Strong Evidence for an Unprecedented Borderline Case of Dissociation and Cycloaddition in Open‐Shell 1,3‐Dipole Chemistry: Transient Nitrilium Phosphane‐Ylide Complex Radical Cations

The reaction of 3‐ferrocenyl‐substituted 2H‐azaphosphirene complexes1a–cin the presence of substoichiometric amounts of ferrocenium hexafluorophosphate yields 3,5‐diferrocenyl‐substituted 2H‐1,4,2‐diazaphosphole complexes3a–cand difluoro(organo)phosphane complexes4a–c. The reaction of1a,cand [FcH]PF6with cyanoferrocene yields3a,cin a straightforward way. The molecular structures of3a,cwere unambiguously identified by multinuclear NMR spectroscopic experiments, mass spectrometry, and single‐crystal X‐ray diffraction studies. DFT calculations on model complexes1d–mand3d–mreveal a close similarity of Mo and W complexes (vs. Cr) and a strong influence of the ferrocenyl substituent on the geometry, spin, and charge distribution of reactive intermediates and the reaction course. Strong support for the assumption of a dissociation–cycloaddition reaction sequence leading to3and thus a surprising “cannibalistic” reaction was obtained.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)