Synthesis of a new bluish pigment from the reaction of a methylpyranoanthocyanin with sinapaldehyde

The synthesis of a new pigment with a bluish color was obtained from the reaction of methylpyranomalvidin-3-glucoside with sinapaldehyde and its formation mechanism seems to involve a charge-transfer reaction pathway. The structure of this compound was fully characterized by LC/DAD-MS and NMR. Its equilibrium forms present in water at different pH values and the respective ionization constants were determined by UV-visible spectroscopy. The results revealed the presence of three equilibria involving only deprotonation reactions at the 7-OH and 4′-OH positions of the pyranoanthocyanin moiety and at the 4′″-OH of the syringol moiety (pK_a1 = 3.64 ± 0.01; pK_a2 = 8.02 ± 0.01; pK_a3 = 11.19 ± 0.01).     

Mechanistic studies on the hydrolysis of a dimeric alkylzinc bis(2-pyridylmethyl)amide

Bis(2-pyridylmethyl)amine 7 reacts with selected dialkylzinc compounds to give dimeric alkylzinc bis(2-pyridylmethyl)amides 8. Regardless of the steric bulk of the alkyl substituent, dimers with central Zn₂N₂ rings are formed. Compounds 8 undergo spontaneous hydrolysis reactions upon exposure to air/moisture which can be partially controlled if the alkyl substituent R is bulky enough [R = CH(SiMe₃)₂]. A dimeric compound 9 containing both zinc-alkyl substituents and a μ-OH functionality results. In the course of this reaction, an amide instead of the expected RH is eliminated. Extensive DFT calculations show that the facile formation of a three-centered Zn[μ-(HO?H?NHR)]Zn functionality is a crucial step. Further evidence for the importance of Zn[μ-(X?H?Y)]Zn intermediates (X, Y = O and now N) in the general mechanism of hydrolysis catalyzed by binuclear zinc compounds is thus provided.     

Linear free energy relationships and kinetic isotope effects reveal the chemistry of the Ado 2′-OH group

Using kinetic isotope effects (KIE) and Hammett correlations, we show that the main role of the adenosine 2′-OH group on deprotonation by the non nucleophilic base DBU during external acyl group transfer is to generate enhanced electron density on the attacking nucleophile through ionization. The small primary KIEs (1.2 and 1.6) and the large Hammett reaction constants (+2.25 and +3.19) obtained for the ethanolysis of 2′/3′-O-p-substituted benzoyl 5′-O-trityl adenosines and 2′-deoxyadenosines are consistent with an A_N + D_N reaction mechanism. The implications of our results are discussed in terms of chemical contributions of the 2′-OH group in the ribosome catalysis of peptide bond formation.     

Theoretical studies of the oxidative addition of PhBr to Pd(PX3)2 and Pd(X2PCH2CH2PX2) (X = Me, H, Cl)

The density functional theory calculations were used to study the influence of the substituent at P on the oxidative addition of PhBr to Pd(PX₃)₂ and Pd(X₂PCH₂CH₂PX₂) where X = Me, H, Cl. It was shown that the C_ipso-Br activation energy by Pd(PX₃)₂ correlates well with the rigidity of the X₃P-Pd-PX₃ angle and increases via the trend X = Cl < H < Me. The more rigid the X₃P-Pd-PX₃ angle is, the higher the oxidative addition barrier is. The exothermicity of this reaction also increases via the same sequence X = Cl < H < Me. The trend in the exothermicity is a result of the Pd(II)-PX₃ bond strength increasing faster than the Pd(0)-PX₃ bond strength upon going from X = Cl to Me. Contrary to the trend in the barrier to the oxidative addition of PhBr to Pd(PX₃)₂, the C_ipso-Br activation energy by Pd(X₂PCH₂CH₂PX₂) decreases in the following order X = Cl > H > Me. This trend correlates well with the filled d_π orbital energy of the metal center. For a given X, the oxidative addition reaction energy was found to be more exothermic for the case of X₂PCH₂CH₂PX₂ than for the case of PX₃. This effect is especially more important for the strong electron donating phosphine ligands (X = Me) than for the weak electron donating phosphine ligands (X = Cl).     

