- Mechanism of the Cope Rearrangement of Acyclic 1,5-Dienes and of the Wacker Oxidation of Alk-1-enes catalysed by Palladium Complexes
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Hexa-1,5-diene is catalytically converted into acetone in an aqueous solution of (PhCN)2PdCl2, CuCl2, and CuCl at 60 deg C in the presence of oxygen, thereby revealing a hitherto unsuspected role of η3-allylic intermediates in both the PdII-catalysed Cope rearrangements of 1,5-dienes and the selective Wacker oxidation of propene and higher alk-1-enes to ketones.
- Hamilton, Robert,Mitchell, Thomas R. B.,Rooney, John J.
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Read Online
- Extrinsic precursor-assisted synthesis of 1,5-hexadiene on Cu(100)
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The reaction between allyl bromide and previously chemisorbed η3-allyl to form 1,5-hexadiene on Cu(100) at cryogenic temperatures has been examined using reflection absorption infrared spectroscopy and temperature-programmed desorption. Above 110 K, the 1,5-hexadiene formation rate decreases with increasing temperature and is controlled by the residence time of dosed allyl bromide, whereas below 100 K, the rate increases with temperature and is controlled by the reaction of weakly adsorbed allyl bromide with chemisorbed η3-allyl. Above 110 K, a precursor state model is used to interpret the data. The activation energy difference, Ed-Er, between desorption and reaction of allyl bromide with η3-allyl is 12 kJ mol-1.
- Celio,Scheer,White
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Read Online
- Reaktion von (1,4-Diazabutadien)bis(alken)nickel(0)-Komplexen mit Ethin
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The (1,4-diazabutadiene)bis(alkene)nickel(0) complexes iPr2Ph)2-dad>Ni(C2H4)2 iPr2Ph)2-dad = 2,6iPr2C6H3-N=CHCH=N-C6H3-2,6iPr2> (1) and iPr2Ph)2-dad>Ni(η2,η2-C6H10) (2) react with ethyne above - 100 deg C (1) or -30 deg C (2) with coupling of two ethyne molecules to afford the dinuclear complex iPr2Ph)2-dad>Ni>2(C4H4) (3) which contains a ferrol-type nickelacyclopentadiene-nickel(O) bonding element.A single-crystal X-ray structure study of 3 revealed strongly distorted coordination geometries of the nickel centers, which are also present in solution at low temperature (1H, 13C-NMR).At higher temperatures dynamic processes take place by which the coordinative distortions at the nickel centers are reversed and the bonding situations of the nickel atoms are exchanged.However, a rotation of the phenyl groups around the N-C bonds can be excluded.Similarly, Ni>2(C4H4) (4) has been obtained and characterized.
- Bonrath, Werner,Michaelis, Stephan,Poerschke, Klaus R.,Gabor, Barbara,Mynott, Richard,Krueger, Carl
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Read Online
- Kinetics and Mechanism of Thermal Decomposition of Bis(Η3-Allyl)Nickel Complexes
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Abstract: The kinetics of thermal decomposition of bis(η3-allyl) nickel complexes in various media is studied. The specific features of the mechanism are determined, including the combination of the stages of trans-cis isomerization of Niall2 and the bimolecular decomposition of the cis-isomer with diallyl formation. The effect of autocatalytic decomposition of complexes with metallic nickel is been detected. The qualitative dependences of the process rate on the nature of the solvent and the structure of the allyl ligand are determined. The activation parameters of individual steps, consistent with quantum chemical calculations, are found.
- Flid,Zamalyutin,Shamsiev,Katsman
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Read Online
- Reductive C(sp3)-C(sp3) homo-coupling of benzyl or allyl halides with H2using a water-soluble electron storage catalyst
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This paper reports the first example of a reductive C(sp3)-C(sp3) homo-coupling of benzyl/allyl halides in aqueous solution by using H2as an electron source {turnover numbers (TONs) = 0.5-2.3 for 12 h}. This homo-coupling reaction, promoted by visible light, is catalysed by a water-soluble electron storage catalyst (ESC). The reaction mechanism, and four requirements to make it possible, are also described.
- Futakuchi, Sayaka,Miyazawa, Keishi,Nakai, Hidetaka,Ogo, Seiji,Shimauchi, Daiki,Takahashi, Yukina,Yatabe, Takeshi,Yoon, Ki-Seok
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p. 39450 - 39454
(2021/12/27)
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- Method for preparing 1, 5-hexadiene
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The invention discloses a method for preparing 1, 5-hexadiene, which is characterized in that under the action of a catalyst and a reducing agent, a substrate is catalyzed to be subjected to a one-step reaction to prepare the 1, 5-hexadiene, and the substrate comprises a polyhydroxy compound and a derivative thereof. Therefore, the invention provides a novel method for synthesizing the 1, 5-hexadiene. According to the reaction path provided by the invention, new application of catalytic conversion of polyhydroxy compounds including glycerol is developed through a carbon chain extension conversion strategy.
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Paragraph 0038-0048; 0057-0062; 0064-0065; 0067-0072; ...
(2021/06/22)
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- Method for preparing 2, 5-hexanedione
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The invention discloses a method for preparing 2, 5-hexanedione, which is characterized in that a polyhydroxy compound and a derivative thereof are used as substrates, and the 2, 5-hexanedione is obtained through a carbon growth-wacker oxidation reaction under the action of a catalyst and an oxidizing agent. According to the method disclosed by the invention, a large amount of by-product glycerol generated in a biodiesel production process is used as a raw material, so that the production cost of 2, 5-hexanedione can be reduced, and a high-added-value conversion and utilization path is provided for glycerol.
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Paragraph 0031-0053
(2021/06/22)
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- Mild olefin formationviabio-inspired vitamin B12photocatalysis
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Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B12-dependent photoreceptor CarH, where photolysis of a cobalt-carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B12-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B12to be a powerful platform for developing mild olefin-forming reactions.
