Reduction of Cobalt and Iron Corroles and Catalyzed Reduction of CO2

Published

May 1, 2002

Author(s)

J Grodkowski, Pedatsur Neta, E Fujita, A Mahammed, L Simkhovich, Z Gross

Abstract

The role of cobalt and iron corroles in catalytic CO₂ reduction has been studied. Chemical, electrochemical, and photochemical reductions of the stable metal corroles Ph₃PCo^III(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole), ClFe^IV^(tpfc), and ClFe^IV(tdcc) (tdcc = 5,10,15-tris(2,6-dichlorophenyl)corrole) have been carried out in acetonitrile solutions. Stepwise reduction to the [M^II(tpfc)]^- and [M^I(tpfc)]^2- states was observed in all cases. Gradual reduction with sodium amalgam permitted recording of the optical absorption spectra of the various oxidation states and showed that the M^I state reacts with CO₂. Cyclic voltammetry in Ar-saturated acetonitrile solutions permitted determination of the following half-wave potentials: for PPh₃Co^III(tpfc), 1.11 V, 0.72 V, -0.42 V (E_pc), -1.44 V, -2.3 V (E_pc); for ClFe^IV(tpfc), 0.44 V, -1.01 V (E_pc), -1.60 V, -2.2 V (E_pc); for ClFe^IV(tdcc), 0.24 V, -1.18 V (E_pc), -1.78 V vs SCE with a scan rate of 0.1 V s^-1. Cyclic voltammetry in CO₂-saturated solutions indicated that the Co^I and Fe^I complexes react with CO₂ and that the reduced Fe(tdcc) complex is the most efficient electrocatalyst for CO₂ reduction, showing the largest catalytic currents among these corroles. Photochemical reduction in CO₂-saturated acetonitrile solutions containing p-terphenyl (TP) as a sensitizer and triethylamine (TEA) as a reductant led to production of CO and H₂. These experiments also show that Fe(tdcc) is more effective than the other corroles as a CO₂ reduction catalyst. The present finding that the M^I oxidation states of the cobalt and iron corroles can react with CO₂ is in contrast with the case of the respective porphyrins and phthalocyanines, which do not react with CO₂ until they are reduced beyond the M^I state.

Citation

Journal of Physical Chemistry A

Volume

106

Issue

No. 18

Pub Type

Journals

Keywords

catalysis, CO₂ reduction, cobalt, corroles, electrochemistry, iron, photochemistry

Citation

Grodkowski, J. , Neta, P. , Fujita, E. , Mahammed, A. , Simkhovich, L. and Gross, Z. (2002), Reduction of Cobalt and Iron Corroles and Catalyzed Reduction of CO₂, Journal of Physical Chemistry A (Accessed April 30, 2024)