- Pumice-Supported Pd-Pt Bimetallic Catalysts: Synthesis, Structural Characterization, and Liquid-Phase Hydrogenation of 1,3-Cyclooctadiene
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A series of pumice-supported palladium-platinum bimetallic catalysts were prepared and investigated by X-ray scattering (WAXS and SAXS) and XPS technique.An alloy Pd-Pt was formed.The less abundant metal was found to segregate to the surface.The catalysts were tested in the liquid-phase hydrogenation of 1,3-cyclooctadiene to cyclooctene, and compared with similarly prepared pumice-supported palladium and platinum catalysts and other supported Pd-Pt catalysts reported in the literature.The addition of platinum reduces the activity and the selectivity of the palladium catalysts.Differences between the activity of these pumice-supported catalysts and the activity of previously described Pd and Pd-Pt catalysts on other supports, are attributed to the presence, in the latter, of diffusional processes.
- Deganello, Giulio,Duca, Dario,Liotta, Leonarda F.,Martorana, Antonino,Venezia, Anna Maria,et al.
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- The functionalization of saturated hydrocarbons part XXIX. Application of tert-butyl hydroperoxide and dioxygen using soluble Fe(III) and Cu(II) chelates
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New methodology for the selective transformation of saturated hydrocarbons into ketones/alcohols and alkenes is described. A crucial aspect of this new process is that no reaction solvent is required since the Fe(III) and Cu(II) complexes used are completely soluble in the hydrocarbon substrates. Thus, the large quantity of pyridine, acetic acid or acetonitrile required in previous systems is no longer a prerequisite.
- Barton, Derek H. R.,Beviere, Stephane D.,Hill, David R.
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- Homogeneous Catalytic Photochemical Functionalization of Alkanes by α-Dodecatungstophosphate. Rate Behavior, Energetics, and General Characteristics of the Processes
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The photochemical functionalization of saturated hydrocarbons catalyzed by the heteropolytungstate α-dodecatungstophospate in acetonitrile solution has been examined in detail.Under anaerobic conditions, the net processes involve oxidation of alkane, RH, and evolution of hydrogen (RH->R+1/2H2) with conversion of light into chemical energy (ΔHo>+30 kcal/mol of RH oxidized in some cases).The processes are catalytic in the polyoxotungstate with or without Pt(0) or other hydrogen evolution catalyst, but Pt(0) greatly accelerates the reoxidation of the photoreduced polyoxotungstate, the slow step, resulting in increased turnover rates.Two oxidative titration procedures adapted for these hydrophobic media, and the sizes and shapes of the electronic absorption chromophores generated as a function of time upon irradiation in the near-UV of α-H3PW12O40 (1) in acetonitrile solutions of representative alkanes, establish that the principal form of the photoreduced catalyst is the one-electron heteropoly blue species α-PW12O40(4-), in contrast to the case for photooxidation of alcohols and other organic substrates by 1.The product distributions have been established for the functionalization of representative branched alkanes and cycloalkanes.The relative yields of the initial alkane-derived oxidation products in these processes, alkene, N-alkylacetamide, alkylalkane dimer, and alkyl methyl ketone, vary with the alkane substrate, the form of the polyoxotungstate, and the reaction conditions.All these organic products are remarkably stable under the reaction conditions.Alcohols are not produced in these polyoxotungstate-based systems.The highest selectivities (ca. 100percent for alkene production) are seen with 1 in the absence of Pt(0).Quantum yields average 0.1 but vary with the form of the polyoxotungstate and the reaction conditions and can be considerably higher.For the exemplary system, substrate = cyclooctane and catalyst = 1, production of α-PW12O40(4-) is a one-photon process that is first order in alkane, inverse order in water for low concentrations of water, and zero order in 1 for high concentrations of 1.A rate law that involves the substrate, solvent, initial products, catalyst, and light intensity in accord with substantial kinetic data is derived.The relative observed rate constants for the production of α-PW12O40(4-) under optically dense conditions by photooxidation of several normal, branched, and cyclic alkanes by 1 are unlike those seen in radical, hydride abstraction, electrophilic, or any type alkane activation process documented for homogeneous liquid-phase reactions.These relative rates, the primary kinetic isotope effects kcyclohexane-h12/kcyclohexane-d12 = 1.38 and kcis-Decalin-h12/Kcis-Decalin-d12 = 1.39, and the product distribution studies are most compatible with electron transfer as the principal alkane activation process in the mechanism.These data also allow analysis...
- Renneke, Roman F.,Hill, Craig L.
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- Mechanism of alkane transfer-dehydrogenation catalyzed by a pincer-ligated iridium complex
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The mechanism of (PCP)Ir-catalyzed transfer-dehydrogenation has been elucidated for the prototypical substrate/acceptor couple, COA/TBE, at 55 °C (COA = cyclooctane; TBE = tert-butylethylene). The catalytic cycle may be viewed as the sum of two reactions: (i) hydrogenation of TBE by (PCP)IrH2 and C-H addition of a second mole of TBE to give (PCP)IrH(tert-butylvinyl), and (ii) dehydrogenation of COA by (PCP)IrH(tert-butylvinyl) to give (PCP)IrH2, COE, and TBE. These two stoichiometric reactions have been observed independently and their kinetics determined. The overall catalysis has also been monitored in situ, and (PCP)IrH2 and (PCP)IrH(tert-butylvinyl) have been observed as the resting states; the ratio of these two complexes is found to be proportional to [TBE]2. Based upon the proportionality constant thus obtained and the catalytic rate as a function of [TBE] (which reaches a maximum at ca. 0.3 M), the respective rate constants for the hydrogenation and dehydrogenation segments can be obtained. Good agreement is found between the rates independently obtained from stoichiometric and catalytic runs. Within the overall TBE-hydrogenation reaction, labeling experiments indicate that the rate-determining step is the reductive elimination of TBA (2,2-dimethylbutane) from (PCP)IrH(tert-butylethyl) (which is formed via insertion of TBE into an Ir-H bond of (PCP)IrH2). Based upon considerations of microscopic reversibility, it can be further inferred that the rate-determining step for the alkane dehydrogenations is C-H addition (and not β-H elimination). Copyright
- Renkema, Kenton B.,Kissin, Yury V.,Goldman, Alan S.
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- Catalytic Alkane Transfer Dehydrogenation by PSP-Pincer-Ligated Ruthenium. Deactivation of an Extremely Reactive Fragment by Formation of Allyl Hydride Complexes
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Iridium complexes bearing PCP-type pincer ligands are the most effective catalysts reported to date for the low-temperature (≤ca. 200 °C) dehydrogenation of alkanes. To investigate the activity of formally isoelectronic ruthenium complexes, we have synthesized the neutral 2,7-di-tert-butyl-4,5-bis(diisopropylphosphino)-9,9-dimethylthioxanthene (iPrxanPSP) pincer ligand and several Ru complexes thereof. The (iPrxanPSP)Ru complexes catalyze alkane transfer dehydrogenation of the benchmark cyclooctane/t-butylethylene (COA/TBE) couple with turnover frequencies up to ca. 1 s-1 at 150 °C and 0.2 s-1 at 120 °C, the highest rates for alkane dehydrogenation ever reported at such temperatures. Dehydrogenation of n-octane, however, is much less effective. A combination of experiment and DFT calculations allow us to explain why (iPrxanPSP)Ru is more effective than (iPrPCP)Ir for dehydrogenation of COA, while the reverse is true for dehydrogenation of n-alkanes. Considering only in-cycle species and simple olefin complexes, the (iPrxanPSP)Ru fragment is calculated to be much more active than (iPrPCP)Ir for dehydrogenation of both COA and n-alkanes. However, the resting state in the (iPrxanPSP)Ru-catalyzed transfer dehydrogenation of n-alkane is a very stable linear-allyl hydride complex, whereas the corresponding cyclooctenyl hydride is much less stable.
- Zhou, Xiaoguang,Malakar, Santanu,Zhou, Tian,Murugesan, Sathiyamoorthy,Huang, Carlos,Emge, Thomas J.,Krogh-Jespersen, Karsten,Goldman, Alan S.
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- A highly active alkane dehydrogenation catalyst: Stabilization of dihydrido rhodium and iridium complexes by a P-C-P pincer ligand
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The novel P-C-P pincer complex, [IrH2{C6H3(CH2PBut 2)2-Z1O}] has long-term stability at 200°C and catalyses the transfer dehydrogenation of cyclooctane to cyclooctene at the rate of 12 turnovers min-1.
- Gupta, Mukta,Hagen, Chrystel,Flesher, Robert J.,Kaska, William C.,Jensen, Craig M.
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- Metal dependence in gif-type reactions. The Cu(II)-catalyzed olefination of saturaed hydrocarbons by tert-butyl hydroperoxide
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Cycloalkanes are transformed into the corresponding cycloalkanes by treatment with tert-butyl hydroperoxide (TBHP) in pyridine/acetic acid solution in the presence of Cu(OAc)2.H2O. When iron salts are used instead of copper salts, the major reaction product is the corresponding ketone. Differences between the iron-catalyzed and the copper-catalyzed reactions support a metal-dependent reaction pathway.
- Barton,Beviere,Chavasiri,Doller,Hu
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- The photochemistry of optically active (E)-cyclooctene: Lamp versus laser
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The photochemistry of optically active (E)-cyclooctene in cyclopentane was initiated with a lamp at ca. 254 nm and a Nd-YAG laser at 266 nm. The alkene racemizes slightly faster than it isomerizes to (Z)-cyclooctene, suggesting a previously hidden mechanism of E-Z photointerconversion. The photoreaction at 266 nm may be multiphoton in character.
- Gao, Fang,Li, Run-Hua,Compton, Robert N.,Pagni, Richard M.
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- β',β-Carbanionic Elimination Reaction of a Carboxylic Ester
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The β',β-elimination reaction of the ester (1) gives cis-cyclo-octene in >70 percent yield; the corresponding reactions of the stereoselectively deuterium labelled compounds (1a) and (1b) show that the elimination is syn.
- Aubert, Corinne,Begue, Jean-Pierre,Biellmann, Jean-Francois
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- Bioorthogonal prodrug activation driven by a strain-promoted 1,3-dipolar cycloaddition
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Due to the formation of hydrolysis-susceptible adducts, the 1,3-dipolar cycloaddition between an azide and strained trans-cyclooctene (TCO) has been disregarded in the field of bioorthogonal chemistry. We report a method which uses the instability of the adducts to our advantage in a prodrug activation strategy. The reaction of trans-cyclooctenol (TCO-OH) with a model prodrug resulted in a rapid 1,3-dipolar cycloaddition with second-order rates of 0.017 M-1 s-1 and 0.027 M-1 s-1 for the equatorial and axial isomers, respectively, resulting in release of the active compound. 1H NMR studies showed that activation proceeded via a triazoline and imine, both of which are rapidly hydrolyzed to release the model drug. Cytotoxicity of a doxorubicin prodrug was restored in vitro upon activation with TCO-OH, while with cis-cyclooctenol (CCO-OH) no activation was observed. The data also demonstrates the potential of this reaction in organic synthesis as a mild orthogonal protecting group strategy for amino and hydroxyl groups.
