Computational Studies of Metal−Ligand Bond Enthalpies across the Transition Metal Series

Relative to the p-block of the periodic table, data for transition metal−ligand bond dissociation enthalpies are less comprehensive. Recent developments in computational methods make systematic assessment of trends in metal−ligand bond enthalpies across the transition series a relatively rapid and accurate exercise. We report a systematic study of metal−ligand bond enthalpies for saturated transition metal complexes that encompasses the entire d-block of the periodic table and a wide assortment of ligands. The saturated complexes have the form MH n −L such that closed-shell molecules are formed with the maximum number of two-center, two-electron (2c/2e) bonds under the constraint that the metal electron count does not exceed 12. Bond enthalpies for MH n −L molecules with higher electron counts (14 and 16 electrons) are assessed for some group 10 and 11 metals. The primary methods are density functional theory (DFT) using the hybrid B3LYP density functional and CCSD(T) ab initio computations. Bond enthalpies are reported as the first bond dissociation enthalpies for neutral and cationic complexes of the type MH n −R (R = H, CH3, C2H5, CH(CH3)2, C(CH3)3, CH2F, C2H, C2H3, NH2, OH, F, and BH2) for all transition elements. Electronic structure analysis of the complexes features natural bond orbital (NBO) analysis of bond polarity.