Spectroscopically Characterized Synthetic Mononuclear Nickel–Oxygen Species

Abstract

Iron, copper, and manganese are the predominant metals found in oxygenases that perform efficient and selective hydrocarbon oxidations and for this reason, a large number of the corresponding metal-oxygen species has been described. However, in recent years nickel has been found in the active site of enzymes involved in oxidation processes, in which nickel-dioxygen species are proposed to play a key role. Owing to this biological relevance and to the existence of different catalytic protocols that involve the use of nickel catalysts in oxidation reactions, there is a growing interest in the detection and characterization of nickel-oxygen species relevant to these processes. In this Minireview the spectroscopically/structurally characterized synthetic superoxo, peroxo, and oxonickel species that have been reported to date are described. From these studies it becomes clear that nickel is a very promising metal in the field of oxidation chemistry with still unexplored possibilities.

Structure, Bonding, Reactivity and Spectral Features of Putative NiIII=O Species: A Theoretical Perspective

“…The close proximity of the methyl substituents to the oxo‐nickel unit facilitates the self‐decay of the ligand by intramolecular hydrogen atom abstraction and leads to the formation of a ligand hydroxylated Ni II product. This has been witnessed in the experimental report . A detailed mechanism adapted for our calculations is shown in Scheme and the developed potential energy surface is shown in Figure .…”

“…are few examples of metalloenzymes containing nickel ion in their active sites. The Ni III oxidation state is very unusual for nickel chemistry because the synthesis and characterization of stable Ni III complexes are challenging , . Nevertheless, over the last few years, the study of high‐valent central Ni ions are gaining great attention because of their proposed involvement in a variety of Ni‐based oxidation reactions , .…”

Dinuclear Iron(III) and Nickel(II) Complexes Containing N‐(2‐Pyridylmethyl)‐N′‐(2‐hydroxyethyl)ethylenediamine: Catalytic Oxidation and Magnetic Properties

“…These results indicate that the Ni II −OOC(O)R intermediate 3 underwent the partition of heterolysis (55.8 %) and homolysis (44.2 %), affording high‐valent complexes. Importantly, the presence of high‐valent Ni III =O and Ni III –oxyl species has been proposed in only few studies . Notably, the high‐valent complexes (Ni III =O and Ni IV =O) are observed using the mechanistic probe PPAA.…”

“…Importantly,t he presence of high-valent Ni III =Oa nd Ni III -oxyl species hasb een proposed in only few studies. [47][48][49][66][67][68][69] Notably,t he high-valent complexes (Ni III =O and Ni IV =O) are observed using the mechanistic probe PPAA. On the other hand, the dangling OH groups in 2 might act as ag enerala cid catalysis to facilitate OÀOb ond heterolysis to produce the intermediate 4.…”

Nickel and Palladium Complexes with Reactive σ‐Metal‐Oxygen Covalent Bonds

“…However, on moving to the right along the d transition series, this class of ligands become less common. [3] The reason is that, as the metal ions becomes more electronrich and less electropositive, the M-alkoxo or M-amido linkages turn more reactive, to the point that such complexes become increasingly difficult to isolate and characterize. Although late transition metal hydroxide and alkoxide species have been long known to be intermediates in catalytic processes, e. g. palladium-catalyzed Wacker olefin oxidation, [4] or olefin alkoxycarbonylations, [5] well-characterized alkoxides of metals of groups 9 to 11 were chemical oddities until relatively recent times.…”