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The diruthenium(II,II) complex [Ru2(L¹)(OAc)3]Cl (1), spanned by a naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation (AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a diverse range of alcohols, and it is shown to be particularly effective for the conversion of primary alcohols to the corresponding aldehydes without undesired side products such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols afforded the corresponding olefins in high yields with excellent E selectivity. The liberated dihydrogen gas was identified and measured to be 1 equiv with respect to alcohol. Deuteration studies with PhCD2OH revealed the absence of isotope scrambling in the product, indicating the involvement of a Ru-monohydride intermediate. Kinetic studies and DFT calculations suggest a low-energy bimetallic β-hydride elimination pathway where rate-limiting intramolecular proton transfer from alcohol to metal-bound hydride constitutes the dehydrogenation step. The general utility of metal-metal bonded compounds for alcohol AD and subsequent coupling reactions is demonstrated here. [ABSTRACT FROM AUTHOR]

Water oxidation is a primary step in natural as well as artificial photosynthesis to convert renewable solar energy into chemical energy/fuels. Electrocatalytic water oxidation to evolve O 2 , utilizing suitable low-cost catalysts and renewable electricity, is of fundamental importance considering contemporary energy and environmental issues, yet it is kinetically challenging owing to the complex multiproton/electron transfer processes. Herein, we report the first cobalt-based pincer catalyst for catalytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role during electrocatalysis. A significant potential jump (∼300 mV) was achieved toward a lower positive value when the aromatized cobalt complex was transformed into a (pseudo)dearomatized cobalt species. The dearomatized species catalyzes the water oxidation reaction to evolve oxygen at a much lower overpotential (∼340 mV) on the basis of the onset potential (at a current density of 0.5 mA/cm 2 ) of catalysis at pH 10.5, outperforming other Co-based molecular catalysts reported to date. These observations may provide a new strategy for the judicious design of earth-abundant transition-metal-based water oxidation catalysts.