Switching O-O bond formation mechanism between WNA and I2M pathways by modifying the Ru-bda backbone ligands of water-oxidation catalysts

Understanding the seven coordination and O-O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earth-abundant metals. This work reports the synthesis, characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda (H-2 bnda = 2,2'-bi(nicotinic acid)-6,6'-dicarboxylic acid) featuring steric hindrance and enhanced hydrophilicity on the backbone. Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid), Ru-pda (H(2)pda = 1,10-phenanthroline-2,9-dicarboxylic acid), and Ru-biqa (H(2)biqa = (1,1'-biisoquinoline)-3,3'-dicarboxylic acid), we emphasized that seven coordination clearly determines presence of Ru-v =O with high spin density on the O-RuV=o atom, i.e. oxo with radical properties, which is one of the necessary conditions for reacting through the O-O coupling pathway. However, an additional factor to make the condition sufficient is the favorable intermolecular face-to-face interaction for the generation of the pre-reactive [Ru-V=O center dot center dot center dot O=Ru-V], which may be significantly influenced by the secondary coordination environments. This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O-O bond formation. (C) 2020 The Authors. Published by ELSEVIER B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences.

Automated summary

This study provides insights into the structure-activity relationship of water-oxidation catalysts based on Ru-bnda and related catalysts, emphasizing the importance of seven coordination for the reaction pathway and conditions necessary for O-O bond formation.