Oligomerization Of Alkynes Research Articles

Styrene-alkyne cross ene-yne metathesis: Catalyst screening and optimization for unbranched terminal alkyne substrates

Cross metathesis between styrenes and unbranched terminal alkynes is reported. Styrene cross metathesis with terminal alkynes that lack branching at the propargylic position are unknown. In general, unbranched terminal alkynes have been problematic in cross metathesis due to competing alkyne oligomerization. A catalyst screen was performed for a variety of Grubbs catalysts to optimize the yield of the desired 1,3‑diene product. This catalyst screen identified two ruthenium carbene complexes that have been rarely used for cross metathesis applications. Additionally, a side product arising from a competing alkene metathesis was minimized by choice of catalyst and through reaction optimization.

Functionalization of Gold Nanoparticles with Ru-Porphyrin and Their Selectivity in the Oligomerization of Alkynes.

Gold nanoparticles (AuNPs) were functionalized by ruthenium porphyrins through a sulfur/gold covalent bond using a three-steps reaction. The catalyst was characterized by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) in order to control the binding of ruthenium porphyrin on AuNPs’ surface. The catalyst was tested and compared with an analog system not bound to AuNPs in the oligomerization reaction using 1-phenylacetylene as the substrate.

Self-Assembly of N-Phenyl-2,5-dimethylpyrrole from Acetylene and Aniline in KOH/DMSO and KOBut/DMSO Superbase Systems: A Quantum-Chemical Insight.

By employing the contemporary B2PLYP(D3)/6-311+G**//B3LYP/6-31+G* method of quantum chemistry, we unraveled the mechanism of a recently discovered cascade assembly of N-phenyl-2,5-dimethylpyrrole from one molecule of aniline and three molecules of acetylene activated by KOH/DMSO and KOBut/DMSO superbase systems. For the established mechanism, we compare and analyze the activity of these two superbases. The reaction is found to be activated by the interaction of aniline with acetylene, and the barrier associated with this interaction turns out to be the limiting one. Another barrier close in value to the limiting one is found along the cascade assembly pathway and relates to ethynylation of N-but-3-yn-2-yl-aniline by the ethynide ion. The cascade reaction turns out to be selective with respect to propyne-allene rearrangements. The alternative mechanism of N-phenyl-2,5-dimethylpyrrole self-assembly, which involves a preliminary stage of acetylene oligomerization, is shown to be kinetically less favorable.

“Golden Age” of Homogeneous Catalysis Chemistry of Alkynes: Dimerization and Oligomerization of Alkynes

History of the development and use of homogeneous metal complex catalysts in the chemistry of acetylene and its derivatives is considered. Achievements of the catalytic chemistry of alkynes in the creation of affective catalytic systems (based on Groups 3—11 and 13 of the Periodic Table) for alkyne dimerization, capable of producing desired dimeric isomers possessing high chemo-, stereo- and regioselectivity are analyzed. The nature of elementary stages in four mechanisms of dimerization and the relations of the nature of organometallic intermediates to the nature of catalyst (metal and ligand), substrate, and type of mechanism, and, hence, to the selectivity of dimerization process are discussed.

Model-Based Optimization of an Acetylene Hydrogenation Reactor To Improve Overall Ethylene Plant Economics

The steam cracking process is a common technology for producing ethylene from naphtha. However, one of the major contaminants in the ethylene product stream is acetylene, which poisons catalysts used in downstream polymerization processes and must be converted to ethylene by selective catalytic hydrogenation in order to upgrade product quality and increase overall ethylene yield. The selective hydrogenation process is usually carried out in a multistage fixed-bed catalytic reactor with internal cooling between stages to ensure that the outlet concentration of acetylene does not exceed 1 ppm. Nevertheless, side reactions also occur, including total hydrogenation to ethane, which increases energy consumption at the recycle furnace and decreases overall plant productivity. Moreover, in a tail-end hydrogenation process, the catalyst surface often becomes covered by so-called green oil generated from acetylene oligomerization, which causes catalyst deactivation and lowers the selectivity to ethylene. A key cha...

Metal-Free Acetylene Coupling by the (C6 F5 )2 B-X 1,2-Halogenoboration Reaction.

