Ferrocene Compounds. XXXI. Structure of 3-Ferrocenylpropanoic Acid

The title compound was prepared by modified procedure and characterized by means of IR, [¹H] and [¹³C] NMR spectroscopy. The structure was also determined by a single-crystal X-ray diffraction (XRD). 3-Ferrocenylpropanoic acid crystallizes as orange prisms in the triclinic space group P with a = 7.645(1) Å, b = 7.953(1) Å, c = 9.961(1) Å, = 81.67(1), = 68.43(1), = 83.76(1), V = 556.3(1) ų, Z = 2, R = 0.0435. In the ferrocene skeleton, Fe-C distances are in the range 2.033(2)–2.052(2) Å and C C distances in the range 1.412(5)–1.431(3) Å. The angle defined by ring centers and Fe atom is 177.7(1). The cyclopentadienyl rings are twisted from the eclipsed conformation by 8.3(2) (average value). In the structure was observed strong intermolecular hydrogen bond of 2.670(3) Å forming cyclic dimers of the R₂ ² (8) type.     

H-, C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Using ¹H- and ¹³C-NMR spectroscopies, cationic intermediates formed by activation of L₂ZrCl₂ with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L₂ are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R)₂ZrCl₂ (R=Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, Me₅, n-Bu, t-Bu), rac-ethanediyl(Ind)₂ZrCl₂, rac-Me₂Si(Ind)₂ZrCl₂, rac-Me₂Si(1-Ind-2-Me)₂ZrCl₂, rac-ethanediyl(1-Ind-4,5,6,7-H₄)₂ZrCl₂, (Ind-2-Me)₂ZrCl₂, Me₂C(Cp)(Flu)ZrCl₂, Me₂C(Cp-3-Me)(Flu)ZrCl₂ and Me₂Si(Flu)₂ZrCl₂. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R)₂ZrCl₂/MAO (R=H, Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, Me₅, n-Bu, t-Bu) and rac-Me₂Si(Ind)₂ZrCl₂ were established. The catalysts (Cp-R)₂ZrCl₂/AlMe₃/CPh₃⁺B(C₆F₅)₄⁻ (R=Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R)₂ZrMe⁺←Me⁻-Al≡MAO (IV) with different [Me-MAO]⁻ counteranions have been identified in the (Cp-R)₂ZrCl₂/MAO (R=n-Bu, t-Bu) systems at low Al/Zr ratios (50-200). At Al/Zr ratios of 500-1000, the complex [L₂Zr(μ-Me)₂AlMe₂]⁺[Me-MAO]⁻ (III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr=200-1000) for the systems (Cp-R)₂ZrCl₂/MAO (R=H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R)₂ZrCl₂/MAO (R=1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄) and rac-Me₂Si(Ind)₂ZrCl₂/MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems.     

The psuedo‐michael reaction of 2‐aminoimidazolines 2. Part 1. Synthesis and structure assignment of isomeric 5(1H)‐Oxo and 7(1H)‐Oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates

The pseudo‐Michael reaction of 1‐aryl‐2‐aminoimidazolines‐2 with diethyl ethoxymethylenemalonate (DEEM) was investigated. Extensive structural studies were performed to confirm the reaction course. For derivatives with N1 aromatic substituents, it was found that the reaction course was temperature dependent. When the reaction temperature was held at ?10 °C only the formation of 1‐aryl‐7(1H)‐oxo‐2,3‐dihydroimi‐dazo[1,2‐a]pyrimidine‐6‐carboxylates ( 4 ) was observed in contrast to earlier suggestions. Under the room temperature conditions, the same reaction yielded mixtures, with varying ratio, of isomeric 1‐aryl‐7(1H)‐oxo‐ ( 4a‐4f ) and 1‐aryl‐5(1H)‐oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates ( 5a‐5f ). The molecular structure of selected isomers, 4b and 5c , was confirmed by X‐ray crystallography. Frontal chro‐matography with delivery from the edge was applied for the separation of the isomeric esters. The isomer ratio of the reaction products depended on the character of the substituents on the phenyl ring. The 1‐aryl‐7(1H)‐oxo‐carboxylates ( 4a‐4f ) were preferably when the phenyl ring contained H, 4‐CH₃, 4‐OCH₃ and 3,4‐Cl₂ substituents. Chloro substitution at either position 3 or 4 in the phenyl ring favored the formation of isomers 5a‐5f . The isomer ratios were confirmed both by ¹H NMR and chromatography. The reaction of the respective hydrobromides of 1‐aryl‐2‐aminoimidazoline‐2 with DEEM, in the presence of triethylamine, gave selectively 5(1H)‐oxo‐esters ( 5a‐5f ).     

Intramolecular cycloaddition/cycloreversion of (E)-3β,17β-diacetoxy-5,10-secoandrost-1(10)-en-5-one

Treatment of 3β,17β-diacetoxy-5,10-secoandrost-1(10)-en-5-one with BF₃·Et₂O was shown to proceed with cleavage of the macrocycle and formation of a new compound containing a cyclopentenone ring. Based on DFT calculations, an intramolecular Lewis acid promoted [2+2]cycloaddition, followed by a cycloreversion of the intermediate oxetane, is proposed as a possible reaction mechanism.     

Does charge carrier dimensionality increase in mixed-valence salts of tetrathiafulvalene-terminated dendrimers?

