Electrochromic and spectroelectrochemical properties of polythiophene β-substituted with alkyl and alkoxy groups

Journal of Solid State Electrochemistry - Polythiophenes are conjugated polymers that are highly promising candidates for use as an active layer in flexible optoelectronic devices. The...     

Aliphatic acid dihydrazide derivatives of dicyclopentadienylzirconium(IV) dichloride and their reactions with β-diketones. Formation of cyclic compounds

The reactions of dicyclopentadienylzirconium(IV) dichloride with bidentate aliphatic acid dihydrazide (LH₂) derived from oxalic, succinic, and adipic acids (metal to ligand molar ratios 1 : 1 and 1 : 2, respectively) in anhydrous tetrahydrofuran in the presence of base led to the formation of the [Cp₂Zr(L)] and [CpZr(LH)₂Cl] complexes. The complexes were characterized by elemental analyses, electrical conductance, magnetic measurements and spectroscopic studies. These ligands appear to behave as bidentate chelate agents. All the complexes contain terminal amino or terminal hydrazinc nitrogen atoms with an unshared electron pair, enabling nucleophilic condensations. Therefore, the reactions of these complexes with β-diketones (acetylacetone, benzoylacetone, dibenzoylmethane, thenoyltrifluoroacetone) in the presence of glacial acetic acid have been studied viz., ring closure and formation of macrocyclic ligand (mac) complexes. Two types of cyclic products viz., [Cp₂Zr(mac)] and [CpZr(Mac)Cl] were isolated. The spectral studies of these cyclic products are reported.     

High-pressure rate rules for alkyl + O2 reactions. 2. The isomerization, cyclic ether formation, and β-scission reactions of hydroperoxy alkyl radicals

The unimolecular reactions of hydroperoxy alkyl radicals (QOOH) play a central role in the low-temperature oxidation of hydrocarbons as they compete with the addition of a second O(2) molecule, which is known to provide chain-branching. In this work we present high-pressure rate estimation rules for the most important unimolecular reactions of the β-, γ-, and δ-QOOH radicals: isomerization to RO(2), cyclic ether formation, and selected β-scission reactions. These rate rules are derived from high-pressure rate constants for a series of reactions of a given reaction class. The individual rate expressions are determined from CBS-QB3 electronic structure calculations combined with canonical transition state theory calculations. Next we use the rate rules, along with previously published rate estimation rules for the reactions of alkyl peroxy radicals (RO(2)), to investigate the potential impact of falloff effects in combustion/ignition kinetic modeling. Pressure effects are examined for the reaction of n-butyl radical with O(2) by comparison of concentration versus time profiles that were obtained using two mechanisms at 10 atm: one that contains pressure-dependent rate constants that are obtained from a QRRK/MSC analysis and another that only contains high-pressure rate expressions. These simulations reveal that under most conditions relevant to combustion/ignition problems, the high-pressure rate rules can be used directly to describe the reactions of RO(2) and QOOH. For the same conditions, we also address whether the various isomers equilibrate during reaction. These results indicate that equilibrium is established between the alkyl, RO(2), and γ- and δ-QOOH radicals.     

How far do electrons move? A semiempirical investigation of thermal electron-transfer distances in cationic bis(hydrazine) and bis(hydrazyl) mixed-valence compounds.

A computational approach for estimating thermal electron-transfer reaction distances in symmetrical mixed-valence compounds is described and applied to a series of bis(hydrazine) and bis(hydrazyl) radical cations and derivatives, some of which have been investigated experimentally by Nelsen and co-workers. Ground-state semiempirical charge distributions are obtained by using optimized reactant geometries. Advantage is then taken of the approximate C(2) symmetry, or the approximate mirror symmetry, of each of the targeted compounds, and the inherent degeneracy of the corresponding electron-transfer reactions, such that the change in dipole moment (Delta-mu) upon charge transfer can be estimated from an appropriately distance-weighted sum of charge differences between approximately symmetry-equivalent atoms found on the donor and acceptor sides of the molecule. Delta-mu can then be related directly to the effective one-electron-transfer distance. We find that calculated adiabatic electron-transfer distances can differ appreciably from the geometric donor-site/acceptor-site separation distances. Furthermore, for a fixed geometric separation distance, the effective electron-transfer distance can vary considerably, depending on chemical substituent composition and/or isomeric configuration. Further advantage is taken of the approximate donor-site/acceptor-site symmetry, in the context of a Newton-Cave type analysis, to establish the relative importance of electronic delocalization effects versus self-polarization and inductive effects in diminishing or enhancing effective one-electron-transfer distances.     

