- Efficient aryl-(hetero)aryl coupling by activation of C-Cl and C-F bonds using nickel complexes of air-stable phosphine oxides
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(Chemical Equation Presented) A couple of couplings: Air-stable diamino-and dioxophosphine oxides are used as preligands in the nickel-catalyzed Kumada cross-coupling reactions of aryl Grignard reagents. A sterically hindered preligand allows for highly efficient cross-coupling of aryl fluorides at ambient temperature (acac = acetylacetonate).
- Ackermann, Lutz,Born, Robert,Spatz, Julia H.,Meyer, Daniel
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- Association Reactions of Trimethylsilyl Ions
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Adduct ions, (1+), were produced by bimolecular association reactions of trimethylsilyl ions, (CH3)3Si(1+), with acetone, cyclohexanone, anisole, dimethyl ether, 2,5-dimethylfuran, 2-methylfuran and furan in ion cyclotron resonance experiments at 300 K and at pressures of ca. 10-7 Torr (1 Torr = 133,3 Pa).The rate constants, ka, for the association reactions varied from 100percent to 2 percent of the collision rate constants, kc.The rate constants were independent of pressure, except for furan.Measurements were also made of bond dissociation energies for these adduct ions, D, from equilibrium measurements.The a ssociation efficiency, ka/kc, increased with increasing bond dissociation energy and with increasing numbers of degrees of freedom, in qualitative aggreement with theoretical predictions.Observations pertinent to the dependence of ka on reactant temperature and relative kinetic energy are discussed.The possibility of determining ion-neutral complex binding energies from radiative association rate constants is considered.
- Lin, Yi,Ridge, D. P.,Munson, Burnaby
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- Ortho-selective methylation of phenol catalyzed by CeO2-MgO prepared by citrate process
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Vapor-phase alkylation of phenol with methanol was investigated over CeO2-MgO catalysts prepared utilizing a molten mixture of the corresponding nitrates and citric acid. The CeO2-MgO had attractive catalytic performance without decay of activities at the temperature range between 450 and 550°C, and it had excellent selectivities to the sum of o-cresol and 2,6-xylenol higher than 98%. The CeO2-MgO catalysts were found to be mixtures of MgO and an interstitial solid solution of MgxCe1-x/2O2 as a result of XRD measurement. It is confirmed that citric acid used in the preparation heightens the dispersion of the solid solution in the MgO matrix. The pure CeO2, which also exhibited efficient ortho-selectivity, had only weak basic sites in the TPD experiment of adsorbed CO2, while the pure MgO with strong basicity showed very low reaction rate in the methylation. The solid solution of MgxCe1-x/2O2 in the CeO2-MgO catalyst probably provides active centers for the methylation of phenol. In the results of methanol decomposition, methanol was converted into CO, CO2, and CH4 over the CeO2-MgO catalysts, without producing dimethyl ether. The reaction mechanism of the ortho-methylation over the CeO2-MgO catalyst is speculated: the ortho position of phenol adsorbed perpendicularly on weak basic sites on the MgxCe1-x/2O2 solid solution is selectively alkylated by methanol which is possibly activated in the form of formyl or hydroxy methyl group rather than methyl cation.
- Sato, Satoshi,Koizumi, Kaoru,Nozaki, Fumio
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- Dehydrogenative coupling of primary alcohols to form esters catalyzed by a ruthenium N-heterocyclic carbene complex
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The ruthenium complex [RuCl2(IiPr)(p-cymene)] catalyzes the direct condensation of primary alcohols into esters and lactones with the release of hydrogen gas. The reaction is most effective with linear aliphatic alcohols and 1,4-diols and is believed to proceed with a ruthenium dihydride as the catalytically active species.
- Solvhoj, Amanda,Madsen, Robert
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- Ionic liquids as recyclable and separable reaction media in Rh-catalyzed decarbonylation of aromatic and aliphatic aldehydes
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Ionic liquids (ILs) have been applied as recyclable reaction media in the decarbonylation of aldehydes in the presence of a rhodium-phosphine complex catalyst. The performance of several new catalytic systems based on imidazolium-based ILs and [Rh(dppp)2]Cl (dppp: 1,3-diphenylphosphinopropane) were excellent in the decarbonylation of both aromatic and aliphatic aldehydes providing >99 yield of benzenes and alkanes, respectively. The catalytic performance depended, however, strongly on the employed IL and its thermal stability. In addition, the ILs afforded good catalyst immobilization as well as a biphasic system with the product allowing recovery and reuse of the employed catalyst.
- Malcho, Phillip,Garca-Surez, Eduardo J.,Riisager, Anders
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- Cationic nickel porphyrinoids with unexpected reactivity
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Cationic nickel(ii) complexes of two ring-contracted porphyrinoid ligands distantly related to the corrins were prepared by metal templated macrocyclisation. The compounds show reversible electron transfer processes and were found to be the first porphyrinoid-based catalysts for C-C cross-coupling.
- Wicht, Richard,Bahnmüller, Stefanie,Brandhorst, Kai,Schweyen, Peter,Br?ring, Martin
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- Fluoroform-derived CuCF3 for low-cost, simple, efficient, and safe trifluoromethylation of aryl boronic acids in air
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Easy does it: Aryl boronic acids undergo smooth and selective trifluoromethylation with low-cost fluoroform-derived CuCF3 in DMF in non-dried air. The reaction occurs under mild conditions (1 atm, room temperature), exhibits unprecedented funct
- Novak, Petr,Lishchynskyi, Anton,Grushin, Vladimir V.
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- Nucleophilic trifluoromethylation of aryl halides with methyl trifluoroacetate
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When associated with an alkaline halide, such as cesium fluoride or cesium chloride, and Cu(I) species, methyl trifluoroacetate (MTFA) constitutes a valuable trifluoromethylating agent for substituting aromatic (or heteroaromatic) iodides and bromides. The reaction can be carried out in DMF at 180 °C or, better, in sulfolane which allows he reaction to proceed at a lower temperature (from 140 °C).
- Langlois, Bernard R.,Roques, Nicolas
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- PdCl2-catalyzed hydrogenolysis of a C-O bond in monoaryl sulfates by sodium phosphinate in an aqueous alkaline medium
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The hydrogenolysis of the C-O bond in monoaryl sulfates by the action of an excess of NaH2PO2 in the presence of catalytic amounts of PdCl2 and KOH is studied.The reaction proceeds chemoselectively with complete ester conversion to the corresponding arenes.
