Kinetics and mechanistic studies of the interaction of thiosulfate with cis-diaqua-bis[1-alkyl-2-(arylazo)imidazole]ruthenium(II) complexes |
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| Authors: | Harasit Kumar Mandal Pradip Kumar GhoshAmbikesh Mahapatra |
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| Affiliation: | Department of Chemistry, Jadavpur University, Kolkata 700 032, India |
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| Abstract: | The nucleophilic substitution reaction of S2O32− with [Ru(HaaiR′)2(OH2)2](ClO4)2 (1) [HaaiR′ = 1-alkyl-2-(phenylazo)imidazole] and [Ru(ClaaiR′)2(OH2)2](ClO4)2 (2) [ClaaiR′ = 1-alkyl-2-(chlorophenylazo)imidazole] [where R′ = Me(a), Et(b) or Bz(c)] in acetonitrile–water (50% v/v) medium to yield Na2[Ru(HaaiR′)2(S2O3)2] (3a, 3b or 3c) and Na2[Ru(ClaaiR′)2(S2O3)2] (4a, 4b or 4c) has been studied. The products were characterized by microanalytical data and spectroscopic techniques (UV–Vis, NMR and mass spectroscopy). The reaction proceeds in two consecutive steps (A → B → C); each step follows first order kinetics with respect to each complex and S2O32−, and the first step second order rate constant (k′2) is greater than the second step one (k″2). An increase in the π-acidity of the ligand increases the rate. Thermodynamic parameters, the standard enthalpy of activation (Δ‡H0) and the standard entropy of activation (Δ‡S0), have been calculated for both steps using the Eyring equation from variable temperature kinetic studies. The low Δ‡H0 and large negative Δ‡S0 values indicate an associative mode of activation for both aqua ligand substitution processes. |
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| Keywords: | Kinetic elucidation ctc-Ru(II) complex π-Acidity Thiosulfate Substituent effect Ru&ndash OH2 cleavage |
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