Free energy ab initio metadynamics:: A new tool for the theoretical study of organometallic reactivity?: Example of the C-C and C-H reductive eliminations from platinum(IV) complexes

Metadynamics and static DFT calculations have been performed on the C-H and C-C reductive elimination from Pt(IV) octahedral complexes L2Pt(CH3)(3)X (X = H or CH3, L-2 = diphosphine ligand, viz., a model of a dppe and dppbz ligand). The use of metadynamics simulations is shown to be a powerful tool to describe the reactivity of organometallic compounds and provide us with the activation free energy of the different processes involved in these reactions: ligand dissociation; C-C and C-H formation. The computational results bring to the fore three mechanisms: direct and dissociative pathways, but also a concomitant mechanism with a simultaneous C-H formation and Pt-P dissociation. The dissociative pathway, which proceeds through a five-coordinate intermediate, is favored for the C-C reductive elimination, whereas the two other mechanims are observed for the C-H reductive elimination. The basicity of the phosphine used as much as its intrinsic rigidity strongly influences the mechanism of the C-H reductive elimination: direct or with concomitant dissociation of one arm of the diphosphine ligand. On the contrary, it has no influence on the C-C reductive elimination. The computed free activation energies from metadynamics calculations are in good agreement with experimental values measured for the different complexes. We also report computed activation free energy with inclusion of the entropy effect for the dissociation of the diphosphine ligand, a necessary step for the C-C reductive elimination.