Yang Qingning, Li Xiyi, Chen Lu, Han Xiaoyu, Wang Feng Ryan, Tang Junwang
Department of Chemical Engineering, University College London Torrington Place, London, WC1E 7JE, UK.
Department of Chemistry, University of Manchester, Manchester, M13 9PL, UK.
Angew Chem Int Ed Engl. 2023 Oct 23;62(43):e202307907. doi: 10.1002/anie.202307907. Epub 2023 Sep 18.
Carbon-carbon (C-C) coupling of organic halides has been successfully achieved in homogeneous catalysis, while the limitation, e.g., the dependence on rare noble metals, complexity of the metal-ligand catalylst and the poor catalyst stability and recyclability, needs to be tackled for a green process. The past few years have witnessed heterogeneous photocatalysis as a green and novel method for organic synthesis processes. However, the study on C-C coupling of chloride substrates is rare due to the extremely high bond energy of C-Cl bond (327 kJ mol ). 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 has been validated for C-C coupling of 10 benzylic chlorides all with high yields. In addition, the excellent stability has been observed for 8 cycles of reactions. With detailed characterization and DFT calculation, the high selectivity is attributed to the enhanced adsorption of reactants, stabilization of intermediates (benzyl radicals) for the selective coupling by the Cu loading and the moderate oxidation ability of the ZnO support, besides the promoted charge separation and transfer by Cu species.
有机卤化物的碳-碳（C-C）偶联已在均相催化中成功实现，但对于绿色工艺而言，其局限性，例如对稀有贵金属的依赖、金属-配体催化剂的复杂性以及较差的催化剂稳定性和可回收性，仍需解决。在过去几年中，多相光催化作为一种绿色且新颖的有机合成方法崭露头角。然而，由于C-Cl键的极高键能（327 kJ·mol），关于氯化物底物的C-C偶联研究较少。在此，我们报道了一种稳健的多相光催化剂（Cu/ZnO），可高效驱动苄基氯的均偶联反应，在室温下实现了前所未有的高选择性二苄基（93%）和92%的产率。此外，该光催化过程已被验证可用于10种苄基氯化物的C-C偶联反应，且产率均很高。另外，在8次循环反应中观察到了优异的稳定性。通过详细的表征和DFT计算，除了Cu物种促进电荷分离和转移外，高选择性归因于反应物吸附增强、Cu负载对中间体（苄基自由基）的稳定作用以实现选择性偶联以及ZnO载体适度的氧化能力。
