- Proton Order-Disorder Phenomena in a Hydrogen-Bonded Rhodium-η5-Semiquinone Complex: A Possible Dielectric Response Mechanism
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A newly synthesized one-dimensional (1D) hydrogen-bonded (H-bonded) rhodium(II)-η5-semiquinone complex, [CpRh(η5-p-HSQ-Me4)]PF6 ([1]PF6; Cp=1,2,3,4,5-pentamethylcyclopentadienyl; HSQ=semiquinone) exhi
- Mitsumi, Minoru,Ezaki, Kazunari,Komatsu, Yuuki,Toriumi, Koshiro,Miyatou, Tatsuya,Mizuno, Motohiro,Azuma, Nobuaki,Miyazaki, Yuji,Nakano, Motohiro,Kitagawa, Yasutaka,Hanashima, Takayasu,Kiyanagi, Ryoji,Ohhara, Takashi,Nakasuji, Kazuhiro
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Read Online
- Preparation, crystal structure and photochemistry of a novel molecular compound between duroquinone and durene
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A 2:1 crystalline molecular compound (3) of duroquinone (1) and durene (2) has been prepared in two ways of evaporating the solution and solidifying the melt. The crystal structure of 3 was determined by X-ray crystallography. Irradiation of 3 caused the intermolecular hydrogen abstraction reaction, which was specific in the solid state, to give durohydroquinone (4) and a photoadduct (5).
- Koshima, Hideko,Yao, Xinkan,Wang, Honggen,Wang, Ruji,Matsuura, Teruo
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Read Online
- Understanding the binding properties of phosphorylated glycoluril-derived molecular tweezers and selective nanomolar binding of natural polyamines in aqueous solution
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A modular synthetic platform for the construction of flexible glycoluril-derived molecular tweezers was developed. The binding properties of four exemplary supramolecular hosts obtained via this approach towards 16 organic amines were investigated by means of 1H NMR titration. In this work, we compare the Ka values obtained this way with those of three structurally related molecular tweezers and provide a computational approach towards an explanation of the observed behavior of those novel hosts. The results showcase that certain structural modifications lead to very potent and selective binders of natural polyamines, with observed binding of spermine below 10 nM. This journal is
- Heilmann, Michael,Knezevic, Melina,Piccini, Giovannimaria,Tiefenbacher, Konrad
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supporting information
p. 3628 - 3633
(2021/05/04)
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- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
- Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
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p. 13655 - 13664
(2019/10/28)
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- Reactivity of iPrPCPIrH4 with para-benzoquinones
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In the interest of investigating new hydrogen acceptors for pincer–iridium catalyzed dehydrogenations with the ability to be catalytically recycled, a series of para-benzoquinones have been reacted with iPrPCPIrH4 in various solvents and conditions. Preliminary results indicate that a wide range of quinones are capable of dehydrogenating iPrPCPIrH4, and that several turn-overs in alcohol dehydrogenation by iPrPCPIr are possible at room temperature using benzoquinone acceptors. However, strong acceptor–catalyst interactions are inhibitory toward catalysis when the acceptor is used in excess. A new class of (bis)-η2 pi-adducts, formed between iPrPCPIr and benzoquinones, nicknamed “barber-chairs”, has been identified and 3 examples have been characterized.
- Wilklow-Marnell, Miles,Brennessel, William W.,Jones, William D.
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p. 209 - 214
(2017/11/24)
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- Pd0-PyPPh2@porous organic polymer: Efficient heterogeneous nanoparticle catalyst for dehydrogenation of 3-methyl-2-cyclohexen-1-one without extra oxidants and hydrogen acceptors
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In this contribution, we have developed an efficient and recyclable porous organic polymer (POP) supported Pd nanoparticle catalyst (Pd°-PyPPh2@POP) for dehydrogenation of 3-methyl-2-cyclohexen-1-one. This heterogeneous catalytic system represents a totally clean process without using any extra oxidant and hydrogen acceptors. The SEM-EDS mapping images of the Pd°-PyPPh2@POP catalyst reveal the highly uniformly dispersed character of C, Pd, P and N elements. The coordination bonds between Pd nanoparticle and exposed P atom as well as N atom on the surface of PyPPh2@POP polymer are confirmed by means of solid-state 31P NMR and XPS. Importantly, both P atom and pyridyl ring on the PyPPh2@POP polymer are themselves used as solid base over the Pd°-PyPPh2@POP catalyst, leading to a catalytic conversion of 88.2% even without the employment of inorganic base additives (K2CO3). Our results have provided a strategy for designing highly active bifunctional POP supported nanoparticle catalysts.