- Bam, Radha,Pollatos, Alexandros S.,Moser, Austin J.,West, Julian G.
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p. 1736 - 1744
(2021/02/22)
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- The Synthesis of Chiral Allyl Carbamates via Merger of Photoredox and Nickel Catalysis
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A mild, and versatile, organophotoredox/Ni-mediated protocol was developed for the direct preparation of diverse, enantioenriched allyl carbamates. The reported approach represents a significant departure from classical step-by-step synthesis of allyl carbamates. This dual photoredox/Ni based strategy offers unrivalled capacity for convergent unification of readily available alkyl halides and chiral carbamates derived from 1-bromo-alken-3-ols with high chemoselectivity and efficiency. The reported photoredox/Ni catalyzed cross-coupling reaction is not limited to carbamates, but also to other O-derivatives such as esters, ethers, acetals, carbonates or silyl ethers. To demonstrate the utility of the reported protocol, the resulting allyl carbamates were transformed into functionalized non-racemic allylamines through a sigmatropic rearrangement reaction in enantiospecific manner. This approach allowed for synthesis of enantiomeric allylamines by a simple control of the geometry of a double bond of allyl carbamates. (Figure presented.).
- Garbacz, Mateusz,Stecko, Sebastian
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supporting information
p. 3213 - 3222
(2020/07/06)
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- Chlorinating preparation method for low-carbon olefins
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The invention discloses a chlorinating preparation method for low-carbon olefins. According to the method, chlorine gas is diluted with inert gas and then reacts with low-carbon olefins, thus, influence caused by microscopic mixing can be obviously reduced, namely, a too high local temperature can be avoided, thus, side reactions including a decarbonization phenomenon caused by the too high localtemperature can be obviously reduced, and a relatively good chloride yield can be obtained.
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Paragraph 0034-0036
(2020/01/12)
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- Nickel-Catalyzed Homo- And Cross-Coupling of Allyl Alcohols via Allyl Boronates
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A nickel-catalyzed homo- and cross-coupling of allylic alcohols to 1,5-dienes in the presence of B2pin2 with excellent regioselectivity has been developed. Mechanistic studies indicate that the reaction proceeds via sequential nickel-catalyzed borylation of allyl alcohols followed by cross-coupling of the resulting allyl boronates with allyl alcohols. The method was effectively applied to nickel-catalyzed allylation of aldehydes using allylic alcohols directly.
- Gan, Yi,Hu, Hui,Liu, Yuanhong
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supporting information
p. 4418 - 4423
(2020/06/27)
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- Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0)
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The mechanism of the reactions between dppf-Ni0 complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(κ2-dppf)(κ1-dppf)], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The rates of the reactions of [Ni(COD)(dppf)] with alkyl halides and the yields of prototypical nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are shown to be significantly improved by the addition of free dppf ligand.
- Greaves, Megan E.,Lloyd-Jones, Guy C.,Maseras, Feliu,Nelson, David J.,Ronson, Thomas O.,Sproules, Stephen
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p. 10717 - 10725
(2020/11/09)
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- First use of a divalent lanthanide for visible-light-promoted photoredox catalysis
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We report the first catalytic use of a divalent lanthanide in visible-light-promoted bond-forming reactions. Our new precatalyst uses europium in the +2 oxidation state and is active in the presence of blue light from light-emitting diodes. The use of low-energy visible light reduces the occurrence of potential side reactions that might be induced by higher-energy UV light. The system described here uses zinc metal as a sacrificial reductant and is tolerant to wet, protic solvents. The catalyst can be made in situ from relatively inexpensive and air-stable EuCl3·6H2O, and the ligand can be synthesized in large quantities in two steps. With 0.5% loading of precatalyst, an average of 120 turnovers was observed in six hours for reductive coupling of benzyl chloride. We expect that the results will initiate the study of visible-light-promoted photoredox catalysis using divalent europium in a variety of reactions.
- Jenks, Tyler C.,Bailey, Matthew D.,Hovey, Jessica L.,Fernando, Shanilke,Basnayake, Gihan,Cross, Michael E.,Li, Wen,Allen, Matthew J.
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p. 1273 - 1278
(2018/02/09)
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- Photocatalytic Barbier reaction-visible-light induced allylation and benzylation of aldehydes and ketones
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We report a photocatalytic version of the Barbier type reaction using readily available allyl or benzyl bromides and aromatic aldehydes or ketones as starting materials to generate allylic or benzylic alcohols. The reaction proceeds at room temperature under visible light irradiation with the organic dye 3,7-di(4-biphenyl)1-naphthalene-10-phenoxazine as a photocatalyst and DIPEA as sacrificial electron donor. The proposed cross-coupling mechanism of a ketyl- and an allyl or benzyl radical is supported by spectroscopic investigations and cyclic voltammetry measurements.
- Berger, Anna Lucia,Donabauer, Karsten,K?nig, Burkhard
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p. 7230 - 7235
(2018/10/02)
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- Photochemical Production of Ethane from an Iridium Methyl Complex
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An iridium methyl complex, [Cp?Ir(bpy)(CH3)]+, was prepared by electrophilic methylation of Cp?Ir(bpy) with CH3I and characterized electrochemically, photophysically, crystallographically, and computationally. Irradiation of the MLCT transition of [Cp?Ir(bpy)(CH3)]+ in the presence of CH3I in acetonitrile produces ethane, methane, propionitrile, and succinonitrile. A series of mechanistic studies indicates that C-C bond formation is mediated by free methyl radicals produced through monometallic photochemical homolysis of the Ir-CH3 bond.
- Pitman, Catherine L.,Miller, Alexander J. M.
