Oxygenation by Ruthenium Monosubstituted Polyoxotungstates in Aqueous Solution: Experimental and Computational Dissection of a Ru(III)-Ru(V) Catalytic Cycle

Molecular polyoxometalates with one embedded 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 nanodimensional 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)-mu-peroxo-POM dimeric intermediate has been accessed by density functional theory. This observation indicates a new landmark for tracing POMbased manifolds for multiredox oxygen reduction/activation, where metal-centered oxygenated species play a pivotal role.