- Davydov, D. V.,Beletskaya, I. P.
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- Gold-catalysis: Reactions of organogold compounds with electrophiles
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Different arylgold(I), one alkynylgold(I), and one vinylgold(I) triphenylphosphane complexes were subjected to electrophilic halogenation reagents. With N-chlorosuccinimid, N-bromosuccinimid, and N-iodosuccinimid as well as the Barluenga reagent, selectively halogenated compounds were obtained. Trifluoroacetic acid, as a source of protons, leads to a clean protodeauration. With N-fluorobenzenesulfonimide or Selectfluor, exclusively a homocoupling was observed. For the precursor of the vinylgold(I) complex, a similar oxidative coupling could be induced by gold(III) chloride. Reactions with silicon or tin electrophiles failed. CSIRO 2010.
- Hashmi, A. Stephen K.,Ramamurthi, Tanuja Dondeti,Todd, Matthew H.,Tsang, Althea S.-K.,Graf, Katharina
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- Protodecarboxylation of benzoic acids under radical conditions
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A new approach to protodecarboxylation is described that enhances the substrate scope for benzoic acids. The reaction uses oxidative radical conditions to decarboxylate a variety of acids in acetonitrile.
- Seo, Sangwon,Taylor, John B.,Greaney, Michael F.
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- Carbon-Oxygen Bond Cleavage Reactions by Electron Transfer. 1. Electrochemical Studies on the Formation and Subsequent Reaction Pathways of Cyanoanisole Radical Anions
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The radical anions of three isomers of cyanoanisole have been electrochemically generated and subsequently shown to react by at least three different reaction pathways in dry N,N-dimethylformamide (DMF).The o-cyanoanisole radical anion (Epc = -2.3 V vs.SCE) dimerizes (k2 = 3.2*102 M-1 s-1) to form an intermediate dimeric dianion.The dianion, which can be oxidized (Epa = -1.1 V vs.SCE), undergoes a slow intramolecular disproportionation reaction to form o-cyanophenoxide ion, methide ion, and unreduced substrate (k3 = 1.9*10-2 s-1).Subsequent protonation results in the formation of methane and p-cyanophenol in an overall two-electron process.The m-cyanoanisole radical anion (Epc = -2.3 V vs.SCE) is very stable (t1/2 > 103 s) under anhydrous DMF conditions.Overall, slow carbon-carbon bond cleavage with loss of cyanide occurs competitively with β-carbon-oxygen bond cleavage to produce anisole and m-cyanophenol, respectively.The final products of the reduction of p-cyanoanisole are p-cyanophenol and methane; however, the radical anion of p-cyanoanisole (Epc = -2.5 V vs.SCE) undergoes a relatively rapid unimolecular fragmentation reaction (k1 = 7 s-1).The initial products of the fragmentation are p-cyanophenoxide ion and the methyl radical, which is reduced further to methide ion.Hydrogen atom abstraction reactions by the methyl radical can also occur in the bulk solution to produce methane.
- Koppang, Miles D.,Woolsey, Neil F.,Bartak, Duane E.
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- Regioselective hydrogenolysis of aryl ether C-O bonds by tungsten carbides with controlled phase compositions
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Evenly dispersed tungsten carbides with controlled phase compositions that exhibit an impressive capacity to carry out the regioselective hydrogenolysis of inert aryl ether C-O bonds instead of aliphatic C-O bonds to produce aromatic compounds are reported.
- Fang, Huihuang,Du, Junmou,Tian, Chenchen,Zheng, Jianwei,Duan, Xinping,Ye, Linmin,Yuan, Youzhu
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- Heterogeneous palladium catalysts for a new one-pot chemical route in the synthesis of fragrances based on the Heck reaction
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The one-pot synthesis of the fragrance 4(p-methoxyphenyl)butan-2-one, with raspberry scent, has been carried out using palladium on different supports such as magnesium oxide (MgO), hydrotalcite, hydroxyapatite (HA), aluminium oxide (γAl2O3) and titanium dioxide (TiO2). The first pathway consists of a Heck coupling between 4-methoxyiodoanisole and methyl vinyl ketone followed by hydrogenation. Palladium supported on titanium dioxide showed the best performance for carrying out both consecutive steps giving 4-(p-methoxyphenyl)butan-2-one with high yields and selectivity. The PdTiO2 catalyst is more active than a homogeneous palladium complex that is well accepted in the literature as being highly active for performing Heck reactions.
- Climent, Maria Jose,Corma, Avelino,Iborra, Sara,Mifsud, Maria
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- Nucleophilic Photoreaction of Chlorobenzene in Methanol as Studied by Emission Spectroscopy
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The photoreaction of chlorobenzene in methanol has been studied by means of emission spectroscopy.Upon irradiation with UV light, chlorobenzene reacts with methanol to form anisole with a quantum yield of 0.049 at 18 deg C.Contrary to the case of chlorobenzene, the photoreaction of p-dichlorobenzene with methanol is not observed.By combining these results with those of our recent studies on the dual phosphorescence from low-lying triplet states of halogenated benzenes, it is suggested that the photoreaction of chlorobenzene with methanol, which is a nucleophilic substitution reaction, occurs in the 3(?,?*) state.From the temperature dependence of the quantum yield, the activation energy for the nucleophilic photoreaction is estimated to be larger by about 3 - 4 kcal mol-1 than the apparent activation energy for a combination of the nonradiative 3(?,?*)->S0 process and the homolytic dissociative process concerning the C-Cl bond in the 3(?,?*) state.It is suggested that the nucleophilic photoreaction contrasts with the radical reaction leading to the dissociation of the C-Cl bond; the latter reaction occurs in the 3(?,?*) state as well as in the 3(?,?*) state.
- Nagaoka, Shin-ichi,Takemura, Takeshi,Baba, Hiroaki
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- Highly efficient photocatalytic dehalogenation of organic halides on TiO2 loaded with bimetallic Pd-Pt alloy nanoparticles
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UV irradiation of TiO2 loaded with bimetallic Pd-Pt alloy particles promotes highly efficient dehalogenation of organic halides with alcohol as a hydrogen source.
- Shiraishi, Yasuhiro,Takeda, Yoshinori,Sugano, Yoshitsune,Ichikawa, Satoshi,Tanaka, Shunsuke,Hirai, Takayuki
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- Efficient Catalysis of Hydrodediazoniations in Dimethylformamide
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For hydrodediazoniations (the replacement of a diazo group by hydrogen) in DMF, several substances act as catalysts through their ability to serve as electron donors and initiate free-radical reactions.A general procedure has been developed in which FeSO4 speeds the conversion and leads to higher yields.Trapping experiments demonstrated the presence of free-radical intermediates.N,N-Dimethylacetamide was found to rival DMF as a source of hydrogen atoms.
