Stable heteroaromatic carbenes of the benzimidazole and 1,2,4-triazole series

Abstract

The review is focused on new data concerning the syntheses and selected properties of stable heteroaromatic monocarbenes of the benzimidazole and 1,2,4-triazole series, biscarbenes, anionocarbenes of the 1,2,4-triazole series, and cryptocarbenes. The syntheses of the precursors to these compounds are also described. Special attention is paid to C-H insertion reactions, X-ray structural data and spectral characteristics of the carbenes and their analogues.

Ag(I) N-Heterocyclic Carbene Complexes: Synthesis, Structure, and Application

“…Öfele and Wanzlick first pioneered the metalation of imidazol-2-ylidenes, better known as N-heterocyclic carbenes (NHCs), from imidazolium salts in 1968. , Lappert and co-workers followed this work with the investigation of N-heterocyclic carbene complexes synthesized from electron-rich olefins. , However, it was not until the isolation of the first free carbene by Arduengo, in 1991, that significant interest was given to the area . Since then the complexation chemistry of these new ligands has become a major area of research. − This new class of ligand has shown to equal, if not exceed, phosphines in their ability to bind to a variety of metals.…”

A new stable CNHC⁁CH⁁CNHCN-heterocyclic dicarbene ligand: its mono- and dinuclear Ir(i) and Ir(i)–Rh(i) complexes

“…In particular, C NHC CHC NHC or C NHC NC NHC dicarbene ligands have been isolated (II, III, IV and V, Scheme 1) and their reactivity, mostly in the case of C NHC NC NHC ligands, has been investigated towards organic reagents 20 and transition metals. 18,19,21 However, the dicarbene ligands containing a methylene spacer, C NHC ∧ CH ∧ C NHC and C NHC ∧ N ∧ C NHC , have not been isolated but generated 10 and/or used in situ for the preparation of Ag, 22-27 Au, 28 Cu, 29 Pd, 23-25,27,30-36 rare-earth, 37 Ir 38 and Rh 24 complexes, and remain less studied than the C NHC CHC NHC and C NHC NC NHC systems.…”

Halogen-containing heteroaromatic carbenes of the 1,2,4-triazole series and their transformations

“…For the synthesis of haloaromatic derivatives of 1,2,4-triazol-5ylidenes and their non-halogenated analogues, we used the method previously described by us, 6,32-38 including: (1) the preparation of 3,4-diaryl-1,2,4-triazoles 2c-k by recyclization of 2-aryl-1,3,4-oxadiazoles 1a,b with arylamines in o-dichlorobenzene in the presence of triuoroacetic acid; 39,40 (2) subsequent quaternization of triazoles 2c-k with tert-butyl iodide in acetic acid, and (3) deprotonation of the resulting salts 3c-k with potassium tert-butoxide in a mixture of toluene and isopropanol thus forming carbenes 4c-k (Scheme 3). Compounds 2a,b, 3a,b and 4a,b, described earlier, 33,38 are used in this work for discussion, calculations and transformations.…”