N-Heterocyclic Carbenes Supported on Vinylic Addition Polynorbornene: A Recyclable and Recoverable Organocatalyst

Abstract

A bromoalkyl functionalized vinylic addition polynorbornene has been used as an inert new scaffold to support imidazolium salts by straightforward nucleophilic substitution using different imidazoles ImR (R=Me, mesityl, 2,6-iPr2C6H3). These polymers, VA-PNB-(CH2)4ImRBr, are precursors of N-heterocyclic carbenes which are useful as heterogeneous organocatalysts. The polymeric carbenes have been tested in two model reactions: The synthesis of saturated esters from α,β-unsaturated aldehydes and the conjugate umpolung reaction of α,β-unsaturated aldehydes for the synthesis of γ-butyrolactones. The supported catalyst (R=mesityl) is fully recyclable and can be recovered as an imidazolium salt and stored for further use.