- Matikonda, Siddharth S.,Orsi, Douglas L.,Staudacher, Verena,Jenkins, Imogen A.,Fiedler, Franziska,Chen, Jiayi,Gamble, Allan B.
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- Epoxidation of trans-cyclooctene by methyltrioxorhenium/H2O2: Reaction of trans-epoxide with the monoperoxo complex
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The epoxidation of trans-cyclooctene (trans-1) with the MTO/H2O2, MTO/UHP, and NaY/MTO/H2O2 oxidants leads to a mixture of trans/cis-olefins 1, trans/cis-epoxides 2, and the cis-diol 3. While the oxygen transfer proceeds stereoselectively, the monoperoxo rhenium complex A, which is generated in situ during the catalytic cycle, is responsible for the facile deoxygenation, isomerization, and hydrolysis of the trans-epoxide. In the case of the homogeneous MTO/H2O2 system, rapid decomposition of the catalytically active rhenium species into HReO4 circumvents the formation of such side products. In contrast, for the heterogeneous oxidants MTO/UHP and NaY/MTO/H2O2, the catalytically active rhenium species are sufficiently stabilized and survive long enough to promote the observed side reactions.
- Adam, Waldemar,Saha-Moeller, Chantu R.,Weichold, Oliver
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- First asymmetric photochemistry with nucleosides and DNA: Enantiodifferentiating Z-E photoisomerization of cyclooctene
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Thymidine and uridine, as well as calf thymus DNA (ctDNA), have been shown for the first time to function as chiral photosensitizers in aqueous solution, to effect the enantiodifferentiating photoisomerization of (Z)-cyclooctene, giving the chiral (E)-isomer in enantiomeric excesses of up to 15%.
- Wada, Takehiko,Sugahara, Norimitsu,Kawano, Mahito,Inoue, Yoshihisa
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- Entropy-controlled supramolecular photochirogenesis: Enantiodifferentiating Z-E photoisomerization of cyclooctene included and sensitized by permethylated 6-0-modified β-cyclodextrins
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Permethylated 6-O-modified β-cyclodextrins 2a-2d were synthesized as novel photosensitizing hosts with a flexible skeleton. Circular dichroism (CD) and 2D NMR spectral examinations of benzoate 2a revealed that the benzoate moiety is deeply included into its own cavity in aqueous solution. Upon addition of (Z)-cyclooctene (1Z) to a 50% aqueous methanol solution of 2a at 25 °C, the benzoate moiety of 2a was gradually excluded from the cavity as indicated by the CD spectral changes; the Job's plot revealed the formation of a 1:1 complex of 2a with 1Z. The binding constants for the complexation of 1Z by 2a were determined by CD spectral titration in 50% aqueous methanol at various temperatures. The van't Hoff analysis of the obtained data afforded the thermodynamic parameters (ΔH° = -3.1 kJ mol-1, ΔS° = 48.5 J mol-1 K-1), demonstrating the entropy-driven complexation by the permethylated cyclodextrin. This is in sharp contrast to the complexation of 1Z by nonmethylated β-cyclodextrin benzoate that is driven by enthalpy (ΔH° = -31.8 kJ mol-1 and ΔS° = -51.1 J mol-1 K-1). Upon supramolecular photosensitization with 2a-2d, 1Z isomerized to the (E)-isomer (1E) in moderate enantiomeric excesses (ee's), which however displayed significant temperature dependence with accompanying switching of the product's chirality in an extreme case. Such dynamic behavior of ee is very different from that reported for the photosensitization with nonmethylated cyclodextrin benzoate, where the product's ee is controlled by host occupancy. Eyring treatment of the ee obtained at various temperatures (-1 mol -1. The origin of the contrasting behavior of permethylated versus nonmethylated cyclodextrin hosts is inferred to be the conformational flexibility of the former host, which enables the entropy-driven guest complexation in the ground state and the entropy-controlled enantiodifferentiation in the excited state.
- Fukuhara, Gaku,Mori, Tadashi,Wada, Takehiko,Inoue, Yoshihisa
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- Dinuclear iridium and rhodium complexes with bridging arylimidazolide-N3,C2 ligands: Synthetic, structural, reactivity, electrochemical and spectroscopic studies
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Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n-butyl lithium afforded the corresponding derivatives (1-aryl-1H-imidazol-2-yl)lithium (1a, Ar = Mes; 1b, Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of [Ir(cod)(μ-Cl)]2 yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex [Ir(cod){μ-C3H2N2(Mes)-κC2,κN3}]2 (3), 3H-H, a head-to-head (H-H) isomer of CS symmetry, and 3H-T, the thermodynamically preferred head-to-tail (H-T) isomer of C2 symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3H-H and 3H-T afforded the tetracarbonyl complexes [Ir(CO)2{μ-C3H2N2(Mes)-κC2,κN3}]24H-H and 4H-T, respectively. The reaction with PMe3, which gave only one complex, [Ir(CO)(PMe3){μ-C3H2N2(Mes)-κC2,κN3}]2 (5), demonstrates that the isomerization of the central core Ir[μ-C3H2N2(Mes)-κC2,κN3]2Ir from H-H to H-T on going from 4H-H to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal-metal bonded d7-d7 complex [Ir2(CO)2(PMe3)2(Me)I{μ-C3H2N2(Mes)-κC2,κN3}2] (6). The blue [Ir(C2H4)2{μ-C3H2N2(Mes)-κC2,κN3}]2 (7) and purple [Rh(C2H4)2{μ-C3H2N2(Dipp)-κC2,κN3}]2 (9) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3H-T, 4H-T and 5, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3H-T undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(i)/Ir(ii) system. The energy of the intervalence band for the orange dirhodium complex [Rh(cod){μ-C3H2N2(Mes)-κC2,κN3}]2 (8) is shifted toward lower energies in comparison with 3H-T, reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(i)/Ir(ii) and Rh(i)/Rh(ii) systems. The molecular structures of 3H-H, 3H-T, 8 and 9 have been determined by X-ray diffraction.
- He, Fan,Ruhlmann, Laurent,Gisselbrecht, Jean-Paul,Choua, Sylvie,Orio, Maylis,Wesolek, Marcel,Danopoulos, Andreas A.,Braunstein, Pierre
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- A binuclear alkenyl-bridged zirconium complex catalyzes the chemoselective hydrogenation of 1,3-cyclooctadiene to cyclooctene
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The oligomeric hydrido zirconium complex 2Zr(H)(CH2PPh2)>n (1) reacts with (η4-butadiene)zirconocene to yield the (μ-1-η1 : 1,2-η2-butenyl), (μ-phosphinomethylene) doubly bridged binuclear zirconocene complex 2Zr(μ-CH=CHC2H5)(μ-CH2PPh2)ZrCp2> 2.Complex 1 reacts with butadiene to give 2 and Ph2PCH3.At 80 deg C complex 2 catalyzes the chemoselective hydrogenation of 1,3-cyclooctadiene to cyclooctene.Formation of a binuclear μ-alkenyl zirconium(IV)/zirconium(II) intermediate, similar to 2, is proposed to explain the effective protection of the remaining C=C double bond in the catalytic cycle.
- Raoult, Yveline,Choukroun, Robert,Gervais, Daniele,Erker, Gerhard
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- Efficient and Selective Catalytic Dehydrogenation of Alkanes using Rhodium(I) Arsine Complexes
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Arsine complexes of rhodium(I) efficiently catalyze the transfer dehydrogenation of alkanes under an atmosphere of hydrogen, while at the same time producing decreased levels of 'direct hydrogenated' sacrificial olefin relative to that derived from similar phosphine-based catalysts.
- Miller, Joseph A.,Knox, Linda K.
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- Catalytic Activity and Structural Analysis of Polymer-Protected Au-Pd Bimetallic Clusters Prepared by the Simultaneous Reduction of HAuCl4 and PdCl2
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The colloidal dispersions of the poly(N-vinyl-2-pyrrolidone)-protected gold/palladium bimetallic clusters were prepared by simultaneous reduction of HAuCl4 and PdCl2 in the presence of poly(N-vinyl-2-pyrrolidone).The bimetallic clusters were relatively uniform in size (e.g., 1.6 nm in average diameter) and were used as a catalyst for the selective partial hydrogenation of 1,3-cyclooctadiene at 30 deg C under 1 atm of hydrogen.The initial rate of the hydrogenation depended on the metal composition of the cluster catalyst, and the maximum catalytic activities were achieved at Au/Pd = 1/4.The catalytic activities of the mixtures of the monometallic Au and Pd clusters were higher than those expected for the two kinds of the monometallic clusters without reciprocal actions.The structures of the bimetallic clusters were studied using extended X-ray absorption fine structure (EXAFS).The structural parameters were determined by fitting the experimental data for the two absorption edges simultaneously using improved computer program.As a consequence of this improvement, the coordination numbers of Au atoms around the Pd atom and of Pd atoms around the Au atom could be determined with greater confidence.The EXAFS data of the Au/Pd(1/4 amd 1/1) bimetallic clusters prepared by simultaneous reduction indicate that the surface of the particle entirely consists of palladium atoms and the core of gold atoms (an Au core structure).
- Toshima, Naoki,Harada, Masafumi,Yamazaki, Yoshinao,Asakura, Kiyotaka
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- Singlet Photosensitization of Simple Alkenes. Part 1. cis-trans-Photoisomerization of Cyclo-octene sensitized by Aromatic Esters
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The use of aromatic carboxylic esters, e.g. methyl benzoate, as sensitizers gave an unusual cis-trans-photoisomerization of cyclo-octene, in which the trans : cis-ratio in the photostationary state was anomalously high, provided the usual triplet sensitization is operating (Table 1).From Stern-Volmer quenching studies and the consequent comparison of the decay ratios for three different sensitizers in two different solvents with those for direct or triplet-sensitized photoisomerizations (Table 4), it is concluded that the present photoisomerization takes place via a singlet mechanism which involves non-vertical singlet energy transfer from an excited aromatic ester to the cyclo-octene moiety in an exciplex resulting in 90 deg twisted cyclo-octene (1p), which in turn decays to ground state cis- or trans-cyclo-octene in the ratio of 0.56 : 0.44.The asymmetric cis-trans-photoisomerization induced by chiral aromatic esters also supports the involvement of an exciplex.
- Inoue, Yoshihisa,Takamuku, Setsuo,Kunitomi, Yoko,Sakurai, Hiroshi
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- Unusual Stereochemistry in the Thermal Deazetation of a Bicyclic Azo Compound
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Thermolysis of the stereospecifically deuteriated azo-compound (1D) led to bicyclo-octane (3) with complete retention and octadiene (4) with partial loss of stereochemistry.
- Samuel, Christopher J.
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- First asymmetric photosensitization in supercritical fluid. Exceptionally high pressure/density dependence of optical yield in photosensitized enantiodifferentiating isomerization of cyclooctene
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The photosensitized enantiodifferentiating isomerization of (Z)-cyclooctene (1Z) in supercritical carbon dioxide has been performed for the first time. The critical control of the enantiomeric excess (ee) of chiral product, (E)-cyclooctene (1E), and even the switching of the product's chirality were achieved through a small change of pressure particularly in the low-density region near the critical density. Quantitative evaluation of these ee changes was achieved by estimating differential activation volumes between the diastereomeric transition states of the reaction.
