Benzotriazole complexes with amines and phenol: cooperativity mediated by induction effects in the crystal state

[structure: see text] Benzotriazole forms complexes of different stoichiometries with amines and phenols. Four of them have been characterized by single-crystal X-ray diffraction. The trends of donor-acceptor hydrogen-bond distances between corresponding molecular entities in the different complexes are related to induction-mediated cooperativity effects.     

Absorption spectrometric and thermodynamic study of charge transfer complexes of menadione (Vitamin K3) with a series of phenols

The electron donor-acceptor (EDA) interactions between menadione (i.e., 2-methyl-1,4-naphthoquinone, which is also called 'Vitamin K3') and a series of phenols (viz., phenol, resorcinol and p-quinol) have been studied in CCl4 medium. In all the cases, charge transfer (CT) bands have been located. The CT transition energies (h nu(CT)) of the complexes are found to change systematically with change in the number and position of the -OH groups in the aromatic ring of the phenol moiety. From the trends in the h nu(CT) values, the Hückel parameters (h(O) and k(C-O)) for the -OH group have been obtained. The CT transition energies are well correlated with the ionisation potentials of the phenols. From an analysis of this variation the electron affinity of Vitamin K3 has been found to be 2.28 eV. The stoichiometry of the complexes in each case has been found to be 1(menadione):2 (phenol). Formation constants of the complexes have been determined at four different temperatures from which the enthalpies and entropies of formation of the complexes have been estimated.     

Fluorescence Studied of Dissociation Constant of Cyclodextrin With Phenol Derivatives

α-and β-cyclodextrins consisting of six and seven glucose residues respectively, have lipophilic cavities with different inner diameters. They form host-guest inclusion complexes with hydrophobic organic and organometallic guest molecules in aqueous solution. These host-guest complexes have proved to be excellent model systems for studying the nature of noncovalent bonding forces in aqueous media. They have provided valuable insights into the hydrophobic effect and London dispersion forces and are good model for understanding the specificity of enzyme substrate interactions [1] Evidence for the formation of inclusion complexes have been provided from calovimetric titration [2] NMR[33], circular dichroism[4], U V[1] and fluorescence spectra[5] and conductometric method[6] etc. H ere we report a new fluorimetric method for a study on the reaction of the host-guest inclusion complexes of cyclodextrin with phenols. Dissociation constants (Kd) of the inclusion complexes of some phenols with α-β-cyclodextrin are estimated based on the variation of the fluorescent intensity and modified Harad' equations.     

Untersuchungen zur anwendung ternärer komplexe in der photometrie—IV: Das chelat FeY− (H4Y = EDTE) als reagens für phenole

Both theoretical considerations and experimental investigations have shown the iron(III)-EDTA complex to be a useful reagent for phenols, many of which form strongly-coloured ternary complexes with the proposed reagent, as well as weaker binary complexes with iron(III) alone. The sensitivity, selectivity (towards phenols as a group) and reproducibility of the proposed method are such that it can be firmly recommended.     

三辛胺萃取多元酚的研究

采用三辛胺为络合剂，苯或正辛醇为稀释剂研究了邻苯干分配，间苯三酚稀溶液的萃取相平衡，讨论了稀释剂，溶液ｐＨ值和硫酸钠度对分配系数的影响。确定了萃合物的组成，负载有机相的红外谱图分析表明，三辛胺与酚类的萃取同时存在氢键缔合溶剂化和离子缔合成盐历程。     

超分子体系中的分子识别研究(Ⅻ)──环糊精及环糊精双核铜配合物对4-取代苯酚的分子识别

用分光光度滴定法在25.0℃时测定了不同pH值下α-,β-,γ-环糊精以及1mol/LNaOH水溶液中α-和β-环糊精双核铜配合物与4-取代苯酚形成超分子配合物的稳定常数.化学计量法表明,主体环糊精及环糊精双核铜配合物与客体4-取代苯酚形成了1：1的超分子配合物.从主-客体间的尺寸关系、pH值、多点识别和诱导契合作用等因素讨论了环糊精及环糊精双核铜配合物对客体4-取代苯酚的分子识别机制.结果表明,β-环糊精双核铜配合物对4-取代苯酚具有特殊的键合能力和分子选择性。     

Molecular complexes of phenols with DDQ

Molecular complexes of phenols with DDQ have been studied spectrophotometrically in the temperature range of 10–30‡C in a solvent (CHC1₃) of low polarity under low donor concentrations. All the complexes exhibit one CT band each in the wavelength region where acceptor and donor do not have any absorption. The complexes are inferred to be of the π2π type and have R_y configuration in which the donor molecular orbital encompasses the substituent. The ionization potentials of the donors, the stability constants and thermodynamic parameters of the complexes have been evaluated.     

