Ethylene polymerization catalyzed by bridging Ni/Zn heterobimetallics

Abstract

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(CH)ZnBr (5). Each precatalyst could be activated (or promoted) by ZnX (X = Cl, Br, Et) to polymerize ethylene. In situ recruitment of ZnX by the free imine binding pocket of the NON complexes results in the generation of heterobimetallic active species that produce lower M polyethylene than monometallic controls. Room temperature ZnX-promoted polymerizations with these catalysts resulted in bimodal M distributions that result from different catalyst speciation: "dangling" imine-ligated ZnX species yield higher M polymer while N,O-chelated ZnX species yield lower M polymer. Running polymerizations at higher temperature yields in only lower M 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.

A simple and versatile nickel platform for the generation of branched high molecular weight polyolefins

“…In addition, polyethylene with substantially enhanced molecular weights and slightly decreased branching densities were generated (Table 3, entries 9-11). The polymerization activities slightly increased with increasing ethylene pressure ( Table 3, entries [12][13][14]. In addition, the polyethylene molecular weights and polymer branching densities remained constant, which is similar to the results for homogeneous catalyst Ni2.…”

“…1, I) were capable of producing high molecular weight polyethylene with activities rivaling many early transition metal catalysts [7][8][9] . The salicylaldimine nickel catalysts (II) developed by Grubbs and co-workers in 2000 represent another notable advance in this field [10][11][12][13][14] . SHOP-type nickel catalysts (III; SHOP = Shell Higher Olefin Process) have been commercialized for the synthesis of linear α-olefins 15 .…”

A Self‐Supporting Strategy for Gas‐Phase and Slurry‐Phase Ethylene Polymerization using Late‐Transition‐Metal Catalysts

“…Late-transition-metal-based olefin-polymerization catalysts have attracted much attention from both academia and industry. [6][7][8][9] These catalysts possess unique advantages compared with their early-transition-metal counterparts,s uch as their ability to generate branched polyethylenes using only ethylene as the feedstock, [10][11][12] the ability to conduct polymerizations in polar media, [13,14] and the ability to directly copolymerize ethylene with polar comonomers. [15][16][17][18][19] Brookhart-type a-diimine nickel and palladium catalysts have been extensively studied due to their ability to generate branched polyethylenes via ac hain walking mechanism, in which the metal atom can migrate along the polymer chain through bhydride elimination and reinsertion with opposite regiochemistry.…”

A Self‐Supporting Strategy for Gas‐Phase and Slurry‐Phase Ethylene Polymerization using Late‐Transition‐Metal Catalysts

“…Late‐transition‐metal‐based olefin‐polymerization catalysts have attracted much attention from both academia and industry . These catalysts possess unique advantages compared with their early‐transition‐metal counterparts, such as their ability to generate branched polyethylenes using only ethylene as the feedstock, the ability to conduct polymerizations in polar media, and the ability to directly copolymerize ethylene with polar comonomers . Brookhart‐type α‐diimine nickel and palladium catalysts have been extensively studied due to their ability to generate branched polyethylenes via a chain walking mechanism, in which the metal atom can migrate along the polymer chain through β‐hydride elimination and reinsertion with opposite regiochemistry .…”