- Cyclopropenylgold(I) Complexes as Aurated Carbenoids or Quasi-Carbenes
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Highly strained hydrocarbons have always been a research target of high interest. Due to their untypical electronic structure, they show interesting reactivity patterns and can easily be activated by π-coordination to or insertion reactions with metal complexes. Herein we report the synthesis of a range of 3,3-disubstituted cyclopropenylgold(I) complexes. The synthesis of such compounds with a metal, which usually easily activate cyclopropenes is a double-edged sword. We found σ-bound vinylic gold to generally have a strong stabilizing effect in terms of ring strain. The complexes show a strong distortion, preactivating the cyclopropenyls towards the ring-opening mode which thermally generates 1-aurated vinylcarbenes which is reflected by a much faster conversion (Ea of 10 kcal/mol instead of 40 kcal/mol, the reaction proceeds at temperatures as low as ?20 °C instead of 200 °C reported in the literature). In 3-phenyl-cyclopropenyl complexes, these could be trapped intramolecularly to give indenylgold(I) complexes. The properties of these highly strained complexes were investigated, utilizing a range of analytical and experimental procedures and Kohn-Sham density functional theoretic methods. (Figure presented.).
- Mulks, Florian F.,Antoni, Patrick W.,Rominger, Frank,Hashmi, A. Stephen K.
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p. 1810 - 1821
(2018/03/21)
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- The Manganese-Catalyzed Cross-Coupling Reaction and the Influence of Trace Metals
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The substrate scope of the MnCl2-catalyzed cross-coupling between aryl halides and Grignard reagents has been extended to several methyl-substituted aryl iodides by performing the reaction at elevated temperature in a microwave oven. A radical clock experiment revealed the presence of an aryl radical as an intermediate leading to the proposal of an SRN1 pathway for the coupling. The mechanistic information gave rise to suspicion about two previously published cross-coupling reactions catalyzed by manganese(II) salts. As a result, the coupling between aryl halides and organostannanes as well as between aryl halides and amines were revisited. Both reactions were found impossible to reproduce without the addition of small amounts of palladium or copper and are therefore not believed to be catalyzed by manganese.
- Santilli, Carola,Beigbaghlou, Somayyeh Sarvi,Ahlburg, Andreas,Antonacci, Giuseppe,Fristrup, Peter,Norrby, Per-Ola,Madsen, Robert
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p. 5269 - 5274
(2017/09/29)
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- Endo-selective pd-catalyzed silyl methyl heck reaction
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A palladium (Pd)-catalyzed endo-selective Heck reaction of iodomethylsilyl ethers of phenols and aliphatic alkenols has been developed. Mechanistic studies reveal that this silyl methyl Heck reaction operates via a hybrid Pd-radical process and that the silicon atom is crucial for the observed endo selectivity. The obtained allylic silyloxycycles were further oxidized into (Z)-alkenyldiols.
- Parasram, Marvin,Iaroshenko, Viktor O.,Gevorgyan, Vladimir
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supporting information
p. 17926 - 17929
(2015/03/04)
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- Silver-catalyzed ring-opening of cyclopropenes: Preparation of tertiary α-branched allylic amines
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Herein we report a silver-catalyzed ring-opening of cyclopropenes by addition of amines. This transformation is thought to occur via an argentocarbenium intermediate and affords tertiary α-branched allylic amines in good yields and high regioselectivity. The protocol applies to various primary and secondary amines, as well as sterically hindered cyclopropenes. Friedel-Crafts cyclization of the cationic intermediate occurs as a competitive pathway to form methyl-indene.
- Phan, Diem T.H.,Dong
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p. 5726 - 5731
(2013/07/05)
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- Enantiopure C1-symmetric bis(imino)pyridine cobalt complexes for asymmetric alkene hydrogenation
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Enantiopure C1-symmetric bis(imino)pyridine cobalt chloride, methyl, hydride, and cyclometalated complexes have been synthesized and characterized. These complexes are active as catalysts for the enantioselective hydrogenation of geminal-disubstituted olefins.
- Monfette, Sebastien,Turner, Zoe R.,Semproni, Scott P.,Chirik, Paul J.
