Pentacoordinated transition states of cisplatin hydrolysis—ab initio study

Abstract Pentacoordinated platinum transition state (TS) geometries for both steps of cisplatin S N 2 hydrolysis reaction were fully optimized using Moller–Plesset second order perturbation (MP2) and density functional (DFT) calculations. Both reactions proceed by one step mechanism and relevant TS's adopt the shape of a substantially distorted trigonal bipyramid with considerably prolonged bonds to the leaving and entering ligands (Pt–O bond of about 0.3 A, Pt–Cl bond of about 0.4 A). Only negligible distortions were recognized for the remaining ligands (including the ligand in the trans -position). Influence of the liquid phase on the energetics of the reaction was considered using the SCIPCM model implemented in Gaussian94 . Both steps of hydrolysis are endothermic. The activation barrier of the first step attains 21.3 kcal/mol. For the second step the values of 26.1 kcal/mol relative to the absolute minimum structure and of 21.6 kcal/mol for the local minimum confirmed by the IRC method were obtained.