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New single- Mao Part IVB family transition metal complexes Synthesis, structure and catalytic activity

Author: SunQi
Tutor: Maxim V. Borzov
School: Northwestern University
Course: Organic Chemistry
Keywords: 1-methyl-1H-imidazole cyclopentadienyl ligands titanium zirconium catalytic ethylene polymerization
CLC: O621.13
Type: Master's thesis
Year: 2010
Downloads: 73
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Abstract


Since the development of Zeigler-Natta catalysts, a tremendous amount of the research efforts have been focused on catalysts and catalytic systems for olefin polymerization, copolymerization and oligmerization. Among all types of these catalysts, the so-called "constrained geometry" metallocene-type catalysts (CGC-s) (entered first into practice by DOW company) exhibit top-advantageous characteristics for production of polyolefins of regulated tacticity. The initial idea of this Master Degree work, actually, lays in the CGC chemistry area and, namely, is to introduce the novel 1-methyl-lH-imidazolyl side-chain functionalized cyclopentadienes as ligands into the organochemistry of the Group 4 elements (Ti and Zr) and to study the catalytic activity of the resultant complexes for olefin polymerization.The present investigation naturally comprises three interconnected parts. At the first stage, we have developed synthetic approaches to target 2-[(cyclopentadienyl)diphenylmethyl]-and 2-[(cyclopentadienyl)phenylmethyl]-1-methyl-lH-imidazoles (denoted as 3a and 3b in the body of the manuscript) by reactions of 2-lithio-l-methyl-lH-imidazole with 6,6-diphenyl-and/or 6-phenylfulvenes. Compounds 3a and 3b have been fully characterized by appropriate instrumental methods and have been shown to exist as mixtures of isomers (tautomers) in respect to the position of the substituent at the cyclopentadienyl ring, with the (cyclopenta-1,3-dien-2-yl) ones dominating. Occasionally, we have got managed to isolate and characterize 2-[(n-butylcyclopentadienyl)phenylmethyl]-1-methyl-lH-imidazole (4) as a side-product in one of the reaction runs. Compounds 3a and 3b have been converted into corresponding lithium cyclopentadienides (2a and 2b), with the molecular structure of the salt 2a (adduct with 2 molecules of THF) established by X-ray diffraction analysis.At the second step of the investigation, we have prepared four Ti and Zr complexes derived from cyclopentadienes 3a and 3b starting directly from lithiated forms 2a and/or 2b or via their intermediate conversion into trimethylsilylated cyclopentadienes. Crystal and molecular structure of trichloro{ 2-[(η5-cyclopentadienyl)diphenylmethyl]-l-methyl-1H-imidazole-κN3}(tetrahydrofuran-κO)zirconium(Ⅳ) (6a) was established by X-ray diffraction analysis. On an example of Zr-complex 6a, we have examined its catalytic activity in respect to ethylene polymerization in presence of methylalumoxane (MAO; molar ratio Al:Zr 3000). The tests revealed catalytic activity of the system of question up to 1.30×105 g·(mol·h)-1. Studies of the prepared polyethylene by GPC analysis have pointed out unimodal molecular weigh distribution with moderate average weighs and small weigh dispersions. Attempts to perform polymerization tests with the silica-immobilized 6a were also undertaken.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Theory of organic chemistry,physical organic chemistry > Organic Chemistry Structure Theory
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