Theoretical study of the hydroxylation of phenols mediated by an end-on bound superoxo–copper(II) complex

Phenolate-bonded bis(μ-oxido)-bis-copper(III) intermediates: hydroxylation and dehalogenation reactivities

Exogenous phenolate ortho-hydroxylation by copper oxidants formed from dioxygen is generally thought to occur through one of two limiting mechanisms defined by the structure of the active oxidant: an electrophilic μ-η²:η²-peroxo-bis-copper(II) species as found in the oxygenated form of the binuclear copper enzyme tyrosinase (oxyTyr), or an isomeric bis(μ-oxido)-bis-copper(III) species (O) with ligated phenolate(s) as evidenced by most synthetic systems. The characterization of the latter is limited due to their limited thermal stability. This study expands the scope of an O species with ligated phenolate(s) using N,N'-di-tert-butyl-1,3-propanediamine (DBPD), a flexible secondary diamine ligand. Oxygenation of the [(DBPD)Cu(I)]¹⁺ complex at low temperatures (e.g., 153 K) forms a spectroscopically and structurally faithful model to oxyTyr, a side-on peroxide intermediate, which reacts with added phenolates to form a bis(μ-oxido)-bis-copper(III) species with ligated phenolates, designated as an A species. The proposed stoichiometry of A is best understood as possessing 2 rather than 1 bonded phenolate. Thermal decomposition of A results in regiospecific phenolate ortho-hydroxylation with the ortho-substituent as either a C-H or C-X (Cl, Br) group, though the halogen displacement is significantly slower. DFT and experimental studies support an electrophilic attack of an oxide ligand into the π-system of a ligated phenolate. This study supports a hydroxylation mechanism in which O-O bond cleavage of the initially formed peroxide by phenolate ligation, which precedes phenolate aromatic hydroxylation.

Introducing a closed system approach for the investigation of chemical steps involving proton and electron transfer; as illustrated by a copper-based water oxidation catalyst

We present an ab initio molecular dynamics approach to characterize proton-coupled electron transfer catalytic steps and identify the preferred reaction mechanism.

DFT studies on the mechanism of veratryl alcohol oxidation catalyzed by Cu–phen complexes

Density functional theory (DFT) calculations have been performed to investigate the catalytic mechanism for the oxidation of veratryl alcohol to veratraldehyde by Cu–phen catalyst. In this work, the most favorable mechanism has been predicted and we hope the obtained results could provide useful insights for the reaction process.

Mechanistic insight into the alcohol oxidation mediated by an efficient green [CuBr(2)(2,2'-bipy)]-TEMPO catalyst by density functional method

Density functional theory (DFT) calculations have been performed to investigate the alcohol oxidation to acetaldehyde catalyzed by [CuBr(2)(2,2'-bipy)]-TEMPO (TEMPO stands for 2,2,6,6-tetramethylpiperidinyloxy; bipy stands for bipyridine). The total charge for the studied catalytic system is +1. The catalytic cycle consists of two parts, namely, alcohol oxidation and TEMPO regeneration. In alcohol oxidation, the reaction follows the Sheldon's mechanism for the proposed two mechanisms, i.e., Semmelhack's mechanism and Sheldon's mechanism. The water participation plays minor role in the H atom abstraction step. In TEMPO regeneration, the proposed three paths are competitive in energy. By comparing with experimental observation, it is found that the path, in which alcohol provides the proton to TEMPO(-) to produce TEMPOH followed by the oxidation of TEMPOH directly to TEMPO by O(2), is favored. In TEMPO regeneration, CH(3)CN acts as the ligand to stabilize the Cu(I) species during the catalytic cycle.