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

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(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.

Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

“…The boron atom is surrounded by three carbon atoms of three pentafluorophenyl rings and one oxygen atom of the ligand. The B–C bonds were found to be 1.643(3), 1.644(3), and 1.649(3) Å, which correspond to the values of the bond lengths in the literature‐known tris(perfluorophenyl)borate of 2‐(3‐alkyl‐1 H ‐imidazolium‐1‐yl)phenolates . The B–O bond has a length of 1.522(3) Å.…”

Non-Classical Anionic Naked N-Heterocyclic Carbenes: Fundamental Properties and Emerging Applications in Synthesis and Catalysis

“…To our knowledge, a review of anionic NM,NR-NHCs and naked N,NR-NHCs has not been published to date. Consequently, this review focuses on imidazole-based anionic NHCs with N,NR substitution patterns, thus excluding mixed normal/abnormal classical NR,NR NHCs which are anionic due to deprotonation of the azolium salt at two different sites ( Figure 2) [32][33][34][35][36]. Specifically, the fundamental structural and electronic properties of these systems and their applications in synthesis are discussed.…”

Anionic N-heterocyclic carbenes derived from sydnone imines such as molsidomine. Trapping reactions with selenium, palladium, and gold

“…Other examples of conjugated systems with related structures have been described as well. [24][25][26][27][28][29][30][31][32] Scheme 1.…”