Computational Assessment of the Effect of σ−π Bonding Synergy and Reorganization Energies on Experimental Trends in Rhodium−Phosphine Bond Enthalpies

Via a series of systematic density functional (B3LYP/LANL2DZ) computational experiments, we have examined the origin of opposing Rh−PR3 bond enthalpy trends involving two different square-planar Rh(I) complexes with a series of different π-accepting phosphines (Huang, J. K.; Haar, C. M.; Nolan, S. P.; Marshall, W. J.; Moloy, K. G. J. Am. Chem. Soc. 1998, 120, 7806). Computational results rule out reorganization energies as the cause of the contradictory trends in thermodynamic analyses of metal−ligand bonding. Rather, calculations show that synergy of σ-donor and π-acceptor ligands linked to a metal is pivotal for interpreting the contradictory trends in Rh−P bond enthalpies. We conclude that metal−phosphine bond energies cannot be regarded as intrinsic, universal, or transferable.