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

Area of Science:

• Inorganic Chemistry
• Catalysis Science
• Materials Science

Background:

• Water oxidation is crucial for artificial photosynthesis.
• Developing efficient water oxidation catalysts (WOCs) remains a challenge.
• Ruthenium complexes with 2,2'-bipyridine-6,6'-dicarboxylate (bda) ligands are promising WOC candidates.

Purpose of the Study:

• To synthesize and characterize a novel cyclic dinuclear ruthenium(bda) complex for homogeneous catalytic water oxidation.
• To investigate its catalytic activity and mechanism compared to mononuclear analogs.
• To evaluate its performance in photocatalytic water oxidation for artificial photosynthesis.

Main Methods:

• Synthesis of a cyclic dinuclear ruthenium(bda) complex with oligo(ethylene glycol)-functionalized axial calix[4]arene ligands.
• Homogeneous catalytic water oxidation experiments (chemical and photocatalytic).
• Kinetic investigations, including kinetic isotope effect studies.
• Photocatalytic water oxidation using [Ru(bpy)3]Cl2 as a photosensitizer.

Main Results:

• The novel cyclic dinuclear Ru(bda) complex exhibited significantly higher catalytic activity than mononuclear references.
• Kinetic studies revealed a unimolecular water nucleophilic attack mechanism involving the second coordination sphere.
• Photocatalytic water oxidation achieved a turnover frequency of 15.5 s⁻¹ and a turnover number of 460.
• The catalyst demonstrated excellent water solubility.

Conclusions:

• The cyclic dinuclear Ru(bda) complex is a highly efficient water oxidation catalyst.
• The design incorporating oligo(ethylene glycol)-functionalized calix[4]arene ligands enhances catalytic performance.
• This water-soluble catalyst shows great potential for artificial photosynthesis and sustainable energy applications.