Halogen Photoreductive Elimination from Gold(III) Centers

Monomeric complexes of the type Au-III(PR3)X-3 and bimetallic complexes of the type Au-2(I,III)[u-CH2(R2P)(2)]X-4 and Au-2(III,III)[u-CH2(R2P)(2)]X-6 (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 X-2 from a monomeric center and (ii) four-electron photoelimination of X-2 from a bimetalllic center. The quantum yields for X-2 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 X-2 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.