Poly(ionic liquid)s based on imidazolium hydrogen carbonate monomer units as recyclable polymer-supported N -heterocyclic carbenes: Use in organocatalysis

Abstract

Synthesis of novel poly(ionic liquid)s, namely, poly(1‐vinyl‐3‐alkylimidazolium hydrogen carbonate)s, denoted as poly([NHC(H)][HCO3])s or PVRImHCO3, where R is an alkyl group (R = ethyl, butyl, phenylethyl, dodecyl), is described. Two distinct synthetic routes were explored. The first method is based on the free‐radical polymerization (FRP) of 1‐vinyl‐3‐alkylimidazolium monomers featuring a hydrogen carbonate counter anion (HCO3−), denoted as VRImHCO3. The latter monomers were readily synthesized by alkylation of 1‐vinylimidazole (VIm), followed by direct anion exchange of 1‐vinyl‐3‐alkylimidazolium bromide monomers (VRImBr), using potassium hydrogen carbonate (KHCO3) in methanol at room temperature. Alternatively, the same anion exchange method could be applied onto FRP‐derived poly(1‐vinyl‐3‐alkylimidazolium bromide) precursors (PVRImBr). All PVRImHCO3 salts proved air stable and could be manipulated without any particular precautions. They could serve as polymer‐supported precatalysts to generate polymer‐supported N‐heterocyclic carbenes, referred to as poly(NHC)s, formally by a loss of “H2CO3” (H2O +CO2) in solution. This was demonstrated through selected organocatalyzed reactions of molecular chemistry, known as being efficiently mediated by molecular NHC catalysts, including benzoin condensation, transesterification and cyanosilylation of aldehyde. Of particular interest, recycling of the polymer‐supported precatalysts was possible by re‐carboxylation of in situ generated poly(NHC)s. Organocatalyzed reactions could be performed with excellent yields, even after five catalytic cycles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4530–4540

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

“…They have been employed to catalyze different transesterification reactions, including also the conversion of brown grease into biodiesel [42–43]. Recycling tests of polymeric ionic liquids proved their robustness for prolonged use (Fig.…”

Structures and Synthesis of Zwitterionic Polymers

“…Similar considerations apply to the addition of CO 2 to polymeric amidines, or to polymeric carbenes obtained from imidazolium salts (Figure 17c,d) [441][442][443][444]. Although the last reaction seems to be limited to non-aqueous systems, in any case, such chemically induced "switching" systems have been hardly studied up to now, so that they cannot be adequately judged yet.…”

“…Hence, addressing the open merocyanine form as "zwitterionic" is misleading, as it typically shows a strong dipole moment only but does not dispose of ionic sites. [128,445]; (b) via bisulfite-aldehyde addition [425,446]; (c) and (d) via addition of CO 2 to amidines [441] or carbenes [442,443], respectively. Redox reactions offer better chances for implementing a switching process, though reversible organic redox systems, for which the oxidized as well as the reduced states are stable under aqueous conditions, are rare.…”

Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications

“…In all cases, pre-catalyst 39 exhibited higher catalytic activity than the corresponding monomeric analogue 38. Moreover, 39 showed higher catalytic activity and reusability in the benzoin condensation reaction compared to the polymerized pre-catalysts obtained from 1-vinylimidazolium [32,33]. The pre-catalyst 39 was recovered and reused without loss of performance over seven cycles.…”