Hydrogenolysis of glycerol to propanediols over heteropolyacids promoted AgCu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Various amounts and different types of heteropolyacids promoted 5Ag15Cu/Al₂O₃ catalysts were prepared by impregnation method and analyzed through many techniques. The synthesized catalysts were evaluated for hydrogenolysis of glycerol to propanediols. The results demonstrated that heteropolyacids loading facilitated the reduction, promoted the dispersion, enhanced the acidity, and increased Broensted acid sites of the AgCu catalysts, which benefited the generation of 1,3-propanediol. Compared with phosphotungstic acid and phosphomolybdic acid, silicotungstic acid promoted AgCu catalyst had a better performance for 1,3-propanediol due to the better Cu dispersion and higher Broensted acidity. In addition, when the reaction was performed at 220 °C under 3.5 MPa for 8 h, the chosen 5Ag15Cu-10HSiW/Al₂O₃ achieved a 69.6% glycerol conversion with 35.6% 1,2-propanediol selectivity and 21.5% 1,3-propanediol selectivity.     

Preparation of CuCr<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders using two different chromium sources

CuCr₂O₄ spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr₂O₃) and (ii) ammonium dichromate ((NH₄)₂Cr₂O₇). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO₃)₂·3H₂O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr₂O₃, Cu(NO₃)₂·3H₂O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr₂O₃). In the second case (ii), (NH₄)₂Cr₂O₇, Cu(NO₃)₂·3H₂O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH₄)₂Cr₂O₇ took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr₂O_3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr₂O₄) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr₂O₄ was highlighted by XRD and FTIR analyses.     

Crystal Structure of (CM-TTF)<Subscript>2</Subscript>Hg<Subscript>2</Subscript>Cl<Subscript>6</Subscript> with short intradimer S···S stacking

At room temperature, the reaction of 2-[4,5-bis(methylsulfanyl)-1,3-dithiol-2-ylidene-]-4,5-bis(2-cyanoethylsulfanyl)-1, 3-dithiole (CM-TTF) with mercury chloride resulted in a black radical salt constructed by dimeric cations and chloromercurate anions in formula (CM-TTF)₂Hg₂Cl_6. The S···S stacking of 3.289(3) and 3.334(3) Å within the TTF dimer are very strong in comparing with those of other TTF radical salts. Effective C···C stacking (3.349(10) Å) was also found within the dimeric structure.     

Specific Features of 1,3-Diazole Adsorption on the Surface of NiO and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Variation of the electrokinetic potential of the surface of the oxides and of the amount of adsorbed diazole and its concentration in solution in systems constituted by aqueous solutions of 1,3-diazole and NiO and Fe₂O₃ adsorbents was studied in the course of a long time after bringing the phases in contact.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 741–746.Original Russian Text Copyright © 2005 by Dmitrieva, Tikhomolova, Chukhno.     

Asymmetric Diels-Alder reaction of 1,3-butadienes with (−)-dimenthyl fumarate in the presence of BBr<Subscript>3</Subscript> and BBr<Subscript>3</Subscript>·OEt<Subscript>2</Subscript>

Asymmetric synthesis of substituted cyclohexenes was performed by [4+2]-cycloaddition of (-)-dimenthyl fumarate to 1,3-butadienes in the presence of BBr₃ and BBr₃·OEt₂. The latter are efficient catalysts for this reaction. The effect of various factors on the chemical and optical yield of compounds synthesized was studied. The lowering of the reaction temperature to ?70°C favors increase in the enantiomeric purity of products up to 81%. The overall yield of adducts grows with temperature and catalyst amount. The solvent character insignificantly affects the overall and optical yield of compounds obtained.     

[η<Superscript>5</Superscript>-C<Subscript>9</Subscript>H<Subscript>5</Subscript>(1,3-SiMe<Subscript>3</Subscript>)<Subscript>2</Subscript>]HfCl<Subscript>3</Subscript>: A monomeric 12-electron half-sandwich complex

The half-sandwich hafnium complex [gh⁵-C₉H₅(1,3-SiMe₃)₂]HfCl₃ (II) has been synthesized for the first time. The molecular structures of II and its synthetic precursor C₉H₅(1,1,3-SiMe₃)₃ (I) have been determined by X-ray crystallography. Compound II in the crystalline state, is a rare example of a monomeric 12-electron half-sandwich complex.     

