A d¹⁰ Ni–(H₂) Adduct as an Intermediate in HH Oxidative Addition across a NiB 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 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. (1) H 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.