Mononuclear,dinuclear and hydroxo-bridged tetranuclear complexes from reactions of Cu ions,mandelic acid and diimine ligands

The reaction of copper(II) hydroxocarbonate, mandelic acid (H₂MANO) and 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) in water affords [Cu(bpy)(μ₂-MANO)]₂ · 8H₂O (1), [Cu(bpy)(MANO)] · 4H₂O (2) and the opened tetranuclear hydroxo-bridged copper(II) complexes of formulae [Cu₄(μ₃-OH)₂(μ₂-MANO)₂(bpy)₄](phglyo)₂ · 8H₂O (3) (phglyo = phenylglyoxylate) or [Cu₄(μ₃-OH)₂(μ₂-OH)₂(OH₂)₂(phen)₄](Bza)₂(OH)₂ · 5H₂O (4) (Bza = benzoate), respectively. The compounds have been characterized by spectroscopic techniques and studied by single-crystal X-ray diffractometry. The formation of 3 and 4 takes place in basic media through dehydrogenation or oxidative dehydrogenation followed by in situ oxidative decarboxylation of mandelic acid to phenylglyoxylate or benzoate, respectively. These results indicate that cooperative catalysis of diimine ancillary ligands and copper(II) is essential.     

Heterometallic Cr2/Ag2 1D polymer: Synthesis,structure and properties

A 1D heterometallic Cr₂/Ag₂ polymer formulated as {[Ag(μ-H₂O)Ag(nta)Cr(μ-OH)(μ-AcO,O′)Cr(nta)]·H₂O}_n (1) (H₃nta = nitrilotriacetic acid) has been prepared and structurally characterized. {Cr(μ-OH)(μ-OAc)Cr} dimeric units containing two different bridging ligands, hydroxo and acetate groups are coordinated to six Ag atoms forming the 1D network. The temperature dependence of magnetic susceptibility for 1 which was fitted with an isotropic Hamiltonian including biquadratic exchange parameters, yielded antiferromagnetic interaction parameters (J = −8.5(1), j = −0.50(7) cm⁻¹ g = 2.0).     

Macrocycles with two exclusive hydrogen-bonding modes

A series of large, 44-membered macrocycles 7a-e were synthesized and characterized, which display two different diagonal binding modes. The unsubstituted macrocycle 7a strongly binds naphthalene-2,6-dicarboxylate through hydrogen bonds with the association constant (K_a ± 15%) of 4500 M⁻¹ in 40% (v/v) CD₃CN/CDCl₃ at 23 ± 1 °C. Introduction of an electron-withdrawing substituent (Cl) at all four corners increases the binding affinity (22,000 M⁻¹ for 7b), while that of an electron-donating substituent (pyrrolidinyl) greatly decreases it (150 M⁻¹ for 7c). The same propensity has been observed with macrocycles 7d and 7e bearing different substituents at two diagonal corners, suggesting that the relative population of the binding modes would be modulated by controlling the electron density of the aromatic ring.     

Kinetic studies on Brook-type isomerization of acylpolysilanes to silenes

First-order rate constants of Brook-type isomerization of acylpolysilanes (Me₃Si)₃SiCOR (R = iso-Pr, tert-Bu, Ad, 2,6-xylyl, and Mes) leading to silenes (Me₃Si)₂SiC(OSiMe₃)R at various temperatures were determined. Their Eyring plots gave kinetic parameters of ΔH^‡ = 26.6-29.4 kcal mol⁻¹ and ΔS^‡ = −11.5 to −14.6 cal mol⁻¹ K⁻¹. The isomerization was accelerated by introducing an electron-donating alkyl substituent on the carbonyl carbon. These results are in accordance with a concerted mechanism involving a four-centered transition state.     

Synthesis,structure characterization and thermal properties of [Zr6(μ3-O)4(μ3-OH)4(OOCCH2Bu)9(μ2-OH)3]2

Oxo/hydoxo zirconium(IV) complex of the general formula [Zr₆(μ₃-O)₄(μ₃-OH)₄(OOCCH₂^tBu)₉(μ₂-OH)₃]₂ has been isolated, when Zr(OⁱPr)₄ reacted with a 2-fold excess of 3,3-dimethylbutyric acid. Single crystal X-ray diffraction data, collected at 103 and 153 K, showed that the studied compound crystallizes in hexagonal system (P6₃/m (no. 176)). Structure consists of dimers composed of [Zr₆(μ₃-O)₄(μ₃-OH)₄(OOCCH₂^tBu)₉] sub-units, linked by six μ₂-OH bridges. Infrared spectroscopic studies proved the presence of hydroxo groups in the structure of studied clusters and formation of different types of oxo/hydroxo bridges. The application of variable temperature infrared spectroscopy and differential scanning calorimetry revealed that the structure of this complex undergoes the phase transitions at 143–183 and 203–293 K. Comparison of spectral and crystallographic data suggests that these phase transitions might be related to changes in the strength of Zr–O bonds of μ₂-OH bridges linking complex sub-units, and change in symmetry of the crystal lattice (from hexagonal to trigonal). Analysis of thermogravimetric data showed that decomposition of [Zr₆(μ₃-O)₄(μ₃-OH)₄(OOCCH₂^tBu)₉(μ₂-OH)₃]₂ proceeds with complete conversion to ZrO₂ (monoclinic form) between 603 and 803 K.     

