Electronic Structure and Evolution of a Terminal Butadienylphosphinidene Complex

The DFT study of the 1-butadienylphosphinidene complex [CH₂CHCHCHP−Cr(CO)₅] shows a delocalized structure with a short P−C bond at 1.789 Å and a long C_αC_β double bond at 1.367 Å. The W(CO)₅ complex has been synthesized by copper-catalyzed decomposition of the appropriate 7-phosphanorbornadiene complex. It gives the normal reaction products with alkynes (phosphirenes) and with conjugated dienes (phospholenes and dihydrophosphepines via a phospha-Cope rearrangement), but when no trapping reagent is added to the reaction mixture, it gives a complex pentacyclic product whose structure has been established by X-ray crystal structure analysis and whose formation involves a cascade of reactions starting at the dienyl substituent of the precursor.