Reactivity Properties of Mixed- and High-Valent Bis(μ-Hydroxide)-Dinickel Complexes.

Despite their potential role in enzymatic systems, there is a dearth of hydroxide-bridged high-valent oxidants. We recently reported the synthesis and characterization of NiNi(μ-OH) () and Ni (μ-OH) () species supported by a dicarboxamidate ligand (,'-bis(2,6-dimethyl-phenyl)-2,2-dimethylmalonamide). Herein, we explore the oxidative reactivity of these species using a series of para-substituted 2,6-di--butyl-phenols (4-X-2,6-DTBP, X = -OCH, -CHCH, -CH, -C(CH), -H, -Br, -CN, and -NO) as a mechanistic probe. Interestingly, upon reaction of with the substrates, the formation of a new transient species, was observed. is postulated to be a protic congener of . All three species were demonstrated to react with the substituted phenols through a hydrogen atom transfer reaction mechanism, which was elucidated further by analysis of the postreaction mixtures. Critically, was demonstrated to react at far superior rates to and , and oxidized substrates more efficiently than any bis-μ-oxo-Ni reported to date. The kinetic superiority of with respect to and was attributed to a stronger bond in the product of oxidation by when compared to those calculated for and .