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supporting information
p. 1906 - 1914
(2017/06/14)
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- Ring Opening of Biomass-Derived Cyclic Ethers to Dienes over Silica/Alumina
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We show that cyclic ethers, such 2-methyltetrahydrofuran (2-MTHF), can undergo dehydration to produce pentadienes over SiO2/Al2O3. The catalyst exhibited reversible deactivation due to coke deposition, with the yield to pentadienes decreasing from 68% to 52% at 623 K over 58 h time on stream. A reaction network for 2-MTHF dehydration was proposed on the basis of the results of space time studies. Pentadienes can be produced directly by a concerted hydride shift and dehydration of carbenium intermediates or indirectly through dehydration of pentanal and pentenol. Reaction kinetics studies were performed at temperatures ranging from 573 to 653 K and 2-MTHF partial pressures from 0.21 to 2.51 kPa. The apparent activation energy barrier for 2-MTHF conversion to pentadienes and the reaction rate order for ring opening were determined to be 74 kJ mol-1 and 0.24, respectively, indicating strong interaction between 2-MTHF and the SiO2/Al2O3 surface. Other solid acids such as γ-Al2O3, H-ZSM-5, and Al-Sn-Beta were found to be active for 2-MTHF dehydration to pentadienes. The rate of ring opening decreased in the order 2,5-dimethyltetrahydrofuran > 2-MTHF > tetrahydropyran > tetrahydrofuran. Over SiO2/Al2O3, the dehydration of 2,5-dimethyltetrahydrofuran resulted in 75% yield to hexadiene isomers. (Figure Presented).
- Kumbhalkar, Mrunmayi D.,Buchanan, J. Scott,Huber, George W.,Dumesic, James A.
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p. 5248 - 5256
(2017/08/17)
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- Study of the Formation of the First Aromatic Rings in the Pyrolysis of Cyclopentene
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The thermal decomposition of cyclopentene was studied in a jet-stirred reactor operated at constant pressure and temperature to provide new experimental information about the formation of the first aromatic rings from cyclic C5 species. Experim
- Herbinet, Olivier,Rodriguez, Anne,Husson, Benoit,Battin-Leclerc, Frédérique,Wang, Zhandong,Cheng, Zhanjun,Qi, Fei
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p. 668 - 682
(2016/02/23)
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- Enzymatic Oxidative Tandem Decarboxylation of Dioic Acids to Terminal Dienes
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The biocatalytic oxidative tandem decarboxylation of C7–C18dicarboxylic acids to terminal C5–C16dienes was catalyzed by the P450 monooxygenase OleT with conversions up to 29 % for 1,11-dodecadiene (0.49 g L–1). The sequential nature of the cascade was proven by the fact that decarboxylation of intermediate C6–C11ω-alkenoic acids and heptanedioic acid exclusively gave nonconjugated 1,4-pentadiene; scale-up allowed the isolation of 1,15-hexadecadiene and 1,11-dodecadiene; the system represents a short and green route to terminal dienes from renewable dicarboxylic acids.
- Dennig, Alexander,Kurakin, Sara,Kuhn, Miriam,Dordic, Andela,Hall, Mélanie,Faber, Kurt
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supporting information
p. 3473 - 3477
(2016/07/29)
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- A Low-Valent Iron Imido Heterocubane Cluster: Reversible Electron Transfer and Catalysis of Selective C-C Couplings
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Enzymes and cofactors with iron-sulfur heterocubane core structures, [Fe4S4], are often found in nature as electron transfer reagents in fundamental catalytic transformations. An artificial heterocubane with a [Fe4N4] core is reported that can reversibly store up to four electrons at very negative potentials. The neutral [Fe4N4] and the singly reduced low-valent [Fe4N4]- heterocubanes were isolated and fully characterized. The low-valent species bears one unpaired electron, which is localized predominantly at one iron center in the electronic ground state but fluctuates with increasing temperatures. The electrons stored or released by the [Fe4N4]/[Fe4N4]- redox couple can be used in reductive or oxidative C-C couplings and even allow catalytic one-pot reactions, which show a remarkably enhanced selectivity in the presence of the [Fe4N4] heterocubanes.
- Lichtenberg, Crispin,Garcia Rubio, Inés,Viciu, Liliana,Adelhardt, Mario,Meyer, Karsten,Jeschke, Gunnar,Grützmacher, Hansj?rg
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supporting information
p. 13012 - 13017
(2015/11/02)
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- Direct reduction of 1,2- and 1,6-dibromohexane at silver cathodes in dimethylformamide
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Electrochemical reduction of 1,2-dibromohexane (1) and 1,6-dibromohexane (2) at silver cathodes in dimethylformamide (DMF) containing tetramethylammonium perchlorate (TMAP) has been investigated with the aid of cyclic voltammetry and controlled-potential electrolysis. Cyclic voltammograms for reduction of 1 and 2 both exhibit a single irreversible cathodic peak associated with reduction of carbon-bromine bonds; however, the cathodic peak potential (-0.33 V) for 1 is significantly less negative than that (-1.00 V) for 2, and the peak current for 1 is approximately half of that for 2. Cyclic voltammograms for 0.5-20.0 mM solutions of 1 and 2, separately, show that the parameter Ipc/C?increases as the concentration (C?) decreases; this trend is likely due to a combination of adsorption phenomena and a potential-dependent transfer coefficient (α). Coulometric n values and product distributions arising from bulk electrolyses of 5.0 mM solutions of 1 and 2 depend on the positions of the bromine atoms: (a) for 1, n was 2.13 and 1-hexene was the only product; (b) for 2, n was 2.12 and a mixture of products was obtained [1-hexene (21%), n-hexane (37%), 1,5-hexadiene (22%), 5-hexen-1-ol (9%), and a trace of n-dodecane]. When 2 was electrolyzed in the presence of a proton or deuteron donor (2,2,2-trifluoroethanol or D2O), the n value and the amount of n-hexane increased, whereas 1-hexene and 1,5-hexadiene decreased in yield. We conclude that reduction of 1 follows a concerted mechanism, but that reduction of 2 proceeds via carbanionic intermediates.
- Martin, Erin T.,Strawsine, Lauren M.,Mubarak, Mohammad S.,Peters, Dennis G.
