25267-51-0Relevant academic research and scientific papers
Pumice-Supported Pd-Pt Bimetallic Catalysts: Synthesis, Structural Characterization, and Liquid-Phase Hydrogenation of 1,3-Cyclooctadiene
Deganello, Giulio,Duca, Dario,Liotta, Leonarda F.,Martorana, Antonino,Venezia, Anna Maria,et al.
, p. 125 - 134 (1995)
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.
The functionalization of saturated hydrocarbons part XXIX. Application of tert-butyl hydroperoxide and dioxygen using soluble Fe(III) and Cu(II) chelates
Barton, Derek H. R.,Beviere, Stephane D.,Hill, David R.
, p. 2665 - 2670 (1994)
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.
Homogeneous Catalytic Photochemical Functionalization of Alkanes by α-Dodecatungstophosphate. Rate Behavior, Energetics, and General Characteristics of the Processes
Renneke, Roman F.,Hill, Craig L.
, p. 5461 - 5470 (1988)
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...
Mechanism of alkane transfer-dehydrogenation catalyzed by a pincer-ligated iridium complex
Renkema, Kenton B.,Kissin, Yury V.,Goldman, Alan S.
, p. 7770 - 7771 (2003)
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
Catalytic Alkane Transfer Dehydrogenation by PSP-Pincer-Ligated Ruthenium. Deactivation of an Extremely Reactive Fragment by Formation of Allyl Hydride Complexes
Zhou, Xiaoguang,Malakar, Santanu,Zhou, Tian,Murugesan, Sathiyamoorthy,Huang, Carlos,Emge, Thomas J.,Krogh-Jespersen, Karsten,Goldman, Alan S.
, p. 4072 - 4083 (2019)
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.
A highly active alkane dehydrogenation catalyst: Stabilization of dihydrido rhodium and iridium complexes by a P-C-P pincer ligand
Gupta, Mukta,Hagen, Chrystel,Flesher, Robert J.,Kaska, William C.,Jensen, Craig M.
, p. 2083 - 2084 (1996)
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.
Metal dependence in gif-type reactions. The Cu(II)-catalyzed olefination of saturaed hydrocarbons by tert-butyl hydroperoxide
Barton,Beviere,Chavasiri,Doller,Hu
, p. 567 - 570 (1993)
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.
The photochemistry of optically active (E)-cyclooctene: Lamp versus laser
Gao, Fang,Li, Run-Hua,Compton, Robert N.,Pagni, Richard M.
, p. 297 - 299 (2004)
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.
β',β-Carbanionic Elimination Reaction of a Carboxylic Ester
Aubert, Corinne,Begue, Jean-Pierre,Biellmann, Jean-Francois
, p. 351 - 352 (1984)
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.
Bioorthogonal prodrug activation driven by a strain-promoted 1,3-dipolar cycloaddition
Matikonda, Siddharth S.,Orsi, Douglas L.,Staudacher, Verena,Jenkins, Imogen A.,Fiedler, Franziska,Chen, Jiayi,Gamble, Allan B.
, p. 1212 - 1218 (2015)
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.
