Substitution Kinetics of [Fe(PDT/PPDT)_n(phen)_m]²⁺(n≠m;n,m= 1,2) with 2,2′-Bipyridine, 1,10-Phenanthroline, and 2,2′,6,2″-Terpyridine

Abstract

The triazines 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT), 3-(4-phenyl-2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PPDT), and 1,10-phenanthroline (phen) were coordinated to the Fe 2+ ion to form Fe(PDT) 2 (phen) 2+ (1), Fe(PPDT) 2 (phen) 2+ (2), Fe(PDT)(phen) 2+ 2 , (3) and Fe(PPDT)(phen) 2+ 2 (4). The complexes were synthesized and characterized by mass spectroscopy and elemental analysis. The rate of substitution of these complexes by 2,2 -bipyridine (bpy), 1,10-phenanthroline (phen), and 2,2 ,6,2 -terpyridine (terpy) was studied in a sodium acetate-acetic acid buffers over the range 3.6-5.6 at 25, 35, and 45°C under pseudo-first-order conditions. The reactions are first order with respect to the concentration of the complexes. The reaction rates increase with increasing [bpy/phen/terpy] and pH, whereas ionic strength has no influence on the rate of reaction. Plots of k obs versus [bpy/phen/terpy] and 1/[H + ] are linear with positive slopes and significant y-intercepts. This indicates that the reactions proceed by both dissociative as well as associative pathways for which the associative pathway predominates the substitution kinetics. Observed temperature-depended rate constants at the three temperatures at which substitution reactions were studied together with the protonation constants of the substituting ligands (phen, bpy, terpy) were used to evaluate the specific rate constants (k 1 and k 2 ) and thermodynamic parameters (E a , H # , S # , and G # ). The reactivity order of the four complexes depends on the phenyl groups present on the triazine (PDT/PPDT)Correspondence to: R. Bellam; e-mail: rajeshchowdarybellam@ gmail.com.Supporting Information is available in the online issue at www.wileyonlinelibrary.com.C 2017 Wiley Periodicals, Inc. SUBSTITUTION KINETICS OF [Femolecule. The π -electrons on phenyl rings stabilizes the charge on the metal center by inductive donation of electrons toward the metal center resulting in a decrease in reactivity of the complex, and the order is 1 < 2 < 3 < 4. The rate of substitution is also influenced by the basicity of the incoming ligand (bpy/phen/terpy), and it decreased in the order: phen > terpy > bpy. Higher rate constants, low E a values , and more negative entropy of activation (− S # ) values were observed for the associative path, revealing that substitution reactions at the octahedral iron(II) complexes by bpy, phen, and terpy occur predominantly by the associative mechanism. Density functional theory calculations support the interpretations.

Seven membered chelate Pt(ii) complexes with 2,3-di(2-pyridyl)quinoxaline ligands: studies of substitution kinetics by sulfur donor nucleophiles, interactions with CT-DNA, BSA and in vitro cytotoxicity activities

“…15 The relatively smaller enthalpy of activation (DH # ) values suggests that it is energetically favorable to form a bond in a bimolecular transition state. 16 It is also well-known that relatively large negative entropy of activation (DS # ) values signify the bimolecular nature of a transition state. Bond formation results in the formation of highly ordered and more compact transition state relative to reactants.…”

Effect of the extended π-surface and N-butyl substituents of imidazoles on their reactivity, electrochemical behaviours and biological interactions of corresponding Pt(ii)-CNC carbene complexes: exploring DFT and docking interactions

“…This is further reinforced by the large −Δ S # and positive Δ H # values ( vide supra Table 1) for the associatively activated mechanism for the chloride substitution by thiourea nucleophiles. 44,45…”

“…This is further reinforced by the large ÀDS # and positive DH # values (vide supra Table 1) for the associatively activated mechanism for the chloride substitution by thiourea nucleophiles. 44,45 The erudition of the role of the C^N^C pincer ligands on the rate was fostered by extending phenyl pendant rings and N-butyl arms, respectively on the cis position to the leaving group of the core C^N^C pincer ligand of PtL 2 and PtL 3 relative to the structure of PtL 1 . Comparing the rate constant values for the chloride substitution from the complexes (PtL 1 -PtL 3 ) with S-donor thiourea Nus (Table 1), all complexes follow the reactivity order PtL 3 o PtL 2 o PtL 1 .…”

Preparation of Some as-Triazines, Their Evaluation as Spectrophotometric Reagents and Determination of Trace Amount of Iron in Certain Food and Natural Samples

“…Ferroin functional group is quite selective reagent for iron. 1,2,4-triazines containing the ferroin-producing chromogen are highly sensitive to the formation of colorful complexes with iron (II) ions [13][14][15][16][17][18] . 1,2,4-triazines can be easily made in the laboratory using readily accessible, relatively inexpensive chemicals 13,19 .…”