TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Stable Carbenes or Betaines?
JF  - European journal of organic chemistry
N2  - 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.
KW  - Carbenes
KW  - Betaines
KW  - Mesomerism
KW  - Through-space NMR shieldings (TSNMRS)
KW  - NMR spectroscopy
KW  - Conformation analysis
Y1  - 2018
U6  - https://doi.org/10.1002/ejoc.201800462
SN  - 1434-193X
SN  - 1099-0690
VL  - 2018
IS  - 24
SP  - 3114
EP  - 3121
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Baier, Heiko
A1  - Kelling, Alexandra
A1  - Jackstell, Ralf
A1  - Holdt, Hans-Jürgen
T1  - Rhodium(I) and Silver(I) Complexes of 4,5-Dicyano-1,3-dimesityl- and 4,5-Dicyano-1,3-dineopentylimidazol-2-ylidene
JF  - Zeitschrift für anorganische und allgemeine Chemie
N2  - 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.
KW  - Carbenes
KW  - Rhodium
KW  - Silver
KW  - Crystal structure
KW  - Diaminomaleonitrile
Y1  - 2013
U6  - https://doi.org/10.1002/zaac.201300250
SN  - 0044-2313
SN  - 1521-3749
VL  - 639
IS  - 10
SP  - 1731
EP  - 1739
PB  - Wiley-VCH
CY  - Weinheim
ER  -