- Oxidation of 3,5,3′,5′-tetra-tert-butyl-4,4′ -dihydroxybiphenyl with atmospheric oxygen in the absence of base catalysts
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Use of dimethylformamide as solvent and preliminary addition of 3,5,3′,5′-tetra-tert-butyl-4,4′-diphenoquinone allow oxidation of 3,5,3′,5′-tetra-tert-butyl-4,4′ -dihydroxybiphenyl with atmospheric oxygen to be efficiently performed in the absence of base catalysts.
- Bukharov,Fazlieva,Mukmeneva,Akhmadullin,Morozov
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- Selective Electrochemical versus Chemical Oxidation of Bulky Phenol
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The electrochemical oxidation of selected tert-butylated phenols 2,6-di-tert-butyl-4-methylphenol (1), 2,6-di-tert-butylphenol (2), 2,4,6-tri-tert-butylphenol (3), 2-tert-butylphenol (4), and 4-tert-butylphenol (5) was studied in an aprotic environment using cyclic voltammetry, square-wave voltammetry, and UV-vis spectroscopy. All compounds exhibited irreversible oxidation of the corresponding phenol or phenolate ion. Compound 2 was selectively electrochemically oxidized, while other phenol analogues underwent mostly chemical oxidation. The electrochemical oxidation of 2 produced a highly absorbing product, 3,5,3′,5′-tetra-tert-butyl-4,4′-diphenoquinone, which was characterized by X-ray crystal diffraction. The electrochemical oxidation was monitored as a function of electrochemical parameters and concentration. Experimental and theoretical data indicated that the steric hindrance, phenoxyl radical stability, and hydrogen bonding influenced the outcome of the electrochemical oxidation. The absence of the substituent at the para position and the presence of the bulky substituents at ortho positions were structural and electrostatic requirements for the selective electrochemical oxidation.
- Zabik, Nicole L.,Virca, Carolyn N.,McCormick, Theresa M.,Martic-Milne, Sanela
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- Enantioselective Desymmetrization of 1,4-Dihydropyridines by Oxidative NHC Catalysis
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The unprecedented desymmetrization of prochiral dialdehydes catalyzed by N-heterocyclic carbenes under oxidative conditions was applied to the highly enantioselective synthesis of 1,4-dihydropyridines (DHPs) starting from 3,5-dicarbaldehyde substrates. Synthetic elaboration of the resulting 5-formyl-1,4-DHP-3-carboxylates allowed for access to the class of pharmaceutically relevant 1,4-DHP-3,5-dicarboxylates (Hantzsch esters). DFT calculations suggested that the enantioselectivity of the process is determined by the transition state involving the oxidation of the Breslow intermediate by the external quinone oxidant.
- Di Carmine, Graziano,Ragno, Daniele,Brandolese, Arianna,Bortolini, Olga,Pecorari, Daniel,Sabuzi, Federica,Mazzanti, Andrea,Massi, Alessandro
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- Solvent-free oxidative coupling of 2-naphthols catalyzed by hydrotalcite-like compounds in aerobic conditions
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Abstract: The hydrotalcite-like compound having ruthenium ions, cobalt ions, and iron ions in the Brucite layer and CO3 anions in the interlayer (Ru-Co-Fe-CO3 HTLC) was found to be effective heterogeneous catalyst for the solvent-free oxidative coupling of 2-naphthols in aerobic conditions. The catalyst could be easily recovered and reused repeatedly for the reaction.
- Sugamoto, Kazuhiro,Matsushita, Yoh-Ichi,Matsui, Takanao
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- Spectrophotometric determination of formation constants for the Cu-ethylenediamine-halogen (chloride and bromide) system and their catalytic effect on the oxidative coupling of 2,6-di-tert-butyl-phenol
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In order to explain the mechanism of the dimerization of 2,6-di-tert-butyl-phenol when catalyzed by the copper-ethylenediamine complexes, a spectrophotometric study of the speciation of copper(II) complexes in methanol of Cu(II), ethylendiamine and Cl- or Br- was carried out at 303 K. The formation constants obtained for the copper chloride system are: log β101 = 2.90 ± 0.03, log β102 = 6.39 ± 0.03 and log β103 = 8.62 ± 0.04, for the copper bromide system are log β101 = 3.01 ± 0.10, log β102 = 5.50 ± 0.08, for the copper-ethylendiamine complexes are log β110 = 6.13 ± 0.05 and log β120 = 10.54 ± 0.08, and for the ternary copper-ethylenediamine chloride or bromide systems are log β111 = 10.21 ± 0.03 and log β111 = 10.07 ± 0.03, respectively. Knowing the speciation of the copper-ethylenediamine-halide systems, the kinetic studies can be correlated with the species in solution. Comparative studies of the oxidation reaction of 2,6-di-tert-butyl-phenol using different copper(II) complexes with chloride or bromide and ethylenediamine as catalyst are reported. Their catalytic activity in the oxidation of 2,6-di-tert-butyl-phenol was monitored in methanol solution, following the corresponding quinone formation, at 418 nm ( = 3.95 × 104 mol-1 L cm-1 at 303 K). The results indicate that the most active species are [Cu(en)X]+, where X is bromide or chloride, Both complexes have similar activity.
- Segoviano-Garfias, José J.N.,Moreno-Esparza, Rafael,Mendoza-Díaz, Guillermo
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- Singlet Character of Coordinatively Bound Oxygen, II
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The oxygenation of 1,5-dihydroxynaphthalene (1) and 2,6-di-t-butylphenol (4) with Co-salen as a catalyst has been examined.The activation of oxygen in these reactions is different.From reactions with specific quenchers and the measurement of ultraweak chemiluminescence it is concluded that, depending on the nature of the substrate, Co-salen activates oxygen in the singlet state or in the radical state.This behavior must be considered when cobalt complexes are investigated as model substances of enzymatic oxygenation reactions.
- Duchstein, Hans-Juergen
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- EPR-spectroscopic Experiments with the Co-Salen/O2-Complex, VI: Differentiation of the Bound Oxygen
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EPR-spectroscopic experiments of Co-Salen depending on solvent, substrate and oxygen are described.We explain the EPR-inactivity in acetonitrile with a Co-salen-dimer.Co-Salen, depending on the nature of the substrate, is able to activate oxygen into different species, which allow 1. (4+2)-cycloadditions very similar to the reactions with singlet oxygen in the case of 1,5-dihydroxy-naphthalene (1) and 2. radical-reactions with 2,6-di-t-butylphenol (4).These experiments are consistent with former chemiluminescence measurements.We describe an activation model of Co-salen/02 with the investigated reactions.
- Duchstein, Hans-Juergen,Baumgarten, Martin
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- Structural characterization and electrochemical properties of the 3,3′-5,5′-tetra-tert-butyl-4,4′-diphenoquinone
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Crystals of the 3,3′-5,5′-tetra-tert-butyl-4,4′-diphenoquinone (TTBDQ) in the reaction mixture DCM/MeOH (1:1, v/v) were obtained as a result of C{single bond}C coupling reaction of the sterically hindered phenol (2,6-di-tert-butylphenol, DTBP) using the binuclear Co(II) complexes. The oxidation product (TTBDQ), C28H40O2, crystallizes in the space group P over(1, ) with one-half molecule in the asymmetric unit and the other half generated by an inversion centre. The diphenoquinone moiety is planar within ±0.016(3) A. The crystal structure is stabilized by intramolecular C{single bond}H...O hydrogen bonds. The spectroscopic and electrochemical properties of the TTBDQ also have been studied.
- Tuemer, Mehmet,Aslantas, Mehmet,Sahin, Ertan,Deligoenuel, Nihal
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- Physical and Chemical Properties of Mononuclear Cobalt Dioxygen Complexes with Tetraimidazolyl-Substituted Pyridine Chelates
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A new class of mononuclear superoxocobalt complexes containing four equal imidazolyl-donors and one pyridyl-donor per cobalt(II) ion was prepared and their chemical and physical properties were compared with those of cobalt(II) Schiff-base type dioxygen complexes.
