Effective Activation of Strong C−Cl Bonds for Highly Selective Photosynthesis of Bibenzyl via Homo‐Coupling

Abstract

Carbon‐carbon coupling of organic halides as an important process in organic synthesis has been successfully achieved in homogeneous catalysis, while the dependence on rare noble metals, complicated metal‐complex and poor catalyst stability and recyclability, need to be tackled. The past few years have witnessed heterogeneous photocatalysis as green and novel methods for organic synthesis processes. However, the study on C–C coupling of chloride substrates is very limited due to the extremely high bond energy of C–Cl bond (327 kJ mol‐1). Here, we report a robust heterogeneous photocatalyst (Cu/ZnO) to drive the homo‐coupling of benzyl chloride with high efficiency, which achieves an unprecedented high selectivity of bibenzyl (93%) and yield rate of 92% at room temperature. Moreover, this photocatalytic process can be applied to 10 benzyl chlorides with high yields. With detailed characterisation (XPS, EPR, TPD) and DFT calculation, the high selectivity is attributed to the enhanced adsorption of reactants, stabilisation of intermediates (benzyl radicals) for the selective coupling by the Cu loading and the moderate oxidation ability of ZnO support, besides the promoted charge separation and transfer by Cu species. Therefore, this work offers a new route to highly selective synthesise bibenzyl from chloride substrates by a stable heterogeneous system.