From Imidazole toward Imidazolium Salts and N-Heterocyclic Carbene Ligands: Electronic and Geometrical Redistribution

Abstract

Investigations dealing with N-heterocyclic carbenes and their derivatives are usually centered on the influence that they exert by acting as catalysts, ionic liquids, or metallodrugs and consequently on their capabilities to tune the properties and reactivity of these systems. In this context, we aimed to focus on the internal molecular changes undergone by imidazole derivatives, from electronic and geometrical points of view. This work represents an empirical evidence of the molecular modifications that an imidazole skeleton undergoes upon protonation, alkylation, and metalation.

Synthesis and Characterization of Ag(I) Complexes Derived from New N-Heterocyclic Carbenes

“…Similarly, the chemical shifts related to benzene ring carbon atoms appeared at 123.69, 128.79, 133.54 and 134.64 ppm. 1 H NMR spectra of silver(I) complexes (5 and 6) confirmed the disappearance of (NCHN) signals, which was appeared in the spectra of two imidazolium salts at 10.9 and 9.7 ppm, respectively, as a result of generation of carbene (NCN) upon coordination with silver ion. The signals of imidazole ring for complex 5 were shifted from 8.4 and 8.27 ppm to 7.3 and 7.2 ppm due to the resonance loss of imidazole which resulted in the formation of complex 5.…”

“…The spectrum also revealed two signals with integration of 2H and 3H assigned, respectively to (CH2) and (CH3) of para-substituted ethyl group. 1 H NMR spectrum of precursor 2 in DMSO-d6 showed a singlet signal at (1.9, 6H) ppm, related to two methyl groups. The signals of imidazole ring were also noticed at (7.1 ppm, 2H) and (7.7 ppm, 1H).…”

“…Imidazolium salts have great attention as a precursor of N-heterocyclic carbene compounds due to its easy synthesis, where several methodologies have been achieved for its preparation [1][2][3][4][5][6][7]. By modifying the substituents on N-atoms of imidazole compound,variety of imidazole salts can be obtained and used to prepare many transition metals complexes type N-heterocyclic carbene complexes (NHCs) under appropriate conditions [8][9][10][11].…”

Coinage metal complexes of N‐heterocyclic carbene bearing nitrile functionalization: Synthesis and photophysical properties

“…In the 13 C NMR spectra, the most characteristic chemical shifts are observed in the range ca 142.3–142.6 ppm, attributed to pre‐carbenic carbon (N C HN) . The chemical shifts are also observed in the range ca 113–132 ppm that are attributed to the benzimidazolium ring carbon.…”

N-Heterocyclic Carbenes: A Powerful Catalyst for Polymerization

“…Besides, their distinctive coordination chemistry, N-heterocyclic carbenes have other advantages one of them is they can be easily be modulated bearing in mind the large library of heterocyclic chemistry as shown in Figure 4. However, several methods of preparation can be categorized in imidazolium deprotonation, imidazole-thione reduction, and NHCs-adducts thermolysis [12][13][14][15][16].…”