Mechanistic aspects of ligand substitution incis-diaquabis(bipyridine)ruthenium(II) ion by acetyl acetone

Abstract

The effects of pH, temperature, acetyl acetone (acacH) concentration and substrate complex concentration on the rate of aqua ligand substitution in the title complex in aqueous medium have been studied. The following rate expression is proposed for the 5.0–6.5 pH range. $$\begin{gathered} d[Ru(bipy)_2 (acac)^ + ]/dt \hfill \\ = \frac{{k_1 k_2 [Ru(bipy)_2 (H_2 O)_2^{2 + } ][(acacH]}}{{k_{ - 1} + k_2 [(acacH]}} \hfill \\ \end{gathered} $$ where k1 is the water dissociation rate constant of the substrate complex, k−1 is the aquation rate constant and k2 is the ligand capture rate constant of the reaction intermediate. Activation parameters were obtained from Eyring plots and are compared with other systems. The reaction rates increase with an increase in pH and temperature, whereas the ionic strength has little effect. A mechanism involving unimolecular activation is proposed.