- Photochemistry and photophysics of triarylmethane dye leuconitriles
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The photochemical reactions of crystal violet leuconitrile (CVCN) were investigated by the means of product analysis and trapping experiments, laser flash and steady-state photolysis, and steady-state fluorescence. The influence of oxygen on the reaction was examined in detail. The photochemistry of malachite green leuconitrile (MGCN), basic fuchsin leuconitrile (BFCN), and crystal violet leucomethyl (CVMe) and leucobenzyl (CVBn), as well as triphenylacetonitrile, was studied. The results suggest ionization occurs from S1, while the di-π-methane reaction is the photochemical route from T1.
- Jarikov,Neckers
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- Generation and reactivity of the 4-aminophenyl cation by photolysis of 4-chloroaniline
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4-Chloroaniline and its N,N-dimethyl derivative are photostable in cyclohexane but undergo efficient photoheterolysis in polar media via the triplet state and give the corresponding triplet phenyl cations. CASSCF and UB3LYP calculations show that the 4-aminophenyl triplet cation has a planar geometry and is stabilized by > 10 kcal mol-1 with respect to the slightly bent singlet. The triplet has a mixed carbene-diradical character at the divalent carbon. This species either adds to the starting substrate forming 5-chloro-2,4′-diaminodiphenyls (via an intermediate cyclohexadienyl cation) or is reduced to the aniline (via the aniline radical cation) in a ratio depending on the hydrogen-donating properties of the solvent. Transients attributable to the triplet aminophenyl cation as well as to the ensuing intermediates are detected. Chemical evidence for the generation of the phenyl cation is given by trapping via electrophilic substitution with benzene, mesitylene, and hexamethylbenzene (in the last case the main product is a 6-aryl-3-methylene-1,4-cyclohexadiene). Relative rates of electrophilic attack to benzene and to some alkenes and five-membered heterocycles are measured and span over a factor of 15 or 30 for the two cations. The triplet cation formed under these conditions is trapped by iodide more efficiently than by the best π nucleophiles, However, in contrast to the singlet cation, it does not form ethers with alcohols, by which it is rather reduced.
- Guizzardi,Mella,Fagnoni,Freccero,Albini
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- Characterizing ionic liquids as reaction media through a chemical probe
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The triplet N,N-dimethylaminophenyl cation, a highly reactive but chemospecific electrophile, has been used as a probe for characterizing the properties of reaction media for a series of imidazolium ILs. With the N-hexyl-N-methyl imidazolium derivatives (not with the W-butyl analogues), hydrogen transfer leading to the aniline was the main process. Trapping by iodide occurred with an inverse dependence on viscosity. Trapping by it nucleophiles exhibited a more complex behavior. This was explained by the effect of both the bulk viscosity and the structure of the IL cation on both steps of the reaction, namely, initial electrophilic attack and ensuing cation elimination or nucleophile addition. However, with an excellent nucleophile, such as thiophene, or when the latter step was intramolecular, as with 4-pentenol, the difference was obliterated and trapping became uniform. Incorporation of the probe into the IL cation (through insertion into the C-H bond a to the imidazolium ring) was demonstrated, while no addition to the anion tested (including bis(trifluoromethanesulfonimide)) took place.
- Dichiarante, Valentina,Betti, Cecilia,Fagnoni, Maurizio,Maia, Angelamaria,Landini, Dario,Albini, Angelo
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- Oxovanadium(V)-catalyzed oxidative biaryl synthesis from organoborate under O2
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Oxidative ligand coupling of organoborates was catalyzed by VO(OEt)Cl 2 under oxygen atmosphere, which provides a versatile method for the selective synthesis of symmetrical or unsymmetrical biaryls. The Royal Society of Chemistry.
- Mizuno, Hidenori,Sakurai, Hidehiro,Amaya, Toru,Hirao, Toshikazu
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- Cobalt-catalyzed cross-coupling reactions of aryl- And alkylaluminum derivatives with (hetero)aryl and alkyl bromides
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A simple cobalt complex, such as Co(phen)Cl2, turned out to be a highly efficient and cheap precatalyst for a host of cross-coupling reactions involving aromatic and aliphatic organoaluminum reagents with aryl, heteroaryl and alkyl bromides. New C(sp2)-C(sp2) and C(sp2)-C(sp3) bonds were formed in good to excellent yields and with high chemoselectivity, under mild reaction conditions.
