The reactions of methylenediphosphanes 1a-c with hexafluoroacetone (HFA) an
d hexafluorothioacetone dimer (HFTA) gave the respective carbodiphosphorane
s 5a, 5b, 6, 15, and 19. The carbodiphosphoranes 6 and 19, with phenyl grou
ps at phosphorus, were able to react further with C=O or C=S functions. Com
pound 6 added one equivalent of HFA across one of the ylidic P=C bonds to g
ive compound 9, a stable intermediate of the Wittig reaction. The addition
of HFTA to 19 gave, unexpectedly, the isomeric compound 21. The molecular s
tructures of 9, 15, and 21 were confirmed by X-ray investigations.