The association of Grignard reagents to LiCl (turbo Grignard reagents) constitutes a pivotal step-forward in main-group organometallic chemistry. This combination yields more accessible Grignard-like compounds that produce more powerful and controllable reactions. Despite their undisputed success, the enhancing role of lithium salts in the Grignard reaction, one of many examples of the synergistic effect of lithium in heterometallic systems, has remained ununderstood. Better insight is hampered by the difficulty to determine the structures of these compounds in solution. The Grignard reagent forms a diversity of species bearing various ligands coexisting in fast equilibria, as exemplified by the Schlenk equilibrium, and whose exact composition depends on the experimental conditions. Likewise, multiple forms of LiCl have been observed in solid-state. The detected species, putatively existing also in solution, comprise molecular monomeric, dimeric, , fused rings, and cubane moieties, or polymeric and periodic aggregates, including both neutral and charged states. 27, Combining LiCl with Grignard reagent only obscures the situation further. Attempts to determine the nature of turbo Grignard reagents suffer from the fact that experimental characterization, by crystallization or spectroscopic methods, requires experimental conditions different from those at which reactions occur. Thus, for decades, no neutral Li:Mg moiety was reported in either gas phase or solid-state but this was not conclusive on their existence in solution. Indeed, very recently tBu2MgClLi(THF)4 was isolated and characterized by X-ray crystallography, and its presence in solution was assessed by NMR, its monomeric form possibly being promoted by the bulky tBu groups. In view of the experimental challenges, computational modeling offers a valuable complementary tool. Specifically, ab initio molecular dynamics simulations (AIMD) 32 are wellsuited for studying highly dynamic systems in solution, as shown by its successful use for the characterization of the Schlenk equilibrium involving CH3MgCl in tetrahydrofuran (THF), and the related Grignard reaction with acetaldehyde and fluorenone. Here, we apply this methodology to shed light on the structural preferences of LiCl in THF, and its interaction with a Grignard reagent represented by CH3MgCl and its Schlenk-associated compounds MgCl2 and Mg(CH3)2 (computational details in Supporting Information (SI)). While the structure of lithium-halide aggregates is debated, there is ample evidence that the four-member Li2X2 ring represents an underlying structural motif. For this reason, we started from Li2Cl2 for determining the structural forms of LiCl in THF (Figure ). The diamondshaped ring Li2Cl2 has two bridging chlorides and two THF at each lithium, yielding the expected Li2Cl2(THF)4. AIMD provides a solvated structure in satisfactory agreement with that from X-ray diffraction (Table ), with differences of 1.5-3% for bond distances. AIMD show that attraction between two Li2Cl2(THF)4 units starts at a relatively far distance of 8 Å between their respective centers of mass. We observed spontaneous partial desolvation, and formation of two new Li-Cl bonds, yielding Li4Cl4(THF)6 (B6, Figure ) indicating direct solvent control onto the multimerization of LiCl. B6 has three condensed four-member rings in boat-type structure, with the two external rings in a cis-arrangement. The lithium atoms of the peripheral rings are solvated by two THFs, while those of the central ring accommodate each a single THF. While a trans-arrangement cannot be excluded, we note that the structure of B6 resembles the motif of the THF-solvated LiCl and LiBr 35 polymers characterized by Xray diffraction (Table , and Figure ). The Helmholtz free energy (ΔA) against THF solvation evidences how B6 is a metastable configuration over a rather flat plateau containing, at a higher solvation, bicyclic [4.2.0] structures (R6, R7) corresponding to solid-state moieties isolated with tetramethylethylenediamine (TMEDA) (Figure ). 22 B6 evolves toward more stable, less solvated species (C4, C5), with a higher number of Li-Cl bonds (Figures ). Both C4 and C5 have cubane-like structures with Li's and Cl's at the vertices of two imbricated tetrahedra. The more symmetric C4 arrangement has each Li bonded to three Cl's, with distances 2.43 ± 0.16 Å, and to one THF. It nicely resembles the solid-state structures of Li4Cl4(L)4, with L = Et2O, and hexamethylphosphoramide (HMPA) (Table ). The pentasolvated cluster C5, Li4Cl4(THF)5 is more stable than C4 by 1.4 ± 0.6 kcal mol -1 . Unlike C4, in C5 one of the twelve Li-Cl bonds is broken, with a Li-Cl distance of 3.81 ± 0.03 Å. Two THFs solvate the dangling Li center, maintaining its tetrahedral coordination; the associated Cl passes from a µ3to a µ2bridging position between two proximate Li's. Overall, C5 shows larger flexibility than C4the root-mean-square-fluctuations of the LiCl core increasing from 0. The interaction between the Grignard and LiCl is triggered by the dangling lithium, which coordinates preferentially to the chloride of the Mg species, at the expense of expelling a THF from its coordination sphere. Subsequently, the µ2-Cl binds to the incoming Mg. Such generalized acid/base interactions are favored by the higher charges, negative at the µ2-Cl and positive at the open Li, relative to the other Li's and Cl's of the cluster (Figure ). On the contrary, for Mg(CH3)2, Mg prefers to coordinate with a less electrondonating µ3-Cl, even if initially positioned nearby a µ2-Cl. This could be due to the stronger electron-donating effect of the methyl groups, enhancing repulsion with a more electron-rich chloride in the LiCl aggregate. To evaluate the interactions between the Mg fragments and the LiCl cluster, the three Grignard-LiCl complexes were investigated by Energy Decomposition Analysis (EDA) (Table ). The interactions are mostly driven by the electrostatic term, with additional charge-transfer contribution. These two components are the most stabilizing for MgCl2 and the least for Mg(CH3)2. This is in line with the high ionic character of the Mg-Cl bond that enhances both terms. The preference for Mg(CH3)2 to coordinate a weaker electron donor µ3-Cl agrees with the reduced Pauli repulsion between the two fragments. The strongest binding of Li4Cl4 to MgCl2 has several implications. The energetic unbalance in favor of MgCl2•Li4Cl4 pushes the Schlenk equilibrium to the right, enhancing disproportionation of CH3MgCl, and formation of the more electron-rich Mg(CH3)2. This does not exclude the occurrence of further equilibria yielding other species.