The insertion of sulfur and selenium into the 1,2-dihydrophosphete ring

Sulfur and selenium react with a 1,2-dihydrophosphete P-W(CO)₅ complex at ca. 120°C to give the corresponding 2,5-dihydro-1,2-thiaphosphole and 2,5-dihydro-1,2-selenaphosphole complexes, respectively. These products result from an insertion of S or Se into the P C sp³ bond of the four-membered ring.