Ligand bond energies in cis- and trans-[L-Pd(PH3)2Cl]+ complexes from coupled cluster theory (CCSD(T)) and density...

The Pd-L ligand bond dissociation energies (BDEs) of cis- and trans-[L-Pd(PH(3))(2)Cl](+) were predicted using coupled cluster CCSD(T) theory and a variety of density functional theory (DFT) functionals at the B3LYP optimized geometries. trans-[L-Pd(PH(3))(2)Cl](+) is the more stable isomer when Pd forms a donor-acceptor bond with a C atom of the ligand, including the π-bond in norbornene; for the remaining complexes, the cis-[L-Pd(PH(3))(2)Cl](+) isomer is substantially lower in energy. For cis-[L-Pd (PH(3))(2)Cl](+) complexes, the Pd-L bond energies are 28 kcal/mol for CO; ∼40 kcal/mol for AH(3) (A = N, P, As, and Sb), norbornene, and CH(3)CN; and ∼53 kcal/mol for CH(3)NC, pyrazole, pyridine, and tetrahydrothiophene at the CCSD(T) level. When Pd forms a donor-acceptor bond with the C atom in the ligand (i.e., CO, CH(3)NC, and the π-bond in norbornene), the Pd-L bond energies for trans-[L-Pd(PH(3))(2)Cl](+) are generally ∼10 kcal/mol greater than those for cis-[L-Pd(PH(3))(2)Cl](+) with the same L; for the remaining ligands, the ligand bond energy increases are ∼3-5 kcal/mol from the cis-isomer to the trans-isomer. The benchmarks show that the dispersion-corrected hybrid, generalized gradient approximation, DFT functional ω-B97X-D is the best one to use for this system. Use of the ω-B97X-D/aD functional gives predicted BDEs within 1 kcal/mol of the CCSD(T)/aug-cc-pVTZ BDEs for cis-[L-Pd(PH(3))(2)Cl](+) and 1.5 kcal/mol for trans-[L-Pd(PH(3))(2)Cl](+).