Buffer anion effects on water oxidation catalysis: The case of Cu(III) complex

Water oxidation is the bottleneck of artificial photosynthesis. Since the first ruthenium-based molecular water oxidation catalyst, the blue dimer, was reported by Meyer's group in 1982, catalysts based on transition metals have been widely employed to explore the mechanism of water oxidation. Because the oxidation of water requires harsh oxidative conditions, the stability of transition complexes under the relevant catalytic conditions has always been a challenge. In this work, we report the redox properties of a Cu-III complex (TAML-Cu-III) with a redox-active macrocyclic ligand (TAML) and its reactivity toward catalytic water oxidation. TAML-Cu-III displayed a completely different electrochemical behavior from that of the TAML-Co-III complex previously reported by our group. TAML-Cu-III can only be oxidized by one-electron oxidation of the ligand to form TAML(center dot+)-Cu-III and cannot achieve water activation through the ligand-centered proton-coupled electron transfer that takes place in the case of TAML-Co-III. The generated TAML(center dot+)-Cu-III intermediate can undergo further oxidation and ligand hydrolysis with the assistance of borate anions, triggering the formation of a heterogeneous B/CuOx nanocatalyst. Therefore, the choice of the buffer solution has a significant influence on the electrochemical behavior and stability of molecular water oxidation catalysts. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

Water oxidation is a key process in artificial photosynthesis, and transition metal-based catalysts have been widely used to study this mechanism. This study focuses on the redox properties of a Cu-III complex and its reactivity towards catalytic water oxidation, highlighting the importance of ligands and buffer solutions in the stability of water oxidation catalysts.