- Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
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Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
- Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
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supporting information
p. 9102 - 9112
(2020/03/30)
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- Catalytic dehydrogenation of cyclooctane with titanium, zirconium and hafnium metallocene complexes
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Metallocene complexes in combination with cocatalysts like methylalumoxane (MAO) are not only excellent catalysts for olefin polymerization but also appropriate catalysts for the activation of alkanes in homogeneous (autoclave) and heterogeneous (fixed be
- Taubmann, Sandra,Denner, Christine E.,Alt, Helmut G.
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experimental part
p. 2005 - 2019
(2009/09/26)
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- Catalytic thermal and photo-induced CH and CC activation reactions of alkanes with ansa amido functionalized half-sandwich complexes and methylalumoxane
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In the literature most of the dehydrogenation reactions of alkanes are described as CH activation reactions of cyclooctane. The best results of CH activation reactions have been found for the reaction of MAO activated metallocene complexes and cyclooctane
- Alt,Denner, Christine E.
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scheme or table
p. 3270 - 3275
(2010/01/11)
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- Carbenes in Constrained Systems, 3. Solid-State Photolysis of Cycloheptane- and Cyclooctanespirodiazirine within Cyclodextrins and Zeolites
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Inclusion complexes of cycloheptanespirodiazirine (1) and cyclooctanespirodiazirine (8) in α-, β-, and γ-cyclodextrin, and faujasite type zeolites (NaX and NaY), have been prepared.The guest-host complexes (1- and 8CD and 1- and 8zeolite) were irradiated with UV light in the solid state and the reaction products were separated from the host and analyzed.Product ratios from photolysis of complexes were compared with those obtained from pure compounds and in solution.Cycloheptanespirodiazirine (1) gives cycloheptene (2), bicycloheptane (3), and methylenecyclohexane (4).Photolysis products from cyclooctanespirodiazirine (8) are cyclooctene (9), bicyclooctane (10), and bicyclooctane (11). 10 results from a 1,5-C-H insertion reaction of the carbene derived from 8.As the cavity size of the cyclodextrins becomes larger, the formation of 10 seems to increase.In β-cyclodextrin and in non-polar solvents substantial amounts of azine were found.In addition to hydrocarbons, photolyses in zeolites afforded alcohols and small amounts of the corresponding ketones. - Keywords: Diazirines / Zeolites / Cyclodextrins / Photochemistry / Carbenes
- Kupfer, Rene,Brinker, Udo H.
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p. 1721 - 1726
(2007/10/03)
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- Radiolysis of Cyclooctane with γ-Rays and Helium Ions
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Iodine scavenging techniques have been used to examine the role of the cyclooctyl radical in the radiolysis of cyclooctane with γ-rays and with 5-20-MeV helium ions.In γ-radiolysis about 70percent of the total yield of 6.6 cyclooctyl radicals/100 eV are scavenged with E-4 M iodine, which agrees well with other studies on cycloalkanes that show most of the radicals produced in these systems react in the bulk medium at times longer than 1 μs.However, it is found that 2.5 radicals/100 eV (38percent) are produced by H atom precursors as copmpared to a value of 1.5 cyclohexyl radicals/100 eV (25percent) in cyclohexane.With 10-MeV helium ions (average LET of 106 eV/nm), only 8percent of the cyclooctyl radicals survive longer than a few microseconds due to the increased initial radical concentration in the helium ion track.The yield of the cross-bridged product bicyclooctane (pentalane) was found to be independent of iodine concentration up to 0.03 M with both types of radiation.However, the pentalane yield found with 10-MeV helium ions was only one-third of that found in γ-radiolysis.The most likely reason for this result is the decreased yield of singlet-state formation due to the enhanced probability of cross combination reactions of electron-cation pairs in the high-density region of the helium ion track.
- Wojnarovits, Laszlo,LaVerne, Jay A.
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p. 8014 - 8018
(2007/10/02)
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- Dehydrogenation of Cycloalkanes by Suspended Platinum Catalysts
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Heterogenized cluster complex 52- and reduced platinum metal have catalyzed cyclooctane dehydrogenation at comparable rates, whereas dehydrogenoaromatization of ethylcyclohexane proceeded predominantly with the latter.Active-site ensembles for the formation of cyclooctene, bicyclooctane and aromatics were discussed on reference to the appropriate stretch of platinum metal atoms.
- Hama, Shunichi,Li, Xiaomei,Yukawa, Kiyoshi,Saito, Yasukazu
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p. 2463 - 2466
(2007/10/02)
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- PHOTOCHEMISTRY OF BENZOCYCLOBUTENE
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Photolysis of benzocyclobutene (1) in pentane solution at 254 nm yields 1,2-dihydropentalene (2) and 1,5-dihydropentalene (3) as the major isomeric products; formation of 2 and 3 is consistent with a "prebenzvalene"-carbene rearrangement mechanism.
- Turro, N. J.,Zhang, Z.,Trahanovsky, W. S.,Chou, C.-H.
