Bifunctional Fluorophosphonium Triflates as Intramolecular Frustrated Lewis Pairs: Reversible CO₂ Sequestration and Binding of Carbonyls, Nitriles and Acetylenes

Abstract

Electrophilic fluorophosphonium triflates bearing pyridyl (3[OTf]) or imidazolyl (4[OTf])‐substituents act as intramolecular frustrated Lewis pairs (FLPs) and reversibly form 1 : 1 adducts with CO2 (5+ and 6+). An unusual and labile spirocyclic tetrahedral intermediate (72+) is observed in CO2‐pressurized (0.5–2.0 bar) solutions of cation 4+ at low temperatures, as demonstrated by variable‐temperature NMR studies, which were confirmed crystallographically. In addition, cations 3+ and 4+ actively bind carbonyls, nitriles and acetylenes by 1,3‐dipolar cycloaddition, as shown by selected examples.

Frustrated Lewis pair chemistry of alkynes

“…98,99 A related example is the reaction of phosphabenzene with H 2 , 100 which proceeds via an FLP-type activation in which the phosphorus centre acts as the Lewis acid and the para -carbon as the nucleophile. Applying P( v ) Lewis acids in reactions with alkynes, Weigand and coworkers 101 exploited fluorophosphonium cations as Lewis acids. By incorporating pyridyl or other N-donor substituents, the resulting cations functioned as intramolecular FLPs reacting with alkynes to give novel N/P heterocycles (Scheme 36).…”