- Wassmundt, Frederick W.,Kiesman, William F.
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- Pd-PEPPSI-type expanded ring N-heterocyclic carbene complexes: Synthesis, characterization, and catalytic activity in Suzuki-Miyaura cross coupling
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The synthesis and characterization of the new six- and seven-membered Pd-PEPPSI-type N-heterocyclic carbene (NHC) complexes 3 and 4 is described. Complexes of the general formula [Pd(NHC)(3ClPy)Cl2] (NHC = 6- or 7-Mes, 3ClPy = 3-chloropyridine) are accessed via the oxidation of the well-defined parent palladium(0) complexes 1 and 2. Complexes 3 and 4 have been employed in Suzuki-Miyaura cross-coupling and catalytic dehalogenation of a range of aryl halide substrates.
- Dunsford, Jay J.,Cavell, Kingsley J.
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- A Biomass-Derived Non-Noble Cobalt Catalyst for Selective Hydrodehalogenation of Alkyl and (Hetero)Aryl Halides
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Hydrodehalogenation is a straightforward approach for detoxifications of harmful anthropogenic organohalide-based pollutants, as well as removal of halide protecting groups used in multistep syntheses. A novel sustainable catalytic material was prepared from biowaste (chitosan) in combination with an earth-abundant cobalt salt. The heterogeneous catalyst was fully characterized by transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy measurements, and successfully applied to hydrodehalogenation of alkyl and (hetero)aryl halides with broad scope (>40 examples) and excellent chemoselectivity using molecular hydrogen as a reductant. The general usefulness of this method is demonstrated by successful detoxification of non-degradable pesticides and fire retardants. Moreover, the potential of the catalyst as a deprotection tool is demonstrated in a multistep synthesis of (±)-peronatin B (alkaloid).
- Sahoo, Basudev,Surkus, Annette-Enrica,Pohl, Marga-Martina,Radnik, J?rg,Schneider, Matthias,Bachmann, Stephan,Scalone, Michelangelo,Junge, Kathrin,Beller, Matthias
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- Palladium-nanoparticles catalyzed hydrodehalogenation of aryl chlorides in ionic liquids
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Pd-nanoparticles, in molten tetrabutylammonium bromide as the solvent and tetrabutylammonium acetate as the base, catalyze the hydrodehalogenation of various aryl chlorides under hydrogen at atmospheric pressure. Recycling experiments show a decreasing activity of this catalyst due to a small leaching of palladium from the ionic liquid phase during the extraction of the reaction products with cyclohexane. On the contrary, leaching is avoided when vacuum distillation is used to separate the dehalogenated products form the reaction mixture, thus allowing an extensive recycling of the Pd-catalyst.
- Calò, Vincenzo,Nacci, Angelo,Monopoli, Antonio,Damascelli, Anna,Ieva, Eliana,Cioffi, Nicola
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- Hydrodeoxygenation of guaiacol over carbon-supported metal catalysts
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Catalytic bio-oil upgrading to produce renewable fuels has attracted increasing attention in response to the decreasing oil reserves and the increased fuel demand worldwide. Herein, the catalytic hydrodeoxygenation (HDO) of guaiacol with carbon-supported non-sulfided metal catalysts was investigated. Catalytic tests were performed at 4.0MPa and temperatures ranging from 623 to 673K. Both Ru/C and Mo/C catalysts showed promising catalytic performance in HDO. The selectivity to benzene was 69.5 and 83.5% at 653K over Ru/C and 10Mo/C catalysts, respectively. Phenol, with a selectivity as high as 76.5%, was observed mainly on 1Mo/C. However, the reaction pathway over both catalysts is different. Over the Ru/C catalyst, the O-CH3 bond was cleaved to form the primary intermediate catechol, whereas only traces of catechol were detected over Mo/C catalysts. In addition, two types of active sites were detected over Mo samples after reduction in H2 at 973K. Catalytic studies showed that the demethoxylation of guaiacol is performed over residual MoOx sites with high selectivity to phenol whereas the consecutive HDO of phenol is performed over molybdenum carbide species, which is widely available only on the 10Mo/C sample. Different deactivation patterns were also observed over Ru/C and Mo/C catalysts.
- Chang, Jie,Danuthai, Tanate,Dewiyanti, Silvia,Wang, Chuan,Borgna, Armando
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- Palladium-catalyzed aryl-aryl coupling in water using molecular hydrogen: Kinetics and process optimization of a solid-liquid-gas system
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Coupling of substituted chlorobenzenes to the respective biphenyls is effected in water, using hydrogen gas and NaOH in the presence of catalytic PEG-400 and Pd/C. The catalyst can be efficiently recycled. The competing reduction process (e.g. of chlorobenzene to benzene) can be minimized by altering reaction conditions. The roles of the hydrogen, the hydroxide, the Pd catalyst, and the PEG are discussed.
- Mukhopadhyay, Sudip,Rothenberg, Gadi,Wiener, Harold,Sasson, Yoel
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- The mechanism of phenol methylation on acid and basic zeolite catalysts
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The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by 13C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins. Nauka/Interperiodica 2006.
- Borodina,Pomakhina,Ramishvili,Ponomareva,Rebrov,Ivanova
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- Synthesis of arylboronates by the palladium catalysed cross-coupling reaction in ionic liquids
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The palladium catalyzed cross-coupling reaction of aryl iodides and bromides with pinacolborane in ionic liquids producing arylboronates was described. Color changes of the reaction mixture were used to monitor the reaction's progress. Partial deiodination was observed in the cross-coupling reactions of ortho-substituted aryl iodides. The ratio of coupling products and deiodinated products was influenced by both the substituent and the catalyst.
- Wolan, Andrzej,Zaidlewicz, Marek
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- Reactivity in cleavage of dimethoxybenzenes by sodium in liquid ammonia
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The sodium/liquid ammonia cleavage of the dimethoxybenzenes and related substances, reported in large part by Birch in 1947, has been re-examined with use of improved techniques. Remarkable patterns of reactivity (e.g., ortho > meta ? para) that he described are confirmed and extended. They are agreeably rationalized by means of a simple, approximate adaptation from MO theory.
