A study on thermal behaviors of mono ethyl ester azocalix[4]arene derivatives

In the present study, thermal stabilities of five new family of azocalix[4]arene mono ethyl ester derivatives, 4a–e, were investigated using thermogravimetry, differential thermogravimetry, and differential thermal analysis methods. It was found that all compounds showed thermal stability up to 236 °C averagely. After this temperature, decomposition of compounds starts gradually. The decomposition routes of 4a–c compounds are similar and occur with two stages. Ester alkyl groups decompose and remove from the structure in the first stage. Second stage corresponds to rest of structure decomposition. The decomposition routes of the 4d–e compounds are different from the decomposition routes of the 4a–c compounds. These compounds include halogen, and decomposition reactions realize with three and four stages respectively.     

Nickel(II)-α-diimine complexes containing naphthyl substituents for ethylene polymerization under low ethylene pressure

Two new α-diimine containing Ni(II) complexes, {bis[N,N′-(2,6-dimethyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3a and {bis[N,N′-(2-methyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3b were synthesized and characterized. The crystal structures of representative ligand 2a and its complex 3a were determined by X-ray crystallography. Complex 3a bearing 2,6-dimethyl and 4-naphthyl groups, activated by diethylaluminum chloride (DEAC), shows high catalytic activity for the polymerization of ethylene [4.43 × 10⁶ g PE/(mol Ni h bar)]. Interestingly, complexes 3a and 3b bearing the naphthyl substituent in the para-aryl position produced dendritic polyethylenes (branching degree, 3a: 112, 118, and 147; 3b: 113, 127, and 151 branches/1,000 C at 20, 40, and 60 °C, respectively). The dendritic polyethylene particle size obtained by 3a and 3b/DEAC can be controlled in the 1–20 nm range under low ethylene pressure (diameter, 3a: 18.31, 14.44, and 11.09; 3b: 12.29, 8.98 and 6.27 nm at 20, 40, and 60 °C, respectively) and could be expected to produce a nano-targeted drug carrier after modification with water-soluble oligo(ethylene glycol).     

Thermal studies of some biological active oxadiazoles

A series of new unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles (3a–d) has been synthesized to evaluate their antibacterial and thermal properties. All compounds have been tested for their in vitro antibacterial activity against two Gram-positive bacteria namely, Staphylococcus aureus and Bacillus subtilis. Among the tested compounds, compound 2-(4-chlorophenyl)-5-(thiophen-2-yl)-1,3,4-oxadiazole (3c) has been found to be most potent member having minimum inhibitory concentration. Thermal stability and melting point of compounds have been studied by TG and DSC analysis in air atmosphere at heating rate of 10 °C min^?1. Thermal degradation kinetics of the most potent antibacterial compound 3c has been carried out by multiple heating rate model free kinetic methods namely, Ozawa–Flynn–Wall, modified Coats-Redfern, and Kissinger.     

X-ray and computational structural study of neutral <Emphasis Type="Italic">bis</Emphasis>(<Emphasis Type="Italic">N,N,N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-tetramethylthiophosphoramidoyl)-methylamine

The structure of bis(N,N,N′,N′-tetramethylthiophosphoramidoyl)-methylamine 1 has been determined by single-crystal X-ray diffraction. The compound 1 crystallizes in the monoclinic system, with a space group P2₁/c, a = 11.836(2) Å, b = 11.659(2) Å, c = 12.796(5) Å and β = 95.28(3)°, V = 1758.3(5) Å³ and Z = 4. The X-ray crystallographic data have been assessed by semi-empirical and ab-initio density functional theory and by Hartree–Fock molecular orbital methods. A comparative study of the results of the different methods is given.     

