Ethylene polymerization catalyzed by bridging Ni/Zn heterobimetallics.
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 ZnX2by the free imine binding pocket of the NON complexes results in the generation of heterobimetallic active species that produce lower Mnpolyethylene than monometallic controls. Room temperature ZnX2-promoted polymerizations with these catalysts resulted in bimodal Mndistributions that result from different catalyst speciation: "dangling" imine-ligated ZnX2species yield higher Mnpolymer while N,O-chelated ZnX2species yield lower Mnpolymer. Running polymerizations at higher temperature yields in only lower Mnpolymer 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.
Department of Chemistry, University of Minnesota - Twin Cities Minneapolis, MN 55455, USA.
Hsin-Chun
HC
Chiu
Arijit
A
Koley
Peter L
PL
Dunn
Ryan J
RJ
Hue
Ian A
IA
Tonks