Halogen Photoreductive Elimination from Gold(III) Centers

Monomeric complexes of the type Au^III(PR₃)X₃ and bimetallic complexes of the type Au₂^I,III[μ-CH₂(R₂P)₂]X₄ and Au₂^III,III[μ-CH₂(R₂P)₂]X₆ (R = Ph, Cy, X = Cl⁻, Br⁻) undergo facile photoelimination of halogen. M−X bond activation and halogen elimination is achieved upon LMCT excitation of solutions of Au^III complexes in the presence of olefin chemical traps. As opposed to the typical one-electron redox transformations of LMCT photochemistry, the LMCT photochemistry of the Au^III centers allows for the unprecedented (i) two-electron photoelimination of X₂ from a monomeric center and (ii) four-electron photoelimination of X₂ from a bimetalllic center. The quantum yields for X₂ photoproduction, in general, are between 10% and 20% for all species, showing only minimal dependence on the identity of the ligands about gold, or the nuclearity of the complex. Efficient X₂ photoelimination is observed in the absence of a chemical trap, providing a rare example of authentic, trap-free halogen elimination from a transition metal center.