Relative reactivity of N- and S-donor ligands in substitution reactions of aquaethylenedinitrilotetraacetatoruthenium(III) in aqueous solution

4-Sulfanylpyridine, a potential bridging ligand, reacted with [Ru(edta)(H2O)](-) following a facile aqua substitution path through S-co-ordination of the pendant thione group or through N-co-ordination. The substitution reaction was studied as a function of pH (O.4-5.0), temperature (25-45 degrees C), pressure (0.1 to 100 MPa) and concentration. Second-order rate constants for the N- and S-donor complex-formation reactions are 4950 +/- 60 and 1560 +/- 50 M-1 s(-1) at 25 degrees C respectively. The N-co-ordinated ruthenium(III) complex reacts to give the S-co-ordinated product with a rate constant of 0.07 +/- 0.02 s(-1) at 25 degrees C. Detailed kinetic studies, including the determination of all activation parameters (Delta H double dagger, Delta S double dagger and Delta V double dagger), revealed unambiguously that formation of the S-substituted product is favored thermodynamically, whereas that of the N-substituted product is favored kinetically. The N-co-ordinated complex reacts to give the S-co-ordinated complex via a dissociative process. Depending on the reaction conditions, mono-and weakly interacting asymmetric bi-nuclear complexes have been synthesized and characterized.