Spectroscopic Manifestations and Implications for Catalysis of Quasi‐d¹⁰Configurations in Formal Gold(III) Complexes

Abstract

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 ] 1À , 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 dorbital 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.

Rethinking gold(II) porphyrins: an inherent wave distortion

“…The above findings lend an entirely new complexion to the electron structure of Au(II) porphyrins. The tendency of the Au(II) center to increase its effective d-electron count parallels a recent study in which a variety of formally Au(III) complexes have been described as quasi-d 10 , based on theoretical analyses of their bonding interactions [39]. These complexes nevertheless exhibit distinct 2p→5d XANES features, indicative of a 5d hole.…”

Scrutinizing formally NiIVcenters through the lenses of core spectroscopy, molecular orbital theory, and valence bond theory

“…This formalism was extended to Au complexes, with “quasi” vs. intrinsic d 10 differentiated both computationally and by qualitative comparison of L 3 -edge XAS profiles. 37 Experimental quantification of d-count was not provided (an accurate d-count cannot be provided without also obtaining L 2 -edges). We would argue that this is unnecessarily cumbersome as the difference in spectral profile can be ascribed to differences in d-configuration.…”

The Role of Inverted Ligand Field in the Electronic Structure and Reactivity of Octahedral Formal Platinum (IV) Complexes**

“…This bonding picture in square planar complexes allowed the introduction of the concept of Inverted Ligand Field (ILF). [1,5] The ILF theory, nowadays well supported by experimental data and calculations, [1,[5][6][7][8][9][10][11][12][13][14][15][16] provides a critical review of the high formal oxidation state in 11 th group metals suggesting that most of the d 8 Cu(III) and Au(III) square planar complexes could be better considered as d 10 Cu(I) and Au(I) ones with electronic holes on the ligands. This new bond description allows a better knowledge of the reactivity of these systems, not always easily to be rationalized.…”