Turning on Visible-Light Photocatalytic C−H Oxidation over Metal–Organic Frameworks by Introducing Metal-to-Cluster Charge Transfer

The tailorable structure and electronic structure of metal–organic frameworks (MOFs) greatly facilitate their modulated light harvesting, redox power, and consequently photocatalysis. Herein, a representative MOF, UiO-66, was furnished by installing Fe 3+ onto the Zr-oxo clusters, to give Fe-UiO-66, which features extended visible light harvesting, based on metal-to-cluster charge transfer (MCCT). The Fe-UiO-66 with unique electronic structure and strong oxidizing power exhibits visible light-driven water oxidation, which is impossible for pristine UiO-66. More strikingly, under visible irradiation, the generated holes over Fe-UiO-66 are able to exclusively convert H 2 O to hydroxide radicals, initiating and driving the activation of stubborn C-H bond, such as toluene oxidation. The electrons reduce O 2 to O 2 •- radicals that further promote the oxidation reaction. The related catalytic mechanism and the structure–activity relationship have been investigated in detail. As far as we know, this is not only an unprecedented report on activating “inert” MOFs for photocatalytic C-H activation but also the first work on extended light harvesting and enhanced photocatalysis for MOFs by introducing an MCCT process.