title: Formation and evolution of chain-propagating species upon ethylene polymerization with neutral salicylaldiminato nickel(II) catalysts.
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 (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.
authors.affiliation: Institute of Catalysis, Pr. Lavrentieva 5, 630090 Novosibirsk, Russian Federation.
authors.forename: Igor E
authors.initials: IE
authors.lastname: Soshnikov
authors.forename: Nina V
authors.initials: NV
authors.lastname: Semikolenova
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Zakharov
authors.forename: Heiko M
authors.initials: HM
authors.lastname: Möller
authors.forename: Franz
authors.initials: F
authors.lastname: Olscher
authors.forename: Anna
authors.initials: A
authors.lastname: Osichow
authors.forename: Inigo
authors.initials: I
authors.lastname: Göttker-Schnettmann
authors.forename: Stefan
authors.initials: S
authors.lastname: Mecking
authors.forename: Evgenii P
authors.initials: EP
authors.lastname: Talsi
authors.forename: Konstantin P
authors.initials: KP
authors.lastname: Bryliakov
keywords: NMR spectroscopy; nickel; polymerization; reaction mechanisms; reactive intermediates