Oxidation Reactions with Bioinspired Mononuclear Non‐Heme Metal–Oxo Complexes

Abstract

The selective functionalization of strong C-H bonds and the oxidation of water by cheap and nontoxic metals are some of the key targets of chemical research today. It has been proposed that high-valent iron-, manganese-, and copper-oxo cores are involved as reactive intermediates in important oxidation reactions performed by biological systems, thus making them attractive targets for biomimetic synthetic studies. The generation and characterization of metal-oxo model complexes of iron, manganese, and copper together with detailed reactivity studies can help in understanding how the steric and electronic properties of the metal centers modulate the reactivity of the metalloenzymes. This Review provides a focused overview of the advances in the chemistry of biomimetic high-valent metal-oxo complexes from the last 5-10 years that can be related to our understanding of biological systems.

A Mononuclear Nonheme Iron(V)-Imido Complex

“…High-valent iron-imido (Fe n + ═NR) species, which are iron-oxo (Fe n + ═O) analogs, 1 have been proposed as reactive intermediates in aziridination and amination reactions. 2,3 A number of synthetic iron-imido complexes have been isolated and characterized structurally in heme and nonheme iron systems.…”

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3O Macrocyclic Ligand

“…[1] The Fe IV =O moiety is always found in the quintet ( S = 2) spin state, which is predicted by DFT calculations [2] to be more reactive in H-atom transfer (HAT) than the corresponding triplet ( S = 1) spin state. The biological Fe IV =O oxidants all contain at least two weak-field O-based ligands (either carboxylate or water) cis to the oxo donor (Scheme 1A), [3] which can play a significant role in the stabilization of the S = 2 state by modulating the energy gap between the Fe d(xy) and d(x 2 –y 2 ) orbitals.…”

“…For example, the short half-life of 20 s at 25 °C of the S = 2 [Fe IV (O)(H 2 O) 5 ] 2+ complex [5] has inhibited a detailed investigation of its spectroscopic and reactivity properties. On the other hand, employment of strong-field pyridine and tertiary amine donors [1a–b,6] or carbene donors [7] has led to the isolation and characterization of several well-characterized S = 1 Fe IV =O model complexes with high stability and low reactivity. Efforts to stabilize the more reactive S = 2 state by replacing one or more N-donors with weak carboxylate ligands [8] have previously resulted in only a small enhancement (5 – 10 folds) in the HAT abilities of the complexes.…”

Assembly of a mononuclear ferrous site using a bulky aldehyde-imidazole ligand

“…2His enzymes are quite common and comprise the large class of 2His-1-carboxylate oxygenase enzymes along with α-ketoglutarate (α-KG)-dependent halogenase, which activates O 2 to carry out oxidative halogenations of nonactivated and activated carbon centers [8–13]. Several groups have worked on developing ligand systems to mimic these metal binding sites using Histidine mimics such as amine, amide, pyrrole, pyrazole, and pyridine [4,14–16], however, it is anticipated that the imidazolyl group will be the best surrogate for histidine. Incorporation of bulky hydrophobic groups helps to mimic the hydrophobic environment often found at these sites.…”