An investigation of comparative substitution behavior of bifunctional trans‐platinum(II) complexes with symmetric and asymmetric alkylamine ligands. Issue 12 (4th August 2020)

• Record Type: Journal Article
• Authors: Olusegun, Moses Ariyo; Reddy, Desigan; Jaganyi, Deogratius
• Is Part Of: International journal of chemical kinetics. Volume 52:Issue 12(2020)
• Page Start: 884
• Page End: 892
• Publication Date: 2020-08-04
• Subjects: anticancer -- kinetics -- ligand substitution -- mononuclear -- trans‐platinum complexes; Chemical kinetics -- Periodicals; 541.394
• DOI: 10.1002/kin.21407
• Languages: English
• ISSNs: 0538-8066

Abstract

Abstract: This study was undertaken to investigate the comparative substitution behavior of mononuclear trans‐ platinum(II) complexes with symmetric and asymmetric amine ligands. The rate of substitution of the aqua moeities from the complexes trans ‐[Pt(NH3 )2 (H2 O)2 ](ClO4 )2 (tPt), trans ‐[Pt(NH3 )(NH2 C2 H5 )(H2 O)2 ](ClO4 )2 (tPt2H2 O), trans‐ [Pt(NH3 )(NH2 C3 H7 )(H2 O)2 ](ClO4 )2 (tPt3H2 O), [ trans ‐Pt(OH2 )2 (NH2 CH3 )2 ](ClO4 )2 (tPtM), and [ trans ‐Pt(OH2 )2 {NH2 CH(CH3 )2 }2 ](ClO4 )2 (tPtR), by three nucleophiles, namely thiourea (TU), 1, 3‐dimethylthiourea (DMTU), and 1, 1, 3, 3‐tetramethylthiourea (TMTU) was studied under pseudo–first‐order conditions as a function of concentration and temperature by stopped‐flow spectrophotometry. All the substitution reactions of each of the trans ‐platinum(II) complexes proceeds by a stepwise mechanism involving rate‐determining substitution of the first aqua ligand followed by a fast second substitution step, without any intermediates formed. The reactions were second order overall (rate = k obs [complex] where k obs = k 2 [nucleophile]), first order in both [complex] and [nucleophile]. The reactivity of the complexes was essentially governed by both steric and electronic factors. Comparing the second‐order rate constants for the substitution reactions of the mononuclear diaqua trans ‐platinum(II) complexes with the thiourea‐based nucleophiles, the observed trend follows: tPt > tPt2H2 O > tPtM > tPt3H2 O > tPtR. This reactivity trend is consistent with the p K a values obtained for the first deprotonation step. The reactivity of the nucleophiles with the complexes decreases with an increase in steric demand in the following order: TU > DMTU > TMTU. The low positive values of activation enthalpy and large negative values of activation entropy indicate an associative mechanism of substitution in all the complexes. The computational modeling using density functional theory calculations was employed to provide theoretical interpretation of kinetic data.