Substituted tridentate pyrazolyl ligands for chromium and nickel-catalyzed ethylene oligomerization reactions: effect of auxiliary ligand on activity and selectivity
作者:Lucilene L. de Oliveira、Roberta R. Campedelli、Adão L. Bergamo、Ana H. D. P dos Santos、Osvaldo L. Casagrande
DOI:10.1590/s0103-50532010000700019
日期:——
Two new chromium(III) complexes [CrCl3(L)] based on tridentate ligands (1a, L = bis[2-(3-phenyl-1-pyrazolyl)ethyl)]amine; 2a, L = bis[2-(3-methyl-5-phenyl-l-pyrazolyl)ethyl]sulfide) have been prepared and characterized by elemental analysis. Upon activation with methylaluminoxane (MAO), these pre-catalysts showed high turnover frequencies for ethylene oligomerization under optimized conditions (TOFs = 22.9-36.4×10³ mol C2H4 (mol CrIII)-1 h-1, [Cr] = 10.0 µmol, 80 ºC, 20 bar ethylene, MAO: Cr = 300, oligomerization time = 20 min), producing α-olefins in the range C4-C14+ with high selectively (67.71-73.47%). The catalytic performances are substantially affected by the ligand environment, especially the substituents at the 3- and 5-positions of the pyrazolyl rings. In parallel, the use of nickel complexes such as NiCl2bis[2-(3,5-dimethyl-1-pyrazolyl)methyl]benzylamine} (3) and NiCl2bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl)]ether} (5) in oligomerization reactions carried out in the presence of triphenylphosphine (PPh3) afforded highly active catalytic systems with turnover frequencies (TOFs) varying from 36.4 to 154.2×10³ mol C2H4 (mol NiII)-1 h-1. The presence of this auxiliary ligand has a strong impact on the selectivity towards the production of α-olefins, decreasing substantially the amount of 1-butene with a concominat increase of the 2-butene fractions. Attempts to crystallize the nickel complex 3 afforded the tetrametallic [(L)(µ3-Cl)NiCl}4] (4, L = 1-anilinomethyl-3,5-dimethylpyrazole) which was characterized by X-ray diffraction analysis.
两种基于三齿配体的新型铬(III)络合物[CrCl3(L)] (1a, L = 双[2-(3-苯基-1-吡唑基)乙基)]胺; 2a,L=双[2-(3-甲基-5-苯基-1-吡唑基)乙基]硫醚)已被制备并通过元素分析进行表征。用甲基铝氧烷 (MAO) 活化后,这些预催化剂在优化条件下表现出乙烯低聚的高周转频率 (TOF = 22.9-36.4×10³ mol C2H4 (mol CrIII)-1 h-1, [Cr] = 10.0 µmol, 80 ℃,20 bar 乙烯,MAO:Cr = 300,低聚时间 = 20 分钟),以高选择性 (67.71-73.47%) 生产 C4-C14+ 范围内的 α-烯烃。催化性能很大程度上受到配体环境的影响,特别是吡唑环3-和5-位的取代基。同时,使用镍络合物,例如 NiCl2双[2-(3,5-二甲基-1-吡唑基)甲基]苄胺} (3) 和 NiCl2双[2-(3,5-二甲基-1-)吡唑基)乙基)]醚} (5) 在三苯基膦 (PPh3) 存在下进行的低聚反应中提供了高活性催化体系,其周转频率 (TOF) 从 36.4 到 154.2×10³ mol C2H4 (mol NiII)-1 h -1。这种辅助配体的存在对α-烯烃生产的选择性有很大的影响,显着减少了1-丁烯的量,同时增加了2-丁烯的馏分。尝试结晶镍络合物 3 得到四金属 [(L)(μ3-Cl)NiCl}4] (4, L = 1-苯胺基甲基-3,5-二甲基吡唑),通过 X 射线衍射分析对其进行表征。