- Photocatalytic Oxygenation Reactions with a Cobalt Porphyrin Complex Using Water as an Oxygen Source and Dioxygen as an Oxidant
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Photocatalytic oxygenation of hexamethylbenzene occurs under visible-light irradiation of an O2-saturated acetonitrile solution containing a cobalt porphyrin complex CoII(TPP) (TPP2- = tetraphenylporphyrin dianion), water, and triflic acid (HOTf) via a one-photon-two-electron process, affording pentamethylbenzyl alcohol and hydrogen peroxide as products with a turnover number of >6000; in this reaction, H2O and O2 were used as an oxygen source and a two-electron oxidant, respectively. The photocatalytic mechanism was clarified by means of electron paramagnetic resonance, time-resolved fluorescence, and transient absorption measurements as well as 18O-labeling experiments with H218O and 18O2. To the best of our knowledge, we report the first example of efficient photocatalytic oxygenation of an organic substrate by a metal complex using H2O as an oxygen source and O2 as a two-electron oxidant.
- Hong, Young Hyun,Han, Ji Won,Jung, Jieun,Nakagawa, Tatsuo,Lee, Yong-Min,Nam, Wonwoo,Fukuzumi, Shunichi
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supporting information
p. 9155 - 9159
(2019/06/21)
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- Chlorination of benzylic and allylic alcohols with trimethylsilyl chloride enhanced by natural sodium montmorillonite
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A new and practical method for the efficient chlorination of tertiary, secondary, and primary benzylic and allylic alcohols is described. The method is characterized by the formation of hydrogen chloride from trimethylsilyl chloride and trace water, the formation of a carbenium ion through the protonation of an alcohol and subsequent dehydration, and the chlorination of the carbenium ion. During the process, sodium ion-exchanged montmorillonite plays a crucial role in capturing the generated hydrogen chloride, stabilizing the carbenium intermediate as well as promoting the chlorination.
- Tandiary, Michael Andreas,Masui, Yoichi,Onaka, Makoto
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p. 2639 - 2643
(2015/01/09)
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- Bis- N -heterocyclic carbene palladium(IV) tetrachloride complexes: Synthesis, reactivity, and mechanisms of direct chlorinations and oxidations of organic substrates
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This Article describes the preparation and isolation of novel octahedral CH2-bridged bis-(N-heterocyclic carbene)palladium(IV) tetrachlorides of the general formula LPdIVCl4 [L = (NHC)CH 2(NHC)] from LPdIICl2 and Cl2. In intermolecular, nonchelation-controlled transformations LPdIVCl 4 reacted with alkenes and alkynes to 1,2-dichlorination adducts. Aromatic, benzylic, and aliphatic C-H bonds were converted into C-Cl bonds. Detailed mechanistic investigations in the dichlorinations of alkenes were conducted on the 18VE PdIV complex. Positive solvent effects as well as kinetic measurements probing the impact of cyclohexene and chloride concentrations on the rate of alkene chlorination support a PdIV-Cl ionization in the first step. Product stereochemistry and product distributions from various alkenes also support Cl+-transfer from the pentacoordinated PdIV-intermediate LPdIVCl 3+ to olefins. 1-Hexene/3-hexene competition experiments rule out both the formation of π-complexes along the reaction coordinate as well as in situ generated Cl2 from a reductive elimination process. Instead, a ligand-mediated direct Cl+-transfer from LPd IVCl3+ to the π-system is likely to occur. Similarly, C-H bond chlorinations proceed via an electrophilic process with in situ formed LPdIVCl3+. The presence of a large excess of added Cl- slows cyclohexene chlorination while the presence of stoichiometric amounts of chloride accelerates both PdIV-Cl ionization and Cl+-transfer from LPdIVCl3 +. 1H NMR titrations, T1 relaxation time measurements, binding isotherms, and Job plot analysis point to the formation of a trifurcated Cl-...H-C bond in the NHC-ligand periphery as a supramolecular cause for the accelerated chemical events involving the metal center.
- McCall, A. Scott,Wang, Hongwang,Desper, John M.,Kraft, Stefan
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supporting information; experimental part
p. 1832 - 1848
(2011/04/15)
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- Effective and versatile functionalisation of hexamethylbenzene using N-F reagents
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Effective direct introduction of alkoxy, amido, azido or halogeno functional groups on the benzylic position in hexamethyl-benzene was mediated by the N-F reagents F-TEDA-BF4, NFTh, NFSi or FP-B800 in the presence of alcohols, carboxylic acids, cyanides or trimethylsilyl derivatives as sources of an external nucleophile.
- Stavber,Kralj,Zupan
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p. 1152 - 1154
(2007/10/03)
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- Electron Paramagnetic Resonance Spectra of the Radical Cations of Some Benzocyclobutenes, Benzocyclopentenes and Benzocyclohexenes
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1,2,4,5-Tetrahydrobenzodicyclobutene, 1,2,3,5,6,7-hexahydrobenzodicyclopentene and 1,2,3,4,6,7,8,9-octahydrobenzodicyclohexene, and their dimethyl derivatives, and tetramethylbenzocyclo-butene, -pentene and -hexene have been prepared.All except the first compound have been oxidised to their corresponding radical cations, and the EPR spectra have been analysed by assigning McConnell-type Q-values to the substituents in the benzene ring.It is suggested that the ordering of the orbital energy levels (ΨA above ΨS) in 3,6-dimethylbenzobiscyclobutene and -pentene is a manifestation of the Mills-Nixon effect, and results from rehybridisation of the strained molecular framework.In the radical cations of 5,10-dimethyl-1,2,3,4,6,7,8,9-octahydrobenzodicyclohexene and 5,6,7,8-tetramethyl-1,2,3,4-tetrahydrobenzocyclohexene the total unpaired electron density, as implied by the McConnell type of relationship, appears to be less than unity.Various possible causes of this are examined.
