Hydrogenation Of Cis Research Articles

Cis boron hydrogen chains: Theoretical calculations

Ab initio quantum Hartree-Fock and Møller–Plesset approximations used to study cis boron hydrogen cis-(BH)n chains. The ground-state energies, binding energies, Mulliken population and the optimal geometrical configurations of cis-(BH)n are reported in terms of the chain size n. The calculated ground-state energies in terms of chain dimerization un showed two phases cis-transoid and Trans-cisoid. The energies of these two phases at MP2 fitted into the modified Su-Schrieffer-Heeger (SSH) model in order to determine the corresponding parameters. According to this model, the dimerization induces a band gap around 0.12 eV for cis-transoid phase and 0.11 eV for the trans-cisoid one.

Calculations of adsorption energies, coadsorptions, and diffusion barriers of H atoms, and the H2 formation on a nanographene surface (coronene)

AbstractAdsorption and diffusion of ortho, meta, and para cis hydrogen dimers, on central and edge rings of coronene (nanographene), were studied by using the DFT‐D method, considering different multiplicities. Calculated values of adsorption energy, coadsorption energy, diffusion barriers, and reaction barriers for the H2 formation (Langmuir‐Hinshelwood (LH) mechanism) were evaluated for ortho and para locations. The adsorption of an •H atom increases the adsorption energy of another hydrogen (coadsorption). The most stable dimers are those where an •H is adsorbed on hydrogenated‐edge sites. Dimers with multiplicity M = 1, with •H separated by an odd number of bonds, have higher coadsorption energies (higher diffusion barriers) than those where the separation is by an even number. The H2 formation is more feasible on edge‐edge and edge‐center sites; however, on ortho hydrogenated‐edge sites, it is not energetically favored. For M = 3, H2 formation is not observed because desorption of •H occurs.

Rhodium-Catalyzed Oxidative C-H Allylation of Benzamides with 1,3-Dienes by Allyl-to-Allyl 1,4-Rh(III) Migration.

The Rh(III)-catalyzed oxidative C-H allylation of N-acetylbenzamides with 1,3-dienes is described. The presence of allylic hydrogens cis to the less substituted alkene of the 1,3-diene is important for the success of these reactions. With the assistance of reactions using deuterated 1,3-dienes, a proposed mechanism is provided. The key step is postulated to be the first reported examples of allyl-to-allyl 1,4-Rh(III) migration.

ChemInform Abstract: All‐Carbon [3 + 3] Oxidative Annulations of 1,3‐Enynes by Rhodium(III)‐Catalyzed C—H Functionalization and 1,4‐Migration.

1,3-Enynes containing allylic hydrogens cis to the alkyne function as three-carbon components in rhodium(III)-catalyzed, all-carbon [3+3] oxidative annulations to produce spirodialins. The proposed mechanism of these reactions involves the alkenyl-to-allyl 1,4-rhodium(III) migration.

All-Carbon [3+3] Oxidative Annulations of 1,3-Enynes by Rhodium(III)-Catalyzed C-H Functionalization and 1,4-Migration.

1,3-Enynes containing allylic hydrogens cis to the alkyne function as three-carbon components in rhodium(III)-catalyzed, all-carbon [3+3] oxidative annulations to produce spirodialins. The proposed mechanism of these reactions involves the alkenyl-to-allyl 1,4-rhodium(III) migration.

All‐Carbon [3+3] Oxidative Annulations of 1,3‐Enynes by Rhodium(III)‐Catalyzed CH Functionalization and 1,4‐Migration

Abstract1,3‐Enynes containing allylic hydrogens cis to the alkyne function as three‐carbon components in rhodium(III)‐catalyzed, all‐carbon [3+3] oxidative annulations to produce spirodialins. The proposed mechanism of these reactions involves the alkenyl‐to‐allyl 1,4‐rhodium(III) migration.

ChemInform Abstract: Catalytic 1,4‐Rhodium(III) Migration Enables 1,3‐Enynes to Function as One‐Carbon Oxidative Annulation Partners in C—H Functionalizations.

AbstractAn unexpected mode of oxidative annulation in Rh‐catalyzed C‐H functionalizations of arenes having hydroxy‐substituted functionalities with 1,3‐enynes containing allylic hydrogens cis to the alkynes is described.

Effect of acid identity on the geometry of intermolecular complexes: the microwave spectrum and molecular structure of vinyl chloride-HF.

