Free energy of reaction by density functional theory: Oxidative addition of ammonia by an iridium complex with PCP pincer ligands

The Gibbs energy of reaction of oxidative addition of ammonia to an iridium complex in diethyl ether was calculated by seven density functional methods, in particular B3LYP, PBE, CAM-B3LYP, M05, M06, M06-L, and ωB97X. The calculated free energies, based on geometry optimization and frequency calculations in both the gas phase and solution, were compared with the experimental result, -1.3 kcal mol^-1, obtained by Hartwig and coworkers. The M06-L method gives the best result: -1.4 kcal/mol.