

Abstract

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 H_2 activation reactions at late-metal boratranes and herein describe a diphosphine–borane-supported Ni—(H_2) complex, [(^(Ph)DPB^(iPr))Ni(H_2)], which has been characterized in solution. ^1H NMR spectroscopy confirms the presence of an intact H_2 ligand. A range of data, including electronic-structure calculations, suggests a d^(10) configuration for [(^(Ph)DPB^(iPr))Ni(H_2)] as most appropriate. Such a configuration is highly unusual among transition-metal H_2 adducts. The nonclassical H_2 adduct is an intermediate in the complete activation of H_2 across the Ni-B interaction. Reaction-coordinate analysis suggests synergistic activation of the H_2 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—(H_2) interaction and in the H—H cleavage step.