The structure of the gas-phase bimolecular complex formed between vinyl chloride and hydrogen fluoride is determined using Fourier transform microwave spectroscopy from 6.3 to 21.4 GHz. Although all previous examples of complexes formed between protic acids and haloethylenes are observed to have similar modes of binding regardless of the specific identity of the acid, HF, HCl, or HCCH, the planar vinyl chloride-HF complex has HF located at the "top" of the vinyl chloride with the secondary interaction occurring with the cis hydrogen atom as opposed to the "side" binding configuration found for vinyl chloride-HCCH. Nevertheless, the details of the structure, such as hydrogen bond length (2.32 Å) and amount of deviation from linearity (19.8°), do reflect the strength of the interaction and show clear correlations with the gas-phase acidity. Comparison with analogous complexes allows the determination of the relative importance of electrostatic interactions and steric requirements in leading to the observed structures.

Catalytic 1,4‐Rhodium(III) Migration Enables 1,3‐Enynes to Function as One‐Carbon Oxidative Annulation Partners in CH Functionalizations

Abstract1,3‐Enynes containing allylic hydrogens cis to the alkyne are shown to act as one‐carbon partners, rather than two‐carbon partners, in various rhodium‐catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double CH activation, involving a hitherto rare example of the 1,4‐migration of a RhIII species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products.

Catalytic 1,4-rhodium(III) migration enables 1,3-enynes to function as one-carbon oxidative annulation partners in C-H functionalizations.

1,3-Enynes containing allylic hydrogens cis to the alkyne are shown to act as one-carbon partners, rather than two-carbon partners, in various rhodium-catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double C–H activation, involving a hitherto rare example of the 1,4-migration of a RhIII species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products.

ChemInform Abstract: Shape and Size Controlled Pt Nanocrystals as Novel Model Catalysts

AbstractReview: 58 refs.

ChemInform Abstract: Olefin Hydrogenation on Pd Model Supported Catalysts: New Mechanistic Insights

AbstractReview: 39 refs.

Shape and Size Controlled Pt Nanocrystals as Novel Model Catalysts

A tremendous development of nanotechnology enabled us to prepare precisely structure-controlled nanocrystals (NCs). Recently, such structure controlled NCs have been applied as model catalysts with controlled active sites to evaluate reaction mechanisms. Here, we review our recent works on preparation of shape controlled Pt NCs, such as cube and wire, and on application as model catalysts for olefin hydrogenation to assess active Pt sites. A hydrogen reduction method of Pt(II) ion was adopted in an aqueous phase to prepare Pt cube in the presence of shape forming agent (NaI) and organic protective agent (sodium polyacrylate or sodium succinate). We succeed to prepare Pt cube with high size and shape selectivity, followed by very small Pt cube of less than 3 nm. Such simultaneous control of both size and shape of Pt NCs has been successfully achieved by the sophisticated tuning of multiple conditions for the growth kinetics of Pt nuclei during hydrogen reduction of PtCl4 2− in aq. N-, N-dimethylformamide (DMF) solution. The key strategy is to produce small Pt nuclei and to avoid the excessive growth of Pt nuclei, in conjunction with face selective adsorption of anionic protective and shape-forming agents by the control of solvent system. For the preparation of Pt nanowires with high anisotropy, template-assisted methods have been usually used. We have developed facile liquid phase preparation method at room temperature in air without any template. The key factors of the method are: firstly, to use aqueous organic solvent system to control solvent polarity; secondly, to use co-solvent DMF as shape forming agent; thirdly, to use excess NaBH4 as a stabilizer of Pt nuclei to prevent formation of conventional particles. Single-crystalline Pt nanowires of 2 nm diameter and more than micron length were easily obtained by the reduction of Pt(IV) with excess NaBH4 in water–DMF–toluene solution (1:8:5 volume ratio) in a short reaction period of 3 h. Then, we have applied shape-controlled Pt NCs protected with PAA prepared by our original methods, such as cube, tetrahedron and wire, as model catalysts for olefin (cis- and trans-stilbenes) hydrogenation in ethanol to evaluate the active facet of Pt catalysts; e.g., Pt(111) or Pt(100). The estimated TOF values for the hydrogenation of cis- and trans-stilbene decreased in the order: cube > cuboctahedron > tetrahedron ~ nanowire. This tendency indicates that Pt(100) show high activity compared with Pt(111). The result is compatible with measurement of XPS and Raman spectra, suggesting strong adsorption of reactant on Pt(100). Hydrogenation of olefins (1-hexene and cyclohexene) has been carried out over Pt cubes with different sizes (8.2–10.1 nm) as catalysts to get information about active sites of Pt catalysts, e.g., flat facet or edge/corner atoms. The results of similar TOF values among Pt cubes with different sizes imply that the active sites are flat facets.

