Investigation of lipase-catalyzed Michael-type carbon–carbon bond formations

Conjugate additions of carbon nucleophiles to appropriate acceptor molecules were investigated with respect to the synthetic potential and stereochemistry of the products. Reactions of short-chain α,β-unsaturated ketones and mono-substituted nitroalkenes with CH-acidic carboxylic ester derivatives were catalyzed by various immobilized lipases. Using methyl nitroacetate complete conversion with methyl vinyl ketone and trans-β-nitrostyrene was obtained. The reactions proceeded without enantioselectivity. Evidence for enzyme catalysis is provided by the observation that after denaturation of Candida antarctica lipase B or inhibition no reaction took place. Docking studies with the chiral addition product methyl 2-methyl-2-nitro-5-oxohexanoate did not reveal any specific binding mode for this reaction product, which would have been the requirement for stereoselective additions. These results support the experimental findings that the conjugate addition takes place without enantiopreference.     

Ring-opening of cyclic ethers with carbon–carbon bond formation by Grignard reagents

The ring-opening of cyclic ethers with concomitant C–C bond formation was studied with a number of Grignard reagents. The transformation was performed in a sealed vial by heating to ∼160 °C in an aluminum block or at 180 °C in a microwave oven. Good yields of the product alcohols were obtained with allyl- and benzylmagnesium halides when the ether was tetrahydrofuran or 3,3-dimethyloxetane. Lower yields were obtained with substituted tetrahydrofurans while no ring-opening was observed with tetrahydropyran. Only highly reactive allyl and benzyl Grignard reagents participated in the transformation while no reaction occurred with other alkylmagnesium halides.     

On the possibility of homolytic addition of N-bromohexamethyldisilazane to the triple carbon–carbon bond

Russian Journal of General Chemistry - By an example of a reaction of N-bromohexamethyldisilazane with phenylacetylene the possibility of its homolytic addition to the triple carbon-carbon bond...     

Metal free amide synthesis via carbon–carbon bond cleavage

A metal-free oxidative coupling of methyl ketones and primary amines to amides has been developed. The reaction tolerates a variety of functional groups, and is operationally simple. The reaction is proposed to go through a radical pathway to form the triiodomethyl ketone intermediate and the amide is formed by the nucleophilic attack of amine on triiodomethyl ketone carbonyl.     

Kinetic and mechanistic features of carbon dioxide reforming of methane over Co–Ce/ZrO2 catalysts

Carbon dioxide reforming of methane (CDRM) is an effective route to utilize CO₂ and CH₄, the most abundant, thermodynamically stable and hazardous greenhouse gases. To overcome the economical impediments to favor CDRM's industrial applicability, its mechanistic features need to be revealed both for developing efficient catalysts and optimizing operational conditions. In this context, this work aims to obtain power-law type CDRM kinetic expressions over 5%Co–2%Ce/ZrO₂ and 10%Co–2%Ce/ZrO₂ catalysts and compare and analyze mechanistic routes to elucidate the effect of the Co:Ce ratio on kinetics. The empirical power-law type rate expressions were estimated with the reaction orders of 1.63 and 1.12 for CH₄ and 0.29 and –0.12 for CO₂ for 5%Co–2%Ce/ZrO₂ and 10%Co–2%Ce/ZrO₂ catalysts, respectively. Limited CH₄ activation and, thus, carbon formation due to low Co loading lead to accumulation of surface oxygen on ZrO₂ as redox ability of Ce becomes suppressed. This causes higher CO₂ activation barrier. The presence of H₂ in the feed slows down mechanistic steps involving CH_x. The reactions including CH₄ activation, most probably reversible direct CH₄ dissociation, are found to be rate determining.     

Rh-catalyzed decarbonylation of conjugated ynones via carbon–alkyne bond activation: reaction scope and mechanistic exploration via DFT calculations

In this full article, detailed development of a catalytic decarbonylation of conjugated monoynones to synthesize disubstituted alkynes is described. The reaction scope and limitation has been thoroughly investigated, and a broad range of functional groups including heterocycles were compatible under the catalytic conditions. Mechanistic exploration via DFT calculations has also been executed. Through the computational study, a proposed catalytic mechanism has been carefully evaluated. These efforts are expected to serve as an important exploratory study for developing catalytic alkyne-transfer reactions via carbon–alkyne bond activation.     

