Hierarchy of Commonly Used DFT Methods for Predicting the Thermochemistry of Rh-Mediated Chemical Transformations

The accuracy and reliability of 17 commonly used density functionals in conjunction with Poisson-Boltzmann finite solvation model were gauged for predicting the free energy of Rh(I)- and Rh(III)-mediated chemical transformations such as ligand exchange, hydride elimination, dihydrogen elimination, chloride affinity, and silyl hydride bond activation reactions. In total, six Rh-mediated reactions were examined, and the computed density functional theory results were then subjected to comparison with the experimentally reported values. For reaction A, involving replacement of N₂ with η²-H₂ over Rh(I), MPWB1K-D3, B3PW91, B3LYP, and BHandHYLP emerged to be the best functionals of all the tested methods in terms of their deviations ≤2 kcal mol^-1 from experimental data. For reaction B, in which exchange of η²-C₂H₄ with N₂ over Rh(I) takes place, MPWB1K-D3 and M06-2X-D3 functionals performed the best, while as for reaction C (hydride elimination reaction in Rh(III) complex), it is PBE functional that showed impressive performance. Similarly, for reaction D (H₂ elimination reaction in Rh(III) complex), PBE0-D3 and PBE-D3 showed exceptional results compared to other functionals. For reaction E (H₂O/Cl^- exchange), the PBE0 again shows impressive performance as compared to other functionals. For reaction F (Si-H activation), M06-2X-D3, PBE0-D3, and MPWB1K-D3 functionals are undoubtedly the best functionals. Overall, PBE0-D3 and MPWB1K-D3 functionals were impressive in all cases with lowest mean unsigned errors (3.2 and 3.4 kcal mol^-1, respectively) with respect to experimental Gibbs free energies. Thus, these two functionals are recommended for studying Rh-mediated chemical transformations.