A Calix[4]arene-Based Cyclic Dinuclear Ruthenium Complex for Light-Driven Catalytic Water Oxidation

A cyclic dinuclear ruthenium(bda) (bda: 2,2'-bipyridine-6,6'-dicarboxylate) complex equipped with oligo(ethylene glycol)-functionalized axial calix[4]arene ligands has been synthesized for homogenous catalytic water oxidation. This novel Ru(bda) macrocycle showed significantly increased catalytic activity in chemical and photocatalytic water oxidation compared to the archetype mononuclear reference [Ru(bda)(pic)(2)]. Kinetic investigations, including kinetic isotope effect studies, disclosed a unimolecular water nucleophilic attack mechanism of this novel dinuclear water oxidation catalyst (WOC) under the involvement of the second coordination sphere. Photocatalytic water oxidation with this cyclic dinuclear Ru complex using [Ru(bpy)(3)]Cl-2 as a standard photosensitizer revealed a turnover frequency of 15.5 s(-1) and a turnover number of 460. This so far highest photocatalytic performance reported for a Ru(bda) complex underlines the potential of this water-soluble WOC for artificial photosynthesis.

Automated summary

The cyclic dinuclear ruthenium complex with oligo(ethylene glycol)-functionalized axial calix[4]arene ligands showed enhanced catalytic activity in water oxidation compared to the mononuclear reference compound. The kinetic studies revealed a unimolecular water nucleophilic attack mechanism for this novel dinuclear water oxidation catalyst, demonstrating its potential for artificial photosynthesis. The photocatalytic performance of this complex was reported to be the highest among Ru(bda) complexes, indicating its promising application in the field of water oxidation research.