Characterization and electrochemical study of hemoglobin–carbon nanoparticles–polyvinyl alcohol nanoporous hybrid film

A hybrid film is fabricated by casting hemoglobin (Hb)–carbon nanoparticles (CNPs)–polyvinyl alcohol (PVA) suspension on glassy carbon electrode (GCE). The resulting film shows a three-dimensional nanoporous structure. In the hybrid film, the ultraviolet visible (UV–Vis) absorption spectra of Hb keep almost unchanged. The organic–inorganic hybrid material can promote the direct electron transfer of Hb. A pair of well-defined and quasireversible peaks with a formal potential of −0.348 V (vs saturated calomel electrode) is obtained, which is caused by the electrochemical reaction of the Fe(III)/Fe(II) couple of Hb. The electron transfer rate constant (k _s) is estimated to be 3.9 s⁻¹. The immobilized Hb exhibits high stability and excellent electrochemical catalysis to the reduction of oxygen (O₂), hydrogen peroxide (H₂O₂), and nitrite (). The catalytic currents are linear to the concentrations of H₂O₂ and from 1.96 to 112 μM and from 0.2 to 1.8 mM, respectively. Therefore, the hybrid film may be a good matrix for protein immobilization and biosensor fabrication.     

Insertion of arynes into the carbon–oxygen double bond of amides and its application into the sequential reactions

The reaction of arynes, generated from ortho-(trimethylsilyl)aryl triflates, with the CO bond of formamides gave salicylaldehyde derivatives via the formation of formal [2+2] adducts. The sequential transformation of arynes into ortho-disubstituted arenes, o-aminoalkylphenols or o-hydroxyalkylphenols, was achieved by one-pot procedure using dialkylzincs.     

Adsorption and DSC study of mineral–carbon sorbents obtained from coal tar pitch–polymer compositions

The purpose of this study was to determine the possibility of producing hydrophobic mesoporous mineral–carbon sorbents from aluminum hydroxide and compositions of coal tar pitch–polymers on carbonization at 600 °C in a nitrogen atmosphere. Blends of the products of co-precipitation of aluminum hydroxide in the carbonaceous substances medium were subjected to carbonization process. The extent of porous structure development was evaluated using low temperature nitrogen adsorption, adsorption of benzene vapors, and adsorption of iodine from aqueous solution. The highest value of BET surface area of about 370 m²/g was achieved for the carbonization product obtained from co-precipitated raw components with 10 wt% compositions coal tar pitch–polymer. These materials demonstrated high capacity to reduce organic pollutions from sewage. Pitch–polymer composition containing poly(ethylene terephthalate) or phenol–formaldehyde resin was studied by the means of DSC method in order to determine the high-temperature transformations taking place under the conditions of carbonization. DSC method enables to determine i.a. the decomposition temperatures of carbonizates produced from pitch–polymer compositions and the evaluation of their sorption abilities. The additive of poly(ethylene terephthalate) and phenol–formaldehyde resin caused the increase of thermal resistance of the pitch expressed by higher decomposition temperatures.     

Novel carboncarbon bond formation induced by depalladation of organometallic compounds

Two internal alkynes undergo insertion at 20°C into the PdC bond of the cyclopalladated derivative of dimethylaminomethylferrocene to give new organometallic compounds. When the reaction with diphenylacetylene is performed at higher temperatures, depalladation occurs readily to give six- and seven-membered ortho-fused rings through new annulation reactions of phenyl groups, formation of one of these involving also the cleavage of a CN bond.     

Mössbauer study and magnetic properties of Fe–Si–B–Cu amorphous systems with minor substitution of carbon

Journal of Radioanalytical and Nuclear Chemistry - The effect of minor substitution of carbon on the structure and magnetic properties of Fe–Si–B–Cu-type metallic glasses was...     

Stereoselective reduction of endocyclic carbon–nitrogen double bond: application to the synthesis of biomolecules

Recent advances in the stereoselective synthesis of nitrogen containing heterocyclic compounds using the reduction of endocyclic double carbon–nitrogen bond are surveyed.     

Participation of furoxancarbonitrile oxide in [3+2] cycloaddition reaction toward C–N triple bond: a Molecular Electron Density Theory study of regioselectivity and mechanistic aspect

Structural Chemistry - The [3+2] cycloaddition (32CA) reaction between furoxancarbonitrile oxide (FNO 2) and electron-deficient 2,2,2-trichloroacetonitrile (TCAN 3) in the presence of chloroform...     

Titanium-catalyzed vinylic and allylic cf bond activation-scope, limitations and mechanistic insight

The hydrodefluorination (HDF) of fluoroalkenes in the presence of a variety of titanium catalysts was studied with respect to scope, selectivity, and mechanism. Optimization revealed that the catalyst requires low steric bulk and high electron density; secondary silanes serve as the preferred hydride source. A broad range of substrates yield partially fluorinated alkenes, such as previously unknown (Z)-1,2-(difluorovinyl)ferrocene. Mechanistic studies indicate a titanium(III) hydride as the active species, which forms a titanium(III) fluoride by H/F exchange with the substrate. The HDF step can follow both an insertion/elimination and a σ-bond metathesis mechanism; the E/Z selectivity is controlled by the substrate. The catalysts' ineffieciency towards fluoroallenes was rationalized by studying their reactivity towards Group?6 hydride complexes.     