- Saito, Ryota,Kaneda, Masayuki,Wada, Takehiko,Katoh, Akira,Inoue, Yoshihisa
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- Facile β-trimethylstannyl promoted 1,5-hydride shifts in cyclooctyl and cyclodecyl systems
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Deuterium labelling and 2H NMR mapping demonstrate that cyclooctyl and cyclodecyl mesylates in aqueous EtOH exhibit greatly enhanced or exclusive levels of 1,5-hydride shift, provided a Me3Sn group is β to the migrating hydrogen, and after tin group loss from the formal β-stannyl cation, results in regiospecific, transannular alkene formation.
- Glenn, Matthew P.,Penman, Kerry G.,Kitching, William
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- Inter- and intramolecular thermal activation of aliphatic C-H bonds mediated by complexes containing the fragments [{Cy2P(CH2)nPCy2}M] (n = 1-4, M = Rh, Ru)
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A well defined geometrical structure and a well established catalytic potential for a plethora of processes puts the chelate rings [{R2P(CH2)nPR2)M] (M = Rh, Ru) among the most interesting candidates for catalytic alkane functionalization in homogeneous solution. It is demonstrated that intermolecular thermal C-H activation (3 → 4) is possible with readily accessible complexes [{Cy2P(CH2)nPCy2}Rh(hfacac)] (n = 1-4, 1a-c) and [{Cy2P(CH2)nPCy2)Ru(η 3-C4H7)2] (n = 1-3, 2a-c) containing such fragments. A maximum of 5 catalytic cycles was achieved with complex 2a. In case of Ru complexes containing the same ligands with n = 3 and 4, intramolecular cleavage of three adjacent C- H bonds in one of the cyclohexyl substituents at phosphorus also occurs readily leading to formation of a new polydentate κ2P,P′,η3-allyl ligand. VCH Verlagsgcsellschaft mbH,.
- Leitner, Walter,Six, Christian
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- Model Pumices Supported Metal Catalysts: II. Liquid Phase Selective Hydrogenation of 1,3-Cyclooctadiene
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The catalyzed, selective hydrogenation, in liquid phase, of 1,3-cyclooctadiene was studied on a series of Pd catalysts supported on natural pumice, model pumices (with variable content of alkali metal ions), silica, and sodium-doped silica. At constant pressure of H2 (1 atm.) the reaction follows a zero-order kinetic for all the Pd catalysts. At low metal dispersion (Dx x, the binding energy shift of Pd 3d level is negative in Pd/pumice and positive in Pd/silica with respect to unsupported Pd metal. The different performances of the Pd/pumice catalysts are explained by the presence of alkali metal ions in the framework of the support. Addition of sodium ions to Pd/silica catalysts produces a negative shift of the binding energy, but the activity is not improved because the number of active sites diminished due to decoration of palladium particles by sodium ions. The Pd catalysts with alkali metal ions in the support are resistant to air oxidation. In Pd catalysts containing alkali metal ions the selectivity to cyclooctene is practically 100% and the constant rates ratio k1/k2 is more than 1000 with a maximum at dispersion 35-40%, whereas the selectivity in Pd catalysts without alkali metal ions decreases continuously at increasing dispersion.
- Liotta, Leonarda F.,Venezia, Anna Maria,Martorana, Antonino,Deganello, Giulio
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- Thermal Dehydrogenation of Cyclooctane by Supported Noble Metal Catalysts
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Under boiling and refluxing conditions, cyclooctane has been dehydrogenated to cyclooctene and molecular hydrogen selectively with carbon- and alumina-supported Pd, Rh, and Ru catalysts.The activity order among these metal catalysts was Pd>Rh>Ru.The most
- Fujii, Takahiro,Yukawa, Kiyoshi,Saito, Yasukazu
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- A photochemical synthesis of functionalized trans-cyclooctenes driven by metal complexation
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Described is a scalable procedure for driving photochemical sytheses of trans-cyclooctene derivatives through metal complexation. During photoirradiation, reaction mixtures are continuously pumped through a column of a AgNO3-impregnated silica gel. The trans-cyclooctene derivative is selectively retained by the AgNO3-impregnated silica, but the cis-isomer elutes from the column back to the reaction flask, where it is photoisomerized and recirculated through the column. The method provides access to a range of usefully functionalized derivatives of trans-cyclooctene, including a derivative of 5-aza-trans-cyclooctene that underwent transannular cyclization upon treatment with bromine. The alkene stereochemistry is transferred with high fidelity to the hexahydropyrrolizine framework in the transannular cyclization. Copyright
- Royzen, Maksim,Yap, Glenn P. A.,Fox, Joseph M.
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- A Readily Synthesized and Highly Active Epoxide Carbonylation Catalyst Based on a Chromium Porphyrin Framework: Expanding the Range of Available β-Lactones
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(Martix presented) Catalytic carbonylation of epoxides to β-lactones was effected by a highly active and selective bimetallic catalyst comprised of a chromium(III) porphyrin cation and a cobalt tetracarbonyl anion. The complex is readily synthesized from commercially available compounds in high yield. Carbonylation of numerous linear epoxides, as well as bicyclic epoxides derived from 8- and 12-membered hydrocarbons, proceeded with high activity, selectivity, and yield.
- Schmidt, Joseph A. R.,Mahadevan, Viswanath,Getzler, Yutan D. Y. L.,Coates, Geoffrey W.
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- Thermocatalytic Formation of Molecular Hydrogen and Cyclo-octene from Cyclo-octane by Rhodium Complexes
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Dehydrogenation of cyclo-octane, yielding cyclo-octene and molecular hydrogen, proceeds catalytically with the Wilkinson complex RhClL3 or with its dimeric homologue without photo-irradiation under reflux conditions.
- Fujii, Takahiro,Saito, Yasukazu
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- First absolute asymmetric synthesis with circularly polarized synchrotron radiation in the vacuum ultraviolet region: Direct photoderacemization of (E)-cyclooctene
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A newly developed polarizing undulator installed in a storage ring was employed for the first time as a source of circularly polarized synchrotron radiation in the vacuum ultraviolet to effect enantiodifferentiating direct photoisomerization of (E)-cyclooctene; the photolysis is taken as a terrestrial mimic or proof of extraterrestrial absolute asymmetric synthesis on interstellar grains by the polarized synchrotron radiation from fast electrons orbiting a neutron star, which is thought to be a distant origin of the homochirality in the biosphere.
- Inoue, Yoshihisa,Tsuneishi, Hiroshi,Hakushi, Tadao,Yagi, Kazutoshi,Awazu, Koichi,Onuki, Hideo
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- Variable-Temperature Fluorine-19 Nuclear Magnetic Resonance Spectra of Fluorocyclooctane
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Two conformational processes have been observed for fluorocyclooctane by variable-temperature, protondecoupled fluorine NMR.The observations are in good agreement with predictions by molecular mechanics of ring inversion and pseudorotation among nonequivalent boat-chairs.
- Weigert, F.J.,Middleton, W.J.
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- Synthesis of new ferrocenyl amine sulfide and selenide complexes of group 10 metals and their catalytic activites toward selective hydrogenation, isomerisation, and asymmetric Grignard cross-coupling reactions
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Two series of previously unknown ferrocenyl amine sulfide and selenide ligands (S,R)-C5H4FeC5H3 and C5H4FeC5H3, where E = S and Se; R = Me, Ph, Bz, 4-tolyl, and 4-ClPh, have been prepared.Lithation of (S)-ferrocene and ferrocene first in the presence of ether and then TMEDA followed by treatment with different diselenides and disulfides resulted in the synthesis of these new ligands.Palladium and platinum dichloride adducts of these compounds have been prepared from a benzene solution of (PhCN)2MCl2 where M = Pd and Pt.The palladium complexes are active catalysts for selective hydrogenation of dienes to monoenes both under homogeneous and heterogeneous conditions.In the case of hydrogenation of 2,3-dimethyl-1,3-butadiene, isomerization has been observed.Nickel complexes of the new sulfide ligands were prepared in situ and used as catalysts for the asymmetric Grignard cross-coupling reactions.The possible structures of Pd and Pt complexes are discussed.The X-ray crystal structure was determined for C5H4FeC5H3; it reveals that the Pd atom is coordinated to the S and N atoms of the same cyclopentadienyl ring.
- Naiini, Ahmad A.,Lai, Chung-Kung,Ward, Donald L.,Brubaker, Carl H.
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- Allylic C-H deprotonation of olefins with PtII(OH) to form η3-allyl PtII complexes in water and aprotic organic solvents
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Hydroxo olefin platinum(II) complex (dpms)PtII(OH)(olefin) (olefin = cis-cyclooctene) reacts in water, in methanol, and, much faster, in aprotic solvents, DMF, acetone, or CH2Cl2 at 20 °C to produce the corresponding η3-allylic complex. Allylic C-H bond deprotonation in (dpms)PtII(OH)(cis-cyclooctene) is reversible, leading to the selective H/D exchange of the olefin in D2O solutions. Attempted olefin-for-olefin ligand exchange in (dpms)PtII(OH)(C 2H4) with olefin = cycloheptene or cyclopentene aimed at the preparation of other (dpms)PtII(OH)(olefin) complexes in water-organic solvent mixtures leads to corresponding η3-allylic derivatives via the intermediacy of (dpms)PtII(OH)(olefin) species. Consistent with mechanistic tests and results of DFT calculations, the Pt II(OH) group is responsible for deprotonation of the allylic C-H bond of the coordinated olefin.
- Khusnutdinova, Julia R.,Zavalij, Peter Y.,Vedernikov, Andrei N.
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- Synthesis of thiiranes by rhodium-catalyzed sulfur addition reaction to reactive alkenes
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A rhodium complex derived from RhH(PPh3)4, dppe, and 4-ethynyltoluene catalyzes the addition reaction of sulfur to norbornenes giving the corresponding thiiranes under acetone reflux conditions. The rhodium complex effectively transfers a sulfur atom to the double bond from sulfur, and exo-adducts are obtained. The reaction is also applicable to (E)-cyclooctene and cyclic allenes. The ring-opening reaction of the thiiranes with lithium aluminium hydride gives the corresponding thiols. This journal is
- Arisawa, Mieko,Ichikawa, Takuya,Yamaguchi, Masahiko
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- Diverse Mechanistic Pathways in Single-Site Heterogeneous Catalysis: Alcohol Conversions Mediated by a High-Valent Carbon-Supported Molybdenum-Dioxo Catalyst
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With the increase in the importance of renewable resources, chemical research is shifting focus toward substituting petrochemicals with biomass-derived analogues and platform-molecule transformations such as alcohol processing. To these ends, in-depth mechanistic understanding is key to the rational design of catalytic systems with enhanced activity and selectivity. Here we discuss in detail the structure and reactivity of a single-site active carbon-supported molybdenum-dioxo catalyst (AC/MoO2) and the mechanism(s) by which it mediates alcohol dehydration. A range of tertiary, secondary, and primary alcohols as well as selected bio-based terpineols are investigated as substrates under mild reaction conditions. A combined experimental substituent effect/kinetic/kinetic isotope effect/EXAFS/DFT computational analysis indicates that (1) water assistance is a key element in the transition state; (2) the experimental kinetic isotopic effect and activation enthalpy are 2.5 and 24.4 kcal/mol, respectively, in good agreement with the DFT results; and (3) several computationally identified intermediates including Mo-oxo-hydroxy-alkoxide and cage-structured long-range water-coordinated Mo-dioxo species are supported by EXAFS. This structurally and mechanistically well-characterized single-site system not only effects efficient transformations but also provides insight into rational catalyst design for future biomass processes.
