Structural Characterization of a Hydroperoxo Nickel Complex and Its Autoxidation: Mechanism of Interconversion between Peroxo, Superoxo, and Hydroperoxo Species

Abstract

Pincer-stabilized nickel(I) complexes readily react with molecular oxygen to form dinuclear 1,2-μ-peroxo-bridged nickel(II) complexes, which are the major components of a dynamic equilibrium with the corresponding mononuclear superoxo species. The peroxo complexes further react with hydrogen peroxide to give the corresponding nickel(II) hydroperoxides. One of these hitherto elusive species was characterized by X-ray diffraction for the first time [O-O bond length: 1.492(2) Å].

Transient Formation and Reactivity of a High-Valent Nickel(IV) Oxido Complex

“…27 This conclusion is supported by the DFT-calculated IR spectrum for 3a (Figure S36), which shows an O–O stretching band (Δ[ 18 O] in parentheses) at 892 (841) cm –1 , a Ni–N stretching mode at 768 (768) cm –1 , and Ni–O bending/stretching modes at 663 (633), 601 (594), 585 (571), and 536 (516) cm –1 . Of these modes, the 663 and 768 cm –1 modes are strongly IR active.…”

Spectroscopically Characterized Synthetic Mononuclear Nickel–Oxygen Species

“…In this case, at ridentate anionic ligand occupiedt hree of the coordination positionso ft he square-planar nickel center,a nd the coordinations phere was completed by ah ydroperoxide ligand in an end-on coordination mode. [39] In both cases,O ÀOb ond lengths of approximately 1.48 determinedb yX -ray analysisw ere clearlyi ndicative of ap eroxide ligand.…”

“…Recently, the group of Gade reported the structure of a diamagnetic square planar hydroperoxonickel(II) species with the general formula [Ni II (OOH)(iso‐pmbox)] obtained by reaction of a nickel(II) species with H 2 O 2 (Figure a, Table ). In this case, a tridentate anionic ligand occupied three of the coordination positions of the square‐planar nickel center, and the coordination sphere was completed by a hydroperoxide ligand in an end‐on coordination mode . In both cases, O−O bond lengths of approximately 1.48 Å determined by X‐ray analysis were clearly indicative of a peroxide ligand.…”

Activation of Dioxygen at a Lewis Acidic Nickel(II) Complex: Characterization of a Metastable Organoperoxide Complex

“…There have been some sporadic publications reporting nickel(II) complexes that actually showed reactivity towards O 2 via unknown mechanisms, but the nature of the initial products and the metal‐based final products remained very vague . O 2 activation by nickel complexes with clear‐cut product identification and structural information has so far been restricted to a few examples containing the metal in the oxidation state +1 or 0 . In this context, the recent observation that a quercetin‐2,4‐dioxygenase (quercetinase) activates O 2 at a [(N His ) 3 Ni II ] site to yield a Ni–O 2 species with unknown electronic structure (suggested to represent a nickel(II) superoxide, however) is a fascinating stimulus for intensifying research on O 2 activation with nickel(II).…”