- Bunnett, Joseph F.,Jenvey, Judy
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- Transfer hydrodehalogenation of aryl halides accelerated by a saturated sodium acetate aqueous solution
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Development of catalytic hydrodehalogenation of halogenated organic compounds is an important topic from the viewpoint of environment protection. Herein, we conducted the first work on the utilization of a saturated aqueous solution of sodium acetate (CH3COONa) as an efficient and environmentally-friendly reaction medium for transfer hydrodehalogenation of various aryl halides using Pd/C as the catalyst. It was found that the transfer hydrodehalogenation could be accelerated significantly by the saturated CH3COONa aqueous solution due to the surfactant-similar effect of CH3COONa and the activation of the C-Cl bond by the dissolved solvated ions.
- Xue, Zhimin,Zhao, Xinhui,Wang, Jinfang,Mu, Tiancheng
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p. 102193 - 102197
(2016)
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- Guaiacol Hydrogenation in an Aqueous Medium in the Presence of a Palladium Catalyst Supported on a Mesoporous Dendrimer-Containing Polymer
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Guaiacol hydrogenation in an aqueous medium in the presence of a palladium catalyst supported on a mesoporous dendrimer-containing polymer and the effect of addition of sulfuric acid to the catalyst system have been studied. It has been found that the main hydrogenation product is 2-methoxycyclohexanol. After the addition of sulfuric acid to the catalyst system, the reaction mechanism significantly changes and cyclohexanol becomes the main hydrogenation product.
- Karakhanov,Boronoev,Filippova, T. Yu.,Maksimov
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- Preparation of aromatic amines by copper-catalyzed coupling of boronic acids with aqueous ammonia
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A simple, highly efficient, and environmentally friendly protocol for the synthesis of primary aromatic amines by catalytic coupling of aromatic boronic acids with aqueous ammonia has been developed by using commercial and inexpensive CuSO4·5H2O as catalyst without addition of other solvents under mild reaction conditions.
- Jiang, Zhaoqiong,Wu, Zhiqing,Wang, Lixia,Wu, Di,Zhou, Xiangge
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- Nickel complexes catalyzed hydrodechlorination of aryl chlorides in ionic liquid
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The hydrodechlorination performance of nickel complex catalysts, Ni[phen]2(PF6)2 and Ni[bpy]3(PF 6)2, were investigated with [Bmim]Br as the ionic liquid solvent. It is proved that Ni[phen]2(PF6)2 is efficient for the hydrodechlorination of aryl chlorides under mild conditions with water as the hydrogen source. The hydrogen source of reaction is from the water which was confirmed by the deuterium incorporation experiments. Recycling experiments showed a decreasing activity of this catalyst due to a small leaching of nickel complex from the ionic liquid phase during the recycling process where n-heptane was used as the extractant. A plausible reaction route has been suggested.
- Sun, Guanghui,Zhang, Lirong,Zhang, Guanlin,Fan, Yuehui,Wang, Yuhong,Lu, Guanzhong
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- Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity
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Decarbonylation of furfural to furan was efficiently catalyzed by ZrO2-supported Pd clusters in the liquid phase under a N2atmosphere without additives. Although Pd/C and Pd/Al2O3have frequently been used for decarbonylation, Pd/ZrO2exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO2. ZrO2with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al2O3despite their high surface areas. The catalytic activity of Pd/ZrO2was enhanced with a decrease in particle size, and the smallest Pd/ZrO2was the most active catalyst for decarbonylation. When CeO2was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO2with a high surface area, with a strong interaction through the formation of a Pd?O?Ce bond, which led to a lower catalytic activity than that of Pd/ZrO2. This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO2maintained its catalytic activity until its sixth use.
- Ishida, Tamao,Kume, Kurumi,Kinjo, Kota,Honma, Tetsuo,Nakada, Kengo,Ohashi, Hironori,Yokoyama, Takushi,Hamasaki, Akiyuki,Murayama, Haruno,Izawa, Yusuke,Utsunomiya, Masaru,Tokunaga, Makoto
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- Microwave-assisted Ullmann-type coupling reactions in alkaline water
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Upon microwave irradiation, homocoupling reaction of aryliodides catalyzed by Pd/C in alkaline water media can be readily accelerated to form biaryls with excellent conversions and selectivities. Copyright Taylor & Francis Group, LLC.
- Gaedda, Thomas M.,Kawanishi, Yuji,Miyazawa, Akira
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- Base-promoted protodeboronation of 2,6-disubstituted arylboronic acids
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Facile based promoted deboronation of electron-deficient arylboronate esters was observed for arylboronates containing two ortho electron-withdrawing group (EWG) substituents. Among 30 representative boronates, only the diortho-substituted species underwe
- Lozada, Jerome,Liu, Zhibo,Perrin, David M.
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- Chan-Evans-Lam C?N Coupling Promoted by a Dinuclear Positively Charged Cu(II) Complex. Catalytic Performance and Some Evidence for the Mechanism of CEL Reaction Obviating Cu(III)/Cu(I) Catalytic Cycle
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In the present study, we report the synthesis of a series of copper(II) complexes with a wide range of ligands and their testing in the copper catalyzed Chan-Evans-Lam (CEL) coupling of aniline and phenylboronic acid. The efficiency of the coupling was directly connected with the ease of the reduction of Cu(II) to Cu(I) of the complexes. The most efficient catalyst was derived from 4-t-butyl-2,5-bis[(quinolinylimino)methyl]phenolate and two Cu(II) ions. Depending on the counter-anion nature and the concentration of the reaction mixture, the reaction can be directed to predominant C?N-bond formation. Forty-three derivatives of diphenylamine were prepared under the optimized conditions. The proposed mechanism of the catalysis was based on the reduction potential of a series of complexes, molecular weight measurements of the catalytic complex in MeOH and the kinetic studies of aniline and phenylboronic acid coupling. In addition, an 1H NMR experiment in a sealed NMR tube, without external oxygen supply available, proved that no complete Cu(II) to Cu(I) conversion was observed under the condition, ruling out the usually accepted mechanism of the C?N coupling, which included the oxygenation of the intermediately formed Cu(I) complexes after the key step of C?N conversion had already been completed. Instead, a mechanism was proposed, involving an oxygen molecule coordinated to two copper ions in the key C?N bond formation without any detectable conversion of the Cu(II) complexes to Cu(I).
