Axial Ligand Tuning of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Dinuclear Cobalt Complex.
4 affiliations
- 1Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, Berlin12489, Germany.
- 2XAS@KMC-3, BESSY-II+, Helmholtz Zentrum Berlin fur Materialien und Energie GmbH , Albert-Einstein-Straße 15, Berlin12489, Germany.
- 3Department of Chemistry, Technische Universität Berlin, Berlin10623, Germany.
- 4Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, Leiden2300 RA, The Netherlands.
Abstract
Controlling the two- versus four-electron oxygen reduction reaction (ORR) remains a central challenge, as the factors that determine whether peroxide is released as H2O2 or further reduced to H2O are often difficult to define at the molecular level. Here we show that axial ligation provides a direct tool for switching ORR selectivity in a flexible dicobalt platform, Co2L1,3 (where L1,3 = 1,3-bis[(bis(2,2'-bipyridin-6-yl)amino)methyl]benzene). In acetonitrile (MeCN), the solvent-bound complex mediates a mixed 2e-/4e- ORR, whereas the presence of additional ligands like triphenylphosphine (PPh3) or 2,6-dicyclohexylimidazole (DCHIm) biases the reaction toward sole H2O2 formation. An anionic thiophenolato coordination, in contrast, redirects the reaction toward a near-quantitative 4e-/4H+ reduction to water. Kinetic studies reveal distinct empirical rate laws, indicating a ligand-dependent change in the turnover-limiting sequence. A dicobalt(III)-peroxido intermediate has been identified as the key branching point by spectroscopic and structural characterization of the O2-derived intermediate. Neutral axial ligands (MeCN, PPh3 or DCHIm) stabilize this intermediate against O-O bond cleavage, thereby leading to the release of H2O2 upon protonation. In contrast, anionic thiophenolato binding promotes irreversible O-O bond cleavage to form a structurally characterized dicobalt(III) bis-μ-oxido moiety, with the concomitant oxidation of thiophenolato to phenylthiyl radical and the eventual release of water in the presence of a proton donor. These results establish an axial-ligand-controlled mechanism for tuning ORR selectivity. In particular, the thiophenolate-induced cobalt-mediated O-O bond cleavage represents a bioinspired model of the proposed role of cysteine-assisted O-O bond cleavage in cytochrome P450 enzymes.
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BibTeX
@article{bera2026axial,
title = {{Axial Ligand Tuning of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Dinuclear Cobalt Complex.}},
author = {Ayan Bera and Xinyang Peng and Dibya Jyoti Barman and Michael Haumann and Sagie Katz and Dennis G H Hetterscheid and Peter Hildebrandt and Kallol Ray},
journal = {Journal of the American Chemical Society},
year = {2026},
month = oct,
doi = {10.1021/jacs.6c12922},
url = {https://europepmc.org/article/MED/42913563},
note = {CC BY},
}
RIS
TY - JOUR
TI - Axial Ligand Tuning of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Dinuclear Cobalt Complex.
AU - Ayan Bera
AU - Xinyang Peng
AU - Dibya Jyoti Barman
AU - Michael Haumann
AU - Sagie Katz
AU - Dennis G H Hetterscheid
AU - Peter Hildebrandt
AU - Kallol Ray
PY - 2026
DA - 2026/10/01
JO - Journal of the American Chemical Society
DO - 10.1021/jacs.6c12922
UR - https://europepmc.org/article/MED/42913563
AB - Controlling the two- versus four-electron oxygen reduction reaction (ORR) remains a central challenge, as the factors that determine whether peroxide is released as H2O2 or further reduced to H2O are often difficult to define at the molecular level. Here we show that axial ligation provides a direct tool for switching ORR selectivity in a flexible dicobalt platform, Co2L1,3 (where L1,3 = 1,3-bis[(bis(2,2'-bipyridin-6-yl)amino)methyl]benzene). In acetonitrile (MeCN), the solvent-bound complex mediates a mixed 2e-/4e- ORR, whereas the presence of additional ligands like triphenylphosphine (PPh3) or 2,6-dicyclohexylimidazole (DCHIm) biases the reaction toward sole H2O2 formation. An anionic thiophenolato coordination, in contrast, redirects the reaction toward a near-quantitative 4e-/4H+ reduction to water. Kinetic studies reveal distinct empirical rate laws, indicating a ligand-dependent change in the turnover-limiting sequence. A dicobalt(III)-peroxido intermediate has been identified as the key branching point by spectroscopic and structural characterization of the O2-derived intermediate. Neutral axial ligands (MeCN, PPh3 or DCHIm) stabilize this intermediate against O-O bond cleavage, thereby leading to the release of H2O2 upon protonation. In contrast, anionic thiophenolato binding promotes irreversible O-O bond cleavage to form a structurally characterized dicobalt(III) bis-μ-oxido moiety, with the concomitant oxidation of thiophenolato to phenylthiyl radical and the eventual release of water in the presence of a proton donor. These results establish an axial-ligand-controlled mechanism for tuning ORR selectivity. In particular, the thiophenolate-induced cobalt-mediated O-O bond cleavage represents a bioinspired model of the proposed role of cysteine-assisted O-O bond cleavage in cytochrome P450 enzymes.
SN - 0002-7863
SN - 1520-5126
ER -