Microsolvation and Encapsulation Effects on Supramolecular Catalysis: C-C Reductive Elimination inside [Ga4L6]12- Metallocage

The host effect of the supramolecular [Ga4L6](12-) tetrahedral metallocage on reductive elimination of substrate by encapsulated Au(III) complexes is investigated by means of computational methods. The behavior of the reactants in solution and within the metallocage is initially evaluated by means of classical molecular dynamics simulations. These results guided the selection of proper computational models to describe the reaction in solution and inside the metallocage at the DFT level. The calculated Gibbs energy barriers are in very good agreement with experiment both in solution and inside the metallocage. The analysis in solution revealed that microsolvation around the Au(III) complex increases the Gibbs energy barrier. The analysis within the metallocage shows that its encapsulation favors the reaction. The process can be formally described as removing explicit microsolvation around the gold complex and encapsulating the metal complex inside the metallocage. Both processes are important for the reaction, but the removal of the solvent molecules surrounding the Au(III) metal complex is fundamental for the reduction of the reaction barrier. The energy decomposition analysis of the barrier among strain, interaction, and thermal terms shows that strain term is very low whereas the contribution of thermal (entropic) effects is moderate. Interestingly, the key term responsible for reducing the Gibbs energy barrier is the interaction. This term can be mainly associated with electrostatic interactions in agreement with previous examples in the literature.