Synthesis and characterization of a series of chiral NHC–Pd complexes derived from l-phenylalanine

The synthesis of a series of chiral Pd(L)PyBr₂ (3a–3e) and Pd(L)PyCl₂ (4d and 4e) complexes from l-phenylalanine is presented (L = (S)-3-allyl-4-benzyl-1-(2,6-diisopropylphenyl)-imidazolin-2-ylidene (a), (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(naphthalen-2-ylmethyl)imidazolin-2-ylidene (b), (S)-4-benzyl-3-(biphenyl-4-ylmethyl)-1-(2,6-diisopropylphenyl)imidazolin-2-ylidene (c), (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(naphthalen-1-ylmethyl)imidazolin-2-ylidene (d) or (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(2,4,6-trimethylbenzyl)imidazolin-2-ylidene (e). The complexes were characterized by physicochemical and spectroscopic methods, and the X-ray crystal structures of 3a–3c and 4d are reported. In each case, there is a slightly distorted square-planar geometry around palladium, which is surrounded by imidazolylidene, two trans halide ligands and a pyridine ligand. There are π–π stacking interactions in the crystal structures of these complexes. Complex 3a showed good catalytic activity in the Cu-free Sonogashira coupling reaction under aerobic conditions.     

Crystalline inclusion compounds of lower rim propyl substituted calix[4]arenes featuring different number and positions of the modifying groups

Three lower rim n-propyl substituted calix[4]arenes (1–3) with varied number and position of the modifying groups have been prepared. Inclusion compounds (five species) involving different kinds of guest solvents have been isolated. Their X-ray crystal structures were determined and comparatively discussed using isostructurality calculations. Two of the inclusion compounds obtained (1a and 1b) are polymorphs containing the same host and guest molecules in equal stoichiometric ratio but different Z′ values caused by a phase transition around 140 K. The inclusion compounds 2a and 2b refer to the interesting case of a mixed solvent complex while 3a allows studying the effect of full lower rim n-propyl substitution.     

Electronic structures and spectroscopic properties of promising highly efficient red phosphorescent Os(II)(LR)2(PH3)2 complexes: a theoretical exploration

The red phosphorescent osmium(II) complexes [Os(LR)₂(PH₃)₂] (L = 2-pyridyltriazole (ptz): R = H (1a), CF₃ (1b), t-Bu (1c)); L = 2-pyridylpyrazole (ppz): R = H (2a), CF₃ (2b), t-Bu (2c)); L = 2-phenylpyridine (ppy): R = H (3a)) were explored using density functional theory (DFT) methods. The ground- and excited-state geometries of the complexes were optimized at the B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively. The absorption and phosphorescence of the complexes in CH₂Cl₂ media were calculated based on the optimized ground- and excited-state geometries using time-dependent density functional theory method with the polarized continuum model. The optimized geometry structural parameters of the complexes in the ground state agree well with the corresponding experimental values. The lower-lying unoccupied molecular orbitals of the complexes are dominantly localized on the L ligand, while the higher-lying occupied ones are composed of Os(II) atom and L ligand. The low-lying metal-to-ligand and intraligand charge transfer (MLCT/ILCT) transitions and high-lying ILCT transitions are red-shifted with the increase in the π-donating ability of the L ligand and the π electron-donating ability of R substituent. The calculation revealed that the phosphorescence originated from ³MLCT/³ILCT excited state. However, the complex 3a displayed different types of MLCT/ILCT excited state compared with that of 1a–2c, and the different types of transition were also found in the absorption. In addition, we found that the phosphorescence quantum efficiency of Os(II) complexes is related to the metal composition in the high-energy occupied molecular orbitals, it will be helpful to designing highly efficient phosphorescent materials.     

Synthesis and thermal behavior study of complexes of the type [Pd(μ-X)(4-eb-p-phen)]2 (X = Cl,Br, I,N3, NCO,SCN) and 4-eb-p-phen [bis(4-ethylbenzyl)p-phenylenediimine]

The Schiff base bis(4-ethylbenzyl) p-phenylenediimine, 4-eb-p-phen (1), and six new dimeric Pd(II) complexes of the type [Pd(μ-X)(4-eb-p-phen)]₂ {X = Cl (2), Br (3), I (4), N₃ (5), NCO (6), SCN (7)} have been synthesized and characterized by elemental analysis, IR spectroscopy, and ¹H and ¹³C{¹H}-NMR experiments. The thermal behavior of the complexes 2–7 has been investigated by means of thermogravimetry and differential thermal analysis. From the final decomposition temperatures, the thermal stability of the complexes can be ordered in the following sequence: 3 > 4 > 7 > 2 ≈ 5 > 6. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction (XRD).     