- Chen, Xingkun,Wang, Wenlong,Zhu, Hejun,Yang, Wenshao,Ding, Yunjie
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- Method for preparing hydrocarbyl phenol by catalytic conversion of phenolic compound in presence of molybdenum-based catalyst
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The invention discloses a method for preparing hydrocarbyl phenol by catalytic conversion of a phenolic compound in the presence of a molybdenum-based catalyst. The method comprises mixing a phenoliccompound, a molybdenum-based catalyst and a reaction solvent, adding the mixture into a sealed reactor, feeding gas into the reactor, heating the mixture to 150-350 DEG C, carrying out stirring for areaction for 0.5-2h, then filtering to remove a solid catalyst and carrying out rotary evaporateion to obtain a liquid product. The phenolic compound has a wide source, a cost is low, product alkyl phenol selectivity is high, an added value is high, alcohol or an alcohol-water mixture is used as a reaction solvent, environmental friendliness is realized, pollution is avoided, any inorganic acids and alkalis are avoided in the reaction process, the common environmental pollution problems in the biomass processing technology are solved, the reaction conditions are mild, the process can be carried out at a low temperature, high-efficiency conversion of the reactants can be realized without consuming hydrogen gas and the method is suitable for large-scale industrial trial production.
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Paragraph 0043-0044; 0070
(2018/04/02)
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- Reduction of quinones by NADH catalyzed by organoiridium complexes
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One electron at a time: Half-sandwich organometallic cyclopentadienyl- IrIII complexes containing N,N-chelated ligands can catalyze the reduction of quinones (Q), such as vitaminK3, to semiquinones (Q .-) by coenzyme NADH (see picture). DFT calculations suggest that the mechanism involves hydride transfer followed by two one-electron transfers and the unusual IrII oxidation state as a key transient intermediate. Copyright
- Liu, Zhe,Deeth, Robert J.,Butler, Jennifer S.,Habtemariam, Abraha,Newton, Mark E.,Sadler, Peter J.
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supporting information
p. 4194 - 4197
(2013/05/21)
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- The influence of lateral apolar substituents on the mesomorphic behaviour of tetracatenar liquid crystals
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Several series of new tetracatenar mesogens consisting of a five-ring aromatic core and bearing one or more apolar lateral substituents in the central benzene ring of the molecule have been synthesized and their mesomorphism is characterized by polarizati
- Smirnova,Zharnikova,Donnio,Brus
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experimental part
p. 1331 - 1340
(2011/02/27)
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- Enantiocomplementary chemoenzymatic asymmetric synthesis of (R)- And (S)-chromanemethanol
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A non-lipase-based, enantiocomplementary chemoenzymatic route towards enantiopure (R)- and (S)-chromane-methanol (12), which are the key building blocks for the synthesis of stereoisomerically pure α-tocopherols, has been achieved by the biocatalytic reso
- Fuchs, Michael,Simeo, Yolanda,Ueberbacher, Barbara T.,Mautner, Barbara,Netscher, Thomas,Faber, Kurt
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experimental part
p. 833 - 840
(2009/07/05)
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- Intramolecular hydroarylation of alkynes catalyzed by platinum or gold: Mechanism and endo selectivity
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The cyclization of differently substituted aryl alkynes with Pt II or AuI catalysts proceeds by endo-dig pathways. When AgI was used to generate reactive cationic AuI catalysts, 2H-chromenes dimerize to form cyclobutane derivatives by a Ag I-catalyzed process. A DFT study on the cycliza-tion mechanism shows a kinetic and thermodynamic preference for 6-endodig versus 5-exo-dig cyclizations in PtII-catalyzed processes. Calculations indicate that although Friedel-Crafts and the cyclopropanation processes via metal cyclopropyl carbenes show very similar activation energies, platinum cyclopropyl carbenes are the stationary points with the lowest energy.
