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

The polarized, cationic diphosphene [(ClImDipp)P=P(Dipp)]+ as the triflate salt 7[OTf](ClImDipp=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 [(ClImDipp)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 Me3SiN3 and NaN3 give the unusual diphosphenimine derivatives [(ClImDipp)P−P(Dipp)=N(SiMe3)]+ (11[OTf]) and [(ClImDipp)P−P(Dipp)=N(GaCl3)] (12), respectively, featuring an acyclic P2N 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.