- Akatyev, Nikolay,Il'in, Mikhail,Il'in, Mikhail,Peregudova, Svetlana,Peregudov, Alexander,Buyanovskaya, Anastasiya,Kudryavtsev, Kirill,Dubovik, Alexander,Grinberg, Valerij,Orlov, Victor,Pavlov, Alexander,Novikov, Valentin,Volkov, Ilya,Belokon, Yuri
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- Homolytic C-S bond scission in the desulfurization of aromatic and aliphatic thiols mediated by a Mo/Co/S cluster: Mechanistic aspects relevant HDS catalysis
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The kinetics of the reaction of a series of aromatic and aliphatic thiols with cluster 1 were determined. These reactions form cluster 2 and the arene or alkane corresponding to the thiol: Cp'2Mo2Co2S3(CO)4 (1) + RSH → Cp'2Mo2Co2S4(CO)2 (2) + RH + 2CO. These reactions are first order in thiol and first order in cluster 1 with appreciable negative entropies of activation. These data suggest that the rate determining step of the desulfurization reaction is the initial association of the thiol to the cluster. The more nucleophilic thiolate anions react with 1 at -40°C to form an adduct in which the thiolate anion is bound η1 to the Co atom. At -25°C, the initial adduct rearranges to a fluxional μ2, η1-bound thiolate. The fluxional process is proposed to involve a concerted 'walking' of the thiolate and a μ2-bound sulfide ligand on the surface of the cluster. Near 35°C, the thiolate-cluster adduct undergoes C-S bond homolysis to give the paramagnetic anion of cluster 1 and the phenyl or alkyl radical. The radical nature of the C-S bond cleavage was confirmed by the desulfurization of the radical clock reagents, cyclopropylmethanethiol and -thiolate anion, that form the cyclopropylmethyl radical which rearranged to the butenyl radical. The possible similarity in the C-S bond cleavage mechanism in these desulfurization reactions to those occurring in hydrodesulfurization (HDS) over Co/Mo/S catalysts is discussed.
- Curtis, M. David,Druker, Scott H.
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- Pd/NHC-catalyzed cross-coupling reactions of nitroarenes
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N-Heterocyclic carbene (NHC) ligands effective for the cross-coupling of nitroarenes were identified. A rational design of the NHC ligand structures enabled significant reduction of catalyst loadings compared with the previous system employing BrettPhos as a phosphine ligand. Experimental and theoretical studies to compare these ligands gave some insights into high activity of the newly developed NHC ligands.
- Kashihara, Myuto,Zhong, Rong-Lin,Semba, Kazuhiko,Sakaki, Shigeyoshi,Nakao, Yoshiaki
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- The Mechanism of Titanium Complex-Catalyzed Reduction of Aryl Halides by Sodium Borohydride Is Strongly Solvent Dependent
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The titanium complex-catalyzed reduction of aryl halides by sodium borohydride in dimethylacetamide (DMA) or ethers proceeds by electron transfer from a reduced titanium species, yielding an intermediate aryl radical.
- Liu, Yumin,Schwartz, Jeffrey
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- THE COUPLING OF ORGANIC GROUPS BY THE ELECTROCHEMICAL REDUCTION OF ORGANIC HALIDES: CATALYSIS BY 2,2'-BIPYRIDINENICKEL COMPLEXES
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The electrochemical reduction of a dilute solution of NiX2bipy (bipy = 2,2'-bipyridine) in N-methylpyrrolidone gives the corresponding Ni0 complex, which undergoes oxidative addition with an excess of an organic halide RX to form RNiX.Decomposition of RNiX gives the dimer R2 in good yield and nickel(II).The nickel(0) species is regenerated to give an electrocatalytic process.The possible mechanism of these reactions is discussed briefly.
- Rollin, Yolande,Troupel, Michel,Tuck, Dennis G.,Perichon, Jacques
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- Palladium catalytic systems with hybrid pyrazole ligands in C-C coupling reactions. Nanoparticles versus molecular complexes
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This paper reports the comparison of the chemoselectivity of two different Pd catalytic systems, namely molecular and colloidal systems, in C-C coupling reactions. For this purpose, new hybrid pyrazole derived ligands containing alkylether, alkylthioether or alkylamino moieties have been synthesized and used to form Pd(ii) complexes and to stabilize Pd nanoparticles (Pd NPs). With the aim of studying the coordination mode of the ligands and further to understand their role in catalysis, both types of Pd species were characterized by appropriate techniques. In C-C coupling reactions promoted by different Pd colloidal systems, several reports evidenced that active species are molecular catalysts leached from Pd NPs. The most important feature of this work relies on the differences observed in the output of C-C coupling reactions, depending on the colloidal or molecular nature of the catalyst employed. Thus, molecular systems carry out typical Suzuki-Miyaura cross-coupling, together with the dehalogenation of the substrate in different proportions. In contrast, Pd NPs catalyze either Suzuki-Miyaura or C-C homocoupling reactions depending on the haloderivative used. Interestingly, Pd NPs catalyze the quantitative dehalogenation of 4-iodotoluene. Differences observed in the chemoselectivity of these two catalytic systems support that reactions carried out with Pd NPs stabilized with the hybrid pyrazole ligands employed here take place on the surface of the colloids. The Royal Society of Chemistry 2013.
- Peral, Daniel,Gomez-Villarraga, Fernando,Sala, Xavier,Pons, Josefina,Carles Bayon,Ros, Josep,Guerrero, Miguel,Vendier, Laure,Lecante, Pierre,Garcia-Anton, Jordi,Philippot, Karine
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- Stannylated Vinylic addition polynorbornene: Probing a reagent for friendly tin-mediated radical processes
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Vinylic addition polynorbornenes (VA-PNB) with stannyl functional groups have been prepared and used in tinmediated radical dehalogenation reactions. The aliphatic and robust scaffold of VA-PNB is well suited for a support in radical processes. VA-PNB-(CH2)nSnHBu2 can be used as a stoichiometric reagent and VA-PNB-(CH2)nSnBu2Cl as a catalyst in the presence of a hydride donor for the reduction of RBr. The mixture KF (aq.)/polymethylhydrosiloxane (PMHS) is the most convenient hydride source to generate VA-PNB-(CH2)nSnHBu2 in situ. Al-though quite popular in this context, boron hydrides, being a source of radicals themselves, are not adequate to correctly evaluate the performance of the anchored organotin group. VAPNB-(CH2)4SnBu2Cl can be recycled and, even if it loses activity upon reuse, it is still useful after ten cycles. The stannylated VAPNB can be separated from the products by simple filtration, and it leads to very low tin contamination (at least 250 times lower than that with use of conventional separation methods).
