Thermodynamics and reactivity for the interconversion of active sites on a magnesium surface in the Grignard reaction

Density functional theory (B3PW91/6-31G (d)) is used to study the energy and electronic parameters of Mg42-Mg58 clusters simulating the structure of point defects in a magnesium surface, which are supposed to act as active sites in the Grignard reaction. The energy effects of detachment of a Mg atom from defects of various structures and the energies required for their mutual transformations and migration over the (0001) crystallographic plane are calculated. It is demonstrated that, for clusters containing single-atom and noncompact defects, the energy of detachment of a magnesium atom is less than 20–60 kJ mol-1, which is comparable with the activation energy of the formation of the Grignard reagent, whereas for most other structures, it can substantially exceed this value. It is shown that defective clusters have more pronounced metallic properties than perfect structures with similar nuclearity. The reactivity of different models of defects in terms of the possibility of the activation of molecules of organic halides is analyzed.