Rationally Designed Metal Cocatalyst for Selective Photosynthesis of Bibenzyls via Dehalogenative C–C Homocoupling

The construction of C–C bonds by coupling reactions is an important process in synthetic chemistry though expensive catalysts are required. Heterogeneous photocatalysis offers a platform for C–C coupling of aromatic halides via hydro-dehalogenation by employing alcohols as the hydrogen donor; however, a designed photocatalyst with high activity and selectivity is lacking. Here, we show that Cu is a promising candidate to promote the coupling of aromatic halides due to the optimized adsorption energy of the reaction intermediates (benzyl radical and Br atom) over a series of transition metals. The Cu-modified TiO2 shows a remarkable apparent quantum efficiency (15%) and a great tolerance of harsh reaction conditions for the homocoupling of benzyl bromides into bibenzyl under UV irradiation. The low-cost photocatalyst also shows high performance upon scaling-up and selective coupling of a series of benzyl bromide derivatives, demonstrating the heterogeneous photocatalytic C–C coupling as an attractive process for applications. Additionally, the design strategy can be applied to modify other photocatalysts (i.e., g-C3N4) to realize the C–C coupling of benzyl bromide under visible light.