On the Mechanism of the Reactivity of 1,3‐Dialkylimidazolium Salts under Basic to Acidic Conditions: A Combined Kinetic and Computational Study

Abstract

Comprehensive spectroscopic kinetic studies illustrate an alternative mechanism for the traditional free-carbene intermediated H/D exchange reaction of 1,3-dialkylimidazolium salts under neutral (D 2 O) and acidic conditions (DCl/ D 2 O3 5wt% solution). The deuteration of high purity [bmim]Cl in D 2 Oi ss tudied at different temperatures,i n absence of catalyst or impurities,toyield an activation energy. DFT transition-state modelling,o fasmall water cluster and [bmim] cation, also yields an activation energy which strongly supports the proposed mechanism. The presence of basic impurities are shown to significantly enhance the exchange reaction, which brings into question the need for further analysis of technical purities of ionic liquids and the implications for aw ide range of chemical reactions in such media.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Genuine carbene versus carbene‐like reactivity

“…This corroborates the absence of any observable carbene decomposition products such as 3 when heating 2 OAc under vacuum at 130 °C. In comparison, the presence of copper chloride enables an alternative reaction pathway wherein the acetate anion facilitates nucleation, followed by a CMD (concerted metalation deprotonation) or AMLA (ambiphilic metal ligand assistance) type mechanism, [22] which we found to be exothermic by 5.9 kcal/mol with an overall barrier of 17.2 kcal/mol [6b,c] . Altogether, in line with experimental findings regarding the thermal stability of 2 OAc and its reactivity with CuCl the more facile sans carbene pathway seems to be the operative mechanism.…”

Liquid Dynamics Determine Transition Metal‐N‐Heterocyclic Carbene Complex Formation

“…The multiple contradictions and discrepancies in the mechanistic picture on these reactions [33] were resolved through suggesting a direct, concerted mechanism, in which the deprotonation of the azolium salt and the formation of the substrate‐catalyst bond occur simultaneously, avoiding the formation of a free carbene in solution (Figure 2). [33–36] Analogous reaction mechanisms have been considered also for the biochemical reactions of thiamine, [36] the proton‐deuteron exchange of azolium salts, [37,38] and the formation of azolium‐2‐dithiocarboxylate zwitterions [39] …”