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

[Image: see text] 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 Ni(II)Ni(III)(μ-OH)(2) (2) and Ni(2)(III)(μ-OH)(2) (3) species supported by a dicarboxamidate ligand (N,N′-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-tert-butyl-phenols (4-X-2,6-DTBP, X = −OCH(3), −CH(2)CH(3), −CH(3), −C(CH(3))(3), −H, −Br, −CN, and −NO(2)) as a mechanistic probe. Interestingly, upon reaction of 3 with the substrates, the formation of a new transient species, 2′, was observed. 2′ is postulated to be a protic congener of 2. 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, 3 was demonstrated to react at far superior rates to 2 and 2′, and oxidized substrates more efficiently than any bis-μ-oxo-Ni(2)(III) reported to date. The kinetic superiority of 3 with respect to 2 and 2′ was attributed to a stronger bond in the product of oxidation by 3 when compared to those calculated for 2 and 2′.