Oxidation mechanism of phenols by dicopper-dioxygen (Cu(2)/O(2)) complexes

The first systematic studies on the oxidation of neutral phenols (ArOH) by the mu-eta(2):eta(2)-peroxo)dicopper(II) complex (A) and the bis(mu-oxo)dicopper(III) complex (B) supported by the 2-(2-pyridyl)ethylamine tridentate and didentate ligands L(Py2) and L(Py1), respectively, have been carried out in order to get insight into the phenolic O-H bond activation mechanism by metal-oxo species. In both cases (A and B), the C-C coupling dimer was obtained as a solely isolable product in approximately 50% yield base on the dicopper-dioxygen (Cu(2)/O(2)) complexes, suggesting that both A and B act as electron-transfer oxidants for the phenol oxidation. The rate-dependence in the oxidation of phenols by the Cu(2)/O(2) complexes on the one-electron oxidation potentials of the phenol substrates as well as the kinetic deuterium isotope effects obtained using ArOD have indicated that the reaction involves a proton-coupled electron transfer (PCET) mechanism. The reactivity of phenols for net hydrogen atom transfer reactions to cumylperoxyl radical (C) has also been investigated to demonstrate that the rate-dependence of the reaction on the one-electron oxidation potentials of the phenols is significantly smaller than that of the reaction with the Cu(2)O(2) complexes, indicative of the direct hydrogen atom transfer mechanism (HAT). Thus, the results unambiguously confirmed that the oxidation of phenols by the Cu(2)O(2) complex proceeds via the PCET mechanism rather than the HAT mechanism involved in the cumylperoxyl radical system. The reactivity difference between A and B has also been discussed by taking account of the existed fast equilibrium between A and B.     

Some Cyclopentadienyl and Indenyl Niobium(V) Phenoxides

Some cyclopentadienyl and indenyl niobium(V) phenoxides are reported in this communication. The effect of different types of groups in the phenoxide ring is related with the stability of the compounds. It has been established that only those phenols which have two hydroxyl groups in the ortho position are able to form chelates. The cyclopentadienyl and the indenyl rings are π-bonded to niobium atom. The complexes have been characterised by elemental analysis and i.r. spectra.     

Correlations and predictions of pKa values of fluorophenols and bromophenols using hydrogen-bonded complexes with ammonia

Density functional theory calculations have been preformed on a series of the hydrogen-bonded fluorophenol-ammonia and bromophenol-ammonia complexes. Intermolecular and intramolecular properties, particularly those related to hydrogen bonding, have been carefully analyzed. Several properties, such as the bond length and stretching frequency of the hydroxyl group, the hydrogen bond length and binding energy, are shown to be highly correlated with each other and are linearly correlated with known experimental pKa values of the halogenated phenols. The linear correlations have been used to predict the pKa values of all fluorophenols and bromophenols in the series. The predicted pKa values are shown to be consistent from different molecular properties and are in good agreement with available experimental values. This study suggests that calculated molecular properties of hydrogen-bonded complexes allow the effective and systematic prediction of pKa values for a large range of organic acids using the established linear correlations.     

Infrared study of hydrogen bonds involving 2,2′-bipyridine and 2,2′-bipyrimidine. Influence of equivalent nitrogen atoms on the hydrogen bond strength

Hydrogen bonding between proton donors (phenols and water) and 2,2′-bipyridine (BPR) or 2,2′-bipyrimidine (BPM) has been investigated by infrared and FT-infrared techniques. The thermodynamic parameters (K, - ΔH, - ΔS°) and the frequency shifts of the ν_OH stretching vibrations have been determined in carbon tetrachloride solution. The spectroscopic results suggest that the complexes formed between phenols covering a large pK_a range (10.3–3.50) and BPR or BPM are of the normal OH⋯N type. The thermodynamic and spectroscopic properties of the BPR and BPM complexes are compared with those previously reported for the interaction between the same proton donors and the model molecules pyridine and pyrimidine. The BPR and pyridine complexes belong to the same series. The behaviours of BPM and pyrimidine are in complete contrast, the thermodynamic parameters and the related proton affinity being much higher for BPM than for pyrimidine. The results are probably ascribable to the presence of two equivalent neighbouring nitrogen atoms, the approach of a hydroxylic proton donor being greatly favoured in this electron-rich region. This effect does not exist in BPR, owing to its transoid configuration in solvents of weak polarity.     

