Studies On The Reaction Of CO₂ Insertion Into P-C Bond Catalyzed By Bisamino Hydrospirophosphoranes As Frustrated Lewis Pairs

Frustrated Lewis pairs（FLPs）,namely the combination of a Lewis acid and a Lewis base that cannot fulfil their natural propensity to form stable Lewis adducts,have been recently exploited to activate small molecules。Since 2006,FLPs have been successfully used as a new metal-free catalyst for the activation of H₂ by the Stephan group.After a decade of research,FLPs have shown bright prospects for the activation of small molecules such as CO₂,alkenes and alkynes.Then,one of the devolopment direction of FLPs is to expand the types of FLPs by main group elements.Bisamino hydrospirophosphorane is a kind of unique pentacoordinated phosphorus compounds.The phosphorus atom of hydrospirophosphoranes has both an electron-accepting LOMO empty orbit and a HOMO orbital whicn can offer electron pair.In this paper,with an intelligent use of bisamino hydrospirophosphorane as Lewis base and alkyl halides as Lewis acid,we studied the reaction to activate CO₂.The mechanism of the activation of CO₂ by bisamino hydrospirophosphorane as FLPs was also investigated.Furthermore,we have unexpectedly discovered the reaction of the N-H site of hydrospirophosphoranes.Firstly,we synthesized different types of bisamino hydrospirophosphoranes.Then,the phosphoranide with lone pair of electronic successfully activated CO₂ by combination of carbocations of alkyl halide.After the reaction conditions optimization,17 novel CO₂ insertion P-C bond compounds were synthesized.All compounds were characterized by IR,NMR and HRMS.Secondly,the activation mechanism of CO₂ by bisamino hydrospirophosphorane was studied.Density functional theory calculations and the experimental results show that the intermolecular FLPs is formed to activate CO₂ between chlorophosphonane intermediate acts as Lewis acid and secondary amine acts as Lewis base in the reaction of hydrospirophosphoranes with secondary amine.On the other hand,for the reaction of hydrospirophosphoranes with alkyl halide to activate CO₂,the essence is bisamino hydrospirophosphorane anion as Lewis base and alkyl carbonate as Lewis acid.They also constitute the intermolecular FLPs to activate CO₂.Finally,we investigated the reaction of N-H site of hydrospirophosphoranes and explored the applicability.Four novel bisamino hydrospirophosphorane derivatives were synthesized and the absolute configuration of the compounds was determined according to the single crystal structure.The reaction mechanism with the N-H site is studied,and its essence is an electrophilic substitution reaction carried out in two steps,with the product of CO₂ insertion of the P-C bond as the intermediate.In this paper,we successfully activated CO₂ by bisamino hydrospirophosphorane and alkyl halide for the first time.Combined with theoretical calculations and validation experiments,we studied the mechanism of the activation of CO₂ by bisamino hydrospirophosphorane with secondary amine or bisamino hydrospirophosphorane with alkyl halide,the reaction mechanism of CO₂ catalyzed by pentacoordinated phosphoranes as FLPs was proposed.In this study,the bisamino hydrospirophosphorane was first extended to the field of FLPs.It not only studies the reaction activity of pentacoordinated bisamino hydrospirophosphorane in depth,but also provides more choices for further develops new of FLPs which based on the pentacoordinated phosphoranes compounds.