- Tamagaki, Seizo,Kanamaru, Yutaka,Ueno, Masanori,Tagaki, Waichiro
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- Carboxamidate Ligand Noninnocence in Proton Coupled Electron Transfer
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Recent breakthroughs have brought into question the innocence (or not) of carboxamidate donor ligands in the reactivity of high-valent oxidants. To test the reactivity properties of high-valent carboxamidate complexes, [NiII(tBu-terpy)(L)] (1, tBu-terpy = 4,4′,4′′-tri-tert-butyl-2,2′6′,2″-terpyridine; L = N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate) was prepared and converted to [NiIII(tBu-terpy)(L)]+ (2) using ceric ammonium nitrate. 2 was characterized using electronic absorption and electron paramagnetic resonance spectroscopies and electrospray ionization mass spectrometry. 2 was found to be a capable oxidant of phenols and through kinetic analysis was found to oxidize these substrates via a nonconcerted or partially concerted proton coupled electron transfer (PCET) mechanism. The products of PCET oxidation of phenols by 2 were phenoxyl radical and the protonated form of 1, 1H+. 1H+ was crystallographically characterized providing convincing evidence of 1's ability to act as a proton acceptor. We demonstrate that the complex remained intact through a full cycle of oxidation of 1 to 2, PCET of 2 to yield 1H+, and deprotonation of 1H+ to yield 1 followed by reoxidation of 1 to yield 2. The N-H bond dissociation energy of the protonated amide in 1H+ was determined to be 84 kcal/mol. Our findings illuminate the role carboxamidate ligands can play in PCET oxidation.
- McManus, Caitilín,Mondal, Prasenjit,Lovisari, Marta,Twamley, Brendan,McDonald, Aidan R.
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- The facile oxidative coupling of a hindered phenol, 2,6-di-t-butylphenol, driven by N,N′-bis(ethoxy-carbonyl)-1,4-benzoquinone diimine; The reaction pattern traced by 1H NMR spectroscopy
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Good yields of 3,3′,5,5′-tetra-t-butyl-4,4′-dipheno- quinone were obtained by the reaction of 2,6-di-t-butylphenol with N,N′-bis(ethoxycarbonyl)-1,4-benzoquinone diimine, which had been shown to undergo addition with aniline derivatives and phenols. The reaction was followed with 1H NMR spectroscopy to deduce the reaction intermediates.
- Miyagi, Yo,Banjyo, Noriko,Yamamura, Emiko
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- Spectrophotometric determination of the formation constants of the cupric halogen complexes with 1,3-propanediamine and 1,4-butanediamine in methanol solution and their activity on the oxidative coupling of the 2,6-di-tert-butylphenol
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In order to understand the effect that diamine ligands induce in the cupric complexes used as catalyst in the oxidative coupling of 2,6-di-tert- butylphenol, a spectrophotometric study of the speciation of copper(II) with 1,3-propanediamine and 1,4-butanediamine both with Cl- or Br - in methanol solution, was carried out at 303 K. The formation constants and the individual calculated electronic spectra of each species in methanol solution were obtained. The obtained formation constants for the copper(II)-1,3-propanediamine system are: log β110 = 6.70 ± 0.06, log β120 = 11.59 ± 0.09, while for the ternary-chloro or -bromo complexes are log β111 = 10.23 ± 0.06 and log β111 = 10.39 ± 0.02, respectively. On the other hand, for the copper(II)-1,4-butanediamine system are log β110 = 7.44 ± 0.04, log β210 = 11.07 ± 0.04, log β120 = 11.86 ± 0.05, log β230 = 22.53 ± 0.09, though for the ternary systems copper(II)-1,4-butanediamine-chloro or -bromo, the formation constants cannot be determined. A comparative study of the kinetics for the oxidation reaction of 2,6-di-tert-butylphenol, catalyzed using the different cupric complexes with 1,3-propanediamine or 1,4-butanediamine and -chloro or -bromo, has been carried out. The catalytic activity of each complex on the oxidation of 2,6-di-tert-butylphenol was monitored in methanol solution, following the corresponding quinone formation, at 418 nm (ε = 3.95 × 104 L mol-1 cm-1 at 303 K). These kinetic studies indicate that all the copper(II)-1,4-butanediamine complexes, show a remarkable high activity, while the complexes with 1,3-propanediamine are less active although much more active than 1,2-ethylenediamine complexes.
- Segoviano-Garfias, José J.N.,Mendoza-Díaz, Guillermo,Moreno-Esparza, Rafael
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- 4-Hydroxyaryl complexes of group 10 metals
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Attempts have been made to synthesize group 10 metal complexes bearing σ-bonded 4-hydroxyaryl ligands that are potential precursors to metallaquinones. Treatment of 4-bromo-2,6-di-tert-butylphenol with [Pd(PPh3)4] led to formation of the phosphaquinone Ph3P = C6H3tBu2-3,5-O-4 (1), whereas that with [M(PPh3)4] (M = Ni, Pt) yielded the biquinone [C6H3tBu2-3,5-O-4]2 (2). The solid-state structure of 1 features a short C=O double bond and alternate phenyl C-C single and double bonds that are characteristic of quinoidal compounds. Alkylation of [NiCl2(PPh3)2] with (C6H2Me2-3,5-OSiMe3-4)MgBr afforded cis-[Ni(PPh3)2Br(C6H2Me2-3,5-OSiMe3-4)] (3) that reacted with nBu4NF to yield [Ni(PPh3)(C6H2Me2-3,5-OH-4)]2(μ-OH)2 (4) containing a σ-bonded 4-hydroxyaryl ligand.
- So, Shiu-Chun,Cheung, Wai-Man,Sung, Herman H.-Y.,Williams, Ian D.,Leung, Wa-Hung
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- Three Cu(II) complexes based on mixed ligands: Their structures and catalytic behaviour
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The Cu(II) complexes, [Cu(2,5-pydc)(bmi)(H2O)]n, [Cu2(H2O)2(2,6-pydc)2(btx)] ·2H2O and [Cu(btc)2(bmi)2]·1. 5H2O, (bmi = 1-[(benzotriazol-yl)methyl)-1H-1,3-imidazole; 2,5-H 2pydc = pyridine-2,5-dicarboxylic acid; btx = 1,4-bis(1,2,4-triazol- 1-ylmethyl)benzene; H3btc = 1,3,5-benzenetricarboxylate) have been synthesised and their X-ray structures show that hydrogen bonds and π···π stacking interactions are employed in their construction. The complexes can effectively catalyse the oxidative coupling reaction of 2,6-di-tert-butylphenol in good yield and unique selectivity.
- Hu, Jiyong,Liao, Chunli,Zhao, Jin'an
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- Destabilizing Character of a π-Conjugated Boron Center in Bisphenol Radicals
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Although boron-containing radicals are promising materials for molecular electronic devices, the electronic effect of the σ-donating yet π-accepting boron center on the stability of open-shell species has been less discussed. In this work, the role of a tricoordinate boron center in π-conjugated radicals was explored through electron paramagnetic resonance measurement of several boron-linked bisphenol radicals and diradicals. Replacing the bridging methine fragment of a neutral Galvinoxyl radical with an arylboryl group led to the corresponding boron-linked radical anion that requires excessive steric protection at the boron center to be persistent in solution. Experimental and theoretical investigations revealed that the introduction of boron would diminish the quinoidal character of the phenoxyl radical and increase both the electrophilicity and nucleophilicity of the open-shell species. Therefore, it is important to consider the steric protection of the boron center in boron-containing π-conjugated organic radicals.
- Chung, Ming-Han,Yu, Isaac Furay,Liu, Yi-Hung,Lin, Tien-Sung,Peng, Shie-Ming,Chiu, Ching-Wen
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- The Stoichiometric and Catalytic Oxidation of Various Substrates with a Novel Macrocyclic Binuclear Copper(I) Dioxygen Complex as an Intermediate
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The stoichiometric oxidations of hydroquinones, phenols, 3,5-di-tert-butylcatechol and 3,4-dimethylaniline with a macrocyclic Cu(I) dioxygen complex and with a Cu(II) complex show that in some cases the substrate is oxidized both by the Cu(I) dioxygen complex and by the corresponding Cu(II) complex, while in other cases the Cu(II) complex shows no activity; the combination of the Cu(I) dioxygen complex and the Cu(II) complex as oxidants results in catalytic oxidation of the substrate, but no catalysis is observed when only the Cu(I) dioxygen complex is active.
