Halogen photoreductive elimination from gold(III) centers.

Monomeric complexes of the type Au(III)(PR(3))X(3) and bimetallic complexes of the type Au(2)(I,III)[mu-CH(2)(R(2)P)(2)]X(4) and Au(2)(III,III)[mu-CH(2)(R(2)P)(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.