- Bedzyk, Michael J.,Das, Anusheela,Kratish, Yosi,Li, Jiaqi,Ma, Qing,Marks, Tobin J.
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p. 1247 - 1257
(2022/02/07)
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- Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis
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The value of catalytic dehydrogenation of aliphatics (CDA) in organic synthesis has remained largely underexplored. Known homogeneous CDA systems often require the use of sacrificial hydrogen acceptors (or oxidants), precious metal catalysts, and harsh reaction conditions, thus limiting most existing methods to dehydrogenation of non- or low-functionalized alkanes. Here we describe a visible-light-driven, dual-catalyst system consisting of inexpensive organophotoredox and base-metal catalysts for room-temperature, acceptorless-CDA (Al-CDA). Initiated by photoexited 2-chloroanthraquinone, the process involves H atom transfer (HAT) of aliphatics to form alkyl radicals, which then react with cobaloxime to produce olefins and H2. This operationally simple method enables direct dehydrogenation of readily available chemical feedstocks to diversely functionalized olefins. For example, we demonstrate, for the first time, the oxidant-free desaturation of thioethers and amides to alkenyl sulfides and enamides, respectively. Moreover, the system's exceptional site selectivity and functional group tolerance are illustrated by late-stage dehydrogenation and synthesis of 14 biologically relevant molecules and pharmaceutical ingredients. Mechanistic studies have revealed a dual HAT process and provided insights into the origin of reactivity and site selectivity.
- Zhou, Min-Jie,Zhang, Lei,Liu, Guixia,Xu, Chen,Huang, Zheng
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supporting information
p. 16470 - 16485
(2021/10/20)
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- Selective C-O Bond Reduction and Borylation of Aryl Ethers Catalyzed by a Rhodium-Aluminum Heterobimetallic Complex
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We report the catalytic reduction of a C-O bond and the borylation by a rhodium complex bearing an X-Type PAlP pincer ligand. We have revealed the reaction mechanism based on the characterization of the reaction intermediate and deuterium-labeling experiments. Notably, this novel catalytic system shows steric-hindrance-dependent chemoselectivity that is distinct from conventional Ni-based catalysts and suggests a new strategy for selective C-O bond activation by heterobimetallic catalysis.
- Hara, Naofumi,Nakao, Yoshiaki,Saito, Teruhiko,Seki, Rin
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p. 6388 - 6394
(2021/05/31)
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- Catalytic Dehydrogenation of Alkanes by PCP-Pincer Iridium Complexes Using Proton and Electron Acceptors
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Dehydrogenation to give olefins offers the most broadly applicable route to the chemical transformation of alkanes. Transition-metal-based catalysts can selectively dehydrogenate alkanes using either olefinic sacrificial acceptors or a purge mechanism to remove H2; both of these approaches have significant practical limitations. Here, we report the use of pincer-ligated iridium complexes to achieve alkane dehydrogenation by proton-coupled electron transfer, using pairs of oxidants and bases as proton and electron acceptors. Up to 97% yield was achieved with respect to oxidant and base, and up to 15 catalytic turnovers with respect to iridium, using t-butoxide as base coupled with various oxidants, including oxidants with very low reduction potentials. Mechanistic studies indicate that (pincer)IrH2 complexes react with oxidants and base to give the corresponding cationic (pincer)IrH+ complex, which is subsequently deprotonated by a second equivalent of base; this affords (pincer)Ir which is known to dehydrogenate alkanes and thereby regenerates (pincer)IrH2.
- Shada, Arun Dixith Reddy,Miller, Alexander J. M.,Emge, Thomas J.,Goldman, Alan S.
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p. 3009 - 3016
(2021/03/09)
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- Ruthenium-Catalyzed Dehydrogenation Through an Intermolecular Hydrogen Atom Transfer Mechanism
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The direct dehydrogenation of alkanes is among the most efficient ways to access valuable alkene products. Although several catalysts have been designed to promote this transformation, they have unfortunately found limited applications in fine chemical synthesis. Here, we report a conceptually novel strategy for the catalytic, intermolecular dehydrogenation of alkanes using a ruthenium catalyst. The combination of a redox-active ligand and a sterically hindered aryl radical intermediate has unleashed this novel strategy. Importantly, mechanistic investigations have been performed to provide a conceptual framework for the further development of this new catalytic dehydrogenation system.
- Huang, Lin,Bismuto, Alessandro,Rath, Simon A.,Trapp, Nils,Morandi, Bill
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supporting information
p. 7290 - 7296
(2021/03/01)
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- Organometallic iridium complexes of (Z)-1-Phenyl-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ate: Structural aspects, reactivity and applications in the catalytic dehydrogenation of Alkanes#
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The treatment of [IrCl(cod)]2 with (Z)-1-phenyl-2-(4′,4′- dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ol (HL) in the presence of base yields the first Ir complex of this ligand class: Ir(κ2- N,O-L)(cod) (3). Complex 3 is reactive with MeI or HSnPh3 to yield the oxidative addition products 4 (trans-Ir(Me)I(κ2-N,OL)( cod)) and 5 (cis-IrH(SnPh3)(κ2-N,O-L)(cod)), respectively. All three of these derivatives have been fully characterised including via single crystal X-ray diffraction data. Complex 3 is generally resistant to cod ligand substitution but shown to be reactive with CO (g) to give Ir(κ2-N,O-L)(CO)2 (6). In addition, 3 is demonstrated to be a dehydrogenation catalyst for the conversion of C8H16 into cyclooctene and H2 under acceptorfree conditions.
- Clément, Roxanne,Gossage, Robert A.,Lough, Alan J.,May, Kathleen L.
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supporting information
p. 2042 - 2047
(2021/09/16)
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- Cobalt Complexes of Bulky PNP Ligand: H2Activation and Catalytic Two-Electron Reactivity in Hydrogenation of Alkenes and Alkynes
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The reactivity of cobalt pincer complexes supported by the bulky tetramethylated PNP ligands Me4PNPR(R = iPr, tBu) has been investigated. In these ligands, the undesired H atom loss reactivity observed earlier in some classical CH2-arm PNP cobalt complexes is blocked, allowing them to be utilized for promoting two-electron catalytic transformations at the cobalt center. Accordingly, reaction of the formally CoIMe complex 3 with H2 under ambient pressure and temperature afforded the CoIII trihydride 4-H, in a reaction cascade reasoned to proceed by two-electron oxidative addition and reductive eliminations. This mechanistic proposal, alongside the observance of alkene insertion and ethane production upon sequential exposure of 3 to ethylene and H2, prompted an exploration into 3 as a catalyst for hydrogenation. Complex 4-H, formed in situ from 3 under H2, was found to be active in the catalytic hydrogenation of alkenes and alkynes. The proposed two-electron mechanism is reminiscent of the platinum group metals and demonstrates the utility of the bulky redox-innocent Me4PNPR ligand in the avoidance of one-electron reactivity, a concept that may show broad applicability in expanding the scope of earth-abundant first-row transition-metal catalysis.
- Fayzullin, Robert R.,Gallagher, James M.,Khaskin, Eugene,Khusnutdinova, Julia R.,Lapointe, Sébastien,Osborne, James,Pandey, Dilip K.
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supporting information
p. 3617 - 3626
(2021/11/16)
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- η2-Alkene Complexes of [Rh(PONOP-iPr)(L)]+Cations (L = COD, NBD, Ethene). Intramolecular Alkene-Assisted Hydrogenation and Dihydrogen Complex [Rh(PONOP-iPr)(η-H2)]+
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Rhodium-alkene complexes of the pincer ligand κ3-C5H3N-2,6-(OPiPr2)2 (PONOP-iPr) have been prepared and structurally characterized: [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; ArF = 3,5-(CF3)2C6H3]. Only one of these, alkene = COD, undergoes a reaction with H2 (1 bar), to form [Rh(PONOP-iPr)(η2-COE)][BArF4] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η2-bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP-iPr)(η2-H2)][BArF4], which has been independently synthesized and undergoes exchange with free H2 on the NMR time scale, as well as with D2 to form free HD. When the H2 addition to [Rh(PONOP-iPr)(η2-ethene)][BArF4] is interrogated using pH2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1H NMR signal for the bound H2 ligand, as well as that for free H2, are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted.
- Johnson, Alice,Royle, Cameron G.,Brodie, Claire N.,Martínez-Martínez, Antonio J.,Duckett, Simon B.,Weller, Andrew S.
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supporting information
p. 13903 - 13912
(2021/03/01)
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- Understanding the Activation of Air-Stable Ir(COD)(Phen)Cl Precatalyst for C-H Borylation of Aromatics and Heteroaromatics
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A newly developed robust catalyst [Ir(COD)(Phen)Cl] (A) was used for the C-H borylation of three dozen aromatics and heteroaromatics with excellent yield and selectivity. Activation of the catalyst was identified by the use of catalytic amounts of water, alcohols, etc., when B2pin2 was used in noncoordinating solvents, while for THF catalytic use of HBpin was required. The results were on par with the in situ based expensive system [Ir(OMe)(COD)]2/dtbbpy or Me4Phen.
- Slack, Eric D.,Colacot, Thomas J.
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supporting information
p. 1561 - 1565
(2021/02/20)
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- Nickel-catalyzed deoxygenation of oxiranes: Conversion of epoxides to alkenes
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Deoxygenation of epoxides takes place under the catalysis of nickel in the presence of diethylzinc as a deoxygenation agent to yield alkenes. Epoxides with a wide variety of substitution patterns are deoxygenated in this catalytic system to give terminal, 1,1-disubstituted, 1,2-disubstituted, trisubstituted, and tetrasubstituted alkenes in high yields. Reactions of 1,2-disubstituted epoxides we examined proceeded in an E-stereoselective manner. High compatibility with other functional groups through this transformation was also observed.
- Mori, Takamichi,Takeuchi, Yoshihito,Hojo, Makoto
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supporting information
(2020/01/24)
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- NCP-Type Pincer Iridium Complexes Catalyzed Transfer-Dehydrogenation of Alkanes and Heterocycles?