Synthesis,structure, and conductivity of molecular conductor (PyEt)[Ni(dmit)<Subscript>2</Subscript>]<Subscript>2</Subscript>

A new electrical conductive crystal PyEt[Ni(dmit)₂]₂ (dmit = 4,5-dimercapto-1,3-dithiole-2-thione) has been synthesized and its X-ray structure has been determined to be in monoclinic system, C2/c space group. In PyEt[Ni(dmit)₂]₂ crystal, the conducting component [Ni(dmit)₂]^0.5- is face-to-face packed forming molecular column along the c-direction, and these molecular columns are then side-by-side extended along the a-direction forming a kind of two-dimensional conducting sheet on (010). The measured conductivity at room temperature along a certain direction on (010) plane is 10 S · cm^-1. From 282 to 269 K, the crystal shows metallic behavior but changes to semiconductor below 269 K. Based on the measured crystal structure and calculated band structure, this conductor-semiconductor phase transformation can be primarily interpreted: The metallic conductivity is corresponding to the uniform molecular column and the atomic-lattice-chain structure of Ni chain, while the semi-conductive behavior to staggered molecular column and the atomic-zigzag-chain structure of Ni chain.     

Bifunctional decamethylcyclohexasilanes X<Subscript>2</Subscript>Si<Subscript>6</Subscript>Me<Subscript>10</Subscript> (X = Cl,H, or OH): molecular and crystal structures and mesomorphic properties

Isomer separation of mixtures, which were prepared by chlorination followed by transformations of dodecamethylcyclohexasilane (Me₂Si)₆ into bifunctional decamethylcyclohexasilanes X₂Si₆Me₁₀ (X = Cl, H, or OH), was carried out. As a result, mixtures of the corresponding 1,3- and 1,4-derivatives were separated to obtain structural isomers, and stereoisomers, viz., cis- and trans-1,4-dihydrocyclohexasilanes, were isolated in individual form. The molecular and crystal structures of the resulting bifunctional decamethylcyclohexanes X₂Si₆Me₁₀ (X = H or OH) and decamethyl-7-oxahexasilanorbornane were established by X-ray diffraction analysis. Bifunctional cyclohexasilanes form a mesophase as a plastic crystal. The temperature range of its existence was determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1566–1575, July, 2005.     

Oxidation with CrO<Subscript>3</Subscript>·2Py of levoglucosenone and 1,3-dienes Diels-Alder adducts

Diels-Alder adducts of levoglucosenone with 1,3-butadiene, piperylene, and isoprene, and also some of their derivatives undergo allylic oxidation with CrО₃·2Py only in the case when the effect of a keto group or of another electron-acceptor group in the γ-position with respect to the double bond is removed.     

Preparation and photocatalytic activity of TiO<Subscript>2</Subscript> films with Ni nanoparticles

Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)₂ (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO₂ sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO₂ films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO₂ solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO₂ system revealed well-dispersed Ni nanoparticles supported on TiO₂ and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO₂ films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO₂.     

Variation in coordinative property of two different N<Subscript>2</Subscript>O<Subscript>2</Subscript> donor Schiff base ligands with nickel(II) and cobalt(III) ions: characterisation and single crystal structure elucidation

A nickel(II) and a cobalt(III) complex of two different potentially tetradentate Schiff bases with different binding modes have been synthesised. The nickel(II) complex [NiL¹] · CH₃OH (1) was formed, on reacting the metal salt with a perfectly symmetrical N₂O₂ tetradentate Schiff base ligand H ₂ L ¹ , which is the 1:2 condensation product of 1,3-diamino propane and 2-hydroxyacetophenone. The cobalt(III) complex [Co(HL²)₃] · (ClO₄)₃ · H₂O (2) was synthesised using an asymmetric N₂O₂ tetradentate Schiff base ligand HL ² on condensing N,N-dimethyl-1,3-diamino propane with o-vanillin in 1:1 mmol ratio. Although both Schiff bases are N₂O₂ functionalised, they showed variation in their coordinative property with nickel(II) and cobalt(III) ions. Both the complexes were characterised by IR spectroscopy and cyclic voltammetry and their single crystal structures clearly indicate that 1 is a mononuclear species whereas 2 is a hydrogen-bonded dimer.     

