Related Experiment Video
Updated: Jul 19, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Electron-deficient cyclopropenium cations as Lewis acids in FLP chemistry
Dipendu Mandal1,2, Zheng-Wang Qu3, Stefan Grimme3
1Institute of Drug Discovery Technology, Ningbo University, Ningbo 315211, Zhejiang, China.
Abstract:
Cyclopropenium cations incorporating electron deficient substituents are Lewis acidic despite the presence of π-electrons. The chloride and electron affinities are examined computationally and experimentally, respectively. These cations form classic Lewis acid-base adducts with PPh3, while sterically demanding phosphines yield frustrated Lewis pairs (FLPs) which participate in FLP additions. Depending on the basicity of the phosphine used, addition to alkynes or alkyne deprotonation is observed. In either case, new C-C bonds are formed, thus extending the utility of the concept of FLP chemistry to these delocalized π-cations.
Related Concept Videos
Aromatic Hydrocarbon Cations: Structural Overview
Removing one hydrogen from the intervening CH2 group...
Lewis Acids and Bases
Aromatic Hydrocarbon Anions: Structural Overview
Due to the absence of continuous...
Electrophiles
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...
Electrophilic Addition to Alkynes: Halogenation
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Cycloaddition Reactions: MO Requirements for Thermal Activation