Olefin hydrogenation catalysis of platinum nanocrystals with different shapes

We have investigated the catalysis of Pt nanocrystals for olefin hydrogenation in liquid phase by using several kinds of Pt nanocrystals with different shapes, whose results suggest that Pt cube shows the highest catalytic activity without significant shape change after the repeated hydrogenation. We prepared four nanocrystals according to our original methods: four kinds of Pt cubes (6.7, 8.2, 9.5, and 10.1 nm), Pt tetrahedron (4.6 nm), Pt nanowire (2.0 nm), and Pt cuboctahedron (7.5 nm) with high shape selectivity and narrow size distributions. To avoid the effect of different surface protecting agent on hydrogenation, we use the same polymer (polyacrylic acid) to stabilize four kinds of Pt nanocrystals. We adopted olefins with different structural characteristics, such as hexene, cyclohexene, cis-, and trans-stilbene. Turnover frequency (TOF) values for the hydrogenation of both cis- and trans-stilbene exhibit the following order: Pt cube > Pt cuboctahedron > Pt tetrahedron ≈ Pt nanowire, in accord with the ratio of Pt(100) on the surface of Pt nanocrystals. Raman spectroscopy of chemically adsorbed trans-stilbene on Pt cube and Pt tetrahedron indicates that the C–C double bonds of olefin group and phenyl group prefer to interact with Pt(100) facet, coinciding with its highest activity for olefin hydrogenation. The hydrogenation of cyclohexene as well as 1-hexene over Pt cubes with different sizes gave similar TOF values, suggesting that the hydrogenation takes place preferentially on the planes of Pt(100) facet in liquid phase.

Alternative pathways for Heck intermediates: palladium-catalyzed oxyarylation of homoallylic alcohols.

Alternative pathways for Heck intermediates: palladium-catalyzed oxyarylation of homoallylic alcohols.

Design and synthesis of novel dinucleotide analogs

Syntheses of dinucleotide analogs, (S,R) cis-(4-((4-amino-2-oxopyrimidin-1(2H)-yl)methyl)-1,3-dioxolan-2-yl)methyl (2R,3R,5R)-2-(hydroxymethyl)-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-tetrahydrofuran-3-yl hydrogen phosphate (5a) and (S,R) cis-(5-((4-amino-2-oxopyrimidin-1(2H)-yl)methyl)-1,3-oxathiolan-2-yl)methyl (2R,3R,5R)-2-(hydroxymethyl)-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-tetrahydrofuran-3-yl hydrogen phosphate (5b), were accomplished by the use of a new strategy. The use of phenyldichlorophosphate (Method A) as the coupling reagent was shown to possess superiority relative to the reported use of di(1H-benzo[d][1,2,3]triazol-1-yl)phenyl phosphonate (Method B).

Conversion of cis- and trans-2-butene with Deuterium on a Pd/Fe 3O 4 model catalyst

Combining molecular beam (MB) techniques, reflection–absorption infrared spectroscopy (RAIRS), and temperature-programmed desorption (TPD), we have investigated the adsorption and kinetics of conversion of cis- and trans-2-butene with deuterium on a well-defined model supported Pd catalyst. Particular emphasis was placed on the quantitative comparison of the reaction rates of the competing cis-trans isomerization and hydrogenation pathways between both steric isomers. It was observed that the reaction temperature critically affects the cis-trans selectivity of 2-butene in both reaction paths. At low-temperatures (195–210 K), cis-2-butene shows higher activity toward both hydrogenation and isomerization reactions han the trans isomer. At temperatures above 250 K, on the other hand, very similar reaction rates were found for both isomers. Remarkably, deposition of sub-monolayer amounts of strongly dehydrogenated carbonaceous species on the Pd particles results in a significant decrease of the cis-trans isomerization rate for trans-2-butene, but does not affect the rate of this pathway for the cis isomer. Additionally, under high-temperature conditions (250–260 K), co-deposited carbon was shown to assist the catalytic and sustained hydrogenation of both cis- and trans-2-butene, both at similar rates.