- Avila, David V.,Davies, Alwyn G.,Li, Elizabeth R.,Ng, Kai M.
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p. 355 - 362
(2007/10/02)
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- Synthesis and Reactions of 5-Methylenebicyclohex-2-ene Derivatives from Hexamethyl(Dewar benzene)
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Treatment of hexamethyl(Dewar benzene) (HMDB) with tert-butyl hypochlorite provides a rearranged chlorinated derivative, exo-6-chloro-1,2,3,4,6-pentamethyl-5-methylenebicyclohex-2-ene (1).Thermal rearrangement of 1 gives pentamethylbenzyl chloride (4); the activation energy decreases in more polar solvents, suggesting an ionic intermediate during the chloride migration and/or ring opening.The intermediate is postulated to be a delocalized carbocation that can be intercepted by nucleophiles to give substitution products.Treatment of 1 with NaOCH3 in methanol gives two isomeric methoxide substitution products, 2 and 3, in 60:40 ratio.The structure of 2 involves the same skeletal structure and retention of stereochemistry relative to 1; the structure of 3 indicates neighboring group participation of the transannular ? bond.The rate law for the formation of 2 and 3 is first order in 1 and independent of NaOCH3 concentration.A common ion rate depression is observed, added chloride ion causing a decreased rate of formation of both 2 and 3 equally, indicating reversible ionization to a common delocalized carbocation.Thermolysis of 2 gives hexamethylbenzene plus formaldehyde; NMR spectra provide evidence for a methylenecyclohexadiene intermediate, indicating that the ring opening precedes loss of formaldehyde.Inclusion of basic alumina in the thermolysis of 2 diverts the reaction to formation of pentamethylbenzyl methyl ether (5).Thermolysis of 3 gives a complex mixture of products, including 5.
- Wamser, Carl C.,Ngo, David D.,Rodriguez, Michael J.,Shama, Sami A.,Tran, Thuan L.
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p. 2162 - 2168
(2007/10/02)
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- Direct Observation of the Kinetic Acidities of Transient Aromatic Cation Radicals. The Mechanism of Electrophilic Side-Chain Nitration of the Methylbenzenes
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The transient cation radicals ArCH3(.+) are spontaneously generated by the 532-nm excitation of the charge-transfer complexes with a 10-ns laser pulse.The decay kinetics of the spectral transients in the presence of added base establish the kinetic acidities (kH) for various methylarene cation radicals with different pyridines and trinitromethide.Such a proton transfer from ArCH3(.+) proceeds with a deuterium kinetic isotope effect of kH/kD ca. 3.Side-chain nitration of hexamethylbenzene (HMB) is shown to proceed in high yields via the intimate triad of reactive fragments II, , that is produced upon the charge-transfer excitation.The subsequent annihilation of the reactive triad II occurs via a rapid succession of bimolecular steps involving either (i) the initial ion-pair collapse of by proton transfer, as shown in Scheme VI, or (ii) the alternative sequence with the initial ion-radical collapse of by homolytic coupling, as shown in Scheme VII.The marked variations of kH/kD with solvent polarity and added innocuous salt (Bu4N(+)ClO4(-)), as reflected in ion-pair separation and the "special" salt effect, serve to effectively distinguish these pathways.The direct bearing of Schemes VI and VII on the mechanism of the thermal (adiabatic) nitration of methylarene side chains with nitric acid is delineated.
- Masnovi, J. M.,Sankararaman, S.,Kochi, J. K.
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p. 2263 - 2276
(2007/10/02)
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- Electron Transfer Reactions in Organic Chemistry. VII. Oxidative Acetoxylation of Aromatic Compounds by Tungsten Hexachloride
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Tungsten hexachloride, a high-potential oxidant, causes fast oxidative acetoxylation of ring and/or α positions of aromatic compounds, even as difficalty oxidizable ones as mesitylene and p-xylene.Chlorination is a completing reaction which cannnot be completely suppressed.The acetoxylation process in all likelihood proceeds via an electron transfer mechanism, involving initial formation of the radical cation of the substrate.
- Eberson, Lennart,Joensson, Lennart,Saenneskog, Owe
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p. 113 - 122
(2007/10/02)
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- FLUORATION ANODIQUE DANS LE CHLORURE DE METHYLENE (POLYMETHYL- et VINYLBENZENES)
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The anodic oxidation of polymethyl and of ethylenic derivatives of benzene in CH2Cl2/Et4NF, 3HF or Et3N, 3HF has been studied.The fluoro complounds are obtained in good yields.With the ethylenic compounds cis-addition products predominate.
- Bensadat, A.,Bodennec, G.,Laurent, E.,Tardivel, R.
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p. 333 - 340
(2007/10/02)
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