Kinetics and mechanism of reactions of bis(biguanide)copper(II) ion with glycine and α-alanine in aqueous media

Summary The kinetics of the reaction of [Cu(bigH)₂]²⁺ (bigH = biguanide) with an excess of amino acid (LH), namely glycine or -alanine, in aqueous solution in the 7.6–9.0 pH range at different temperatures (30–40° C) have been followed by stopped-flow spectrophotometry. The ligand replacement process has been found to pass through intermediate formation of a ternary complex, [Cu(bigH)L]⁺ at the slower step, followed by rapid transformation into the binary complex, [CuL₂]. The overall ligand replacement process has a ligand dependent (k ₁) path which is first order with respect to the incoming ligand (L^-), and a ligand independent (k ₀) path. Under pseudo-first order conditions containing excess amino acid, the experimental observations conform to the rate law k _obs = k ₀ + k ₁ K _a[L]_T/([H⁼] + K _a), where [L]_T stands for the total concentration of amino acid and K _a gives the deprotonation constant of LH. The solvent assisted dissociation (i.e. k ₀ path) leads to a copper(II) mono-biguanide complex followed by rapid nucleophilic substitution; the k ₁ path is in agreement with an associative mechanism. The activation parameters (H , S ) for each step have been determined.     

Synthesis and characterization of β-diketiminate germanium(II) compounds

Reactions of LGeCl (L = CH[C(Me)N(Ar)](2); Ar = 2,6-iPr(2)C(6)H(3)) with KOtBu or LiR (R = 2-thienyl, N(H)Ar, PPh(2)) yielded the germanium(II) compounds LGeR [R = OtBu (1), 2-thienyl (2), N(H)Ar (3), PPh(2) (4)]. The reduction of (2-thienyl)(2)PCl with lithium afforded the diphosphane [(2-thienyl)(2)P](2) (5). The treatment of (2-thienyl)(2)PCl with LiAlH(4) or KHBtBu(3) led to the formation of (2-thienyl)(2)PH (6). The NHC-assisted reaction of LGeCl and 6 resulted in the isolation of LGeP(2-thienyl)(2) (7). This is the first example where NHC is used for eliminating HCl from compounds with P-H and Ge-Cl bonds. All solid products were characterized by elemental analysis, NMR and IR spectroscopy, and single-crystal X-ray structure determination.     

Mechanistic comparison of β-H elimination, β-OH elimination, and nucleophilic displacement reactions of β-hydroxy alkyl rhodium porphyrin complexes

This article reports on kinetic studies for three alternate pathways, including β-hydrogen elimination, β-hydroxy elimination, and intramolecular nucleophilic displacement reactions, for rhodium porphyrin β-hydroxy alkyl reactions in water and DMSO to form ketone, alkene, and epoxide, respectively. Comparisons of activation parameters for these processes indicate that the β-hydroxy elimination process has the lowest activation enthalpy in water, but the intramolecular nucleophilic displacement pathway predominates in DMSO.     

Solid state reactions of nitrogenous heterocyclic compounds (Ⅱ)——Solid state reactions of indole with carbonyl compounds

Solid state Michael addition reaction of indole with α,β-unsaturaled carbonyl compounds was carried out,by which a series of compounds containing three different heterocyclic groups binding to one carbon atom were obtained.In the presence of Lewis acid,indole could undergo the solid state condensation reaction with aromatic ketones and aldehydes or quinones.The solid state reaction showed higher selectivity and yield than solution reaction The structures of products were identified by IR,1H NMR,MS,elemental analysis and X-ray crystal analysis.The reaction mechanism was also proposed.     