Sterically hindered inversion of nitrogen atoms in cyclic hydrazines:N,N′-dialkyl-1,3,4-oxadiazolidines; 1,3,4-thiadiazolidine; and 4,5-benzo-1,2,3,6-tetrahydropyridazine

N,N′-Diisopropyl-substituted 1,3,4-oxadiazolidine3c, 1,3,4-thiadiazolidine6, 4,5-benzo-1,2,3,6-tetrahydropyridazine8, and new 3,4-dialkyl-1,3,4-oxadiazolidines9–14 were synthesized and studied. The configurational stability of the N atoms does not change on going from compound3c to itsS-analog6 and decreases in the case of pyridazine8. 3,4-Di-tert-alkyl-1,3,4-oxadiazolidines3d and11–14 were found to be promising objectes for optical resolution.     

Microwave promoted improved regioselective synthesis of 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones by radical cyclisation

In this work, two new effective methodologies have been adopted for the preparation of 5-(2′-bromobenzyloxy)pyrimidine-2,4-diones 6(a–k). In the first methodology, 5-hydroxy uracils 4(a–f) were alkylated with 2-bromobenzyl bromide 5a or 2-bromo-5-methoxy benzyl bromide 5b under phase transfer catalysis condition using lithium hydroxide/tetrabutyl ammonium bromide in N,N-dimethylformamide at 45 °C, and in the second method, the microwave irradiation (MWI) protocol has been exploited by mixing 5-hydroxy uracils 4(a–f) with 30 % excess of 2-bromobenzyl bromide 5a or 2-bromo-5-methoxy benzyl bromide 5b. A catalytic amount of TBAB and potassium carbonate was added and irradiated in an open Erlenmeyer flask in a microwave oven for 3–12 min. The tributyltin hydride-mediated radical cyclisation of 6(a–k) was carried out under MWI to generate 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones 7(a–k) in 80–89 % yield, and the reaction time was shortened compared to the previously reported conventional radical cyclisation method.     

Guest inclusion in cyclic imides containing flexible tethers

Guest inclusion properties of two cyclic imides which have carboxylic acids connected through flexible tether, namely, 4-(1,3-dioxo-1,3-dihydro-isoindol-2-ylmethyl)-cyclohexanecarboxylic acid (1) and 4-(1,3-dioxo-1H,3H-benzo[de]isoquinolin-2-ylmethyl)-cyclohexanecarboxylic acid (2) are studied. The crystals of host 1 containing one molecule of 1, the crystals of 4,4′-bipyridine (bpy) cocrystal of 1 containing one molecule of 1 and half molecule of bpy (1a), the crystals of 1,4-dioxane solvate of 1 containing two molecule of 1 and one and half molecule of 1,4-dioxane (1b) and the crystals of quinoline solvate of 1 containing one molecule of 1 and one molecule of quinoline (1c) in their crystallographic asymmetric units are investigated. Intermolecular hydrogen bonded two dimensional (2D) sheet structure of 1 and 3D channel network of 1b are comprised of cyclic R ₂ ² (8) hydrogen bond motifs; whereas cleavage of dimeric carboxylic acid R ₂ ² (8) motifs occurs in the structures of 1a and 1c in which 3D host–guest networks are comprised of discrete O–H···N and cyclic R ₂ ² (7) interactions, respectively. Various types of weak interactions between the two symmetry nonequivalent host molecule are found to be responsible for the formation of channels (14 × 11 Å) filled by guest 1,4-dioxane molecules in the crystal lattice of 1b. Two different solvates of 2 containing one molecule of 2 with a water molecule (2a) and one molecule of 2 with a quinoline molecule (2b) in their crystallographic asymmetric units, respectively, are also crystallized in different space groups. The quinoline molecules are held with host molecules by discrete O–H···N and C–H···O interactions and reside inside the voids formed by 3D repeated hexameric assemblies of host molecules in the crystal lattice of 2b.     