(C6 F5 )2 B-halides were conveniently prepared by treatment of (C6 F5 )2 BH with tritylchloride or -bromide, respectively. With cyclopropylacetylene, (C6 F5 )2 BBr underwent sequential cis-1,2-halogenoboration followed by 1,2-carboboration to give the 4-bromo-2,4-dicyclopropylbutadienyl-B(C6 F5 )2 product. It reacted further with additional cyclopropylacetylene to give the linear triene and tetraene products in a metal-free alkyne oligomerization reaction. The pyridine adduct of the initial diene product was characterized by X-ray diffraction. (C6 F5 )2 BCl reacted analogously. Similar (C6 F5 )2 BX induced oligomerization reactions were carried out with two conjugated enynes.

First-principles theoretical assessment of catalysis by confinement: NO-O2 reactions within voids of molecular dimensions in siliceous crystalline frameworks.

Density functional theory methods that include dispersive forces are used to show how voids of molecular dimensions enhance reaction rates by the mere confinement of transition states analogous to those involved in homogeneous routes and without requiring specific binding sites or structural defects within confining voids. These van der Waals interactions account for the observed large rate enhancements for NO oxidation in the presence of purely siliceous crystalline frameworks. The minimum free energy paths for NO oxidation within chabazite (CHA) and silicalite (SIL) frameworks involve intermediates similar in stoichiometry, geometry, and kinetic relevance to those involved in the homogeneous route. The termolecular transition state for the kinetically-relevant cis-NOO2NO isomerization to trans-NOO2NO is strongly stabilized by confinement within CHA (by 36.3 kJ mol-1 in enthalpy) and SIL (by 39.2 kJ mol-1); such enthalpic stabilization is compensated, in part, by concomitant entropy losses brought forth by confinement (CHA: 44.9; SIL: 45.3, J mol-1 K-1 at 298 K). These enthalpy and entropy changes upon confinement agree well with those measured and combine to significantly decrease activation free energies and are consistent with the rate enhancements that become larger as temperature decreases because of the more negative apparent activation energies in confined systems compared with homogeneous routes. Calculated free energies of confinement are in quantitative agreement with measured rate enhancements and with their temperature sensitivity. Such quantitative agreements reflect preeminent effects of geometry in determining the van der Waals contributions from contacts between the transition states (TS) and the confining walls and the weak effects of the level of theory on TS geometries. NO oxidation reactions are chosen here to illustrate these remarkable effects of confinement because detailed kinetic analysis of rate data are available, but also because of their critical role in the treatment of combustion effluents and in the synthesis of nitric acid and nitrates. Similar effects are evident from rate enhancements by confinement observed for Diels-Alder and alkyne oligomerization reactions. These reactions also occur in gaseous media at near ambient temperatures, for which enthalpic stabilization upon confinement of their homogeneous transition states becomes the preeminent component of activation free energies.

Carbon Domains on MoS2/TiO2 System via Catalytic Acetylene Oligomerization: Synthesis, Structure, and Surface Properties.

Carbon domains have been obtained at the surface of a MoS2/TiO2 (Evonik, P25) system via oligomerization and cyclotrimerization reactions involved in the interaction of the photoactive material with acetylene. Firstly, MoS2 nanosheets have been synthesized at the surface of TiO2, via sulfidation of a molybdenum oxide precursor with H2S (bottom-up method). Secondly, the morphology and the structure, the optical and the vibrational properties of the obtained materials, for each step of the synthesis procedure, have been investigated by microscopy and spectroscopy methods. In particular, transmission electron microscopy images provide a simple tool to highlight the effectiveness of the sulfidation process, thus showing 1L, 2L, and stacked MoS2 nanosheets anchored to the surface of TiO2 nanoparticles. Lastly, in-situ FTIR spectroscopy investigation gives insights into the nature of the oligomerized species, showing that the formation of both polyenic and aromatic systems can be taken into account, being their formation promoted by both Ti and Mo catalytic sites. This finding gives an opportunity for the assembly of extended polyenic, polyaromatic, or mixed domains firmly attached at the surface of photoactive materials. The presented approach, somehow different from the carbon adding or doping processes of TiO2, is of potential interest for the advanced green chemistry and energy conversion/transport applications.

