Ossidazioni sostenibili di substrati organici catalizzate da eteropolianioni

Nine novel Polyoxometalates (POM) have been studied as catalysts for sustainable oxidative process of organic substrates. Five peroxo ZrIV and HfIV POMs, three dimeric compound [M2(O2)2(α-XW11O39)2]12- (1-3) and two trimeric compound [M6(O2)6(γ-SiW9O36)3]18- (4-5), have been used for L-Methionine and D,L-Methonine sulfoxide oxidation, collecting kinetic traces of reactions by means of 1H-NMR spectroscopy. Stoichiometric and catalytic reactions have been carried out to get information on both the mechanism of the reaction and on the reaction scope. Compound 1-3 are very efficient for such reactions, yielding conversion of L-Methionine into D,L-Methonine sulfoxide of 90-99% in less than 1h and of D,L-Methonine sulfoxide into Methonine sulfone of 80-96% in 1,5-2h. Two Al-subtituted Krebs-type POM, [Al4(XW9O33)2]6- with X=As (tungstoarsenate 6) and X=Sb (tungstoantimonate 7), have been studied as catalysts for the oxidation of alcohols and alkenes with hydrogen peroxide in organic, halide-free solvent, yielding conversion of H2O2 of 19-99% in 1-2h. An interesting selectivity towards alcoholic functionalities has allowed to obtain high regioselectivity for the oxidation of hydroxyl group to the corresponding carbonyl, even in presence of alkene functionality. UV-Vis and CD analysis have been carried out to understand how the substrate may coordinate to the metal centre. Two Ru-substituited, Keggin-type polyoxometalates, with different apical ligands [Ru(L)(α-SiW11O39)] (L=H2O 8, L=DMSO 9) have been used as catalysts for the aerobic oxidation of alcohols, yielding carbonylic products with conversion of 13-14% in 50min. The stability of all compounds was confirmed by FT-IR and UV-vis analysis.