Regio- and stereo-specific addition of organotellurium trihalides to ferrocenylacetylene: Molecular and crystal structure of (Z)-halovinyl organotellurium dihalides

Organotellurium(IV) trihalides RTeX₃ (X = Br, I) reacts readily with ferrocenylacetylene to give (Z)-products of electrophilic addition to C-C triple bond: (Z)-FcXC = CTeX₂R (R = Ph, X = Br (1) or I (2); R = trans-8-ethoxy-4-cyclooctenyl, X = Br (3)). In case of PhTeX₃ (X = Br or I) the room temperature reaction is spontaneous and the structure of the product does not depends on the polarity of the solvent used; this is in contrast to the reaction of aryl-acetylenes with RTeBr₃ which were reported to afford (E)-bromovinyl aryltellurium dibromides in methanol and its (Z)-isomer in benzene. Molecular and crystal structures of new compounds and effect of bulky and electron-rich ferrocenyl substituent on the reactivity of acetylene moiety are discussed in this paper.     

Electron transfer reactions of organic sulfoxides with photochemically generated ruthenium(III)-polypyridyl complexes

The electron transfer (ET) reaction of aryl methyl sulfoxides with ruthenium(III)-polypyridine complexes is sensitive to the change of substituent in the aryl moiety of ArS(O)CH₃ and ligand of Ru(III) complex. The detection of sulfoxide radical cation as the transient by conventional flash photolysis confirms ET in the rate-controlling step. The successful application of Marcus cross relation of ET leads to the evaluation of self-exchange rate constant of ArS⁺(O)CH₃/ArS(O)CH₃ as 4.0×10⁵ M⁻¹ s⁻¹ similar to organic sulfides. Comparison with the reactivity of iron(III)-polypyridyl complexes points out that both reactivity and ρ values are higher with Ru(III) complexes.     

Intra- and intermolecular hydrogen bonds in [Ag(PPh3)3(HL)] complexes [H2L: H2xspa = 3(aryl)-2-sulfanylpropenoic acids; H2cpa = 2-cyclopentylidene-2-sulfanylacetic acid]

Compounds of the type [Ag(PPh₃)₃(HL)] {H₂xspa=3(aryl)-2-sulfanylpropenoic acids: x = Clp [3-(2-chlorophenyl)-], -o-mp [3-(2-methoxyphenyl)-], -p-mp [3-(4-methoxyphenyl)-], -o-hp [3-(2-hydroxyphenyl)-], -p-hp [3-(4-hydroxyphenyl-); H₂cpa = 2-cyclopentylidene-2-sulfanylacetic acid} were synthesized and characterised by IR and NMR (¹H ¹³C and ³¹P) spectroscopy and by FAB mass spectrometry. The crystal structures of [Ag(PPh₃)₃(HClpspa)], [Ag(PPh₃)₃(H-o-mpspa)], [Ag(PPh₃)₃(H-p-mpspa)] and [Ag(PPh₃)₃(Hcpa)] reveal the presence of discrete molecular units containing an intramolecular O-H···S hydrogen bond between the S atom and one of the O atoms of the COOH group. This intramolecular hydrogen bond remains in [Ag(PPh₃)₃(H-o-hpspa)]·EtOH and [Ag(PPh₃)₃(H-p-hpspa)] but in both cases polymeric structures are built on the basis of O-H···O interactions that involve the -OH substituent of the phenyl group of the sulfanylpropenoate fragment.     

New ferromagnetic dinuclear triply-bridged copper(II) compounds containing carboxylato bridges: Synthesis,X-ray structure and magnetic properties

