我们报告了在苯酚基团的邻位具有咪唑基团的五齿 N4O 配体的合成。通过使用先前报道的叔丁基取代配体和咪唑取代配体以两种不同的质子化状态报告锌 (II) 配合物的合成和晶体结构。我们描述了邻位取代基(叔丁基、咪唑和咪唑鎓)对锌 (II) 配合物电化学行为的影响。邻位的叔丁基被咪唑基团取代使酚盐的氧化电位偏移超过 300 mV。邻叔丁基取代的配体允许在电化学氧化时形成稳定的自由基苯氧基锌 (II) 配合物,但在咪唑取代的配合物的情况下它是不稳定的。
我们报告了在苯酚基团的邻位具有咪唑基团的五齿 N4O 配体的合成。通过使用先前报道的叔丁基取代配体和咪唑取代配体以两种不同的质子化状态报告锌 (II) 配合物的合成和晶体结构。我们描述了邻位取代基(叔丁基、咪唑和咪唑鎓)对锌 (II) 配合物电化学行为的影响。邻位的叔丁基被咪唑基团取代使酚盐的氧化电位偏移超过 300 mV。邻叔丁基取代的配体允许在电化学氧化时形成稳定的自由基苯氧基锌 (II) 配合物,但在咪唑取代的配合物的情况下它是不稳定的。
Cyclometallation, steric and electronic tendencies in a series of Pd(II) complex pre-catalysts bearing imidazole–phenol ligands and effects on Suzuki–Miyaura catalytic efficiencies
作者:Abiodun O. Eseola、Helmar Görls、Joseph A.O. Woods、Winfried Plass
DOI:10.1016/j.molcata.2015.06.001
日期:2015.9
A series of new structurally and electronically diversified palladium complexes derived from seven less sterically crowded 2-(4,5-diinethyl-1H-imidazol-2-yl) pheno1/2-(4,5-diethyl-1H-imidazol-2-yl) phenol ligands and fourteen 2-(4,5-diphenyl-1H-imidazol-2-yl) phenols/2-(1H-phenanthro[9,10-d]imidazol-2-yl) phenols bearing varying degrees of higher steric bulk have been prepared and characterized. While single crystals grown from precipitated products of complexation reactions confirmed the bis-ligand Pd(NO)(2) coordination, few crystals obtained from reaction filtrates involving the 244,5-diphenyl-1H-imidazol-2-yl) phenols provided evidence for formation of N (O) over cap(C) over cap chelation species achieved by cyclometallation. Results from structural analyses and catalytic outcomes generally indicate that desirable variables on the ligand frameworks for obtaining superior catalyst activities either provides hemilabile or sterically strained chelation characters, which would both favour generation of monodentate coordination species at the catalysis temperature. In particular, correlation was observed between tendency for cyclometallation in the palladium complexes and poor Suzuki-Miyaura catalytic prospects. Based on hopeful activity obtained for the complex bearing 4-bromo-2-(4,5-dimethyl-1H-imidazol-2-yl) phenol, it was also concluded that sterically bulky ligand is not a necessity for high coupling efficiency, while presence of potentially cyclometallating substituent moieties in the vicinity of the palladium centre may in fact destroy catalytic prospects. (C) 2015 Elsevier B.V. All rights reserved.