High Oxidation State Iridium Mono-μ-oxo Dimers Related to Water Oxidation Catalysis

• Published in: Journal of the American Chemical Society Vol. 138; no. 49; pp. 15917 - 15926
• Main Authors: Sharninghausen, Liam S, Sinha, Shashi Bhushan, Shopov, Dimitar Y, Choi, Bonnie, Mercado, Brandon Q, Roy, Xavier, Balcells, David, Brudvig, Gary W, Crabtree, Robert H
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.12.2016; American Chemical Society (ACS)
• Subjects: catalysis (homogeneous), catalysis (heterogeneous), solar (photovoltaic), solar (fuels), photosynthesis (natural and artificial), bio-inspired, hydrogen and fuel cells, electrodes - solar, defects, charge transport, spin dynamics, membrane, materials and chemistry by design, optics, synthesis (novel materials), synthesis (self-assembly)
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.6b07716

The highly active iridium “blue solution” chemical and electrochemical water oxidation catalyst obtained from Cp*IrL­(OH) precursors (L = 2-pyridyl-2-propanoate) has been difficult to characterize as no crystal structure can be obtained because of the multiplicity of geometrical isomers present. Other data suggest complete loss of the Cp* ligand and the formation of a LIr-O-IrL unit. We have now developed a route to a series of well-defined Ir­(IV,IV) mono-μ-oxo dimers, containing the closely related L2Ir-O-IrL2 unit. Unlike the catalyst, these model compounds are separable by silica gel chromatography and readily form single crystals. We report three stereoisomers with the formula ClL2Ir-O-IrL2Cl, which are fully characterized, including by X-ray crystallography, and are compared to the “blue solution”. To the best of our knowledge, these species represent the first examples of structurally characterized dinuclear μ-oxo Ir­(IV,IV) compounds without metal–carbon bonds.