The effect of the trans axial ligand of cobalt corroles on water oxidation activity in neutral aqueous solutions

Abstract

A series of cobalt complexes of 5,10,15-tris(pentafluorophenyl)-corrole [Co(tpfc)] (1) with various axial ligands were synthesized and examined as single-site catalysts for water oxidation. The used axial ligands include 4-cyanopyridine (py-CN), pyridine (py), 4-(dimethylamino)pyridine (py-NMe), 4-methoxypyridine (py-OMe), 1-methylimidazole (im-Me), and thiophenolate (thi). Complexes 1-py and 1-py-OMe were structurally characterized. The Co ion in both structures has an almost identical distorted octahedral coordination environment with the four N atoms of tpfc defining the equatorial plane and the two molecules of pyridine (for 1-py) or 4-methoxypyridine (for 1-py-OMe) occupying the axial positions. Electrochemical studies of these Co corroles in acetonitrile showed that they all display two oxidation events and the oxidation waves shift to the cathodic direction with electron-donating axial ligands, a trend that is consistent with increased electron densities on Co ions. All these Co corroles were found to be active for electrocatalytic water oxidation: by using catalyst-coated fluorine-doped tin oxide (FTO) working electrodes, cyclic voltammograms displayed pronounced catalytic waves for water oxidation in 0.1 M pH 7.0 phosphate buffer solutions. The onset overpotentials are in the range of 510 to 580 mV, depending on the electron-donating ability of the trans axial ligands. These results demonstrate that the catalytic activities of Co corroles for water oxidation are considerably affected by the trans axial ligands on Co centers and provide valuable insights into the design of new catalysts for water oxidation.

From Enzymes to Functional Materials—Towards Activation of Small Molecules

“…[96] In addition, the influence of axial ligands was also reported for Co corroles comprising different axial N-donors ( Figure 9). [97] The highest catalytic activityw itha no nset potential of 530 mV vs. NHE was obtainedf or complex 14 possessing the ligand with highest electron-donating properties. Along this line, complex 16 shows the lowest activity with an onset potentialo f5 80 mV vs. NHE.…”

Quantum Chemical Study of the Mechanism of Water Oxidation Catalyzed by a Heterotrinuclear Ru2Mn Complex

“…[1][2][3][4][5] During the past few decades, extraordinary efforts have been dedicated to the synthesis of manganese-based molecular complexes to mimic the structure and function of the OEC. [6][7][8][9][10] Other transition metals were also used for the synthesis of water oxidation catalysts, including Ru, [11][12][13][14][15][16][17][18][19][20][21][22][23][24] Ir, [25,26] Fe, [27][28][29][30][31] Co, [32][33][34] Ni, [35][36][37] and Cu. [38][39][40] Recently,the Llobet group disclosed the synthesisofaheterotrinuclear Ru 2 Mn complex A 0 {[Ru II (tpy)] 2 (m-[Mn II (bpp) 2 ]) (OAc) 2 } 2 + [tpy = 2,2':6',2''-terpyridine, bpp = 3,5-bis(2-pyridyl)pyrazolate].…”

Mono‐/Multinuclear Water Oxidation Catalysts

“…ChemSusChem 2019, 12,3209 -3235 www.chemsuschem.org 2019 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim macrocycle with fluorobenzene and this modified cobalt corrole (CoH bF CXÀCO 2 H) was stable during the OER. [154] They synthesized [Co(tpfc)] complexes with different axial ligands and found that [Co(tpfc)],w ith an electrondonating trans-axial ligand,e xhibited high activity owing to the trans effect. [151] It was revealed that the fluorobenzene might be away to improvethe electrophilicity of MÀO( Mi sm etal), which would contribute to nucleophilic attack by water.C hen and co-workersf urthers tudied OÀOb ond formation on CoH bF CX-CO 2 Ht hrough DFT calculations.…”

“…In 2017, Cao and co-workerss tudied the influence of the trans-axial ligand on the catalytic activity of [Co(tpfc)]. [154] They synthesized [Co(tpfc)] complexes with different axial ligands and found that [Co(tpfc)],w ith an electrondonating trans-axial ligand,e xhibited high activity owing to the trans effect. With regard to the ligand,C ao and co-workers found that the Co-corrolew ith base pendant L CH 2 POðOHÞ 2 ÀCo showedh igher OER activity than that with acid pendants, thus indicating that the CH 2 PO(OH) 2 group, as an intramolecular base, contributedt oO ÀOb ond formation for the OER.…”