- García-Loma, Rodrigo,Alb é Niz, Ana C.
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- SRN1 reactions of aryl halides with carbanions initiated by sodium amalgam in liquid ammonia
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The reaction of 1-chloronaphthalene with acetone (2a) and acetophenone (2b) enolate ions was initiated by sodium amalgam [Na(Hg)] in liquid ammonia giving good yields of the substitution products 3a and 3b respectively. 2-Chloroquinoline and 2-chloropyridine gave good yields of substitution product with 2b, and moderate to good yields with 2a. 4-Bromobenzophenone and 2a gave 78% of the substitution product 5. With aryl halides whose radical anions fragment fast and consequently close to the Na(Hg) surface, such as bromobenzene and p-bromoanisole, only dehalogenation products were observed. However, when benzonitrile was used as a redox catalyst, about 50% of the substitution product 6 was obtained with p-bromoanisole and 2a. However, with the more reactive carbanionic nucleophile, such as anthrone anion 4, good yields of the substitution product 7 were obtained with bromobenzene. In all these reactions neither reduction of the aromatic moiety nor the ketone functionality was observed. It is therefore suggested that Na(Hg) amalgam initiates these SRN1 reactions.
- Austin, Eduardo,Ferrayoli, Carlos G.,Alonso, Ruben A.,Rossi, Roberto A.
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- Role of copper- or cerium-promoters on NiMo/Γ-Al2O3 catalysts in hydrodeoxygenation of guaiacol and bio-oil
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Effect of copper (Cu) or cerium (Ce) as promoters for nickel-molybdenum/γ-alumina (NiMo/γ-Al2O3) catalyst on the hydrodeoxygenation (HDO) of guaiacol (GUA), a model oxygenated compound found in a bio-oil derived from woody biomass, was comparatively investigated. The addition of Cu- or Ce-promoters affected the physicochemical properties of the NiMo catalyst. The NiMo catalyst promoted by Cu showed the higher reducibility, whilst the Ce-promoter (2–8 wt% based on γ-Al2O3 content) provided the NiMo catalyst with a higher distribution of active metals and induced a greater difficulty in the reduction under hydrogen (H2) atmosphere. For the HDO of GUA at a mild reaction condition (10 bar initial H2 pressure and 300 °C) in the absence of solvent, the Cu-promoter enhanced the hydrogenation activity of the NiMo catalyst to convert GUA to phenol and methylphenols, one-atomic oxygen species. Whereas, the addition of Ce obviously inhibited the formation of coke on the catalyst surface after a long reaction period (6 h) and gave a higher GUA conversion level with increasing yield of phenols. For the HDO of real bio-oil obtained from the fast pyrolysis of cassava rhizome, the NiMo catalysts promoted by Cu or Ce at 4 wt% based on the γ-Al2O3 content showed a higher performance at eliminating the oxygenated compounds in the bio-oil, reducing the oxygen/carbon (O/C) molar ratio by over seven-fold from 1.75 to 0.24–0.25. Moreover, the gross heating value of the bio-oil was improved from 21.5 to ca. 29.0 MJ/kg after the HDO process. However, the addition of the Cu or Ce promoter did not inhibit coke deposition, possibly due to the acidic properties of the bio-oil that deteriorated the catalyst performance by metal leaching.
- Sangnikul, Patiphat,Phanpa, Chanisara,Xiao, Rui,Zhang, Huiyan,Reubroycharoen, Prasert,Kuchonthara, Prapan,Vitidsant, Tharapong,Pattiya, Adisak,Hinchiranan, Napida
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- Alkyl methyl carbonates as methylating agents. The O-methylation of phenols
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The O-methylation reaction of a variety of phenols (ArOH: Ar = Ph, p- CH3C6H4, p-ClC6H4, o- and p-CH3COC6H4, and 2-naphthyl) can be conducted in a highly selective manner by using asymmetric alkyl methyl carbonates CH3 OCOOR (R = n-Pr, 3b; n-Bu, 3d; CH3O(CH2)2O(CH2)2, 3e) as alkylating agents. For example, at 150 °C, phenol can be quantitatively converted into anisole in 4.5 h, using 2-(2-methoxyethoxy)ethyl methyl carbonate 3e in the presence of K2CO3 as a catalyst. Compared to the methylation reactions using dimethyl carbonate which require sealed pressurized reaction vessels, asymmetric alkyl methyl carbonates allow much simpler and safer alkylations at ambient pressure. The selectivity towards O- methylation is scarcely affected by the temperature (in the range of 120-150 °C), while it depends on the nature and on the amount of the solvent. DMF and triglyme (triethylene glycol dimethyl ether) have proven to be the better reaction media.
- Perosa, Alvise,Selva, Maurizio,Tundo, Pietro,Zordan, Francesco
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- Continuous in situ generation, separation, and reaction of diazomethane in a dual-channel microreactor
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A fierce dog: A method for the continuous in-situ on-demand generation, separation, and reaction of diazomethane in a dual-channel microreactor has been developed (see picture; Diazald=N-methyl-N-nitroso-p-toluenesulfonamide). The microchemical system allows a variety of diazomethane reactions to be performed without the most common problems of preparation, handling, transfer, and decomposition.
- Maurya, Ram Awatar,Park, Chan Pil,Lee, Jang Han,Kim, Dong-Pyo
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- Carbon - Carbon bond formation via palladium-catalyzed reductive coupling in air
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(matrix presented) Palladium-catalyzed reactions in general are known to be carried out under an inert atmosphere because the palladium intermediates in the catalytic cycle are often known to be sensitive to oxygen. Herein we report a novel palladium-catalyzed Ullmann-type reductive coupling of aryl halides under an air atmosphere and in aqueous acetone.
