3 years ago

Reactivity of Bridged and Nonbridged Zirconocenes toward Biorenewable Itaconic Esters and Anhydride

Reactivity of Bridged and Nonbridged Zirconocenes toward Biorenewable Itaconic Esters and Anhydride
Eugene Y.-X. Chen, Fernando Vidal
This work investigates the reactivity of neutral and cationic complexes of both bridged ansa-zirconocenes, rac-[C2H4(Ind)2]ZrMe[OC(OiPr)═CMe2] (1) and rac-[C2H4(Ind)2]Zr+(THF)[OC(OiPr)═CMe2][MeB(C6F5)3] (1+), and nonbridged zirconocenes, Cp*(nPrCp)ZrMe[OC(OiPr)═CMe2] (13) and Cp*(nPrCp)Zr(THF)[OC(OiPr)═CMe2]+[MeB(C6F5)3] (13+), toward biorenewable itaconic dialkyl esters (itaconates) and anhydride (IA). Behaving similarly, both cationic complexes 1+ and 13+ react readily with itaconates to form cleanly single monomer addition products, eight-membered-ring metallacycles 2 and 15, respectively, and neutral enolate complexes 1 and 13 insert 1 equiv of IA to afford single-IA-addition products 5 and 17. Behaving differently, eight-membered-ring chelates 2 derived from the bridged metallocene framework undergo slow isomerization at room temperature via ligand exchange between the coordinated and uncoordinated ester groups to form thermodynamically favored seven-membered-ring chelates 4, while eight-membered chelates 15 derived from the sterically more crowded unbridged metallocene framework are stable at room temperature and do not undergo such isomerization. The above cationic complexes exhibit no reactivity toward further additions of itaconates. Replacing itaconates with more basic monomers such as N,N-dimethylacrylamide that can ring open the chelating resting intermediate, however, brings about effective and controlled polymerization by eight-membered Zr-itaconate metallacycles 2 and 15, but not seven-membered 4, producing either highly isotactic polymers (>99% mm, by 2) or polymers with narrow molecular weight distributions (Đ < 1.19, by 15). These results further highlight the ansa effects in the metallocene polymerization chemistry and the importance of the formation and ring opening of the eight-membered chelating intermediates involved in the metallocene-mediated conjugate-addition polymerization.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00358

DOI: 10.1021/acs.organomet.7b00358

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.