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Formation and Evolution of Chain‐Propagating Species Upon Ethylene Polymerization with Neutral Salicylaldiminato Nickel(II) Catalysts
Author(s) -
Soshnikov Igor E.,
Semikolenova Nina V.,
Zakharov Vladimir A.,
Möller Heiko M.,
Ölscher Franz,
Osichow Anna,
GöttkerSchnettmann Inigo,
Mecking Stefan,
Talsi Evgenii P.,
Bryliakov Konstantin P.
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201301037
Subject(s) - nickel , ethylene , pyridine , catalysis , chemistry , ligand (biochemistry) , dissociation (chemistry) , toluene , polymerization , crystallography , polymer chemistry , medicinal chemistry , polymer , organic chemistry , biochemistry , receptor
Formation of Ni–polymeryl propagating species upon the interaction of three salicylaldiminato nickel(II) complexes of the type [(N,O)Ni(CH 3 )(Py)] (where (N,O)=salicylaldimine ligands, Py=pyridine) with ethylene (C 2 H 4 /Ni=10:30) has been studied by 1 H and 13 C NMR spectroscopy. Typically, the ethylene/catalyst mixtures in [D 8 ]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=(C 2 H 4 ) 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 , Δ H ≠ 298 =(11.7±0.5) kcal mol −1 , Δ S ≠ 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.