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p. 369 - 376
(2015/11/17)
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- Dual Catalytic Decarboxylative Allylations of α-Amino Acids and Their Divergent Mechanisms
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The room temperature radical decarboxylative allylation of N-protected α-amino acids and esters has been accomplished via a combination of palladium and photoredox catalysis to provide homoallylic amines. Mechanistic investigations revealed that the stability of the α-amino radical, which is formed by decarboxylation, dictates the predominant reaction pathway between competing mechanisms.
- Lang, Simon B.,O'Nele, Kathryn M.,Douglas, Justin T.,Tunge, Jon A.
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supporting information
p. 18589 - 18593
(2016/01/25)
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- Metal-free C-C coupling reactions with tetraguanidino-functionalized pyridines and light
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Herein we report on metal-free C-C coupling reactions mediated by the pyridine derivative 2,3,6,7-tetrakis(tetramethylguanidino)pyridine under the action of visible light. The rate-determining step is the homolytic N-C bond cleavage of the initially formed N-alkyl pyridinium ion upon excitation with visible light. The released alkyl radicals subsequently dimerize to the C-C coupling product. 2,3,6,7-Tetrakis(tetramethylguanidino)pyridine, which is a strong electron donor (E1/2(CH2Cl2)=-0.76 V vs. ferrocene) is oxidized to the dication. For alkyl=benzyl and allyl, relatively high first-order rate constants of 0.23±0.03 and 0.13±0.03 s -1 were determined. Regeneration of neutral 2,3,6,7- tetrakis(tetramethylguanidino)-pyridine by reduction allows to drive the process in a cycle. Light on C-C coupling: Tetraguanidino-substituted pyridines are used for metal-free C-C coupling reactions with visible light (see figure).
- Stang, Simone,Kaifer, Elisabeth,Himmel, Hans-Joerg
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p. 5288 - 5297
(2014/05/20)
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- CATALYTIC DEHYDRATION OF ALCOHOLS AND ETHERS OVER A TERNARY MIXED OXIDE
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A ternary V—Ti—P mixed oxide is shown to catalytically dehydrate 2-methyl-tetrahydrofuran in high conversion to give piperylene, in good yield. Volatile products collected from this reaction contain piperylene in concentrations as high as 80 percent by weight. Dehydration of glycerol to acrolein in high conversion and moderate selectivity is also demonstrated. The catalyst is also shown to dehydrate other alcohols and ether substrates. The catalyst is resistant to deactivation and maintains activity between runs.
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Paragraph 0043; 0046
(2013/03/28)
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- Reversible carbon-carbon bond formation induced by oxidation and reduction at a redox-active cobalt complex
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The electronic structure of the diamagnetic pyridine imine enamide cobalt dinitrogen complex, (iPrPIEA)CoN2 (iPrPIEA = 2-(2,6-iPr2-C6H3N=CMe)-6-(2,6- iPr2-C6H3NC=CH2)C 5H3N), was determined and is best described as a low-spin cobalt(II) complex antiferromagnetically coupled to an imine radical anion. Addition of potential radical sources such as NO, PhSSPh, or Ph3Cl resulted in C-C coupling at the enamide positions to form bimetallic cobalt compounds. Treatment with the smaller halocarbon, PhCH2Cl, again induced C-C coupling to form a bimetallic bis(imino)pyridine cobalt chloride product but also yielded a monomeric cobalt chloride product where the benzyl group added to the enamide carbon. Similar cooperative metal-ligand addition was observed upon treatment of (iPrPIEA)CoN2 with CH 2=CHCH2Br, which resulted in allylation of the enamide carbon. Reduction of Coupled-(iPrPDI)CoCl (Coupled-( iPrPDI)CoCl = [2-(2,6-iPr2-C6H 3N=CMe)-C5H3N-6-(2,6-iPr 2-C6H3N=CCH2-)CoCl]2) with NaBEt3H led to quantitative formation of (iPrPIEA) CoN2, demonstrating the reversibility of the C-C bond forming reactions. The electronic structures of each of the bimetallic cobalt products were also elucidated by a combination of experimental and computational methods.
- Hojilla Atienza, Crisita Carmen,Milsmann, Carsten,Semproni, Scott P.,Turner, Zo? R.,Chirik, Paul J.
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p. 5403 - 5417
(2013/06/05)
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- C-S bond activation of thioethers using (dippe)Pt(NBE)2
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The complex (dippe)Pt(NBE)2 (NBE = norbornene) reacts with thioethers RSR′ upon heating to give C-S oxidative addition products (RSR′ = Ph2S, PhSMe, PhSallyl, MeSallyl, PhSvinyl, PhCH 2SMe, PhSCF3, and dithiane)
- Kundu, Sabuj,Snyder, Benjamin E.R.,Walsh, Aaron P.,Brennessel, William W.,Jones, William D.
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- Transition-metal-promoted chemoselective photoreactions at the cucurbituril rim
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When included in a supramolecular barrel with transition-metal ions as lids, bicyclic azoalkanes undergo phase-selective photolysis to afford new photoproducts and photoproduct distributions. In the presence of the macrocycle cucurbit[7]uril and Ag+ ions, 2,3-diazabicyclo[2.2.1]hept-2-ene forms a ternary host-guest inclusion complex in which the cations are coordinated to the carbonyl rims of the host. Direct photolysis of this ternary complex provides cyclopentene as a new photoproduct.
- Koner, Apurba L.,Marquez, Cesar,Dickman, Michael H.,Nau, Werner M.
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supporting information; experimental part
p. 545 - 548
(2011/03/16)
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- Thermolysis studies on platinacycloalkane complexes
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Thermal decomposition studies on platinacycloalkanes of the type Pt(CH 2)mL2 (where m = 6,7,8,10 and L2 = dppp {1,3-bis(diphenylphosphino)propane}, dppe {1,2-bis(diphenylphosphino) ethane} or L = PPh3, tBu3P) are described. The results reveal that the organic product distribution depends on various factors such as the nature of ligand, the metal system, the mode of decomposition, the ring size and the temperature. Possible mechanistic pathways for the formation of various products are discussed. These platinacycloalkanes can be used as models for metallacycloalkane intermediates in catalytic reactions.