Synthesis and properties of new (−)-menthol-derived chiral liquid crystal compounds with alkyl or alkoxy terminal groups

Two series of chiral mesogenic compounds derived from (?)-menthol with varying length of alkyl or alkoxy terminal groups respectively were designed and synthesised. Their chemical structures were characterised by FT-IR and ¹H-NMR spectra. The thermal properties and optical textures were investigated by differential scanning calorimetry and polarising optical microscopy. Bragg selective reflection spectra of the compounds with the alkoxy chain in the N* phase were measured by ultraviolet/visible spectrometer. The results showed that the alkyl series homologues melt directly to the isotropic phase on heating and display cubic blue phase and focal conic textures of chiral nematic phase on cooling, whereas the alkoxy series displayed oily streak textures with iridescent colours on heating, and platelet textures of blue phase and focal conic textures were observed on cooling cycles. The chain structure and length of the terminal groups have profound influence on the isotropic temperature and a large odd–even effect is observed for the compounds. The selective reflection colours of alkoxy series shifted to longer wavelength with the increasing of temperature.     

Reactivity of thio (amino) derivatives of the ω-(4-hydroxyaryl)alkyl type in radical reactions

The enthalpies, activation energies, and rate constants of the reactions of thio (amino) alkylphenols of different structures were calculated and compared with those of the reactions of alkyl-substituted phenols, alkoxyl and alkyl radicals, hydroperoxides, and nitrogen dioxide, as well as the reactions of phenoxyl radicals with molecules of the substrate being oxidized. The calculation was performed by the intersecting parabolas method using O-H bond energy data for phenols. The correlation between the molecular structure of the thio (amino) alkylphenols and their reactivity in radical reactions is considered.     

Kinetics and mechanism of reactions of bis(biguanide)copper(II) ion with 2,2′-bipyridyl and 1,10-phenanthroline in aqueous solution

Summary In aqueous solution [Cu(bigH)₂]²⁺ (bigH=biguanide) reacts with 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) through intermediate formation of ternary complexes [Cu(bigH)(L)]²⁺ and [Cu(bipy)(phen)]²⁺ and binary complexes [CuL₂]²⁺ (L=bipy, phen). The rates of the different steps have been followed in borax buffer (pH 8.0±0.1) by stopped-flow spectrophotometry. For each step k_obs=k₀+k_L[L] and the k_L path appears to be associative. H and S values for the k_L path conform to an isokinetic trend.     

DFT, NBO, and NRT analysis of alkyl and benzyl β-silyl substituted cations: carbenium ion vs. silylium ion

The effect of β-trimethylsilyl (TMS) substituent on the structure, stability, natural charges, electrostatic potential map, natural bond orders, rotational energy barrier, and hyperconjugative interactions of five acyclic β-silyl carbocation derivatives of RR′C⁺–CH₂Si(Me)₃ including α-dimethyl 1 (R,R′ = Me), α-methyl phenyl 2 (R = Me, R′ = Ph), α-methyl para-aminophenyl 3 (R = Me, R′ = p-NH₂Ph), α-methyl para-nitrophenyl 4 (R = Me, R′ = p-NO₂Ph) and diphenyl 5 (R,R′ = Ph) was investigated in the gas phase and in solution using polarized continuum model (PCM) at B3LYP/6-311 ++G** level of theory. The resonance structures weighting of cations 1–5 were determined using natural resonance theory (NRT). The contribution of carbenium ion (RR′C⁺–CH₂Si(Me)₃) and silylium ion (RR′C=CH₂ Si(Me) ₃ ⁺ ) to the stability depend upon substituents. The former form dominants when R,R′ = Ph, but the latter is major the contributor when R,R′ = Me. The weighting of carbocation forms of β-silyl benzyl cation overwhelms silylium cation due to the delocalization of positive charge on the phenyl ring. The calculated molecular orbital (MO) diagrams, energy decomposition analysis (EDA) and ²⁹Si and ¹³C nuclear magnetic resonance (NMR) chemical shifts complement these predictions.     

Molybdenum(VI) dioxo and oxo-imido complexes of fluorinated β-ketiminato ligands and their use in OAT reactions

