Rare-Earth-Encapsulated Phosphotungstates with Dawson and Lindqvist Units for Catalytic Oxidation of Benzyl Alcohol

Abstract Three rare-earth-embedded phosphotungstates with a dimeric sandwich structure containing two types of building blocks (BBs) [NH2(CH3)2]11H[RE(P2W17O61)(W5O18H)]·9H2O [RE = Dy3+ (1), Er3+ (2), Pr3+ (3)] have been synthesized via a one-pot self-assembly strategy. A distinctive feature is that the polyanion [Dy(P2W17O61)(W5O18H)]12– was composed of one monolacunary Dawson [P2W17O61]10– and one monolacunary Lindqvist [W5O18]5– segments. To the best of our knowledge, this is the first successful synthesis of a rare-earth-embedded polyoxotungstate incorporating both Dawson-type and Lindqvist-type BBs. In the presence of compounds 1–3, the oxidation of benzyl alcohol (0.5 mmol) to benzaldehyde was accomplished using H2O2 as a green oxidant. Notably, within 9.5 h, conversions of 99.5, 98.3, and 93.6% and selectivities of 97.3, 99.5, and 92.5% were obtained, respectively. A plausible reaction mechanism is proposed and verified by radical quenching experiments and electron paramagnetic resonance (EPR) trapping experiments. The results indicate that these compounds can effectively activate H2O2 to generate singlet oxygen (1O2), thereby achieving the selective oxidation of benzyl alcohol to benzaldehyde.