Poly(N-heterocyclic-carbene)s and their CO2 Adducts as Recyclable Polymer-Supported Organocatalysts for Benzoin Condensation and Transesterification Reactions

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• 作者：Julien Pinaud ; Joan Vignolle ; Yves Gnanou ; Daniel Taton
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：April 12, 2011
• 年：2011
• 卷：44
• 期：7
• 页码：1900-1908
• 全文大小：917K
• 年卷期：v.44,no.7(April 12, 2011)
• ISSN：1520-5835

文摘

The synthesis of poly(N-heterocyclic carbene)s, denoted poly(NHC)s, and of their poly(NHC鈭扖O₂) adducts for a use in organocatalysis is described. Poly(NHC)s were readily obtained in a three-step sequence of reactions, involving i) the free-radical polymerization of ionic liquid monomers, that is, 1-vinyl-3-alkylimidazolium-type monomers with bromide (Br^{鈭?/sup>) as counteranion, followed by ii) anion exchange of Br鈭?/sup> for bis(trifluoromethanesulfonyl)imide (鈭?/sup>NTf₂), of the poly(1-vinyl-3-alkylimidazolium bromide) precursors, affording poly(1-vinyl-3-alkylimidazolium bis(trifluoromethanesulfonyl)imide) derivatives, and iii) deprotonation of the latter polymeric ionic liquids with a strong base. Carbon dioxide (CO₂) was found to reversibly react with poly(NHC)s forming relatively air-stable and thermolabile poly(NHC鈭扖O₂) adducts. Both poly(NHC)s and their poly(NHC鈭扖O₂) adducts were used as polymer-supported organic catalysts and precatalysts, respectively, in transesterification and benzoin condensation reactions under homogeneous conditions. Both types of polymer-supported NHCs were recycled and used several times, but the manipulation of poly(NHC)s 鈭抣ike their molecular NHC analogues- was more complicated owing to their air and moisture sensitivity. In this regard, zwitterionic poly(NHC鈭扖O₂) adducts like their molecular NHC鈭扖O₂ analogues could be easier manipulated than their bare poly(NHC) counterparts, providing good to excellent yields even after several organocatalytic cycles, in particular toward the transesterification reaction.}