High molecular weight polyethylenes of narrow dispersity promoted using bis(arylimino)cyclohepta[b]pyridine-cobalt catalysts ortho-substituted with benzhydryl & cycloalkyl groups

В журнале Dalton Transactions (IF 4,052) опубликована статья с участием сотрудников Института   д.х.н. И.И. Олейника (внс, ЛЭИСМ ) и к.х.н. И.В. Олейник (снс, ЛЭАСМ):

High molecular weight polyethylenes of narrow dispersity promoted using bis(arylimino)cyclohepta[b]pyridine-cobalt catalysts ortho-substituted with benzhydryl & cycloalkyl groups

Abstract

A one-pot template strategy has been utilized to synthesize sterically enhanced bis(imino)cyclohepta[b]pyridine-cobalt(II) chlorides, [2-{(Ar)NCMe}-9-{N(Ar)}C₁₀H₁₀N]CoCl₂ (Ar = 2-(C₅H₉) -4,6-(CHPh₂)₂C₆H₂ Co1, 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂  Co2, 2-(C₈H₁₅)-4,6-(CHPh₂) ₂C₆H₂ Co3, 2-(C₁₂H₂₃)-4,6-(CHPh₂ )₂C₆H₂ Co4, 2,6-(C₅H₉)₂ -4-(CHPh₂)C₆H₂ Co5). All five complexes have been characterized by a combination of FT-IR spectroscopy, elemental analysis and single crystal X-ray diffraction. The molecular structures of Co1, Co3 and Co5 highlight the substantial steric hindrance imparted by the 2-cycloalkyl-6-benzhydryl or 2,6-dicyclopentyl ortho-substitution pattern; distorted square pyramidal geometries are exhibited in each case. On activation with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the complexes (apart from Co4/MAO) were active ethylene polymerization catalysts (up to 3.70 ? 10⁶ g PE per mol (Co) per h for Co5/MMAO), operating effectively at temperatures between 50 °C and 60 °C, producing polyethylenes with high molecular weights (up to 589.5 kg mol^-1 for Co3/MAO). Furthermore, all polymers were highly linear (T_m > 130 °C) with narrow dispersities (M_w/M_n range: 2.0–3.0). The coexistence of two chain termination pathways, β-H elimination and transfer to aluminum, has been demonstrated using ¹³ C/¹H NMR spectroscopy.

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