Suzuki-Miyaura cross-coupling reaction of monohalopyridines and l-aspartic acid derivative

Suzuki-Miyaura cross-coupling reaction of halogenated pyridines and a borated l-aspartic acid derivative was conducted. The reactivity of chloro-, bromo-, and iodo-pyridines with substituents at the C2, C3, and C4 positions was investigated. Electron density of halogenated pyridines was also estimated by density functional theory (DFT) calculations. The order of experimental yield of halogen substituents was Br?>?I?>>?Cl and C3?>?C2, C4 whereas the DFT results indicated the reactivity order as I?>>?Br, Cl and C4?>?C2, C3. Optimized experimental conditions (3-bromopyridine) afforded the coupling product quantitatively.     

Nucleophilic substitution in the series of (1,2,3-triazol-1-yl)-1,2,5-oxadiazoles. Reactions with N-, O-, and S-nucleophiles

Methods for the synthesis of amino(1,2,3-triazol-1-yl)-1,2,5-oxadiazoles (amino-triazolylfurazans) with CH₂Cl and COCH₂Br substituents in the triazole ring were developed and nucleophilic substitution for their halogen atom in reactions with N-, O-, and S-nucleophiles were studied. The possibility of displacing the NO₂ group from the furazan and triazole rings in triazolylfurazans by an azido group was investigated. Novel compounds of this series were synthesized; the reaction rate and pathway were found to depend on the nature of the substrate and the reagent and the position of the substituent in isomers. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1866–1876, August, 2005.     

Halogen bonding in mono- and dihydrated halobenzene

Density functional theory calculations were performed on halogen-bonded and hydrogen-bonded systems consisting of a halobenzene (XPh; X = F, Cl, Br, I, and At) and one or two water molecules, using the M06-2X density functional with the 6-31+G(d) (for C, H, F, Cl, and Br) and aug-cc-pVDZ-PP (for I, At) basis sets. The counterpoise procedure was performed to counteract the effect of basis set superposition error. The results show halogen bonds form in the XPh-H₂O system when X > Cl. There is a trend toward stronger halogen bonding as the halogen group is descended, as assessed by interaction energy and X•••O_w internuclear separation (where O_w is the water oxygen). For all XPh-H₂O systems hydrogen-bonded systems exist, containing a combination of CH•••O_w and O_wH_w•••X hydrogen bonds. For all systems except X = At the X•••H_w hydrogen-bonding interaction is stronger than the X•••O_w halogen bond. In the XPh-(H₂O)₂ system halogen bonds form only for X > Br. The two water molecules prefer to form a water dimer, either located around the C H bond (for X = Br, At, and I) or located above the benzene ring (for all halogens). Thus, even in the absence of competing strong interactions, halogen bonds may not form for the lighter halogens due to (1) competition from cooperative weak interactions such as C H•••O and OH•••X hydrogen bonds, or (2) if the formation of the halogen bond would preclude the formation of a water dimer. © 2018 Wiley Periodicals, Inc.     

ANODIC OXIDATION OF 1,n-HALO(ALKYLTHIO)ALKANES AND 1,n-CHLORO(ALKYLSULFINYL)ALKANES

Abstract

Anodic oxidation of 1,n-halo(alkylthio)alkanes [X-(CH₂)_n-S-R, X = Cl, Br, I] and l,nhalo(alkylsulfinyl)alkanes [Cl-(CH₂)_n-S(O)-R] was studied by cyclic voltammetry in anhydrous acetonitrile and by controlled potential electrolyses. The ease of sulfur oxidation was not affected by the alkyl substituents R or the number of methylene groups n in compounds with n > 2. The oxidation of the 1,2-halo(alkylthio)ethanes (n = 2) occurred at slightly higher potentials. The peak potentials decreased slightly in the order Cl > Br > I which is probably due to the electronegativity of the halogen atoms. The investigated anodic oxidation was shown to be a two electron irreversible process. Electrolyses in aqueous acetronitrile led to the corresponding sulfoxides and sulfones in good yields.     

Evidence for Interfacial Halogen Bonding

A homologous series of donor–π–acceptor dyes was synthesized, differing only in the identity of the halogen substituents about the triphenylamine (TPA; donor) portion of each molecule. Each Dye‐X (X=F, Cl, Br, and I) was immobilized on a TiO₂ surface to investigate how the halogen substituents affect the reaction between the light‐induced charge‐separated state, TiO₂(e^?)/ Dye‐X⁺ , with iodide in solution. Transient absorption spectroscopy showed progressively faster reactivity towards nucleophilic iodide with more polarizable halogen substituents: Dye‐F < Dye‐Cl < Dye‐Br < Dye‐I . Given that all other structural and electronic properties for the series are held at parity, with the exception of an increasingly larger electropositive σ‐hole on the heavier halogens, the differences in dye regeneration kinetics for Dye‐Cl , Dye‐Br , and Dye‐I are ascribed to the extent of halogen bonding with the nucleophilic solution species.     

