Accurate metal-ligand bond energies in the (2)-C2H4 and (2)-C-60 complexes of Pt(PH3)(2), with application to their Bis(triphenylphosphine) analogues

We have investigated the metal-ligand bond energies in C2H4-Pt(PH3)(2) and C-60-Pt(PH3)(2) by means of ab initio correlated methods (MP2, MP4(SDQ), MP4, QCISD, CCSD and CCSD(T)) in conjunction with large basis sets. For D-e(C2H4-Pt(PH3)(2)), an accurate value of 17.2 kcal/mol is established at the CCSD(T) level of theory. Due to the size of the system, the bond energy for the Buckminsterfullerene system was explored in terms of a sequence of model systems of increasing size, providing a D-e estimate of 28.2 kcal/mol at the ONIOM(CCSD(T)/C14H8:MP2/C-60) level of theory. The performance of a range of high-end density functionals (with and without dispersion) is evaluated for these systems by comparison to the best ab initio results. Among these, we find density functionals BLYP and B3LYP, augmented by Grimme's D3 dispersion correction (to give the corresponding DFT-D methods), to provide good and consistent agreement with our best estimates. Next, DFT-optimised structures for C2H4-Pt(PPh3)(2) and C-60-Pt(PPh3)(2) are presented for the first time. Ligand binding energies were computed for ethylene and C-60 using DFT-D, thus allowing the first computational estimate of the driving force in the ligand substitution reaction ((2)-C2H4)Pt(PPh3)(2) + C-60 ((2)-C-60)Pt(PPh3)(2) + C2H4.