Isolation of a phosphinidene sulfide and selenide

We describe the synthesis of an isolable phosphinidene sulfide and phosphinidene selenide (BnArNP[double bond, length as m-dash]Ch; Ch = S, Se) by reaction of a sterically protected phosphinidene oxide (BnArNP[double bond, length as m-dash]O) with Lawesson's or Woollins' reagents, respectively. These compounds reveal short P[double bond, length as m-dash]E bonds consistent with a high degree of p_π-p_π double bond character. The pendant amido group on the phosphorus atom plays an important role in their stabilization through nitrogen lone pair donation into the P-Ch π* orbital, and evidence for isomerism about the N-P bond was observed for both species. Dimeric intermediates featuring mixed phosphorus(iii)/phosphorus(v) centers could be isolated and structurally authenticated during the course of these studies providing some insight into the mechanism of formation of the titular compounds.