Recent progress of N-heterocyclic carbenes in heterogeneous catalysis

Abstract

The aim of this tutorial review is to highlight the potential application of N-heterocyclic carbenes (NHC) in heterogeneous catalysis. The unique combination of the high reactivity of NHCs together with the ease of separation, purification and recyclability of the solid catalyst makes the heterogeneous system one of the most promising strategies for the synthesis of fine chemicals on an industrial scale. This tutorial review focuses on the most representative examples of this nascent research area and highlights recent achievements of NHCs in heterogeneous catalysis (other than metathesis reactions).We hope this serves as inspiration for further progress in this field.

Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N-Heterocyclic Carbene Polymers

“…As useful ligands in organometallic chemistry and catalysis, N -heterocyclic carbene (NHC) complexes have attracted considerable attention due to their unique sigma donor properties and remarkable similarity to electron-rich phosphine ligands123. To improve recyclability of such NHC complexes, great efforts have been devoted to develop heterogeneous NHC organometallic catalytic systems34567.…”

“…To improve recyclability of such NHC complexes, great efforts have been devoted to develop heterogeneous NHC organometallic catalytic systems34567. Imidazolium-based ionic salts are well known to be excellent precursors of metal NHCs, and various solid supports containing imidazolium groups have been used as precursors of heterogeneous palladium NHCs3456.…”

“…To improve recyclability of such NHC complexes, great efforts have been devoted to develop heterogeneous NHC organometallic catalytic systems34567. Imidazolium-based ionic salts are well known to be excellent precursors of metal NHCs, and various solid supports containing imidazolium groups have been used as precursors of heterogeneous palladium NHCs3456. In the context, di- or poly-cationic imidazolium salts were well known to possess superior performances over monocationic analogues, but heterogeneous catalytic systems consisting of stable chelating palladium NHC units were seldom explored34, despite the discrete chelating palladium NHC complexes were frequently investigated in catalysis2.…”

“…Imidazolium-based ionic salts are well known to be excellent precursors of metal NHCs, and various solid supports containing imidazolium groups have been used as precursors of heterogeneous palladium NHCs3456. In the context, di- or poly-cationic imidazolium salts were well known to possess superior performances over monocationic analogues, but heterogeneous catalytic systems consisting of stable chelating palladium NHC units were seldom explored34, despite the discrete chelating palladium NHC complexes were frequently investigated in catalysis2. Very recently, a series of metal-organic frameworks (MOFs) containing methylene-bridged bis-imidazolium groups were reported8, but the relative instability of these MOFs against moisture, acid or base have restricted the scope of catalytic applications.…”

Adamantylated trisimidazolium-based tritopic guests and their binding properties towards cucurbit[7]uril and β-cyclodextrin

“…Cationic moieties are frequently based on alkylammonium, pyridinium or imidazolium salts. However, imidazolium salts have some additional advantages as they display catalytic activity [43][44][45][46][47] and an ability to be transformed into N-heterocyclic carbenes to coordinate metals [48][49][50][51][52][53].…”