A THEORETICAL STUDY OF UNSATURATED OLEFIN HYDROGENATION AND ISOMERIZATION ON Pd(111)

The addition of hydrogen to the carbon–carbon double bond of 2-butenes adsorbed on Pd (111) was studied within the density functional theory (DFT) and using a periodic slab model. For that purpose, the Horiuti–Polanyi mechanisms for both complete hydrogenation and isomerization were considered. The hydrogenation of cis and trans-2-butene to produce butane proceeds via the formation of eclipsed and staggered-2-butyl intermediates, respectively. In both cases, a relatively high energy barrier to produce the half-hydrogenated intermediate makes the first hydrogen addition the slowest step of the reaction. The competitive production of trans-2-butene from cis-2-butene requires the conversion from the eclipsed-2-butyl to the staggered-2-butyl isomer. As the corresponding energy barrier is relatively small and because the first of these isomers is less stable than the second, an easy conversion is predicted.

The role of carbon deposits in the hydrogenation of C5 hydrocarbons

Abstract The hydrogenation of pentenes, pentenenitriles and 1-pentyne has been studied over Al 2 O 3 -supported Ni and Pd catalysts. In particular the role of hydrocarbonaceous residues in such reactions has been probed. This has been achieved through the use of a tapered element oscillating microbalance to record mass changes in situ during the catalytic reactions with simultaneous analysis by gas chromatography. Sequential adsorption and reaction studies demonstrate that the influence exerted by hydrocarbonaceous deposits is critically dependent upon the compound from which they are derived, with deposits from different isomers of the same compound exhibiting different effects. In particular, in the case of 2-pentenes, a hydrocarbonaceous overlayer resulting from the hydrogenation of cis -2-pentene significantly activates Ni/Al 2 O 3 towards hydrogenation of trans -2-pentene and vice versa . In the case of pentenenitrile hydrogenation however, trans -3-pentenenitrile deposits an overlayer which renders inactive the sites responsible for the selective hydrogenation of cis -2-pentenenitrile to pentanenitrile. Results from 1-pentyne hydrogenation studies over Pd/Al 2 O 3 support previous conclusions regarding the development of a carbon-rich active phase. This work demonstrates the importance of the consideration of heterogeneous catalysts as dynamic materials which evolve during reaction and adds to the increasing awareness of the potential positive roles played by carbonaceous deposits in such reactions.

Functional gel-type resin based palladium catalysts: The role of polymer properties in the hydrogenation of the C [dbnd]C bond of maleic and fumaric acids, the isomers of dicarboxylic acids

Functional gel-type resins (OFP) composed of 2-hydroxyethyl methacrylate (HEMA, 20 mol%), styrene (60–77 mol%) and diethylene glycol dimethacrylate, the crosslinking reagent (DEGDMA, 3–20 mol%) are used as supports for palladium catalysts (0.25–2 wt% Pd). The influence of polymer mass expansion on the activity of Pd/OFP catalysts in the hydrogenation of cis- and trans-isomers of unsaturated dicarboxylic acids, maleic (MA) and fumaric (FA), is examined. Starting polymer swells very well in THF and this solvent is used in the hydrogenation experiments. Swelling ability of polymer decreases after insertion of palladium ions due to the crosslinking effect. Reduction of Pd/OFP by NaBH 4 leads to further decrease in swelling ability of polymer caused by the changes in polymer structure observed in FTIR spectroscopy. In the reduced form of the catalysts the nano-particles of Pd (2–3 nm) are formed. Hydrogenation experiments performed in a wide range of operating conditions (Pd loading, catalysts concentration, crosslinking degree of polymer, the size of catalysts grains) show that the swelling of polymer mass during the hydrogenation is a crucial factor for activity of Pd/OFP catalysts. When the catalyst does not swell, the rates of hydrogenation for both isomers are practically the same. They differ only when the catalysts grains are in swollen state. Much higher rate of hydrogenation is observed for MA (the cis-isomer) than for FA (the trans-isomer). This is related to easier penetration of cis-isomer (MA) inside the bulk of the polymer mass which results in more effective utilization of substrates, MA and FA, when present in THF both enhance the expansion of polymer mass but especially cis-isomer, MA. Substrate effect is attributed to the interaction between functional groups present in the reduced catalysts and the hydrogenated reagents, maleic or fumaric acids.