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oai:figshare.com:article/34030494 2026-09-30T07:15:54Z category_1 category_4 category_12 category_14 category_873 category_64 category_135 portal_63 item_type_6 month_year_09_2026

Axial Ligand Tuning of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Dinuclear Cobalt Complex Ayan Bera (22958021) Xinyang Peng (18386331) Dibya Jyoti Barman (25142331) Michael Haumann (1455718) Sagie Katz (1498420) Dennis G.H. Hetterscheid (10131864) Peter Hildebrandt (373077) Kallol Ray (1610719) Biophysics Biochemistry Cell Biology Molecular Biology Chemical Sciences not elsewhere classified Cancer Computational Biology key branching point determine whether peroxide cytochrome p450 enzymes bound complex mediates 2 ′- bipyridin neutral axial ligands axial ligation provides structurally characterized dicobalt flexible dicobalt platform tuning orr selectivity switching orr selectivity sup >–</ sup sup >+</ sup anionic thiophenolato coordination 3 </ sup bis [( bis 2 </ sub bond cleavage represents 3 </ sub axial ligand tuning bond cleavage versus four upon protonation thereby leading structural characterization results establish reaction toward quantitative 4e proton donor proposed role phenylthiyl radical oxido moiety often difficult molecular level mixed 2e limiting sequence induced cobalt direct tool dependent change 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, Co₂L^1,3 (where L^1,3 = 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. 2026-09-30T00:00:00Z Text Journal contribution 10.1021/jacs.6c12922.s001 https://figshare.com/articles/journal_contribution/Axial_Ligand_Tuning_of_the_Catalytic_Two-_versus_Four-Electron_Reduction_of_Dioxygen_by_a_Dinuclear_Cobalt_Complex/34030494 CC BY-NC 4.0