- Hydrodehalogenation of organohalides by Et3SiH catalysed by group 4 metal complexes and B(C6F5)3
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Catalytic hydrodehalogenation (HDH) of aliphatic organohalides such as trifluorotoluenes by Et3SiH proceeds in the presence of readily available group 4 metal compounds: Cp′2MX2 (Cp′ = η5-C5H5 or η5-C5Me5; X = F, Cl, or Me; M = Ti, Zr, or Hf), CpTiCl3 and TiCl4 with a catalytic amount of B(C6F5)3. The use of metallocenes in combination with the borane activator leads to a better selectivity of the reaction, i.e., suppression of Friedel-Crafts alkylations of arenes.
- ?ilková, Nadě?da,Dunlop, David,Horá?ek, Michal,Lama?, Martin,Pinkas, Ji?í
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supporting information
p. 2771 - 2775
(2020/03/13)
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- ORGANOSILICON ON SOLID OXIDES, AND RELATED COMPLEXES, COMPOSITIONS, METHODS AND SYSTEMS
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Organosilicon Lewis acids supported on activated oxides and metal oxo complexes grafted on the organosilicon Lewis acids as heterogeneous catalysts and the related compositions, methods and systems are described. These organosilicon Lewis acids and the grafted metal oxo complexes catalyze industrially important chemical reactions including, respectively, C—F bond activation and olefin metathesis reactions such as homocoupling and polymerizations.
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Paragraph 0274-0276
(2020/04/09)
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- Activation of C?F Bonds by Electrophilic Organosilicon Sites Supported on Sulfated Zirconia
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The reaction of allyltriisopropylsilane with partially dehydroxylated sulfated zirconium oxide (SZO) forms surface organosilicon species. Solid-state NMR studies of the organosilicon functionalized SZO shows that electrophilic [TIPS][SZO] sites are present on the surface, in addition to less reactive TIPS-Ox and SiOx species. The electrophilic [TIPS][SZO] sites are strong Lewis acids from solid-state 31P NMR analysis of triethylphosphine oxide (O=PEt3) contacted materials. [TIPS][SZO] is active in hydrodefluorination reactions in the presence of Et3SiH.
- Culver, Damien B.,Conley, Matthew P.
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supporting information
p. 14902 - 14905
(2018/10/24)
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- Lewis acidity of organofluorophosphonium salts: Hydrodefluorination by a saturated acceptor
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Prototypical Lewis acids, such as boranes, derive their reactivity from electronic unsaturation. Here, we report the Lewis acidity and catalytic application of electronically saturated phosphorus-centered electrophilic acceptors. Organofluorophosphonium salts of the formula [(C6F 5)3-xPhxPF][B(C6F5) 4] (x = 0 or 1; Ph, phenyl) are shown to form adducts with neutral Lewis bases and to react rapidly with fluoroalkanes to produce difluorophosphoranes. In the presence of hydrosilane, the cation [(C 6F5)3PF]+ is shown to catalyze the hydrodefluorination of fluoroalkanes, affording alkanes and fluorosilane. The mechanism demonstrates the impressive fluoride ion affinity of this highly electron-deficient phosphonium center.
- Caputo, Christopher B.,Hounjet, Lindsay J.,Dobrovetsky, Roman,Stephan, Douglas W.
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p. 1374 - 1377
(2013/10/08)
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- Ti-catalyzed homolytic opening of ozonides: A sustainable C-C bond-forming reaction
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The unprecedented homolytic opening of ozonides promoted and catalyzed by titanocene(III) is reported. This novel reaction proceeds at room temperature under neutral, mild conditions compatible with many functional groups and provides carbon radicals suitable to form C-C bonds via both homocoupling and cross-coupling processes. The procedure has been advantageously exploited for the straightforward synthesis of the natural product brittonin A.
