Photooxidation in water by new hybrid molecular photocatalysts integrating an organic sensitizer with a polyoxometalate core

Hybrid compounds consisting of an organic sensitizer and a polyoxometalate unit were synthesized following two strategies: a) the covalent functionalization of lacunary decatungstosilicate with organosilylfulleropyrrolidines; b) the charge interaction between cationic sensitizers and the polyoxoanions, yielding electrostatic aggregates. These hybrid complexes effect catalytic photooxygenation in water under heterogeneous conditions, 25degreesC and O-2 (1 atm), using visible light irradiation (lambda > 375 nm). As representative target substrates, phenol (4 mM) is oxidized in 150 min with a COD loss up to 30% (TON up to 50), while L-methionine methyl ester (15 mM) undergoes selective photooxygenation to the corresponding sulfoxide in 90 min (TON up to 200). The photocatalyst stability has been evaluated on the basis of system recycling along three oxidation runs. The inhibition exerted by sodium azide, a typical O-1(2) quencher, suggests the occurrence of a Type II photooxidation mechanism.