Cobalt Corroles as Electrocatalysts for Water Oxidation: Strong Effect of Substituents on Catalytic Activity

NEUMAN, NICOLÁS I.; ALBOLD, UTA; FERRETTI, ELEONORA; CHANDRA, SHUBHADEEP; STEINHAUER, SIMON; RÖßNER, PAUL; MEYER, FRANC; DOCTOROVICH, FABIO; VAILLARD, SANTIAGO E.; SARKAR, BIPRAJIT

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Año: 2020

0020-1669

Two Co(III) complexes (1Py2and2Py2) of new corroleligandsH3L1(5,15-bis(p-methylcarboxyphenyl)-10-(o-methylcarboxyphenyl)corrole) andH3L2(5,15-bis(p-nitrophenyl)-10-(o-methylcarboxyphenyl)corrole) with two apical pyridine ligands havebeen synthesized and thoroughly characterized by cyclic voltammetry,UV−vis−NIR, and EPR spectroscopy, spectroelectrochemistry, single-crystal X-ray diffraction studies, and DFT methods. Complexes1Py2and2Py2possess much lower oxidation potentials than cobalt(III)-tris-pentafluorophenylcorrole (Co(tpfc)) and similar corroles containingpentafluorophenyl (C6F5) substituents, thus allowing access to highoxidation states of the former metallocorroles using mild chemicaloxidants. The spectroscopic (UV−vis−NIR and EPR) and electronicproperties of several oxidation states of these complexes have beendetermined by a combination of the mentioned methods. Complexes1Py2and2Py2undergo three oxidations within 1.3 V vs FcH+/FcH in MeCN, and we show that both complexes catalyze wateroxidation in an MeCN/H2O mixture upon the third oxidation, withkobs(TOF) values of 1.86 s−1at 1.29 V (1Py2) and 1.67 s−1at1.37 V (2Py2). These values arefive times higher than previously reported TOF values for C6F5-substituted cobalt(III) corroles, afinding we ascribe to the additional charge in the corrole macrocycle due to the increased oxidation state. This work opens up newpossibilities in the study of metallocorrole water oxidation catalysts, particularly by allowing spectroscopic probing of high-oxidationstates and showing strong substituent-effects on catalytic activity of the corrole complexes.