An Unusual Reaction of Hexafluoroacetone with Methylenediphosphanes: Facile Synthesis of Carbodiphosphoranes

Interaction of Some Methylenediphosphanes with Hexafluoroacetone and Hexafluorothioacetone Dimer

“…The carbodiphosphorane 6 is stable in solution at room temperature for several hours and quickly decomposes in the absence of the solvent. The decomposition of the molecule proceeds analogously to that of 5a or 5b, and gives methylene bis(difluorophosphorane) 7 [6] and methylenediphosphane oxide 8. It is interesting that the formation of the dioxide 8 is not accounted for by the hydrolysis of the bisdifluorophosphorane 7, as the reaction was carried out under anaerobic conditions.…”

“…The formation of the analogous dioxide was also observed for 5a and 5b. [6] Unlike compounds 5a and 5b, the carbodiphosphorane 6 is able to add one more equivalent of HFA across one of the ylidic PϭC bonds with the formation of the cyclic product 9, which is poorly soluble and crystallizes from the reaction mixture in good yield. It can be considered as a Wittig reaction intermediate, which are usually unstable at room temperature and cannot be isolated.…”

“…The two CF 3 groups connected to the four-membered ring are equivalent and display a common signal rather than the two quadruplets that we observed earlier for an analogous compound. [6] The equivalence of these CF 3 groups could be a result of the appropriate symmetry of the molecule: for example, if the plane of symmetry were to coincide with the four-membered cycle. However, the appearance of such symmetry in this molecule is very unlikely.…”

“…We have already tried to obtain phosphonium-substituted carbenes, however (17), C(2)ϪC(1)ϪP(2)ϪO(1) 3.97 (14) they were very unstable and we could isolate only the products of their decomposition. [6] We think that cleavage of the C(2)ϪO(1) bond [141.0(3) pm] is less preferable than that of the P(2)ϪO(1) bond, as in the latter case it would form the more stable zwitterionic structure 9a. The reversible cleavage of the PϪO bond of the intermediate oxaphosphetanes has also been postulated by other authors for the Wittig reaction mechanism.…”

“…It is well-known that the reaction of hexafluoroacetone (HFA) with phosphorus(III) derivatives can lead to the formation of 1,3,2-or 1,4,2-dioxaphospholanes. [1Ϫ4] Recently we found that the interaction of HFA with the methylenediphosphanes 1a and 1b proceeds in a different way to yield quantitatively the carbodiphosphoranes 5a and 5b, [5,6] but not the expected 1,3,2-dioxaphospholanes 2a and 2b (Scheme 1).…”