On the reactivity and stability of electrogenerated N-heterocyclic carbene in parent 1-butyl-3-methyl-1H-imidazolium tetrafluoroborate: Formation and use of N-heterocyclic carbene-CO2 adduct as latent catalyst

The electrochemical reduction of CO2 on a copper electrode in 1-n -butyl-3-methyl imidazolium tetrafluoroborate (BMI.BF4 ) monitored by surface-enhanced Raman scattering (SERS)

“…One of the probable reduction products is the BMI carbene, because the anodic wave observed at approximately −0.3 V is associated with the oxidation of the carbene formed during the BMI + reduction . According to Wu et al and Feroci et al , the BMI carbene reacts with CO 2 to form the BMI‐CO 2 carboxylate adduct. Therefore, it is expected that this kind of adduct is formed during the reduction of CO 2 in BMI.BF 4 .…”

NMR Study of the Reductive Decomposition of [BMIm][NTf2] at Gold Electrodes and Indirect Electrochemical Conversion of CO2

“…Besides the formation of radical 2,i tw as inferred that electron transfer to ad ialkylimidazolium cation may also induce dealkylation, yielding af ree alkyl radicala nd the mono-alkylimidazole 7. [42] It mustb es tressed that the electrosynthesis of carbenes was highlighted only through their trapping with an additional reagent such as sulfur, [36] water, [43] oxygen [44] and especially CO 2 [45][46][47][48] or by comparison with the electrochemical behaviour of carbenes formed chemically. [34][35][36][37][38][39][40][41] The formation of the tetraazafulvalene dimer 8 by recombination of two carbenes was reported.…”

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

“…In fact, recently many groups reported the use of NHC-CO 2 adducts as source of NHCs in organic synthesis [76,77] and references therein. The lower stability of electrogenerated NHCs than electrogenerated NHC-CO 2 adducts (both in the parent imidazolium salt as solvent) was proved according to a voltammetric investigation [30]. As a consequence, the lower catalytic efficiency of free NHC than NHC-CO 2 latent catalyst was ascertained using the benzoin condensation and the oxidative esterification of cinnamaldehyde with benzyl alcohol as test reactions.…”

“…More recently, the voltammetric behavior of neat azolium salts (imidazolium-, triazolium-, and thiazolium-based) or of their solutions (N,N-dimethylformamide (DMF), and MeCN as solvents) was reconsidered [28][29][30][31][32]. The NHCH + reduction and NHC oxidation potentials are obviously dependent on structure of the azolium cation, of the counter-ion, the presence and the nature of the solvent, and the electrode material ( Figure 5).…”

“…In this contest, the use of "latent catalysts", i.e., stable structures able-suitably triggered-to release catalysts, could be a solution [75]. As NHC-CO 2 adducts, triggered by heating (120 • C) or US irradiation, are able to release free NHC [30], these structures may be regarded as latent catalysts. In fact, recently many groups reported the use of NHC-CO 2 adducts as source of NHCs in organic synthesis [76,77] and references therein.…”