A trinuclear ruthenium complex as a highly efficient molecular catalyst for water oxidation

Abstract

A trinuclear ruthenium complex, 3, was designed and synthesized with the ligand 2,2'-bipyridine-6,6'-dicarboxylic acid (bda) and we found that this complex could function as a highly efficient molecular catalyst for water oxidation in homogeneous systems. This trinuclear molecular water oxidation catalyst, 3, displayed much higher efficiencies in terms of turnover numbers and initial oxygen evolution rate than its counterparts, a binuclear catalyst, 2, and a mononuclear catalyst, 1, in both chemically driven and photochemically driven water oxidation based on either the whole catalytic molecules or just the active Ru centers. The reasons for the superior performance of catalyst 3 were discussed and we believe that multiple Ru centers in a single molecule are indeed beneficial for increasing the probability of the formation of O-O bonds through an intramolecular radical coupling pathway.

P4VP–RuII(bda) polyelectrolyte–metal complex as water oxidation catalyst: on the unique slow-diffusion and multi-charge effects of the polyelectrolyte ligand

“…27 Würthner et al reported the preparation and catalysis behavior of Ru(bda) based supra-molecular macro-cycles as water oxidation catalysts, similarly, the supra-molecular catalysts were found to oxidize water via WNA mechanism because of the rigid ligand structure of supra-molecular assemblies. 18,31 Accordingly, the rst-order reaction kinetics was observed in these studies. On the other hand, Ru(bda) based heterogeneous catalysts were also reported to catalyze water oxidation via WNA mechanism, which is generally explained by the restriction effect on motion of Ru catalytic centers located at interface of heterogeneous system.…”

“…18,25,27 In contrast, only a few studies reported the rst-order kinetics for Ru(bda) based catalysis, which can be roughly divided into the following three specic cases: (1) the ligand rigidity induced mechanism change; 18,19,27 (2) the restriction of motion of Ru catalytic centers located at interface of heterogeneous system; [28][29][30] (3) the intramolecular dimerization of two neighboring Ru V ]O species to form -O-Obond. 31 For example, Sun et al reported that the replacement of bda with 1,10-phenanthroline-2,9-dicarboxylate (pda) could lead to the change of catalytic mechanism from I2M to WNA because of the exibility difference of ligand structure. 27 Würthner et al reported the preparation and catalysis behavior of Ru(bda) based supra-molecular macro-cycles as water oxidation catalysts, similarly, the supra-molecular catalysts were found to oxidize water via WNA mechanism because of the rigid ligand structure of supra-molecular assemblies.…”

Artificial photosynthesis: opportunities and challenges of molecular catalysts

“…143 Introduction of halogen substituents into the p-extended axial ligand further improved the catalytic activity of the Ru-bda catalysts, complex 16 with record TOF 4 1000 s À1 and complex 17 with record TON 4 100 000. To obtain higher catalytic activity, based on the bimolecular I2M mechanism of Ru-bda catalysts, various strategies have been tested to enhance the intermolecular interaction [167][168][169][170] or to create facile intramolecular reactions by linking two or more Ru-bda units, 171,172 e.g., complex 18.…”

Mono‐/Multinuclear Water Oxidation Catalysts

“…[115] The initial TOF and TON values of the trinuclearRu-bda catalyst with Ce IV as an oxidant were 86 498 and 126 s À1 ,r espectively,w hichw ere higher than those of bi-and mononuclear Ru-bda due to the presence of more catalytic centers in trinuclearR u-bda. [115] The initial TOF and TON values of the trinuclearRu-bda catalyst with Ce IV as an oxidant were 86 498 and 126 s À1 ,r espectively,w hichw ere higher than those of bi-and mononuclear Ru-bda due to the presence of more catalytic centers in trinuclearR u-bda.…”

“…In 2016, the OER performances of trinuclearR u-bda (bda: 2,2'-bipyridine-6,6'-dicarboxylic acid) were compared with those of bi-and mononuclear Ru-bda. [115] The initial TOF and TON values of the trinuclearRu-bda catalyst with Ce IV as an oxidant were 86 498 and 126 s À1 ,r espectively,w hichw ere higher than those of bi-and mononuclear Ru-bda due to the presence of more catalytic centers in trinuclearR u-bda. The catalytic activity of the mononuclear Ru-bda catalystw as the lowest amongt he three catalysts, which indicatedt hat OÀOb ond for- mation with mononuclearR u-bda proceeded througha ni ntermolecular reaction.…”