- Alkali Metal Adducts of an Iron(0) Complex and Their Synergistic FLP-Type Activation of Aliphatic C-X Bonds
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We report the formation and full characterization of weak adducts between Li+ and Na+ cations and a neutral iron(0) complex, [Fe(CO)3(PMe3)2] (1), supported by weakly coordinating [BArF20] anions, [1·M][BArF20] (M = Li, Na). The adducts are found to synergistically activate aliphatic C-X bonds (X = F, Cl, Br, I, OMs, OTf), leading to the formation of iron(II) organyl compounds of the type [FeR(CO)3(PMe3)2][BArF20], of which several were isolated and fully characterized. Stoichiometric reactions with the resulting iron(II) organyl compounds show that this system can be utilized for homocoupling and cross-coupling reactions and the formation of new C-E bonds (E = C, H, O, N, S). Further, we utilize [1·M][BArF20] as a catalyst in a simple hydrodehalogenation reaction under mild conditions to showcase its potential use in catalytic reactions. Finally, the mechanism of activation is probed using DFT and kinetic experiments that reveal that the alkali metal and iron(0) center cooperate to cleave C-X via a mechanism closely related to intramolecular FLP activation.
- Tinnermann, Hendrik,Sung, Simon,Csókás, Dániel,Toh, Zhi Hao,Fraser, Craig,Young, Rowan D.
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supporting information
p. 10700 - 10708
(2021/07/31)
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- Metal- and base-free synthesis of aryl bromides from arylhydrazines
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An efficient method was developed to synthesize brominated aromatic compounds from arylhydrazine hydrochlorides by using BBr3 in DMSO/CPME (cyclopentyl methyl ether) under air at 80 °C for 1 h without the use of bases or metal catalysts. In particular, this method could be carried out satisfactorily using electron-withdrawing groups to afford aryl bromides in a moderate to excellent yields.
- Phuc Tran, Dat,Nomoto, Akihiro,Mita, Soichiro,Dong, Chun-ping,Kodama, Shintaro,Mizuno, Takumi,Ogawa, Akiya
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supporting information
(2020/05/08)
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- Nanolayered cobalt-molybdenum sulphides (Co-Mo-S) catalyse borrowing hydrogen C-S bond formation reactions of thiols or H2S with alcohols
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Nanolayered cobalt-molybdenum sulphide (Co-Mo-S) materials have been established as excellent catalysts for C-S bond construction. These catalysts allow for the preparation of a broad range of thioethers in good to excellent yields from structurally diverse thiols and readily available primary as well as secondary alcohols. Chemoselectivity in the presence of sensitive groups such as double bonds, nitriles, carboxylic esters and halogens has been demonstrated. It is also shown that the reaction takes place through a hydrogen-autotransfer (borrowing hydrogen) mechanism that involves Co-Mo-S-mediated dehydrogenation and hydrogenation reactions. A novel catalytic protocol based on the thioetherification of alcohols with hydrogen sulphide (H2S) to furnish symmetrical thioethers has also been developed using these earth-abundant metal-based sulphide catalysts.
- Corma, Avelino,Sorribes, Iván
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p. 3130 - 3142
(2019/03/13)
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- Catalytic Sandmeyer bromination
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An efficient catalyst system for Sandmeyer bromination is proposed. Aryl bromides and dibromides can be obtained with excellent yield by this synthetic protocol. Georg Thieme Verlag Stuttgart.
- Beletskaya, Irina P.,Sigeev, Alexander S.,Peregudov, Alexander S.,Petrovskii, Pavel V.
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p. 2534 - 2538
(2008/03/13)
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- Hydro-dediazoniation of diazonium salts using trichlorosilane: New cleavage conditions for the T1 traceless linker
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An efficient, selective cleavage of triazenes and in situ hydro- dediazoniation of the intermediately formed diazonium salts with trichlorosilane (HSiCl3) in liquid as well on solid phase is reported. Starting from anilines, attachment to solid support and subsequent cleavage gives rise to the corresponding unsubstituted arenes. This cleavage reagent is compatible with various functionalities (esters, amides, nitro groups, halides, aliphatic double and triple bonds). (C) 2000 Elsevier Science Ltd.
