NMR study of the leaving ligand and solvent effects on the solvolysis of (μ-oxo)bis(μ-acetato)diruthenium(III) complexes

Abstract A mechanistic 1 H NMR kinetic study on the solvolysis of complexes [Ru 2 (μ-O)(μ-O 2 CCH 3 ) 2 (4-picoline) 6 ](PF 6 ) 2 ( 1 ), [Ru 2 (μ-O)(μ-O 2 CCH 3 ) 2 (pyridine) 6 ](PF 6 ) 2 ( 2 ), and [Ru 2 (μ-O)(μ-O 2 CCH 3 ) 2 (4-picoline) 4 (pyridine) 2 ](PF 6 ) 2 ( 3 ) in DMSO-d 6 , CD 3 OD and CD 3 CN was carried out. All rate constants were calculated from the kinetic data, which fit in a series of reversible pseudo first order and second order reactions. The comparative kinetic study and the large Δ H ‡ and positive Δ S ‡ values for all solvolysis support the dissociative nature of the ligand exchange mechanism. The leaving ligand effect, determined by comparison of the forward reactions for complexes 1 and 3 , showed that the rate constants for 4-picoline substitution are smaller than for pyridine. An apparent contradiction with the proposed mechanism for the reverse reaction in DMSO-d 6 where the less basic ligand coordinates faster, was explained by a ligand–solvent interaction, which was demonstrated by our kinetics results, molecular modeling and through the determination of diffusion coefficients in DMSO-d 6 and CD 3 OD using DOSY.