Full Quantum Mechanical Investigation of the Unimolecular versus Bimolecular Acetylene to Vinylidene Rearrangement in the Prototype trans-Cl-Rh(Pi-Pr3)2 Complex

We report a full quantum mechanical investigation, based on DFT calculations, on the unimolecular and bimolecular alkyne-vinylidene rearrangements in the prototype [Cl-Rh(Pi-Pr3)2(HCCH)] complex, to solve the discrepancy between theory and recent experimental data and to provide a definitive answer concerning the largely debated molecularity issue of the 1,3-shift in d8 metal complexes. We calculate the intramolecular pathway to be kinetically favored over the intermolecular one by 15.0 kcal/mol, in agreement with recent crossover experiments. Comparison of our DFT calculations performed on the real systems with reduced models shows that a full quantum mechanical description of the investigated systems is mandatory for a correct description of their reactivity, owing to the relevant role played by the electron-donating phosphine ligands.