Study On The Mechanism Of CO₂ Activation Involving Hydrospirophosphorane And Fragmentation Pathways Of Related Products By ESI-MSⁿ

The pentacoordinate hydrospirophosphorane is an important kind of pentacoordinate phosphorane compounds.The specialty of hydrospirophosphorane is the P-H bond,which is very active to be the precursors for organic synthesis.CO₂ is one of the main components of the greenhouse effect and an inexhaustible C1 source in nature.How to fix CO₂ under more mild conditions is also a topic that scientists are committed to studying.In the process of studying the Atherton-todd-type reaction between pentacoordinate bisamino hydrospirophosphorane and amines,our group obtained the products of CO₂ insertion into P-N bond.Further studies have shown that bisamino hydrospirophosphorane react with alkyl halides under the atmosphere of CO₂,and the products of CO₂ insertion into P-C bond also can be obtained.However,at present,the mechanism of CO₂ activation reactions involving bisamino hydrospirophosphorane is not clear,so the study of such reaction mechanism is conducive to further understanding of CO₂ reactivity and using CO₂ to synthesize valuable compounds.Firstly,based on the reaction mechanism of Atherton-todd-type of bisamo hydrospirophosphorane with amines,the corresponding spirophosphorane that the CO₂ inserted into P-N bond was synthesized by the reaction of chlorinated spirophosphorane intermediate and carbamate under the atmosphere of N₂.The result verified the reaction mechanism was through carbamate anion formed from a secondary amine,which acted as a nucleophilic reagent to attack at the chlorinated spirophosphorane intermediate to yield the CO₂ insertion product.On the other hand,as for the reaction mechanism of bisamino hydrospirophosphorane with alkyl halides under the atmosphere of CO₂,the structure of the intermediates was predicted by the³¹P NMR tracking experiments and was further characterized by electrospray ionization multistage mass spectrometry?ESI-MSⁿ?.Meanwhile,the single crystal of an insertion product was obtained by investigating the reaction of hydrospirophosphorane and alkyl halides with higher steric resistance.The result of single crystal determined the change of phosphorus configuration in the reaction process.Then,the reaction mechanism was proposed that phosphoranides formed from deprotonation of hydrospirophosphorane firstly.Thephosphoranidesactivated CO₂ to produce the spirophosphorane formate anion intermediate,and then,the spirophosphorane formate anion as a nucleophilic reagent attacked at alkyl halides to yield the CO₂insertion product.In addition,the reaction was testified to proceed with retention of phosphorus configuration in the whole reaction process.The DFT theoretical calculation were further used to verifiy the reaction mechanism proposed.Furthermore,we studied the fragmentation pathways of the related pentacoordinate spirophosphorane products including P-O-C?O?-N or P-C?O?-O-C unit by ESI-MSⁿ.The fragmentation pathways of[M+Na]⁺ion were proposed separately for two series of compounds.The structural characteristics related neutral CO₂ loss during mass fragmentation were summarized.The results will be helpful for understanding of the gas-phase fragmentation and structure identification of pentacoordinate spirophosphorane analogues.Finally,the reactivity of N-H bond at the spiroring of different spirophosphoranes was explored by H/D exchange and NMR tracking experiments.The results demonstrated that the reactivity of N-H bond of spirophosphoranes was influenced by species of substituent at phosphorus atom,and the strong electron-withdrawing group at phosphorus resulted in more reactive N-H bond of spirophosphoranes.These results are beneficial to further understand and explore the characteristics of pentacoordinate spirophosphoranes.