Straightforward synthesis of a porous chromium-based porphyrinic metal-organic framework for visible-light triggered selective aerobic oxidation of benzyl alcohol to benzaldehyde

Abstract

Among MOFs, chromium-based metal–organic frameworks (Cr-MOFs) represent attractive scaffolds for variety of potential applications due to their high porosity and stability. Nevertheless, Cr-MOFs are not very common due to complicate synthesis. Cr-MOFs of large linkers are one clear example of synthetic limitations, since their preparation takes place by post-synthetic routes, commonly starting from Fe-MOFs as precursors. Hence, in this work, the direct synthesis of a phorphyrinic chromium-based MOF, Cr-PCN-600 (PCN stands for Porous Coordination Network) under solvothermal conditions is reported. The resulting Cr-MOF exhibits high surface area, permanent porosity, and broad light absorption wavelength range. Interestingly, this Cr-MOF is a highly effective heterogeneous photocatalyst for the selective aerobic oxidation of benzyl alcohol to benzaldehyde under visible light irradiation without any additive. Importantly, the Cr-MOF showed good recyclability maintaining its activity for three runs. The present results lay the foundation for both synthesis and applications of Cr-MOFs as robust photocatalysts in advanced organic transformations. Notably, quenching studies confirmed the generation of superoxide radical anion (O2−) and singlet oxygen (1O2) (mostly) as reactive species under the reaction conditions.