Thermodynamic investigation of the molecular interactions of 4-nitrophenol with free-bases meso-tetraarylporphyrins

The molecular interactions of 4-Nitrophenol (4NP) with free-base meso-tetraarylporphyrins (H₂T(4-X)PP; X = OCH₃, CH₃, H, Cl) have been studied. The formation constants and other thermodynamic parameters were calculated by using UV-Vis spectrophotometry titration results. The formation constants show the following trend relative to X substituent of porphyrins: H₂T(4-CH₃O)PP > H₂T(4-CH₃)PP > H₂TPP > H₂T(4-Cl)PP.     

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : III. Proton data at 100 MHz and the derived Hammett σ-constant of the trimethyltin group

Proton NMR data at 100 MHz are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, XC₆H₄Sn(CH₃)₃, where X = para-N(CH₃)₂, para-OCH₃, para-OC₂H₅, para-CH₃, meta-CH₃, -H, para-F, meta-OCH₃, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH₃)₃. Correlation coefficients with Hammett σ-constants of greater than 0.95 are obtained with the methyltin proton chemical shifts and coupling constants to carbon [¹J(¹³C¹H)] and tin [²J(SnC¹H)]. Solvent effects and other extraneous factors invalidate comparisons of ? values in terms of the relative attenuation of the transmission of substituent effects through homologous carbon, silicon, germanium and tin systems, but coupling constant data reflect a diminution of ca. one tenthfold per bond in the order ?[C(1)Sn] > ? [SnC] > ? [CH]. Satisfactory correlations (r > 0.95) are obtained in this series of closely-related compounds among the conventionally recorded two-bond, ²J(SnC¹H) and the constituent, one-bond ¹J (Sn¹³C) and J(¹³C¹H) coupling constants, but the correlation coefficient for the comparison between the two one-bond couplings, ¹J(Sn¹³C) and ¹J(¹³C¹H) is lower (r = 0.872). Changes in the couplings at the methyltin carbon bond tin-119 atoms are interpreted in terms of isovalent hybridization; a model based upon effective nuclear charges is tested with respect to both NMR coupling constants and ¹¹⁹Sn Mössbauer Isomer shifts at tin and is invalidated. Proton and carbon-13 NMR, chemical shift and coupling constant data are used to derive a Hammett σ-constant for the para-trimethyltin group of ?0.14, and the significance of this value is discussed.     

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : II. (119Sn-13C) coupling constants and 13C chemical shifts of meta- and para-derivatives

Carbon-13 NMR data are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, RC₆H₄Sn(CH₃)₃, where R = para-N(CH₃)₂, para-OCH₃, para-OC₂H₅, para-CH₃, meta-CH₃, -H, para-F, meta-OCH₃, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH₃)₃. In the para-derivatives, correlation coefficients with Hammet σ-constants of greater than ca. 0.9 are obtained with the tin-carbon couplings to methyl, C₁ and C₄ carbons, and with the carbon-13 chemical shifts δ(C(1)). In the meta-derivatives, the couplings |J(Sn-CH₃)|:, |:J(Sn-C(1))|:, |:J(Sn-C(3))|: and |:J(Sn-C(6))|:, and the shifts δ(C(1)) and δ(C(5)) correlate well with Hammett σ. In the para-derivatives, sensitivity to change in substituent falls off C(4) > C(3, 5) > C(1) > C(2, 6) > CH₃ as registered by the δ(C), while in the meta-derivatives δ(C) changes decrease C(3) > C(2), C(4) > C(1) > C(5), C(6) > CH₃. The magnitudes of the tin coupling constants decrease C(1) > CH₃ > C(3, 5) > C(2, 6) > C(4) in the para-derivatives, while in the meta-series the order is C(1) > CH₃ > C(3), C(5) > C(2) > C(6) > C(4). The two sets of one-bond |:J(Sn-CH₃)|: and |:J(Sn-C(1)|: values correspond closely to the 0.25/0.33 ratio of coefficients in the LCAO approach, and are interpreted in terms of s-electron redistributions at the tin atom with change in substituent.     

