Synthesis, structure, and reactivity of a stabilized phosphiranylium salt

Phosphiranes with a three-membered PC2 ring have unique electronic properties.[1] Although their ring strain is smaller than that in cyclopropanes, they are highly reactive and display remarkable chemistry, such as [2+1] cycloreversions to olefins and phosphinidenes [R P],[2] cationic ring-opening polymerization to poly(ethylenephosphine),[3] and special properties as ligands in transition-metal complexes for catalysis.[4] Positively charged species are even more reactive. Species such as A (phosphirenylium ion) or B (phosphiranylium ion), which may be viewed as p-complexes of P+ to alkynes or alkenes,[5] respectively (Scheme 1), have never been isolated.[6] A notable exception is the crystalline diphosphirenium ion C.