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

• Published in: Chinese journal of catalysis Vol. 42; no. 8; pp. 1338 - 1344
• Main Authors: Chen, Qifa, Du, Haoyi, Zhang, Mingtian
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2021
• Subjects: Artificial photosynthesis; Buffer anion effect; Copper catalyst; Redox-active ligand; Water oxidation; Redox-active ligand; Copper catalyst; Buffer anion effect; Water oxidation; Artificial photosynthesis
• DOI: 10.1016/S1872-2067(20)63729-9
• ISSN: 1872-2067

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 CuIII complex (TAML-CuIII) with a redox-active macrocyclic ligand (TAML) and its reactivity toward catalytic water oxidation. TAML-CuIII displayed a completely different electrochemical behavior from that of the TAML-CoIII complex previously reported by our group. TAML-CuIII can only be oxidized by one-electron oxidation of the ligand to form TAML•+-CuIII and cannot achieve water activation through the ligand-centered proton-coupled electron transfer that takes place in the case of TAML-CoIII. The generated TAML•+-CuIII 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. In this work, the effect of buffer anions on the catalytic performance and stability of a molecular catalyst (TAML-CuIII) was investigated. TAML-CuIII showed catalytic activity for water oxidation in borate buffer, where it triggered the formation of a heterogeneous active species, B/CuOx, by a macrocyclic ligand open-ring reaction.