Thermodynamic studies of sitting-atop (SAT) complexation of uranyl and free base meso -tetraarylporphyrins

The interaction of uranyl with meso-tetraphenylporphyrin and its para-substituted derivatives (H₂t(4-X)pp, X : H, Br, Cl, CH(CH₃)₂, OCH₃, CH₃) in chloroform produced 1 : 1 sitting-atop (SAT) complexes ((uranyl)H₂t(4-X)pp). Formation constants were calculated by computer fitting of complex absorbance versus mole ratio data to appropriate equations and found to decrease with temperature increase. Thermodynamic parameters, ΔG ⁰, ΔH ⁰ and ΔS ⁰ were obtained. The formation constants vary with changing of the substituent on the aryl rings of H₂t(4-X)pp in the following order: (uranyl)H₂t(4-OCH₃)pp?>?(uranyl)H₂t(4-CH₃)pp?>?(uranyl)H₂t(4-CH(CH₃)₂)pp?>?(uranyl)H₂tpp?>?(uranyl)H₂t(4-Br)pp?>?(uranyl)H₂t(4-Cl)pp.     

Thermodynamic studies of sitting-atop complexation between free base meso-tetraarylporphyrins and antimony(III) chloride in chloroform

Interaction of para, meta and ortho-substituted meso-tetraarylporphyrins, (H₂t(X)pp, X: OMe, Me, H and Cl) with SbCl₃ in chloroform solution afforded 1 : 1 sitting-atop (SAT) complexes ([(SbCl₃)(H₂t(X)pp)]). The formation constants were calculated by KINFIT and found to decrease with increasing temperature. The thermodynamic parameters, ΔH°, ΔS° and ΔG°, were obtained. Formation constants of these complexes change with changing substituent (X) on the aryl rings of H₂t(X)pp in the following order: (SbCl₃)H₂t(4-OMe)pp >?(SbCl₃)H₂t(4-Me)pp >?(SbCl₃)H₂tpp >?(SbCl₃)H₂t(4-Cl)pp >?(SbCl₃)H₂t(3-OMe)pp >?(SbCl₃)H₂t(3-Me)pp> (SbCl₃)H₂t(2-OMe)pp >?(SbCl₃)H₂t(2-Me)pp.     

The role of water release from the cyclodextrin cavity in the complexation of benzoyl chlorides by dimethyl-β-cyclodextrin

The influence of temperature on the solvolysis of substituted benzoyl chlorides in the presence of dimethyl-β-cyclodextrin (DM-β-CD) was studied. Based on the influence of the DM-β-CD concentration on chemical reactivity in this process, the cyclodextrin has a catalytic effect on the solvolysis of 4-nitrobenzoyl chloride (4-NO₂) but an inhibitory effect on that of 4-methoxy-(4-MeO), 3-chloro-(3-Cl) and 3-trifluoromethyl-(3-CF₃) benzoyl chlorides. These disparate effects are related to a difference in reaction mechanism; thus, DM-β-CD catalyses associative solvolysis and inhibits dissociative solvolysis. Examining the influence of temperature on the solvolytic process allowed the stoichiometry of the host-guest complexes formed to be established. The formation constants for the complexes of meta-substituted benzoyl chlorides increased with increasing temperature. On the other hand, the equilibrium formation constants for the 1:1 host-guest complexes of para-substituted benzoyl chlorides exhibited the opposite trend. The equilibrium formation constant for 2:1 host-guest complexes for the para-substituted benzoyl chlorides increased with increasing temperature. These differences are ascribed to the release of water from the DM-β-CD cavity during the formation of the host-guest complex.     

ESR study of the free radical intermediates formed during the electrolytic process: III. Electrooxidation of substituted anilines

Active free radicals formed by the electrooxidation of substituted anilines RC₆H₄NH₂ (R = H, p-Br, p-Cl, p-I, p-Me, p-COOH, p-MeCO, p-NO₂, m-CO₂H, and m-Cl) are trapped by spin trap 2-methyl-2-nitroso propane (MNP). A multiple ESR signal of the solution containing electrolytic aniline and MNP is identified with the spin adduct of MNP and radical cation 1 by theoretical simulation of observed spectrum. Furthermore, ESR spectra of para- or meta-substituted anilines give a reasonable explanation about spin adducts of MNP and the cation 2 or 3 by the same method.     