Weak σ-Hole Triel Bond between C5H5Tr (Tr=B,Al, Ga) and Haloethyne: Substituent and Cooperativity Effects

The replacement of a CH group of benzene by a triel (Tr) atom places a positive region of electrostatic potential near the Tr atom in the plane of the aromatic ring. This σ-hole can interact with an X lone pair of XCCH (X=F, Cl, Br, and I) to form a triel bond (TrB). The interaction energy between C₅H₅Tr and FCCH lies in the range between 2.2 and 4.4 kcal/mol, in the order Tr=B<Ga<Al. This bond is strengthened by halogen substituents on the ring, particularly on the site adjacent to Tr. There is a much stronger strengthening trend as the F of the FCCH nucleophile is replaced by the heavier halogen atoms, rising up to 22 kcal/mol for ICCH. Adding a Li⁺ cation above the ring pulls density toward itself and thus magnifies the Tr σ-hole. The TrB to the XCCH nucleophile is thereby magnified as is the strength of the TrB. This positive cooperativity is particularly large for Tr=B.     

Molecular quadrupole moments and magnetic anisotropies of non-dipolar 1,3,5-trisubstituted benzenes

The molecular quadrupole moments and magnetic anisotropies of a series of non-dipolar 1,3,5-trisubstituted benzenes (C₆H₃X₃; X=H, Me, t-Bu, F, Cl, Br) are analysed to obtain information concerning the charge distributions. Whereas alkyl groups have relatively little effect on benzene. halogen substituents are strongly interactive and the moments become progressively less negative from 1.3.5-tribromo-to 1.3.5-trifluoro-benzene.     

Properties of halogen atoms for representing intermolecular electrostatic interactions related to halogen bonding and their substituent effects

The electrostatic properties of halogen atoms are studied theoretically in relation to their ability of halogen bonding, which is an attractive intermolecular interaction of a covalently bonded halogen atom with a negatively charged atom of a neighboring molecule. The electric quadrupole (of electronic origin) with a positive zz component Θ_zz of a covalently bonded halogen atom, where the z axis is taken along the covalent bond involving the halogen atom, is mainly responsible for the attractive electrostatic interaction with a negatively charged atom. This positive Θ_zz is an intrinsic property of halogen atoms with the p_x²p_y²p_z configuration of the valence electronic shell, as shown by ab initio molecular orbital calculations for isolated halogen atoms with this electronic configuration, and increases in the order of F < Cl < Br < I, in parallel with the known general sequence of the strength of halogen bonding. For halogen‐containing aromatic compounds, the substituent effects on the electrostatic properties are also studied. It is shown that the magnitude of Θ_zz and the electric field originating from it are rather insensitive to the substituent effect, whereas the electric field originating from atomic partial charges has a large substituent effect. The latter electric field tends to partially cancel the former. The extent of this partial cancellation is reduced in the order of Cl < Br < I and is also reducible by proper substitution on or within the six‐membered ring of halobenzene. Perspectives on the development of potential function parameters applicable to halogen‐bonding systems are also briefly discussed. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Thermodynamics of vinyl ethers—XV : Halogen-containing vinyl ethers

Thermodynamics of geometrical and prototropic isomerization reactions on some halogen-containing vinyl ethers of the types ROCH–CHX (X = Cl, Br), ROC(CH₂X)CH₂ (X = F, Cl, Br), and ROC(CHMeCl)CH₂ (R = Me, Et, Et₂CH) have been studied. In ROCH_αCH_βX the cis (or Z) isomer is thermodynamically the more stable isomer, the higher stability of the Z isomer being due to its lower enthalpy. The relative stability of the E and Z forms is, however, reversed if the α H atom is replaced by a Me group. In systems like OCCX the double-bond stabilizing ability of the halogen atom decreases in the order Cl > Br > F, in contrast to the case in haloalkenes, where the corresponding order is F > Cl > Br.     

Aromatic polymides. VII. Synthesis of sulfonated poly(para-phenyleneterephthalamide): Polymerization of 1,4-bis(trichloromethyl) benzene with para-phenylenediamine sulfate in SO3

para-Phenylenediamine sulfate polymerized with 1,4-bis(trichloromethyl)benzene in SO₃ at > 20% polymer concentration to form highly anisotropic (liquid crystalline) sulfonated poly(para-phenyleneterephthalamide) (S-PPT) solutions with inherent viscosities as high as 1.2. Analogous to the polymerization of para-phenylenediamine sulfate with terephthalic acid in SO₃ reported previously, sulfonation of the aromatic diamine ring of S-PPT was not competitive with the polymerization reaction, but it was a major side reaction.     