- Dilauro, Giuseppe,Messa, Francesco,Bona, Fabio,Perrone, Serena,Salomone, Antonio
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supporting information
p. 10564 - 10567
(2021/10/19)
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- Pd-PEPPSI complexes based on 1,2,4-triazol-3-ylidene ligands as efficient catalysts in the Suzuki—Miyaura reaction
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The palladium complexes of the Pd-PEPPSI type with N-heterocyclic carbenes of the 1,2,4-triazole series were synthesized in 76—99% yields by the reactions of PdCl2 with 1,4-di- alkyl-1,2,4-triazolium salts in pyridine in the presence of KBr or KI as sources of halide ions and tetrabutylammonium salts as phase-transfer catalysts. The obtained complexes can be used as efficient catalysts for the Suzuki—Miyaura cross-coupling and are not inferior to the commercially available Pd-PEPPSI catalysts in activity.
- Chernenko, A. Yu.,Astakhov,Pasyukov,Dorovatovskii,Zubavichus, Ya. V.,Khrustalev,Chernyshev
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- Palladium(II) complexes of Y,C,Y-chelated phosphines: Synthesis, structure, and catalytic activity in Suzuki-Miyaura reaction
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The phosphines L1PPh2 (1) and L2PPh 2 (2) containing different Y,C,Y-chelating ligands, L1 = 2,6-(tBuOCH2)2C6H3 - and L2 = 2,6-(Me2NCH2) 2C6H3-, were treated with PdCl 2 and di-Aμ-chloro-bis[2-[(N,N-dimethylamino)methyl]phenyl- C,N]-dipalladium(II) and yielded complexes trans-{[2,6-(tBuOCH 2)2C6H3]PPh2} 2PdCl2 (3), {[2,6-(Me2NCH2) 2C6H3]PPh2} PdCl2 (4), {[2,6-(tBuOCH2)2C6H 3]PPh2}Pd(Cl)[2-(Me2NCH2)C 6H4] (5) and {[2,6-(Me2NCH2) 2C6H3]PPh2}Pd(Cl)[2-(Me 2NCH2)C6H4] (6) as the result of different ability of starting phosphines 1 and 2 to complex PdCl2. Compounds 3-6 were characterized by 1H, 13C, 31P NMR spectroscopy and ESI-MS. The molecular structures of 3,4 and 6 were also determined by X-ray diffraction analysis. The catalytic activity of complexes 3-6 was evaluated in the Suzuki-Miyaura cross-coupling reaction.
- Reznicek, Tomas,Dostal, Libor,Ruzicka, Ales,Kulhanek, Jiri,Bures, Filip,Jambor, Roman
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experimental part
p. 173 - 179
(2012/04/23)
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- Nickel-catalyzed cross-coupling of aryltrimethylammonium iodides with organozinc reagents
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Broad scope and good tolerance: An efficient cross-coupling of aryltrimethylammonium iodide salts with aryl-, methyl-, and benzylzinc chlorides catalyzed by [Ni(PCy3)2Cl2] has been achieved (see scheme). The reaction involves cleavage of the C-N bond and displays broad substrate scope and good functional group tolerance. NMP=N-methylpyrrolidine. Copyright
- Xie, Lan-Gui,Wang, Zhong-Xia
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supporting information; experimental part
p. 4901 - 4904
(2011/06/22)
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- Using phenyl cations as probes for establishing electrophilicity - Nucleophilicity relations
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(Chemical Equation Presented) N,N-Dimethyl-4-aminophenyl cation is used as an electrophilic probe for determining the relative reactivity of nucleophiles. The singlet state (11) of this cation is completely unselective (reaction rates with benzene, MeCN, and trifluoroethanol within a factor of 5). The corresponding triplet (31) does not react with alcohols and MeCN. The rates of reaction of the latter intermediate with 23 π, σ, and n nucleophiles are measured by competition experiments and found to vary over only 2 orders of magnitude over a range of 22 units of the nucleophilicity parameter N introduced by Mayr. As far as one can judge with the considerable scatter of the data, fitting the data of both amines and π nucleophiles is possible only by using a modified Mayr's equation: log k = s(E + eN) with e = 0.33. The reduced dependence on N is explained by the fact that in the case of diradicalic triplet 31 interaction with the nucleophile involves a half-filled (σ) orbital, which is empty in singlet 11. It is suggested that Mayr's equation can be extended to quite diverse reactions, but a scaling factor of e 1 may have to be introduced in some cases, according to the electronic structure of the electrophilic probe used.
