Ricerc@Sapienza

N‐heterocyclic carbenes (NHCs) are key intermediates in a variety of chemical reactions. Owing to their transient nature, the interception and characterization of these reactive species have always been challenging. Similarly, the study of reaction mechanisms in which carbenes act as catalysts is still an active research field. This Minireview describes the contribution of electrospray ionization mass spectrometry (ESI‐MS) to the detection of charge‐tagged NHCs resulting from the insertion of an ionic group into the molecular scaffold.

In the last twenty years, N-heterocyclic carbenes (NHCs) have been extensively studied for their application as organocatalysts in stereoselective synthesis as well as ligands for transition metals-promoted synthetic methodologies. Derived mainly from azolium salts, NHCs have demonstrated exceptional versatility in their generation usually performed by deprotonation or reduction (chemical or electrochemical).

Safer electrolytes for ambient temperature sodium batteries were prepared by blending the N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, PYR 14 TFSI, ionic liquid with the sodium bis(trifluoromethylsulfonyl)imide, NaTFSI, salt. The physicochemical as well as the electrochemical properties of the PYR 14 TFSI-NaTFSI binary electrolyte system were investigated as a function of the temperature and sodium salt mole fraction, and compared with those of organic electrolytes of interest for sodium batteries.

The unambiguous quantification of the proton transfer in Protic Ionic Liquids (PILs) and its differentiation from the concept of ionicity are still unsolved questions. Albeit researchers awfully quickly treat them as synonyms, the two concepts are intrinsically different and imply a dramatic modification in the expected chemical and physical properties of a PIL. Some attempts have been made to shed light on this discrimination, but single-technique-based approaches fail in giving a clear answer.

Ionic liquids (ILs) are considered in the majority of cases green solvents, due to their virtually null vapor pressure and to the easiness in recycling them. In particular, imidazolium ILs are widely used in many fields of Chemistry, as solvents or precursors of N-heterocyclic carbenes (NHCs). The latter are easily obtained by deprotonation of the C2-H, usually using strong bases or cathodic reduction. Nevertheless, it is known that weaker bases (e.g., triethylamine) are able to promote C2-H/D exchange.

The benzoin condensation starting from benzaldehyde and the subsequent benzoin amidation to benzamide can be efficiently carried out under very mild conditions in an electrolysis cell. Among the advantages of using electrochemistry to generate our active reagents, the use of the easily dosed and non pollutant electron, instead of stoichiometric amounts of redox reagents or bases, usually renders the electrochemical methodology “greener” than classical organic reactions. Benzoin is obtained in good yield (85 %) carrying out the reaction in the room temperature ionic liquid BMIm-BF4.

N-Heterocyclic olefin (NHO) can be generated by simple
cathodic reduction of BDMImBF
4
-DMF solution or neat
BDMImBF
4
(BDMImBF
4
=
1-butyl-2,3-dimethyl-1
H
-imidazolium
tetrafluoroborate; DMF
=
dimethylformamide). In the latter case,
the use of any organic solvent and chemical base is avoided. To
prove the presence of NHO, its adduct with benzaldehyde was
isolated. The electrochemical behavior of NHO is very similar to

The growing number of applications of ionic liquids (ILs) in industry have brought attention to the green credentials of synthesis, as well as their cytotoxicities and ecotoxicities both for their use and accidental leakage into the environment. With the abovementioned properties in mind, we designed a class of ILs with either cations bearing a gluconamide motif and aliphatic side chains or the anion incorporating a gluconic acid (derived from food waste) moiety.

We have recently shown that some protic ionic liquids (PILs) are characterized by an unexpected complex dynamic of proton transfer (M. Campetella et al., Phys. Chem. Chem. Phys. 19, 11,869, (2017)). These liquids are based on a combination of cholinium cations and amino acid (AA) deprotonated anions. The side chain proton migration, can take place both within the same anion and between different anions. The intra-molecular proton transfer leads to a tautomerization of the AA anion that gives rise to the appearance of an anionic zwitterionic form.

An analysis of the complex proton transfer processes in certain protic ionic liquids, based on amino acid anions, has been carried out through ab initio molecular dynamics in the view of finding naturally conductive and pure mediums. The systems analyzed here might serve as chemical prototypes for pure and dry ionic liquids where mobile protons can act as fast charge carriers. We have exploited the natural tendency of these liquids to form a complex network of hydrogen bonds.