Accelerated Direct Hydroxylation of Aryl Chlorides with Water to Phenols via Proximity Effect in Heterogeneous Metallaphotocatalyst

The proximity of different active sites in multi-catalytic systems is crucial in influencing the catalytic reactions, i.e. , to occur or to be accelerated. Here we reported a heterogeneous metallaphotocatalyst prepared by embedding Ni(II) species in a photosensitive covalent organic framework (COF). A concerted triad catalytic behavior executed by electron, hole, and Ni species triggered a dramatic catalytic enhancement on the activation of aryl chlorides with water to phenols. It demonstrated a 50-fold increment in its activity when compared to homogeneous analog, e.g., NidabpyBr 2 . Also, it was able to tolerate a broad range of functional groups even for those hardly achieved by the thermal catalysts. Based on the detailed study, the proximity of the photoactive COF and Ni(II) sites facilitates rapid electron transfer to produce Ni(I) active sites for the oxidative addition. Meanwhile, the photogenerated holes oxidized water to hydroxyl radical, which then attacked Ni(III) intermediates to complete the catalytic cycle.