Polytantalotungstates Stabilized Iron Catalysts for Carbonylation of Benzylic C-H Bonds.

Selective oxidation of benzylic C(sp3)-H bonds to ketones is critical to the production of fine chemicals but typically requires toxic/precious metal catalysts under harsh conditions. While iron-based complexes have recently served as catalysts for photocatalytic C-H bond activation, most systems operate via homogeneous catalysis. Developing a light-driven strategy under visible light with O2 as an oxidant is of major importance. Here, we have synthesized three Fe-based polytantalotungstates, [Fe4(CH3COO)2(OH)5(H2O)9]2[Fe4(CH3COO)(OH)4(H2O)10(P2W12 Ta6O62)]2·166H2O (1), K4[Fe4(OH)2(H2O)14(P2W12Ta6O62)]2·72H2O (2), and K4H2[Fe4(HCOO)2(OH)(H2O)12(P2W12Ta6O62)]2·121H2O (3), using K11Li[P2W12(TaO2)6O56]·19H2O ({P2W12(TaO2)6}), [Fe3O(CH3COO)6(H2O)3]NO3·4H2O, and [Fe3O(O2CH)6(H2O)3]NO3. Enhanced basicity/nucleophilicity of Ta-bound oxygen atoms in {P2W12(TaO2)6} eliminates peroxo groups, enabling metal-ion incorporation. Catalyst 1 achieves quantitative THN oxidation (99%) through unprecedented Fe-ligand-POM cooperation, exhibiting broad visible absorption, tailored band positions, and prolonged charge separation. As the first robust heterogeneous system for aerobic THN photooxidation under an O2 atmosphere, it sets new standards for polyoxometalate photocatalyst design. However, the requirement of blue-light irradiation and limited substrate scope highlight areas for future optimization.