Effect of core substituents on the intramolecular exchange interaction in N,N′‐dioxy‐2,6‐diazaadamantane biradical: DFT studies

Density‐functional theory calculations of a series of organic biradicals on the basis of the N,N′‐dioxy‐2,6‐diazaadamantane core with different substituents at carbon atoms adjacent to the nitroxyl groups have been performed by the UB3LYP/6‐311++G(2d,2p) method. Using the breaking symmetry approach, the values of the exchange interaction parameter, J, between the radical centers are calculated. It is shown that the intramolecular exchange interaction for the most part is ferromagnetic in nature, but the J parameter gradually decreases, changing its sign to antiferromagnetic interaction for the last substituent in the following sequence: CF₃(CH₃)COH > CH₂F(H)COH > CH₂OH > H > CBr₃ > CH₂F > CCl₃ > CF₃ > CH₂Br > CH₂Cl > CH₃ > C₂H₅ > C₃H₇ > i‐C₄H₉ > F > Br > OCH₃ > Cl > CH₂C₆H₅. The calculations at the UHSEH1PBE/6‐311++G(2d,2p) level with the most of substituents show nearly the same variation sequence for the J parameter. It is concluded that spin polarization effects in the diazaadamantane cage and a direct through‐space antiferromagnetic exchange interaction between the nitroxyl groups are the main mechanisms contributing to the exchange interaction parameter value in the studied series of compounds. The exchange coupling constant, J, depends on the electronic effects and geometry of the substituents, as well as on their specific interactions with the nitroxyl radical groups.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

Summary. 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Structures, IR, NMR Spectra and Thermodynamics Properties of Halogenated Compounds X-1-ZB11H10 (Z=O, S, Se;X=F, Cl, Br): A DFT Study

The halogenated compounds of twelve‐vertex closo‐1‐ZB₁₁H₁₁(Z=O, S, Se; X=F, Cl, Br) have unusual stability. The structures of halogenated isomers obtained by DFT method indicate that the halogen atoms are more likely to attack the meta vertexes. The chemical thermodynamic properties show that the halogenations are spontaneous and exothermic. The result that both the optimized and experimental cages of closo‐thiaborane have not changed after chlorination indicates that the substitution of a chlorine atom for a hydrogen atom of closo‐thiaborane happens at outer of the cage. The calculated electronic structures show that the three‐dimensioned aromaticity of cage would like positive chlorine atoms to attack. The halogenations by elemental halogen in the presence of metal halides were proved to belong to the electrophilic substitutions and the mechanism was discussed in details. The suggested transition state interpreted the experiments. The thermal rearrangement which was supposed early according to experiments was verified by the thermodynamic properties of chlorination theoretically. The IR and ¹¹B/¹H NMR isotropic chemical shifts were calculated and compared with the experimental data to reconfirm the structures of chlorinated closo‐thiaborane. Furthermore, the predictions on the halogenated closo‐oxaborane and closo‐selenaborane are significant for the syntheses.     

Modification of PET with sterically hindered diols

Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (T_g). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH₃ > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET.     

Aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene and ethyl α-cyano-phenylacetate benzyl anion

The aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene (DNHB; halogeno =F, Cl, Br) with ethyl α-cyanophenylacetate (ECPA) benzyl anion has been studied by means of UV and IR spectrophotometry as well as gas chromatography. The rates of intermediate formation and product formation were determined respectively. In contrast with common S _N Ar reactions, the formation rate constant of the intermediates, substituted cyclohexadienates, was in the order of halogen =F>Br>Cl, whereas the rate constant of product formation was in the order F>Cl>Br, which revealed that the departure of the halogen atom was the rate-limiting step for the overall reaction in the presence of a sterically hindered nucleophile. These reactions could be catalyzed by the solvated electrons. The corresponding reaction intermediates, radical species, were detected by ESR and the reactions were proved to proceed mainly by a solvated-electron induced radical chain reaction mechanism.     

Coordination Polyhedra OsXn(X = F, Cl, Br, I) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of compounds containing complexes [Os _a X _b ] ^z–(X = F, Cl, Br, I). Atoms of Os(V) at X = F and Cl, of Os(IV) at X = Cl, Br, and of Os(III) at X = Br were found to exhibit a coordination number of 6 with respect to the halogen atoms and to form OsX₆octahedra. The coordination polyhedra of Os(III) for X = Cl, I are square pyramids OsX₄. Each Os(III) atom forms one Os–Os bond; as a consequence, the OsBr₆octahedra share a face in forming Os₂Br^3– ₉complexes, while the OsX₄pyramids (X = Cl, I) dimerize to produce [X₄Os–OsX₄]^2–ions. The influence of the valence state of the Os atoms and of the nature of the halogen atoms on the composition and structure of the complexes formed and some characteristics of the coordination sphere of Os were considered.     

