The Core Difference between a Mesoionic and a Normal N-Heterocyclic Carbene

Abstract

The properties of the abnormal N -heterocyclic carbene (NHC) 1,4-dimesityl-3-methyl-1,2,3-triazolin-5-ylidene were comprehensively compared to those of the related normal carbene 1,3-dimesitylimidazolin-2-ylidene using a range of steric and electronic probe techniques (% V bur , steric maps, Tolman electronic parameter, alane, Huynh electronic parameter, selone, and p K a values). The two NHCs were determined to be sterically equivalent (isostructural), while the triazolin-5-ylidene was found to be a stronger σ-electron donor and a much weaker π-electron acceptor. These results were used to demonstrate that the electronic properties of these NHCs could affect the stereochemical outcome of an NHC-catalyzed reaction.

Counterintuitive Chemistry: Carbene Stabilization of Zero-Oxidation State Main Group Species

“… , By comparison to that of the CAAC-based silylone 14 (66.7 ppm in C 6 D 6 ), the 29 Si NMR resonances of 17 (−80.1 ppm in C 6 D 6 ) and 18 (−54.6 ppm, in the solid state) are obviously higher-field shifted, indicating the presence of more electron-rich silicon cores in NHC and mesoionic carbene-based silylones. This should be ascribed to the weaker π-electron accepting capabilities of NHCs and mesoionic carbenes than CAACs. , As a result, the electron-rich silylone cores of 17 and 18 favor the formation of the corresponding binuclear complexes.…”

“…This should be ascribed to the weaker πelectron accepting capabilities of NHCs and mesoionic carbenes than CAACs. 19,53 As a result, the electron-rich silylone cores of 17 and 18 favor the formation of the corresponding binuclear complexes. Imino-NHC 54 and diiminoNHC 55 ligands have also been utilized in accessing cyclic germylones.…”

Mesoionic carbene-based self-assembled monolayers on gold

“… 47 This higher activation temperature is presumably required due to the higher p K a of the MIC precursor. 48 Beyond 160 °C, volatilization of MIC iPr ·H 2 CO 3 occurs, but is slower than NHC iPr ·H 2 CO 3 and has a temperature profile that suggests decomposition accompanies this process (Fig. S1 † ).…”

Understanding Gold‐Alkyne Activation from Bond Dissociation Energies of Gold‐Alkyne Complexes

“…The electrostatic interaction is identical for MIC and IPr (Table 2, entre 15 and 16), whereas IPr is known to be less of a donor than MIC. [27] Due to the minimal variation observed in the EDA results, interpreting these findings in a rational manner proves to be quite challenging.…”