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A series of NCP-type pincer iridium complexes, (RNCCP)IrHCl (2a—2c) and (BQ-NCOP)IrHCl 3, have been studied for catalytic transfer alkane dehydrogenation. Complex 3 containing a rigid benzoquinoline backbone exhibits high activity and robustness in dehydrogenation of alkanes to form alkenes. Even more importantly, this catalyst system was also highly effective in the dehydrogenation of a wide range of heterocycles to furnish heteroarenes.
- Wang, Yulei,Qian, Lu,Huang, Zhidao,Liu, Guixia,Huang, Zheng
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supporting information
p. 837 - 841
(2020/05/18)
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- Amido PNP complexes of iridium: Synthesis and catalytic olefin and alkyne hydrogenation
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In situ lithiation of HN(o-C6H4PPh2)2 (H[1a]) or HN(o-C6H4PiPr2)2 (H[1b]) with nBuLi in THF at ?35°C followed by addition of [Ir(μ-Cl)(COD)]2 (COD = 1,5-cyclooctadiene) in toluene at ?35°C generates 5-coordinate [1a]Ir(η4-COD) (2a) or 4-coordinate [1b]Ir(η2-COD) (2b), respectively. Oxidative addition of N-H in H[1b] to [Ir(μ-Cl)(COD)]2 affords square pyramidal [1b]Ir(H)(Cl) (3b). Metathetical reaction of 3b with LiBHEt3 in the presence of 1 atm of H2 in toluene produces [1b]Ir(H)2 (4b). Both 2a and 4b are active for catalytic hydrogenation of olefins and alkynes under extremely mild conditions.
- Huang, Mei-Hui,Zou, Xue-Ru,Liang, Lan-Chang
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p. 353 - 360
(2019/12/24)
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- Hydrogenation of Alkenes Catalyzed by a Non-pincer Mn Complex
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Hydrogenation of substituted styrenes and unactivated aliphatic alkenes by molecular hydrogen has been achieved using a Mn catalyst with a non-pincer, picolylphosphine ligand. This is the second reported example of alkene hydrogenation catalyzed by a Mn complex. Mechanistic studies showed that a Mn hydride formed by H2 activation in the presence of a base is the catalytically active species. Based on experimental and DFT studies, H2 splitting is proposed to occur via a metal-ligand cooperative pathway involving deprotonation of the CH2 arm of the ligand, leading to pyridine dearomatization.
- Rahaman, S. M. Wahidur,Pandey, Dilip K.,Rivada-Wheelaghan, Orestes,Dubey, Abhishek,Fayzullin, Robert R.,Khusnutdinova, Julia R.
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p. 5912 - 5918
(2020/10/30)
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- Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions
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The development of selective olefin metathesis catalysts is crucial to achieving new synthetic pathways. Herein, we show that cis-diiodo/sulfur-chelated ruthenium benzylidenes do not react with strained cycloalkenes and internal olefins, but can effectively catalyze metathesis reactions of terminal dienes. Surprisingly, internal olefins may partake in olefin metathesis reactions once the ruthenium methylidene intermediate has been generated. This unexpected behavior allows the facile formation of strained cis-cyclooctene by the RCM reaction of 1,9-undecadiene. Moreover, cis-1,4-polybutadiene may be transformed into small cyclic molecules, including its smallest precursor, 1,5-cyclooctadiene, by the use of this novel sequence. Norbornenes, including the reactive dicyclopentadiene (DCPD), remain unscathed even in the presence of terminal olefin substrates as they are too bulky to approach the diiodo ruthenium methylidene. The experimental results are accompanied by thorough DFT calculations.
- Ivry, Elisa,Lemcoff, N. Gabriel,Nechmad, Noy B.,Phatake, Ravindra,Poater, Albert
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p. 3539 - 3543
(2020/02/04)
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- Synthesis of a hybrid Pd0/Pd-carbide/carbon catalyst material with high selectivity for hydrogenation reactions
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We present a highly selective and active Pd carbon catalyst prepared by an easy hydrothermal synthesis method. This synthetic procedure allows the stabilization under mild conditions of interstitial carbon atoms on the surface of a Pd0 carbon catalyst. The so formed Pd carbide phase appears on the upper surface layers of the Pd carbon catalyst, as demonstrated by X-ray photoelectron depth profile analysis using variable synchrotron X-ray energies. The presence of carbon in the palladium carbide species modifies the electronic state of surface Pd atoms, resulting in more electron positive Pd species (Pdδ+). This influences the adsorption of reactants and reaction intermediates during the hydrogenation of alkynes, dienes and imines, resulting in high selectivities at practically 100percent conversion.
- Climent, Maria José,Concepción, Patricia,Cored, Jorge,Corma, Avelino,Garcia-Ortiz, Andrea,Iborra, Sara,Pérez-Dieste, Virginia,Ruano, Daniel,Vidal, Juan Diego
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p. 706 - 713
(2020/08/05)
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- Catalytic Activity of a Zr MOF Containing POCOP-Pd Pincer Complexes
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A metal-organic framework assembled from POCOP-Pd pincer complex metallolinkers (1-PdBF4, Zr6O4(OH)4(L-PdMeCN)3(BF4)3, L = (2,6-(OPAr2)2C6H3, Ar = p-C6H4CO2-) has been generated via postsynthetic oxidative I-/BF4- ligand exchange with NOBF4. 1-PdBF4 catalyzes a range of organic transformations, including transfer hydrogenation of unsaturated organic substrates, terminal alkyne hydration, and intramolecular hydroarylation of alkynes. The homogeneous analogue, tBu4POCOP-PdBF4, shows poor catalytic activity for transfer hydrogenation and alkyne hydration and decomposes under the catalytic reaction conditions. Solubility limitations and catalyst deactivation pathways observed for the homogeneous pincer complex propound the advantages of using porous solid supports to immobilize organometallic species.
- Kassie, Abebu A.,Wade, Casey R.
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p. 2214 - 2221
(2020/07/06)
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- A Cp-based Molybdenum Catalyst for the Deoxydehydration of Biomass-derived Diols
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Dioxo-molybdenum complexes have been reported as catalysts for the deoxydehydration (DODH) of diols and polyols. Here, we report on the DODH of diols using [Cp*MoO2]2O as catalyst (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of [Cp*MoO2]2O, 1.1 equiv. of PPh3 as reductant, and anisole as solvent. Aliphatic vicinal diols are converted to the corresponding olefins by [Cp*MoO2]2O in up to 65 % yield (representing over 30 turnovers per catalyst) and 91 % olefin selectivity, which rivals the performance of other Mo-based DODH catalysts. Remarkably, cis-1,2-cyclohexanediol, which is known as quite a challenging substrate for DODH catalysis, is converted to 30 % of 1-cyclohexene under optimized reaction conditions. Overall, the mass balances (up to 79 %) and TONs per Mo achievable with [Cp*MoO2]2O are amongst the highest reported for molecular Mo-based DODH catalysts. A number of experiments aimed at providing insight in the reaction mechanism of [Cp*MoO2]2O have led to the proposal of a catalytic pathway in which the [Cp*MoO2]2O catalyst reacts with the diol substrate to form a putative nonsymmetric dimeric diolate species, which is reduced in the next step at only one of its Mo-centers before extrusion of the olefin product.
- Li, Jing,Lutz, Martin,Klein Gebbink, Robertus J. M.
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p. 6356 - 6365
(2020/11/30)
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- Colloid and Nanosized Catalysts in Organic Synthesis: XXII. Hydrogenation of Cycloolefins Catalyzed by Immobilized Transition Metals Nanoparticles in a Three-Phase System
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The processes of unsaturated cyclic hydrocarbons hydrogenation in a three-phase gas-liquid-solid catalyst system in the presence of nanostructured nickel, cobalt, or iron catalysts in a flow reactor at 130°C and atmospheric pressure have studied. RX3Extra activated carbon, γ-Al2O3, NaX zeolite, and Purolite CT-175 cation-exchange resin have been used as supports; NaBH4 and NH2NH2·H2O were used as reducing agents. The catalytic activity of supported nanoparticles and their selectivity with respect to the product of exhaustive hydrogenation have been investigated.
- Nebykov,Popov, Yu. V.,Mokhov,Latyshova,Shcherbakova,Nemtseva,Shishkin
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p. 1985 - 1989
(2019/11/29)
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- Cobalt-Catalyzed Hydrogenations via Olefin Cobaltate and Hydride Intermediates
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Redox noninnocent ligands are a promising tool to moderate electron transfer processes within base-metal catalysts. This report introduces bis(imino)acenaphthene (BIAN) cobaltate complexes as hydrogenation catalysts. Sterically hindered trisubstituted alkenes, imines, and quinolines underwent clean hydrogenation under mild conditions (2-10 bar, 20-80 °C) by use of the stable catalyst precursor [(DippBIAN)CoBr2] and the cocatalyst LiEt3BH. Mechanistic studies support a homogeneous catalysis pathway involving alkene and hydrido cobaltates as active catalyst species. Furthermore, considerable reaction acceleration by alkali cations and Lewis acids was observed. The dinuclear hydridocobaltate anion with bridging hydride ligands was isolated and fully characterized.
- Sandl, Sebastian,Maier, Thomas M.,Van Leest, Nicolaas P.,Kr?ncke, Susanne,Chakraborty, Uttam,Demeshko, Serhiy,Koszinowski, Konrad,De Bruin, Bas,Meyer, Franc,Bodensteiner, Michael,Herrmann, Carmen,Wolf, Robert,Von Jacobi Wangelin, Axel
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p. 7596 - 7606
(2019/08/20)
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- A convenient method for the generation of {Rh(PNP)}+ and {Rh(PONOP)}+ fragments: Reversible formation of vinylidene derivatives
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The substitution reactions of [Rh(COD)2][BArF4] with PNP and PONOP pincer ligands 2,6-bis(di-tert-butylphosphinomethyl)pyridine and 2,6-bis(di-tert-butylphosphinito)pyridine in the weakly coordinating solvent 1,2-F2C6H4 are shown to be an operationally simple method for the generation of reactive formally 14 VE rhodium(i) adducts in solution. Application of this methodology enables synthesis of known adducts of CO, N2, H2, previously unknown water complexes, and novel vinylidene derivatives [Rh(pincer)(CCHR)][BArF4] (R = tBu, 3,5-tBu2C6H3), through reversible reactions with terminal alkynes.
- Gyton, Matthew R.,Hood, Thomas M.,Chaplin, Adrian B.
