Organometallic synthesis in ambient temperature chloroaluminate(III) ionic liquids. Ligand exchange reactions of ferrocene

The ambient temperature ionic liquid system [bmim]Cl-AlCl3 (where [bmim](+) = 1-butyl-3-methylimidazolium cation) has been used to prepare a number of arene(cyclopentadienyl)iron(II) complexes of the type [Fe(C5H5)(arene)](+) from ferrocene. The ionic liquid acts as both solvent and Lewis acid source ([Al2Cl7](-)). The products were only formed on addition of a proton source, [bmim][HCl2](2), confirming mechanistic formulations involving a combination of Lewis and Bronsted acid activity. The X-ray crystal structure analysis of [Fe(eta(5)-C5H5)(eta(6)-C6H5C6H4Br)][PF6] is also reported. The structure clearly shows both pi-pi stacking interactions between neighbouring cations and hydrogen bonds between the cations and anions.