Theoretical study on the singlet and triplet potential energy surfaces of NH (X3Σ−) + HCNO reaction

Both the singlet and triplet potential energy surfaces (PESs) of the NH (X³Σ^?) + HCNO reaction have been investigated at the BMC-CCSD level based on the UB3LYP/6-311++G(d, p) structures. The results show that the title reaction is more favorable through the singlet potential energy surface than the triplet one. For the singlet potential energy surface of the NH (X³Σ^?) + HCNO reaction, the most feasible association of NH (X³Σ^?) with HCNO is found to be a non-barrier nitrogen-to-carbon attack forming the adduct a (trans-HNCHNO), which can isomerize to the adduct b (cis-HNCHNO). The most feasible channel is that the 1, 3-H shift with N2–H2 and C–N1 bonds cleavage associated with the N1–H2 bond formation of adduct a leads to the product P ₁ (HCN + HNO). Moreover, P ₂ (HNC + HNO) should be the competitive product. The other products, including P ₃ (NH₂ + NCO) and P ₄ (N₂H₂ + CO), are minor products. The product P ₁ can be obtained through two competitive channels Path 1: R → a → P ₁ and Path 3: R → b → d → P ₁ , whereas the product P ₂ can be formed through Path 2: R → b → d → P ₂ . At high temperatures, the nitrogen-to-nitrogen approach may become feasible. For the triplet potential energy surface of the NH (X³Σ^?) + HCNO reaction, the Path 10: R → ³ a → ³ a ₁ → P ₁ should be the most feasible pathway due to the less reaction steps and lower barriers. These conclusions will have impacts on further experimental investigations.     

Naphthologs of overcrowded bistricyclic aromatic enes: (E)-bisbenzo[a]fluorenylidene

(E)-11H-Bisbenzo[a]fluorenylidene (E-6) was synthesized by Barton’s double extrusion diazo-thione coupling method from 11H-benzo[a]fluoren-11-thione (11) and 11-diazo-11H-benzo[a]fluorene (13). The reaction is probably thermodynamically controlled; in the event that the less stable Z -6 is also formed, it would rapidly undergo Z → E diastereomerization to give E -6. The B3LYP/6-311G(d,p) calculated diastereomerization barrier for Z -6 → E -6 is ΔG ₂₉₈ = 57.0 kJ/mol (13.6 kcal/mol). The calculated equilibrium constant K _eq(E -6 → Z -6) = 92:8 (at 298 K) is indicative of a marked diastereoselectivity of the reaction leading to E -6. The structure of E-6 was established by ¹H-NMR and ¹³C-NMR spectroscopies and by X-ray analysis. PAE E-6 crystallizes in the monoclinic space group C2/c. The unit cell of the crystal structure E -6 contains eight molecules, arranged as four pairs of enantiomers. PAE E -6 adopts a twisted conformation with the pure twist of the central C¹¹=C^11′ bond ω = 39°. The dihedral angle ν in E -6 is 60.6°, which is significantly higher than the respective dihedral angle in PAEs Z -6, 2, E -7, Z -7, 14, and 15. The large syn-pyramidalization angles at C¹¹ and C^11′ (χ = 12.6° and 14.8°) of E-6 indicates the enhanced strain in the fjord regions of the molecule. The enhanced twist is primarily attributed to the double benzo[a]annelation of the bifluorenylidene moiety at the fjord regions. The B3LYP/6-311G(d,p) calculated structure of E -6 is in a very good agreement with the experimental X-ray structure. PAE E -6 adopts a twisted conformation in solution, with the downfield chemical shift of H¹/H^1′ (8.31 ppm); H¹⁰/H^10′ (δ = 7.20 ppm) and H⁹/H^9′ (δ = 6.86 ppm) in E -6 are positioned above the planes of the opposing naphthalene rings. PAEs E -6 and Z -6 are significantly higher in energy than their corresponding benzo[b]annelated isomers E -7 and Z -7.     