- Nevado, Cristina,Echavarren, Antonio M.
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p. 3155 - 3164
(2007/10/03)
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- Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution
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The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (.QH/Q.-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the .QH/Q.- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.
- Goerner, Helmut
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p. 440 - 448
(2007/10/03)
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- Solid-State Photochemistry of the Mixed Crystals between Benzoquinones and Polymethylbenzenes
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Nine mixed crystals combined 1,4-benzoquinone (1), 2,5-xyloquinone (2) and duroquinone (3) with durene (a), pentamethylbenzene (b) and hexamethylbenzene (c) were prepared by a melting-resolidifying process and characterized by powder X-ray diffractometry, DSC and IR.Only the mixed crystal of 3 and a formed a 2:1 novel molecular crystal (4); other eight mixed crystals were simple polycrystalline mixtures of the two components.Irradiation of the molecular crystal 4 (3/a) and the mixed crystals 1/a, 1/b and 3/b caused intermolecular hydrogen abstraction to give hydroquinones and in some cases adducts.Product selectivities in the solid state were different from those in solution.Correlation between the crystal structure and the reactivity of 4 is discussed.
- Koshima, Hideko,Chisaka, Yosuke,Wang, Yang,Yao, Xinkan,Wang, Honggen,et al.
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p. 13617 - 13630
(2007/10/02)
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- Ditopic thiacyclophanes containing the S(CH2)2X(CH2)2S (X = O, S) linkage. Synthesis and structures of 2,5,8,17,20,23-hexathia(1,2)(4,5)cyclophane and 5,20-dioxa-2,8,17,23-tetrathia(1,3)(4,6)-2,5-bis(ethoxy)cyclophane
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The Cs+/DMF mediated reactions of 1,2,4,5-tetra(bromomethyl)benzene and 1,2,4,5-tetra(bromomethyl)-3,6-bis(ethoxy)benzene with dithiols HSCH2CH2XCH2CH2SH (X = S, O) were explored in order to ascertain the effect of structural variations on the regioselectivity of double ring-closure. Although a structure with bis(ortho) geometry was the target molecule, the major products are those with a bis(meta) structure. Two crystal structures, one with a bis(ortho) structure, 2,5,8,17,20,23-hexathia(1,2)(4,5)cyclophane, 1, and one with a bis(meta) structure, 5,20-dioxa-2,8,17,23-tetrathia(1,3)(4,6)-2,5-bis(ethoxy)cyclophane, 7, are reported. 1 crystallized in the triclinic space group P with a = 8.583(3), b = 11.806(3), c = 5.448(2) Angstroem, α = 97.18(2), β = 107.18(2), γ = 99.40(2) deg, V = 511.6(6) Angstroem3, and Z = 1. The structure refined to R = 6.48percent and Rw = 7.13percent for 1020 reflections with F02 > 3?(F02). 7 crystallized in the triclinic space group P with a = 9.568(2), b = 9.577(2), c = 8.312(2) Angstroem, α = 113.53(2), β = 94.58(2), γ = 114.94(2) deg, V = 604.3(7) Angstroem3, and Z = 1. The structure refined to R = 3.86percent and Rw = 4.20percent for 1129 reflections with F02 > 3?(F02). Both compounds sit on a crystallographic centre of symmetry and have the thioether linkages oriented on opposite sides of the central aromatic ring.
- Loeb, Stephen J.,Shimizu, George K. H.
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p. 1728 - 1734
(2007/10/02)
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- Oxidative Dealkylation of Hydroquinone Ethers with Nitrogen Dioxide in the Convenient Preparation of Quinones
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Various Hydroquinone dialkyl ethers (R2Q) are effectively converted by nitrogen dioxide into the corresponding quinone (Q) and alkyl nitrite (RONO) in dichloromethane at room temperature or below.The preparative procedure for the isolation of crystalline quinones in quantitative yield merely involves the convenient removal of the low boiling solvent in vacuo.Isotopic labelling studies demonstrate that the oxidative dealkylation proceeds via alkoxy scission of the labile cation radical (R2Q-cation radical) formed via the oxidation of the hydroquinone ether by nitrogen dioxide ( as the disproportionated ion pair NO+NO3-).The electron-transfer mechanism is confirmed by the spectral observation of R2Q-cation radical (identified by the isolation of the crystalline salt R2Q-cation radical-SbCl6-) and its rapid conversion into quinone and alkyl nitrite by combination with nitrate (NO3-) and nitric oxide (NO).
