Rational Design of First-Row Transition Metal Complexes as the Catalysts for Oxidation of Arenes: A Homogeneous Approach

Abstract

Researchers have always been intrigued by one-step selective hydroxylation of aromatic compounds since achieving adequate selectivity toward the target product and avoiding overoxidation are challenging. However, the naturally available oxygenase enzymes efficiently and selectively perform such transformations under normal atmospheric conditions. Inspired by naturally occurring oxygenase enzymes, researchers have undertaken numerous attempts to catalyze the oxidation of arenes using homogeneous and heterogeneous catalysts. In this regard, the first-row transition metal complexes are considered as candidates due to their abundance and redox characteristics. Therefore, this review focuses on catalyst design strategies to improve the efficiency and selectivity of arene oxidation and illustrates the distinctive homogeneous approaches reported in this area by employing first-row transition metal complexes.

Effect of Flexible Chain Length of Graphene‐Supported Palladium Complex Catalyst on Suzuki‐Miyaura Coupling Activity

“…Homogeneous metal complex catalysts usually have good selectivity and high efficiency, so they have been greatly developed in the past decades. [15,16] However, homogeneous catalysts have residues in the synthetic products and are difficult to recover, which has become a key factor limiting their development. In order to overcome these shortcomings, the usual approach is to fix the homogeneous catalyst on the surface of the solid support to prepare the so-called supported heterogeneous catalyst.…”

“…Homogeneous metal complex catalysts usually have good selectivity and high efficiency, so they have been greatly developed in the past decades [15,16] . However, homogeneous catalysts have residues in the synthetic products and are difficult to recover, which has become a key factor limiting their development.…”

Nonlinear Acid Promotion of Oxidation Reactions by Mononuclear Nonheme Iron(III)-Aqua Complexes

“…Binding acids to oxidants results in much enhancement of the oxidizing capability by increasing the positive charge of the atom that can react with reductants. − Acids can bind with oxygen atoms of not only organic oxidants but also inorganic oxidants, such as metal-oxo, − -hydroxo, , -peroxo, , -hydroperoxo, and -superoxo complexes . Binding not only Bro̷nsted acids but also Lewis acids to high-valent iron- and manganese-oxo complexes results in a positive shift in the one-electron reduction potentials, thus remarkably enhancing the oxidizing capability in electron transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. − ,− In the case of nonheme iron­(IV)-oxo and Mn­(IV)-oxo complexes, not only one but also two acid molecules are bound to the oxo group to enhance the oxidizing capability. − In the case of organic oxidants, such as p -benzoquinone as well, two acid molecules bind to the one-electron reduced species (semiquinone radical anion) to exhibit the second-order dependence of the rate constants of electron-transfer reduction of p -benzoquinone on concentration of acids .…”

Bio-inspired Cu(ii) amido-quinoline complexes as catalysts for aromatic C–H bond hydroxylation

“…6 Inspired by the reactivity of these metalloenzymes, several bioinspired first-row transition metal complexes have been developed for intramolecular aromatic hydroxylation and the reactive intermediates were extensively studied using various spectroscopic techniques. 7 The oxidation of benzene to phenol by hydrzonato vanadium( v ) and vanadium( v ) peroxo-picolinic acid complexes has been investigated. 8 a , b Biologically inspired manganese complexes successfully achieved aromatic C–H bond oxidation in fluorinated alcohol solvents via the formation of an Mn( v )–oxo intermediate.…”