“Fiddler crab-type” imidazolium salt as remote substituents tuning organocatalyst for the cycloaddition of epoxides with carbon dioxide

Assessing the pKa‐Dependent Activity of Hydroxyl Hydrogen Bond Donors in the Organocatalyzed Cycloaddition of Carbon Dioxide to Epoxides: Experimental and Theoretical Study

“…A similar result was previously observed when exploring the difference of activity between 3 and ascorbic acid. [30] As discussed above, a possible explanation for their lower observed catalytic activity compared to 4, 5 and phenol, despite the lower calculated energy barriers, could be protonation of the alkoxide intermediate produced in step I by the acidic conjugated enediolic proton. Remarkably, the lowest upper reaction barriers overall were calculated for ascorbic acid and its derivative 3 ( Table 2, Entries 1, 2).…”

“…[35] Interestingly, the cycloaddition of CO 2 to epoxides and the MBH reaction are both catalysed by binary systems composed of a nucleophile and a HBD and involve zwitterionic intermediates (Scheme 1). [30] Based on these factors, the bell-shaped curve in Figure 1 could be tentatively explained as a trade-off between "strong enough" H-bonds (required for the activation of the epoxide), and the undesired protonation, or too strong coordination, of key zwitterionic reaction intermediates occurring for the most acidic HBDs. [36] Similarly, the use of excessively acidic HBDs, could lead to the protonation of the reaction intermediates formed in the mechanistic steps of the cycloaddition of CO 2 to epoxides.…”

“…[23] However, the authors did not attempt to correlate the physico-chemical properties of the HBDs to the observed trend of catalytic activity. [30] In this work, we initially studied the catalytic activity of several, structurally diverse, readily available HBDs for the cycloaddition of CO 2 to epichlorohydrin under ambient conditions (r.t., 1 bar CO 2 ) and we analysed the dependency of the observed performance on the Brønsted acidity of the HBDs and on the number of hydroxyls in the scaffold. [19a] Pyrogallol was found as the most efficient HBD.…”

Imidazolium‐Functionalized Ionic Hypercrosslinked Porous Polymers for Efficient Synthesis of Cyclic Carbonates from Simulated Flue Gas

“…As a result, a great number of IL‐derived materials have been established as adsorbents and catalysts for CO 2 capture and fixation . Specifically, N‐heterocyclic ILs comprising an efficient nucleophile and Lewis base have been shown to be unique, effective species in this field . The aim to facilitate the recycling of ILs drives the construction of IL‐based porous solid materials, encouraging the emergence of various porous ionic polymers with the framework repeating units resembling the structure of classical ILs .…”

Hydrogen bond donors promoted organocatalyzedcycloaddition of CO<sub>2</sub> with epoxides

“…Azaphosphatranes-based organocatalysts [78] 图 14 (网络版彩色)咪唑盐C−H键酸性调控的有机催化剂 [14,80] Figure 14 (Color online) Acidity of C−H bond on imidazolium salt tuned organocatalyst [14,80] 素的研究发现, 氢键给体上氢原子酸性对催化剂活性…”