Synthesis of Branched Polyethylene with “Half-Sandwich” Pyridine-Imine Nickel Complexes

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• 作者：Zhou Chen ; Kate E. Allen ; Peter S. White ; Olafs Daugulis ; Maurice Brookhart
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 13, 2016
• 年：2016
• 卷：35
• 期：11
• 页码：1756-1760
• 全文大小：228K
• 年卷期：0
• ISSN：1520-6041

文摘

Traditional cationic Pd(II) and Ni(II) ethylene polymerization catalysts are supported by ortho-disubstituted aryl diimine ligands. These catalysts are capable of producing high-molecular-weight polyethylene due to positioning of bulk in the two axial sites of the square coordination plane which retards chain transfer. Similar pyridine-imine complexes bearing a single ortho-disubstituted aryl imine moiety were reported to yield very low M_n polyethylene. In earlier studies, “sandwich” diimine nickel catalysts incorporating two 8-arylnaphthylimino groups which provide exceptional shielding of the two axial sites were shown to yield ultrahigh-molecular-weight polyethylene. Here we demonstrate that 8-arylnaphthyl groups incorporated into pyridine-imine nickel catalysts that block only a single axial site are highly effective in retarding chain transfer. These catalysts produce branched polyethylene (ca. 30–90 branches per 1000 carbons) with M_n values up to 2.6 × 10⁴ g/mol. Effects on the catalyst lifetimes and polymerization behavior as a function of substituent variations at the imine carbon and the aryl group are reported.