- Lormann, Matthias,Dahmen, Stefan,Br?se, Stefan
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p. 3813 - 3816
(2007/10/03)
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- Halodediazoniations of dry arenediazonium o-benzenedisulfonimides in the presence or absence of an electron transfer catalyst. Easy general procedures to prepare aryl chlorides, bromides, and iodides
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The paper reports the results of a wide study aimed at preparing aryl chlorides 3 (19 examples), bromides 4 (19 examples), and iodides 5 (9 examples) by halodediazoniation of dry arenediazonium o-benzenedisulfonimides 1 with tetraalkylammonium halides 2. The reactions were carried out in anhydrous acetonitrile at room temperature (~20 °C) in the presence of copper powder and at 60 °C or room temperature without the catalyst. In optimal conditions the yields were from good to excellent (60 reactions, 61- 94% yield), with only a few exceptions (8 reactions, 51-55% yield). A good amount of the o-benzenedisulfonimide (7) was always recovered from the reactions and could then be reused to prepare salts 1. An interesting aspect of this research is the surprising role of the anion of o- benzenedisulfonimide (9) as an electron transfer agent.
- Barbero,Degani,Dughera,Fochi
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p. 3448 - 3453
(2007/10/03)
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- Electrophilic Substitution in Alkylbenzenes: Electrophile Orientation and Medium Acidity
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Apparent rate constants and electrophile orientation (ortho/para ratio) are determined for electrophilic substitution reactions in atkylbenzenes (nitration, bromination) in acidic media (trifluoroacetic acid and a mixture of sulfuric and acetic acids). It is shown that the substrate and regioseleclivity depends on the acidity of the medium, the dependence for the regioselectivity being S-shaped. Acidity functions by changing solvation and, depending to the type of solvation of the reagent, by changing the polarity of the medium. The otho/para ratio is consistent with Pearson's concept.
- Krylov
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- Benzopyridazinone and pyridopyridazinone compounds
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Benzo or pyridopyridazinones and pyridazinthiones of the formula STR1 wherein: X and Y are nitrogen or carbon, provided that at least one is carbon, and Z is oxygen or sulfur; R1 is hydrogen, lower alkyl, aryl, aralkyl, heterocyclo, heterocyclo lower-alkyl, heteroaryl, or heteroaralkyl; R2, R3, R4, R5 and R6 are independently selected from hydrogen, lower alkyl, halo, carboxy, alkoxycarbonyl, carbamoyl, lower-alkyl carbonyl, halocarbonyl, thiomethyl, trifluoromethyl, cyano or nitro; or a pharmaceutically acceptable ester, ether or salt thereof, have been found to be useful as an anti-inflammatory, antasthmatic, immunosuppressive, anti-allograft rejection, anti-graft-vs-host rejection, autoimmune disease or analgetic agent(s).
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- Direct Formation of (Haloaryl)copper Nucleophiles from Haloiodobenzenes and Active Copper
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(o-Halophenyl)-, (m-halophenyl)-, and (p-halophenyl)copper reagents have been formed in moderate to high yields at room temperature from active copper and the corresponding haloiodobenzenes.These reagents have been cross-coupled with a variety of alkyl and acyl halides to produce the respective haloarenes and haloaryl ketones.Remarkably, (o-fluorophenyl)- and (o-chlorophenyl)copper are produced in good yields by this procedure without undergoing elimination to form benzyne making this approach a convenient method for generating o-halophenyl nucleophiles.
- Ebert, Greg W.,Pfennig, Deborah R.,Suchan, Scott D.,Donovan, Thomas A.,Aouad, Emmanuel,et al.
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p. 2361 - 2364
(2007/10/02)
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- Bromination of alkylbenzenes in organic solvents. Substrate and position selectivity and effects of substituents
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The relative reactivity and the orientation of the entering group in the reaction of bromine with alkylbenzenes (C1-C4 alkyl groups, the last two with normal and iso structures) in organic solvents (acetic acid, acetic anhydride, nitromethane) under polythermal conditions (25-75 deg C) are determined mainly by the steric effects of the substituents.Nathan-Baker position and substrate effects are observed.Correlations close to linear are observed between the orientation (in the form of log 2P/O, where P and O are the relative amounts of the isomers in their reaction mixture) and the purely steric constants of the alkyl groups Es0.The substrate selectivity depends nonlinearly and inversely on Es0.The sensitivity of the orientation to change in the steric characteristics of the substituents shows an extremal dependence on the temperature with a maximum at about 50 deg C.
- Krylov, E. N.,Paramonova, O. K.
