Thermally stable pseudo-third-generation Grubbs ruthenium catalysts with pyridine–phosphinimine ligand

The ligand precursors 2-(R₃PN)CH₂Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl₂(CHPh)(Py)₂(H₂IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl₂(CHPh)(PyCH₂(NPR₃))(H₂IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.     

Synthesis,X-ray structure,spectroscopic properties,and theoretical investigations of dinuclear imidazole molybdenum(VI) complex with long MoO bands

One new dinuclear multioxomolybdenum(VI) complex containing long MoO bands with imidazole, [Mo₂O₆(imi)₄] (1) (imi = imidazole), has been prepared and characterized, and the geometric structure, electronic structure and spectroscopic properties, investigated experimentally and theoretically. The rarely observed long MoO bonds in 1 (ca. 0.15 Å longer than documents previously) are analysed by orbital structure analysis. The electronic origins of the optical transitions are also mainly related to the MoO groups with ligand-to-metal charge transfer (LMCT) nature (P_terminal-oxo → d_Mo).     

Unsymmetrical cyrhetrenyl and ferrocenyl azines derived from 5-nitrofurane: Synthesis,structural characterization and electrochemistry

A new series of unsymmetrical cyrhetrenyl and ferrocenyl azines that were monosubstituted [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)]M {with MRe(CO)₃ and RH (1a) or RMe (1b); MFe(η⁵-C₅H₅) and RH (2a) or RMe (2b)} and disubstituted [Fe{(η⁵-C₅H₄)–C(Me)N–NCH(5-NO₂–2-C₄H₂O)}₂] (3a) were prepared by condensation reactions of the corresponding organometallic hydrazone [(η⁵-C₅H₄)–C(R)N–NH₂)]M with 5-nitro-2-furaldehyde. The ¹H and ¹³C{¹H} NMR spectra indicated that these compounds adopted an (E,E)-configuration about the ˃CN − bond and an s-trans conformation about the N1–N2 bond, and this result was confirmed by X-ray crystallographic analyses of 1a and 2b. The opposite electronic effects of the organometallic fragments correlate with the co-planarity of the [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)] system, the reduction potential of the nitro group (E_1/2) and the chemical shifts of the iminic carbons.     

Bridge-splitting of trans-[PtCl2(η2-CH2CH2)]2 by weak nucleophiles: Crystal and molecular structure of trans-[PtCl2(η2-CH2CH2)(MeCN)]

Bridge-splitting of trans-[PtCl₂(η²-CH₂CH₂)]₂, 1, by L in dichloromethane yields trans-[PtCl₂(η²-CH₂CH₂)(L)] (L = THF, 2, or MeCN, 3) with bridge-splitting equilibrium constants of 0.0289 ± 0.0007 and 3601 ± 215 mol^?1 dm³, respectively, as determined by UV/Vis measurements. The reaction of 3 in MeCN with Cl^? is essentially quantitative. The crystal structure of trans-[PtCl₂(η²-CH₂CH₂)(CH₃CN)] is reported.     

Etherification reactions of propargylic alcohols catalyzed by a cationic ruthenium allenylidene complex

The cationic ruthenium allenylidene complex R_RuR_ax −[Ru(indenyl)L(PPh₃)CCCPh₂]⁺PF₆ catalyzes the etherification of secondary and tertiary propargylic alcohols in a formal nucleophilic substitution reaction utilizing primary and secondary alcohols as the nucleophiles. At a catalyst loading of only 1.1 mol%, the corresponding propargylic ether products were obtained in 9 to 73% isolated yields (18 h reaction time at 100 °C); no further additives are required. The reaction exhibits an induction period; as shown by a control reaction, the high reaction temperature may chemically change the allenylidene complex to be employed as the catalyst but does not lead to catalyst deactivation.     

Towards osseointegration of bioinert ceramics: Can biological agents be immobilized on alumina substrates using self-assembled monolayer technique?

Immobilization of biological agents on inert alumina surfaces could promote bone growth and improve osseointegration. We hypothesize that functional groups on alumina surfaces can be used to link biological agents as a supporting factor e.g. for cell attachment. CH₂, OH, COOH, and NH₂ groups were linked to alumina surfaces using self-assembled monolayer technique (SAM). Subsequently, bovine serum albumin (BSA) was immobilized on each functionalized surface. Contact angle, bicinchoninic acid assay and immunofluorescence were used to detect immobilized BSA. The amount of BSA linked to functionalized surfaces increased in the following order CH₂ < OH < COOH = NH₂. The greatest amount, 26.1 μg/cm² of BSA was found on both, NH₂- and COOH-terminated surfaces. Cell tests confirmed cytocompatibility of all surfaces. The highest proliferation was detected on NH₂-terminated samples. Using the model protein, the results confirmed feasibility for immobilization of biological agents to inert alumina ceramic surfaces using SAM technique.     

