Enzyme-like water preorganization in a synthetic molecular cleft for homogeneous water oxidation catalysis

Inspired by the proficiency of natural enzymes, mimicking of nanoenvironments for precise substrate preorganization is a promising strategy in catalyst design. However, artificial examples of enzyme-like activation of H2O molecules for the challenging oxidative water splitting reaction are hardly explored. Here, we introduce a mononuclear Ru(bda) complex (M1, bda = 2,2'-bipyridine-6,6'-dicarboxylate) equipped with a bipyridine-functionalized ligand to preorganize H2O molecules in front of the metal centre as in enzymatic clefts. The confined pocket of M1 accelerates chemically driven water oxidation at pH 1 by facilitating a water nucleophilic attack pathway with a remarkable turnover frequency of 140 s(-1) that is comparable to the oxygen-evolving complex of photosystem II. Single crystal X-ray analysis of M1 under catalytic conditions allowed the observation of a seventh H2O ligand directly coordinated to a Ru-III centre. Another H2O substrate is preorganized via a well-defined hydrogen-bonding network for the crucial O-O bond formation by nucleophilic attack.