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p. 149 - 154
(2007/10/02)
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- Dynamics of endoergic substitution reactions. I. Br+chlorinated aromatic compounds
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The endoergic substitution reactions Br + R-Cl -> Cl + R-Br (R = o-, m-, andp-CH3C6H4, C6H5, C6F5; ΔH0 ca. 15 kcal/mol) have been studied using the crossed molecular beams method in the collision energy (Ec ) range 2-35 kcal/mol.The CH3C6H4Br and C6F5Br products were found to be mostly forward scattered with respect to the incident Br beam indicating that the lifetimes of the Br-R-Cl collision complexes are short compared to their rotational periods.The product translational energy distributions and excitation functions for these reactions are well reproduced by statistical calculations that assume that only a few vibrational modes in the collision complexes participate in intramolecular energy redistribution prior to Cl elimination.Ring substituents are found to affect both the extent of energy redistribution in the complexes and the probability of Br addition.For example, no substitution product was observed with m-CH3C6H4Cl or C6H5Cl.The relative magnitudes of the cross sections are explained in terms of possible features of the potential energy surfaces along their reaction coordinates.
- Robinson, Gary N.,Continetti, Robert E.,Lee, Yuan T.
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p. 6226 - 6237
(2007/10/02)
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- Electron Transfer in Competition with Loss of Nitrogen in Photochemical Reactions of Aryldiazomethane with Diethylamine
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The photolysis of aryldiazomethanes was studied as a function of aryl substituents and the p-nitro group was found to exert a special effect of product distribution.
- Tomioka, Hideo,Tabayashi, Kazuo,Izava, Yasuji
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p. 906 - 907
(2007/10/02)
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- ANOMALOUS ORIENTATION EFFECTS DURING BENZOYLOXYLATIONS BY "SILVER BROMIDE DIBENZOATE"
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The solid complex formed from bromine and silver benzoate reacts with both arenes and alkenes to form aryl and alkyl benzoates, respectively.Highly unusual substituent effects are observed in the benzoyloxylations of arenes.Electron-withdrawing groups (e.g. -NO2, -CN,-CO-) on the aromatic ring facilitate reaction though directing the attacking reagent exclusively to the meta position.In alkanes, tertiary positions are most prone to attack.
- Bryce-Smith, Derek,Isaacs, Neil S.,Tumi, Seddeg O.
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p. 1471 - 1472
(2007/10/02)
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- Bromination of Azobenzenes by Acidified Hypobromus Acid; Orientation, Reactivity and Mechanism
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The rate of bromination of azobenzene by acidified hypobromousacid has been measured and compared with those of benzene, toluene, and bromobenzene under the same conditions.Determination of o/m/p ratios for attack on azobenzene show that the rate of attack at the meta position is much lower than expected on the basis of the Hammett ?m value for the phenylazo substituent.Abnormally low amounts of meta isomer were also observed for the case of bromobenzene, but not toulene.The rates of bromination of two monosubstituted azobenzenes (m-Br, and p-F) were alsodetermined and comparedwith that of azobenzene.
- Christoforou, Demetrius,Happer, Duncan A. R.,Munro, Murray H. G.
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p. 741 - 749
(2007/10/02)
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- Mechanism of the Non-Aryne Hydroxydehalogenation of Unactivated Aryl Halides
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The hydroxydehalogenation of aryl halides upon reaction with aqueous alkali at temperatures up to 333 deg C was examined to determine the nature of an ipso hydroxydehalogenation process reported in 1957 to compete with the aryne mechanism.The reactions of p-iodo-, p-bromo-, and p-chlorotoluene with aqueous solutions of sodium or potassium hydroxide or carbonate, carried out in Pyrex glass tubes with exclusion of traces of transition metals, led in all cases to the same product distribution. m-Cresol and p-cresol, the two main products, formed with a para/meta ratio of0.82+/-0.03, consistent with the occurence of the aryne mechanism only.Addition of traces of copper salts or conducting the reaction in a Monel bomb, as done by other investigators, caused the occurence of a non-aryne ipso hydroxydehalogenation.This effect was not produced by nickel, iron, manganese, or cadmium.The ipso hydroxydehalogenation observed in previous studies is identified as a copper-catalyzed process.
- Zoratti, Mario,Bunnett, J. F.