Schiff pentadentate ligands based on an [ON2O2] core displaying structural isomerism and their coordination to dibutyltin moieties

Two tin compounds [Sn(ⁿBu)₂(Lⁿ)], where L¹{O(C₆H₄-2-NC(H)C₆H₄-2′-O)₂}^2 − and L²{O(C₆H₄-2-C(H)NC₆H₄-2′-O)₂}^2 − enclosing five electron donors in an [ON₂O₂] core, were synthesized and structurally characterized by infrared and NMR spectroscopy and by single crystal X-ray crystallographic studies at room temperature. The hepta-coordinate geometry around the Sn centers is achieved through the bonding of two monodentate n-butyl groups and the coordination of the pentadentate Lⁿ ligands, where the [ON₂O₂] core is forming a pentagonal base. The two types of oxygen atoms displayed different bonding situations around the Sn atom. DFT calculations with Gaussian 09 using PBEPBE/6-31G**/SDD level were carried out for both compounds. The topological analysis indicated that bond critical points are present along the SnO_ether direction.     

Electrically conductive silicon carbide with the addition of TiNbC

The work deals with the preparation of dense SiC based ceramics with high electrical conductivity. SiC samples with different content of conductive TiNbSiCO based phase were hot pressed at 1820 °C for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of 50 wt% TiNbC (molar ratio of Ti/NbC is 1:1.8) and 50 wt% eutectic composition of Y₂O₃SiO₂. Composite with 30% of conductive TiNbSiCO phase showed the highest electrical conductivity 28.4 S mm^?1, while the good mechanical properties of SiC matrix were preserved (fracture toughness K_IC = 5.4 MPa m^1/2 and Vickers hardness 17.8 GPa).The obtained results show that the developed additive system is suitable for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.     

Trans,trans,trans-[ReO2I2(PPh3)2], a rare rhenium(VI) complex — Synthesis and DFT study

The heating of cis-[ReO₂I(PPh₃)₂] at reflux in benzene in air led to the isolation of the rhenium(VI) complex [ReO₂I₂(PPh₃)₂] (1). The compound is centrosymmetric around the octahedrally coordinated rhenium center, and the ReO bond length of 1.797(2) Å is longer than in typical trans-dioxorhenium(V) complexes. The asymmetric ReO stretching frequency occurs at 744 cm^− 1. Density functional theory has been used for the calculation of the vibrational spectrum density which confirms the experimental asymmetric ReO stretching frequency. DFT calculation within the polarizable continuum model shows that complex 1 is more stable in CH₂Cl₂ than in the gas phase. EPR spectroscopy confirms a single d electron in 1. The crystal structure was determined by X-ray single crystal diffraction. In addition, infra-red, redox and electronic properties are also reported.     

Direct conversion of citrus peel waste into hydroxymethylfurfural in ionic liquid by mediation of fluorinated metal catalysts

A new green technology was developed using citrus peel waste to produce hydroxymethylfurfual (HMF). FT-IR analysis of the waste showed 4 characteristic vibration modes (CH, CO, COH, and CO/COO^?), contributing to sugars. XRD and FESEM elucidated that the waste and its hydrolysate consist of highly amorphous clusters. HCl increased HMF yield by 1.4-fold. CrF₃ increased its yield by 1.7-fold. At 0.2 of the stoichiometric ratio value, HMF yield was highest. The highest HMF yield was achieved in the reaction mixture of 4 g [OMIM]Cl, 1 mL ethyl acetate, 0.1 g CrF₃, 5 mL 0.3 M HCl, and 0.5 g biomass.     

Pt nanoparticles deposited over carbon nanotubes for selective hydrogenation of cinnamaldehyde

Two kinds of carbon nanotubes (CNTs) with different inner diameter (less than 10 nm: CNTs-1 and between 60 and 100 nm: CNTs-2) were used as catalyst supports. The platinum particles were simply deposited on the outside surface (CNTs-1) and inside (CNTs-2) and were easily reduced to Pt⁰ by refluxing. The catalysts exhibit high activities in the selective hydrogenation of cinnamaldehyde which contains both CC and CO bonds. But the selectivity of these two catalysts was quite different under same reaction conditions. The high selective hydrogenation of CO bond was observed over catalyst 3%Pt/CNTs-2, while the completely hydrogenation of both CC and CO bonds was found over catalyst 3%Pt/CNTs-1.     

