Heterogeneous Photocatalytic Oxidation of Toluene to Benzaldehyde over Nickel Coordinated Metatungstate, [Ni(dmbpy)3]2H2[H2W12O40].

Photocatalysis of polyoxometalates (POMs) offers a promising route for the effective activation of C(sp3)-H bonds. Herein, a three-dimensional metatungstate-based polyoxometalate photocatalyst [Ni(dmbpy)3]2H2[H2W12O40] (Ni-W12) was synthesized via a solvothermal method using the Keggin-type polyoxoanion [H2W12O40]6- with "electron sponge" characteristics as the building block, Ni2+ as the metal center, and 4,4'-dimethyl-2,2'-bipyridine (dmbpy) as the organic ligand. Under mild conditions of visible light (λ > 420 nm) irradiation in the absence of additional photosensitizers, Ni-W12 catalyzed the selective oxidation of toluene to benzaldehyde, achieving toluene conversion of 58.3% and benzaldehyde selectivity of 95.5% within 5 h. Ni-W12 exhibits excellent visible-light absorption and separation performance of photogenerated charge carrier, which endows it with high catalytic oxidation capability and outstanding cycling stability in toluene oxidation. The catalytic system is also applicable to the selective oxidation of various toluene derivatives, demonstrating good substrate generality. Mechanistic studies confirm that superoxide anion radicals (•O2-) and photogenerated holes (h+) are the key reactive species.