@article{KleinpeterKoch2018,
  author    = {Kleinpeter, Erich and Koch, Andreas},
  title     = {Stable Carbenes or Betaines?},
  series = {European journal of organic chemistry},
  volume    = {2018},
  journal   = {European journal of organic chemistry},
  number    = {24},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1434-193X},
  doi       = {10.1002/ejoc.201800462},
  pages     = {3114 -- 3121},
  year      = {2018},
  abstract  = {The anisotropy effect in H-1 NMR spectroscopy can be readily employed to indicate the position of carbene/betaine mesomeric equilibria. NR2 substituted carbene/betaines tend to adopt betaine structures, whereas in the absence of NR2 substituents, the betaine structures cannot stabilise the structure through both -donation effects of the NMe2 groups and the electronegativity of the nitrogen atoms, and the corresponding carbene-like structures are preferred. These conclusions are supported by calculated bond orders and (C-13)/ppm values. The spatial magnetic properties of isonitriles and carbon monoxide, which can be counted as stable carbenes or, at least, as carbene-analogues, also exist as stable betaine structures, which is again supported by structural and magnetic properties.},
  language  = {en}
}
@article{BaierKellingJackstelletal.2013,
  author    = {Baier, Heiko and Kelling, Alexandra and Jackstell, Ralf and Holdt, Hans-J{\"u}rgen},
  title     = {Rhodium(I) and Silver(I) Complexes of 4,5-Dicyano-1,3-dimesityl- and 4,5-Dicyano-1,3-dineopentylimidazol-2-ylidene},
  series = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie},
  volume    = {639},
  journal   = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie},
  number    = {10},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0044-2313},
  doi       = {10.1002/zaac.201300250},
  pages     = {1731 -- 1739},
  year      = {2013},
  abstract  = {The new N-heterocyclic carbene (NHC) precursors 4,5-dicyano-1, -dimesityl- (9) and 4, 5-dicyano-1, 3-dineopentyl-2-(pentafluorophenyl)imidazoline (14) were synthesized. 9 could be determined by X-ray crystallography. With the 2-pentafluorophenyl-substituted imidazolines 9 and 14, the [AgCl(NHC)], [RhCl(COD)(NHC)], and [RhCl(CO)(2)(NHC)] complexes [NHC = 4, 5-dicyano-1, 3-dimesitylimidazol-2-ylidene (3) and 4, 5-dicyano-1, 3-dineopentylimidazol-2-ylidene (4)] were obtained. Crystal structures of [AgCl(3)] (15), [RhCl(COD)(3)] (17), [RhCl(COD)(4)] (18), and [RhCl(CO)(2)(3)] (19) were solved and with the crystal data of 19, the percent buried volume (\%V-bur) of 31.8(+/- 0.1)\% was determined for NHC 3. Infrared spectra of the imidazolines 9 and 14 and of the complexes 15-20 were recorded and the CO stretching frequencies of complexes 19 and 20 were used to determine the 3 ( (-1)) and 4 ( (-1)), thus proving that 1, 3-substitution of maleonitrile-NHCs does not have a significant effect for the high -acceptor strength of these carbenes.},
  language  = {en}
}