(Phosphanyl)phosphaketenes as building blocks for novel phosphorus heterocycles

Abstract

Although BH₃ simply coordinates the endocyclic P of (phospholidino)phosphaketene <b>1^Dipp</b> , 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 <b>1^Dipp</b> with Na[PCO(dioxane) _<i>x</i> ] is unselective, the same reaction with the sterically bulky (phospholidino)phosphaketene <b>1^Ar**</b> [Ar** = 2,6-bis[di(4-<i>tert</i>-butylphenyl)methyl]-4-methylphenyl selectively affords a sodium bridged dimer containing a hitherto unknown λ³,λ⁵,λ³-triphosphete core. The latter formally results from "P^-" addition to a 1,3-P/C-dipole. Similarly, adamantyl isonitrile adds to <b>1^Dipp</b> giving a 4-membered phosphacycle. In contrast to <b>1</b>, the phosphaketene derived from the electrophilic diazaphospholidine-4,5-dione is unstable and reacts with a second molecule of Na[PCO(dioxane) _<i>x</i> ] to afford a 1,3,4-oxadiphospholonide derivative.