Issue 14, 2023

Mechanistic insights into the electrochemical reduction of CO2 to CO on Ni(salphen) complexes

Abstract

Cyclic voltammetry and bulk electrolysis showed that [Ni(II)(salphen)] [1], [Ni(II)(tBu-salphen)] [2], and a binuclear Ni(II) compound combining salphen and tBu-salphen [3] react with CO2 to yield a metal–carbonyl species that is stable under an oxygen free atmosphere. Upon exposure to air, a stoichiometric amount of CO is released (detected by gas chromatography) and protonation regenerates the initial complex. To shed light on the mechanism of CO2 reduction and O2-dependent CO release by [1], UV-vis, EPR and SEC-IR spectroscopy studies complemented with DFT calculations were performed. It is proposed that the mono reduced [Ni(I)(salphen)], 2[1], formed a CO2 complex, 2[1(CO2)], which was then further reduced to 3[1(CO2)]2−. After addition of two protons, the coordinated CO2 was reduced to CO and released, regenerating 1[1]. Alternatively, 2[1(CO2)] is protonated and then reduced to the same intermediate as before, continuing the same way. In the second cycle, the CO released competed with CO2 and coordinated to 2[1] much more strongly, thereby deactivating the system. The new 2[1(CO)] was reduced to 3[1(CO)]2− which was identified by comparison of experimental spectroscopic (UV-vis, EPR, SEC-IR) data with DFT calculated parameters.

Graphical abstract: Mechanistic insights into the electrochemical reduction of CO2 to CO on Ni(salphen) complexes

Supplementary files

Article information

Article type
Research Article
Submitted
07 mar. 2023
Accepted
21 may. 2023
First published
23 may. 2023
This article is Open Access
Creative Commons BY license

Inorg. Chem. Front., 2023,10, 4175-4189

Mechanistic insights into the electrochemical reduction of CO2 to CO on Ni(salphen) complexes

S. Realista, P. J. Costa, L. B. Maia, M. J. Calhorda and P. N. Martinho, Inorg. Chem. Front., 2023, 10, 4175 DOI: 10.1039/D3QI00424D

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