[structure: see text] In four new dendrimers terminated by 12 electroactive tetrathiafulvalenyl substituents, the tridimensional character of the inter- and intradendrimeric charge and electron transfer, and hence of the electroconductivity, is evidenced by examination of the electronic spectra of their corresponding neutral state and cation radical, dication, and mixed-valence salts, including a closed-shell anion.     

A convenient route to 1-(2-oxiranyl)-1,4-diketones and their application to the synthesis of endo-brevicomin, endo-isobrevicomin, frontalin and related compounds via alkylated 6,8-dioxabicyclo[3.2.1]octan-2-ones

1-(2-Oxiranyl)-1,4-alkanediones were prepared from the ethylene acetals of ethyl 4-oxoalkanoates via the oxidation of the intermediate 1,2-dialkylcyclopropanols having a protected carbonyl group in an aliphatic chain. Intramolecular acetalization of these epoxy dicarbonyl compounds gave alkylated 6,8-dioxabicyclo[3.2.1]octan-2-ones in good yields. The latter were found suitable to be precursors for (±)-endo-brevicomin and its 2-hydroxy derivative, as well as (±)-endo-isobrevicomin and (±)-frontalin.     

Fused isoquinolines: 3-aryl-2,3,4,5-tetrahydro-1H-pyrrolo[2,3-c]isoquinoline-1,5-dione-2-spiro-4′-(1′-alkyl-1′,4′-dihydropyridine)s

Previously unknown 3-arylamino-1,2-dihydro-1-isoquinolones were obtained by condensation of 2-cyanomethylbenzoic acid with arylamines. Isonicotinoylation of the compounds was shown to proceed at the carbon atom in the 4-position to give 3-arylamino-4-isonicotinoyl-1,2-dihydro-1-isoquinolones which were quaternized with alkylating agents and formed the corresponding pyridinium salts. Deprotonation of the latter induced intramolecular conjugated addition with the pyrrole ring closure and formation of spiro compounds. The structure of the products was confirmed by NMR, IR and UV spectroscopy and by synthesis of the model compound, 3-(4-tolyl)-2,3,4,5-tetrahydro-1H-pyrrolo[2,3-c]isoquinoline-1,5-dione.     

Chirale 2,2′-Polyoxaalkano-9,9′-spirobifluorene

Chiral 2,2′-polyoxaalkano-9,9′-spirobifluorenes From 2,2′-diacetyl-9,9′-spirobifluorene (2) , twelve chiral polyethers have been prepared as potential ion- and enantiomer-selective ionophores. The absolute configuration of the polyethers 15 – 17 , 19 – 22 , and 25 has been determined by chemical correlation with vespirenes [11] [29], by circular dichroism, and by X-ray analysis. The circular dichroism of 15 – 17 , 19 and 21 depends on the size of the macrocycle and indicates that the fluorene chromophores of 19 and 21 with 13- and 16-membered rings respectively deviate considerably from orthogonality.     

Magnetic switch of permeability for polyelectrolyte microcapsules embedded with Co@Au nanoparticles

We explored using a magnetic field to modulate the permeability of polyelectrolyte microcapsules prepared by layer-by-layer self-assembly. Ferromagnetic gold-coated cobalt (Co@Au) nanoparticles (3 nm diameter) were embedded inside the capsule walls. The final 5 mum diameter microcapsules had wall structures consisting of 4 bilayers of poly(sodium styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH), 1 layer of Co@Au, and 5 bilayers of PSS/PAH. External alternating magnetic fields of 100-300 Hz and 1200 Oe were applied to rotate the embedded Co@Au nanoparticles, which subsequently disturbed and distorted the capsule wall and drastically increased its permeability to macromolecules like FITC-labeled dextran. The capsule permeability change was estimated by taking the capsule interior and exterior fluorescent intensity ratio using confocal laser scanning microscopy. Capsules with 1 layer of Co@Au nanoparticles and 10 polyelectrolyte bilayers are optimal for magnetically controlling permeability. A theoretical explanation was proposed for the permeability control mechanisms. "Switching on" of these microcapsules using a magnetic field makes this method a good candidate for controlled drug delivery in biomedical applications.     

Selective hydrogenation of butadiene-styrene copolymers using a Ziegler-Natta type catalyst 2. Thermal properties

Three types of butadiene-styrene copolymers, diblock, triblock and random, were partially hydrogenated in their elastomeric units in order to determine the influence of hydrogenation extent on their thermal properties. The hydrogenation reactions were carried out using a Ziegler-Natta type catalyst and the extent of hydrogenation was evaluated by FTIR spectroscopic technique. The percentage of crystallinity was determined by differential scanning calorimetry (DSC), considering the low density polyethylene (LDPE) as reference since the saturation of elastomeric units with low content of 1,2-vinyl bonds gives a structure which resembles to LDPE, thus semi-crystalline polymers were obtained. On the other hand, the glass transition temperature (T_g) for the hydrogenated and non-hydrogenated copolymers as well as their heat of fusion, were also determined by DSC. An equation to evaluate the T_g of partially hydrogenated random copolymers is proposed considering both the saturated and unsaturated fractions. The thermo-oxidative behaviour of certain hydrogenated and non-hydrogenated copolymers was evaluated by thermogravimetric analyses (TGA). The results obtained by TGA suggest that a minimum saturation level is necessary in order to improve the thermo-oxidative resistance of the polymers.