Mechanism of Aerobic Alcohol Oxidation Mediated by Water‐Soluble Cu^II‐TEMPO Catalyst in Water: A Density Functional Theory Study

Abstract

The catalytic mechanism for the aerobic alcohol oxidation in the alkaline water solution catalyzed by a Cu II /2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) catalyst system, ([(L)Cu II (Hen)(H 2 O)] (H 3 L: 3-(5-Chloro-2-hydroxy-3-sulfophenylhydrazo) pentane-2,4-dione; en: Ethylenediamine), is presented by density functional theory (DFT) calculations. Four pathways (path A, path B, path C and path D) are presented. Our calculations demonstrate that path A is the favourable pathway and zwitterionic property of the catalyst is not likely affect the efficiency of alcohol oxidation. In path A, the catalytic cycle consists of catalyst activation, substrate oxidation and catalyst regeneration parts. The calculated turn-over frequency (TOF = 3.89 h À1 ) is in line with the experimental result (TOF = 5.40 h À1 ). It is also found that the H atom migrates from alkoxide to the oxygen atom of TEMPO in the TOF determining transition state (TDTS).

Recent advances in computational studies on Cu-catalyzed aerobic reactions: cooperation of copper catalysts and dioxygen

“…5b). 24 This step is also the rate-determining step with an overall energy barrier of 27.2 kcal mol −1 considering the energy cost of catalyst regeneration from a stable Cu( ii ) hydroperoxide intermediate. The superiority of the outer-sphere mechanism in Cheng et al 's study possibly results from the tridentate ligand that prevents the coordination of TEMPO to the Cu center, while the O terminal of TEMPO is intrinsically more active than the amine nitrogen when a free TEMPO reacts.…”

Copper(II)‐TEMPO Interaction

“…The proposed intermediate corresponds to the copper(II) complex bound to an alcoholate and TEMPO ( X in Scheme 1a) [12] . The electron configuration of this elusive intermediate has been a subject of discussion [13–18] …”

“…[12] The electron configuration of this elusive intermediate has been a subject of discussion. [13][14][15][16][17][18] The interaction between copper(II) and TEMPO has been investigated by X-ray absorption spectroscopy of [(TEMPO) 2 Cu 2 Cl 4 ] clusters. [19] The experimental results and their matching with DFT calculations suggested that the interaction between copper(II) and TEMPO leads to the pairing of the unpaired electrons, and the resulting structure has a character of copper(I) interacting with temponium ions (structure A in Scheme 1b).…”

PolyTEMPO electrocatalyst for organic electrosynthesis of benzonitrile from benzyl alcohol

“…In organic electrosynthesis processes, electrocatalysts play important roles. Among them, 2,2,6,6tetramethylpiperidin-1-oxyl (TEMPO) has been selected as a robust, versatile and well-characterized catalyst for many organic electrosynthesis processes, including oxidation of alcohols, sulfides, thioamides and organometallic compounds [2,3,4]. Besides, the attachment of electrocatalysts to soluble polymer backbones to create a homogeneous electrolyte represents a promising approach for improving both ionic conductivity and electron transfer kinetics [5].…”