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p. 2543 - 2546
(2007/10/02)
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- Evidence for Single Electron Transfer in the Reduction of Organic Halides by Lithium Triethylborohydride
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Product studies involving the reduction of cyclizable alkyl iodides and bromides, trapping of intermediate radicals by dicyclohexylphosphine, and direct EPR observation of radicals have been used to detect the occurence of a single electron transfer pathway in the reduction of these halides by lithium triethylborohydride.
- Ashby, E.C.,Wenderoth, Bernd,Pham, Tung N.,Park, Won-Suh
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p. 4505 - 4509
(2007/10/02)
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- EVIDENCE FOR SINGLE ELECTRON TRANSFER IN THE REACTION OF ALKOXIDES WITH ALKYL HALIDES
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Evidence for a radical process in the reaction of lithium alkoxides with alkyl iodides was obtained by observation of cyclization of appropriate radical probes, by the trapping of radicals, and by EPR spectroscopic observations relating to the one electron donor properties of alkoxides.
- Ashby, E. C.,Bae, Dong-Hak,Park, Won-Suh,Depriest, Robert N.,Su, Wei-Yang
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p. 5107 - 5110
(2007/10/02)
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- BICYCLOOCTA-2,6-DIEN-8-YLIDENE (HOMO-7-NORBORNADIENYLIDENE), A "FOILED" CARBENE
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Bicycloocta-2,6-dien-8-ylidene nearly exclusively rearranges by 1,2-vinyl migrations.The interaction with the double bond of the six-membered ring dominates.
- Brinker, Udo H.,Koenig, Lothar
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- OXIDATION OF 9-BORABICYCLONONANE AND ITS DERIVATIVES WITH PYRIDINIUM CHLOROCHROMATE
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The oxidation of 9-borabicyclononane (1) with chromic acid or pyridinium chlorochromate (PCC) affords a mixture of products, predominantly cyclooctanone (>65percent).However, cis-1,5-cyclooctanediol (2), readily obtained from 1 by oxidation with alkaline hydrogen peroxide, is oxidized by these reagents to provide 9-oxabicyclononan-1-ol (4).Under more drastic conditions, 2 and 4 can be transformed by PCC into 1,5-cyclooctanedione (5).Consequently, it is now possible to proceed easily from 1,5-cyclooctadiene via hydroboration-oxidation to cis-1,5-cyclooctanediol (2), to 9-oxabicyclononan-1-ol (4) and 1,5-cyclooctanedione (5).
- Kulkarni, Surendra U.,Rao, C. Gundu,Patil, Vemanna D.
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p. 321 - 326
(2007/10/02)
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- Hydrogenation Reactions over Catalysts of Very Strong One-Electron Donor Properties
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The results of studies on simple alkenes and conjugated double bonds systems hydrogenation reactions over the catalysts with very strong one-electron donor properties have been presented.The catalysts have been obtained by evaporation of alkali metals onto magnesium oxide surface.High catalytic activity and selectivity of the systems under investigation have been observed.
- Kijenski, Jacek
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- Carbene-carbene rearrangements as a route to 1,5-dihydropentalene
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1,5-Dihydropentalene (4) is formed as the main product on treatment of trans-1,2-bis(2,2-dibromocyclo-propyl)ethene 3 with methyllithium at -40°. In addition the reaction affords 1- and 2-propadienylcyclopentadienes (5a) and (5b), and trans-1,2,4,6,7-octapentaene (6), new CsHs isomers. Diets-Alder adducts of 4,5a and 5b were obtained in the reaction with perfluorobut-2-yne. The formation of 1,5-dihydropentalene 4 is explained by a double ring expansion sequence involving consecutive carbene-carbene rearrangements with 1,3-carbon and subsequent 1,2-hydrogen shifts, supported by the reaction of double labelled (13C-depleted) 3. From readily available 3 at low temperatures formation and fusion of two 5-membered rings are achieved in one step.
- Brinker, Udo H.,Fleischhauer, Ilona
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p. 4495 - 4502
(2015/01/09)
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- UNIMOLECULAR H2 ELIMINATION DURING THE LIQUID PHASE RADIOLYSIS AND PHOTOLYSIS OF ALKANE-ALKANE MIXTURES
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Unimolecular H2 elimination from alkanes was investigated in cyclopentane-cyclohexane, n-hexane-cyclohexane and cyclohexane-cyclooctane mixtures during radiolysis and 7.6 eV photolysis.During the radiolysis of all system, and when the fluorescence shift law allowed it, during the photolysis as well, inhibited H2 detachment was observed from the first component and sensitized hydrogen molecule elimination from the second.It has been concluded that the same excited state (the lowest singlet, S1) is responsible for the H2 elimination during radiolysis and photolysis and this is that one that gives rise to fluorescence in the experiments of other authors.The H2 and H elimination from alkanes generally have different excited precursors.The direct population of S1 by γ-irradiation is of limited importance and this intermediate is mainly produced in "charge neutralization" processes.
- Wojnarovits, L.,Foeldiak, G.
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