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 pseudo tetrahedral frame is promoted by solvent-assisted Li-Cl bond cleavage. Among the Grignard species involved in the Schlenk equilibrium, LiCl prefers coordinating MgCl2 through m-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-(m2-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, in a scenario where LiCl shifts the Schlenk equilibrium promoting a higher concentration of dialkylmagnesium, meanwhile decomposing into smaller, more soluble, mixed Li:Mg:Cl clusters.