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

Abstract

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.