- Rosales, Antonio,Munoz-Bascon, Juan,Lopez-Sanchez, Cristobal,Alvarez-Corral, Miriam,Munoz-Dorado, Manuel,Rodriguez-Garcia, Ignacio,Oltra, J. Enrique
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p. 4171 - 4176
(2012/06/18)
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- Exhaustive chlorination of [B12H12]2- without chlorine gas and the use of [B12Cl12]2- as a supporting anion in catalytic hydrodefluorination of aliphatic C-F bonds
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The fully chlorinated closo-dodecaborate salt Cs2[B 12Cl12] was prepared in high yield from Cs 2[B12H12] and SO2Cl2 in acetonitrile at refluxing temperature. [Ph3C]2[B 12Cl12] was obtained by simple metathesis reactions. Catalytic hydrodefluorination of benzotrifluoride sp3 C-F bonds was accomplished using [Ph3C]2[B12Cl12] as a precatalyst and Et3SiH as a stoichiometric reagent. Full consumption of the sp3 C-F bonds in p-FC6H 4CF3 and C6F5CF3 with a turnover number up to 2000 was achieved.
- Gu, Weixing,Ozerov, Oleg V.
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scheme or table
p. 2726 - 2728
(2011/05/14)
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- C-C coupling reactivity of an alkylgold(III) fluoride complex with arylboronic acids
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Previously, alkylgold(III) fluorides have been proposed as catalytic intermediates that undergo C-C coupling with reagents such as arylboronic acids in Au(I)/Au(III) cross-coupling reactions. Here is reported the first experimental evidence for this elementary mechanistic step. Complexes of the type (NHC)AuMe (NHC = N-heterocyclic carbene) were oxidized with XeF2 to yield cis-(NHC)AuMeF2 products, which were found to be in equilibrium with their fluoride-dissociated, dimeric [(NHC)AuMe(μ-F)] 2[F]2 forms. In one case, a monomeric cis-(NHC)AuMeF 2 complex was favored exclusively in solution, and it was found to react with a variety of ArB(OH)2 reagents to yield Ar-CH3 products.
- Mankad, Neal P.,Toste, F. Dean
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supporting information; experimental part
p. 12859 - 12861
(2010/11/05)
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- Hydrodefluorination and other hydrodehalogenation of aliphatic carbon-halogen bonds using silylium catalysis
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Trialkylsilylium cation equivalents partnered with halogenated carborane anions (such as Et3Si[HCB11H5Cl6]) function as efficient and long-lived catalysts for hydrodehalogenation of C-F, C-Cl, and C-Br bonds with trialkylsilanes as stoichiometric reagents. Only C(sp3)-halogen bonds undergo this reaction. The range of C-F bond-containing substrates that participate in this reaction is quite broad and includes simple alkyl fluorides, benzotrifluorides, and compounds with perfluoroalkyl groups attached to an aliphatic chain. However, CF4 has proven immune to this reaction. Hydrodechlorination was carried out with a series of alkyl chlorides and benzotrichlorides, and hydrodebromination was studied only with primary alkyl bromide substrates. Competitive experiments established a pronounced kinetic preference of the catalytic system for activation of a carbon-halogen bond of a lighter halide in primary alkyl halides. On the contrary, hydrodechlorination of C6F 5CCl3 proceeded much faster than hydrodefluorination of C6F5CF3 in one-pot experiments. A solid-state structure of Et3Si[HCB11H5Cl6] was determined by X-ray diffraction methods.
- Douvris, Christos,Nagaraja,Chen, Chun-Hsing,Foxman, Bruce M.,Ozerov, Oleg V.
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supporting information; experimental part
p. 4946 - 4953
(2010/06/17)
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- Room-temperature catalytic hydrodefluorination of C(sp3)-F bonds
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Room-temperature catalytic hydrodefluorination of the strong C(sp3)-F bonds in benzotrifluorides and fluoropentane is catalyzed by Et3Si[B(C6F5)4] and uses Et3SiH as the source of H. Ar-CF
- Scott, Valerie J.,Celenligil-Cetin, Remle,Ozerov, Oleg V.
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p. 2852 - 2853
(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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- Reductive transformations of organofluorine compounds: II. Hydrodechlorination of chloropolyfluoroarenes by the action of zinc
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Polyfluoroarenes containing chlorine atoms in the aromatic ring and/or in the benzylic position undergo hydrodechlorination by the action of zinc in aqueous dimethylformamide. The use of Zn/Cu and addition of salts (NaCl, Na2SO4, NH4Cl) favor reductive dechlorination of the Carom - Cl bond. Polyfluorobenzotrichlorides react with excess zinc to give the corresponding CH3-substituted derivatives, otherwise CH2Cl- and CHCl2-containing compounds are formed. The reduction of C6F5CCl3 and C6F5CH2Cl with zinc in the presence of copper provides lower yields of the hydrodechlorination products and leads to formation of 1,2-bis(pentafluorophenyl)ethane.