- Rockcliffe, David A.,Martell, Artur E.
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- Heterogeneously catalyzed aerobic oxidative biaryl coupling of 2-naphthols and substituted phenols in water
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The oxidative coupling reaction can efficiently be promoted by supported ruthenium catalyst Ru(OH)x/Al2O3. A variety of 2-naphthols and substituted phenols can be converted to the corresponding biaryl compounds in moderate to excellent yields using molecular oxygen as a sole oxidant in water without any additives. The catalysis is truly heterogeneous in nature, and Ru(OH)x/Al2O3 can easily be recovered after the reaction. The catalyst can be recycled seven times with the maintenance of the catalytic performance, and the total turnover number reaches up to 160. The results of competitive coupling reactions suggest that the present oxidative biaryl coupling reaction proceeds via the homolytic coupling of two radical species and the Ru(OH)x/Al2O3 catalyst acts as an one-electron oxidant. Two radical species are coupled to give the corresponding biaryl product, and the one-electron reduced catalyst is reoxidized by molecular oxygen. The amounts of O2 uptake and H 2O formation were almost one-quarter and one-half the amount of substrate consumed, respectively, supporting the reaction mechanism. The kinetic data and kinetic isotope effect show that the reoxidation of the reduced catalyst is the rate-limiting step for the coupling reaction.
- Matsushita, Mitsunori,Kamata, Keigo,Yamaguchi, Kazuya,Mizuno, Noritaka
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- Oxidation of 2,6-di-tert-butylphenol by dioxygen catalyzed by tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar media
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The oxidation of 2,6-di-tert-butylphenol by dioxygen has been investigated in aqueous micellar aggregates of cetyltrimethylammonium bromide (CTAB) using tetrasodium phthalocyaninatocobalt(II) tetrasulfonate (CoPcTsNa4) as catalyst. The CTAB/CoPcTsNa4 system showed enhanced catalytic activity in the oxidation of 2,6-di-tert-butylphenol compared to that observed in the oxidation reaction in the absence of CTAB. 2,6-Di-tert-butyl-1,4-benzoquinone and 3,5,3',5'-tetra-tert-butyl-4,4-diphenoquinone were identified as reaction products. The initial rate constants of auto-oxidation reaction was found to increase with increasing the pH range from 7.0 to 13.0. The rate constants kobs of auto-oxidation reaction showed linear dependence on catalyst concentration. The rate of auto-oxidation reaction was found to fit a Michealis-Menten kinetic model for the saturation of catalyst sites with increasing 2,6-di-tert-butylphenol concentration and dioxygen pressure. Tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar solution of CTAB was found to be mainly monomeric.
- Hassanein,Sakaran,Shendy
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- Fe(III)-EDTA mediated autoxidation of 2,6-di-t-butylphenol and substituted hydroquinones by molecular oxygen
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Fe(III)-EDTA in aq. MeOH offers a simple environmentally acceptable synthetic tool to oxidize 2,6-di-t-butylphenol to 3,3',5,5'-tetra-t-butyl- 4,4'-diphenoquinone by molecular oxygen with 100% selectivity and several alkyl-substituted hydroquinones to their quinones, in excellent yields, under mild conditions.
- Sain, Bir,Murthy, Pappu S.,Venkateshwar Rao,Prasada Rao,Joshi, Girish C.
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- Hybrid of polyaniline/iron oxide nanoparticles: Facile preparation and catalytic application
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The facile preparative method of iron oxide nanoparticles with polyaniline was developed by thermal reaction of Fe(acac)3. The efficient catalytic activity was demonstrated in the oxidative coupling of 2,6-di-t-butylphenol. Copyright
- Amaya, Toru,Nishina, Yumiko,Saio, Daisuke,Hirao, Toshikazu
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- Autooxidation of 2,6-Di-tert-butylphenol in Water Catalyzed by Cobalt Phthalocyaninetetrasulfonate Bound to Polymer Colloids
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Cobalt phthalocyaninetetrasulfonate (CoPcTs) bound to 54-74-nm styrene-divinylbenzene copolymer latexes substituted with quarternary ammonium ions catalyzes autooxidation of 2,6-di-tert-butylphenol in water ten times faster than does CoPcTs in aqueous solution.
- Turk, Hayrettin,Ford, Warren T.
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- Oxidative C-C coupling of 2,6-di-tert-butylphenol in aqueous media via catalytically active molybdate surfactants
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Long-chain N-alkyliminodiacetatomolybdate catalytic surfactants can be incorporated within a CTAB micellar solution and have shown catalytic activity for the oxidation of 2,6-di-tert-butylphenol to the corresponding diphenoquinone in aqueous media.
- Cull, John E. W.,Richard, Axel,Scott, Jennifer
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- Development of cobalt(3,4-diarylsalen) complexes as tumor therapeutics
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[1,6-Bis(2-hydroxyphenyl)-3,4-diaryl-2,5-diazahexa-1,5-diene]cobalt(II) complexes (cobalt(3,4-diarylsalen)) with 2-, 3-, or 4-OCH3/OH substituents in the 3,4-standing aryl rings were synthesized and tested for antitumor activity in vitro on the MCF-7, MDA-MB 231, and LNCaP/ FGC cell lines. The cytotoxicity depended on both the configuration of the diene ligand and the kind of substituents in the 3,4-standing aromatic rings. d,1-7 (2-OCH 3), d,1-8 (3-OCH3), and d,1-9 (4-OCH3) were equipotent to cisplatin, while the respective hydroxy-substituted complexes (d,1-10 (2-OH), d,1-11(3-OH), and d,1-12 (2-OH)) as well as all of the meso-configured compounds (m-7 to m-12) did not influence the cell growth. Interestingly, a high catalytic potency and a rapid and high accumulation in MCF-7 cells (15- to 25-fold compared to the cell culture medium (5 μM)) were demonstrated for m-7 (2-OCH3), m-8 (3-OCH3), and m-9 (4-OCH3). Therefore, a mode of action based on a cobalt-catalyzed oxidative damage of the DNA is not very likely.
- Gust, Ronald,Ott, Ingo,Posselt, Diana,Sommer, Klaus
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- Template synthesis of polyaniline/Pd nanoparticle and its catalytic application
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Pre-organization of Pd(II) species on polyaniline to form the corresponding d,π-conjugated complex provided a versatile route to a small and well-dispersed nanoparticle, which worked as an efficient redox catalyst for oxidative coupling reaction of 2,6-di-t-butylphenol.
- Amaya, Toru,Saio, Daisuke,Hirao, Toshikazu
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- The Influence of Alkali Metal Ions on the Stability and Reactivity of Chromium(III) Superoxide Moieties Spanned by Siloxide Ligands
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In recent years, it has become clear that the presence of redox-inactive Lewis acidic metal ions can decisively influence the reactivity of metal–dioxygen moieties that are formed in the course of O2 activation, in molecular complexes, and metalloenzymes. Superoxide species are often formed as the primary intermediates but they are mostly too unstable for a thorough investigation. We report here a series of chromium(III) superoxide complexes [L2Cr]M2O2(THF)y (L=?OSiPh2OSiPh2O?, M+=Li+, Na+, K+ and y=4, 5), which could be accessed, studied spectroscopically and partly crystallized at low temperatures. They only differ in the two incorporated Lewis acidic alkali metal counterions (M+) and it could thus be shown that the nature of M+ determines considerably its interaction with the superoxide ligand. This interaction, in turn, has a significant influence on the stability and reactivity of these complexes towards substrates with OH groups. Furthermore, we show that stability and reactivity are also highly solvent dependent (THF versus nitriles), as donor solvents coordinate to the alkali metal ions and thus also influence their interaction with the superoxide moiety. Altogether, these results provide a comprehensive and detailed picture concerning the correlation between spectroscopic properties, structure, and behavior of such superoxides, that may be exemplary for other systems.
