Cyclopentadienylidenephosphinazines

Article abstract of DOI:10.1016/S0040-4020(01)97237-0

Diazocyclopentadienes which are not alkyl- or aryl-substituted at both the 2- and 5-positions react readily with triphenylphosphine to form cyclopentadienylidenephosphinazines. If both of these positions are so substituted phosphinazines are not formed. A phosphinazine was obtained from 2-chloro-3,4,5-triphenyldiazocyclopentadiene while its 2-nitro-analogue apparently formed a readily hydrolysed phosphinazine. Diazotetraphenylcyclopentadiene formed a phosphinazine with tri-n-butylphosphine. The reasons for these differences in reactivity are discussed. When heated to higher temperatures some of the phosphinazines decomposed with loss of nitrogen to give phosphonium cyclopentadienylides. Electron-withdrawing substituents in the five-membered ring make the phosphinazines susceptible to ready hydrolysis to cyclopentadienone hydrazones. Cyclopentadienylidenephosphinazines are protonated by mineral acids on nitrogen rather than on the cyclopentadiene ring.