Multifunctional iron thiocarboxylate complexes: synthesis,reactivity and structure of CpFe(CO)<Subscript>2</Subscript>SCO-3,5-C<Subscript>6</Subscript>H<Subscript>4</Subscript>(COCl)<Subscript>2</Subscript>

A controlled substitution reaction of the chlorine atoms of 1,3,5-benzenetricarbonyl trichloride by the organoiron fragment (CpFe(CO)₂S) has been achieved. The complexes CpFe(CO)₂SCO-3,5-C₆H₃(COCl)₂ (1), 1,3-[CpFe(CO)₂SCO]₂-5-C₆H₃COCl (2) and 1,3,5-[CpFe(CO)₂SCO]₃C₆H₃ (3) were prepared from the reaction of (μ-S _x )[CpFe(CO)₂]₂ (x = 3, 4) with 1,3,5-C₆H₃(COCl)₃ in a 1:1, 2:1, or 3:1 metal to ligand molar ratio. The reactions of (1) with amines, thiols, and carboxylic acids produce the trifunctional mono-iron complexes CpFe(CO)₂SCO-3,5-C₆H₃(COY)₂ [Y = NR₂ (4), SR (5), OCOR (4)]. The X-ray structure determination of (1) is reported.     

Dinuclear complex of gold(III) with 1,3-diaminopropane (HL), [Au<Subscript>2</Subscript>(HL)(L)<Subscript>2</Subscript>](ClO<Subscript>4</Subscript>)<Subscript>3</Subscript>(OH): Synthesis and crystal and molecular structures

The dinuclear gold(III) complex, [Au₂(HL)(L)₂](ClO₄)₃(OH) (I) (HL = 1,3-diaminopropane), with two amide bridges has been synthesized for the first time. According to the X-ray diffraction data, the crystal structure of complex I consists of the complex cations [Au₂(HL)(L)₂]⁴⁺ and anions ClO₄⁻ and OH⁻. The coordination sites AuN₄ are insignificantly distorted squares. In the four-membered ring Au₂N₂, the gold atoms are bound by the bridging nitrogen atoms of the deprotonated primary amine.     

Double helix of the coordination polymer of silver with 1,3-bis(4-pyridyl)propane: Synthesis and crystal structure of [Ag(C<Subscript>13</Subscript>H<Subscript>14</Subscript>N<Subscript>2</Subscript>)](CF<Subscript>3</Subscript>CO<Subscript>2</Subscript>)

The [Ag(Bpp)](CF₃CO₂) complex (Bpp is 1,3-bis(4-pyridyl)propane, C₁₃H₁₄N₂) is synthesized, and its structure is determined. The crystals are monoclinic, space group C2/c, a = 26.169(5), b = 10.521(2), c = 12.906(3) Å, β = 117.99(3)°, V = 3137.7(11) ų, ρ_calcd = 1.775 g/cm³, Z = 8. The structure contains double helices of-Ag-Bpp-Ag-Bpp-cationic chains with a helix period of 21.042 Å. The Ag…Ag distance between a pair of silver atoms from different chains in the helix is 3.201 Å, and the distance between the adjacent helices is 3.279 Å. The silver atom is linked with two bridging nitrogen atoms of two Bpp ligands in an almost linear coordination: Ag-N_avg 2.142 Å; NagN, 171.3(4)°. The CF₃C ₂ ^? anion has a weak contact with the silver ion (Ag…O 2.62(2) Å).     

GeCl<Subscript>2</Subscript> cycloaddition reactions to unsaturated organic compounds taking ethylene,buta-1,3-diene,and hexa-1,3,5-triene as examples: a quantum chemical study

The cycloaddition reactions of dichlorogermylene GeCl₂ to ethylene, buta-1,3-diene, and hexa-1,3,5-triene were studied within the framework of the density functional theory (PBE and B3LYP density functionals) and by the ab initio CBS-QB3 method. The energy characteristics of the reaction of GeCl₂ with ethylene were refined and non-empirical quantum chemical calculations of reaction pathways in the GeCl₂ + buta-1,3-diene and GeCl₂ + hexa-1,3,5-triene systems were carried out for the first time. It was shown that the [2+1] cycloaddition reactions are kinetically hindered and thermodynamically unfavorable, while the [4+1] and [6+1] cycloaddition reactions are characterized by low barriers and result in thermodynamically favorable products. For the [4+1] cycloaddition to buta-1,3-diene and [6+1] cycloaddition to hexa-1,3,5-triene, the most energetically favorable reaction pathways involve a suprafacial and antarafacial approach of reactants, respectively.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Radical–molecule reaction CH<Subscript>2</Subscript>Cl + NO<Subscript>2</Subscript>: a mechanistic study

