Bio-inspired mononuclear nonheme metal peroxo complexes: Synthesis, structures and mechanistic studies toward understanding enzymatic reactions

Abstract

Metalloenzymes utilize inexpensive and earth-abundant transition metal ions as important co-factors to enable binding of a dioxygen molecule so that it can be used in various biological metabolisms. For many important enzymatic reactions, dioxygen binding and activation is the fundamental process used to gen-erate chemically reactive metal-oxygen intermediates. During past decades, a variety of hypothetical metal-oxygen adducts have been proposed as key intermediates in the catalytic reaction of metalloen-zymes. For example, metal peroxo species have been considered and sometimes directly captured spec-troscopically and crystallographically at the active site of several metalloenzymes including Rieske dioxygenase, deformylase and superoxide dismutase. To understand the chemical properties and reactiv-ities of the metal peroxo intermediates, synthetic model chemistry has been advanced with numerous ligand systems and central metal ions. The successful synthesis of well-characterized metal peroxo com-pounds has allowed us to acquire deep insights into the mechanisms of such enzymatic reactions. In this review, we encompass overall studies on the nonheme first-row transition metal peroxo complexes (M = Mn, Fe, Co, Ni and Cu) with physicochemical characterization and structural information. The chem-ical reactivities of the metal peroxo complexes relevant to the biological system are also presented. Nucleophilic aldehyde deformylation has become a representative reaction mediated by the metal peroxo intermediates, and recent findings have revealed unique reaction mechanisms such as nitrile activation. Furthermore, rate-determining H atom abstraction has also been suggested in the current study on the aldehyde deformylation. Extrinsic factors to control the chemical properties and reactivities of the metal peroxo complexes have recently been accomplished through adding the redox inactive metal ion and modifying the ligand topology. It is hoped that the comprehensive knowledge presented in this review will help to broaden and deepen our understanding of the metal peroxo intermediates and be useful to understand enzyme mechanisms and to develop bioinspired catalysts.(c) 2023 Elsevier B.V. All rights reserved.