- Krasnov,Platonov
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p. 1488 - 1499
(2007/10/03)
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- Free radical chemistry associated with H(RSiH) nH
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Polysilanes of the type H(RSiH)nH, where R = n-hexyl or phenyl, have been used as radical-based reducing agents for organic halides. They rival the effectiveness of the other group 14 hydrides in reduction processes. The repetitive hydrogen transfer from the same molecule of H(RSiH)nH allows these compounds to be used in small quantities. Lower (5 × 104 M-1 s-1) and higher (6 × 105 M-1 s-1) limit values for the rate constant of the reaction of primary alkyl radicals with each SiH moiety of H(PhSiH)nH have been obtained by using unimolecular radical reactions as timing devices. The photochemical behavior of these polysilanes in the presence or absence of di-tert-butyl peroxide have been studied by EPR spectroscopy, and the -SiHR-SiR-SiHR radical (R = n-hexyl) has been identified as a transient species. Silyl radicals, obtained from H(RSiH)nH and thermally generated tert-butoxyl radicals, add to a variety of substrates containing double bonds to give the corresponding adducts for which EPR spectra have been recorded.
- Chatgilialoglu,Ferreri,Vecchi,Lucarini,Pedulli
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p. 475 - 481
(2007/10/03)
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- REACTIONS OF POLYFLUOROARYL BROMIDES AND IODIDES WITH C-, Si-, Ge-, Sn- AND Pb-ELECTROPHILES AND TRIS(DIALKYLAMINO)PHOSPHINES
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The reactions of polyfluoroaryl bromides ArFBr or iodides ArFI with P(NR'2)3 and R3MX (R = alkyl; M = Si, Ge, Sn and Pb; X = Cl, Br) led to the formation of ArFMR3.The reactions of C6F5Br with P(NEt2)3 and C-electrophiles (CH3I, C6F5CF3 and (CF3)2C=CFC2F5) gave the products of pentafluorophenylation of these substrates.
- Bardin, V. V.,Pressman, L. S.,Rogoza, L. N.,Furin, G. G.
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p. 213 - 231
(2007/10/02)
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- Reactions of perfluoroaromatic compounds with ethereal solutions of methylmagnesium iodide in the presence of silver(I) and copper(I) salts
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The reactions of hexafluorobenzene, octafluorotoluene, decafluorodiphenyl, and octafluoronaphthalene with ethereal solutions of methylmagnesium iodide in the presence of AgCl or CuI gave the products of the methylation and 1-ethoxy-ethylation of the perfluorinated substrates, whose formation has been suggested to occur with participation of free radicals. Substitution of fluorine atoms by the 1-ethoxyethyl radicals in C6F5CF3 and C6F5C6F5 proceeds with predominant para-orientation; in C10F8, 1- and 2-orientations take place to an equal extent, whereas the methyl radicals attack mainly the 1-position of octafluoronaphthalene and show a low selectivity in the reaction with octafluorotoluene.
- Bogachev,Kobrina,Yakobson
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- Laser-Induced Reactions of Hexafluorobenzene and Selected Hydride Compounds
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Infrared-laser-induced reactions between C6F6 and general hydrides R-H (R = H, D, CH3, HCC, H2C=CH, and Cl) were studied by irradiating C6F6 at 1027 cm-1 in C6F6/R-H mixtures.In general, two competitive pathways involving C-F bond cleavage in C6F6 were observed as follows: (1) C6F6 + R-H C6F5H + R-F and (2) C6F6 + R-H C6F5R + HF.C6F6 decomposition also took place to a minor extent depending on the mole fraction of C6F6 and gave rise to C2F4 and C2H2.From infrared and GC/MS analysis of the product mixtures after 20-200 pulses, C6F5H was observed in all reactions except that involving D2.When D2 was used C6F5D was the major product.C6F5H was the major product in the reactions involving H2 and C2H2.In the reaction with C2H4, C6F5H was the major product derived from C6F6 though C2H2 was the major product of the reaction.The large amount of C2H2 seems to be derived from an additional sensitized decomposition of C2H4.C6F5H was present in minor amounts in the reaction with CH4 and HCl.Besides C6F5H, other monosubstituted products derived from C6F6 were also formed, generally within 20-100 pulses.Thus, C6F5CH3, C6F5CH=CH2, C6F5CCH, and C6F5Cl were produced, respectively, in the reaction of C6F6 with CH4, C2H4, C2H2, and HCl.In the first and last cases these products were the major ones observed.The results are discussed mechanistically in terms of the initial formation of the C6F5. radical and synthetically in terms of the utility of obtaining selective-laser-induced reduction of C6F6.
