Morphological Plasticity of LiCl Clusters Interacting with Grignard Reagent in Tetrahydrofuran

Ab initio molecular dynamics simulations are used to explore tetrahydrofuran (THF) solutions containing pure LiCl and LiCl with CH₃MgCl, as model constituents of the turbo Grignard reagent. LiCl aggregates as Li₄Cl₄, which preferentially assumes compact cubane-like conformations. In particular, an open-edge pseudotetrahedral frame is promoted by solvent-assisted Li-Cl bond cleavage. Among the Grignard species involved in the Schlenk equilibrium, LiCl prefers to coordinate MgCl₂ through μ₂-Cl bridges. Using a 1:1 Li:Mg ratio, the plastic tetranuclear LiCl cluster decomposes to a highly solvated mixed LiCl·MgCl₂ aggregate with prevalent Li-(μ₂-Cl)₂-Mg rings and linear LiCl entities. The MgCl₂-assisted disaggregation of Li₄Cl₄ occurs through transient structures analogous to those detected for pure LiCl in THF, also corresponding to moieties observed in the solid state. This study identifies a synergistic role of LiCl for the determination of the compounds present in turbo Grignard solutions. LiCl shifts the Schlenk equilibrium promoting a higher concentration of dialkylmagnesium, while decomposing into smaller, more soluble, mixed Li:Mg:Cl clusters.