- Wind, Marie-Louise,Hoof, Santina,Herwig, Christian,Braun-Cula, Beatrice,Limberg, Christian
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- Oxidation of activated phenols by dioxygen catalysed by the H5PV2Mo10O40 heteropolyanion
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The H5PV2Mo10O40 heteropolyanion has been found to catalyse the highly selective aerobic oxidation of dialkylphenols to diphenoquinones and the oxidation of 2,3,5-trimethylphenol to the 2,3,5-trimethyl-1,4-benzoquinone. The rate is highly dependent on the oxidation potential of the substrate and is proceeds by electron transfer from the phenol substrate to the heteropolyanion catalyst.
- Lissel,Jansen In De Wal,Neumann
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- Phenol Oxidation by a Nickel(III)–Fluoride Complex: Exploring the Influence of the Proton Accepting Ligand in PCET Oxidation
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In order to gain insight into the influence of the H+-accepting terminal ligand in high-valent oxidant mediated proton coupled electron transfer (PCET) reactions, the reactivity of a high valent nickel–fluoride complex [NiIII(F)(L)] (2, L=N,N’-(2,6-dimethylphenyl)-2,6-pyridinecarboxamidate) with substituted phenols was explored. Analysis of kinetic data from these reactions (Evans–Polanyi, Hammett, and Marcus plots, and KIE measurements) and the formed products show that 2 reacted with electron rich phenols through a hydrogen atom transfer (HAT, or concerted PCET) mechanism and with electron poor phenols through a stepwise proton transfer/electron transfer (PT/ET) reaction mechanism. The analogous complexes [NiIII(Z)(L)] (Z=Cl, OCO2H, O2CCH3, ONO2) reacted with all phenols through a HAT mechanism. We explore the reason for a change in mechanism with the highly basic fluoride ligand in 2. Complex 2 was also found to react one to two orders of magnitude faster than the corresponding analogous [NiIII(Z)(L)] complexes. This was ascribed to a high bond dissociation free energy value associated with H?F (135 kcal mol?1), which is postulated to be the product formed from PCET oxidation by 2 and is believed to be the driving force for the reaction. Our findings show that high-valent metal–fluoride complexes represent a class of highly reactive PCET oxidants.
- Mondal, Prasenjit,McDonald, Aidan R.
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- An efficient oxidation of 2,6-di-tert-butylphenol to 3,3',5,5'-tetra-tert- butyl-4,4'-diphenoquinone catalyzed by Lewis Acid system in the presence of molecular oxygen
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An efficient and simple method for the preparation of 3,3',5,5'-tetra-tert- butyl-4,4'-diphenoquinone (TBDPQ) is reported using Lewis Acid as an effective catalyst in the presence of molecular oxygen from 2,6-di-tert-butylphenol (DBP). The present methodology offers several advantages, such as excellent yields, accessible and inexpensive catalysts, easy work-up and green conditions. The oxidation reaction was found to proceed in two steps and the oxidation kinetics for FeCl3 system was examined in detail.
- Sheng, Hong-Ting,Wang, Hui,Feng, Yan,Shi, Jian-Hua,Jiao, Yong-Hua,Zhu, Man-Zhou
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- A nonheme peroxo-diiron(iii) complex exhibiting both nucleophilic and electrophilic oxidation of organic substrates
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The complex [FeIII2(μ-O2)(L3)4(S)2]4+(L3= 2-(4-thiazolyl)benzimidazole, S = solvent) forms upon reaction of [FeII(L3)2] with H2O2and is a functional model of peroxo-diiron intermediates invoked during the catalytic cycle of oxidoreductases. The spectroscopic properties of the complex are in line with those of complexes formed with N-donor ligands. [FeIII2(μ-O2)(L3)4(S)2]4+shows both nucleophilic (aldehydes) and electrophilic (phenol,N,N-dimethylanilines) oxidative reactivity and unusually also electron transfer oxidation.
- Browne, Wesley R.,Giorgi, Michel,Kaizer, József,T?r?k, Patrik,Unjaroen, Duenpen,Viktória Csendes, Flóra
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supporting information
p. 7181 - 7185
(2021/06/11)
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- Transformation of Formazanate at Nickel(II) Centers to Give a Singly Reduced Nickel Complex with Azoiminate Radical Ligands and Its Reactivity toward Dioxygen
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The heteroleptic (formazanato)nickel bromide complex LNi(μ-Br)2NiL [LH = Mes-NH-N═C(p-tol)-N═N-Mes] has been prepared by deprotonation of LH with NaH followed by reaction with NiBr2(dme). Treatment of this complex with KC8led to transformation of the formazanate into azoiminate ligands via N-N bond cleavage and the simultaneous release of aniline. At the same time, the potentially resulting intermediate complex L′2Ni [L′ = HN═C(p-tol)-N═N-Mes] was reduced by one additional electron, which is delocalized across the π system and the metal center. The resulting reduced complex [L′2Ni]K(18-c-6) has aS=1/2ground state and a square-planar structure. It reacts with dioxygen via one-electron oxidation to give the complex L′2Ni, and the formation of superoxide was detected spectroscopically. If oxidizable substrates are present during this process, these are oxygenated/oxidized. Triphenylphosphine is converted to phosphine oxide, and hydrogen atoms are abstracted from TEMPO-H and phenols. In the case of cyclohexene, autoxidations are triggered, leading to the typical radical-chain-derived products of cyclohexene.
- Ar, Deniz,Kilpatrick, Alexander F. R.,Cula, Beatrice,Herwig, Christian,Limberg, Christian
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supporting information
p. 13844 - 13853
(2021/05/04)
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- Enantiospecific Synthesis of Nepetalactones by One-Step Oxidative NHC Catalysis
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An efficient oxidative NHC-catalyzed one-step transformation of (S)-or (R)-8-oxocitronellal to nepetalactone (NL) in enantio- A nd diastereomerically pure form has been developed. Several new and "easy to make" N-Mes-or N-Dipp-substituted 1,2,4-triazolium salts carrying nitroaromatic groups on N1 were synthesized and evaluated as precatalysts in combination with base and stoichiometric organic oxidant. Under optimized conditions, NLs are accessible in very good yields and diastereomerically pure under mild conditions. The oxidant used could be recovered and recycled under operationally simple conditions.
- Harnying, Wacharee,Neud?rfl, J?rg-M.,Berkessel, Albrecht
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supporting information
p. 386 - 390
(2020/02/04)
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- Method for synthesizing and preparing 3,3',5,5'-tetraalkyl-4,4'-biphenyl quinone
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The invention relates to a method for synthesizing and preparing 3,3',5,5'-tetraalkyl-4,4'-biphenyl quinone. According to the method, a novel bis(2-hydroxyloxo-1,10-o-phenanthroline minus monovalent anion)binuclear cuprous (I) complex is added into a synthesis reaction system, and the 3,3',5,5'-tetraalkyl-4,4'-biphenyl quinone is synthesized and prepared from 2,6-dialkyl phenol in a high-selectivity manner under the conditions that a temperature is relatively low, the reaction time is relatively short, a reaction solvent is economical and air serves as an oxidant.
- -
-
Paragraph 0050-0051; 0061; 0066-0067; 0072
(2020/02/27)
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- Functional models of nonheme diiron enzymes: Reactivity of the μ-oxo-μ-1,2-peroxo-diiron(iii) intermediate in electrophilic and nucleophilic reactions
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The reactivity of the previously reported peroxo-adduct [FeIII2(μ-O)(μ-1,2-O2)(IndH)2(solv)2]2+ (1) (IndH = 1,3-bis(2-pyridyl-imino)isoindoline) has been investigated in nucleophilic (e.g., deformylation of alkyl and aryl alkyl aldehydes) and electrophilic (e.g. oxidation of phenols) stoichiometric reactions as biomimics of ribonucleotide reductase (RNR-R2) and aldehyde deformylating oxygenase (ADO) enzymes. Based on detailed kinetic and mechanistic studies, we have found further evidence for the ambiphilic behaviour of the peroxo intermediates proposed for diferric oxidoreductase enzymes.
