Coinage Metal-Ethylene Complexes Supported by Tris(pyrazolyl)borates: A Computational Study

Data from computational and experimental sources have been combined to address the bonding and structure of [RB(3-(R),5-(R)Pz)3]M(C2H4) complexes, where M ) Cu, Ag, Au. A κ3 to κ2 distortion of the scorpionate ligand was also studied. NMR properties were deemed to be the most useful in assessing the nature of the bonding in these complexes. Using computational recipes, 13C chemical shifts accurately reproduced quantitative experimental values and trends as a function of metal, ligand, and substituent. Au-ethylene complexes are found to be substantially “less π-complex” (T-shaped structure) in their bonding description versus Ag and Cu congeners, although the former are by no means entirely metallacyclopropane in their constitution. Combining the present calculations with prior contributions to coinage metal bonding leads us to propose that similarity of molecular structure among a congeneric series of coinage metal complexes reflects a principally ionic coinage metal-ligand bonding regime, while dissimilarity of structure within the series reflects a primarily covalent bonding regime.