Bonding interactions of a molecular pair of tweezers with transition metals. Theoretical study of bis(eta(2)-alkyne) complexes of copper(I), silver(I), and gold(I)

Quantum chemical calculations at the DFT level of theory using the three-pa rameter fit of the potential B3LYP in conjunction with relativistic effecti ve core potentials and large valence basis sets are reported for the model compounds [Cl2Ti(C=CH)(2)]MCH3 (M = Cu, Ag, Au), [CuCH3(HCCH)(n)] (n = 1, 2 ), and [H2X(C=CH)(2)]CuCH3 (X = Si, C). Theoretically predicted geometries and MCH3 binding energies are given, and the nature of the binding interact ions has been analyzed with the help of the NBO partitioning scheme and the topological analysis of the electron density distribution. The copper comp lex [Cl2Ti(C=CH)(2)]CuCH3 has a much higher bond energy (D-e = 39.2 kcal/mo l) than the analogous silver (D-e = 21.2 kcal/mol) and gold compound (D-e = 17.3 kcal/mol). There is significant --> metal acetylide charge donation i n the complexes, which induces strong Coulomb attraction between MCH3 and t he tweezer ligand. The role of the bridging TiY2 moiety in the bisalkyne co mplexes is a twofold one. It serves to position the alkyne groups in a prop er position for tricoordination around the group 11 metals, and it enhances the Lewis acidity of the ligands.