- Dichiarante, Valentina,Fagnoni, Maurizio,Albini, Angelo
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p. 1282 - 1289
(2008/09/16)
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- The β effect of silicon in phenyl cations
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Irradiation of chloroanisoles, phenols, and N,N-dimethylanilines bearing a trimethylsilyl (TMS) group in the ortho position with respect to the chlorine atom caused photoheterolysis of the Ar-Cl bond and formation of the corresponding ortho-trimethylsilylphenyl cations in the triplet state. The β effect of silicon on these intermediates has been studied by comparing the resulting chemistry in alcoholic solvents with that of the silicon-free analogues and by computational analysis (at the UB3LYP/6-311+G(2d,p) level in MeOH). TMS groups little affect the photophysics and the photocleavage of the starting phenyl chlorides, while stabilizing the phenyl cations, both in the triplet (ca. 4 kcal/mol per group) and, dramatically, in the singlet state (9 kcal/mol). As a result, although triplet phenyl cations are the first formed species, intersystem crossing to the more stable singlets is favored with chloroanisoles and phenols. Indeed, with these compounds, solvent addition to give aryl ethers (from the singlet) competed efficiently with reduction or arylation (from the triplet). In the case of the silylated 4-chloro-N,N- dimethylaniline, the triplet cation remained in the ground state and trapping by π nucleophiles remained efficient, though slowed by the steric bulk of the TMS group. In alcohols, the silyl group was eliminated via a photoinduced protiodesilylation during the irradiation. Thus, the silyl group could be considered as a directing, photoremovable group that allowed shifting to the singlet phenyl cation chemistry and was smoothly eliminated in the same one-pot procedure.
- Dichiarante, Valentina,Salvaneschi, Andrea,Protti, Stefano,Dondi, Daniele,Fagnoni, Maurizio,Albini, Angelo
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p. 15919 - 15926
(2008/09/20)
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- C-C coupling reactions of aryl bromides and arylsiloxanes in water catalyzed by palladium complexes of phosphanes modified with crown ethers
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The complexes [PdCl2L2], where L is a crown-ether-containing triarylphosphane, catalyze the formation of biaryls from arylsiloxanes and aryl bromides with high yields In water as solvent and under air. The water-insoluble catalysts [PdCl2(PhCN)2] and [PdCl 2(PPh3)2] are also efficient, although they decompose more quickly to form black Pd0.
- Gordillo, Alvaro,De Jesus, Ernesto,Lopez-Mardomingo, Carmen
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p. 3517 - 3520
(2007/10/03)
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- Metal-free cross-coupling reactions of aryl sulfonates and phosphates through photoheterolysis of aryl-oxygen bonds
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Photochemical cleavage of Ar-O bonds in phenyl esters substituted with electron-donating groups offers a convenient method for the arylation of alkenes and arenes. The reaction proceeds by an SN1 mechanism via a triplet phenyl cation to form allylbenzene or biphenyl derivatives under mild conditions (see scheme).
- De Carolis, Marco,Protti, Stefano,Fagnoni, Maurizio,Albini, Angelo
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p. 1232 - 1236
(2007/10/03)
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- Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations
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The photodediazoniation of some 4-X-phenyldiazonium tetrafluoborates in MeCN leads to the singlet phenyl cations (X = H, tert-butyl, NMe2, CN), which add to the solvent yielding the corresponding acetanilides. Triplet sensitisation, however, leads to the triplet phenyl cation, which is reduced in neat solvent and is trapped by π nucleophiles (allyltrimethylsilane and benzene), resulting in an ionic analogue of the Meerwein or Gomberg arylations. With the 4-nitro derivative intersystem crossing prevails over dediazoniation from the singlet and with the 4-cyano competes with it, so that in those cases the triplet phenyl cation is formed also upon direct irradiation.
