Spectroscopic Manifestations and Implications for Catalysis of Quasi-d 10 Configurations in Formal Gold(III) Complexes.

Several gold +I and +III complexes are investigated computationally and spectroscopically, focusing on the d-configuration and physical oxidation state of the metal center. Density functional theory calculations reveal the non-negligible electron-sharing covalent character of the metal-to-ligand σ-bonding framework. The bonding of gold(III) is shown to be isoelectronic to the formal Cu III complex [Cu(CF 3 ) 4 ] 1- , in which the metal center tries to populate its formally unoccupied 3d x2-y2 orbital via σ-bonding, leading to a reduced d 10 Cu I description. However, Au L 3 -edge X-ray absorption spectroscopy reveals excitation into the d-orbital of the Au III species is still possible, showing that a genuine d 10 configuration is not achieved. We also find an increased electron-sharing nature of the σ-bonds in the Au I species, relative to their Ag I and Cu I analogues, due to the low-lying 6s orbital. We propose that gold +I and +III complexes form similar bonds with substrates, owing primarily to participation of the 5d x2-y2 or 6s orbital, respectively, in bonding, indicating why Au I and Au III complexes often have similar reactivity.