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p. 4561 - 4564
(2012/04/23)
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- Decomposition, Isomerization, and Ring Expansion in 2-Methylindene: Single-pulse Shock Tube and Modeling Study
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The thermal reactions of 2-methylindene diluted in argon were studied behind reflected shock waves in a 2 in. i.d. pressurized driver single-pulse shock tube over the temperature range 1050-1300 K and overall densities of ～3 × 10-5 mol/cm3. A plethora of products resulting from decompositions, isomerizations, and ring expansion were found in the post shock samples. They were naphthalene as the product of five-membered ring expansion, 1- and 3-methylindene due to isomerizations, and CH4, C2H4 C2H6, C2H 2, benzene, toluene, ethylbenzene, styrene, phenylacetylene, and indene as the result of fragmentation. Very minute yields of some other compounds were also observed. Except for the isomerizations that take place from the reactant as a starting material, the production of all the other products involve free radical reactions. The initiation of the free radical mechanisms in the decomposition of 2-methylindene takes place via ejection of hydrogen atoms from sp3 carbons and dissociation of the methyl group attached to the ring. The H atoms and the methyl radicals initiate a free radical mechanism by abstraction of hydrogen atoms from sp3 carbons and by dissociative recombination of H atom and removal of a methyl group from the ring. In addition to these dissociation reactions there are several breakdown processes that involve cleavage of the five-membered ring to produce both stable and unstable products. The ring expansion process that leads to the production of a high yield of naphthalene takes place only from a methylene indene radical intermediate rather than methylindene itself, whereas isomerizations take place from both the radical intermediates and the molecule. The total decomposition of 2-methylindene in terms of a first-order rate constant is given by: k total = 1013.69exp (-59.4 × 103/RT) s-1. A reaction scheme containing 34 species and 71 elementary reactions was composed and computer simulation was performed over the temperature range 1050-1300 K at 25 K intervals. The agreement between the experimental results and the model prediction for most of the species is satisfactory.
- Lifshitz, Assa,Tamburu, Carmen,Suslensky, Aya,Dubnikova, Faina
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p. 3430 - 3438
(2007/10/03)
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- Upper excited state photochemistry: Solution and gas phase photochemistry and photophysics of 2- and 3-cyclopropylindene
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The cyclopropylcarbinyl radical rearrangement has been used to probe the photochemistry and photophysics of S2 and S1 in 2-cyclopropylindene (2CPI) and 3-cyclopropylindene (3CPI). Studies in solution and the gas phase are described. Population of S2 with 254 nm light excitation in the gas phase produces the anticipated ring expansion products 2,3,3a,8- tetrahydrocyclopenta[a]indene (1, Φ1 = 0.1) and 1,3,3a,8- tetrahydrocyclopenta[a]indene (2, Φ2 = 0.06) from 2CPI and 3CPI, respectively (Scheme 3). Direct excitation into the S2 state (254 nm) of 2CPI in solution also produces compound 1. The efficiency of the solution phase chemistry is a function of excitation wavelength (Φ1 = 0.022 and 0.006 for 254 and 280 nm, respectively). The solution phase excitation spectrum of 2CPI shows an anomalous dependency on monitoring wavelength which is attributed to a conformational equilibrium. The S1 singlet lifetimes of the cyclopropylindenes are quite short (0.39 and 1.0 ns for 2CPI and 3CPI, respectively) relative to the previously measured values for the corresponding methylindenes (2.3 and 13.9 ns). These shortened lifetimes are attributed to cyclopropyl ring opening in S1 with rates of 2.1 x 109 and 9.2 x 108 s-1 for 2CPI and 3CPI, respectively. Semiempirical excited state calculations support descriptions of the S2 and S1 states of alkylindenes as biradicals.
- Waugh, Tim,Morrison, Harry
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p. 3083 - 3092
(2007/10/03)
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- Catalytic cycloisomerization of unsaturated organoiodides
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Catalytic quantities of phenyllithium (PhLi) have been found to initiate novel 5-exo cycloisomerization of a variety of structurally diverse unsaturated organoiodides. The isomerization reaction appears to be a process of broad synthetic utility for the preparation of iodomethyl-substituted five-membered rings. Primary, secondary, tertiary, or aryl iodides tethered to a suitably positioned carbon-carbon π-bond are converted cleanly to their cyclic isomers in good to excellent yield (i.e., 70-90%) by simply allowing a hydrocarbon-MTBE solution of the iodide to stand in the presence of a small quantity of PhLi at an appropriate temperature. The mechanism of the cycloisomerization was found to be substrate dependent: unsaturated aryl and primary alkyl iodides undergo isomerization via a three-step cascades (eqs 1- 3) mediated by two reversible lithium-iodine exchange reactions bracketing an irreversible 5-exo cyclization of an unsaturated organolithium; unsaturated secondary and tertiary alkyl iodides apparently isomerize via a radical- mediated atom transfer process initiated by homolytic fragmentation of the ate-complex generated upon attack of PhLi on the iodine atom of the substrate.
