Olefin Polymerization by Dinuclear Zirconium Catalysts Based on Rigid Teraryl Frameworks: Effects on Tacticity and Copolymerization Behavior

Abstract

Toward gaining insight into the behavior of bimetallic catalysts for olefin polymerization, a series of structurally related binuclear zirconium catalysts with bisamine bisphenolate and pyridine bisphenolate ligands connected by rigid teraryl units were synthesized. Anthracene-9,10-diyl and 2,3,5,6-tetramethylbenzene-1,4-diyl were employed as linkers. Bulky Si i Pr 3 and SiPh 3 substituents were used in the position ortho to the phenolate oxygen. Pseudo-C s and C 2 symmetric isomers are observed for the binuclear complexes of bisamine bisphenolate ligands. In general, binuclear catalysts show higher isotacticity compared to the monozirconium analogues, with some differences between isomers. Amine bisphenolate-supported dizirconium complexes were found to be moderately active (up to 1.5 kg mmol Zr −1 h −1 ) for the polymerization of 1-hexene to isotactically enriched poly-1-hexene (up to 45% mmmm) in the presence of stoichiometric trityl or anilinium borate activators. Moderate activity was observed for the production of isotactically enriched polypropylene (up to 2.8 kg mmol Zr −1 h −1 and up to 25.4% mmmm). The previously proposed model for tacticity control based on distal steric effects from the second metal site is consistent with the observed behavior. Both bisamine bisphenolate and pyridine bisphenolate supported complexes are active for the production of polyethylene in the presence of MAO with activities in the range of 1.1−1.6 kg mmol Zr −1 h −1 and copolymerize ethylene with αolefins. Little difference in the level of α-olefin incorporation is observed between mono-and dinuclear catalysts supported with the pyridine bisphenolate catalysts. In contrast, the size of the olefin affects the level of incorporation differently between monometallic and bimetallic catalysts for the bisamine bisphenolate system. The ratio of the incorporation levels with dinuclear vs mononuclear catalysts decreases with increasing comonomer size. This effect is attributed to steric pressure provided by the distal metal center on the larger olefin in dinuclear catalysts.

Copolymerization of Ethylene and Long-Chain Functional α-Olefins by Dinuclear Zirconium Catalysts

“…Precatalysts 1 – 4 (Figure ) were prepared as previously described . These precatalysts were selected for the current study due to the relative ease by which the C 2 isomers of the bimetallic catalysts could be isolated on moderate scales.…”

“…Our previously reported dizirconium olefin polymerization catalysts represent suitable candidates for studies of early transition metals, addressing the differences in performance of bimetallic and monometallic precatalysts in polar comonomer copolymerization. , We have employed bimetallic versions of the zirconium bisamine bisphenolate catalysts based on a rigid teraryl framework ( G ) and showed that isotactically enriched poly­(α-olefins) are generated via a site epimerization mechanism . The dizirconium catalysts show enhanced activity relative to monozirconium controls, and a subsequent study demonstrated that such catalysts could also be employed for ethylene-α-olefin copolymerization . These results provide a substantial basis for comparison to probe the effect of the catalyst nuclearity on the copolymerization of ethylene and comonomers bearing functional groups such as alcohols.…”

Mono‐ and binuclear nickel catalysts for 1‐hexene polymerization

“…Sampson et al . also reported broader MWDs with multi‐modal distributions for all polymers obtained using bimetallic zirconium catalysts compared to those obtained by monometallic catalysts . It also can be suggested that the polymerization kinetics of bi‐ and multinuclear catalysts is complex and different from that of mononuclear catalysts.…”

“…This observation may for two reasons: first, the electronic effect of acenaphthene group on the backbone that leads to fewer chain transfer reactions; and second, the stronger synergistic effect resulted from chain walking . Also, the poly (1‐hexene) obtained in the presence of binuclear catalysts showed less chain branching than that obtained in the presence of mononuclear catalyst (MN).…”

“…There are some reports on the polymerization of 1‐hexene using various types of catalysts . In this regard, for example, the microstructure of poly(1‐hexene) obtained using α‐diimine nickel catalysts was investigated by Sivaram and co‐workers, and a polymer structure with methyl, butyl and long‐chain branches was demonstrated.…”