Nickel complexes with “click”-derived pyridyl-triazole ligands: weak intermolecular interactions and catalytic ethylene oligomerisation
作者:David Schweinfurth、Cheng-Yong Su、Shi-Chao Wei、Pierre Braunstein、Biprajit Sarkar
DOI:10.1039/c2dt31805a
日期:——
The ligands 1-(cyclohexyl)-4-(2-pyridyl)-1,2,3-triazole (1), 1-(2,6-diisopropylphenyl)-4-(2-pyridyl)-1,2,3-triazole (2), 1-(4-butoxyphenyl)-4-(2-pyridyl)-1,2,3-triazole (3) and 1-(methyl)-4-(2-pyridyl)-1,2,3-triazole (4) were synthesized by the Cu(I) catalyzed âClickâ reaction between 2-pyridylacetylene and the corresponding azides. The ligands were then reacted with NiBr2·3H2O to generate the complexes (1)2NiBr2 (1a), (2)2NiBr2 (2a), (3)2NiBr2 (3a) and (4)2NiBr2 (4a). Structural characterization of 1a confirmed the mononuclear and distorted octahedral environment around the Ni(II) center, with the pyridyl-triazole ligands coordinating in a bis-chelating fashion. Bond length analysis inside the 1,2,3-triazole ring shows a short NN double bond that is flanked by two longer CâN and NâN bonds pointing to the existence of âazoâ character in the ring. The highly polar five-membered 1,2,3-triazole ring makes its CâH bond acidic, and these bonds participate in an extended weak intermolecular CâHâ¯Br interactions with the Br-groups of neighboring molecules, resulting in a 3-D network. The nickel complexes with these âClickâ ligands were tested as pre-catalysts for ethylene oligomerization, and the complexes showed moderate activity in that reaction with good selectivity towards C4 oligomers.
配体1-(环己基)-4-(2-吡啶基)-1,2,3-三唑(1)、1-(2,6-二异丙基苯基)-4-(2-吡啶基)-1,2,3-三唑(2)、1-(4-正丁氧基苯基)-4-(2-吡啶基)-1,2,3-三唑(3)和1-(甲基)-4-(2-吡啶基)-1,2,3-三唑(4)是通过铜(I)催化的“点击”反应,使用2-吡啶乙炔与相应的叠氮化物合成的。然后,将配体与NiBr2·3H2O反应,生成络合物(1)2NiBr2(1a)、(2)2NiBr2(2a)、(3)2NiBr2(3a)和(4)2NiBr2(4a)。1a的结构表征确认了围绕Ni(II)中心的单核和扭曲八面体环境,吡啶-三唑配体呈双螯合方式配位。在1,2,3-三唑环内的键长分析显示了一个短的NN双键,两侧有两个较长的C–N和N–N键,表明环内存在“偶氮”特性。高极性的五元1,2,3-三唑环使其C–H键呈酸性,这些键参与了与相邻分子Br基团之间的扩展弱分子间C–H···Br相互作用,形成了三维网络。这些“点击”配体的镍络合物作为乙烯聚合的前催化剂进行了测试,结果显示这些络合物在此反应中表现出适度的活性,并对C4寡聚物具有良好的选择性。