- Zheng, Feng,Sivaramakrishna, Akella,Moss, John R.
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scheme or table
p. 2457 - 2465
(2011/06/26)
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- Electrochemical allylation of aldehydes in a solvent-free cavity cell with a graphite powder cathode
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Mixtures of carbonyl compounds and allyl halides, adsorbed on a graphite powder cathode, were reduced under aqueous anolyte to give high yields of homoallylic alcohols. Catalytic amounts of silver or tetrabutylammonium tetrafluoroborate improved the yields significantly. Inexpensive allyl chloride gave superior results when compared to allyl bromide.
- De Souza, Ronny F. M.,Areias, Madalena C. C.,Bieber, Lothar W.,Navarro, Marcelo
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body text
p. 1118 - 1120
(2011/06/27)
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- Reactivity of tris(allyl)aluminum toward pyridine: Coordination versus carbometalation
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Tris(allyl)aluminum as its THF adduct, [Al(η1-C 3H5)3(THF)] (1), reacted with pyridine either under substitution to give [Al(η1-C3H 5)3(py)] (7) (py = pyridine) or under carbometalation to give N-metalated 2-allyldihydropyridine depending on the solvent. The substituent pattern of the pyridine substrate and the aluminum center's electrophilicity in [Al(η1-C3H5) 3(L)] (L = neutral ligand) influenced the outcome of the reaction. Reactions of one N-metalated dihydropyridine with electrophiles have been studied. A crystalline derivative of tris(allyl)aluminum, [Al(η1- C3H5)3(OPPh3)] (2), and tetrakis(allyl)aluminate in the ion pair [K(15-crown-5)2] [Al(η1-C3H5)4] (4) were characterized by single-crystal X-ray diffraction and shown to contain four-coordinate aluminum centers.
- Lichtenberg, Crispin,Spaniol, Thomas P.,Okuda, Jun
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experimental part
p. 4409 - 4417
(2011/10/18)
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- Vapor-phase catalytic dehydration of terminal diols
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Vapor-phase catalytic reactions of several terminal diols were investigated over several rare earth oxides, such as Sc2O3, Y 2O3, CeO2, Yb2O3, and Lu2O3. Sc2O3 showed selective catalytic activity in the dehydration of terminal diols with long carbon chain, such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol, to produce the corresponding unsaturated alcohols. In the dehydration of 1,6-hexanediol, 5-hexen-1-ol was produced with selectivity over 60 mol%, together with by-products such as ε-caprolactone and oxacycloheptane. In the dehydration of 1,10-decanediol, 9-decen-1-ol was produced with selectivity higher than 70 mol%. In addition to Sc 2O3, heavy rare earth oxides such as Lu2O 3 as well as monoclinic ZrO2 showed moderate selectivity in the dehydration of the terminal diols.
- Abe, Katsutoshi,Ohishi, Yusuke,Okada, Takuto,Yamada, Yasuhiro,Sato, Satoshi
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experimental part
p. 419 - 424
(2012/02/03)
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- Bis(allyl)aluminum cation, tris(allyl)aluminum, and tetrakis(allyl) aluminate: Synthesis, characterization, and reactivity
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Cationic, neutral, and anionic aluminum allyl compounds were synthesized, and their reactivity toward electrophiles was studied. The THF adduct of the previously elusive tris(allyl)aluminum, [Al(η1-C 3H5)3(THF)] (1), was isolated as an oil. Protonolysis of one allyl ligand in 1 using [NEt3H][BPh4] gave the cationic bis(allyl)aluminum, a fragment of the crystalline [Al(η1-C3H5)2(THF) 3-n]+[BPh4]-·(n+1)THF (n = 0, 1) (2). Single-crystal X-ray diffraction of [Al(η1-C 3H5)2(THF)2]+[BPh 4]- (2a) revealed a tetrahedral aluminum center, while [Al(η1-C3H5)2(THF) 3]+[BPh4]- (2b) contains a trigonal-bipyramidal aluminum center with both allyl ligands in the equatorial plane. The tetrakis(allyl)aluminate K+[Al(η1-C 3H5)4]- (3) was also synthesized from the reaction of 1 with K(C3H5). Reactions of the allyl compounds 1-3 with (i) benzophenone, (ii) allyl halides C 3H5X (X = Cl, Br, I), and (iii) halogen X2 (X = Br, I) showed considerable difference with respect to the ionic charge of the aluminum allyl.
- Lichtenberg, Crispin,Robert, Dominique,Spaniol, Thomas P.,Okuda, Jun
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experimental part
p. 5714 - 5721
(2011/02/17)
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- Facile photochemical transformation of alkyl aryl selenides to the corresponding carbonyl compounds by molecular oxygen: Use of selenides as masked carbonyl groups
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(Chemical Equation Presented) Alkyl aryl selenides with and without functional groups on the alkyl group were transformed efficiently into the corresponding carbonyl compounds, particulary primary alkyl aryl selenides in good yields, by a simple photolysis in the presence of air or oxygen. This transformation can be conducted without protection of functional groups. The yield of carbonyl compounds was much affected by the solvent viscosity, reaction temperature, concentration of dissolved oxygen in the solvents, wavelength of light, and structure of the aryl substituents. The present study indicates that aryl selenides can be considered as a masked carbonyl group that can be easily converted to a carbonyl group by very mild reaction conditions even in the presence of various unprotected functional groups. Therefore, this functional group transformation can be used as an important tool in organic synthesis due to its simplicity and mild reaction condition.