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supporting information
p. 2877 - 2880
(2019/03/06)
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- Oxidoperoxidomolybdenum(VI) complexes with acylpyrazolonate ligands: Synthesis, structure and catalytic properties
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Oxidoperoxido-molybdenum(vi) complexes containing acylpyrazolonate ligands were obtained by reaction of [Mo(O)(O)2(H2O)n] with the corresponding acylpyrazolone compounds HQR. Complexes Ph4P[Mo(O)(O2)2(QR)] (R = neopentyl, 1; perfluoroethyl, 2; hexyl, 3; phenyl, 4; naphthyl, 5; methyl, 6; cyclohexyl, 7; ethylcyclopentyl, 8) were obtained if the reaction was carried out with one equivalent of HQR in the presence of Ph4PCl. Alternatively, neutral complexes [Mo(O)(O2)(QR)2] (R = neopentyl, 9; hexyl, 10; cyclohexyl, 11) were formed when two equivalents of HQR were used in the reaction. These complexes were isolated in good yields as yellow or yellow-orange crystalline solids and were spectroscopically (IR, 1H, 13C{1H} and 31P{1H} NMR), theoretically (DFT) and structurally characterised (X-ray for 1, 2, 9 and 10). Compounds 1 and 9 were selected to investigate their catalytic behaviour in epoxidation of selected alkenes and oxidation of selected sulphides, while 10 and 11 were tested as catalyst precursors in the deoxygenation of selected epoxide substrates to alkenes, using PPh3 as the oxygen-acceptor. Complexes Ph4P[Mo(O)(O2)2(QR)] were shown to be poor catalyst precursors in oxidation reactions, while the activity of [Mo(O)(O2)(QR)2] species is good in all the studied reactions and comparable to related oxidoperoxido-molybdenum(vi) complexes. Complex [Mo(O)2(QC6)2], 12, was obtained by treatment of 10 with one equivalent of PPh3, demonstrating that the first step in the epoxide deoxygenation mechanism was the oxygen atom transfer toward the phosphane.
- Begines, Emilio,Carrasco, Carlos J.,Montilla, Francisco,álvarez, Eleuterio,Marchetti, Fabio,Pettinari, Riccardo,Pettinari, Claudio,Galindo, Agustín
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p. 197 - 208
(2017/12/27)
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- NCP ligand, [...] complex, synthesis method, intermediate and application
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The invention discloses an NCP ligand, iridium complex, synthetic method, intermediate and application thereof. The invention provides an NCP ligand and an NCP ligand iridium complex, wherein R1, R2, R3, R4, R5, R6 and R7 separately represent hydrogen atom or C1-C30 alkyl, R' and R'' independently represent C1-C30 alkyl. The invention provides the application of the NCP ligand iridium complex to the catalysis of alkane dehydrogenation reaction, olefin isomerization reaction, alcohol dehydrogenation reaction, ester alpha alkylation reaction, and amide alpha alkylation reaction. The NCP ligand provided by the invention contains dialkyl substituted phosphine, which has strong electron donating ability and can form a NCP ligand iridium complex by complexing with iridium. The NCP ligand iridium complex uses pyridine to replace a conventional alkyl phosphate electron donor, and has the advantages of good stability, high selectivity on alkane dehydrogenation reaction, mild reaction conditions, good catalytic effect, and industrial production prospect.
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Paragraph 0091; 0092; 0191-0193
(2018/07/30)
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- Synthesis and coordination chemistry of new asymmetric donor/acceptor pincer ligands, 1,3-C6H4(CH2PtBu(Rf))2 (Rf = CF3, C2F5)
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Syntheses of new asymmetric pincer precursors 1,3-C6H4{CH2P(tBu,X)}2 (tBu,XPCPH; X = Cl, SiMe3, OPh) and a new class of hybrid donor/acceptor pincer ligands 1,3-C6H4{CH2P(tBu,Rf)}2 (tBu,RfPCPH; Rf = CF3, C2F5) are reported. All tBu,XPCPH compounds are obtained as mixtures of meso and rac diastereomers in varying ratios (meso?:?rac ~ 4?:?1 to 3?:?2) which were used without separation. Treatment of Ru(cot)(cod) with tBu,CF3PCPH under 1 atm H2 in acetone at 20 °C produced the hydride solvate (tBu,CF3PCP)Ru(acetone)xH which was not isolated, but could be trapped as stable diene complexes (tBu,CF3PCP)Ru(L)2H (L2 = cod (1), nbd (2)). Catalytic cyclooctane dehydrogenation studies demonstrate that 2 has ~50% the activity of (CF3PCP)Ru(cod)(H), but significantly higher catalyst stability and is able to operate at higher catalyst loading concentrations without deactivation via bimolecular decomposition.
- Debnath, Suman,Venegas, Gabriel,Arulsamy, Navamoney,Roddick, Dean M.
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supporting information
p. 12420 - 12430
(2018/09/25)
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- Cavitands as Containers for α,ω-Dienes and Chaperones for Olefin Metathesis
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Described herein is the behavior of α,ω-dienes sequestered within cavitands in aqueous (D2O) solution. Hydrophobic forces drive the dienes into the cavitands in conformations that best fill the available space. Shorter dienes (C9 and C10) bind
- Wu, Nai-Wei,Petsalakis, Ioannis D.,Theodorakopoulos, Giannoula,Yu, Yang,Rebek, Julius
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supporting information
p. 15091 - 15095
(2018/10/31)
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- [(NHC)CoR2]: pre-catalysts for homogeneous olefin and alkyne hydrogenation
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A novel synthesis for dialkyl cobalt compounds [(tmeda)CoR2] is presented. In these complexes tmeda is readily replaced by an NHC or a bidentate phosphine ligand to form 3- and 4-coordinate compounds, respectively. [(ItBu)Co(CH2SiMe3)2] (ItBu = 1,3-di-tert-butylimidazolin-2-ylidene) serves as an efficient, homogeneous olefin hydrogenation pre-catalyst and allows the preparation of the novel cobalt bis(alkyne) complex [(ItBu)Co(η2-PhCCPh)2].
- Enachi, Andreea,Baabe, Dirk,Zaretzke, Marc-Kevin,Schweyen, Peter,Freytag, Matthias,Raeder, Jan,Walter, Marc D.
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supporting information
p. 13798 - 13801
(2018/12/14)
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- Efficient approach to medium-sized cyclic molecules containing (E)-Alkene via z to e photochemical isomerization in the presence of AgNO3-impregnated silica gel
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Efficient synthesis of medium-sized cyclic molecules containing an (E)-alkene was performed via the highly (E)selective photochemical isomerization of the (Z)-isomer, facilitated by AgNO3-impregnated silica gel.
- Machida, Kouhei,Yoshida, Yuki,Igawa, Kazunobu,Tomooka, Katsuhiko
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supporting information
p. 186 - 188
(2018/02/06)
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- Iridium catalysts for acceptorless dehydrogenation of alcohols to carboxylic acids: Scope and mechanism
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We introduce iridium-based conditions for the conversion of primary alcohols to potassium carboxylates (or carboxylic acids) in the presence of potassium hydroxide and either [Ir(2-PyCH2(C4H5N2))(COD)]OTf (1) or [Ir(2-PyCH2PBu2t)(COD)]OTf (2). The method provides both aliphatic and benzylic carboxylates in high yield and with outstanding functional group tolerance. We illustrate the application of this method to a diverse variety of primary alcohols, including those involving heterocycles and even free amines. Complex 2 reacts with alcohols to form the crystallographically characterized catalytic intermediates [IrH(η1,η3-C8H12)(2-PyCH2PtBu2)] (2a) and [Ir2H3(CO)(2-PyCH2PtBu2){μ-(C5H3N)CH2PtBu2}] (2c). The unexpected similarities in reactivities of 1 and 2 in this reaction, along with synthetic studies on several of our iridium intermediates, enable us to form a general proposal of the mechanisms of catalyst activation that govern the disparate reactivities of 1 and 2, respectively, in glycerol and formic acid dehydrogenation. Moreover, careful analysis of the organic intermediates in the oxidation sequence enable new insights into the role of Tishchenko and Cannizzaro reactions in the overall oxidation.
- Cherepakhin, Valeriy,Williams, Travis J.
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p. 3754 - 3763
(2018/05/23)
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- Colloid and Nanosized Catalysts in Organic Synthesis: XIX.1 Influence of the Support Nature on Hydrogenation Catalysis of Cyclic Olefins by Nickel Nanoparticles
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Gas-phase hydrogenation of cycloalkenes in the presence of nickel nanoparticles supported on Ceokar-2, BAU-A activated carbon, alumina, and NaX zeolite proceeds at 140–240°C and atmospheric pressure of hydrogen. The conversion and selectivity depend on the type of support and on the hydrogen excess.
- Popov, Yu. V.,Mokhov,Nebykov,Shcherbakova,Dontsova
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- Synthesis and application of pyrrole-based PNP-Ir complexes to catalytic transfer dehydrogenation of cyclooctane
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A series of tBu- and iPr-substituted PNP-pincer Ir and Rh complexes with pyrrole-based core were synthesized and characterized. The structures of the obtained complexes were varied depending on the size of alkyl substituents and ligands other than PNP ligand. All of them exhibit low activity toward transfer dehydrogenation of cyclooctane.
- Nakayama, Shin,Morisako, Shogo,Yamashita, Makoto
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p. 1304 - 1313
(2018/04/30)
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- Iridium PC(sp3)P Pincer complexes with hemilabile pendant arms: Synthesis, characterization, and catalytic activity
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A series of new PC(sp3)P pincer ligands possessing hemilabile alkoxyl side arms as well as their iridium complexes are reported. All new organometallic compounds were structurally characterized including X-ray analysis. The hemilability of the side arms was probed by reactions with CO, revealing the reversible coordination. The catalytic activity of the new complexes was tested by iridium-catalyzed transfer dehydrogenation of alkanes under mild conditions.
- De-Botton, Sophie,Cohen, Shirel,Gelman, Dmitri
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supporting information
p. 1324 - 1330
(2018/04/30)
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- Structural, electronic and catalytic properties of palladium nanoparticles supported on poly(ionic liquid)
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The structural, electronic and support effect on palladium nanoparticles (Pd NPs) prepared by sputtering deposition and chemical reduction of a Pd(II) precursor in/on a poly(ionic liquid) (PIL) was investigated in the selective hydrogenation of α,β-unsaturated carbonyl compounds and dienes. Sputtering deposition generates naked NPs with a narrow size distribution (3.2–3.8 nm) that are predominantly composed of Pd(0) (85–100%). Conversely, chemical reduction produces PIL-covered NPs with almost twice the average size (6.6 nm) and only 15% Pd(0). Regard the catalytic performance, support composition (by ionic liquid (IL) addition or not) and NP location are decisive. The best activity and selectivity was obtained with imprinted Pd NPs on a PIL/IL mixture (D-MPIL.NTf2/IL-Pd catalyst). A kinetic investigation was conducted using 2-cyclohexen-1-one (CHN) and D-MPIL.NTf2/IL-Pd catalyst revealing that this reaction follows the Langmuir-Hinshelwood mechanism. Enthalpies obtaining from a Van't Hoff plot show that the adsorption of the CHN substrate on the surface of the PIL-Pd catalyst is an exothermic process (-9 kJ mol?1), whereas H2 adsorption occurs by an endothermic process (12 kJ mol?1). This distinct behavior is consistent with the rate determining step proposed, in which the independent adsorption of reagents is followed by the hydrogenation of a π-allyl intermediate on the catalyst surface.
- Simon, Nathália M.,Abarca, Gabriel,Scholten, Jackson D.,Domingos, Josiel B.,Mecerreyes, David,Dupont, Jairton
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- Sodium borohydride-nickel chloride hexahydrate in EtOH/PEG-400 as an efficient and recyclable catalytic system for the reduction of alkenes
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An efficient, safe and one-pot convenient catalytic system has been developed for the reduction of alkenes using NaBH4-NiCl2·6H2O in EtOH/PEG-400 under mild conditions. In this catalytic system, a variety of alkenes (including trisubstituted alkene α-pinene) were well reduced and the Ni catalyst could be recycled.