- Koga, Yoshinori,Chen, Ruth,Keehn, Philip M.
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p. 306 - 311
(2007/10/02)
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- REACTION OF AROMATIC COMPOUNDS WITH NUCLEOPHILIC REAGENTS IN LIQUID AMMONIA IV.* THE NUCLEOPHILIC AND PROTOPHILIC ACTIVITY OF METHOXIDE AND HYDROXIDE IONS IN REACTIONS WITH POLYFLUORINATED AROMATIC COMPOUNDS
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In the reaction of polyfluorinated derivatives of benzene with potassium methoxide in liquid ammonia a fluorine atom is substituted by a methoxy group.With potassium hydroxide reactions involving removal of a proton from a ring carbon atom take place preferentially.The possibility of polyfluoroarylation and methylation catalyzed by potassium hydroxide in polyfluorinated aromatic compounds, based on capture of the polyflurinated aryl anion by the electrophile, was demonstrated.
- Shtark, A. A.,Chuikova, T. V.,Shteingarts, V. D.
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p. 960 - 967
(2007/10/02)
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- REACTION OF METHYL AND PHENYL PICRATES WITH NUCLEOPHILES
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The reactions of 2,4,6-trinitroanisole with various nucleophiles Me3SnM, Me3SiLi, BuLi, Me4NBBu4, PhMgI, CN-, lithium (potassium) succinimide, F-, Cl-, Br-, SCN-, NO2-, NO3-, HCO3-, PhSO2-,AcO-, S2- were investigated.It was found that the final products are the picrate and the corresponding methyl derivatives.The formation of intermediate ? complexes was detected in a series of the reactions (Me3SnLi, potassium succinimide, Bu4B-, CN-, NO2-, PhSO2-).Possible mechanisms for the reaction are examined.Reactions of 2,4,6-tricyanoanisole and phenyl picrate with certain nucleophiles were also investigated.
- Artamkina, G. A.,Egorov, M. P.,Beletskaya, I. P.,Reutov, O.A.
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- FLUORINE-CONTAINING CATECHOLAMINES. SYNTHESIS OF DL-2, 5, 6-TRIFLUORODOPA
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DL-2,5,6-trifluoro-3,4-dihydroxyphenylalanine (trifluorodopa) hydroiodide has been synthesized from hexafluorobenzene in a six-step procedure.The key step is the methoxylation of p-methyl tetrafluoroanisole.This reaction affords the desired 2,5,6-trifluoro-3,4-dimethoxytoluene, which is separated by preparative glc from 3,5,6-trifluoro-2,4-dimethoxytoluene.Attempts to obtain trifluorodopa by ether cleavage of the appropriately substituted dihydrobenzodioxin have not been successful.
- Filler, Robert,Rickert, Robert C.
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p. 483 - 496
(2007/10/02)
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- Determination of D by the toluene carrier method
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The pyrolysis of C6F5CH2Br has been studied by the toluene carrier technique over the temperature range 727-800 deg C.Rate constants are based on analysis for residual parent compound by gas chromatography using an internal standard technique.In selected runs a material balance of 100+/-2percent was obtained for bromine based on C6F5CH2Br plus HBr.Within the limits of the experimental technique the process appears to be first order and homogeneous.In addition to HBr the order major products of the thermal decomposition are C6F5CH3, (C6F5CH2)2, C6F5CH2CH2C6H5, and (C6H5CH2)2.The Arrhenius equation obtained is log k1 (s-1) = 14.54+/-0.42 - (225000+/-6000)/19.1T.The log A value is very close to the value of 14.6 recommended by Benson and O'Neal for the decomposition of C6H5CH2Br.The activation energy, 225+/-6 kJ mol-1, should be a reasonable estimate of D.
- Kominar, R. John,Krech, Michael J.,Price, Stanley James W.
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p. 1906 - 1908
(2007/10/02)
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