- Hyugano, Takeshi,Liu, Suyou,Ouchi, Akihiko
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supporting information; scheme or table
p. 8861 - 8866
(2009/04/05)
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- Mild TiIII- and Mn/ZrIV-catalytic reductive coupling of allylic halides: Efficient synthesis of symmetric terpenes
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(Chemical Equation Presented) Two new efficient methods for the regioselective homocoupling of allylic halides using either catalytic Ti III or the combination Mn/ZrIV catalyst have been developed. The regio- and stereoselectivity of the process proved to increase significantly when the Mn/ZrIV catalyst is used as the coupling reagent and when cyclic substituted allylic halides are used as substrates. The use of Lewis acids such as collidine hydrochloride allowed the quantity of catalyst to be lowered up to 0.05 equiv. We have proved the utility of these protocols with the synthesis of different terpenoids such as (+)-β-onoceradiene (1), (+)-β-onocerine (2), squalene (5), and advanced key-intermediates in the syntheses of (+)-cymbodiacetal (3) and dimeric ent-kauranoids as xindongnin M (4a).
- Barrero, Alejandro F.,Herrador, M. Mar,Quilez Del Moral, Jose F.,Arteaga, Pilar,Arteaga, Jesus F.,Dieguez, Horacio R.,Sanchez, Elena M.
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p. 2988 - 2995
(2007/10/03)
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- Factors controlling photochemical cleavage of the energetically unfavorable Ph-Se bond of alkyl phenyl selenides
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(Chemical Equation Presented) Primary photochemical paths of alkyl phenyl selenides (1) were investigated, and an origin of large deviations in the chemical yields of products obtained by carbon radical reactions induced by photolysis of phenyl selenides was clarified. KrF excimer laser photolyses of n-pentyl phenyl selenide (1a) yielded 1-pentene (2a), n-pentane (3a), n-decane (4a), dipentyl selenide (5a), benzene (6), dipentyl diselenide (7a), and diphenyl diselenide (7) as major photoproducts, with compounds 2a, 3a, 4a, 5a, and 7 formed by pentyl-Se bond cleavage, and 5a, 6, and 7a by Ph-Se bond cleavage. The selectivity of the photoproducts revealed the occurrence of an unexpected amount of Ph-Se bond cleavage (35% in n-hexane at 248 nm) during photolysis. Solvent viscosity, wavelength of light, and the structure of alkyl substituents were the major factors that controlled Ph-Se bond cleavage. The ratio of Ph-Se bond cleavage decreased with increasing solvent viscosity and laser wavelength. The effect of alkyl substituents on the ratio of bond cleavages, Ph-Se/total C-Se, was investigated for five alkyl phenyl selenides; the ratio decreased in the order pentyl > 2-methylallyl > allyl > 1-ethylpropyl > tert-butyl groups. The contribution of Ph-Se bond cleavage is most probably the origin of the large deviations in the yields of radical reactions induced by photolyses of 1, which can be minimized by selecting appropriate solvents and wavelength of light.
- Ouchi, Akihiko,Liu, Suyou,Li, Zhong,Kumar, S. Ajaya,Suzuki, Toshiaki,Hyugano, Takeshi,Kitahara, Haruo
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p. 8700 - 8706
(2008/03/12)
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- Electrocatalytic reduction of organic halides with cobalt bipyridine complexes
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The electrocatalytic reduction of organic halides by the [Cobpy] + complexes coordinationally unsaturated with bpy (at potentials of the first wave) and by the coordinationally saturated [Cobpy2] - complexes (at potentials of the second wave) was observed. The apparent rate constant of the process decreased with an increase in the difference of the reduction potentials of the substrate and catalyst in a large range of the driving force of the process.
- Budnikova,Kafiyatullina,Kargin,Sinyashin
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p. 1702 - 1708
(2007/10/03)
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- Indium-catalyzed allylation of imines with electrochemically assisted catalyst regeneration
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The chemo-electrochemical regeneration of low valent indium(I) reagents for Barbier-type carbon-carbon bond formation processes is described for several C=N double bond systems. The homoallylic amines are obtained in good yields from aniline-derived aldim
- Hilt, Gerhard,Smolko, Konstantin I.,Waloch, Christoph
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p. 1437 - 1439
(2007/10/03)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Allylboration of nitrosobenzene
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The allylboration of nitrosobenzene at -70°C resulted in the formation of N- and O-allyl derivatives of N-phenylhydrazine, which were reduced with the second allylborane molecule to N-allylaniline above 100°C.
- Bubnov, Yurii N.,Pershin, Dmitrii G.,Karionova, Anna L.,Gurskii, Mikhail E.
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p. 202 - 203
(2007/10/03)
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- Detection of reaction selectivity on catalyst libraries by spatially resolved mass spectrometry
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In 2-mm microreactors the activity and selectivity of catalyst library components can be monitored directly by robot-controlled mass spectrometry (the principle setup is shown in the scheme). A maximum of 60 seconds per library component are required.
- Orschel, Matthias,Klein, Jens,Schmidt, Hans-Werner,Maier, Wilhelm F.
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p. 2791 - 2794
(2007/10/03)
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- Stereospecific rhenium catalyzed desulfurization of thiiranes
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Methyltrioxorhenium catalyzes the efficient and stereospecific desulfurization of thiiranes by triphenylphosphine at room temperature, moreso when MTO has been pretreated with hydrogen sulfide, with a Re(v) species as the active form of the catalyst.
- Jacob, Josemon,Espenson, James H.
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p. 1003 - 1004
(2007/10/03)
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- Kinetics and modeling of the thermal reaction of propene at 800 K. Part III. Propene in the presence of small amounts of oxygen
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The thermal reaction of propene was studied around 800 K in the presence of less than 20% O. Initially, the production of H2, CH4, C2H4, C2H6, allene, C3H8, 1,3-butadiene, butenes, 3- and 4-methylcyclopentene, a mixture of 1,4- and 1,5-hexadienes, methylcyclopentane, 4-methylpent-1-ene, and hex-1-ene, was observed along with H2O2, CO, and small quantities of ethanal and CO2. O increases the initial production of H and of most hydrocarbons and, particularly, that of C6 dienes and of cyclenes. A kinetic scheme is proposed in which chains are primarily initiated by a bimolecular step which competes with the second-order initiation of propene pyrolysis. Modeling of the reaction based on the proposed scheme accounts well for the concentration-time profiles.
