The d(8)center dot center dot center dot d(10) heterobimetallic [(PtAuI)-Au-II(dppm)(2)PhCl]PF6 (1) complex (dppm = bis(diphenylphosphino)methane) is oxidized by PhICl2 to give the d(7)-d(9) [(PtAuII)-Au-III(dppm)(2)PhCl3]PF6 (2) complex containing a Pt-III-Au-II bond. Facile M-X bond activation is achieved by irradiation of CH3CN solutions of 2 with visible light in the presence of 2,3-dimethyl-1,3-butadiene, inducing a two-electron reduction to regenerate 1.