- Kripli, Balázs,Szávuly, Miklós,Csendes, Flóra Viktória,Kaizer, József
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supporting information
p. 1742 - 1746
(2020/02/20)
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- Concerted proton-electron transfer oxidation of phenols and hydrocarbons by a high-valent nickel complex
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The high-valent nickel(iii) complex Ni(pyalk)2+ (2) was prepared by oxidation of a nickel(ii) complex, Ni(pyalk)2 (1) (pyalk = 2-pyridyl-2-propanoate). 2 and derivatives were fully characterized by mass spectrometry and X-ray crystallography. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy confirm that the oxidation is metal-centered. 2 was found to react with a variety of phenolic and hydrocarbon substrates. A linear correlation between the measured rate constant and the substrate bond dissociation enthalpy (BDE) was found for both phenolic and hydrocarbon substrates. Large H/D kinetic isotope effects were also observed for both sets of substrates. These results suggest that 2 reacts through concerted proton-electron transfer (CPET). Analysis of measured thermodynamic parameters allows us to calculate a bond dissociation free energy (BDFE) of ~91 kcal mol-1 for the O-H bond of the bound pyalk ligand. These findings may shed light onto CPET steps in oxidative catalysis and have implications for ligand design in catalytic systems.
- Fisher, Katherine J.,Feuer, Margalit L.,Lant, Hannah M. C.,Mercado, Brandon Q.,Crabtree, Robert H.,Brudvig, Gary W.
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p. 1683 - 1690
(2020/02/25)
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- Hydrogen Atom Transfer Oxidation by a Gold-Hydroxide Complex
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AuIII-oxygen adducts have been implicated as intermediates in homogeneous and heterogeneous Au oxidation catalysis, but their reactivity is under-explored. Complex 1, ([AuIII(OH)(terpy)](ClO4)2, (terpy = 2,2′:6′,2-terpyridine), readily oxidized substrates bearing C-H and O-H bonds. Kinetic analysis revealed that the oxidation occurred through a hydrogen atom transfer (HAT) mechanism. Stable radicals were detected and quantified as products of almost quantitative HAT oxidation of alcohols by 1. Our findings highlight the possible role of AuIII-oxygen adducts in oxidation catalysis and the capability of late transition metal-oxygen adducts to perform proton coupled electron transfer.
- Lovisari, Marta,McDonald, Aidan R.
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supporting information
(2020/03/13)
-
- Structure, Spectroscopy, and Reactivity of a Mononuclear Copper Hydroxide Complex in Three Molecular Oxidation States
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Structural, spectroscopic, and reactivity studies are presented for an electron transfer series of copper hydroxide complexes supported by a tridentate redox-active ligand. Single crystal X-ray crystallography shows that the mononuclear [CuOH]1+ core is stabilized via intramolecular H-bonds between the H-donors of the ligand and the hydroxide anion when the ligand is in its trianionic form. This complex undergoes two reversible oxidation processes that produce two metastable "high-valent"CuOH species, which can be generated by addition of stoichiometric amounts of 1e- oxidants. These CuOH species are characterized by an array of spectroscopic techniques including UV-vis absorption, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies (XAS), which together indicate that all redox couples are ligand-localized. The reactivity of the complexes in their higher oxidation states toward substrates with modest O-H bond dissociation energies (e.g., 4-substitued-2,6-di-tert-butylphenols) indicates that these complexes act as 2H+/2e- oxidants, differing from the 1H+/1e- reactivity of well-studied [CuOH]2+ systems.
- Garcia-Bosch, Isaac,Lancaster, Kyle M.,Macmillan, Samantha N.,Rajabimoghadam, Khashayar,Siegler, Maxime A.,Wu, Tong
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p. 12265 - 12276
(2020/08/06)
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- Distribution of Spin Density on Phenoxyl Radicals Affects the Selectivity of Aerobic Oxygenation of Phenols
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Phenoxyl radical was generally suggested as the intermediate during copper-catalyzed aerobic oxygenation of phenols. However, the substrate-dependent selectivity has not been well interpreted, due to insufficient characterization of the radical intermediate under reaction conditions. When studying the CuCl-LiCl-catalyzed aerobic phenol oxidation, we obtained EPR spectra of phenoxyl radicals generated by oxidizing phenols with the preactivated catalyst. Upon correlation to the selectivity of benzoquinone, the hyperfine coupling constant of para-site proton (aH, para) was found to be better than the Hammett constant. The catalysis mechanism was studied based on EPR detection and the reaction results of phenoxyl radicals under N2 or O2 atmosphere. It appeared that the chemoselectivity depended on the attack of activated dioxygen on phenoxyl radicals, and the activation of dioxygen by [CunCln+1]- (n = 1, 2, 3) was suggested as the rate-determining step. Understanding of the substrate-dependent selectivity contributed to predicting the chemoselectivity in the aerobic oxidation of phenols.
- Chen, Kaizhou,Du, Renfeng,Fan, Mengtian,Guan, Jun,Jiang, Zheng,Li, Haoran,Lu, Rui,Mei, Bingbao,Wang, Yongtao,Yao, Jia
-
-
- Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O2 at an Iron(II)-Cyclam Center
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In soluble methane monooxygenase enzymes (sMMO), dioxygen (O2) is activated at a diiron(II) center to form an oxodiiron(IV) intermediate Q that performs the challenging oxidation of methane to methanol. An analogous mechanism of O2 activation at mono-or dinuclear iron centers is rare in the synthetic chemistry. Herein, we report a mononuclear non-heme iron(II)-cyclam complex, 1-trans, that activates O2 to form the corresponding iron(IV)-oxo complex, 2-trans, via a mechanism reminiscent of the O2 activation process in sMMO. The conversion of 1-trans to 2-trans proceeds via the intermediate formation of an iron(III)-superoxide species 3, which could be trapped and spectroscopically characterized at-50 °C. Surprisingly, 3 is a stronger oxygen atom transfer (OAT) agent than 2-trans; 3 performs OAT to 1-trans or PPh3 to yield 2-trans quantitatively. Furthermore, 2-trans oxidizes the aromatic C-H bonds of 2,6-di-tert-butylphenol, which, together with the strong OAT ability of 3, represents new domains of oxoiron(IV) and superoxoiron(III) reactivities.
- Kass, Dustin,Corona, Teresa,Warm, Katrin,Braun-Cula, Beatrice,Kuhlmann, Uwe,Bill, Eckhard,Mebs, Stefan,Swart, Marcel,Dau, Holger,Haumann, Michael,Hildebrandt, Peter,Ray, Kallol
-
supporting information
p. 5924 - 5928
(2020/05/08)
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- Catalytic Aerobic Phenol Homo- and Cross-Coupling Reactions with Copper Complexes Bearing Redox-Active Guanidine Ligands
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Due to their large importance in synthetic chemistry, catalytic C?C coupling reactions of phenols are currently intensively studied. Herein, new copper catalysts for the C?C coupling reaction of phenols using dioxygen as a green oxidizing reagent are reported. By using redox-active guanidine ligands, the activity as well as chemoselectivity in the cross-coupling reaction of non-complementary phenols (between an electron-rich phenol and a less nucleophilic second phenol) is significantly improved. Based on the collected data for several test reactions, a reaction mechanism is proposed.
- Sch?n, Florian,Kaifer, Elisabeth,Himmel, Hans-J?rg
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supporting information
p. 8279 - 8288
(2019/06/04)
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- Redox-Active Guanidines in Proton-Coupled Electron-Transfer Reactions: Real Alternatives to Benzoquinones?
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Guanidino-functionalized aromatics (GFAs) are readily available, stable organic redox-active compounds. In this work we apply one particular GFA compound, 1,2,4,5-tetrakis(tetramethylguanidino)benzene, in its oxidized form in a variety of oxidation/oxidative coupling reactions to demonstrate the scope of its proton-coupled electron transfer (PCET) reactivity. Addition of an excess of acid boosts its oxidation power, enabling the oxidative coupling of substrates with redox potentials of at least +0.77 V vs. Fc+/Fc. The green recyclability by catalytic re-oxidation with dioxygen is also shown. Finally, a direct comparison indicates that GFAs are real alternatives to toxic halo- or cyano-substituted benzoquinones.