Spectrophotometric Studies of the Thermodynamics of Molecular Complexation between Free Base Meso-Tetraarylporphyrins and Iodine(III) Chloride

A spectrophotometric method was used for the molecular complexation of ICl₃ with para-substituted meso-tetraarylporphyrins (H₂t(4-X)pp; X: OCH₃, CH(CH₃)₂, CH₃, H and Cl) in methanol/chloroform (2.5% v/v) solution. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically at various temperatures for 1:1 molecular complex formation of meso-tetraarylporphyrins as electron donors with ICl₃ as the electron acceptor. The formation constants for the molecular complexes change according to the following trend: [ICl₃(H₂t(4-OCH₃)pp)]>[ICl₃(H₂t(4-CH(CH₃)₂)pp)]>[ICl₃(H₂t(4-CH₃)pp)]>[ICl₃(H₂tpp)]>([ICl₃(H₂t(4-Cl)pp)]. Further, the thermodynamic parameters, ΔG ^o,ΔH ^o and ΔS ^o, for formation of the complexes were obtained.     

Design,Synthesis, and Biological Evaluation of Pyridazinones Containing the (2-Fluorophenyl) Piperazine Moiety as Selective MAO-B Inhibitors

Twelve pyridazinones (T1–T12) containing the (2-fluorophenyl) piperazine moiety were designed, synthesized, and evaluated for monoamine oxidase (MAO) -A and -B inhibitory activities. T6 was found to be the most potent MAO-B inhibitor with an IC₅₀ value of 0.013 µM, followed by T3 (IC₅₀ = 0.039 µM). Inhibitory potency for MAO-B was more enhanced by meta bromo substitution (T6) than by para bromo substitution (T7). For para substitution, inhibitory potencies for MAO-B were as follows: -Cl (T3) > -N(CH₃)₂ (T12) > -OCH₃ (T9) > Br (T7) > F (T5) > -CH₃ (T11) > -H (T1). T6 and T3 efficiently inhibited MAO-A with IC₅₀ values of 1.57 and 4.19 µM and had the highest selectivity indices (SIs) for MAO-B (120.8 and 107.4, respectively). T3 and T6 were found to be reversible and competitive inhibitors of MAO-B with K_i values of 0.014 and 0.0071, respectively. Moreover, T6 was less toxic to healthy fibroblast cells (L929) than T3. Molecular docking simulations with MAO binding sites returned higher docking scores for T6 and T3 with MAO-B than with MAO-A. These results suggest that T3 and T6 are selective, reversible, and competitive inhibitors of MAO-B and should be considered lead candidates for the treatment of neurodegenerative disorders like Alzheimer’s disease.     

Thermodynamic study of complex formation process of free base meso-tetraphenylporphyrins with dimethyl and dibutyltin(IV) dichloride: a new algorithm for a single thermometric titration

A novel, fast and easy single sample measurement has been developed based upon temperature dependence of equilibrium constant in order to determine the enthalpy and entropy changes of a complexation reaction using spectrophotometric temperature titration. The method can be used in determination of the formation constant and thermodynamic parameters of the solutions that there are difficulties in their titration where volatile compounds are studying. Knowledge of component spectra is not required for the analysis. The formation constants of the interactions of ß-di and tri-brominated meso-tetraphenylporphyrins, and meso-tetrakis(4-methylphenyl) and (4-methoxyphenyl) porphyrins with Me₂SnCl₂ and Bu₂SnCl₂, have been determined in range of 0–25 °C utilizing van’t Hoff relation, mass balance and equilibrium constant equations by an iterative least squares method with ΔH ⁰ as adjustable parameter. The outputs of analysis are the equilibrium constants, ligand and adduct spectral profiles, their concentrations as a function of temperature, the adjusted values of the standard enthalpy ΔH ⁰, and entropy ΔS ⁰ changes. The order of formation constants of the resulting 1:1 complexes decreased with increasing number of bromide substituents and increased with adding methyl and methoxy groups, and vary as H₂T(4-CH₃O)PP > H₂T(4-CH₃)PP > H₂TPP > H₂TPPBr₂ > H₂TPPBr₃ and Me₂SnCl₂ > Bu₂SnCl₂.     

Complexes of Copper(II) Aryl Carboxylates with Picoline N-Oxides

Copper(II) aryl carboxylates on interaction with 2-picoline N-Oxide (2-picNO), 3-picoline N-Oxide (3-picNO) and 4-picoline N-Oxide (4-picNO) in acetone or ethyl acetate yield 1:1 adducts. These are regarded as binuclear bridged complexes of composition Cu₂(RC₆H₄COO)₂L₂ where R is o-, m-, p-CH₂; o-, m-Cl: o-NO₂; m-, p-CH₂O; and L is 2-, 3-, and 4-picNO ligand. With 4-picNO some 1:2 adducts have also been obtained.     

