Supramolecular Approaches to Improve the Performance of Ruthenium-Based Water Oxidation Catalysts

5 years ago

Supramolecular Approaches to Improve the Performance of Ruthenium-Based Water Oxidation Catalysts

Valentin Kunz, Frank Würthner, Roland Mitrić, Merle I. S. Röhr, David Schmidt

Supramolecular principles have been widely applied to enhance the activity of homogeneous ruthenium-based water oxidation catalysts. For catalytic systems in which the OO bond is formed via radical coupling of two metal oxyl subunits, self-assembly of mononuclear catalysts into vesicles or fibrous aggregates can be used to improve the interaction of two catalytic centers. Similarly, the catalytic subunits can be brought into spatial proximity by coordination chemistry, which allows the construction of highly efficient metallosupramolecular multinuclear structures. However, if the OO bond is formed by the nucleophilic attack of water at a metal oxide species, the interaction of the catalytic center with substrate water molecules has to be improved. Here, by introducing tailored ligand systems, the second coordination sphere can be adjusted specifically to preorganize water for OO bond formation whereas the implementation of proton accepting residues can be used to lower the activation barrier of crucial proton-coupled reaction steps. In a particularly outstanding example, both principles were combined in a multinuclear metallosupramolecular macrocycle. Supramolecular principles can be utilized to enhance the activity of homogeneous ruthenium water oxidation catalysts. Focusing on two different water oxidation mechanisms, recent examples from literature are described where noncovalent forces are exploited to accelerate the rate of water oxidation. Those interactions facilitate the interplay of catalytic centers with substrate water molecules or other catalytic subunits to lower activation barriers.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/aenm.201602939