Oxygenation in Water by Ruthenium mono-Substituted Polyoxo-tungstates: Experimental and Computational Dissection of a Ru(III)-Ru(V) Catalytic Cycle

Molecular polyoxometalates embedding one ruthenium center, with general formula [RuII/III(DMSO)XW11O39]n- (X=P, Si; n=4-6), are readily synthesized in gram scale under microwave irradiation by a flash hydrothermal protocol. These nano-dimensional and polyanionic complexes enable aerobic oxygenation in water. Catalytic oxygen transfer to dimethylsulfoxide (DMSO) yielding the corresponding sulfone (DMSO2) has been investigated with a combined kinetic, spectroscopic and computational approach addressing: (i) the Ru(III) catalyst resting state; (ii) the bimolecular event dictating its transformation in the rate determining step; (iii) its aerobic evolution to a high valent ruthenium oxene species; (iv) the terminal fate to diamagnetic dimers. This pathway is reminiscent of natural heme-systems and of bioinspired artificial porphyrins. The in-silico characterization of a key bis-Ru(IV)-μ-peroxo-POM dimeric intermediate has been accessed via density functional theory. This observation sets a new landmark for tracing POM-based manifolds for multi-redox oxygen reduction/activation, where metal-centered oxygenated species play a pivotal role. These include two Holy Grails of oxidation catalysis, i.e. the liquid phase oxygenase cycle and photosynthetic water oxidatio