- Milanesi, Silvia,Fagnoni, Maurizio,Albini, Angelo
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p. 216 - 217
(2007/10/03)
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- Palladium-Catalyzed Inter- and Intramolecular α-Arylation of Amides. Application of Intramolecular Amide Arylation to the Synthesis of Oxindoles
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2A palladium-catalyzed α-arylation of amides is reported. Intermolecular arylation of N,N-dimethylamides and lactams occurs using aryl halides, silylamide base, and a palladium catalyst. Intramolecular arylation of N-(2-halophenyl)amides occurs using alkoxide base and a palladium catalyst. The palladium catalyst was formed in situ from Pd(dba)2 (dba = trans,trans-dibenzylidene acetone) and BINAP (2,2′-bis(diphenylphosphino)-1,1′-binaphthalene). Although the intermolecular arylation of amides is less general than that reported previously for ketones, unfunctionalized and electron-rich aryl halides gave α-arylamides in 48-75% yield and N-methyl-α-phenylpyrrolidinone in 49% yield. These reactions provided the highest yields yet reported for regioselective amide arylations. Intramolecular amide arylation of 2-bromoanilides gave oxindoles in 52-82% yield. Mono- and disubstituted acetanilides gave 1,3-di- and 1,3,3-trisubstituted oxindoles. The use of dioxane, rather than THF, solvent was important for some of the amide arylations.
- Shaughnessy, Kevin H.,Hamann, Blake C.,Hartwig, John F.
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p. 6546 - 6553
(2007/10/03)
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- Photo-induced electron-transfer reaction of aryl perfluoroalkanesulfonates with anilines
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Irradiation of mixtures of aryl perfluoroalkanesulfonates (RfSO3C6H4X-p, X = H, Cl and Me) (1) and aniline (2a), N,N-dimethylaniline (2b) or N,N-diethylaniline (2c) results in the formation of 2-coupling products 3 and 4-coupling products 4.However, in the reactions of 2b and 2c, in addition to 3 and 4, arenes 5 and N-methylaniline (6a) or N-ethylaniline (6b) are also detected.The presence of p-dinitrobenzene, But2NO and hydroquinone suppresses the reaction significantly.A photo-induced electron-transfer mechanism is proposed.
- Chen, Qing-Yun,Li, Zhan-Ting
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- PALLADIUM-CATALYZED CARBON-CARBON COUPLING REACTIONS WITH TETRAARYLBORATES
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A simple synthetic method is described, based on the use of a palladium(0) catalyst, to obtain carbon-carbon coupling reactions of aromatic bromides with sodium tetraaryl borates.
- Catellani, Marta,Chiusoli, Gian Paolo,Fornasari, Vilma
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p. 779 - 781
(2007/10/02)
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- Acid-Catalyzed Reactions of N-Arylhydroxylamines and Related Compounds with Benzene. Iminium-Benzenium Ions
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N-Arylhydroxylamines react with benzene in the presence of trifluoroacetic acid (TFA) at room temperature to give diphenylamines.When TFA was replaced by a strong acid, trifluoromethanesulfonic acid (TFSA), the major products were aminobiphenyls.The nature of the reaction was explored by reactions of 4-substituted phenylhydroxylamines and dialkylaniline N-oxides with benzene.Thus, it was demonstrated that the reactive intermediates are onium-benzenium dications which are trapped by benzene to give aminobiphenyls by a mechanism similar to the Friedel-Krafts alkylation.Further evidence for the proposed reaction mechanism was the observation that nitrosobenzene and azoxybenzene reacted with benzene to give analogous products in the presence of the stronger acid.
- Shudo, Koichi,Ohta, Toshiharu,Okamoto, Toshihiko
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p. 645 - 653
(2007/10/02)
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