- Wild, Ute,Hübner, Olaf,Himmel, Hans-J?rg
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supporting information
p. 15988 - 15992
(2019/11/13)
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- High-Valent d7 NiIII versus d8 CuIII Oxidants in PCET
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Oxygenases have been postulated to utilize d4 FeIV and d8 CuIII oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal-oxygen adducts, [NiIII(OAc)(L)] (1b) and [CuIII(OAc)(L)] (2b), L = N,N′-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [NiII(OAc)(L)]- (1a) and [CuII(OAc)(L)]- (2a). The complexes 1a/b-2a/b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, X-ray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para-substituted 2,6-di-tert-butylphenols (p-X-2,6-DTBP; X = OCH3, C(CH3)3, CH3, H, Br, CN, NO2) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d8 CuIII oxidant displayed a small increase in the rate constant compared to that of the d7 NiIII oxidant. The d8 CuIII oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDEC-H) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b. It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.
- Unjaroen, Duenpen,Gericke, Robert,Lovisari, Marta,Nelis, Daniel,Mondal, Prasenjit,Pirovano, Paolo,Twamley, Brendan,Farquhar, Erik R.,Mcdonald, Aidan R.
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supporting information
p. 16838 - 16848
(2019/12/24)
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- Selective, Catalytic, and Metal-Free Coupling of Electron-Rich Phenols and Anilides Using Molecular Oxygen as Terminal Oxidant
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Selective oxidative homo- and cross-coupling of electron-rich phenols and anilides was developed using nitrosonium tetrafluoroborate as a catalyst. Oxidative coupling of phenols revealed unusual selectivities, which translated into the unprecedented synthesis of inverse Pummerer-type ketones. Mechanistic studies suggest that oxidative coupling of phenols and anilides shares a common pathway via homolytical heteroatom-hydrogen bond cleavage. Nitrosonium salt catalysis was applied for cross-dehydrogenative coupling initiated by generation of heteroatom-centered radicals.
- Bering, Luis,Vogt, Melina,Paulussen, Felix M.,Antonchick, Andrey P.
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supporting information
p. 4077 - 4080
(2018/07/15)
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- Probucol derivative, preparation method and application thereof
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The invention relates to the fields of compounds, and specifically relates to a probucol derivative, a preparation method and the application thereof. The probucol derivative has a structure shown asa general formula I. The probucol derivative provided by the invention can be used for prevention and curing of vascular diseases such as diabetes and cardiovascular and cerebrovascular diseases or complications thereof, can be used for reducing blood glucose, reducing blood fat, reducing cholesterol, reducing the weight, reducing triglyceride, resisting inflammation and oxidation and the like effectively, and has a wide application prospect.
- -
-
Paragraph 0450; 0451; 0452
(2019/06/17)
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- Hydrogen atom transfer by a high-valent nickel-chloride complex
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Oxo-metal-halide moieties have often been implicated as C-H bond activating oxidants with the terminal oxo-metal entity identified as the electrophilic oxidant. The electrophilic reactivity of metal-halide species has not been investigated. We have prepared a high-valent nickel-halide complex [NiIII(Cl)(L)] (2, L = N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamide) by one-electron oxidation of a [NiII(Cl)(L)]? precursor. 2 was characterized using electronic absorption, electron paramagnetic resonance, and X-ray absorption spectroscopies and mass spectrometry. 2 reacted readily with substrates containing either phenolic O-H or hydrocarbon C-H bonds. Analysis of the Hammett, Evans-Polanyi, and Marcus relationships between the determined rate constants and substrate pKa, X-H bond dissociation energy, and oxidation potential, respectively, was performed. Through this analysis, we found that 2 reacted by a hydrogen atom transfer (HAT) mechanism. Our findings shine light on enzymatic high-valent oxo-metal-halide oxidants and open new avenues for oxidative halogenation catalyst design.
- Mondal, Prasenjit,Pirovano, Paolo,Das, Ankita,Farquhar, Erik R.,McDonald, Aidan R.
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supporting information
p. 1834 - 1841
(2018/02/17)
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- Modulation of Nickel Pyridinedicarboxamidate Complexes to Explore the Properties of High-valent Oxidants
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High-valent Ni oxidants have been implicated in hydrocarbon oxidation catalysis, however, little is understood about the properties of these oxidants. Herein, a family of NiII complexes supported by a pyridinedicarboxamidate ligand and different ancillary ligands was synthesized. The series spans coordination numbers 4, 5, and 6, and contains neutral, mono- and di-anionic donor types. X-ray crystallography and magnetic measurements showed that the 4-coordinate complexes were square planar and low spin (S=0) and the 5- and 6-coordinate were intermediate spin (S=1). The NiII complexes could be oxidized by one electron to form a series of metastable NiIII species. EPR analysis confirmed their description as S=1/2 NiIII compounds with signal shape and hyperfine coupling dependent on the coordination environment. The oxidation of phenols by the NiIII species was probed, providing evidence for a correlation between oxidizing power and electron-donating properties of the supporting ligands. Critically, we found that the pyridinedicarboxamidate ligand may be a non-innocent proton acceptor in the oxidation reactions.
- Pirovano, Paolo,Twamley, Brendan,McDonald, Aidan R.
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supporting information
p. 5238 - 5245
(2018/01/27)
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- Synthesis method of 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone
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The invention provides a synthesis method of 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone. 2,6-dialkyl phenol is dissolved in a reaction solvent; a copper ion loaded hydrophobic modified resin catalyst and an oxidizing agent are added; reaction is performed for 2 to 8h at 40 DEG C to 80 DEG C; filtering is performed to obtain filter liquid; then, the filter liquid is distilled; distillation residues are cleaned by alkanol; after the drying, the 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone is obtained. The synthesis method is simple; after being recovered, the catalyst can be repeatedly used; the reaction selectivity is high; the yield of the 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone can reach 95 percent or higher; no by-product of polyphenyl ether is generated; the copper ion content is smaller than 5mu g/g; the product purity is greater than or equal to 99.5 percent.
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-
Paragraph 0081; 0082; 0083
(2017/08/29)
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- Iridium-Catalyzed C4-Alkylation of 2,6-Di-tert-butylphenol by Using Hydrogen-Borrowing Catalysis
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An iridium-catalyzed hydrogen-borrowing process has been developed whereby 2,6-di-tert-butylphenol can be alkylated at the C4-position by using a range of primary alcohols (11 examples, 40-93% yield). Following this, a selection of the products obtained underwent retro-Friedel-Crafts reactions to provide para-substituted phenols, which could potentially undergo further synthetic manipulations.
- Frost, James R.,Cheong, Choon Boon,Donohoe, Timothy J.
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p. 910 - 916
(2017/02/15)
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- 3,3′,5,5′-Tetra- tert -butyl-4,4′-diphenoquinone (DPQ)-Air as a New Organic Photocatalytic System: Use in the Oxidative Photocyclization of Stilbenes to Phenacenes
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We report an organic photocatalytic system, namely 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone (DPQ) and air, capable of coupling efficiently with the photocyclization of stilbenes to afford phenacenes. The potential of this new and mild process is shown with the synthesis of [5]- and [7]phenacene, two semiconductors recently implemented into organic electronic devices, with high yields and remarkable purity.
- Carrera, Manuel,De La Viuda, Mónica,Guijarro, Albert
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supporting information
p. 2783 - 2787
(2016/12/16)
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- Dioxygen Activation by a Hexagonal SrMnO3 Perovskite Catalyst for Aerobic Liquid-Phase Oxidation
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Heterogeneous catalysts, which allow a reductive activation of dioxygen (O2) under mild reaction conditions, are promising candidates for highly efficient aerobic oxidation. An effective hexagonal SrMnO3 (SMO) perovskite catalyst for liquid-phase selective oxidation with O2 was successfully synthesized by the polymerized complex method. The activity of SMO for the aerobic oxidation of alcohols was higher than those of typical manganese oxide-based catalysts and was heterogeneous, so that the recovered catalyst could be reused without heat treatment under oxidative conditions while keeping its high catalytic performance. The reversible reaction on the surface Mn species on SMO with O2 leads to the formation of Mn–superoxo species, which catalyze the selective oxidative transformation of various types of organic substrates into the desired oxygenated or dehydrogenated products.