Measurement of the hydroxyl radical formation from H2O2, NO3−, and Fe(III) using a continuous flow injection analysis

Production of hydroxyl radical (OH) is of significant concern in engineered and natural environment. A simple in situ method was developed to measure OH formation in UV/H₂O₂, UV/Fe(III), and UV/NO₃^? systems using trapping of OH by benzoic acid (BA) and measuring fluorescence signals from hydroxylated products of BA. Method development included characterization of OH trapping mechanism and measurement of quantum yields (Φ_OH) for OH. The distribution of OHBA isomers was in the order of o-OHBA > p-OHBA > m-OHBA, although it changed with the H₂O₂ concentration and light intensity. This supports that OH attacks dominantly on the benzene rings. The quantum yields for OH formation in the UV/H₂O₂ process were 1.02 and 0.59 at 254 and 313 nm, which were in good agreement with the literature values, confirming that the method is suitable for the measurement of OH production from UV/H₂O₂ processes. Using the continuous flow method developed, quantum yields for OH in UV/H₂O₂, UV/Fe(III), and UV/NO₃^? systems were measured varying the initial concentration of OH precursors. The Φ_OH values increased with increasing concentrations of H₂O₂, Fe(III), and NO₃^? and approached constant values as the concentration increased. The Φ_OH values were 0.009 for H₂O₂ at 365 nm, showing that OH production is not negligible at such high wavelength. The Φ_OH values during the photolysis of Fe(OH)²⁺ (pH 3.0) and Fe(OH)₂⁺ (pH 6.0) at 254 nm were 0.34 and 0.037, respectively. The Φ_OH values for NO₃^? approached a constant value of 0.045 at 254 nm at the initial concentration of 10 mM.     

Deposition of carbon nitride films using an electron cyclotron wave resonance plasma source

Hydrogenated amorphous carbon nitride (a-C:N:H) has been synthesised using a high plasma density electron cyclotron wave resonance (ECWR) technique using N₂ and C₂H₂ as source gases, at different ratios and a fixed ion energy (80 eV). The composition, structure and bonding state of the films were investigated and related to their optical and electrical properties. The nitrogen content in the film rises rapidly until the N₂/C₂H₂ gas ratio reaches 2 and then increases more gradually, while the deposition rate decreases steeply, placing an upper limit for the nitrogen incorporation at 30 at%. For nitrogen contents above 20 at%, the band gap and sp³-bonded carbon fraction decrease from 1.7 to 1.1 eV and ∼65 to 40%, respectively. The transition is due to the formation of polymeric CN, CN and NH groups, not an increase in CH bonds. Films with higher nitrogen content are less dense than the original hydrogenated tetrahedral amorphous carbon (ta-C:H) film but, because they have a relatively high band gap (1.1 eV), high resistivity (10⁹ Ω cm) and moderate sp³-bonded carbon fraction (40%), they should be classed as polymeric in nature.     

Thiourea-catalyzed dearomatizing [4+2] cycloadditions of 3-nitroindole

We have developed two efficient thiourea promoted dearomatizing processes involving the cycloadditions of 3-nitroindoles. The C2C3 double bond of the heteroarene can be involved as electron-poor 2π dienophile in [4+2] cycloadditions. While the uncatalyzed process requires harsh conditions, the organocatalyzed reaction takes place at room temperature and atmospheric pressure. The C2C3NO motif of the heteroarene can also react as an electron-poor 4π heterodiene in [4+2] / [3+2] cycloadditions cascades, under high pressure. In contrast to Lewis acid activation, thiourea promotion thus proves efficient even under unconventional activation conditions and in the presence of acid sensitive reactants such as enol ethers.     

The effect of Mg(OH)2 on furfural oxidation with H2O2

The oxidation of furfural in H₂O₂ and H₂O₂–Mg(OH)₂ system were systematically investigated and a rational explanation for the reaction mechanism was proposed. 2-formyloxyfuran, from selective oxidation of HCO group in furfural, was a crucial intermediate. The addition of Mg(OH)₂ suppressed the oxidation of furan ring of furfural and enhanced selectivities of 2(5H)-furanone (44.8%) and succinic acid (38.0%). FT-IR, Gaussian calculation and experimental results indicated that the process of furfural oxidation with H₂O₂ is homogeneous, and the synergy between dissolved Mg^2 + cations and OH⁻ ions facilitates the HOO⁻ attacking the carbon atom of HCO other than the CC bound of furan ring.     

A first mixed heteropentametallic transition metal complex: Synthesis and characterisation

The synthesis and characterisation of a novel [(η²-dppf)(η⁵-C₅H₅)Ru(CC)-1,4-(C₆H₄)PPh₂–Au–CC-bipy({[Ti](μ-σ,π-CCSiMe₃)₂}Cu)]PF₆ (dppf = 1,1′-bis(diphenylphosphino)ferrocene) is reported in which five different transition metals (Fe–Ru–Au–Cu–Ti) are linked by carbon-rich organic bridging units.     