Substitution of a methyl by a trifluoromethyl moiety in well-known β-ketimines afforded the ligands (Ar)NC(Me)CH(2)CO(CF(3)) (HL(H), Ar = C(6)H(5); HL(Me), A r= 2,6-Me(2)C(6)H(3); HL(iPr), Ar = 2,6-(i)Pr(2)C(6)H(3)). Subsequent complexation to the [MoO(2)](2+) core leads to the formation of novel complexes of general formula [MoO(2)(L(R))(2)] (R = H, 1; R = Me, 2; R = iPr, 3). For reasons of comparison the oxo-imido complex [MoO(N(t)Bu)(L(Me))(2)] (4) has also been synthesized. Complexes 1-4 were investigated in oxygen atom transfer (OAT) reactions using the substrate trimethylphosphine. The respective products after OAT, the reduced Mo(IV) complexes [MoO(PMe(3))(L(R))(2)] (R = H, 5; R = Me, 6; R = iPr, 7) and [Mo(N(t)Bu)(PMe(3))(L(Me))(2)] (8), were isolated. All complexes have been characterized by NMR spectroscopy, and 1-4 also by cyclic voltammetry. A positive shift of the Mo(VI)-Mo(V) reduction wave upon fluorination was observed. Furthermore, molecular structures of complexes 2, 4, 5, and 8 have been determined via single crystal X-ray diffraction analysis. Complex 8 represents a rare example of a Mo(IV) phosphino-imido complex. Kinetic measurements by UV-vis spectroscopy of the OAT reactions from complexes 1-4 to PMe(3) showed them to be more efficient than previously reported nonfluorinated ones, with ligand L' = (Ar)NC(Me)CH(2)CO(CH(3)) [MoO(2)(L')(2)] (9) and [MoO(N(t)Bu)(L')(2)] (10), respectively. Thermodynamic activation parameters ΔH(?) and ΔS(?) of the OAT reactions for complexes 2 and 4 have been determined. The activation enthalpy for the reaction employing 2 is significantly smaller (12.3 kJ/mol) compared to the reaction with the nonfluorinated complex 9 (60.8 kJ/mol). The change of the entropic term ΔS(?) is small. The reaction of the oxo-imido complex 4 to 8 revealed a significant electron-donating contribution of the imido substituent.     

Suzuki–Miyaura reactions of the bis(triflates) of 1,3- and 1,4-dihydroxythioxanthone. Electronic and steric effects on the site-selectivity

The palladium(0)-catalyzed Suzuki cross-coupling reactions of the bis(triflates) of 1,3- and 1,4-dihydroxythioxanthone afforded various aryl-substituted thioxanthones. While the Suzuki reactions of the bis(triflate) derived from 1,3-dihydroxythioxanthone proceeded by site-selective attack in favor of position 3, the reactions of the bis(triflate) of 1,4-dihydroxythioxanthone proceeded in favor of position 1. The site-selectivity is controlled by steric and electronic parameters.     

Mechanism of the unusual substituent exchange in the reactions of alkylene oxides with organic compounds bearing β-hydroxyalkyl groups at heteroatoms S,Se, N,and P

The review summarizes the data on the study of the unusual exchange reaction between alkylene oxides and organic compounds of groups 15 and 16 of the Periodic Table bearing β-hydroxyalkyl substituents at the S, Se, N, and P heteroatoms. Despite the apparent identity of one of the starting reagents and the reaction product (retention of the three-membered ring), the structures of the formed alkylene oxide and organic compound with β-hydroxyalkyl group at the heteroatom differ from the structures of the starting materials. Using β-hydroxyalkyl sulfides as a model, the plausible mechanisms of the exchange reactions were discussed taking into account the change in the reaction order in β-hydroxyalkyl sulfide with its concentration increase. Irrespectively of the mechanism, the first stage of the reaction is the formation of an intermediate H-complex due to the H-bond formation between the OH sulfide group and the alkylene oxide oxygen atom and subsequent (for the dilute solutions) monomolecular intracomplex transformation of this H-complex. The mechanism was confirmed by semi-empirical quantum chemical calculations. In the case of concentrated solutions of β-hydroxyalkyl sulfides, possibility of the formation of intermediate sulfonium salt was discussed. Each pathway proceeds via its unique intermediates and transition states but the final stage results in the same intermediate bipolar ion with an intramolecular H-bond thus leading to the same nature and compositions of the reaction products for all reaction pathways.     

Alkylation of aralkyl bromides with tetra alkyl tin compounds in presence of (2,2′-bipyridine)fumaronitrile palladium(0)

(2,2′-bipyridine)fumaronitrile palladium(0) acts catalytically in the alkylation of benzylic halides with tetra alkyl tin even for an alkyl halide with hydrogen atoms on a sp³ carbon β to the leaving group.