Beilstein J. Org. Chem.2016,12, 2673–2681, doi:10.3762/bjoc.12.264
adduct displays two different conformers in the unit cell which differ inter alia in the torsion angles around the Nimidazole–Cphenol bonds [−53.32(16)° vs 114.12(13)°] and the Cphenyl–O bonds [49.43(17)° vs −15.29(18)°] (Figure 2).
A gold complex of the N-heterocyclic carbenetautomer 6B can be obtained
(NHC)2][Cl] by coordination with the carbene carbon atom. The anionic N-heterocyclic carbene 1-(2-phenolate)imidazol-2-ylidene gives the complexes [K][Au(NHC−)2], [Rh(NHC−)3] and [Ni(NHC−)2], respectively. Results of four single crystal analyses are presented.
Keywords: anionic ligand; carbene
tautomer; imidazol-2-ylidene; mesoionic compound; mesomeric betaine; Introduction
Since the first isolation of a stable N-heterocyclic carbene (NHC) [1] in 1991 this compound class has provided numerous highly efficient ligands of NHC-metal catalysts for cross-coupling reactions [2][3][4][5][6][7
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Graphical Abstract
Figure 1:
Examples of anionic N-heterocyclic carbenes.
Beilstein J. Org. Chem.2015,11, 1732–1740, doi:10.3762/bjoc.11.189
. entries 3 and 5) stabilize carbenetautomer 3 slightly. Changing N-alkyl for N-aryl substituents in the imidazolium ring has a relatively small effect on the tautomeric ratio (Table 3, entries 1 and 3). At the same time, the solvent has a dramatic effect on the equilibrium position. In the gas phase
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Graphical Abstract
Scheme 1:
The formation and possible tautomeric equilibria of 2-methoxycarbonyl- and 2-carboxy-3-(1H-imidazol...