3 years ago

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

Isolation of Azadiphosphiridines and Diphosphenimines by Cycloaddition of Azides and a Cationic Diphosphene
Antonio Frontera, Antonio Bauzá, Kai Schwedtmann, Felix Hennersdorf, Roland Fischer, Jan J. Weigand
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. Cyclic versus acyclic: The reaction of a cationic diphosphene with RN3 (R=Dipp, Dmp) leads to the formation of three-membered P2N-heterocyclic azadiphosphiridines. This reaction proceeds by a 1,3-dipolar cycloaddition reaction, release of N2, and a ring-closing reaction. Contrariwise, when the diphosphene is reacted with either Me3SiN3 or NaN3 the formation of the unique diphosphenimine derivatives featuring an acyclic P2N moiety is observed. Dipp=2,6-diisopropylphenyl, Dmp=2,5-dimethylphenyl.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201702058

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