- Bailey, William F.,Carson, Matthew W.
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p. 9960 - 9967
(2007/10/03)
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- Flash vacuum pyrolysis of pyrazoles as an alternative way to study vinylcarbenes
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Flash vacuum pyrolysis (FVP) reactions of 3,5-diphenylpyrazole (1) and 3(5)-methyl-5(3)-phenylpyrazole (2) were carried out. The reaction products expected for nitrogen extrusion were formed through different rearrangements in the vinylcarbene intermediate. Kinetic parameters for nitrogen extrusion from 1 are reported. To show that FVP reactions of pyrazoles are useful to obtain vinylcarbenes, the reactions of other pyrazoles previously studied are also discussed.
- Moyano, Elizabeth L.,Yranzo, Gloria I.,Elguero, Jose
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p. 8188 - 8191
(2007/10/03)
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- Synthesis of o-Dialkenylbenzenes and Indenes Using Heck and Oxypalladation Reactions
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o-Bromostyrenes 2-Br react with various alkenes in the presence of palladium catalysts to give either substituted indene 6 or o-diethenylbenzene derivatives 3, depending on the reaction conditions.Under oxidative conditions the latter can be cyclized to indene derivatives as well. - Keywords: Cross-coupling, Heck; Palladium catalysis; Indanes; Arenes, dialkenyl-N
- Braese, Stefan,Ruemper, Joerg,Voigt, Katharia,Albecq, Stephane,Thurau, Gert,et al.
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p. 671 - 678
(2007/10/03)
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- Chemical reactions in supercritical water -1. pyrolysis of tert.-butylbenzene
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Supercritical water is a powerful solvent and a favourable reaction medium for oxidation of organic material. The role of supercritical water in these processes is not fully understood. The influence of supercritical water on the pyrolysis of tert.-butylbenzene as a model compound was investigated. Experiments were carried out in a flow reactor at pressures between 5 and 25 MPa, at temperatures between 505 and 540°C and residence times between 15 and 55 s. Water, nitrogen, and water-nitrogen mixtures, respectively, were used as reaction media; no significant differences in the product formation rates and distributions were detected. In an experiment with D2O, instead of H2O, it was proved, that deuterium is incorporated in all the product substances in various amounts. Interpretating the results with a reaction model based on a radical mechanism it was made probable that H-D exchange reactions occur with radical intermediates. VCH Verlagsgesellschaft mbH, 1996.
- Kruse, Andrea,Ebert
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- Photochemistry of Alkylindenes in the Gas Phase
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The photochemistry of indene and several alkylindenes has been studied in the gas phase using excitation (254 nm) which populates the S2 state.Reactions observed in the gas phase involve rearrangements different from those observed in solution, as evidenced by the formation of photoproducts explicable in terms of net hydrogen and alkyl migrations.Photodealkylation is also observed at low pressures.In a typical example, gas-phase irradiation of 1-methylindene produces 3-methylindene as the major product, in addition to 2-methylindene, while irradiation in solution leads only to the 2-methyl isomer.The reaction mechanism has been investigated via deuterium-labeling studies, the use of added potential triplet sensitizer and quencher gases, and collisional deactivation by added inert gases.Irradiation of selectively deuterated indenes results in nearly statistical scrambling in the five-membered ring of the indene skeleton, and multiple 1,5 hydrogen or alkyl migrations are proposed.The lack of triplet sensitization, quenching, or enhancement indicates that the photochemistry is derived from a single state.Collisional deactivation results in net quenching of all the photoproducts, with those exclusive to the gas phase quenched at a faster rate than the products observed in solution.Collisional deactivation concomitantly results in an enhancement in fluorescence emission, with little emission observed upon excitation into S2 in the absence of a quencher gas.A reaction scheme is proposed which involves the generation of photoproducts from S2 and S1vib.
