Synthesis of Imidazole-Based Functionalized Mesoionic Carbene Complexes of Palladium: Comparison of Donor Properties and Catalytic Activity toward Suzuki–Miyaura Coupling

Three different backbone-monofunctionalized imidazolium salts have been synthesized using the metal–halogen exchange procedure, and their corresponding mesoionic carbene complexes with palladium were prepared via oxidative addition without protection of the C2 position. The donor properties were evaluated with 31P NMR spectroscopy of the respective palladium complexes. The catalytic activity of these complexes toward Suzuki–Miyaura coupling of aryl bromides was also explored. Also, in one case, a comparison of donor properties was made with those of a “normal” carbene with similar steric bulk.本研究采用金属-卤素交换法（metal–halogen exchange procedure）合成了三种不同的骨架单官能化咪唑鎓盐（backbone-monofunctionalized imidazolium salts），并通过不保护C2位的氧化加成（oxidative addition）反应，制备了它们对应的钯基介离子卡宾（mesoionic carbene）配合物。通过对应钯配合物的31P核磁共振波谱法（31P NMR spectroscopy）评估了其给电子性能。同时，还考察了该类配合物对芳基溴化物（aryl bromides）参与的铃木-宫浦（Suzuki-Miyaura）偶联反应的催化活性。此外，针对其中一种配体，还将其给电子性能与空间位阻（steric bulk）相近的"正常"卡宾进行了对比。