Quantum chemical study of the charged gold atom influence on the mechanism of allylbenzene double bond migration

The DFT calculations of allylbenzene double bond migration were performed in the presence of gold ions Au^? and Au⁺ and the cluster Au₄, which are models of active sites of the gold-containing catalysts. The mechanism of isomerization is determined by the charge of the metal. For the allylbenzene + Au⁺ system, the most appropriate mechanism is the multistage metal-allylic process passing through either the formation of a gold-hydride complex, or no hydride complex is formed in the presence of Au^?. The calculated rate constant of the rate-determining step of the catalytic reaction increases in the order Au₀ < Au^? < Au⁺. The Au^??+ particles are active sites in allylbenzene isomerization. Additional routes of accumulation of the trans-isomer result in the selective formation of trans-??-methylstyrene observed in the catalytic conversion of allylbenzene in the presence of gold nanoparticles. The metal-allylic mechanism is the most preferential in the presence of Au₄ cluster. The high energy of the bond of allylbenzene with the cluster is possibly due to the high reactivity of the latter.