Betaine Adducts of N‐Heterocyclic Carbenes: Synthesis, Properties, and Reactivity

Abstract

N‐Heterocyclic carbenes (NHCs) form stable zwitterionicadducts with a range of heteroallenes, ketenes, and allenes. Although the first representatives of this class of inner salts were first investigated as far back as the 1960s, they have enjoyed a sustained interest from the chemical community over the years. Depending on the nature of their anionic moiety, NHC betaines display a very broad palette of reactivities and have found applications in various fields of organic synthesis and catalysis. In this Microreview, the synthesis, properties, and reactivity of NHC betaines are surveyed. The NHCs under consideration include ylidenes derived from imidazole, benzimidazole, imidazoline, thiazole, or triazole, and the heteroallenes investigated so far are carbon dioxide, carbon disulfide, isocyanates, isothiocyanates, and their selenium analogues. A historical background is provided for each type of adduct under consideration, but emphasis is placed mainly on developments that have appeared in the literature within the past few years. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Advances in the Knowledge of N-Heterocyclic Carbenes Properties. The Backing of the Electrochemical Investigation

“…Later, Louie and coworkers reported a different synthesis, carried out bubbling CO2 into an imidazolium salt and potassium tert-butoxide solution [52]. The various syntheses of NHC-CO2 adducts as well as their chemistry are discussed in both classical and more recent reviews [53][54][55].…”

Recent advances in neutral and anionic N-heterocyclic carbene – betaine interconversions. Synthesis, characterization, and applications

“…A detailed review on betaine adducts of N-heterocyclic carbenes was published in 2009. 66 This review cites 102 references and deals with carbon disulfide, carbon dioxide, isothiocyanate, isocyanate, carbon diselenide, carbodiimide, and prop-1-ene-1,1,3,3-tetracarboxylate adducts of N-heterocyclic carbenes 96 -107 (Scheme 26). All adducts belong to the class of PCCMB.…”

“…66. Some additional compounds have been published meanwhile, such as the adduct of 1,2,4-triazol-5-ylidene with phenylisocyanate, 67 several fluoroalkyl-substituted imidazolium-2-carbodithioates 68 and 2-thiocarboxylates.…”

Self-Assembly Fabrication of Hollow Mesoporous Silica@Co–Al Layered Double Hydroxide@Graphene and Application in Toxic Effluents Elimination

“…5 Imidazolium carboxylates have been shown to successfully catalyse reactions such as the coupling of epoxides and carbon dioxide to produce cyclic carbamates. 6 The more Lewis basic nature of imidazolium dithiocarboxylates has allowed them to be used successfully as catalysts for the cyanosilylation of aldehydes, 7 and in the Staudinger reaction to prepare β-lactams.…”