Trinuclear Ruthenium Macrocycles: Toward Supramolecular Water Oxidation Catalysis in Pure Water

The incorporation of a Ru(bda)(bda = 2,2′-bipyridine-6,6′-dicarboxylate) water oxidation catalyst into a trinuclear metallosupramolecular macrocycle leads to increased stability and activity compared to the mononuclear reference system. To overcome solubility problems of such large structures in water and the need for large amounts of organic cosolvents, new macrocyclic water oxidation catalysts with improved water solubility become desirable. With triethylene glycol side chains, the required amount of acetonitrile as a cosolvent was halved, whereas the application of charged ammonium side chains allowed catalysis in pure water. The catalytic activity was found to be comparable to the parent compound. Kinetic experiments were performed to explain the rate differences between those new derivatives and showed that Coulombic repulsion between the charged side chains and Ce IV leads to slower oxidation processes.