Hydrooligomerization of unsaturated hydrocarbons as a basis of new technologies for the production of motor fuel compounds

A brief analysis is performed for the current state of processes for the production of motor fuels based on the consecutive oligomerization and hydrogenation reactions of unsaturated hydrocarbons. Some new butene hydrooligomerization catalysts based on the bifunctional NiO/В2O3–Al2O3, PdO/В2O3–Al2O3, and MoO3/В2O3–Al2O3 systems are considered. It is shown that the best process performance parameters (a 67 wt % yield of liquid С5+ products at a butene conversion of more than 90%) are achieved with PdO/В2O3–Al2O3 catalyst prereduced in a hydrogen medium. The possibility of acetylene hydrooligomerization on NiO/B2O3–Al2O3 catalyst is demonstrated in principle. It is established that the presence of nickel(II) cations chemically bonded to the surface of a support is of fundamental importance for both acetylene hydrooligomerization and ethylene oligomerization.

Application of parahydrogen for mechanistic investigations of heterogeneous catalytic processes

Parahydrogen-induced polarization technique (PHIP), based on the pairwise addition of molecular hydrogen to a substrate, was successfully applied to obtain novel information on the mechanisms of heterogeneous catalytic hydrogenation, hydrodesulfurization, and oligomerization processes. In particular, the PHIP effects were observed upon hydrogenation with parahydrogen catalyzed by the immobilized neutral complexes of rhodium and iridium, which confirms the similarity in the mechanisms of homogeneous and heterogeneous hydrogenation for such systems. In the study of acetylene oligomerization, a significant NMR signal enhancement was revealed for a number of C4 oligomers, with the enhancement levels by far exceeding that observed in hydrogenation of carbon-carbon triple bonds. The mechanistic features of heterogeneous hydrogenation of a number of six-membered cyclic hydrocarbons over supported metal catalysts were investigated, and their hydrogenation scheme based on the pairwise addition of molecular hydrogen was proposed. Furthermore, the PHIP technique revealed that heterogeneous hydrodesulfurization of thiophene mainly proceeds via hydrogenation followed by a C—S bond cleavage. A significant enhancement of sensitivity in combination with characteristic line shapes of NMR signals make the PHIP method a unique and highly informative tool for the investigation of heterogeneous catalytic processes.

Acetylene Oligomerization over Pd Nanoparticles with Controlled Shape: A Parahydrogen-Induced Polarization Study

Substantial signal enhancements achieved by using parahydrogen in catalytic hydrogenations are powerful tools for mechanistic studies of chemical reactions involving molecular H2. Potentially, this technique can be extended to other reaction classes, providing new information about reaction mechanisms. Moreover, this can lead to new substances with highly polarized spins. Herein, we report strong signal enhancements of oligomerization reaction products observed during the selective hydrogenation of acetylene over Pd nanoparticles of different shapes and sizes supported on SiO2. C4 oligomeric products (1,3-butadiene, 1-butene, 2-butene) demonstrated a high degree of nuclear spin polarization, with the highest degree observed for 1-butene [more than 1.7% vs (2.4 × 10–3)% at thermal equilibrium], which was an order of magnitude larger than that of the triple C—C bond hydrogenation products. No dependence of polarization on the metal surface statistics or, generally, on the nanoparticle morphology (cubic, oct...

Evaluating the Effect of Catalyst Nuclearity in Ni-Catalyzed Alkyne Cyclotrimerizations.

An evaluation of catalyst nuclearity effects in Ni-catalyzed alkyne oligomerization reactions is presented. A dinuclear complex, featuring a Ni-Ni bond supported by a naphthyridine-diimine (NDI) ligand, promotes rapid and selective cyclotrimerization to form 1,2,4-substituted arene products. Mononickel congeners bearing related N-donor chelates (2-iminopyridines, 2,2'-bipyridines, or 1,4,-diazadienes) are significantly less active and yield complex product mixtures. Stoichiometric reactions of the dinickel catalyst with hindered silyl acetylenes enable characterization of the alkyne complex and the metallacycle that are implicated as catalytic intermediates. Based on these experiments and supporting DFT calculations, the role of the dinuclear active site in promoting regioselective alkyne coupling is discussed. Together, these results demonstrate the utility of exploring nuclearity as a parameter for catalyst optimization.