The new triply-bridged dinuclear copper(II) complexes, [Cu₂(μ-O₂CH)(μ-OH)₂(dpyam)₂](ClO₄) · H₂O (1), [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-OH₂)(dpyam)₂](S₂O₈) (2), [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-OH₂)(bpy)₂](NO₃)₂ (3), [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-OH₂)(phen)₂](BF₄)₂ · 0.5H₂O (4), [Cu₂(μ-O₂CCH₂CH₃)(μ-OH)(μ-OH₂)(phen)₂](NO₃)₂ (5) and [Cu₂(μ-O₂CCH₃)(μ-OH)(μ-Cl)(bpy)₂]Cl · 8.5H₂O (6) (dpyam = di-2-pyridylamine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), have been synthesized and characterized crystallographically and also their spectroscopic and magnetic properties have been studied. A structural classification of this type of dimers, based on the data obtained from X-ray diffraction analysis in the present work and those reported in the literature has been performed. In these complexes, the local geometry around the copper centre is generally a distorted square pyramid and distorted trigonal bipyramid with different degrees of distortion. The global geometry of the dinuclear complexes can be described in terms of the relative arrangement of the two five-coordinate environments, giving rise to different classes (A–F) of complexes. The most logical explanations have been provided for each class describing different magnetic interactions. Practically, there is a clear correlation between structural data and J values of the class B complexes. Extended Hückel calculations were performed for the present complexes 1–6, as well as for some other class B complexes, showing the different molecular orbitals involved in their corresponding frontier orbitals, together with their energy. The results are found to be useful for the proper interpretation and correlation of the magnetic data and the dinuclear structure of the present complexes.     

Substitution effects at α-position of divalent five-membered ring XC4H3M (M = C, Si and Ge)

Full geometry optimizations were carried out on singlet and triplet states of α-substitued divalent five-membered rings XC₄H₃M (X = -NH₂, -OH, -CH₃ -H, -CH₃, -Br, -Cl, -F, -CF₃ and -NO₂; M = C, Si and Ge) by B3LYP method using 6-311++G** basis set. Thermal energy gaps, ΔE_s-t; enthalpy gaps, ΔH_s-t; Gibbs free energy gaps, ΔG_s-t, between singlet (s) and triplet (t) states of above structures were calculated using the GAUSSIAN 03 program. The ΔG_s-t of XC₄H₃C was changed in the order: X = -Cl > -Br > -CH₃ > -H > -CF₃ > -F > -NO₂ > -OH > -NH₂. The changes of ΔG_s-t for XC₄H₃Si and XC₄H₃Ge were in the order: X = -NH₂ > OH > F > Cl > Br > CH₃ > H > CF₃ > NO₂. The relationship between all the parameters such as different energy types, geometry parameters, natural bonding orbital (NBO) charge at atoms, HOMO and LUMO energies, chemical hardness (η), chemical potential (μ), dipole Moment (D), electrophilicity (ω) and the maximum amount of electronic charge, ΔN_max, was presented and discussed.     

Self-assembly of para-OH functionalized ECE-metalated pincer complexes

Various para-OH functionalized ECE-pincer metal complexes [MX(ECE-OH)L_n] (ECE-OH = [C₆H₂(CH₂E)₂-2,6-OH-4]⁻, E = NMe₂, PPh₂ and SPh) were synthesized. The X-ray crystal structures of neutral [PdCl(SCS-OH)], [PdCl(NCN-OH)], and cationic [Pd(PCP-OH)(MeCN)](BF₄) are reported. The neutral halide complexes exhibit self-assembly to form polymeric chains via H-bonding involving the para-OH group as donors and the halide ligand on the metal as acceptors. Moreover, the halide ligand can be replaced by a monomeric aryloxy-O ligand leading to the formation of a covalently bonded dimer. The crystal structure of such a dimer derived from [PdI(NCN-OH)] is reported. Furthermore, these pincer-metal complexes were tethered through a carbamate linker to a siloxane functionality with the aim to be immobilized on a silica support. The crystal structure of a siloxane-functionalized [PtI(NCN-Z)] complex exemplifies how other H-bonding interactions not involving the metal-halide groupings can lead to polymeric networks as well.     

Nucleophilic fluoroalkylation of iminium salts

Iminium cations generated by the coupling of aldehydes, N-trimethylsilylamines and TMSOTf or by the methylation of imines with MeOTf smoothly react with silanes of a general formula Me₃SiR_f (R_f = CF₃, CCl₂F, C₆F₅) to afford the corresponding tertiary amines having a fluorinated substituent. The key step, involving C-C bond formation, is promoted by NaOAc or KF in DMF as a solvent.     

