RATES OF OXIDATION OF SOME STERICALLY HINDERED PLATINUM(II) COMPLEXESBY HEXACHLOROIRIDATE(IV)

The oxidation reactions of mixed bisdiamineplatinum(II) complexes, [Pt (NN)(N'N')]2+, by [IrCl6]2-in the presence of chloride ions have been kinetically investigated in aqueous perchlorate medium (NN and/or N'N' = en, meen, s-dmen, alpha-dmen, trimen, tmen). In the absence of adde d [IrCl6]3- , the reaction rates fundamentally obey the rate law: -d[I rCl62-]/dt = 2{k(a)+k(b)[Cl-]}[Pt(NN)(N'N')2+][IrCl62-]. Hexachloroiri date-(III) lowers the rates in a way which is dependent on the concent ration of both [IrCl6]2 and Cl-. Steric hindrance of diamines is sugge sted to be the main factor that affects the reactivity of these comple xes towards oxidation. The reactivities (log k(b)) of the individual p latinum(II) complexes are roughly linearly related to the total steric hindrance surrounding the platinum(II) centre, as measured by an empi rical steric constant. Some indication of the relative tendency of the platinum(III) intermediates to undergo oxidation or reduction is also reported.