From betaines to anionic N-heterocyclic carbenes. Borane, gold, rhodium, and nickel complexes starting from an imidazoliumphenolate and its carbene tautomer

• Ming Liu,
• Jan C. Namyslo,
• Martin Nieger,
• Mika Polamo and
• Andreas Schmidt

Beilstein J. Org. Chem. 2016, 12, 2673–2681, doi:10.3762/bjoc.12.264

• .12.264 Abstract The mesomeric betaine imidazolium-1-ylphenolate forms a borane adduct with tris(pentafluorophenyl)borane by coordination with the phenolate oxygen, whereas its NHC tautomer 1-(2-phenol)imidazol-2-ylidene reacts with (triphenylphosphine)gold(I) chloride to give the cationic NHC complex [Au

• 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

• been prepared from mesoionic compounds (Figure 1). The carbenes 3 [31] and 4 [32][33] originate from a conjugated ylide and a cross-conjugated mesomeric betaine, respectively. A review elucidates the interconversions of mesomeric betaines to different types of N-heterocyclic carbenes (NHC, aNHC, rNHC

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• . Keywords: E/Z isomerism; indazol-3-ylidene; mesomeric betaine; pyrazole; quinazoline; Rh complex; Introduction As a result of their biochemical and pharmacological significance, there has been a considerably growing interest in indazoles in recent years, which is reflected in several book chapters and

• ). The mechanism can be rationalized by formation of an ylide by 1,7-H-shift from the mesomeric betaine III, followed by ring cleavage of the indazole ring and subsequent ring-closure of the resulting 1,6-dipole to give the quinazolines 16a–d. Single crystals of 16b suitable for an X-ray analysis were

Synthesis of mesomeric betaine compounds with imidazolium-enolate structure

• Nina Gonsior,
• Fabian Mohr and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 390–397, doi:10.3762/bjoc.8.42

• 10.3762/bjoc.8.42 Abstract The synthesis of a heterocyclic mesomeric betaine by quaternization reaction of 1-butylimidazole and tetrabromo-1,4-benzoquinone is presented. The structure was verified by means of X-ray single-crystal analysis, NMR and IR spectroscopy. Inclusion complexes of the heterocyclic

• mesomeric betaine with randomly methylated (1.8) β-cyclodextrin were investigated by UV–vis spectroscopy. Furthermore, the reaction conditions were applied to poly(vinylimidazole) and 1,4-bis(1H-imidazol-1-yl)butane to obtain functionalized polymer networks and condensate polymers, respectively. Keywords

• : cyclodextrin; heterocyclic mesomeric betaine; imidazole; polymer; X-ray single-crystal analysis; Introduction Heterocyclic mesomeric betaines [1] are interesting starting materials for heterocycle and polymer synthesis due to there intriguing chemical properties. They can be broadly classified into four main