The electronic effect in supramolecular self-assembly of <Emphasis Type="Italic">para-</Emphasis>substituted tetraphenylporphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) by coordinative bonding

The supramolecular self-assembly of para-substituted tetraphenylporphyrin complexes of zinc(II), Zn(p-X)TPP, with imidazolyl-linked porphyrinatomanganese(III), Mn(p-lmBPTPP)Cl, driven by coordinative bonding has been investigated by fluorescence spectra, electrospray mass spectrometry, ¹H-n.m.r. and u.v.–vis. spectra. The association constants of the supramolecular complexes, K_c, were calculated using fluorescence spectroscopic titration data at suitable dilute concentration ranges in which the fluorescent quenching of Zn(p-X)TPP by Mn(p-ImBPTPP)Cl is a static process. The electronic effect in the supramolecular self-assembly of para-substituted . porphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) is discussed. The non-linear dependence of log K_c on the Hammett constants was found, which suggested that the electronic effect in para-substituents of tetraphenylporphyrin complexes of zinc(II) is an important, but not a sole factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes. The results indicate that the closed conformation of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complex is another important factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes.     

Theoretical study of Diels-Alder reaction: Role of substituent in regioselectivity and aromaticity

A comparative study on the influence of the substituents on the Diels-Alder reaction was performed. The energy profiles for 11 sets of Diels-Alder reaction between monosubstituted derivatives of butadiene and ethylene have been studied and the structures of all transition states were located at B3LYP/6-31+G* level. Four pathways were independently investigated; the reaction between substituted ethylene and 1-substituted butadiene leading to ortho (a ₁) and meta (a ₂) adducts, and in the same manner, the reaction between substituted ethylene and 2-substituted butadiene yields para (b ₁) and meta (b ₂) adducts. Inspection of both the activation barriers and the reaction energies for 44 reactions revealed that the pathway b ₁ is both thermodynamically and kinetically more favorable in all types of Diels-Alder reactions; while the pathway a ₁ can be labeled only as kinetic pathway. The aromaticity of all 44 transition state structures was measured using para delocalization index to study the effect of aromaticity on the reaction path. The calculations suggest that in normal and neutral DA reactions there is a gain in aromatic stabilization of the transition state which reduces slightly the activation barrier of the kinetic pathway a ₁.     

Reactions of palladium(II) cyclometallated benzylideneaniline Schiff's bases. Some relative rates for the synthesis of ortho-substituted carbomethoxy derivatives via CO insertion

The synthesis and characterisation of the complexes [(p-CH₃C₆H₄NCH($\text{C}{}_6\text{H}{}_3\text{Y))P}$d(OAc)]₂ (II) are reported. These complexes react at very different rates with carbon monoxide in methanol to give the ortho-substituted esters, p-CH₃C₆H₄NCHC₆H₃Y - 2R, R = CO₂CH₃, with electron withdrawing Y substituents slowing the reaction. The ¹³C{¹H} data for II show a linear correlation of δ(C(2)) in the 5′-complexes (Y trans to PdC) with δ(C(4)) of monosubstituted benzene compounds. For Y = 5′-NO₂, 4′-NO₂ and 4′-Cl, the bis complex [{p-CH₃C₆H₄NCH(

is formed in a secondary reaction.     

Synthesis of sitting‐atop type adducts of diphenyl and dimethyltin(IV) dihalides with meso‐tetraarylporphyrins

Some molecular adducts of dimethyltin(IV) dichloride, diphenyltin(IV) dichloride and diphenyltin(IV) dibromide with para‐substituted meso‐tetraphenylporphyrin have been prepared. This adducts with general formula [(Me₂SnCl₂)₂H₂T(4‐X)PP], [(Ph₂SnCl₂)₂H₂T(4‐X)PP], and [(Ph₂SnBr₂)₂H₂T(4‐X)PP]; {X= CH₃O, CH₃, H, and Cl} have been synthesized and characterized by means of ¹H NMR, UV‐Vis, and elemental microanalysis methods.     

