Volume 234, 2022

Electrocatalytic alcohol oxidation by a molecular iron complex

Abstract

An efficient electrochemical method for the selective oxidation of alcohols to their corresponding aldehydes/ketones using a biomimetic iron complex, [(bTAML)FeIII–OH2], as the redox mediator in an undivided electrochemical cell with inexpensive carbon and nickel electrodes using water as an oxygen source is reported. The substrate scope also includes alcohols that contain O and N heteroatoms in the scaffold, which are well tolerated under these reaction conditions. Mechanistic studies show the involvement of a high-valent FeV(O) species, [(bTAML)FeV(O)], formed via PCET (overall 2H+/2e) from [(bTAML)FeIII–OH2] at 0.77 V (vs. Fc+/Fc). Moreover, electrokinetic studies of the oxidation of C–H bonds indicate a second-order reaction, with the C–H abstraction by FeV(O) being the rate-determining step. The overall mechanism, studied using linear free energy relationships and radical clocks, indicates a “net hydride” transfer, leading to the oxidation of the alcohol to the corresponding aldehyde or ketone. When the reaction was carried out at pH > 11, the reaction could be carried out at a ∼500 mV lower potential than that at pH 8, albeit with reduced reaction rates. The reactive intermediate involved at pH > 11 is the corresponding one-electron oxidized [(bTAML)FeIV(O)]2− species.

Graphical abstract: Electrocatalytic alcohol oxidation by a molecular iron complex

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
18 okt 2021
Accepted
14 dec 2021
First published
17 feb 2022

Faraday Discuss., 2022,234, 42-57

Electrocatalytic alcohol oxidation by a molecular iron complex

H. Kuiry, D. Das, S. Das, S. Chakraborty, B. Chandra and S. S. Gupta, Faraday Discuss., 2022, 234, 42 DOI: 10.1039/D1FD00074H

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