Syntheses and characterization of a new class of vanadia precursors of oxime-modified oxovanadium(V) isopropoxide,crystal and molecular structure of [VO{ONC10H16}3]

Modification of [VO(OPrⁱ)₃] with oximes in different molar ratios, yielded new class of vanadia precursors, [VO{OPrⁱ}_3?n{L}_n] {where, n = 1–3 and LH = C₉H₁₆C=NOH (1–3) and (CH₃)₂C=NOH (4–6)}.All the products are yellow in colour. (1) and (2) are liquid/viscous liquid, while others are solids. Molecular weight measurements of all these derivatives and the ESI-mass spectral studies of (1), (2), (3) and (5) indicate their monomeric nature. ¹H and ¹³C{¹H} NMR spectra suggest that the oximato moieties are monodentate in solution which was further confirmed by the ⁵¹V NMR signals, appeared in the region expected for tetra-coordinated oxo-vanadium atoms. On ageing, a disproportionation reaction occurs in (1) and some crystals appeared. Single crystal X-ray diffraction analyses of the crystals obtained from (1) as well as from (3) were found to be the same and indicate the presence of side-on {dihapto η ²-(N, O)} binding modes of the oximato ligands, leading to the formation of seven coordination environment around the vanadium atom. Thermogravimetric curve of (1) exhibits multi-step decomposition with the formation of V₂O₅ as the final product at ~850 °C. Sol–gel transformation of (3) yielded (a) VO₂ sintered at 300 °C and (b) V₂O₅ at 600 °C. Similarly, sol–gel transformations of (1) and (2) yielded V₂O₅ (c) and (d) at 600 °C, respectively. Formation of monoclinic phase in (a) and orthorhombic phase in (b), (c) and (d) were confirmed by powder XRD patterns.     

Synthesis of new water-soluble phosphonate calixazacrowns and their use as drug solubilizing agents

This study presents the selective chloromethylation of calix[4](aza)crown ethers 2a–c, using chloromethyl n-octyl ether and SnCl₄ in chloroform at room temperature in good yield for the first time. Chloromethylated products 2a–c are used as key intermediates to synthesize new water-soluble p-phosphonato calix[4](aza)crown ethers 5a–c. Liquid–liquid phase extraction and phase solubility studies with poor water soluble drug molecules such as nifedipine, niclosamide and furosemide are performed to evaluate their binding properties. Among the studied drugs, furosemide was the most effectively dissolved drug by p-phosphonato calix[4](aza)crown ethers 5a–c in water.     

Synthesis of aryl-substituted or aryl-fused N-hydroxyethyl and N-hydroxymethypyrazole derivatives as potential ligands for the estrogen receptor

A new series of N-hydroxyethylpyrazole (12a–f) and N-hydroxymethylpyrazole derivatives (15a–f) were designed for their estrogenic activities, having a 11.0 ± 0.5 Å distance between their two hydroxyl groups, aliphatic–OH and phenolic–OH similar to 17β-estradiol (E2) as an endogenous hormone. To synthesize the title compounds, the key intermediate 1,3-dicarbonyl derivatives (2 and 8), were treated with hydrazine hydrate to produce the pyrazole ring 5 and 9. Further hydroxyalkylation of the latter produced the title pyrazoles. The position of hydroxyethyl or hydroxymethyl substituents in the products was determined through 2D NOE NMR spectroscopy.     

Theoretical investigation on conformational preferences and structural properties of 2-lithio-1,3-diphosphinane and 2-lithio-1,3-dimethyl-1,3-diphosphinane

A new family of dialphosphacyclohexane is introduced which has three nucleophilic centers. The conformational stabilities and structural properties of 2-lithio-1,3-diphosphinane and 2-lithio-1,3-dimethyl-1,3-diphosphinane were investigated computationally by DFT calculations and NBO analyses at B3LYP/6-31+G(d,p). Relative energy trend in 1,3-diphosphinane and 1,3-dimethyl-1,3-diphosphinane conformations explored from steric and hyperconjugative point of view. The stability trend of 2-lithio derivatives based on calculated relative energies in 1,3-diphosphinane is 1d > 1f > 1b > 1a > 1c > 1e and for 1,3-dimethyl-1,3-diphosphinane derivatives is 2f > 2d > 2b > 2a > 2c > 2e. Calculated NBO atomic charges indicate that high positive charge at lithium and small C–Li Wiberg bond indexes in these derivatives are demonstrators of ionic nature of the C–Li bonds. Stereoelectronic interactions, polarizability of phosphorus, and chelate formation between each of phosphorous and lithium are determining factors in stability trend observed in these derivatives. Ease of lithiation in bis(dimethylphosphino)methane, 1,3-diphosphinane, and 1,3-dimethyl-1,3-diphosphinane derivatives was estimated and compared by isodesmic reaction.     

