A unique mode of molecular oxygen activation, involving metal-ligand cooperation, is described. Ir pincer complexes [((BuPNP)-Bu-t)Ir(R)] (R = C6H5 (1), CH2COCH3 (2)) react with O-2 to form the dearomatized hydroxo complexes [((BuPNP)-Bu-t*)Ir(R)(OH)] ((t)BuPNP* = deprotonated (BuPNP)-Bu-t ligand), in a process which utilizes both O-atoms. Experimental evidence, including NMR, EPR, and mass analyses, indicates a binuclear mechanism involving an O-atom transfer by a peroxo intermediate.