- Venkatraman, Sripathy,Li, Chao-Jun
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- Highly Selective Hydrodeoxygenation of Lignin to Naphthenes over Three-Dimensional Flower-like Ni2P Derived from Hydrotalcite
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A strategy for low-temperature synthesis of hydrotalcite-based nickel phosphide catalysts (Ni2P-Al2O3) with flower-like porous structures was proposed. The in situ reduction of red phosphorus at 500 °C enables Ni2P catalysts with small particle size and abundant active and acidic sites, which facilitate the activation of substrates and H2. In the hydrodeoxygenation of guaiacol, a 100% conversion and 94.5% yield of cyclohexane were obtained over the Ni2P-Al2O3 catalyst under 5 MPa H2 at 250 °C for 3 h. Other lignin-derived phenolic compounds could also afford the corresponding alkanes with yields higher than 85%. Moreover, Ni2P-Al2O3 exhibited high hydrodeoxygenation activity in the deconstruction of more complex wood structures, including lignin oil and real lignin. Among the two different types of Ni sites of Ni(1) and Ni(2) in Ni2P, density functional theory (DFT) calculations showed that the Ni(2) site, highly exposed on the Ni2P-Al2O3 surface, possesses a stronger ability to break C-OH bonds during the hydrodeoxygenation of guaiacol in comparison with the Ni(1) site.
- Chen, Guanyi,Diao, Xinyong,Ji, Na,Jia, Zhichao,Li, Changzhi,Li, Xinxin,Liu, Caixia,Liu, Qingling,Lu, Xuebin,Ma, Longlong,Song, Chunfeng,Wang, Shurong,Zhao, Yujun
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p. 1338 - 1356
(2022/02/07)
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- Highly selective Suzuki reaction catalysed by a molecular Pd-P-MOF catalyst under mild conditions: Role of ligands and palladium speciation
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Cross-coupling reactions are a fundamental tool in the large scale synthesis of pharma-, agro-and fine chemicals. Homogeneous palladium complexes remain the state-of-the-art catalysts even though the use of heterogeneous palladium catalysts may have advantages such as catalyst recyclability, precious metal recovery and the possibility of being used in continuous flow operation. However, this is predicated on achieving acceptable process stability and selectivity levels without side reactions, such as e.g. hydrodehalogenation of aryl halides. We report a molecularly-defined heterogeneous palladium catalyst based on a phosphine-metal-organic framework (P-MOF) ligand system. This catalyst performed Suzuki reactions in exceptionally mild conditions while displaying a unique selectivity, higher than that achieved using Pd(PPh3)4, a standard homogeneous catalyst. The new palladium P-MOF catalyst was active for a wide range of substrates. Determination of the palladium speciation showed that molecularly-defined palladium-phosphine sites catalyse the Suzuki cross-coupling with very high selectivity, and that, when formed, palladium nanoparticles promote hydrodehalogenation. The fraction of molecularly defined palladium is maximized by having excess of phosphine ligand in the system. This journal is
- Bachmann, Stephan,Cartagenova, Daniele,Newton, Mark A.,Püntener, Kurt,Peixoto Esteves, Fabio A.,Ranocchiari, Marco,Rohrbach, Thomas,Scalone, Michelangelo,Van Bokhoven, Jeroen A.,Zimmermann, Patrik P.
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p. 954 - 961
(2022/02/17)
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- Protodesilylation of Arylsilanes by Visible-Light Photocatalysis
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The first visible-light-mediated photocatalytic, metal- and base-free protodesilylation of arylsilanes is presented. The C(sp2)-Si bond cleavage process is catalyzed by a 5 mol % loading of a commercially available acridinium salt upon blue-light irradiation. Two simple approaches have been identified employing either aerobic or hydrogen atom transfer cocatalytic conditions, which enable the efficient and selective desilylation of a broad variety of simple and complex arylsilanes under mild conditions.
- García Manche?o, Olga,Kuhlmann, Jan H.,Uygur, Mustafa
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supporting information
p. 1689 - 1694
(2022/03/14)
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- A photoresponsive palladium complex of an azopyridyl-triazole ligand: light-controlled solubility drives catalytic activity in the Suzuki coupling reaction
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Herein, the design and synthesis of a click-derived Pd-complex merged with a photoswitchable azobenzene unit is presented. While in thetrans-form of the switch the complex showed limited solubility, the photogeneratedcis-form rendered the molecule soluble in polar solvents. This light-controllable solubility was exploited to affect the catalytic activity in the Suzuki coupling reaction. The effect of the substrate and catalyst concentration and light intensity on the proceeding and outcome of the reaction was studied. Dehalogenation of the aryl iodide starting material was found to be a major side reaction; however, its occurrence was dependent on the applied light intensity.
- Gazdag, Tamás,Holczbauer, Tamás,Jablonkai, István,Kalapos, Péter Pál,Kunfi, Attila,London, Gábor,Mayer, Péter J.,Németh, Krisztina
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p. 23419 - 23429
(2021/07/13)
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- Design of an Electron-Withdrawing Benzonitrile Ligand for Ni-Catalyzed Cross-Coupling Involving Tertiary Nucleophiles
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The design of new ligands for cross-coupling is essential for developing new catalytic reactions that access valuable products such as pharmaceuticals. In this report, we exploit the reactivity of nitrile-containing additives in Ni catalysis to design a benzonitrile-containing ligand for cross-coupling involving tertiary nucleophiles. Kinetic and Hammett studies are used to elucidate the role of the optimized ligand, which demonstrate that the benzonitrile moiety acts as an electron-acceptor to promote reductive elimination over β-hydride elimination and stabilize low-valent Ni. With these conditions, a protocol for decyanation-metalation and Ni-catalyzed arylation is conducted, enabling access to quaternary α-arylnitriles from disubstituted malononitriles.
- Edjoc, Racquel K.,Mills, L. Reginald,Rousseaux, Sophie A. L.
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supporting information
p. 10422 - 10428
(2021/07/26)
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- Zirconium-redox-shuttled cross-electrophile coupling of aromatic and heteroaromatic halides
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Transition metal-catalyzed cross-electrophile coupling (XEC) is a powerful tool for forging C(sp2)–C(sp2) bonds in biaryl molecules from abundant aromatic halides. While the synthesis of unsymmetrical biaryl compounds through multimetallic XEC is of high synthetic value, the selective XEC of two heteroaromatic halides remains elusive and challenging. Herein, we report a homogeneous XEC method, which relies on a zirconaaziridine complex as a shuttle for dual palladium-catalyzed processes. The zirconaaziridine-mediated palladium (ZAPd)-catalyzed reaction shows excellent compatibility with various functional groups and diverse heteroaromatic scaffolds. In accord with density functional theory (DFT) calculations, a redox transmetallation between the oxidative addition product and the zirconaaziridine is proposed as the crucial elementary step. Thus, cross-coupling selectivity using a single transition metal catalyst is controlled by the relative rate of oxidative addition of Pd(0) into the aromatic halide. Overall, the concept of a combined reducing and transmetallating agent offers opportunities for the development of transition metal reductive coupling catalysis.
