Theoretical Study of Magnesium Compounds:  The Schlenk Equilibrium in the Gas Phase and in the Presence of Et₂O and THF Molecules

The Schlenk equilibrium involving RMgX, R 2 Mg, and MgX 2 (R = Me, Et, Ph and X = Cl, Br) has been studied both in the gas phase and in diethyl ether (Et 2 O) and tetrahydrofuran (THF) solutions by means of the density functional theory (DFT) B3LYP/6-31+G* method. Solvation was modeled using the supermolecule approach. The stabilization due to interaction with solvent molecules decreases in the order MgX 2 > RMgX > R 2 Mg and among the groups (R and X) Ph > Me > Et and Cl > Br. Studied magnesium compounds are more strongly solvated by THF compared to Et 2 O. The magnesium halide is solvated with up to four solvent molecules in THF solution, assuming that trans- dihalotetrakis(tetrahydrofurano)magnesium(II) complex forms. The formation of cis- dihalotetrakis(tetrahydrofurano)magnesium(II) is energetically less favorable than the formation of corresponding disolvated complexes. The predominant species in the Schlenk equilibrium are RMgX in Et 2 O and R 2 Mg + MgX 2 in THF, which is consistent with experimental data.