OXIDATION OF [OS(NH3)5CO]2+ TO [(OS(NH3)4CO)2N2]4+

The oxidation of [Os(NH3)5CO]2+in acidic solution by Ce(IV) when the molar ratio of the two reagents is 1.0 or slightly less yields the µ-dinitrogen species [(Os(NH3)4CO)2N2]4+, almost quantitatively. Under these concentration conditions, [Os(NH3)5CO]3+first forms rapidly and quantitatively and then disproportionates to the binuclear product and [Os-(NH3)5CO]2+at a rate which is second order in [Os(III)] and inverse in [0s(NH3)CO2+]. This evidence points to an irreversible first-order change in an Os(IV) species as being rate determining but leaves open the question of whether the coupling occurs in the Os(IV) product of the rate-determining step or in an Os(V) state which might result from the oxidation of the Os(IV) by [Os(NH3)4CO]3+. It is suggested that deprotonation of coordinated ammonia keeps the Os-CO bond intact, in spite of the increase in oxidation state for osmium. The yields of the binuclear species are high also on oxidation at an anode or using K2S2O8, and the last named reagent leads to a simple high-yield preparation of the binuclear ion. © 1979, American Chemical Society. All rights reserved.