کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1328211 977549 2007 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی معدنی
پیش نمایش صفحه اول مقاله
Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands
چکیده انگلیسی

This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introducing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridin-2-yl]-amine (1a–H, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine (1b–H, Ap∗H). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap2ZrCl2] (3a) and [Ap2∗ZrCl2] (3b) and the dimethyl analogues, [Ap2ZrMe2] (4a) and [Ap2∗ZrMe2] (4b) (Me = methyl) were synthesized, using standard salt metathesis routes. Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral environment with a cis-orientation of the chloride ligands in 3a and a closer to trans-arrangement in 3b. The dimethyl derivatives are proven to be highly active ethylene polymerization catalysts after activation with [R2N(Me)H][B(C6F5)4] (R = C16H33–C18H37). During attempted co-polymerizations of α-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substituted pyridines, switches the catalyst system from producing long chain α-olefins to polymerization of ethylene in a living fashion. In contrast to the dimethyl complexes only [Ap2∗ZrCl2] in the presence of MAO at elevated temperature gave decent polymerization activity. NMR investigations of the reaction of dichloro complexes with 25 equiv. of MAO or AlMe3 at room temperature revealed, that [Ap2ZrCl2] decomposes under ligand transfer to aluminum and formation of [ApAlMe2], while [Ap2∗ZrCl2] remains almost unreacted under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe2] (5a) and [Ap∗AlMe2] (5b) were synthesized independently and structurally characterized. The aluminum complexes 5a and b show no catalytic activity towards ethylene, when “activated” with[R2N(Me)H][B(C6F5)4].

Sterically very demanding aminopyridinato ligands stabilize thermally robust, highly active and selective zirconium ethylene polymerization catalysts. Small changes in the bulky ligand periphery can be used to fine tune the nature of the formed polymers and even “living” ethylene polymerization at elevated temperatures (50 °C) can be observed.Figure optionsDownload as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Organometallic Chemistry - Volume 692, Issue 21, 1 October 2007, Pages 4569–4579
نویسندگان
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