Homogeneous catalysis, O2 evolution, O2 activation, O2 reduction , Earth abundant transition metal complexes
Concept for session Formation and cleavage of the O-O bond of dioxygen is crucial in diverse fundamental chemical and biological processes. Breaking of the O-O bond is a critical step for catalytic 4-electron reduction of O2, which plays an essential role for sustaining life, but also for generating electrical energy. Actually, in aerobic organisms O2 reduction to water, performed by the enzyme cytochrome-c oxidase , drives the successive production of ATP,
whereas in fuel cells (cathode) O2 collects electrons coming from oxidation of H2 or other fuels (anode). The rupture of the O-O dioxygen bond is also implicated in selective oxidations and oxygenations of organic substrates by dioxygen, as exemplified by CytP450 enzyme. Concerning O-O formation, it is the bottleneck step for oxidation of water to O2, a fundamental process that allows to harvest electrons and protons for reduction of substrates. For example, the Oxygen-Evolving-Center (OEC) of photosystem II oxidizes water to O2 in a photo-induced reaction, and released protons and electrons are used to reduce CO2 to glucose. Conversely, in water splitting systems the reducing equivalents resulting from H2O oxidation are employed to produce H2. Both O-O formation and cleavage involve large activation barriers, and require the presence of a transition-metal ion, typically manganese, iron, copper or cobalt, to catalyze the process. The ability of these metals to support different oxidation states, especially high-valent metal-oxo species, constitutes a key element to enable reactivity. In this context, the ICCC2018 session will mainly concern on studies of bio-inspired, earth-abundant first-row transition metal complexes that promote O-O formation or breaking. The following aspects will be considered: (i) catalytic and electrocatalytic systems for O 2 reduction and O 2 evolution ; (ii) catalytic oxidation of organic substrates by O 2 reductive activation ; (iii) mechanistic investigations in homogeneous solution, very useful for a deeper understanding of the fundamental chemical aspects of O-O breaking/formation. The session will include both experimental studies, mainly centered on characterization and reactivity of intermediates, and theoretical studies, extremely valuable in the attempt to rationalize the observed reactivity.