Quantum-chemical study of the Grignard reaction mechanism within the cluster model of reaction center

Structure and energy of EtBr adsorption complexes on (0 0 0 1) magnesium crystal surface in the surrounding of adsorbed solvent molecules L (L = n-pentane, acetonitrile, THF, DMF, DMSO, pyridine, HMPTA) as well as the most probable routes of their transformation with the Grignard reagent (EtMgBr) formation were studied by applying the DFT method (B3PW91/6-31G(d)). Surface complexes were modeled using the Mg50–EtBr, Mg50–L and Mg50–EtBr–L6 clusters. Thermodynamics of elementary reactions of Grignard reagent formation in aprotic solvents on the magnesium surface was studied. It is shown that the overall kinetic rate of the Grignard reagent formation is defined by the competition between the adsorption and desorption steps depending on the donor properties of solvents, while the oxidation step itself is fast. The magnesium oxidation rate correlates with the adsorption energy of oxidizer on a magnesium surface and product’s desorption energy to the reaction mixture volume.