Bis(pyrazolyl)pyridine vanadium(III) complexes as highly active ethylene polymerization catalysts

Submissions invited for themed issue of Arthritis Care & Research: Drug safety in the rheumatic diseases

“…That adverse temperature effect for the vanadium system seems to result from the lower stability of the system: vanadium is reduced to lower oxidation states, which are inactive under such conditions. That relation was observed also for other postmetallocene vanadium catalysts 22, 35–37. Hence, when a weaker reducer is used instead of MAO, for example, Et 2 AlCl, the increasing temperature should enhance the reaction rate, and indeed, for the vanadium catalyst activated by Et 2 AlCl, its activity grows to follow the temperature increase over the whole scope, that is, from 20 to 60 °C, for which the activity climbs up from 168 to nearly 4000 kg/mol.…”

“…The recent research, which covered polymerization processes catalyzed by vanadium complexes, bearing various multidentate ligands, indicated that it was possible to manufacture the products with specific properties and, in particular, to obtain high MW and narrow MW distribution polyethylene,22, 23 copolymers of ethylene and cyclic olefins with unimodal MW distribution,24, 25 ethylene/1‐olefin copolymers with high comonomer contents,25, 26 and/or ethylene/unsaturated alcohol copolymers 27. Those catalysts also offer considerable activity in olefin polymerization processes where no MAO is used 22–29. It is advantageous because apart from borates,1, 4, 5 MAO is commonly used to activate bis(phenoxy‐imine) complexes 1–4, 6–15…”

Chromium(III) complexes with terdentate 2,6-bis(azolylmethyl)pyridine ligands: Synthesis, structures and ethylene polymerization behavior

“…Recently, the [2,6-(3,5-Me 2 pzCH 2 )py]VCl 3 complex has been described as an active precursor, in the presence of AlEtCl 2 as co-catalyst, for ethylene polymerization under relatively mild conditions [12].…”

Synthesis and catalytic properties for olefin polymerization of new vanadium complexes containing silsesquioxane ligands with different denticity

“…NMR data for Ph 8 Si 8 O 10 (OH) 4 : 1 H NMR (300 MHz, toluene‐d8, δ , ppm), 6.79 (bs, OH, 4H), 7.14 − 7.60 (m, 44H, C 6 H 5 ); 13 C NMR (75 MHz, toluene‐d8, δ , ppm), 128.13, 128.28, 130.95, 131.03, 131.62, 132.34, 134.55, 134.72 (C 6 H 5 ); Si NMR (79 MHz, toluene‐d8, δ , ppm), −69.01 (Si − OH, Q2), −79.30 (Si, Q3). Detailed characterization ( 1 H NMR, 13 C NMR, Si NMR) of the other silsesquioxanes is presented in Pochwała et al…”