- Barbe,Baronnet,Martin,Perrin
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p. 503 - 522
(2007/10/03)
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- Organometallic-type reactions in aqueous media. Wurtz-coupling of alkyl halides with manganese/cupric chloride
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Homo-coupling of alkyl halides in aqueous media can be mediated by manganese/cupric chloride to give the dimerisation products in good yield. Cross-coupling can also be controlled to give the desired product.
- Ma, Jihai,Chan, Tak-Hang
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p. 2499 - 2502
(2007/10/03)
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- Detailed kinetics of cyclopentadiene decomposition studied in a shock tube
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Mixtures of cyclopentadiene diluted with argon were used to investigate its decomposition pattern in a single pulse shock tube. The temperatures ranged from 1080 to 1550 K and pressures behind the shock were between 1.7-9.6 atm. The cyclopentadiene concentrations ranged from 0.5 to 2%. Gas-chromatographic analysis was used to determine the product distribution The main products in order of abundance were acetylene, ethylene, methane, allene, propyne, butadiene, propylene, and benzene. The decomposition of cyclopentadiene was simulated with a kinetic scheme containing 44 species and 144 elementary reactions. This was later reduced to only 36 reactions The ring opening process of the cyclopentadienyl radical was found to be the crucial step in the mechanism. 1997 lohn Wiley and Sons, Inc.
- Burcat, Alexander,Dvinyaninov, Michael
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p. 505 - 514
(2007/10/03)
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- Process for the preparation of 1,5-hexadiene
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A one-step process for preparation of 1,5-hexadiene is disclosed. The process comprises contacting magnesium metal with a mixture comprising allyl chloride; one to 15 moles of a dialkyl ether comprising less than seven carbon atoms, per mole of the allyl chloride; and 0.05 to less than two moles of a liquid aromatic hydrocarbon solvent per mole of the dialkyl ether; at a temperature within a range of 5°C. to 200°C.
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- Increasing the heavy atom effect of xenon by adsorption to zeolites: Photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene
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The distribution of products in the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) is determined by the electronic spin state of the cyclohexane-1,4-diyl intermediate. Triplet cyclohexane-1,4-diyl yields 1,5-hexadiene (HD) while singlet cyclohexane-1,4-diyl produces bicyclo[2.2.0]hexane (BCH) as the stable product. Intersystem crossing (ISC) between the two diyls is enhanced by an external heavy atom effect. Direct photolysis (366 nm) of DBO in NaY zeolite containing adsorbed xenon yields a product ratio of 75:25 in favor of the triplet product, HD. This is a 24% increase in triplet product from direct photolysis in n-octane. The dramatic enhancement of ISC may be caused by polarization of the Xe atom in the faujasite cage, thereby allowing it to reach its full potential as a heavy atom perturbant. The 3:1 product ratio derives from complete equilibration of the three triplet electron spin states and the singlet spin state either in the short-lived diazenyl diradical or on a high-energy surface of the 1,4-cyclohexanediyl in which the singlet and triplet states are degenerate. The same 75:25 product ratio is achieved (without Xe adsorbed to the zeolite) when the Na+ cation of the zeolite is exchanged with Cs+ cation. This is not surprising since Xe and Cs+ are isoelectronic and therefore should share similar spin-orbit coupling characteristics. Also reported are the product ratios when photolysis of DBO is carried out in zeolites containing other monovalent cations (Li+, Na+, K+, Rb+).
- Anderson, Mark A.,Grissom, Charles B.
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p. 9552 - 9556
(2007/10/03)
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- Catalytic Conversion of Methane and Propylene to 1-Butene
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The oxidative cross-coupling of methane with propylene has been studied over several catalysts.A material containing 1,9 wt percent Mn and 5 wt percent NaCl on SiO2 was found to be the most effective for this reaction.At 650 deg C, it was possible to attain selectivities to 1-butene and butadiene and 57percent and 8.0percent, respectively, at a propylene conversion of 38percent.Experiments utilizing 13CH4 confirm that methane was indeed involved in the formation of the C4 products.Methyl radicals derived from CH4 and allyl radicals derived from C3D6 were simultaneously detected over the catalysts using a matrix isolation electron spin resonance method.These surface-generated radicals enter the gas phase, where most of the coupling is believed to occur.In addition to the cross-coupling reaction, methyl radicals couple to form ethane, and allyl radicals couple to form 1,5-hexadiene.The latter hydrocarbon reacts extensively back to propylene over the catalysts at 650 deg C.
- Lunsford, Jack H.,Rosynek, Michael P.,Smith, C. Edwin,Xu, Mingting,Yu, Zhenqiang
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p. 12581 - 12587
(2007/10/02)
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- Electrochemical Reduction of 1,6-Dihalohexanes at Carbon Cathodes in Dimethylformamide
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Cyclic voltammograms for the reduction of 1,6-dibromo-, 1,6-diiodo-, 1-bromo-6-chloro-, and 1-chloro-6-iodohexane at glassy carbon electrodes in dimethylformamide containing tetramethylammonium perchlorate exhibit single irreversible waves that correspond to the reductive cleavage of carbon-bromine or carbon-iodine bonds.When large-scale controlled-potential electrolyses of either 1,6-dibromo- or 1,6-diiodohexane are performed at reticulated vitreous carbon, the principal products are n-hexane (30-45percent), 1-hexene (28-34percent), 1,5-hexadiene (6-16percent), and cyclohexane (7percent), with n-dodecane being another significant species obtained from 1,6-diiodohexane.Because a carbon-chlorine bond is not directly reducible, 1-bromo-6-chloro- and 1-chloro-5-iodohexane give rise mainly to 1-chlorohexane (47-64percent), 6-chloro-1-hexene (20-33percent), and 1,12-dichlorododecane (2-25percent).From these product distributions, and with the aid of experiments done in the presence of deuterium-labeled reagents, we conclude that the electrolytic reduction of 1,6-diiodo- and 1-chloro-6-iodohexane involves both radical and carbanion intermediates, whereas only carbanionic pathways are important for electrolyses of 1,6-dibromo- and 1-bromo-6-chlorohexane.