Copolymerizations of ethylene with α-olefin-ω-ols by highly active vanadium(III) catalysts bearing [N,O] bidentate chelated ligands

The copolymerizations of ethylene with polar hydroxyl monomers such as 10-undecen-1-ol, 5-hexen-1-ol and 3-buten-1-ol were investigated by the vanadium(III) catalysts bearing bidentate [N,O] ligands (1, [PhNC(CH₃)CHC(Ph)O]VCl₂(THF)₂; 2, [PhNCHC₆H₄O]VCl₂(THF)₂; 3, [PhNCHC(Ph)CHO]VCl₂(THF)₂). The polar monomers were pretreated by alkylaluminum before the polymerization. High catalytic activities and efficient comonomer incorporations can be easily obtained by changing monomer masking reagents and polymerization conditions in the presence of diethylaluminium chloride as a cocatalyst. The longer the spacer group, the higher the incorporation of the monomer. Under the mild conditions, the incorporation level of 10-undecen-1-ol reached 13.9 mol% in the resultant copolymers was obtained. The reactivity ratios of copolymerization (r₁ = 41.4, r₂ = 0.02, r₁r₂ = 0.83) were evaluated by Fineman–Ross method. According to ¹³C NMR spectra, polar units were located both on the main chain and at the chain end. The end-hydroxylated polymers were probably obtained due to the formation of dormant species after the insertion of the comonomer followed by the chain transfer to alkylaluminum. In addition, the signals derived from polar monomer inverse insertion were detected for the first time.     

Origin of the cluster-size effect in the hydrogenation of cinnamaldehyde over supported Au catalysts

Gold nanoclusters supported on γ-Al₂O₃ were more active and selective than platinum nanoclusters in the high-pressure liquid-phase hydrogenation of cinnamaldehyde to cinnamylalcohol, while in the hydrogenation of cyclohexene gold was less active than platinum. The differences in catalytic performance are ascribed to the weaker interaction of gold with the reactants and products compared to platinum. Gold clusters with a diameter below 2 nm are essential to obtain a high activity and selectivity in the hydrogenation of cinnamaldehyde. The size dependence of the selectivity originates from the stronger dependence of the CO hydrogenation rate on cluster size compared to the CC hydrogenation rate. Small clusters exhibit an enhanced π backbonding, which favors CO adsorption over CC adsorption.     

Copolymerization of N-propargylphosphonamidates. Helicity control of the copolymers by P-chirality

The copolymerization of diastereomeric pairs of N-propargylphosphonamidate monomers 1–3 ((1R,2S,5R)-HCCCH₂NHP(O)R-O-menthyl, 1: R = CH₃, 2: R = C₂H₅, 3: R = n-C₃H₇) carrying P- and C-chiral centers was carried out with (nbd)Rh⁺[η⁶-C₆H₅B⁻(C₆H₅)₃] as a catalyst in CHCl₃ for 24 h to afford the copolymers with number-average molecular weights ranging from 1400 to 12 000 in 65–85% yields. The cis contents of the copolymers were above 80%. The copolymers consisting of a pair of diastereomeric monomer units with a large diastereomeric excess showed a large specific rotation and an intense Cotton effect in CHCl₃, indicating that they take a helical conformation with predominantly one-handed screw sense. On the other hand, the copolymer with a small diastereomeric excess showed a small specific rotation and a CD signal. The copolymerization of P-(R)-1 (1a) with an achiral N-propargylphosphoramidate monomer, HCCCH₂NHP(O)(OPh)₂ (4) was also carried out with various feed ratios. Among the obtained copolymers with various compositions, poly(1a₉₅-co-4₅) showed the largest specific rotation and CD intensity in CHCl₃, and poly(1a₅₀-co-4₅₀) did so in THF. The copolymers decreased the CD intensity upon raising the temperature.     

Electrochemical oxidation of methyl orange azo dye at pilot flow plant using BDD technology

Solutions of methyl orange azo dye were degraded by electrochemical oxidation using a 3 L flow plant with a boron-doped diamond (BDD)/stainless steel cell operating at constant current density, ambient temperature and liquid flow rate of 12 L min^?1. A 2³ factorial design considering the applied current density, azo dye concentration and electrolysis time as variable independents was used to analyze the process by response surface methodology. LC–MS analysis revealed the formation of seven oxidation products from the cleavage of the NN group of the dye, followed by deamination, formation of a nitro group and/or desulfonation of the resulting aromatics.