Hydrogen Bond Basicity of Imidazolium‐Based Ionic Liquids as A Descriptor for Liquid‐Phase Acetylene Hydrochlorination

Ionic liquids (ILs), as liquid‐phase media in acetylene hydrochlorination, not only optimize the mixing environment of reactants but also stabilize the active sites of metal catalysts. Nevertheless, the majority of current research relies on trial‐and‐error methods, with a notable absence of systematic analysis regarding liquid‐phase catalytic systems. In this study, imidazolium‐based ILs ([Bmim]X) with different hydrogen bond basicity (β) values were used to fine‐tune the Ru‐based liquid‐phase catalytic system (Ru‐[Bmim]X). It was found that with the β value of [Bmim]X increases, its solubility for HCl and C2H2 also increases, resulting in a volcanic trend in the activity of the Ru‐[Bmim]X catalysts. Through systematic characterisation and theoretical calculations, we identified the active site structure of the Ru‐[Bmim]Cl catalyst as [RuCl4] and confirmed the reaction mechanism to be Eley‐Rideal (ER). Various anions of [Bmim]X influenced the adsorption of reactants and reactive energy barriers by modulating the electronic and steric effects in the active sites. In particular, the Ru‐[Bmim]Cl catalyst showed a remarkable conversion rate of 86.8% and high stability, even at a low temperature of 110°C. These results provide a scientific basis for the development of novel and efficient liquid‐phase catalytic systems.