Density functional and chemical model study of the competition between methyl and hydrogen scission of propane and ��-scission of the propyl radical

In this work, we study the competence between the reactions of hydrogen and methyl scission during thermal cracking and combustion of propane, the emergence of the two isomers of the propyl radical, n-propyl and i-propyl, and their subsequent ??-scission reaction to ethene and methyl radical. The purpose of the study was to analyze the accuracy of density functional (DFT) methods as applied on this relatively well-known subset of the reactions implied in the production of propylene oxide from propane and propene. Conventional (B3LYP, B3PW91) and state-of-the-art (PBE0, M06, BMK) DFT methods were employed, and their accuracy checked against experimental data and calculations performed using model chemistries (complete basis set CBS-4M, QB3, and APNO, and G4 methods) and ab initio methods (MP2, CCSD(T) with a large 6-311 ++G(3df,2pd) basis set). The results obtained at the BMK level for the thermodynamics of the reactions are closer to experimental data than those afforded by any other DFT method and very similar actually to CBS or CCSD(T) results, even if a medium size basis set is used. Activation energies determined using two- and three-parameter Arrhenius equations are also very good, but the preexponential factors are incorrect. Tunneling and internal rotation corrections must be applied to obtain semiquantitative results.     

Ultrasonic and ir investigations of N–H bond complexes

Complex formation of 1?:?1 mixtures of naphthols, viz. (α-naphthol and β-naphthol) with triethylamine in benzene have been studied at a frequency of 2?MHz in the concentration range of 0.010–0.090 and at varying temperatures of 30, 40 and 50°C. Using the measured ultrasonic velocity, the thermoacoustical parameters such as adiabatic compressibility, intermolecular free length, molar sound velocity, molar compressibility and acoustic impedance have been calculated. The ultrasonic velocity shows a maxima and adiabatic compressibility shows a corresponding minima as a function of concentration for these mixtures. These, in turn, are used to study the solute–solute interaction and the possibility of complex formation between unlike molecules of naphthols and triethylamine through intermolecular hydrogen bonding. The hydrogen bond is formed between hydrogen atom of naphthols and nitrogen atom of triethylamine molecule. The result obtained using infrared spectroscopy for both the systems also supports the existence of complex formation through intermolecular hydrogen bonding.     

Synergy of heterogeneous Co/Ni dual atoms enabling selective C–O bond scission of lignin coupling with in-situ N-functionalization

Selective cleavage of Csp²—OCH₃ bond in lignin without breaking other types of C—O bonds followed by N-functionalization is fascinating for on-purpose valorization of biomass. Here, a Co/Ni-based dual-atom catalyst CoNi_DA@NC prepared by in-situ evaporation and acid-etching of metal species from tailor-made metal–organic frameworks was efficient for reductive upgrading of various lignin-derived phenols to cyclohexanols(88.5%–99.9% yields), which had ca. 4 times hi...     

The chemistry of the carbon–transition metal double and triple bond: annual survey covering the year 1999

This survey is intended to be a comprehensive summary of articles that report on the synthesis, reactivity, or properties of compounds featuring a multiple bond between carbon and a transition metal. Reactions which employ metal carbene complexes as transient intermediates generated through well-established routes [Russ. Chem. Bull. 48 (1999) 16] are not covered unless there is some effort to characterize the carbene complex intermediate. Although a determined effort has been made to include patents, in general only patents which are listed in or at the end of Organometallics section of Chemical Abstracts (Section 29) are included; patents which appeared in Chemical Abstracts in the year 1999 have been included. Only compounds which feature a multiple bond between one carbon atom and one transition metal are discussed in this survey, thus bridging carbene and carbyne complexes are not covered unless there is a multiple bond to at least one transition metal. The complexes of stable carbenes with transition metals have not been included; since the π-donation component of these complexes is minimal, there is no formal carbonmetal multiple bond [J. Chem. Soc., Chem. Commun. (1997) 1963; Polyhedron 16 (1997) 3879]. This survey has been divided into two sections, metal carbene (or alkylidene) complexes and metal carbyne (or alkylidyne) complexes; the carbene complex section represents the vast majority of this article. The metal carbene section has been organized according to metal, starting from the left side of the periodic table. The ionic model [R.H. Crabtree, The Organometallic Chemistry of the Transition Metals, second ed., Wiley-Interscience, New York, 1994, pp. 25–31] has been employed for the discussion of oxidation states and ligand electron count throughout this survey. A special section focusing on alkene metathesis has been included prior to the discussion of carbene complexes of individual metals. The metal carbyne section has been organized according to reaction type.