Solution and structural characterization of iron(II) complexes with ortho-halogenated phenolates: insights into potential substrate binding modes in hydroquinone dioxygenases

The new ligand cis,cis-1,3,5-tris-(E)-(tolylideneimino)cyclohexane (TACH-o-tolyl) forms a 1:1 complex with iron(II). Addition of substituted phenolates forms 1:1:1 ligand:iron:phenolate complexes, which have been characterized both in the solid state and in solution. There is complete binding of the phenolate to the complex only when there are ortho-halogens on the phenolate. The tertiary complexes with ortho-halo-substituted phenolates exhibit short Fe-halogen distances, and the complex containing a non-coordinating but similarly sized ortho-methyl phenolate has a significantly different conformation and coordination geometry. Therefore, it is likely that the metal-halogen interaction stabilizes the complexes. The iron(II)-halogen interaction in these complexes may explain the substrate specificity of PcpA and LinE, enzymes that preferentially bind phenols and hydroquinones containing halogen substituents in ortho positions.     

Inftared study of the interaction between proton donors and 1,10-phenanthroline derivatives

The hydrogen bond complexes between 1,10-phenanthroline derivatives (bathocuproine, neo-cuproine and bathophenanthroline) and phenols have been investigated by i.r. spectrometry. The presence of two adjacent nitrogen atoms influences the thermodynamic and spectroscopic properties to a great extent. Comparison with recent results suggests that the 1,10-phenanthroline derivatives cannot be considered as “proton sponges”.     

The nature of active centers in cyclotrimerization of isocyanates catalyzed by the tertiary amine—α-oxide—proton donor system 1. The role of the proton donor

The rate of cyclotrimerization of phenyl isocyanate in chlorobenzene at 120 °C in the presence of the tertiary amine--oxide-proton donor (PD) ternary catalytic system has been studied using a dual calorimeter and a series of phenols with various acidities as the PD. In the presence of weakly acidic phenols, complexes of quaternary ammonium type bases are formed in the ternary catalytic systems. Acidic phenols afford salt complexes with the transfer or a proton from phenol to the tertiary amine in a quantitative yield, while the -oxide present remains unaffected. The structures of the complexes were studied by IR and by IR and¹H NMR spectroscopy.DeceasedTranslated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1382–1385, lune, 1996.     

(Imido)vanadium(V)‐alkyl,Alkylidene Complexes Exhibiting Unique Reactivities towards Olefins,Phenols, and Benzene via 1,2‐C‐H Bond Activation

Recent examples for synthesis and reaction chemistry with (imido)vanadium(V)‐alkyl, ‐alkylidene complexes have been briefly summarized. (Arylimido)vanadium(V) dichloride complexes especially containing aryloxo ligands exhibited notable activities for ethylene polymerization, and the reacition pathways for the polymerization/dimerization using (imido)vanadium(V) dichloride complexes containing (2‐anilidomethyl)pyridine ligands can be tuned by modification of the steric bulk in the imido substituents; the adamantylimido analogues exhibited exceptionally high both activity and selectivity in the dimerization. These vanadium(V)‐alkyl complexes showed unique reactivity toward phenols; the reaction proceeds via coordination of phenols to the vanadium. The vanadium(V)‐alkylidene complexes were generated by α‐hydrogen elimination from the dialkyl analogues in the presence of PMe₃ etc.; the subsequent 1,2‐C‐H bond activation of benzene with (arylimido)vanadium(V)‐alkylidene containing 1,3‐(2′,6′‐diiso‐propylphenyl)imidazolin‐2‐iminato (Im^DIPPN) ligand took place cleanly.     