- Kawasaki, Shuma,Kamata, Keigo,Hara, Michikazu
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p. 3247 - 3253
(2016/10/24)
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- Functional models of nonheme diiron enzymes: Kinetic and computational evidence for the formation of oxoiron(IV) species from peroxo-diiron(III) complexes, and their reactIVity towards phenols and H2O2
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The reactivity of the previously reported peroxo adducts [Fe2(μ-O2)(L1)4(CH3CN)2]2+, and [Fe2(μ-O2)(L2)4(CH3CN)2]2+, (L1 = 2-(2′-pyridyl)benzimidazole and L2 = 2-(2′-pyridyl)-N-methylbenzimidazole) towards H2O2 as catalase mimics, and towards various phenols as functional RNR-R2 mimics, is described. Kinetic, mechanistic and computational studies gave direct evidence for the involvement of the (μ-1,2-peroxo)diiron(iii) intermediate in the O-H activation process via formation of low-spin oxoiron(iv) species.
- Szávuly, Miklós István,Surducan, Mihai,Nagy, Emoke,Surányi, Mátyás,Speier, Gábor,Silaghi-Dumitrescu, Radu,Kaizer, József
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supporting information
p. 14709 - 14718
(2016/10/03)
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- Tuning the Reactivity of Terminal Nickel(III)-Oxygen Adducts for C-H Bond Activation
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Two metastable NiIII complexes, [NiIII(OAc)(L)] and [NiIII(ONO2)(L)] (L = N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate, OAc = acetate), were prepared, adding to the previously prepared [NiIII(OCO2H)(L)], with the purpose of probing the properties of terminal late-transition metal oxidants. These high-valent oxidants were prepared by the one-electron oxidation of their NiII precursors ([NiII(OAc)(L)]- and [NiII(ONO2)(L)]-) with tris(4-bromophenyl)ammoniumyl hexachloroantimonate. Fascinatingly, the reaction between any [NiII(X)(L)]- and NaOCl/acetic acid (AcOH) or cerium ammonium nitrate ((NH4)2[CeIV(NO3)6], CAN), yielded [NiIII(OAc)(L)] and [NiIII(ONO2)(L)], respectively. An array of spectroscopic characterizations (electronic absorption, electron paramagnetic resonance, X-ray absorption spectroscopies), electrochemical methods, and computational predictions (density functional theory) have been used to determine the structural, electronic, and magnetic properties of these highly reactive metastable oxidants. The NiIII-oxidants proved competent in the oxidation of phenols (weak O-H bonds) and a series of hydrocarbon substrates (some with strong C-H bonds). Kinetic investigation of the reactions with di-tert-butylphenols showed a 15-fold enhanced reaction rate for [NiIII(ONO2)(L)] compared to [NiIII(OCO2H)(L)] and [NiIII(OAc)(L)], demonstrating the effect of electron-deficiency of the O-ligand on oxidizing power. The oxidation of a series of hydrocarbons by [NiIII(OAc)(L)] was further examined. A linear correlation between the rate constant and the bond dissociation energy of the C-H bonds in the substrates was indicative of a hydrogen atom transfer mechanism. The reaction rate with dihydroanthracene (k2 = 8.1 M-1 s-1) compared favorably with the most reactive high-valent metal-oxidants, and showcases the exceptional reactivity of late transition metal-oxygen adducts.
- Pirovano, Paolo,Farquhar, Erik R.,Swart, Marcel,McDonald, Aidan R.
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supporting information
p. 14362 - 14370
(2016/11/13)
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- A copper complex and its preparation method and application
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The invention discloses a copper complex, a preparation method and application thereof. The chemical formula of the copper complex is [Cu(dpca)(phen)(CH3OH)]NO3.H2O, Hdpca is 2,4-dihydroxy pyrimidine-5-carboxylic acid, and phen is phenanthroline. A monocrystal complex by self assembling of molecules has certain granularity, a unique structure, high catalytic activity, high selectivity and good stability, is mild in condition, high in yield, good in reproducibility and free of pollution in production, can be prepared at normal temperature and normal pressure, and has latent economic benefit, social benefit and environmental benefit.
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-
Paragraph 0036; 0037; 0038; 0039
(2016/10/09)
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- The reactivity of manganese dioxide towards different substrates in organic solvents
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The reactivity of manganese dioxide in organic solvents was studied by reacting commercial manganese dioxide MnO2 with different substrates. The reaction of MnO2 with arylimino, indolinonic and quinolinic aromatic nitroxides gave quinoneimine N-oxides via an electron transfer process followed by oxygen transfer. A reduction potential of 0.9 V vs. NHE was roughly estimated for manganese dioxide in aprotic organic solvents by considering the oxidation potentials of those nitroxides able to react with MnO2. By the reaction with para-anisidine the amine radical cation was initially formed through a simple electron transfer process. In the case of substituted phenols, the isolated products were derived instead from the phenoxy radicals generated via hydrogen transfer or an equivalent process. Finally, the quantitative conversion of triphenylphosphine to triphenylphosphine oxide was explained by oxygen atom transfer in a cyclic intermediate derived from an initial nucleophilic attack of phosphorus on MnO2.
- Alberti, Angelo,Astolfi, Paola,Carloni, Patricia,Greci, Lucedio,Rizzoli, Corrado,Stipa, Pierluigi
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p. 8964 - 8970
(2015/11/10)
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- Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols
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Abstract Enzymatic reactions have inspired many chemists to design small molecule mimics that would perform the function of the enzymes in aqueous and or non-aqueous medium. Catechol oxidase (CO) and phenoxazinone synthase (PHS) are two multi-copper enzymes in nature, which has led to model complexes of Mn, Fe, Co, Ni, Cu. Based on our earlier work in this area we have probed the commercially available metal acetates of the above metals to establish a trend in reactivity for catalytic conversions similar to those of the two enzymes. The results show that Mn is the best 3d transition metal for similar catalysis. MnII acetate was found to convert 3,5-di-tert-butylcatechol (DTBC) to 3,5-di-tert-butylquinone (DTBQ) with a kcat of 1.3(1) × 103 h-1and for o-aminophenol (OAP) to 2-aminophenoxazinone (APX) conversion the kcat = 111(2) h-1, demonstrating efficient CO and PHS like activity. Kinetic studies show that DTBC oxidation follows a first order kinetics with respect to the substrate for each of those metal(II) acetates with activity order of Mn >> Co > Cu > Fe ≥ Ni. Through mechanistic investigation we found that the reactive oxygen species detected during the oxidation of DTBC is mostly hydroxyl radical for Mn, Fe and Co whereas Cu and Ni generate H2O2.
- Dey, Suman Kr.,Mukherjee, Arindam
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- Aerobic oxidation of phenols and related compounds using carbon nanotube-gold nanohybrid catalysts
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Gold nanoparticles supported on carbon nanotubes were investigated as catalysts in the aerobic oxidation of various substrates (phenols, hydroquinones, catechols, aminophenols, and thiols). The nanohybrid system compares favorably with other supported noble metal catalysts in terms of overall efficacy as it operates at room temperature, under air atmosphere (no external oxidant needed), and can readily be recycled. Coming up for air: Gold nanoparticles supported on carbon nanotubes were investigated as efficient catalysts in the catalytic aerobic oxidation of phenol-type compounds.
- Jawale, Dhanaji V.,Gravel, Edmond,Geertsen, Valerie,Li, Haiyan,Shah, Nimesh,Namboothiri, Irishi N. N.,Doris, Eric
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p. 719 - 723
(2014/03/21)
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- {Cu2+-Co3+-Cu2+} and {Cu2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co3+-Cu+} (3), {Cu+-Fe3+-Cu+} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu+} (3), {Cu+-Fe3+-Cu+} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes.
