Iodination of triazenide-bridged rhodium and iridium complexes:: oxidative addition vs. one-electron oxidation

The triazenide-bridged tetracarbonyls [(OC)(2)Rh(mu-p-MeC6H4NNNC6H4Me-p)(2)M(CO)(2)] (M = Rh or Ir) undergo oxidative addition of iodine across the dimetal centre, giving the [RhM](4+) complexes [I(OC)(2)Rh(mu-p-MeC6H4NNNC6H4Me-p)(2)M(CO)(2)I], structurally characterised for M = Ir. The anionic tricarbonyl iodide [I(OC)Rh(mu-p-MeC6H4NNNC6H4Me-p)(2)Rh(CO)(2)](-) forms [I-2(OC) Rh(mu-p-MeC6H4NNNC6H4Me-p)(2)Rh(CO)I]-by initial one-electron transfer whereas the analogous tricarbonyl phosphine complexes [(OC)(Ph3P) Rh(mu-p-MeC6H4NNNC6H4Me-p)(2)M(CO)(2)] (M = Rh or Ir) undergo bridge cleavage, giving mononuclear [Rh(p-MeC6H4NNNC6H4Me-p)I-2(CO)(PPh3)] and dimeric [I(OC){RNNN(R)C(O)}M(mu-I)(2)M{C(O)N(R)NNR}(CO)I] (M = Rh or Ir, R = C6H4Me-p) in which CO has been inserted into a metal-nitrogen bond.