- Li, Kaoxue,Liu, Chuanchao,Wang, Kang,Ren, Yang,Li, Fahui
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p. 7761 - 7764
(2018/03/01)
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- Synthesis, Characterization, and Catalytic Properties of Iridium Pincer Complexes Containing NH Linkers
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A series of tert-butyl-substituted pincer ligands based on 1,3-diaminobenzene and 3-aminophenol scaffolds, tBu4PXCYP (1e, X = Y = NH; 1f, X = NH; Y = O) and the corresponding iridium hydridochloro complexes (tBu4PXCYP)IrHCl (2e, X = Y = NH; 2f, X = NH; Y = O) were prepared with moderate yields and high purity and were fully characterized by 1H and 31P NMR spectroscopy. Unsymmetrical hybrid pincer ligands R2PNCOPtBu2 (1g, R = isopropyl; 1h, R = cyclohexyl) were prepared conveniently in high yield via a one-pot procedure by judiciously choosing reaction conditions and base; the corresponding iridium hydrido chloro complexes iPr2PNCOPtBu2IrHCl (2g) and Cy2PNCOPtBu2IrHCl (2h) were synthesized by the reaction of [IrCl(COE)2]2 with ligands. X-ray crystallography reveals that these iridium pincer complexes adopt similar square-pyramidal geometries and exhibit strong intermolecular hydrogen bonding between the NH linker and chloride ions of the adjacent iridium complex in the solid state. 1H NMR chemical shifts of tert-butyl based pincer ligated iridium hydrides move downfield when the electronegativity of the linker between the benzene backbone and phosphine moiety increases for 2a, 2e, 2f, and 2b. Accordingly the corresponding iridium pincer carbonyl complexes (tBu4PXCYP)Ir(CO), 3a, 3e, 3f, and 3b show a blue shift in the CO stretching frequency. The activities of iridium complexes containing NH linkers were briefly examined for transfer dehydrogenation from cyclooctane to tert-butylethylene; (iPr2PNCOPtBu2)IrHCl (2g) exhibits the highest activity among all tested iridium pincer complexes, including the most studied (tBu4PCP)IrHCl (2a) and (tBu4POCOP)IrHCl (2b). The enhanced catalytic activity could be related to combined electronic and steric effects of the NH/O hybrid linker and different alkyl groups at phosphorus. This new class of iridium pincer complexes could have great implications in catalytic transformation of polar compounds due to the strong hydrogen-bond-donating ability of the NH linker.
- Leveson-Gower, Reuben B.,Webb, Paul B.,Cordes, David B.,Slawin, Alexandra M. Z.,Smith, David M.,Tooze, Robert P.,Liu, Jianke
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- Heterobimetallic Rebound: A Mechanism for Diene-to-Alkyne Isomerization with M - -Zr Hydride Complexes (M = Al, Zn, and Mg)
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The reaction of a series of M·Zr heterobimetallic hydride complexes with dienes and alkynes has been investigated (M = Al, Zn, and Mg). Reaction of M·Zr with 1,5-cyclooctadiene led to diene isomerization to 1,3-cyclooctadiene, but for M = Zn also result in an on-metal diene-to-alkyne isomerization. The resulting cyclooctyne fragment is trapped between Zr and Zn metals in a heterobimetallic species that does not form for M = Mg or Al. The scope of diene isomerization and alkyne trapping has been explored leading to the isolation of three new heterobimetallic slipped metallocyclopropene complexes. The mechanism of diene-to-alkyne isomerization was investigated through kinetics. While the reaction is first-order in Zn·Zr at high diene concentration and proceeds with ΔH? = +33.6 ± 0.7 kcal mol-1, ΔS? = +23.2 ± 1.7 cal mol-1 K-1, and ΔG?298 K = +26.7 ± 1.2 kcal mol-1, the rate is dependent on the nature of the diene. The positive activation entropy is suggestive of involvement of a dissociative step. On the basis of DFT calculations, a heterobimetallic rebound mechanism for diene-to-alkyne isomerization has been proposed. This mechanism explains the origin of heterobimetallic control over selectivity: Mg - -Zr complexes are too strongly bound to generate reactive fragments, while Al - -Zr complexes are too weakly bound to compensate for the contrathermodynamic isomerization process. Zn - -Zr complexes have favorable energetics for both dissociation and trapping steps.
- Butler,White,Crimmin
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supporting information
p. 949 - 956
(2018/03/30)
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- Synthesis and characterization of PBP pincer iridium complexes and their application in alkane transfer dehydrogenation
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This work reports on the synthesis of several new complexes of Ir supported by a diarylboryl/bis(phosphine) PBP pincer ligand. The previously reported complexes (PBP)Ir(Ph)- (Cl) (1) and (PBP)Ir(H)(Cl) (2) were converted to the new complexes (PBP)IrH4 (3) and (PBP)Ir(Ph)(H) (4). Complexes 3 and 4 serve similarly as precatalysts for transfer dehydrogenation of cyclooctane. The turnover numbers achieved were relatively modest but were increased (to 220 at 200 °C) when 1-hexene was used as a sacrificial hydrogen acceptor vs tertbutylethylene. The dicarbonyl complex (PBP)Ir(CO)2 (6) was also synthesized, by the reaction of CO with either 3 or 4. Intermediates (PBPhP)Ir(H)(CO)2 (5) and (PBP)IrH2(CO) (7) were observed in these reactions. Complex 7 could be obtained in pure form by comproportionation of 3 and 6. Solid-state structures of 3 and 6 were determined by X-ray crystallography.
- Shih, Wei-Chun,Ozerov, Oleg V.
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p. 228 - 233
(2017/04/04)
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- Cyclohexane-Based Phosphinite Iridium Pincer Complexes: Synthesis, Characterization, Carbene Formation, and Catalytic Activity in Dehydrogenation Reactions
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Metalation of two cyclohexane-based phosphinite pincer ligands, cis-POCyPO (4) and trans-POCyPO (5) (POCyPO = {1,3-bis-[(di-tert-butylphosphinito]cyclohexane}?), is reported. In line with previously published results (Dalton Trans. 2009, 8626, DOI: 10.1039/B910798C), ligand 4 undergoes aromatization to give benzene-based complex (POCOP)IrHCl (3) at high temperatures in the presence of [Ir(COD)Cl]2. However, here we present the isolation of carbene complex (POCyOP)IrCl (6) which is an intermediate in the aromatization process; upon reaction with H2, 6 can be readily transformed to the corresponding hydrido-chloride 8. Metalation of trans-POCyOP ligand 5 gives hydrido-chloride 13 which only upon further heating can be converted to the corresponding carbene 14. A mechanistic study of hydrogenation of carbene 6 is reported, as well as interesting ambient temperature CO-induced C-H activation in β-position of 6, a process that under other circumstances takes place around 200 °C. The cis complex (POCyOP)IrHCl (8), upon activation with base, revealed moderate activity in transfer dehydrogenation of cyclooctane (144 turnover numbers (TON)), while the performance of trans analog 13 was much better (up to 1684 TON). Carbene complex 6 and in situ generated 14 demonstrated promising activity in acceptorless dehydrogenation of alcohols, presumably operating via a novel metal-ligand cooperation type mechanism. Some of the alcohol dehydrogenations generated large amounts of polystyrene.
- Polukeev, Alexey V.,Wendt, Ola F.
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p. 639 - 649
(2017/04/21)
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- Rapid reversible borane to boryl hydride exchange by metal shuttling on the carborane cluster surface
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In this work, we introduce a novel concept of a borane group vicinal to a metal boryl bond acting as a supporting hemilabile ligand in exohedrally metalated three-dimensional carborane clusters. The (POBOP)Ru(Cl)(PPh3) pincer complex (POBOP = 1,7-OP(i-Pr)2-m-2-carboranyl) features extreme distortion of the two-center-two-electron Ru-B bond due to the presence of a strong three-center-two-electron B-H?Ru vicinal interaction. Replacement of the chloride ligand with a hydride afforded the (POBOP)Ru(H)(PPh3) pincer complex, which possesses B-Ru, B-H?Ru, and Ru-H bonds. This complex was found to exhibit a rapid exchange between hydrogen atoms of the borane and the terminal hydride through metal center shuttling between two boron atoms of the carborane cage. This exchange process, which involves sequential cleavage and formation of strong covalent metal-boron and metal-hydrogen bonds, is unexpectedly facile at temperatures above -50 °C corresponding to an activation barrier of 12.2 kcal mol-1. Theoretical calculations suggested two equally probable pathways for the exchange process through formally Ru(0) or Ru(iv) intermediates, respectively. The presence of this hemilabile vicinal B-H?Ru interaction in (POBOP)Ru(H)(PPh3) was found to stabilize a latent coordination site at the metal center promoting efficient catalytic transfer dehydrogenation of cyclooctane under nitrogen and air at 170 °C.
- Eleazer, Bennett J.,Smith, Mark D.,Popov, Alexey A.,Peryshkov, Dmitry V.
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p. 5399 - 5407
(2017/08/01)
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- Photochirogenic nanosponges: phase-controlled enantiodifferentiating photoisomerization of (Z)-cyclooctene sensitized by pyromellitate-crosslinked linear maltodextrin
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Linear maltodextrin (LM) was cross-linked by pyromellitic dianhydride to afford LM polymers of different cross-linking degrees. When soaked in water, these cross-linked LM polymers (nanosponges (NSs)), evolved into several phases from sol to suspension, then to flowing gel, and finally to rigid gel with an increase in their content. Enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to chiral (E)-isomer (1E), which was employed as a benchmark reaction to quantitatively assess the environmental-to-molecular chirality transfer process, was performed in aqueous media containing these pyromellitate-crosslinked LM-NSs in different phases. The enantiomeric excess (ee) of 1E obtained was relatively insensitive to the phases at least up to the flowing gel phase, but became highly sensitive in the rigid gel phase, exhibiting an abrupt drop in the early rigid gel phase followed by a rapid recovery in the late rigid gel phase. A comparison with the phase-dependent ee profiles previously reported for similar pyromellitate-crosslinked cyclodextrin (CD)- and cyclic nigerosylnigerose (CNN)-NSs revealed that the chiral void space created around the pyromellitate linker in NS is responsible for the dramatic changes in ee in the rigid gel phase, whereas the inherent host cavity in CD/CNN plays only limited roles in the supramolecular photochirogenesis mediated by the sensitizer-crosslinked NSs. The latter insight allows us to further expand the applicable range of the present concept and methodology by employing a much wider variety of oligosaccharides as well as substrates and sensitizing cross-linkers.
