Reversible Oxidative Addition and Reductive Elimination of Fluorinated Disulfides at Gold(I) Thiolate Complexes: A New Ligand Exchange Mechanism

Abstract

Reaction of HAuCl4 x 3 H2O with excess HSAr (Ar = C6F5 or C6F4H) in ethanol, followed by addition of [Et4N]Cl, produced [Et4N][Au(SAr)4] (Ar = C6F5 (1a) or C6F4H (1b)) as red crystalline solids in high yield. These complexes are rare examples of homoleptic gold(III) thiolate complexes. The crystal structures 1 show square planar geometry at the gold center with elongated Au-S bonds. Both complexes undergo reversible reductive elimination/oxidative addition processes in solution via thermal and photochemical pathways. Equilibrium constant and photostationary state measurements indicate that the relative importance of the two pathways depends on the nature of the aromatic groups. The metal-containing reductive elimination products, [Et4N][Au(SAr)2] (Ar = C6F5 (2a) or C6F4H (2b)), were confirmed by both independent synthesis and crystallographic characterization. Cross-reactions between either 1 or 2 and various disulfides led to ligand exchange via an addition-elimination process, a previously unknown reaction pathway for ligand exchange at gold(I) centers.