Isoselective Styrene Polymerization Catalyzed by ansa-Bis(indenyl) Allyl Rare Earth Complexes. Stereochemical and Mechanistic Aspects

详细信息    查看全文

• 作者：Liana Annunziata ; Anne-Sophie Rodrigues ; Evgeny Kirillov ; Yann Sarazin ; Jun Okuda ; Lionel Perrin ; Laurent Maron ; Jean-Franc抬ois Carpentier
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：May 10, 2011
• 年：2011
• 卷：44
• 期：9
• 页码：3312-3322
• 全文大小：1088K
• 年卷期：v.44,no.9(May 10, 2011)
• ISSN：1520-5835

文摘

Mechanistic features of the isoselective polymerization of styrene promoted by racemic allyl ansa-lanthanidocene complexes rac-{CMe₂(Ind)₂}Ln(allyl)(THF)_n (Ind =5-indenyl; allyl = C₃H₅, n = 1, Ln = Y (1), Nd (2); allyl =1,3-(SiMe₃)₂C₃H₃, n = 0, Ln = Y (3), Nd (4)), which act as unique single-component catalysts, have been investigated by experimental and theoretical methods. Combined ¹H NMR and MALDI鈭扵oF鈭扢S analyses conducted on low molecular weights isotactic polystyrene (iPS) produced by compounds 1 or 2 established the presence of allyl end-groups and therefore that polymerization is initiated by insertion of styrene into Ln鈭扖(allyl). ¹H, ²D, and ¹³C NMR analyses performed on H(D)-iPS-nBu polymers, selectively produced by coordinative chain transfer polymerization (CCTP) of styrene with the binary system 3/Mg(nBu)₂ (1:10), evidenced that the polymerization is highly regioselective and proceeds in a secondary insertion mode, both in the initiation and propagation steps. Microstructural analyses of the backbone of crude (unfractionated) polymers produced with 1鈭?b>4 evidenced a virtually perfect isoselective (mmmmmm > 0.99) polymerization up to 120 掳C. Stereoerrors observed in the ¹³C{¹H} NMR spectra of the iPS produced at 130 掳C with 1鈭?b>4 are consistent with an enantiomorphic site control operative during the polymerization. DFT computations of the first and second insertions of styrene in 3 confirmed the above features and the overall mechanistic scenario.