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-ordi nation of the pendant thione group or through N-co-ordination. The sub stitution reaction was studied as a function of pH (O.4-5.0), temperat ure (25-45 degrees C), pressure (0.1 to 100 MPa) and concentration. Se cond-order rate constants for the N- and S-donor complex-formation rea ctions are 4950 +/- 60 and 1560 +/- 50 M-1 s(-1) at 25 degrees C respe ctively. 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 dagg er and Delta V double dagger), revealed unambiguously that formation o f the S-substituted product is favored thermodynamically, whereas that of the N-substituted product is favored kinetically. The N-co-ordinat ed complex reacts to give the S-co-ordinated complex via a dissociativ e process. Depending on the reaction conditions, mono-and weakly inter acting asymmetric bi-nuclear complexes have been synthesized and chara cterized.