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2015/04/27)
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- A green mesostructured vanadosilicate catalyst and its unprecedented catalytic activity for the selective synthesis of 2,6-disubstituted p-benzoquinones
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We have developed a green method for the production of 2,6-disubstituted p-benzoquinones (DSBQs) by liquid-phase oxidations of di/tri-substituted phenols using two-dimensional hexagonally thick-walled mesoporous vanadosilicate catalysts. In particular, 2,6-di-tert-butyl-p-benzoquinone was synthesized by the oxidation of 2,6-di-tert-butylphenol, using various reaction parameters, over mesoporous VSBA-15 catalysts synthesized with various vanadium contents. A promising chemical treatment method for the preparation of green mesoporous VSBA-15(5) or W-VSBA-15(5) (W: washed) catalysts was successfully used in the presence of ammonium acetate solution to remove moderately toxic non-framework V2O5 crystallite species from the active surface, and the catalytic activity of the recovered green mesoporous VSBA-15(5) catalyst was determined. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. The combined results show that the green mesoporous VSBA-15(5) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of DSBQs (98-100%), and has unprecedented catalytic activity compared with other mesoporous vanadosilicate catalysts. The Royal Society of Chemistry 2014.
- Selvaraj,Park,Kim
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p. 958 - 966
(2014/01/06)
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- {Cu2+-Co3+-Cu2+} and {Cu 2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co 3+-Cu+} (3), {Cu+-Fe3+-Cu +} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu 2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu +} (3), {Cu+-Fe3+-Cu+} (4), {Cu 2+-Co3+-Cu2+} (5), and {Cu2+-Fe 3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes. Copyright
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2014/05/06)
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- Selective oxidative homo-and cross-coupling of phenols with aerobic catalysts
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Simple catalysts that use atom-economical oxygen as the terminal oxidant to accomplish selective ortho-ortho, ortho-para, or para-para homo-couplings of phenols are described. In addition, chromium salen catalysts have been discovered as uniquely effective in the cross-coupling of different phenols with high chemo-and regioselectivity.
- Lee, Young Eun,Cao, Trung,Torruellas, Carilyn,Kozlowski, Marisa C.
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supporting information
p. 6782 - 6785
(2014/06/09)
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- Role of steric hindrance in the Newman-Kwart rearrangement and in the synthesis and photophysical properties of arylsulfanyl tetrapyrazinoporphyrazines
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Conditions for the Newman-Kwart rearrangement of phenols into thiophenols were investigated in relation to the bulkiness of substituents at the 2 and 6 positions of the starting phenol derivative with an emphasis on eliminating side reactions. Thiophenols with different 2,6-disubstitution patterns (including hydrogen, methyl, isopropyl or tert-butyl groups) were used for the synthesis of 5,6-bis(arylsulfanyl)pyrazine-2,3-dicarbonitriles that underwent cyclotetramerization leading to the corresponding zinc tetrapyrazinoporphyrazines (TPyzPz), aza-analogues of phthalocyanines. Several methods for the cyclotetramerization were attempted to eliminate problematic side reactions. Magnesium butoxide was found as the most suitable cyclotetramerization agent and afforded TPyzPzs in reasonable yields of approximately 30% under mild conditions. The varying arrangements of the peripheral substitutions resulting from the different bulkiness of the substituents were demonstrated by the X-ray structures of the pyrazine-2,3-dicarbonitriles. The prepared zinc arylsulfanyl TPyzPzs showed an absorption maximum at a Q-band over 650 nm, fluorescence quantum yields between 0.078 and 0.20, and singlet oxygen quantum yields ranging 0.58-0.69. TPyzPzs with isopropyl groups were found to be the best derivatives in this series as they combined facile cyclotetramerization, no aggregation, and good photophysical properties, which makes them potentially suitable for photodynamic therapy.
- Novakova, Veronika,Miletin, Miroslav,Filandrova, Tereza,Lenco, Juraj,Ruiszicka, Ales,Zimcik, Petr
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p. 2082 - 2093
(2014/04/03)
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- Electron-deficient naphthalene diimides as efficient planar π-acid organocatalysts for selective oxidative C-C coupling of 2,6-di-tert-butylphenol: A temperature effect
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An efficient planar π-acid electron transfer organocatalyst based on electron-deficient substituted naphthalene diimide has been developed for oxidative C-C coupling of 2,6-di-tert-butylphenol to its dimeric derivative or unexpected ring-rearranged trimeric quinone methide by controlling the reaction temperatures.
- Ke, Hua,Wang, Li,Chen, Yong,Lin, Mei-Jin,Chen, Jian-Zhong
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- Bismuth-based cyclic synthesis of 3,5-di-tert-butyl-4-hydroxybenzoic acid via the oxyarylcarboxy dianion, (O2CC6H2 tBu2O)2-
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3,5-Di-tert-butyl-4-hydroxybenzoic acid can be made under mild conditions in a cyclic process from carbon dioxide and 3,5-di-tert-butyl-4-phenol using bismuth-based C-H bond activation and CO2 insertion chemistry starting with the Bi3+ complex, Ar′BiCl2, of the NCN pincer ligand, Ar′ = 2,6-(Me2NCH2) 2C6H3. Complexes of the recently discovered oxyaryl dianion, (C6H2tBu2-3,5-O-4) 2-, and the oxyarylcarboxy dianion, [O2C(C 6H2tBu2-3,5-O-4)]2-, are intermediates in the process. Further studies of the oxyarylcarboxy dianion in Ar′Bi[O2C(C6H2tBu 2-3,5-O-4)-κ2O,O′], show that it undergoes decarboxylation upon reaction with I2 and it reacts with trimethylsilyl chloride to produce the trimethylsilyl ether of the trimethylsilyl ester of 3,5-di-tert-butyl-4-hydroxybenzoic acid and the Ar′BiCl2 starting material.
- Kindra, Douglas R.,Evans, William J.
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supporting information
p. 3052 - 3054
(2014/03/21)
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- Efficient oxidative coupling of 2,6-disubstituted phenol catalyzed by a dicopper(II) complex
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Complexation of a rigid multi-pyridine ligand bis(2-pyridyl)-1,8- naphthyridine (bpnp) with [Cu2(TFA)4] (TFA = trifluoroacetate) resulted in the formation of a dinuclear copper(ii) complex, namely [Cu2(bpnp)(μ-OH)(TFA)3] (1). This complex has been characterized by X-ray crystallographic, spectroscopic and elemental analyses. Complex 1 is an efficient catalyst for the oxidative coupling of various 2,6-disubstituted phenols with molecular oxygen. Yields and selectivity depend on the reaction conditions employed, the best results being obtained in isopropanol or dioxane at 90 °C with yields of >99%. Mechanistic pathway of the catalysis is discussed.
- Liao, Bei-Sih,Liu, Yi-Hung,Peng, Shei-Ming,Liu, Shiuh-Tzung
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scheme or table
p. 1158 - 1164
(2012/03/07)
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- Halochromic phenolate perylene bisimides with unprecedented NIR spectroscopic properties
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C-C coupling of 1,7-dibromoperylene bisimide with sterically hindered 2,6-di-tert-butylphenol by a carbon nucleophilic substitution reaction in the absence of transition-metal catalysts gave novel halochromic perylene bisimides (see picture). The corresponding phenolate ions of these compounds exhibit unprecedented NIR spectroscopic properties including strong absorption with maxima at around 1200 nm.
- Lin, Mei-Jin,Fimmel, Benjamin,Radacki, Krzysztof,Wuerthner, Frank
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supporting information; experimental part
p. 10847 - 10850
(2012/01/02)
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- A simple and efficient oxidative coupling of aromatic nuclei mediated by manganese dioxide
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Oxidative intramolecular coupling of the aryl rings of various stilbenes for direct construction of the phenanthrene ring system is promoted efficiently by manganese dioxide-trifluoroacetic acid at room temperature in excellent yields. This approach is also applied to the intermolecular biaryl coupling of 2-naphthols, 2-naphthalenethiol, 2-naphthylamine, a phenol ether and a phenol under very mild conditions. An electron-transfer mechanism is proposed in which manganese dioxide acts as a two-electron oxidant.
- Wang, Kailiang,Hu, Yanna,Li, Zheng,Wu, Meng,Liu, Zhihui,Su, Bo,Yu, Ao,Liu, Yu,Wang, Qingmin
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experimental part
p. 1083 - 1090
(2010/06/13)
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