- Rathore, Rajendra,Bosch, Eric,Kochi, Jay K.
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p. 1157 - 1166
(2007/10/02)
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- Amino-, Aminophenoxy- and Aminobenzoyl Derivatives of Durene
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Various durene derivatives have been prepared including 4-hydroxy-, 4-aryloxy- and 4-aroyl- derivatives of 2,3,5,6-tetramethylaniline and bis(4-aminophenoxy)- and bis-(4-aminobenzoyl)durene.
- Barclay, George G.,Candlin, Jack P.,Lawne, William,Pauson, Peter L.
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p. 2169 - 2187
(2007/10/02)
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- Total synthesis of naturally occurring α-tocopherol. Assymetric alkylation and asymmetric epoxidation as means to introduce (R)-configuration at C(2) of the chroman moiety
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Based on the reductive, stereospecific ring closure of (2R,4'R,8'R)-α-'Tocopherylquinone' or corresponding analogues with a short, functionalized side chain (B, Scheme 1) to 1 resp. the chroman system of 1 (C), two different approaches for the introduction of the required tertiary methyl-substituted alcohol structure in the side chain of the aromatic precursors (A, Scheme 1) were developed. The first approach uses asymmetric alkylation in three different versions featuring a) diastereoselective steering with chiral auxiliaries I-IV (Scheme 2) attached as esters to α-keto acids, b) intermediate transfer of chirality in an ester enolate (from 18, Scheme 4) derived from an optically active α-hydroxyacid, c) enantioselective alkylation of phytenal (20) and subsequent ring closure with chirality transfer (Schemes 5-7). The second approach is based on the asymmetric epoxidation of β-metallylalcohol (Sharpless epoxidation), the corresponding epoxyalcohol being converted in situ to the (S)- or (R)-chlorodiol (S)- and (R)-29, respectively, for isolation (Schemes 8 and 9). Nucleophilic epoxide opening with a (3R,7R)-3,7,11-trimethyldodecyl (C15**) and an ArCH2 unit in appropriate sequence is used to assemble the C-framework of the target molecule via corresponding epoxide intermediates from either chlorodiol. Combined with the use of the methoxymethyl-ether function for protection of the hydroquinone system, the epoxide approach provides a short route to 1 (Scheme 10).
- Hubscher,Barner
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p. 1068 - 1086
(2007/10/02)
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- Repetitive Diels-Alder Reactions for the Growth of Linear Polyacenequinoid Derivatives
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Starting from 2,3,5,6-tetramethylidene-7-oxanorbornane, repetitive quinone Diels-Alder/oxidation reactions produced a series of epoxypolyacenequinones with up to eleven linearly annulated rings.Epoxide ring opening-oxidation gave polyacenequinones with se
- Thomas, Alan D.,Miller, Larry L.