Synthesis,crystal structure and magnetic properties of a new dinuclear copper(II) amino acid complex [Cu2(l-arg)2(μ-HPO4-O)(μ-HPO4-O,O′)(μ-OH)] · (H3O) · (H2O)6

A novel dinuclear copper(II) complex with the amino acid l-arginine (l-arg), with mono and bidentate HPO₄²⁻ oxoanions and an OH⁻ anion. [Cu₂(l-arg)₂(μ-HPO₄-O)(μ-HPO₄-O,O′)(μ-OH)]⁻ · (H₃O)⁺ · 6H₂O (1) was prepared and its structure was determined by X-ray diffraction methods. The two independent copper ions are in a distorted square pyramidal coordination, each bonded to one l-arginine molecule. These two Cu(l-arg) units are bridged by two monoatomic equatorial–apical oxygen ligands belonging to a monodentate hydrogenphosphate group, and to the hydroxyl group. The copper ions in the dinuclear unit at d = 3.1948(8) Å are also connected by two equatorial oxygen belonging to a bidentate hydrogenphosphate. This dinuclear character and bridging scheme, not common for metal–amino acid compounds, is a consequence of the properties of the phosphate anions. The magnetic susceptibility at temperatures between 2 and 300 K and the isothermal magnetization curves at T = 2.29(1) K with applied fields up to 9 T were measured. The magnetic data indicate an antiferromagnetic intradinuclear exchange coupling J/k_B = −3.7(1) K and using a molecular field approximation we estimated a weaker ferromagnetic interaction J′/k_B ∼ 0.3 K between neighbour dinuclear units.     

Viologen-based benzylic dendrimers: selective synthesis of 3,5-bis(hydroxymethyl)benzylbromide and conformational analysis of the corresponding viologen dendrimer subunit

Convergent and divergent strategies for the synthesis of viologen dendrimers with 1,3,5-tri-methylene-branching units are discussed. The title compound is easily transformed into 1-[3,5-bis(hydroxymethyl)benzyl]-4-(pyridin-4-yl)pyridinium hexafluorophosphate, which is used in sequential growth and activation steps as a CB₂ compound in the cascade-type dendrimer synthesis (B = -OH, activation = -OH → Br). Analysis of the dendrimer structure reveals that three torsional angles, that is, τ₁ between the two pyridinium units, τ₂ between the methylene and pyridinium and τ₃ between the methylene and phenyl, determine the conformational space of the dendrimers. We report here the crystal structure of 1-[3,5-bis(hydroxymethyl)benzyl]-4-(pyridin-4-yl)pyridinium as PF₆⁻ salt which represents the smallest subunit of the dendrimer that shows the same three torsional angles. The crystal structure together with the results from PM3 calculations opens an avenue to judge the structure of benzylic viologen-based dendrimers.     

Thomson scattering on argon surfatron plasmas at intermediate pressures: Axial profiles of the electron temperature and electron density

The axial profiles of the electron density n_e and electron temperature T_e of argon surfatron plasmas in the pressure range of 6–20 mbar and microwave power between 32 and 82 W have been determined using Thomson Scattering of laser irradiation at 532 nm. For the electron density and temperature we found values in the ranges 5 × 10¹⁸ < n_e < 8 × 10¹⁹ m^− 3 and 1.1 < T_e < 2.0 eV. Due to several improvements of the setup we could reduce the errors of n_e and T_e down to 8% and 3%, respectively. It is found that n_e decreases in the direction of the wave propagation with a slope that is nearly constant. The slope depends on the pressure but not on the power. Just as predicted by theories we see that increasing the power leads to longer plasma columns. However, the plasmas are shorter than what is predicted by theories based on the assumption that for the plasma-wave interaction electron–atom collisions are of minor importance (the so-called collisionless regime). The plasma vanishes long before the critical value of the electron density is reached. In contrast to what is predicted by the positive column model it is found that T_e does not stay constant along the column, but monotonically increases with the distance from the microwave launcher. Increases of more than 50% over 30 cm were found.     

3-(o-Trifluoroacetamidoaryl)-1-propargylic esters: common intermediates for the palladium-catalyzed synthesis of 2-aminomethyl-, 2-vinylic, and 2-alkylindoles

3-(o-Trifluoroacetamidoaryl)-1-propargylic esters have been used as common synthetic intermediates for the preparation of a variety of 3-unsubstituted 2-substituted indoles. Treating ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates unsubstituted or containing an aryl substituent at the propargylic carbon with piperazines and Pd(PPh₃)₄ in THF at 80 °C affords 2-(piperazin-1-ylmethyl)indoles in excellent yields. Good to excellent yields of 2-aminomethylindoles are also obtained with other secondary amines. Ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates bearing an alkyl substituent at the propargylic carbon and ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic acetates disubstituted at the propargylic carbon give 2-vinylic indoles with the Pd(OAc)₂/PPh₃ combination and Et₃N in THF at 80 °C. Formation of 2-vinylic indoles is quite stereoselective, generating trans vinylic derivatives, at least with the substrates that we have investigated. In the presence of formic acid, Et₃N, and Pd(PPh₃)₄ in MeCN at 80 °C, ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates afford 2-alkylindoles in good to excellent yields.