Phenoxy Derivatives of Dicyclopentadienyl Tungsten(VI) Oxydichloride and Bisindenyl Tungsten (VI) Oxydichloride

Phenoxy complexes containing π-bonded cyclopentadienyl and indenyl groups attached to metals ytterbium¹⁾, titanium¹⁾, and cerium¹⁾. are reported in the literature. These phenoxide derivatives were prepared by the actious of various phenols on the cyclopentadienyl or indenyl metal halide complexes in benzene or tetrahydrofuran. There is no mention the literature about the prepartion and characterization of phenolic derivatives of π-cyclopentadienyl and π-indenyl oxotungsten (VI). The effect of electron releasing or electron attracting substiuents in the phenols on the nature of the complexes and the metal-phenoxide bond has not been reported. The possibility of formation of hydrogen bond between hydrogen atom of the free hydroxyl group of a polyhydric phenoxide group and the oxygen atom attached to the metal atom has not also been explored. This communication deals with such an attempt and reports the synthesis and characterization of 26 phenoxy derivatives of dicyclopentadienyl and bisindenyltungsten (VI) oxydichlorides and conclusions derived from their infrared spectral study.     

Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

The electron donor–acceptor (EDA) interactions between o-chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hν_CT values change systematically as the number and position of the –OH groups change in the aromatic ring of the phenol moiety. From the trends in the hν_CT values, the Hückel parameters (h_Ö and k_C–Ö) for the –OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences.     

Self-Assembly and X-Ray Crystal Structures of Novel Sn(IV)Porphyrin Phenolates

A series of complexes of the type [Sn(TTP)L₂] have been prepared by the condensation of [Sn(TTP)OH₂] (TTP = meso-tetratolylporphyrin) with a range of substituted phenols. The resulting complexes were characterised using ¹H NMR and single crystal X-ray diffraction techniques. In each case, the condensation of the phenols with the Sn(IV)porphyrin in CDCl₃ solution is slow (h) but essentially quantitative. The slow kinetics of the formation of the diaxial phenolate complexes allows for the identification, by ¹H NMR spectroscopy, of three independent complexes within this process, namely an outer-sphere (H-bonded) complex as well as two independent phenolate complexes. The rate of condensation is in the order phenol 4-methoxyphenol > 4-nitrophenol and suggests a steric rather than pKa dependency.     

Phenols as Novel Photocatalytic Platforms for Organic Synthesis

In recent years, organic chemists have devoted a great deal of effort towards the implementation of novel green photocatalytic synthetic protocols. To this end, the development of new effective, non-toxic, inexpensive photocatalysts, which are capable of driving value-added chemical transformations, is highly desirable. Interestingly, phenols fulfill all these requirements due to their outstanding physicochemical features, therefore emerging as promising metal-free photocatalytic platforms for organic synthesis. This Perspective aims at highlighting the most recent applications of phenols in organic photocatalysis. More specifically, phenolate anions, formed upon deprotonation of phenols, are photo-active organic intermediates that may absorb light within the visible region. Thus, when in the excited states, these anions may be used as reductants to generate reactive open shell species from suitable precursors under mild operative conditions. Alternatively, phenolate anions and suitable radical precursors can form electron donor-acceptor (EDA) complexes. Specifically, the photochemical activity of these molecular aggregates can be used to initiate organic radical reactions. Lastly, forward-looking opportunities within this research field have been discussed.     

Formation of hydrogen-bonded chains between a strong base with guanidine-like character and phenols with various pKa values - an FT-IR study

The complexes formed by phenols with 1,3,4,6,7,8-hexahydro-l-methyl-2H-pyrimido[1,2-a]pyrimidine (mTBD), an N-base with guanidine-like character, were studied as a function of the pK_a of the phenols by FT-IR spectroscopy. The following phenols were used: 4-cyanophenol (4-CNPh), pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DNPh). In the case of chloroform solutions of 1: 1 mixtures of the phenols with MTBD the corresponding complexes are formed completely. With increasing acidity of the phenols the hydrogen bonds become increasingly asymmetrical. The O … N ⁻O … H⁺N hydrogen bond in the 4-CNPh-MTBD complex shows large proton polarizability. In the other cases only the polar structure is realized. With increasing phenol MTBD ratio, the formation of chains with two phenol molecules is observed. With decreasing pK_a of the phenols the fluctuation is limited to the phenol-phenolate bond and finally, the phenol-protonated MTBD bond begins to dissociate. In acetonitrile solutions, N⁺H …O⁻ hydrogen bonds are observed in the case of the 1:1 mixture of 4-CNPh with MTBD. A weak continuum indicates the presence of homoconjugated phenol-phenolate bonds with large proton polarizability. In the case of 2:1 mixtures only protonated MTBD and homoconjugated phenol-phenolate bonds are observed, independent of the pK_a of the phenols. The results are discussed with regard to the proton pathway in bacteriorhodopsin.