CATALYSIS IN SUBSTITUTION ON RUTHENIUM(III) BY IODIDE

The kinetics of replacement of water by iodide on trans-[Ru(NH3)4(isn)H2O]3+ (isn=isonicotinamide) have been studied in 0.1 M acid at 25°C (reaction 1). In contrast to anation by chloride and bromide, which proceeds with simple first-order dependence on halide, the rate of iodide anation is given by-d In [RuIIIH2O]/dt=+ kh[I-]2. The first term arises from catalysis of substitution by [Ru(NH3)4(isn)H2O]2+ which is maintained at equilibrium with aquoruthenium(III), I-, and I3-. The second term is believed to indicate a presubstitution electron transfer (I-→Ru(lII)) not involving production of free iodine. The data give a value of 0.20±0.04 M-1 s-1 for the specific rate of iodide substitution on [Ru(NH3)4(isn)H2O]2+. Stopped-flow experiments give the rate of aquation of I- in [Ru(NH3)4(isn)I]+ as 0.91±0.17 s-1. The equilibrium quotient for reaction 1 was determined (86±4 M-1). © 1979, American Chemical Society. All rights reserved.