The investigation on the N H reactivity of pentacoordinate spirophosphoranes by H/D exchange and NMR experiments

Different pentacoordinate spirophosphoranes were investigated by H/D exchange and NMR tracking experiments. The H/D exchanged site of spirophosphoranes was confirmed to be the N H bond instead of the P H bond according to the integration of the signal changes in proton-decoupled, proton-coupled 31P NMR and 1H NMR tracking experiments. The reactivity of N H bond at the spiroring of spirophosphoranes was explored by the rate constant of H/D exchange of different spirophosphoranes. The results demonstrated that the reactivity of N H bond of spirophosphoranes was influenced by steric hindrance and the species of substituent at phosphorus atom, and the electronic effect of the substituent was the main effect factor on the reactivity of the N H bond. 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.