介孔碳负载钯催化剂应用于水介质中芳环C-H键活化反应的研究

Palladium catalyzed C-H bond activation reactions have emerged as a powerful tool in synthetic chemistry due to the direct transformation of C-H bonds into C-C or C-Y (heteroatom) bonds. However, the C-H bond is stable and of low polarity, making it fairly unreactive. Consequently, direct C-H bond activation processes enabled by heterogeneous Pd catalysts are relatively rare. Herein, heterogeneous palladium supported on mesoporous carbon would be used to C-H bond activation reactions of indole, N-([1,1'-biphenyl]-2-yl)acetamide and their derivatives in aqueous media, which would lead to the formation of C-C or C-N bonds directly and effectively. The preparation of Pd could be conducted by self-assembly of surfactants possessing specific ligands, by which Pd nanoparticles could be introduced into the mesoporous carbon frame in one step. Such kind of controlled self-assembly process would be useful to modulate the dispersity of Pd nanoparticles. Meanwhile, the catalytic reactivity and stability of the Pd catalysts could be further improved by introducing a second metal (Au, Ni etc.) or incorporating metal oxide such as CeO2, MnO into the mesoporous carbon support, and the coordination state and electronic properties of palladium atoms on the surface could be regulated by this process. In addition, the nature of the true catalytic species and the possible catalytic principles would be carefully studied. This project would address some problems of traditional C-H activation reactions such as the difficulty in separating a homogenous Pd catalyst from the reaction mixture and reusing of it in consecutive reactions, products contamination from palladium residues, requirement of special organic ligands and the low activity of supported heterogeneous palladium catalyst, metal palladium leaching as well as the utilization of organic solvents.

钯催化C-H键活化反应可直接将C-H键转化为C-C或C-Y(杂)键，在化学合成中具有广泛应用价值。但是，C-H键结构相对稳定且极性很小，反应活性低，多相催化剂研究相对较少。本项目提出利用介孔碳负载钯催化剂，以水为反应溶剂，催化吲哚、2-乙酰胺联苯及其衍生物C-H键反应，直接、高效地通过C-H键构建C-C或C-N键。催化剂的制备采用含配体表面活性剂自组装技术，一步将钯纳米颗粒引入到介孔碳骨架中，可控的自组装过程有利于调控钯纳米颗粒分散度。同时可通过引入第二种金属(Au、Ni等)或在载体中引入金属氧化物(CeO2、MnO等)，调变Pd配位状态和表面电子性质，稳定贵金属，提高催化剂活性和稳定性。阐明催化活性中心以及可能的催化作用机理。解决传统C-H键活化反应中均相钯催化剂难以重复使用、不易与产物分离、可能造成产物金属污染、使用有机配体以及负载钯催化剂活性低、金属钯易流失、使用有机溶剂等问题。

针对C-H键活化中普遍存在的均相催化剂难以重复使用、金属流失、产物中重金属残留、使用有机溶剂等问题，建立了水介质中介孔碳负载Pd纳米催化剂表面C-H键活化的绿色化学体系。采用配位辅助自组装技术结合热还原、离子交换等策略制备了被介孔碳限域固定的Pd纳米颗粒，纳米颗粒尺寸均一且高度分散。在载体中引入N物种、TiO2等氧化物，利用其与Pd与之间较强的相互作用，调变Pd表面电子性质，增强Pd与载体结合力，限制了Pd纳米粒子的迁移和团聚，稳定贵金属，提高了催化剂活性和稳定性。所制备Pd纳米催化剂在水介质吲哚以及衍生物C‒H键活化、吡咯及其衍生物C‒H键双芳基化反应、8-甲基喹啉C(SP3)‒H键活化中，展现出与均相催化剂相当或更高的反应活性，部分产物产率达到98%，TOF值达到121 h-1。通过热过滤实验和巯基功能化二氧化硅捕获反应溶液中钯物种实验等揭示了活性中心为固载的钯纳米粒子。催化剂具有较高的稳定性，多次循环使用后(10次以上)未见明显催化活性下降。研究成果在本领域顶级期刊ACS Catalysis 发表相关论文2篇，申请中国发明专利2项。