Bifunctional Fluorophosphonium Triflates As Intramolecular Frustrated Lewis Pairs: Reversible Co2 Sequestration And Binding Of Carbonyls, Nitriles And Acetylenes

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 (7(2+)) 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.