Aromatic polyamides. V. A general synthesis of polyamides from aromatic diacids and aromatic diamines in sulfur trioxide

The reaction of terephthalic acid (TA) and para-phenylenediamine sulfate (PPD-S) in sulfur trioxide to form anisotropic, sulfonated poly(p-phenyleneterephthalamide) (SPT) dopes was reported in Part IV of this series. We have found now that the TA/PPD-S polymerization is only one example of a more general polyamide condensation reaction of aromatic diamines and aromatic diacids. Sulfonation of the aromatic diamine ring during TA/PPD-S polymerization in SO₃ was a major side reaction. Sulfonation was reduced or eliminated by aromatic diamine ring substitution with unreactive substituents, particularly chlorine and fluorine. Polymerization of 2,3,5,6-tetrafluoro-phenylenediamine with TA in SO₃ at 80°C (18% concentration) produced unsulfonated poly(tetrafluoro-para-phenyleneterephthalamide) (F-PPT) with an inherent viscosity of 2.2. The halogenated, all-para aromatic polymers formed highly anisotropic (liquid crystalline) dopes. Monomers that formed polymers in which the chain bond angle deviated from 180° (e.g., meta-oriented monomers) yielded only isotropic polymer solutions. The mechanism and rate of diamine–diacid reactivity in SO₃ was related to diamine basicity. Whereas the less basic aromatic diamines (as sulfates) polymerized with aromatic diacids in SO₃, the more basic aliphatic diamines (as sulfates) would not. Aliphatic, cycloaliphatic, and aryl-aliphatic diacids were degraded by or reacted with the solvent (SO₃). Thermogravimetric analyses of F-PPT and monosulfonated poly(chloro-para-phenyleneterephthalamide) at 20°C/min showed weight loss only above 380 and 370°C, respectively.     

Theoretical study on the interactions of halogen‐bonds and pnicogen‐bonds in phosphine derivatives with Br2, BrCl,and BrF

The MP2 ab initio quantum chemistry methods were utilized to study the halogen‐bond and pnicogen‐bond system formed between PH₂X (X = Br, CH₃, OH, CN, NO₂, CF₃) and BrY (Y = Br, Cl, F). Calculated results show that all substituent can form halogen‐bond complexes while part substituent can form pnicogen‐bond complexes. Traditional, chlorine‐shared and ion‐pair halogen‐bonds complexes have been found with the different substituent X and Y. The halogen‐bonds are stronger than the related pnicogen‐bonds. For halogen‐bonds, strongly electronegative substituents which are connected to the Lewis acid can strengthen the bonds and significantly influenced the structures and properties of the compounds. In contrast, the substituents which connected to the Lewis bases can produce opposite effects. The interaction energies of halogen‐bonds are 2.56 to 32.06 kcal·mol^?1; The strongest halogen‐bond was found in the complex of PH₂OH???BrF. The interaction energies of pnicogen‐bonds are in the range 1.20 to 2.28 kcal·mol^?1; the strongest pnicogen‐bond was found in PH₂Br???Br₂ complex. The charge transfer of lp(P) ? σ*(Br? Y), lp(F) ? σ*(Br? P), and lp(Br) ? σ*(X? P) play important roles in the formation of the halogen‐bonds and pnicogen‐bonds, which lead to polarization of the monomers. The polarization caused by the halogen‐bond is more obvious than that by the pnicogen‐bond, resulting in that some halogen‐bonds having little covalent character. The symmetry adapted perturbation theory (SAPT) energy decomposition analysis showes that the halogen‐bond and pnicogen‐bond interactions are predominantly electrostatic and dispersion, respectively.     

Density Functional Study on the Reactivity of Carbenes Toward 1,2‐H Shifts

The 1,2‐H shift reactions of simple carbenes (CH₂Y‐C‐X) have been studied using density functional theory (DFT). The influence of the substituent X and Y groups on the activation energy (Ea) of 1,2‐H shifts were examined. The ‘by stander’ Y substituents lower E_a in the order of Me, F > Cl, Br > H. Our analysis shows that the X effect is more significant than the by stander Y effect. X substitutions increase E_a of carbenes in the order of F > Cl > Br > Me > H. The influence of X on E_a is governed by the singlet‐triplet energy separation (ΔE_S‐T) of the carbene, i.e., E_a of a carbene is larger as its ΔE_S‐T in creases due to an X substitution. The X effect was also found to be related to the magnitude of the exothermicity: Ea of reaction is smaller when the reaction is more exothermic. Origin of the Y effect is attributed to the inter play between two factors: ‘lateness’ of transition state on the potential energy surface, and the exothermicity of the reaction.