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Ethylene polymerization catalyzed by bridging Ni/Zn heterobimetallics

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The effect of proximal Zn halides on Ni-catalyzed ethylene polymerization is reported in this work. A series of (NON)NiLX (NON = 2,6-bis-((2,6-diisopropylphenyl)imino)methyl phenoxide; LX = methallyl or L = py, X = tolyl, 2–4) ethylene polymerization precatalysts have been synthesized, as well as a heterobimetallic Ni/Zn complex, (NON)Ni(C4H7)ZnBr2 (5). Each precatalyst could be activated (or promoted) by ZnX2 (X = Cl, Br, Et) to polymerize ethylene. In situ recruitment of ZnX2 by the free imine binding pocket of the NON complexes results in the generation of heterobimetallic active species that produce lower Mn polyethylene than monometallic controls. Room temperature ZnX2-promoted polymerizations with these catalysts resulted in bimodal Mn distributions that result from different catalyst speciation: “dangling” imine-ligated ZnX2 species yield higher Mn polymer while N,O-chelated ZnX2 species yield lower Mn polymer. Running polymerizations at higher temperature yields in only lower Mn polymer resulting from exclusive formation of the thermodynamically favored N,O chelated Ni/Zn heterobimetallic. DFT calculations indicate that this bridging bimetallic complex undergoes β-H elimination more facilely than monometallic Ni analogues, resulting in lower molecular weight polymers.

Graphical abstract: Ethylene polymerization catalyzed by bridging Ni/Zn heterobimetallics

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The article was received on 18 Jan 2017, accepted on 13 Mar 2017, published on 13 Mar 2017 and first published online on 13 Mar 2017

Article type: Communication
DOI: 10.1039/C7DT00222J
Citation: Dalton Trans., 2017, Advance Article
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    Ethylene polymerization catalyzed by bridging Ni/Zn heterobimetallics

    H. Chiu, A. Koley, P. L. Dunn, R. J. Hue and I. A. Tonks, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT00222J

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