Effect of magnesium cluster size on Grignard reagent formation mechanism. A quantum-chemical study

Abstract

The density functional theory (B3PW91/6-311[Formula: see text]G(2d,2p)) was used to obtain optimized geometry, energy and electronic properties of Mg[Formula: see text]EtBr adsorption complexes, Et[Formula: see text]Mg[Formula: see text]Br intermediates and transition states for ethyl bromide reaction with the magnesium atom and Mgn ([Formula: see text]–20) clusters modeling the distorted surface of the metallic magnesium. We suggest a consecutive multi-stage scheme of EtBr[Formula: see text]Mgn process in vacuum that includes adsorption of reagents on external cluster atoms, chemical interaction with Grignard reagent formation and desorption of products to the volume. Two fundamentally different reaction channels were investigated — the radical and molecular ones. Influence of Mgn cluster size on the preference of each of channels was established. It is shown that the reaction route is primarily determined with the position of the reactive group of atoms participating in formation of the transition state or radical intermediates and the activation energy of EtMgBr formation correlates with the energy of atom detachment from a cluster. For both pathways, reaction activation energies and thermodynamic parameters of the elementary steps were calculated.