Isolation of Azadiphosphiridines and Diphosphenimines by Cycloaddition of Azides and a Cationic Diphosphene.

The polarized, cationic diphosphene [((Cl) Im(Dipp) )P=P(Dipp)](+) as the triflate salt 7[OTf]((Cl) Im(Dipp) =4,5-dichloro-1,3-bis(Dipp)-imidazol-2-yl; Dipp=2,6-diisopropylphenyl) reacts with azides of type RN3 (R=Dipp or Dmp; Dmp=2,5-dimethylphenyl) in a [2+3] cycloaddition reaction followed by the release of N2 and a subsequent electrocyclic ring-closing reaction to azadiphosphiridine salts [((Cl) Im(Dipp) )P-P(Dipp)-N(R)]10a,b[OTf] (R=Dipp or Dmp). The reaction of 7[X] (X=OTf, GaCl4 ) with the electron-rich azides Me3 SiN3 and NaN3 give the unusual diphosphenimine derivatives [((Cl) Im(Dipp) )P-P(Dipp)=N(SiMe3 )](+) (11[OTf]) and [((Cl) Im(Dipp) )P-P(Dipp)=N(GaCl3 )] (12), respectively, featuring an acyclic P2 N moiety. Theoretical calculations provide insights into the reaction mechanisms to the cyclic and acyclic forms, in which the thermodynamic stability of the latter prevents the electrocyclic ring closure.