MERCURY(II)-CATALYZED AQUATION OF FAC-RHCL3(OH2)3 IN AQUEOUS-SOLUTION

In the presence of excess Hg2+ ion, the title complex in strongly acidic aqueous solution changes fairly rapidly to cis-RhCl2(OH2)4+ at room temperature. Subsequent catalyzed aquations to produce successively RhCl(OH2)52+ and Rh(OH2)63+ are much slower, and all three steps are readily separable kinetically. The reaction mechanism appears to involve preassociation of Hg2+ with the parent complex and each of its two chloride-containing products, followed by dissociative interchange of water for HgCl+. The rate law for each step thus takes the form kobsd=kK[Hg2+]/(1+K[Hg2+]). By determining Kobsd over a range of [Hg2+] values, it is possible to evaluate both the interchange rate constants (k) and the reactant association constants (K). The latter are essentially temperature independent over the experimental range and have the values 137±5, 10.0±1.0, and 3.0±0.6 M-1 for the tri-, di-, and monochloro species, respectively. The corresponding interchange rate constants at 40°C are (10.7±0.4)X10-3, (4.3±0.3)X10-5, and (8.9±1.8)X10-6 s-1. These have the following temperature parameters, respectively: ΔH‡ (kcal mol-1), 19.0±0.4, 22.2±0.7, and 23.3±0.3; ΔS‡ (cal deg-1 mol-1), -6.4±1.5, -7.5±2.2, and -5.0±0.9. Some significant comparisons are made with recently published studies of Hg(II)-catalyzed reactions of several haloaminerhodium(III) complex ions. © 1979, American Chemical Society. All rights reserved.