Ligand control on molecular oxygen activation by rhodium quinone complexes

Reaction of 9,10-phenanthrenequinone with [Rh(PPh3)(3)Cl] afforded a peroxysemiquinonate complex of rhodium(III) (1), presumably via the formation of a reactive rhodium(II)-semiquinone intermediate followed by reaction with molecular oxygen. Similar reaction of [Rh(PPh3)(3)Cl] with a more oxidizing quinone, viz. 3,4,5,6-tetrachloro-1,2-benzoquine, however, yielded a stable catecholate complex of rhodium(III) (2).