Synthesis and Structural Studies of NCN Diimine Palladium Pincer Complexes Bearing <i>m</i>-Terphenyl Scaffolds

The reaction of 2,6-[2-{RNC(H)}C6H4]2C6H3I [R = Ph (4), Cy (5), 2,6-Me2C6H3 (6), 2,4,6-Me3C6H2 (7), (S)-α-methylbenzyl (8)] with Pd2(dba)3 afforded the NCN diimine pincer palladium complexes [2,6-[2-{RNC(H)}C6H4]2C6H3PdI] (9−13) by oxidative addition of the C−I bonds of the ligand precursors. Single-crystal X-ray diffraction analyses of complexes 9−13 reveal formal C2-symmetric environments. Variable-temperature NMR studies of complexes 11 and 12 show hindered rotation about the N−Ar bonds and also suggest that atropisomers of complexes 9−13 do not interconvert on the NMR time scale. Consistent with this proposal, isolation of the two possible isomers of 13 (13a and 13b) was possible, and their structures and NMR properties have been examined in detail.配体前体2,6-[2-{RN=C(H)}C₆H₄]₂C₆H₃I [其中R分别为苯基(Ph，编号4)、环己基(Cy，编号5)、2,6-二甲基苯基(编号6)、2,4,6-三甲基苯基(编号7)、(S)-α-甲基苄基(编号8)]与三(二亚苄基丙酮)二钯(Pd₂(dba)₃)发生反应，通过配体前体的C−I键氧化加成，得到NCN二亚胺钳形钯配合物[2,6-[2-{RN=C(H)}C₆H₄]₂C₆H₃PdI]（编号9−13）。对配合物9−13的单晶X射线衍射分析显示，其具有形式上的C₂对称空间环境。对配合物11和12的变温核磁共振(NMR)研究表明，该类配合物存在N−Ar键的旋转受阻现象，同时提示配合物9−13的阻转异构体在核磁共振时间尺度上无法相互转化。与该推论相符，研究人员成功分离得到配合物13的两种同分异构体(13a和13b)，并对其结构与核磁共振波谱性质进行了详细表征。