pK_a Scale for Cyclopropenium Ions with Applications in CO₂ Capture

Abstract

Molecular acid–base properties are core to understanding chemical systems and the prediction of reactivity. This axiom holds for cyclopropenium ions in terms of their broad use as (organo)­catalysts, ligands, redox-flow batteries, and applications in materials sciences. In view of this significant status, and with it, the critical importance of acidity, we disclose in this report the first comprehensive computational study of the pK a values of cyclopropenium ions employing a subset of 70 structurally diverse cyclopropenium derivatives, density functional computations, and Hammett linear free-energy relationships. Capitalizing upon these computed findings, and with an eye toward greenhouse gas trapping, we further document the timely use of a cyclopropenium–cyclopropenylidene coupled platform for CO2 capture and light-triggered release.

Organocatalysis Linked to Charge-Enhanced Acidity with Superelectrophilic Traits

“…Our long-standing history in working with cyclopropenium ions − and catalysis ,, prompted this development. Coupled to this was the prospect of synthesizing a structurally unprecedented cationic catalyst, bearing two highly strained aromatic ring systems, namely, a cyclopropenium and a squaramide, together with an electron-deficient aryl group.…”

Electron-deficient cyclopropenium cations as Lewis acids in FLP chemistry

“…17 In addition, Dudding and co-workers have also examined the pKa of disubstituted cyclopropenium cations in the capture of CO 2 . 18 Applications as components of fluorophores have also garnered attention 19,20 as have derivatization for the generation of ionic liquids 21 and as components in redox-flow batteries. [22][23][24] Electron deficient analogues are much less studied.…”