Formation and Evolution of Chain‐Propagating Species Upon Ethylene Polymerization with Neutral Salicylaldiminato Nickel(II) Catalysts |
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Authors: | Dr Igor E Soshnikov Dr Nina V Semikolenova Prof Vladimir A Zakharov Prof?Dr Heiko M Möller Franz Ölscher Anna Osichow Dr Inigo Göttker‐Schnettmann Prof?Dr Stefan Mecking Prof?Dr Evgenii P Talsi Prof?Dr Konstantin P Bryliakov |
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Institution: | 1. Institute of Catalysis, Pr. Lavrentieva 5, 630090 Novosibirsk (Russian Federation), Fax: (+7)383‐3308056;2. University of Konstanz, Chair of Chemical Material Science, Department of Chemistry, Universit?tstrasse 10, 78457 Konstanz (Germany), Fax: (+49)?7531‐885152 |
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Abstract: | 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 (C2H4/Ni=10:30) has been studied by 1H and 13C 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 1H NMR measurements provide an estimate of the average length of polymeryl chain (polymeryl=(C2H4)nH, 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)2Ni(Py)] complex. In (N,O)2Ni(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)2Ni] 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. |
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Keywords: | nickel NMR spectroscopy polymerization reaction mechanisms reactive intermediates |
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