Kinetic and mechanistic studies on the substitution of aqua ligands from diaquaethylenediamineplatinum(II) ion by vicinal dioximes

Abstract

Kinetics of aqua ligand substitution from diaquaethylenediamineplatinum(II) ion by three vicinal dioximes, namely dimethylglyoxime, 1,2-cyclohexanedione dioxime, and a-furil dioxime have been studied spectrophotometrically in the 40-55°C temperature range. All the above substitution reactions have been monitored at 297, 298, and 314 nm where the differences in absorbances between the reactant and products are maximum. At pH 4.0, all the three reactions have been found to proceed via two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentrations of ligands: first step is [ligand] dependent but the second step is [ligand] independent. The rate constants for the processes are k 1 * 10 -3 and k 2 * 10 -5 s -1 . The activation parameters, calculated from Eyring plots, suggest an associative mechanism for the interaction processes. From the temperature dependence of the outer sphere association equilibrium constants (K E ) for the first step, the thermodynamic parameters were also calculated, which gives a negative DG 0 1 value at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex in the first step. The products of the reactions have been characterized with the help of Job's method, IR and ESI-MS spectroscopic analysis. Graphical abstract

Relative reactivity of N,N-donor ligands in substitution reactions of cis-diaqua(2-aminomethylpiperidine)platinum(II): a detailed kinetic and mechanistic study

“…The rate constant for the first step, A → B was calculated from the absorbance data using the Origin 6.0 software, as discussed in our previous work. 22 The rate increases for all the three studied systems with increases in [ligand] before reaching a limiting value, (Figures 4, S2 and S3, Supplementary Information) which is probably due to the completion of the outer-sphere association complex formation through H-bonding.…”

“…The kinetic measurements of these systems were done according to our previous work. 22 In this work the nature of the two typical plots (ln(A ∞ − A t ) vs time and ln vs time) are also the same as discussed in our previous work. 22 Origin software was used for computational analysis.…”

“…22 In this work the nature of the two typical plots (ln(A ∞ − A t ) vs time and ln vs time) are also the same as discussed in our previous work. 22 Origin software was used for computational analysis. Rate data, represented as an average of duplicate runs, were reproducible to within ±4%.…”

“…Based on Scheme 2, a rate expression can be derived as discussed in the earlier paper. 22 Depending upon the final equation as stated below.…”

Dramatic Effect of A Ring Size of Alicyclic α-Dioximate Ligand Synthons on Kinetics of the Template Synthesis and of the Acidic Decomposition of the Methylboron-Capped Iron(II) Clathrochelates

“…Indeed, the above clathrochelates quantitatively form in the diluted aqueous and/or aqueous–organic solutions in a wide range of the corresponding semiconversion reaction times, thus allowing their photometrical detection using the characteristic of this type of the quasiaromatic polyazomethine complexes intensive metal-to-ligand charge transfer (MLCT) Fed→Lπ* bands in the visible range with maxima at approximately 450 nm. Such experimental conditions seem to be more beneficial than those known from the literature [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ] for their oximate and amine analogs. Recently, we performed [ 6 ] a detailed study of the kinetics and thermodynamics of both the template synthesis and the acidic decomposition of the macrobicyclic iron(II) tris-cyclohexanedion-1,2-dioximate (nioximate, Nx 2− ) FeNx 3 (BCH 3 ) 2 that is formed by a cross-linking with methylboronic acid.…”