The Bis(η6‐benzene)lithium Cation: A Fundamental Main‐Group Organometallic Species

• Published in: Angewandte Chemie International Edition 2021-10, Vol.60 (42), p.22879-22884
• Main Authors: Jie, Xiaoming, Li, Jun, Daniliuc, Constantin G., Wübker, Anna‐Lena, Hansen, Michael Ryan, Eckert, Hellmut, Mück‐Lichtenfeld, Christian, Kehr, Gerald, Erker, Gerhard
• Format: Article
• Language: English
• Subjects: Acetylene; Benzene; borates; Boron; Boron compounds; Cations; cation–π interactions; Crystallization; Durene; Hydrocarbons; Lithium; Lithium isotopes; Magnetic resonance spectroscopy; metallocenes; NMR; NMR spectroscopy; Nuclear magnetic resonance; Reagents; Salts; Toluene; weakly coordinating anions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202108376

The synthesis and characterization of the bis(η6‐benzene)lithium cation, the benzene metallocene of the lightest metal, is reported. The boron compound FmesBCl2 [Fmes: 2,4,6‐tris(trifluoromethyl)phenyl] reacted with three molar equivalents of the lithio‐acetylene reagent Li‐C≡C‐Fmxyl [Fmxyl: 3,5‐bis(trifluoromethyl)phenyl]. Subsequent crystallization from benzene gave the [bis(η6‐benzene)Li]+ cation with the [{FmesB(‐C≡C‐Fmxyl)3}2Li]− anion. This parent [(arene)2Li]+ cation shows an eclipsed arrangement of the pair of benzene ligands at the central lithium cation with uniform carbon‐lithium bond lengths. The corresponding [(η6‐toluene)2Li]+ and [(η6‐durene)2Li]+ containing salts were similarly prepared. The bis(arene)lithium cations were characterized by X‐ray diffraction, by solid‐state 7Li MAS NMR spectroscopy and their bonding features were analyzed by DFT calculations. The bis(η6‐benzene)lithium cation, the lightest main‐group metal analogue of E. O. Fischer's bis(η6‐benzene)Cr, was prepared and characterized in the solid state.