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p. 1769 - 1776
(2007/10/02)
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- Reactivities of Several Nucleophiles toward 4-Methylbenzyne in Very Hot Water
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By means of competition experiments, the relative rates of reaction of several nucleophiles with 4-methylbenzyne in aqueous solution at temperatures up to 318 deg C have been determined.The relative nucleophilicities vs. chloride ion are as follows: PhS-, 46; I-, 6.2; piperidine, 3.0; Br-, 1.7; aniline, 1.3; Cl-, (1.0); PhO-, 1.0; ammonia, 0.55; F-, 0.20.For all but PhS-, piperidine, and iodide, the p/m product ratio is 0.83+/-0.02.In the cases of PhS- and piperidine a competing mechanism of ipso substitution, probably involving catalysis by copper ions, caused the observed p/m ratios to be high and variable.Our experimental design precluded determination of the p/m ratio for iodide ion.Because of chemical complications, only rough estimates could be made of the nucleophilicities of nitrite and benzenesulfinate ions.
- Zoratti, Mario,Bunnett, J. F
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p. 1776 - 1782
(2007/10/02)
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- Polar Radicals. 14. On the Mechanism of Trialkylstannane Reductions. Positive ρ Values for the Tri-n-butylstannane Reduction of Benzyl Halides. A Correlation with ?-
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The relative reactivities towards reduction by tri-n-butylstannane of a series of substituted benzyl halides have been determined.The order of reactivity was shown to be I > Br > Cl, the same as that reported for alkyl halide reductions.Under the reaction conditions (90 deg C, benzene as solvent, benzoyl peroxide initiation), both aralkyl and alkyl fluorides were shown to be completely unreactive.Activation energies were estimated for the direct abstraction of halogen by tri-n-butyl radicals, and on the basis of these estimates all of the halogens would be predicted to readily undergo abstraction.To explain the non-reactivity of the fluorides several other mechanisms were considered: reversible tin radical addition to the halogen to form an intermediate with an expanded octet, and a free radical chain mechanism involving an electron-transfer reaction between the trialkyltin radical and the benzyl halide. The benzyl halide reductions showed excellent Hammett correlations with positive ρ values; all of these correlations were obtained using ?- substituent constants.The demonstration (the first ever reported) that ?- substituent constants correlate with the relative reactivities for reduction infers that bond breaking takes place in the transition state for the reaction.The magnitudes of the ρ values were not found, as were expected, to be in the inverse order of the relative reactivities: ρ for the iodides (+0.81), for the bromides (+0.17), and for the chlorides (+0.34).To explain the anomalously high value of ρ found for the iodide reduction, it was suggested that the benzyl iodides underwent reduction by a different mechanism than the chlorides and the bromides.The relative rates of reduction of the benzyl iodides in a more polar solvent than benzene, acetonitrile, showed decreased sensitivity to substituents, whereas the reduction of the bromides and chlorides was relatively insensitive to solvent effects.
- Blackburn, Edward V.,Tanner, Dennis D.
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p. 692 - 697
(2007/10/02)
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- Nickel Catalysis in Halogen Exchange with Aryl and Vinylic Halides
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Halogen exchange between haloarenes and inorganic halide salts is readily induced by catalytic amounts of certain nickel complexes.Exchange of cis- and trans-β-bromostyrenes with chloride is stereospecific.Although various nickel complexes with different formal oxidation states such as Ni0(PEt3)4, NiII(PEt3)3, and ArNiIIBr(PEt3)2 may be employed as catalysts (or catalyst precursors), others such as NiIIBr2 or NiIIBr2(PEt3)2 are completely ineffective.The distinction between the two classes of nickel complexes lies in whether they are converted under reaction conditions to nickel(I) species, assigned as the active catalyst.The latter is supported by the study of direct halide exchange between haloarenes and arylnickel(II) halides, in which a radical-chain process showing an induction period and inhibition by quinones and nitro aromatics is attributed to a labile nickel(I) species.A mechanism for nickel(I) catalysis of halide exchange is proposed.
- Tsou, T. T.,Kochi, J. K.
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p. 1930 - 1937
(2007/10/02)
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- Reactions of Alkyl-lithium Compounds with Aryl Halides
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Reation of methyl-lithium with tribromophenols and with other aryl polyhalides leads directly to bi- and tri-aryl products. para-Substituents (Y) of 2,6-dibromo-4-Y-phenols promote arylation of substrates by their own lithiation products as Y becomes more electron-withdrawing.An aryne epoxide is not an intermediate in these reactions. 2,4,6-Tribromo-Z-benzenes react to form coupling products when Z can co-ordinate to an introduced ortho-lithium atom or when Z can be directly lithiated.Dimeric aggregation of the organolithium intermediates occurs so as to favor coupling to halogenated substrates.Both polar (ionic) and free-radical pathways are involved.
- Huddle, Penelope A.,Perold, Guido W.
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p. 2617 - 2625
(2007/10/02)
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