- Liang, Wenting,Zhao, Meiling,Wei, Xueqin,Yan, Zhiqiang,Wu, Wanhua,Caldera, Fabrizio,Trotta, Francesco,Inoue, Yoshihisa,Su, Dan,Zhong, Zhihui,Yang, Cheng
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p. 17184 - 17192
(2017/03/30)
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- Solvent-free selective hydrogenation of 1,5-cyclooctadiene catalyzed by palladium incorporated TUD-1
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Palladium (Pd) was incorporated into TUD-1 mesoporous siliceous material by using one-pot synthesis procedure. The catalytic activity of the prepared samples was evaluated in the selective hydrogenation of 1,5-cyclooctadiene (COD) at 80 °C in a solvent-free condition. Pd-TUD-1 showed > 95% conversion of COD with a selectivity > 90% towards cyclooctene (COE).
- Benaissa, Mhamed,Alhanash, Abdullah M.,Eissa, Murad,Hamdy, Mohamed S.
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- Revealing Hydrogenation Reaction Pathways on Naked Gold Nanoparticles
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Gold nanoparticles (AuNPs) display distinct characteristics as hydrogenation catalysts, with higher selectivity and lower catalytic activity than group 8-10 metals. The ability of AuNPs to chemisorb/activate simple molecules is limited by the low coordination number of the surface sites. Understanding the distinct pathways involved in the hydrogenation reactions promoted by supported AuNPs is crucial for broadening their potential catalytic applications. In this study, we demonstrate that the mechanism of the hydrogenation reactions catalyzed by AuNPs with "clean" surfaces may proceed via homolytic or heterolytic hydrogen activation depending on the nature of the support. The synthesis of naked AuNPs employing γ-Al2O3 and ionic liquid (IL)-hybrid γ-Al2O3 supports was accomplished by sputtering deposition using ultrapure gold foils. This highly reproducible and straightforward procedure furnishes small (~6.6 nm) and well-distributed metallic gold nanoparticles (Au(0)NPs) that are found to be active catalysts for the partial and selective hydrogenation of substituted conjugated dienes, alkynes, and α,β-unsaturated carbonyl compounds (aldehydes and ketones). Kinetic and deuterium labeling studies indicate that heterolytic hydrogen activation is the primary pathway occurring on the AuNPs imprinted directly on γ-Al2O3. In contrast, AuNPs supported on IL-hybrid γ-Al2O3 materials cause the reaction to proceed via a homolytic hydrogen activation pathway. The IL layer surrounds the AuNPs and acts as a cage, influencing the frequency of the interaction of the catalytically active species and the metal surface and, consequently, the catalytic performance of the AuNPs. The IL layer is shown to improve the product selectivity by the enhancement of the substrate/product discrimination, and to decrease the catalytic activity by shifting the rate-determining step to the H2 and substrate competitive adsorption/activation on the same active sites. A series of kinetic experiments suggest that AuNPs imprinted on an IL-hybrid γ-Al2O3 support are more efficient (lower activation energy, Ea) than group 8-10 metal based catalysts for hydrogenation reactions at moderate to high temperatures (75-150 °C).
- Luza, Leandro,Rambor, Camila P.,Gual, Aitor,Alves Fernandes, Jesum,Eberhardt, Dario,Dupont, Jairton
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p. 2791 - 2799
(2017/05/31)
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- Unconventional Pd@Sulfonated Silica Monoliths Catalysts for Selective Partial Hydrogenation Reactions under Continuous Flow
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Doubly functionalized, hierarchical-porosity silica monoliths were synthesized by postgrafting of sulfonic groups and in situ growth of Pd nanoparticles in that order. PdNP of 3.1 nm size located in the mesopores of the material showed to be evenly distributed within 4.6 % wt Pd monoliths. The system was explored in the continuous-flow, catalytic partial hydrogenation reaction of 3-halogeno-nitrobenzenes and 3-hexyn-1-ol in the liquid phase, showing remarkable conversion, selectivity, and resistance under very mild conditions.
- Liguori, Francesca,Barbaro, Pierluigi,Said, Bilel,Galarneau, Anne,Santo, Vladimiro Dal,Passaglia, Elisa,Feis, Alessandro
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p. 3245 - 3258
(2017/08/29)
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- Rotaxane synthesis exploiting the M(i)/M(III) redox couple
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In the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1p;:p;1 mixtures of 2 and bipy in CH2Cl2, which proceeds with disparate rates to afford [M(bipy)H2(PPh3)2][BArF4] (M = Rh, 4a[BArF4], t = 18 h @ 50 °C; Ir, 4b[BArF4], t 2Cl2 (1 atm H2). These rates are reconciled by (a) the inherently slower reaction of 2a with H2 compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh3. On the basis of this information, operationally convenient and mild conditions (CH2Cl2, RT, 1 atm H2, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh3)2]2[BArF4]2 (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.
- Emerson-King, Jack,Knighton, Richard C.,Gyton, Matthew R.,Chaplin, Adrian B.
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p. 11645 - 11655
(2017/09/18)
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- Saturation kinetics and relative reactivity of the double bonds of alicyclic dienes in their hydrogenation
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The kinetics of the liquid-phase hydrogenation of cyclodienes with various structures (endo-tricyclo[ 5.2.1.02,6]decadiene-3,8 and cis,cis-1,5-cyclooctadiene) by hydrogen over a finely dispersed 1%Pd/C catalyst at atmospheric pressure has been studied. The catalyst provides the possibility for successive saturation of the double bonds of the dienes. The reactivities of the cyclodienes determined by their electron-donating properties have been compared. The solvent nature is the determining factor in the ratio of hydrogen absorption rates in the case of successive saturation of the double bonds of the hydrocarbons. The hydrogenation kinetics of cyclic dienes, including dicyclopentadiene, can be modeled using the Langmuir–Hinshelwood equation when the process is carried out in a perfectly mixed flow reactor.
- Vereshchagina,Antonova,Kopushkina, G. Yu.,Abramov
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p. 255 - 261
(2017/07/25)
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- The cyclooctadiene ligand in [IrCl(COD)]2is hydrogenated under transfer hydrogenation conditions: A study in the presence of PPh3and a strong base in isopropanol
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The interaction of [IrCl(COD)]2with PPh3in isopropanol has been investigated for various P/Ir ratios, in the absence or presence of a strong base (KOtBu), at room temperature and at reflux. At room temperature, PPh3adds to
- Rahaman,Daran, Jean-Claude,Manoury, Eric,Poli, Rinaldo
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- Synthesis of Pincer Hydrido Ruthenium Olefin Complexes for Catalytic Alkane Dehydrogenation
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A series of new hydrido Ru(II) olefin complexes supported by isopropyl-substituted pincer ligands have been synthesized and characterized. These complexes are thermally robust and active for catalytic transfer and acceptorless alkane dehydrogenation. Notably, the alkane dehydrogenation catalysts are tolerant of a number of polar functional species.
- Zhang, Yuxuan,Fang, Huaquan,Yao, Wubing,Leng, Xuebing,Huang, Zheng
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supporting information
p. 181 - 188
(2016/02/05)
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- Catalytic alkane transfer-dehydrogenation by PSCOP iridium pincer complexes
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A series of new (tBu2PSCOPR2)IrHCl iridium complexes with ‘hybrid’ phosphinothious-phosphinite PSCOP ligands ([tBu2PSCOPR2?=?1-(SPtBu2)-3-(OPR2)-C6H4], R?=?tBu, 4a, R?=?Cy, 4b, R?=?iPr, 4c, and R?=?Et, 4d) have been synthesized and characterized. Treatment of complexes 4a–d with sodium tert-butoxide generates the active species for catalytic transfer-dehydrogenation of cyclooctane (COA) or n-octane using tert-butylethylene (TBE) as hydrogen acceptor to form cyclooctene (COE) or octenes, respectively. The catalytic activity of these complexes and the product selectivity in alkane dehydrogenation is greatly influenced by the steric properties of the pincer ligand. In general, the less sterically bulky complex exhibits higher catalytic activity than the more hindered complex. Among the new (PSCOP)Ir-type complexes, the least crowded complex (tBu2PSCOPEt2)IrHCl 4d is most active for n-octane/TBE transfer-dehydrogenation. The relatively crowded, less active, complexes (tBu2PSCOPtBu2)IrHCl (4a) and (tBu2PSCOPCy2)IrHCl (4b) exhibit high regioselectivity for α-olefin formation at the early stages of the reaction.
- Yao, Wubing,Jia, Xiangqing,Leng, Xuebing,Goldman, Alan S.,Brookhart, Maurice,Huang, Zheng
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- Efficient low-cost preparation of trans-cyclooctenes using a simplified flow setup for photoisomerization
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Bioorthogonal ligations have emerged as highly versatile chemical tools for biomedical research. The exceptionally fast reaction between 1,2,4,5-tetrazines and trans-cyclooctenes (TCOs), also known as tetrazine ligation, is frequently used in this regard. Growing numbers of applications for the tetrazine ligation led to an increased demand for TCO compounds, whose commercial availability is still very limited. Reported photochemical procedures for the preparation of TCOs using flow chemistry are straightforward and high yielding but require expensive equipment. Within this contribution, we present the construction and characterization of a low-cost flow photoreactor assembled from readily accessible components. Syntheses of all commonly used trans-cyclooctene derivatives were successfully carried out using the described system. We are convinced that the presented system for photoisomerization will promote access to bioorthogonally reactive TCO derivatives.
- Svatunek, Dennis,Denk, Christoph,Rosecker, Veronika,Sohr, Barbara,Hametner, Christian,Allmaier, Günter,Fr?hlich, Johannes,Mikula, Hannes
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p. 579 - 585
(2016/03/19)
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- A mild method for the replacement of a hydroxyl group by halogen. 1. Scope and chemoselectivity
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α-Chloro-, bromo- and iodoenamines, which are readily prepared from the corresponding isobutyramides have been found to be excellent reagents for the transformation of a wide variety of alcohols or carboxylic acids into the corresponding halides. Yields are high and conditions are very mild thus allowing for the presence of sensitive functional groups. The reagents can be easily tuned allowing therefore the selective monohalogenation of polyhydroxylated molecules. The scope and chemoselectivity of the reactions have been studied and reaction mechanisms have been proposed.
- Munyemana, Fran?ois,George, Isabelle,Devos, Alain,Colens, Alain,Badarau, Eduard,Frisque-Hesbain, Anne-Marie,Loudet, Aurore,Differding, Edmond,Damien, Jean-Marie,Rémion, Jeanine,Van Uytbergen, Jacqueline,Ghosez, Léon
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p. 420 - 430
(2015/12/31)
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- Colloidal and nanosized catalysts in organic synthesis: XV. Gas-phase hydrogenation of alkenes catalyzed by supported nickel nanoparticles
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Gas-phase hydrogenation of alkenes and their derivatives, catalyzed by nickel nanoparticles supported on zeolite or silica gel support occurs at 150–250°С and an atmospheric hydrogen pressure and results in a high conversion. The selectivity of the hydrogenation depends on the amount of hydrogen: at a low diene (triene)–hydrogen ratio, selective hydrogenation of one multiple bond in the substrate is possible.
- Popov, Yu. V.,Mokhov,Nebykov,Latyshova,Panov,Dontsova,Shirkhanyan,Shcherbakova
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p. 2589 - 2593
(2017/03/22)
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