(Phosphanyl)phosphaketenes as building blocks for novel phosphorus heterocycles.

Although BH3 simply coordinates the endocyclic P of (phospholidino)phosphaketene 1(Dipp) , the bulkier B(C6F5)3 gives rise to a zwitterionic diphosphirenium, which is a novel type of 2π-electron aromatic system as shown by the calculated NICS values. While the reaction of 1(Dipp) with Na[PCO(dioxane) x ] is unselective, the same reaction with the sterically bulky (phospholidino)phosphaketene 1(Ar**) [Ar** = 2,6-bis[di(4-tert-butylphenyl)methyl]-4-methylphenyl selectively affords a sodium bridged dimer containing a hitherto unknown λ(3),λ(5),λ(3)-triphosphete core. The latter formally results from "P(-)" addition to a 1,3-P/C-dipole. Similarly, adamantyl isonitrile adds to 1(Dipp) giving a 4-membered phosphacycle. In contrast to 1, the phosphaketene derived from the electrophilic diazaphospholidine-4,5-dione is unstable and reacts with a second molecule of Na[PCO(dioxane) x ] to afford a 1,3,4-oxadiphospholonide derivative.