Formation and evolution of chain-propagating species upon ethylene polymerization with neutral salicylaldiminato nickel(II) catalysts.
Formation and evolution of chain-propagating species upon ethylene polymerization with neutral salicylaldiminato nickel(II) catalysts.
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DOI：
10.1002/chem.201301037
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发表时间：
2013-08
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通讯作者：
I. Soshnikov;N. V. Semikolenova;V. Zakharov;H. Möller;Franz Olscher;Anna Osichow;I. Göttker-Schnettmann;S. Mecking;E. P. Talsi;K. Bryliakov
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作者：
I. Soshnikov;N. V. Semikolenova;V. Zakharov;H. Möller;Franz Olscher;Anna Osichow;I. Göttker-Schnettmann;S. Mecking;E. P. Talsi;K. Bryliakov
通过 (1) H 和 (13) C NMR 研究了 [(N,O)Ni(CH3 )(Py)] 类型的三种水杨醛亚胺镍 (II) 络合物（其中 (N,O)=水杨醛亚胺配体，Py=吡啶）与乙烯 (C2 H4 /Ni=10:30) 相互作用时形成 Ni-聚合基增长物质 光谱学。通常，将[D8]甲苯中的乙烯/催化剂混合物在+60°C下短时间储存以生成[(N,O)Ni(聚合基)]物质，然后快速冷却，并在-20°C下进行NMR测量。在该温度下，[(N,O)Ni(聚合基)]物质可以稳定数天；扩散 (1) H NMR 测量提供了聚合基链平均长度的估计（聚合基=(C2 H4 )n H，n=6-18）。在高乙烯消耗量下，[(N,O)Ni(聚合基)]中间体下降，释放游离聚合物链并产生[(N,O)Ni(Et)(Py)]物质，其也进一步分解形成最终的催化剂降解产物，顺磁性[(N,O)2 Ni(Py)]络合物。 [(N,O)2 Ni(Py)]中，吡啶配体不稳定（解离活化能为(12.3±0.5) kcal mol(-1) , ΔH(≠) 298 =(11.7±0.5) kcal mol(-1) , ΔS(≠) 298 =(-7±1) cal K(-1) mol(-1) )。添加非极性溶剂（戊烷）后，吡啶配体完全消失，产生抗磁性[(N,O)2 Ni]络合物晶体。对形成的聚乙烯的核磁共振光谱分析表明，链增长物质的演变最终导致形成主要具有内部和末端亚乙烯基而不是乙烯基的聚乙烯。
Formation of Ni-polymeryl propagating species upon the interaction of three salicylaldiminato nickel(II) complexes of the type [(N,O)Ni(CH3 )(Py)] (where (N,O)=salicylaldimine ligands, Py=pyridine) with ethylene (C2 H4 /Ni=10:30) has been studied by (1) H and (13) C NMR spectroscopy. Typically, the ethylene/catalyst mixtures in [D8 ]toluene were stored for short periods of time at +60 °C to generate the [(N,O)Ni(polymeryl)] species, then quickly cooled, and the NMR measurements were conducted at -20 °C. At that temperature, the [(N,O)Ni(polymeryl)] species are stable for days; diffusion (1) H NMR measurements provide an estimate of the average length of polymeryl chain (polymeryl=(C2 H4 )n H, n=6-18). At high ethylene consumptions, the [(N,O)Ni(polymeryl)] intermediates decline, releasing free polymer chains and yielding [(N,O)Ni(Et)(Py)] species, which also further decompose to form the ultimate catalyst degradation product, a paramagnetic [(N,O)2 Ni(Py)] complex. In [(N,O)2 Ni(Py)], the pyridine ligand is labile (with activation energy for its dissociation of (12.3±0.5) kcal mol(-1) , ΔH(≠) 298 =(11.7±0.5) kcal mol(-1) , ΔS(≠) 298 =(-7±1) cal K(-1) mol(-1) ). Upon the addition of nonpolar solvent (pentane), the pyridine ligand is lost completely to yield the crystals of diamagnetic [(N,O)2 Ni] complex. NMR spectroscopic analysis of the polyethylenes formed suggests that the evolution of chain-propagating species ends up with formation of polyethylene with predominately internal and terminal vinylene groups rather than vinyl groups.