Acetylene oligomerization on the surface of TiO2: a step forward in the in situ synthesis of nanostructured carbonaceous structures on the surface of photoactive oxides

In situ acetylene oligomerization allows synthesis of polycyclic condensed hydrocarbons in close contact with the TiO2 surface. These products represent intermediate steps in the production of photoactive graphene-like layers on TiO2.

Acetylene Cyclotrimerization with an Iron(II) Bis(imino)pyridine Catalyst

Acetylene oligomerization with an activated iron bis(imino)pyridine complex with low steric hindrance leads to benzene as the major product, in contrast to this reaction with a more sterically encumbered analogue, which leads to polyacetylene. The mechanism of benzene formation was studied and likely occurs via metallacycle intermediates; this process can be interrupted by addition of ZnEt2 as a chain transfer agent to generate hexadiene instead.

Intensification catalytic reaction by integration of magnetic catalyst and magnetically stabilized bed reactor or magnetic separator

Utilizing the excellent hydrogenation activity and magnetism of the amorphous Ni catalyst, a magnetically stabilized bed reactor was developed for the purification of caprolactam, to ensure higher reactor and process efficiency. Integration of amorphous Ni catalyst and magnetic separator has enhanced the benzoic acid hydrogenation reaction to reduce the Pd/C catalyst consumption by 50%, and to increase the plant output by 15%, respectively. Integration of the appropriate magnetic catalyst into the magnetically stabilized bed reactor also allowed improved performances in selective hydrogenation of acetylene and olefin oligomerization, compared with current processes, and thus constitutes a highly effective technique for process intensification.

Evaluation of mid-to-late transition metal imine catalysts for acetylene oligomerisation: A high activity bis(imino)pyridine iron( II) catalyst

Bis(imino)pyridine complexes of Co and Fe, and diimine complexes of Ni and Pd, have been tested as catalysts for acetylene oligomerisation and polymerisation. While Co, Ni and Pd complexes displayed low activity, an Fe complex led to an extremely active system for acetylene polymerisation after activation with methylaluminoxane (MAO). The product output could be shifted towards short-chain oligomers by addition of the chain transfer reagent ZnEt 2, leading to polyene oligomeric chains bound to Zn. Complex branched and cyclic higher oligomers were partially identified, and some possible mechanisms for their formation proposed. The Fe system did not successfully catalyse copolymerisation of acetylene and ethylene, although there was evidence of limited acetylene incorporation into ethylene oligomers.

Endo-Selective Enyne Ring-Closing Metathesis Promoted by Stereogenic-at-W Mono-Pyrrolide Complexes

The utility of W-alkylidene complexes for enyne ring-closing metathesis is demonstrated in a direct comparison with Mo-based analogs. Tungsten complexes lead to less alkyne oligomerization and higher levels of endo-selectivity and enantioselectivity.

ChemInform Abstract: Pyrazole and (Pyrazol‐1‐yl)metal Complexes as Carbon—Carbon Coupling Catalysts

AbstractReview: 156 refs.

Acetylene Oligomerization with Metallocene Catalysts and Triethylaluminum: The Peculiar Course of the Aufbau Reaction with Acetylene

The oligomerization of acetylene to liquid-range products has been investigated. While early transition metal and lanthanide metallocenes do not appear to be very effective catalysts, stoichiometric chain growth at triethylaluminum is observed, which leads to acetylene oligomers. This reaction produces an unexpected distribution of branched oligomers, and some possible routes to these products have been explored. Efforts to promote chain transfer at aluminum centered on the introduction of dihydrogen and high concentrations of Cp2ZrCl2. While some evidence of chain termination was found, the process was not made catalytic in terms of aluminum.

Nanosized clusters of molybdenum chlorides—Active sites in catalytic acetylene oligomerization

Nanosized clusters of molybdenum chlorides—Active sites in catalytic acetylene oligomerization