Methylenephosphinophosphoranes. Unusual Addition Reaction in Organophosphorus Chemistry

Intermediate 4 is unstable and rearranges into 5. Substitution of chlorine atoms in 5 by dialkylamino groups gives 8 and 9. 8 reacts with TEA to give phosphaalkene 10, which slowly dimerizes into 11. Methylenephosphinophosphorane 9 shows unusual properties. It adds isocyanates to two phosphorus atoms to give zwitterionic structural isomers 12a,b. The structure of 12a was resolved by X-ray analysis. 9 reacts with azides unexpectedly giving the zwitterionic product 13. Reaction of 9 with hexafluoroacetone is unusual and leads to the ylid 14a,b. According to the X-ray data it exists in zwitterionic form 14b and displays a new type of coordination at phosphorus atom. HFA can react in a similar way with other phosphines. For example, with 15 it gives the double ylid 16.