QM/MM(ABEEM) Study on the Ligand Substitution Processes of Ruthenium(III) Complex NAMI-A

QM combined with ABEEMσπ (atom-bond electronegativity equalization method) fluctuating charge polarizable force field [QM/MM(ABEEM)] has been employed to investigate the hydrolysis mechanism of ruthenium(III) complex NAMI-A. Eleven possible hydrolysis paths of NAMI-A and its hydrolysates have been unveiled. Structures obtained by QM/MM (ABEEM) method were used to calculate the activation free energy by free energy perturbation theory. Based on analysis of structures and activation free energies, it is found that the rate of DMSO dissociation is faster than that of Cl− dissociation in the first step, which is in agreement with experimental results. Hydrolysates of the first step continue to hydrolyze with lower activation free energies than that of the first hydrolysis step, but the trans-position Cl− hydrolysis in the second step needs more time to perform. This can account for experimental phenomenon reasonably. We have simulated further hydrolysis paths of the hydrolysates, then found that both Cl− dissociation and DMSO dissociation take place in the third hydrolysis step and [RuCl(H2O)4(Im)]2+ is the main solute in aqueous solution after the fourth hydrolysis step.