Zirconium and hafnium complexes supported by linked bis(β-diketiminate) ligands: synthesis, characterization and catalytic application in ethylene polymerization
作者:Shaogang Gong、Haiyan Ma、Jiling Huang
DOI:10.1039/b905392a
日期:——
Zirconium and hafnium complexes bearing new 1,2-ethanediyl- or 1,3-propanediyl-linked bis(β-diketiminate) ligands, [CnH2n-(BDIAr)2}MCl2] (Ar = 2,6-Me2-C6H3, 2,6-Cl2-C6H3, 2,6-iPr2-C6H3; M = Zr, n = 2 (4aâc), n = 3 (5aâc); M = Hf, n = 2 (6b)), were synthesized via the reaction of MCl4·2THF and one equivalent of dilithium salt of the corresponding ligand. Distorted trigonal prismatic and octahedral coordination geometries as well as C1-symmetric structures are found for zirconium complexes 4c and 5c in the solid state. Variable temperature 1H NMR spectra indicated the fluxional nature of 4a and 5a in solution. Upon activation with methylaluminoxane (MAO), all these complexes except hafnium complex 6b displayed moderate catalytic activities for ethylene polymerization. 1,2-Ethanediyl-linked complexes 4a and 4b are generally more active than their 1,3-propanediyl-linked analogues. The substituents at the ortho-positions of the phenyl rings have different effect on the catalytic activities of 1,2-ethanediyl-linked series or 1,3-propanediyl-linked series. It is noteworthy that even at a low Al/Zr molar ratio of 500, the catalytic activities of these zirconium complexes could be retained. Polyethylenes with broad molecular weight distributions (MWD = 15.3â20.3) were produced, which might result from the fluxional character of the zirconium complexes. The linear structure of obtained polyethylenes was further determined by 13C NMR spectroscopy and DSC analysis.
含有新1,2-乙二基或1,3-丙二基连接的双(β-二酮亚胺)配体的锆和铪配合物[CnH2n-(BDIAr)2}MCl2](Ar = 2,6-Me2-C6H3, 2,6-Cl2-C6H3, 2,6-iPr2-C6H3;M = Zr, n = 2(4a–c), n = 3(5a–c);M = Hf, n = 2(6b))通过MCl4·2THF与相应配体的二锂盐反应合成。在固态下,锆配合物4c和5c具有扭曲的三方棱柱和八面体配位几何结构以及C1对称结构。变温1H NMR谱表明,溶剂中的4a和5a表现出流动性特性。使用甲基铝氧烷(MAO)活化,这些配合物(除铪配合物6b外)均显示出中等的乙烯聚合催化活性。1,2-乙二基连接的配合物4a和4b通常比相应的1,3-丙二基连接的类似物活性更高。苯环上的邻位取代基对1,2-乙二基系列或1,3-丙二基系列催化活性的影响不同。值得注意的是,即使在较低的Al/Zr摩尔比500下,这些锆配合物的催化活性也能得以保持。生成了分子量分布较宽(MWD = 15.3–20.3)的聚乙烯,这可能是由于锆配合物的流动性特征所致。通过13C NMR光谱和DSC分析进一步确定了所得聚乙烯的线性结构。