Generation and reactions of transient nitrilium phosphane ylide complexes

Thermal decomposition of a 2H-azaphosphirene tungsten complex in the presen ce of N-piperidino nitrile and various trapping reagents (different nitrile s, a ketone and an alkyne) yielded five-membered heterocycles, that are coo rdinated to pentacarbonyltungsten. These reactions are described as 1,3-dip olar cycloadditions of in situ generated nitrilium phosphane ylide complexe s with the pi-electron systems of the latter trapping reagents. The regiose lectivity of this 1,3-dipol system is directed by the substituent attached to the dicoordinated carbon atom e.g. with phenyl the regioselectivity of s uch intermediates is nitrile sulfides-like, whereas with the N-piperidino s ubstituent an Umpolung is achieved and it becomes nitrile ylides-like.