Pd loaded TiO2 as recyclable catalyst for benzophenone synthesis by coupling benzaldehyde with iodobenzene under UV light

• Published in: Chinese journal of catalysis 2024-04, Vol.59, p.159-168
• Main Authors: Li, Yang, Wang, Xiong, Hu, Xing-Sheng, Hu, Biao, Tian, Sheng, Wang, Bing-Hao, Chen, Lang, Chen, Guang-Hui, Peng, Chao, Shen, Sheng, Yin, Shuang-Feng
• Format: Article
• Language: English
• Subjects: Benzophenone synthesis; Cross-coupling of benzaldehyde and iodobenzene; Heterogeneous catalysis; Pd/C-TiO2; Photocatalytic Pd recycling
• ISSN: 1872-2067; 1872-2067
• DOI: 10.1016/S1872-2067(23)64616-9

The benzophenone structural unit is one of the most important functional groups in organic chemistry, which has a wide range of applications in drugs, light-curing agent, UV-light absorbent and so on. However, the traditional synthetic methods of benzophenone generally involve additives or toxic regents, leading to a large amount of waste and non-recyclable of [Pd] catalyst. Herein, we report Pd loaded carbon-modified TiO2 (Pd/C-TiO2) as an efficient and recyclable catalyst realized the generation of benzophenone through cross-coupling of benzaldehyde and iodobenzene under UV light irradiation, with the yield of 98% and selectivity up to 99%. Based on density functional theory (DFT) calculation and electron paramagnetic resonance (EPR) analysis, the reaction undergoes the Pd0-PdII-PdIII catalytic pathway, that is, benzaldehyde directly activated to acyl radical under UV light and then attracted by Pd-iodobenzene complex to proceed the coupling reaction for benzophenone generation. Owing to the in-situ reduction of dissolved [Pd] through TiO2 photocatalyst in the reaction system, good recyclability of metallic Pd can be achieved. This work not only shed light on a facile method for the synthesis of carbonyl-containing compounds but also offered a practical approach for minimizing the leaching of active metals in transition metal-catalyzed coupling reactions. We developed Pd loaded TiO2 as recyclable catalyst for benzophenone synthesis through the coupling of benzaldehyde with iodobenzene under UV light. Direct light-induced activation of iodobenzene and photocatalytic reduction of [Pd] on to the surface of TiO2 are crucial for efficient and recyclable synthesis of benzophenone.