Ab initio study of structures, energetics, and bonding in formally high-oxidation-state copper organometallics

Abstract

Geometry-optimized structures, energies, and harmonic vibrational frequencies of closed-shell states of CuL⁺, XCu^IL, and XCu^IIIL fragments (L = CO, C₂H₄, C₂H₂; X = H^-, F^-, OH^-, O^2-, N^3-) have been obtained at the MP2 level using valence-DZP-quality basis sets with effective core potentials. Natural population analyses have been used to interpret the nature of metal-ligand interactions. The computed data for all the Cu(I) species are along expected lines. Interestingly, the formally high-oxidation-state species also have effectively d¹⁰ configurations, with the electron deficiency localized in the ligands. As a result, the Cu-X bonds are long and, in a few cases, the ligand L dissociates during geometry optimization. In the computed minima, the Cu-L interaction energies are fairly large, primarily due to electrostatic interactions. The extent of π-back-donation is generally low in "Cu(III)" systems. However, a strong π-donor group enhances the ability of the metal to engage in dπ-pπ bonding with CO, C₂H₄, or C₂H₂, making it comparable to a typical Cu^IL system in all respects. The trends are virtually identical in all three lowest energy closed-shell states of the ethylene and acetylene complexes.