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

摘要

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)(H2O) (H3L: 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(-1)) is in line with the experimental result (TOF = 5.40 h(-1)). It is also found that the H atom migrates from alkoxide to the oxygen atom of TEMPO in the TOF determining transition state (TDTS).