Über cyclische Guanidin—Mesityloxid- und Guanidin—Phoron-Kondensate

The basic product synthesized byTraube andSchwarz from mesityl oxide and guanidine has not been 4.4.6-trimethyl-4.5-dihydro-2-pyrimidinamine (1), but a mixture containing the 4.4.6-trimethyl-3.4-dihydro-2(1H)-pyrimidinimine (resp. an isomeric pyrimidinamine)2 a (resp.2 b, 2 c) and the dimeric 4.4′-methylenedi[2(1H)-pyrimidinimine] (resp. an isomeric methylenedipyrimidinamine)3 a (resp.3 b, 2 c) and the dimerisation reaction were studied in a series of experiments. The product of the reaction of guanidine and phorone is not the guanidinopropylpyrimidine8 ⁴, but the 4.4′-spirobi[2(1H)-pyrimidinimine] (resp. a spirobipyrimidinamine)11 a (resp.11 b, 11 c). No determination was possible on the basis of NMR whether the condensation products of guanidine—in solutions ofDMSO-d₆—are pyrimidinimines (2 a, 3 a, 11 a) or pyrimidinamines (2 b resp.2 c, 3 b resp.3 c, 11 b resp.11 c) or mixtures of the isomeric compounds. The NMR-and mass spectra of2 a (resp.2 b, 2 c),3 a (resp.3 b, 3 c),11 a (resp.11 b, 11 c) and their derivates are discussed.     

Synthese von Pyridonen aus Enaminen und Cyanessigsäuren

Reaction of enamines1 a–e with cyanoacetic acids2 a,b in acetic anhydride at about 100°C yields the α-cyanoacetylated enamines3 a–g. Under the same conditions methyl 4-cyano-2-(2-pyridyl)-acetoacetate3 h is obtained from methyl 2-pyridylacetate and2 a. Compounds3 are cyclized in hydrochloric acid yielding the 4-hydroxy-2-pyridones4; on the other hand in ethanolic sodium ethoxide solution the 2-amino-4-pyridones are obtained. The esters5 a,b andd are saponified to give the acids7 a–c which decarboxylate at 250°C to8 a–c.     

Zur Kenntnis der Struktur der Chalkon-Guanidin-Kondensate Über Heterocyclen, 75. Mitt.

Guanidine reacts with chalkone1 a, 4-methylchalkone1 b and 4′-methylchalkone1 c resp. to yield mixtures of pyrimidinamines2 a,3 b and3 c (=3 b) resp. with (2:1)-condensatesA,B andC resp. The structures of the compoundsA-C (whicha priori could be dihydropyrimidopyrimidines4 a-c or5 a-c or6 a-c) are elucidated. NMR-investigations show that the saltsA-C · HCl must be symmetrically substituted pyrimidopyrimidinyliumchlorides4 a-c · HCl or5 a-c · HCl (and not6 a-c · HCl). Furthermore, it is proved by chemical methods that the condensatesB · HCl andC · HCl are pyrimidopyrimidinyliumchlorides4 b andc · HCl (and not5 b andc · HCl): The structure ofB · HCl (=4 b · HCl) was established by total synthesis of dimethylpyrimidopyrimidinyliumpicrate9 b-Pi from10 c (via13 c · HI-18 · HCl) and transformation ofB · HCl into an identical salt9 b-Pi via hexahydropyrimidopyrimidine8 b · HCl. The structure ofC · HCl (=4 c · HCl) was determined by comparison of its hydrogenation product (=8c · HCl) with8 b · HCl. The structure of condensateA · HCl (=4 a · HCl) results from conclusion by analogy. The spatial structure of4 a-c · HCl and8 a-c · HCl is discussed; it was established by NMR that the salts are racemic mixtures of stereoisomers4 a-c K · HCl and8 a-c K · HCl resp. and their antipodes (with C₂ symmetry).