Enhanced Acidity and Activity of Aluminum/Gallium-Based Ionic Liquids Resulting from Dynamic Anionic Speciation

To explore if the catalytic activity of single-metal species in halometallate catalysts can be enhanced with mixed-metal species, aluminum and gallium were simultaneously introduced to prepare a mixed-metal ionic liquid (IL) through a one-pot reaction of [HN222]­Cl, AlCl3, and GaCl3 in various amounts. The Lewis acidity in Friedel–Crafts acylation and alkylation reactions of these IL compositions were evaluated and all mixed-metal [HN222]­[xAlCl3 + (2 – x)­GaCl3]Cl ILs exhibited higher catalytic activity than AlCl3, GaCl3, [HN222]­[Al2Cl7], or [HN222]­[Ga2Cl7]. The broadening in 27Al nuclear magnetic resonance (NMR) of these ILs indicates the presence of dynamic anionic species, whereas matrix-assisted laser-desorption ionization time-of-flight (MALDI-TOF) and acetonitrile-probed Fourier transform infrared (FT-IR) analyses correlates the structure–activity relationship, for instance, identifying the presence of mixed-metal-containing [Cl2GaOClAlClOGaCl2]− species in the better-performing ILs.