Nitrile ylide

Nitrile ylides also known as nitrilium ylides or nitrilium methylides, are generally reactive intermediates[1] formally consisting of a carbanion of an alkyl or similar group bonded to the nitrogen atom of a cyanide unit. With a few exceptions, they cannot be isolated. However, a structure has been determined on a particularly stable nitrile ylide by X-ray crystallography.[2] Another nitrile ylide has been captured under cryogenic conditions.[3]

As ylides, they possess a negative charge and a positive charge on adjacent atoms. However, they also have resonance, including 1,3-dipole contributing structures:

The most appropriate resonance structure is dependent upon the substituent pattern (the identity of the R and R′ groups). The 3-dimensional structure of the nitrilium ylide itself may also provide a clue as to the most appropriate resonance structure, with a linear R–C≡N–C unit supportive of the charge distribution indicated for resonance structures 1a & 1b and also consistent with the nomenclature nitrilium ylide. As resonance structures 1c and 1d become more important the nitrilium ylide distorts its geometry from linear in favor of a different valence tautomer 2 that is distinctly bent:

Nitrile ylides are isoelectronic with nitrile oxides:

  1. ^ Escolano, C.; Duque, M. D.; Vázquez, S. (2007). "Nitrile Ylides: Generation, Properties and Synthetic Applications". Current Organic Chemistry. 11 (9): 741–772. doi:10.2174/138527207780831710.
  2. ^ Janulis, Eugene P. Jr.; Wilson, Scott R.; Arduengo, Anthony J. III (1984). "The synthesis and structure of a stabilized nitrilium ylide". Tetrahedron Letters. 25 (4): 405–408. doi:10.1016/S0040-4039(00)99896-4.
  3. ^ Nunes, Cláudio M.; Reva, Igor; Fausto, Rui (2013). "Capture of an Elusive Nitrile Ylide as an Intermediate in Isoxazole-Oxazole Photoisomerization". J. Org. Chem. 78 (21): 10657–10665. doi:10.1021/jo4015672. PMID 24073594.
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