- Suarez, Marie L.,Duguid, Robert J.,Morrison, Harry
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p. 6384 - 6391
(2007/10/02)
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- THE GAS-PHASE REACTION OF FREE PHENYLIUM IONS WITH 1,3-BUTADIENE
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Formation of trans-1-phenyl-1,3-butadiene, 3-methylindene, naphthalene and isomeric dihydronaphthalenes, together with polymerization products, from gas-phase phenylium ion attack on 1,3-butadiene, reveals novel reaction pathways ascribable to the carbenic nature of phenylium ion.
- Fornarini, Simonetta,Speranza, Maurizio
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p. 341 - 343
(2007/10/02)
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- Photoinduced Skeletal Rearrangement of Alkylindenes
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The indene phototransposition reaction, a skeletal rearrangement of certain alkylindenes involving an interchange of carbons 1 and 1 (eq 2), is described.The postulated mechnism (Scheme II) involves a closure followed by a sigmatropic shift, opening to an isoindene and 1,5 hydrogen shifts to re-form the indene system.Results of experiments with indenes containing different alkyl groups at C1 and C2 and with 1,1-dimethylindene lend support to the proposed scheme.Experiments with (+)-1,2-dimethylindene indicate that the net migration of C1 to C3,necessary for transposition, occurs with clean inversion at C1 (as would be expected for a ground-state, four-electron, electrocyclic reaction).The reaction derives from the excited singlet state, and partial movement along the initial reaction surface appears to provide an efficient path for S1 radiationless decay.
- Morrison, Harry,Giacherio, David,Palensky, Frederick J.
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p. 1051 - 1058
(2007/10/02)
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- On the Pyrolysis of Cycloalkenoaromatics.
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The products of pyrolysis of tetraline (1), indane (2), 2-methylindane (3), and tetrahydroacenaphthene (4) in mixtures of n-paraffins were analyzed by gas chromatography.Results show that by temperatures between 700 deg C and 800 deg C and residence times of about 0.2 s more than 80percent of the reaction products are aromatics.The main pathway of the decomposition of 1, 2, and 4 is the dehydrogenation in direction to the corresponding complete aromatic systems or indene respectively.In the case of 3 we found less than 10percent of 2-methylindene but more than 40percent of skeleton isomeres.The formation of skeleton isomeres can be explained by the concept of radical rearrangements.
- Guenschel, H.,Zimmermann, G.,Lorenz, R.,Ondruschka, B.,Nowak, S.
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p. 607 - 615
(2007/10/02)
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- Radical Pathways of Coal Dissolution in Hydrogen Donor Media. 2. β Scission and 1,2 Aryl Migration Reactions of Radicals Derived from Methylindans and Tetralin at 327-627 deg C
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The 1,2-aryl migration and fragmentation reactions of 1-indanylmethyl (1), 2-tetralyl (2), 2-indanylmethyl (3), 1-tetralyl (4), 2-methyl-1-indanyl (5), and 1-methyl-2-indanyl (6) radicals were studied by flash vacuum pyrolysis of the tert-butyl perester precursors at 327-627 deg C and 10-2 torr.Radicals 1 and 2 are interconverted via 1,2 aryl migration which is readily reversible at all temperatures.This equilibrium is depleted by β scission of 1 and recyclization to 4 and by β scission of 2 followed by recyclization to 2 or 3 in modest yields.The reverse neophyle-like rearrangement of 2 to 1 occurs with a lower activation barrier than β-scission of 1 to form a 2-(o-vinylphenyl)ethyl radical.Enthalpies, entropies, and free energies of reactions were calculated for the above reactions from group additivity parameters, and activation energies were estimated from values reported for simple alkyl radicals.It is shown that the β scission of 4 and recyclization to 1 is important only at very high temperatures (>500 deg C) as a mechanism for the isomerization of tetralin and related hydroaromatic structures to alkylindans and that the reverse neophyl-like rearrangement of 2 to 1 is the favored pathway for isomerizations observed during dissolution of coal in hydroaromatic media at elevated temperatures.
- Franz, James A.,Camaioni, Donald M.
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p. 5247 - 5255
(2007/10/02)
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