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p. 4160 - 4169
(2007/10/02)
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- Clusters 2- as Novel Catalysts in Organic Reductions
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The cluster 2- catalyzed the redudtions of nitro compounds, quinones and N-oxide compounds to amines, hydroquinones, and deoxygenated compounds, respectively, in the presence of thiols in CH3CN solution.The reaction mechanism was also investigated by electron spin resonance spectroscopy, and it was concluded that these reactions proceed via one-electron transfer from the cluster to the substrates.Keywords - ferredoxin; cluster; electron transfer; iron-sulfur protein; reduction; superoxidized cluster
- Itoh, Takashi,Nagano, Tetsuo,Hirobe, Masaaki
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p. 2013 - 2017
(2007/10/02)
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- Solid-state Reactivity of Crystalline Hydroquinones with Quinone Vapour; Crystal Structures of 2,5-Dimethylhydroquinone and 2,3,5,6-Tetramethylhydroquinone
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Use of single crystals of 2,5-dimethylhydroquinone and 2,3,5,6-tetramethylhydroquinone in studies of their reactions with 1,4-benzoquionone vapour has been found to give information not obtainable from previous studies of reaction powders.Structures of the two crystalline hydroquinones were determined by X-ray analysis.Crystals of the dimethylhydroquinone are orthorhombic, a = 13.256(2), b = 4.5609(8), c = 11.977(2) Angstroem, Z = 4, space group Pca21; and the structure has been refined to an R factor of 0.0335 on 704 non-zero reflections.Molecules have an anti-arrangement of hydroxy groups and form hydrogen-bonded chains with a motif like that of γ-hydroquinone.Slight differences in the geometry of the hydrogen bonding at the two ends of the molecule are responsible for the polar nature of the structure.Results of both the test for second harmonic generation and a pyroelectric test for non-centrosymmetry are positive with these crystals.The pyroelectric test applied to crystals in which twinning is known to occur shows clear evidence of such twinning and might be useful in certain other cases as a test for twinning.Crystals of the tetramethylhydroquinone are monoclinic, a = 8.317(3), b = 4.728(2), c = 13.514(5) Angstroem, β = 125.85(2) deg, Z = 2, space group P21/c; the structure has been refined to an R factor of 0.0367 on 813 non-zero reflections.Microscopic studies show evidence that the reaction is initiated at nucleation sites on reactive faces and that both quinone and hydroquinone molecules migrate during reaction.The faster reaction occurs at those faces where hydroxy groups emerge.It has been found that the shapes of the OH stretching regions of the Fourier transform i.r. spectra of these and other hydroquinones as well as the positions of the absorption maxima provide structural evidence useful for distinguishing among these compounds, and can be correlated with their crystal structures.
- Pennington, W. T.,Patil, A. O.,Paul, I. C.,Curtin, D. Y.
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p. 557 - 564
(2007/10/02)
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- ON THE 1,6-ADDITION OF ALKYLALUMINIUM COMPOUNDS TO para-QUINONES
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Ethyl, n-butyl and i-butylaluminium dichlorides undergo 1,6-addition to a conjugated bond system O=C-C=C-C=O of para-quinones.Methylaluminium dichloride is inactive in this addition, and triethylaluminium gives low yields.The reactivities of the quinones vary with their electron affinities, and the highest yields of 1,6-addition are obtained in the reactions of chlorine derivatives of 1,4-benzoquinone.The results are discussed in terms of a radical mechanism involving a homolytic cleavage of the Al-C bond in the donor-acceptor complex formed between the reactants followed by combination of alkyl radicals and aluminium derivatives of semiquinone within a cage.The stable donor-acceptor complexes and aluminium derivative of semiquinone were isolated and characterized from the reactions of aluminium trichloride with 2,3,5,6-tetramethyl-1,4-benzoquinone and 2,3,5,6-tetrachloro-1,4-benzoquinone, respectively.
- Florjanczyk, Zbigniew,Szymanska-Zachara, Ewa
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p. 127 - 138
(2007/10/02)
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- Photochemical Dediazoniation of Arene Diazonium Salts Catalyzed by Quinones
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The rate constants of the hydrogen abstraction of triplet-excited p-benzoquinone (BQ), duroquinone (DQ), p-chlorophenyl-p-benzoquinone (PQ) and 2,5-di(p-chlorophenyl)-p-benzoquinone (P2Q) from n-heptane and acetonitrile are determined by laser flash photolysis as well as the rate constants for the reactions with oxygen. The semiquinones formed are in equilibrium with their respective semiquinone anions; at pH 3 and pH 7, respectively, it was possible in acetonitrile/water solution to determine separately the rate constants for their disproportionation affording quinones and hydroquinones and the rate constants for electron transfer to p-chlorbenzene diazonium tetrafluoroborate.It comes out that the electron transfer to the diazonium compound only competes favorably with the disproportionation in the case of the semiquinone anions.
- Becker, H. G. O.,Jirkovsky, J.,Fojtik, A.,Kleinschmidt, J.
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p. 505 - 511
(2007/10/02)
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