The radical–molecule reaction mechanism of CH₂Cl with NO₂ has been explored theoretically at the B3LYP/6–311G(d,p) and MC–QCISD (single-point) levels of theory. Our results indicate that the title reaction proceeds mostly through singlet pathways, less go through triplet pathways. The initial association between CH₂Cl and NO₂ is found to be the carbon-to-nitrogen attack forming the adduct a H₂ClCNO₂ with no barrier, followed by isomerization to b ₁ H₂ClCONO-trans which can easily convert to b ₂ H₂ClCONO-cis. Subsequently, the most feasible pathway is the C–Cl and O–N bonds cleavage along with the N–Cl bond formation of b (b ₁ , b ₂ ) leading to product P ₁ CH₂O + ClNO, which can further dissociate to give P ₅ CH₂O + Cl + NO. The second competitive pathway is the 1,3-H-shift associated with O–N bond rupture of b ₁ to form P ₂ CHClO + HNO. Because the intermediates and transition states involved in the above two favorable channels all lie below the reactants, the CH₂Cl+NO₂ reaction is expected to be rapid, as is confirmed by experiment. The present results can lead us to understand deeply the mechanism of the title reaction and may be helpful for further experimental investigation of the reaction.     

A facile ZrO<Subscript>2</Subscript> nanoparticles catalyzed synthesis of 2-amino-5-arylpyrimido[4,5-<Emphasis Type="Italic">b</Emphasis>]quinolinediones

In this investigation, an efficient and ecofriendly multicomponent reaction is described for the green synthesis of 2-amino-5-arylpyrimido[4,5-b]quinolinedione derivatives using ZrO₂ (NPs). In this protocol, the reaction of 2,6-diaminopyrimidin-4(1H)-one, arylaldehyde and 1,3-cyclohexanedione or 5,5-dimethyl-1,3-cyclohexanedione in the presence of ZrO₂ (NPs) in ethylene glycol at 120 °C produced the desired products in excellent yields (90–98 %) and short reaction times (8–60 min.). Use of recyclable catalyst, green solvent, easy workup and excellent yields are the notable features of this method.     

CO<Subscript>2</Subscript>-responsive Polymeric Fluorescent Sensor with Ultrafast Response

Abstract Response speed is one of the most important evaluation criteria for CO₂ sensors. In this work, we report an ultrafast CO₂ fluorescent sensor based on poly[oligo(ethylene glycol) methyl ether methacrylate]-b-poly[N,N-diethylaminoethyl methacrylate-r-4-(2-methylacryloyloxyethylamino)-7-nitro-2,1,3-benzoxadiazole] [POEGMA-b-P(DEAEMA-r-NBDMA)], in which DEAEMA units act as the CO₂-responsive segment and 4-nitrobenzo-2-oxa-1,3-diazole (NBD) is the chromophore. The micelles composed of this copolymer could disassemble in 2 s upon CO₂ bubbling, accompanying with enhanced fluorescence emission with bathochromic shift. Furthermore, the quantum yield of the NBD chromophore increases with both the CO₂ aeration time and the NBD content. Thus we attribute the fluorescent enhancement to the inhibition of the photo-induced electron transfer between unprotonated tertiary amine groups and NBD fluorophores. The sensor is durable although it is based on “soft” materials. These micellar sensors could be facilely recycled by alternative CO₂/Ar purging for at least 5 times, indicating good reversibility.     

Mild template synthesis of a macrocyclic Cu(II) chelate complex with 1,10-diamino-1,10-dimercapto-5,6-dimethyl-4,7-diazadeca-1,4,6,9-tetraene-3,8-dithione in Cu<Subscript>2</Subscript>[Fe(CN)<Subscript>6</Subscript>]-gelatin-immobilized matrix implantates

Complexation in Cu₂[Fe(CN)₆]-gelatin-immobilized matrix implantates in contact with alkaline (pH > 10) aqueous solutions containing propane-1,3-dithioamide and butane-2,3-dione, as well as with an ethanolic solution containing the same organic compounds, was studied. It was found that room-temperature complexation in the gelatin matrix gives a macrocyclic complex CuL¹with a tetradentate N,S,S,N-donor ligand via a template synthesis, while complexation in solution at room and higher temperatures yields only a bischelate Cu(II) complex with monodeprotonated propane-1,3-dithioamide. Schemes of the complexation processes were proposed. It was demonstrated that when propane-1,3-dithioamide and butane-2,3-dione are in direct contact in solution, the above N,S,S,N-donor ligand was formed in neither the presence nor the absence of Cu²⁺.