Reactive Cobalt⁻Oxo Complexes of Tetrapyrrolic Macrocycles and N-based Ligand in Oxidative Transformation Reactions.

Atif Ali,Waseem Akram,Hai-Yang Liu

doi:10.3390/molecules24010078

Atif Ali, Waseem Akram + Show 1 more

Open Access

https://doi.org/10.3390/molecules24010078

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Abstract

High-valent cobalt–oxo complexes are reactive transient intermediates in a number of oxidative transformation processes e.g., water oxidation and oxygen atom transfer reactions. Studies of cobalt–oxo complexes are very important for understanding the mechanism of the oxygen evolution center in natural photosynthesis, and helpful to replicate enzyme catalysis in artificial systems. This review summarizes the development of identification of high-valent cobalt–oxo species of tetrapyrrolic macrocycles and N-based ligands in oxidation of organic substrates, water oxidation reaction and in the preparation of cobalt–oxo complexes.

Highlights

In biological systems, metalloenzymes, typically containing Mn, Fe and Cu centers, are known to catalyze a wide range of reactions including aliphatic and aromatic C–H hydroxylation, epoxidation, desaturation, and heteroatom (S, N or O) dealkylation or oxidation [1,2]
Clean energy production by maneuvering natural photosynthesis in water oxidation reactions to develop artificial photosynthesis [19,20,21] for efficient water splitting is a hot topic of research [22,23,24]
The high-valent cobalt–oxo complexes of N-based ligand can be implicated as reactive species in the O–O bond-forming event during water oxidation [29,30]

Summary

Introduction

Metalloenzymes, typically containing Mn, Fe and Cu centers, are known to catalyze a wide range of reactions including aliphatic and aromatic C–H hydroxylation, epoxidation, desaturation, and heteroatom (S, N or O) dealkylation or oxidation [1,2]. The high-valent cobalt–oxo complexes of N-based ligand can be implicated as reactive species in the O–O bond-forming event during water oxidation [29,30]. Cobalt complexes based on tetrapyrrolic macrocycles are often used in mimicking the peroxidase-like activity for the selective oxidation of organic substrates via high-valent cobalt(IV)–oxo intermediates [31,32]. To substrates; identification of cobalt–oxo species involved in heterogeneous and homogeneous water mimic thereactions; enzymes-like environment, different types of support are used as protein backbone for oxidation and preparation of high-valent cobalt–oxo complexes. Cobalt-substituted polyoxotungstate was proved to be a good catalyst They proposed the involvement of different cobalt–oxo species with the different oxidants. Cobalt(IV)–oxo porphyrin radical [41] were proposed to be involved in C-H bond activation reaction These species are quite reactive towards the oxidation of alkane and alcohol, respectively.

Possible

Cobalt–Oxo Species Involved in Water Oxidation Reaction

Cobalt–Oxo

Mechanism

Preparation of Cobalt–Oxo Complexes

Summary and Outlook