Diphosphiranes - Formation And Ionic Ring-Opening, A Theoretical Approach

The process of addition of methylene to diphosphene was studied theoretically using ab initio theory (SCF + CI level). Two possible mechanisms (addition to the pi-system and addition to the lone pair of phosphorus) were analyzed. The preferential process corresponds to a pi-addition leading to the diphosphirane ring. The cationic and anionic ring opening processes of the diphosphirane have been investigated at the same level of theory (ab initio SCF + CI). The results were analyzed by comparison with those of cyclopropane and in terms of the Woodward-Hoffmann rules. For the cations, the cleavage of the P-P bond (disrotatory motion) leads directly to an exo-endo open-chain structure. In the case of the anions, in contrast, a cyclic intermediate was located, which leads to an exo-exo open-chain species in a conrotatory ring opening.