Between T and Y: Asymmetry in the Interaction of LAu(I) with Bipy and β-Diiminate-like Ligands

The combination of an LAu(I) fragment with a potentially chelating ligand (Formula presented.) can result in different coordination modes of (Formula presented.) : strictly monodentate, symmetrically bidentate, or intermediate with asymmetric bidentate binding of (Formula presented.). Density Functional calculations indicate that for π-acceptor ancillary ligands L (C2H4, CO) and bis(nitrogen) donors (Formula presented.) (bipyridine, phenanthroline, β-diiminate) symmetric chelate structures are obtained. With primarily σ-donating ancillary ligands L (Me−, Cl−, MeCN) the asymmetric coordination mode is the norm. Phosphine ancillary ligands L are on the edge and display the highest sensitivity to ligand variation. Asymmetry increases when (a) going from anionic (β-diiminate) to neutral (bipyridine, phenanthroline) bidentates (Formula presented.); (b) making (Formula presented.) less electron-rich e. g. through having aryl instead of alkyl groups at N or through introduction of CF3 substituents. Inversion of the asymmetry through “gold hopping” is remarkably facile (barrier mostly <6 kcal/mol, often ∼1 kcal/mol). The high-temperature fluxionality reported for two (PPh3)Au(β-diiminate) complexes is tentatively assigned to imine inversion (rather than gold hopping) as the rate-limiting step.