- Mubarak, Mohammad S.,Peters, Dennis G.
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p. 681 - 685
(2007/10/02)
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- - the Wet Chemical Route to a Highly Reactive Titanium Hydride
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The reaction between catalytically prepared magnesium hydride (MgH2*) and in a molar ratio of 1.5:1 in THF yields a highly pyrophoric, X-ray amorphous titanium hydride precipitate with the composition (2).This novel titanium hydride precipitate with the composition (2).This novel titanium hydride has been characterized through hydrolysis and iodolysis, as well as through thermolysis to Ti* and H2 in the solid state and in organic solvents. 2 is slightly soluble in THF and proves itself as an active reagent in a variety of reactions. - Keywords: Magnesium Hydride, Titanium Hydride, McMurry-Reaction, Titanium
- Becker, Beate,Bogdanovic, Borislav
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p. 476 - 482
(2007/10/02)
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- Kinetics and Thermochemistry of the Reversible Combination Reactions of the Allyl and Benzyl Radicals with NO
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The equilibrium kinetics of the reversible additions of NO to the benzyl (C6H5CH2) and allyl (CH2CHCH2) radicals have been studied at atmospheric pressure and over the temperature range 400 1/k-1 and k3/k-3) for the forward and reverse processes: C6H5CH2 + NO + N2 C6H5CH2NO + N2 (reactions 1, -1) and CH2CHCH2 + NO +N2 CH2CHCH2NO + N2 (reactions 3, -3).Thermodynamic treatment of the data by both second law and third law methods of analysis yielded values for the enthalpy and entropy of reaction 1 and 3 which were self consistent and hence the following average values: reaction 1, ΔH0298 = -123 +/- 5 kJ mol-1 (thus ΔH00 = -117 +/- 6 kJ mol-1 and ΔH0f298(C6H5CH2-NO) = 176 +/- 7 kJ mol-1, ΔS0298 = -159 +/- 9 J K-1 mol-1); reaction 3, ΔH0298 = -110 +/- 5 kJ mol-1 (thus ΔH00 = -105 +/- 4 kJ mol-1 and ΔH0f298(CH2CHCH2NO) = 148 +/- 8 kJ mol-1 ΔS0298 = -154 +/- 9 kJ mol-1).The bond dissociation energies for these adducts (= -ΔH0298) are compared and discussed in relation to those for other alkyl nitrosos.Also as part of the study, some measurements of the rate coefficients for the benzyl and ally association reactions with NO (reactions 1 and 3) and their radical self-recombinations (reaction 4, C6H5CH2 + C6H5CH2, and reaction 5, CH2CHCH2 + CH2CHCH2) were made under similar experimental conditions, yielding (in units 1E-11 cm3 molecule-1 s-1): k1(415, 443, 466 K) = 0.91 +/- 0.08, 0.81 +/- 0.05, and 0.62 +/- 0.09, k3(403 K) = 0.71 +/- 0.04, k4(435-519 K) = 2.9 +/- 0.3, k5(403-540 K) = 2.6 +/- 0.2.
- Boyd, A.A.,Noziere, B.,Lesclaux, R.
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p. 10815 - 10823
(2007/10/02)
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- Photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene: Electronic spin determines the distribution of products
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The distribution of products from the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) is determined primarily by the electronic spin state of the cyclohexane-1,4-diyl intermediate. DBO undergoes photolysis by direct irradiation of the N=N chromophore and singlet-sensitization to produce 1,5-hexadiene and bicyclo[2.2.0]hexane with a product ratio of 51:49 in n-octane. Triplet-sensitized photolysis in n-octane produces a product ratio of 70:30 1,5-hexadiene - bicyclo[2.2.0]hexane. The 14N/15N kinetic isotope effect on deazatization is 1.025 for DBO and 1.004 for the more-strained analogue, 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH). The large kinetic isotope effect on DBO photolysis is consistent with rate-limiting C - N bond scission in excited DBO. The amount of hexadiene can be increased by heavy atom solvents that contain bromine and iodine, or by an increase in photolysis intensity, to a maximum of 70:30 hexadiene:bicyclohexane. The product distribution and 15N kinetic isotope effect is insensitive to solvent viscosity, temperature, and magnetic field (up to 7.05 T). The ratio of products can be quantitatively accounted for by fast intersystem crossing (ISC) due to spin - orbit coupling as the boat conformer of the cyclohexane-1,4-diyl is forming. A statistical distribution of 25:75 singlet-triplet cyclohexane-1,4-diyl in the boat geometry is produced by direct and singlet-sensitized photolysis. The singlet cyclohexane-1,4-diyl boat collapses to form bicyclohexane with unit efficiency, whereas the triplet boat is long-lived such that relaxation to the twist-boat occurs. The triplet cyclohexane-1,4-diyl twist-boat is unreactive toward ring closure or bond scission and can only undergo further reaction after ISC to the singlet spin state. In the twist-boat, the singlet cyclohexane-1,4-diyl undergoes ring-opening to 1,5-hexadiene at a rate that is 7/3 faster than it undergoes ring closure to [2.2.0] bicyclohexane. Triplet-sensitized photolysis also produces cyclohexane-1,4-diyl in the boat geometry, but the singlet spin state is not populated because it is 22 kcal/mol higher in energy.
- Anderson, Mark A.,Grissom, Charles B.
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p. 5041 - 5048
(2007/10/02)
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