Exchange of organometallic compounds with mercury metal : VI. Substituted diarylthallium cations; evidence for intermediate ArTl+HgAr species

Substituted diphenylthallium chlorides, (XC₆H₄)₂T1C1 (X = p-OCH₃, p-CH₃, m-CH₃, H, p-Cl, p-CH₃COO) have been prepared. Polarography and chronopotentiometry were used for study of electrochemical reduction and interaction of these compounds with mercury metal. Intermetallic cations, ArTl⁺HgAr, were shown to be intermediates in the transmetallation reaction between Ar₂Tl⁺ and mercury metal:

     

Organo group VB chemistry : IV. vibrational study of some tertiary substituted aryl-group VB compounds

The IR and Raman spectra of a series para- and meta-substituted aryl-Group VB compounds (XC₆H₅)₃M (X = Cl, F) (M = P, As, Sb, Bi) measured over the spectral range 4000 to 100 cm^-1, are reported. The results of a complete vibrational analysis are used to discuss the identification of the products. The shifts of substituent-sensitive vibrations are discussed.     

Syntheses of (η6-p-cymene)ruthenium(II) piano-stool amine complexes: molecular structure of [(η6-C10H14)RuCl2(H2N-C6H4-p-Cl)]

The dimeric complex [{(η⁶-p-cymene)Ru(μ-Cl)Cl}₂] (1) reacts with S,N-donor Schiff base ligands, para-substituted S-(thiophen-2-ylmethylene)phenylamines in methanol to give mononuclear amine complexes of the type [(η⁶-p-cymene)RuCl₂(NH₂–C₆H₄–p-X)] {X?=?H (2a); X?=?CH₃ (2b); X?=?OCH₃ (2c); X?=?Cl (2d); Br (2e) X?=?NO₂ (2f), respectively} by hydrolysis of the imine group of the ligand after coordination to the metal. The complexes were characterized by analysis and IR and NMR spectroscopy. The molecular structure of [(η⁶-C₁₀H₁₄)RuCl₂(H₂N–C₆H₄–p-Cl)] (2d) was established by a single-crystal X-ray diffraction study.     

Double nucleophilic attack on η6-arene(pentamethylcyclopentadienyl)iridium dications. Routes from substituted benzenes to substituted cyclohexenes by addition of two hydrides and two protons

The complexes [(C₅Me₅)Ir(η⁶-arene)][BF₄]₂ (arene = toluene, toluene-d₈, t-butylbenzene, methoxybenzene, chlorobenzene, o-xylene, p-xylene, tetralin and phenol) were prepared from the arene and reduced with NaBH₄ to the η⁵-cyclohexadienyl complexes. Attack was exo at the arene and, with one exception, never at the substituent. Toluene showed no site preference but t-butylbenzene was attacked preferentially para, and chlorobenzene, ortho. Methoxybenzene was attacked ipso as well as ortho, meta (predominant), and para, and phenol gave only the meta-isomer. p-Xylene gave one isomer and o-xylene and tetralin gave two. Further reduction occurred on reaction with stronger hydride reducers (e.g., sodium bis(methoxyethoxy)dihydroaluminate) to give mixtures of 1- and 2-substituted cyclohexa-1,3-diene complexes (t-Bu, 2- ( > 95%); Me, 1- (25%), 2- (75%); Cl, 1- ( > 95%); and OMe, 1- (33%), 2- (67%)). The p-xylene complex gave a mixture of the η⁴-1,4-dimethylcyclohexa-1,3- and 1,4-diene complexes. Reaction of the cyclohexadiene complexes with HCl gas gave the free substituted cyclohexenes and [(C₅Me₅Ir)₂Cl₄]. The product from t-butylbenzene was predominantly (92%) the 3-substituted cyclohexene; that isomer (65%) and the 1-isomer (34%) were formed from toluene and the 1- (34%) and the 4-isomer (58%) were formed from chlorobenzene. Phenol gave only cyclohexanone. Overall these reactions yield the cyclohexene from the substituted benzene by addition of two hydrides and two protons and the iridium can be recycled.     

Application of the Seth-Paul-Van Duyse equation—I : A simple relation defining new X+(R) substituent constants on the basis of electrophilic σ+ constants

The Seth-Paul-Van Duyse equation (SPVDE) correlating the CO stretching frequencies of a great number of R₁COR₂ molecules with X (R) substituent constants has been reinvestigated. A simple empirical relation defining new X⁺(R) constants on the basis of electrophilic σ constants has been derived: X⁺ (R) = 0·238 σ⁺ + 1·077. The three earlier reported relationships between the X(R) constants and Hammett σ values have been replaced by this single relationships and a set of new X⁺(R) constants has been calculated. The new X⁺(R) constants applied to 287 R₁COR₂ compounds containing the para- or meta-substituted benzene rings fit very well the SPVDE. It has been possible to extend the SPVDE to various aromatic systems.