- Fu, Yue,Liu, Fang-Jie,Liu, Peng,Tang, Jian-Tao,Toste, F. Dean,Wu, Ting-Feng,Ye, Baihua,Zhang, Yue-Jiao
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supporting information
p. 1963 - 1974
(2021/07/07)
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- Untangling the Complexity of Mixed Lithium/Magnesium Alkyl/Alkoxy Combinations Utilised in Bromine/Magnesium Exchange Reactions
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While it is known that the addition of Group 1 alkoxides to s-block organometallics can have an activating effect on reactivity, the exact nature of this effect is not that well understood. Here we describe the activation of sBu2Mg towards substituted bromoarenes by adding one equivalent of LiOR (R=2-ethylhexyl), where unusually both sBu groups can undergo efficient Br/Mg exchange. Depending on the substitution pattern on the bromoarene two different types of organometallic intermediates have been isolated, either a mixed aryl/alkoxide [{LiMg(2-FG-C6H4)2(OR)}2] (FG=OMe; NMe2) or a homoaryl [(THF)4Li2Mg(4-FG-C6H4)4] (FG=OMe, F). Detailed NMR spectroscopic studies have revealed that these exchange reactions and the formation of their intermediates are controlled by a new type of bimetallic Schlenk-type equilibrium between heteroleptic [LiMgsBu2(OR)], alkyl rich [Li2MgsBu4] and Mg(OR)2, with [Li2MgsBu4] being the active species performing the Br/Mg exchange process.
- Bole, Leonie J.,Judge, Neil R.,Hevia, Eva
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supporting information
p. 7626 - 7631
(2021/03/08)
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- Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers
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Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylationviaradical-mediated pathways, with optimized conditions that only require the photocatalyst and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.
- Shon, Jong-Hwa,Kim, Dooyoung,Rathnayake, Manjula D.,Sittel, Steven,Weaver, Jimmie,Teets, Thomas S.
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p. 4069 - 4078
(2021/04/06)
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- Nickel-Catalyzed Photodehalogenation of Aryl Bromides
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Herein, we describe a Ni-catalyzed photodehalogenation of aryl bromides under visible-light irradiation that utilizes tetrahydrofuran as hydrogen source. The protocol obviates the need for exogeneous amine reductants or photocatalysts and is characterized by its simplicity and broad scope, including challenging substrate combinations.
- Higginson, Bradley,Sanjosé-Orduna, Jesus,Gu, Yiting,Martin, Ruben
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supporting information
p. 1633 - 1636
(2021/04/23)
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- Cavity-promotion by pillar[5]arenes expedites organic photoredox-catalysed reductive dehalogenations
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The efficiency of the photo-induced electron transfer in photoredox catalysis is limited by the diffusional collision of the excited catalyst and the substrate. We herein present cavity-bound photoredox catalysts, which preassociate the substrates, leading to significantly shortened reaction times. A pillar[5]arene serves as the cavity and phenothiazine as a catalyst in the reductive dehalogenation of aliphatic bromides as a proof of concept reaction.
- Esser, Birgit,Schmidt, Maximilian
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supporting information
p. 9582 - 9585
(2021/09/28)
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- Efficient base-free hydrodehalogenation of organic halides catalyzed by a well-defined diphosphine-ruthenium(II) complex
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A base-free, robust catalytic system based on the diphosphine-ruthenium(II) complex cation has been developed for the hydrodehalogenation of a wide range of aryl- and alkyl-chlorides/bromides (27 examples) with molecule hydrogen. Notably, the reaction proceeds at 120 °C with low catalyst loading (0.1 mol%) and exhibits a good tolerance toward functional groups, such as amido, carboxyl, sulfonyl, methoxyl, ester groups. All dehalogenation products are confirmed by GC, GC–MS and NMR spectroscopy. Moreover, a mechanism for the diphosphine-ruthenium(II) complex cation catalyzed dehalogenation process has been proposed. This hydrodehalogenation methodology shows a potential application for the organic transformation and degradation of organic halides.
- Gao, Pengxiang,Liu, Qingbin,Liu, Yahuan,Ma, Ning,Wang, Zheng,Zhao, Ziwei
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- Ceramic boron carbonitrides for unlocking organic halides with visible light
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Photochemistry provides a sustainable pathway for organic transformations by inducing radical intermediates from substrates through electron transfer process. However, progress is limited by heterogeneous photocatalysts that are required to be efficient, stable, and inexpensive for long-term operation with easy recyclability and product separation. Here, we report that boron carbonitride (BCN) ceramics are such a system and can reduce organic halides, including (het)aryl and alkyl halides, with visible light irradiation. Cross-coupling of halides to afford new C-H, C-C, and C-S bonds can proceed at ambient reaction conditions. Hydrogen, (het)aryl, and sulfonyl groups were introduced into the arenes and heteroarenes at the designed positions by means of mesolytic C-X (carbon-halogen) bond cleavage in the absence of any metal-based catalysts or ligands. BCN can be used not only for half reactions, like reduction reactions with a sacrificial agent, but also redox reactions through oxidative and reductive interfacial electron transfer. The BCN photocatalyst shows tolerance to different substituents and conserved activity after five recycles. The apparent metal-free system opens new opportunities for a wide range of organic catalysts using light energy and sustainable materials, which are metal-free, inexpensive and stable. This journal is
- Yuan, Tao,Zheng, Meifang,Antonietti, Markus,Wang, Xinchen
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p. 6323 - 6332
(2021/05/19)
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- Mechanistic studies into visible light-driven carboxylation of aryl halides/triflates by the combined use of palladium and photoredox catalysts
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The reaction mechanism of palladium-catalyzed visible light-driven carboxylation of aryl halides and triflates with a photoredox catalyst was examined in detail. Experimental and theoretical studies indicated that the active species for photoredox- catalyzed reduction was cationic ArPd(II)+ species to generate nucleophilic ArPd(I) or its further reduced ArPd(0)- species, which reacted with CO2 to give carboxylic acids. Hydrodehalogenated compounds, main byproducts in this carboxylation, were thought to be generated by protonation of these reduced species.
- Caner, Joaquim,Iwasawa, Nobuharu,Martin, Ruben,Murata, Kei,Shimomaki, Katsuya,Toriumi, Naoyuki
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supporting information
p. 1846 - 1853
(2021/08/13)
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- New insight into the electrochemical reduction of different aryldiazonium salts in aqueous solutions
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Electrochemical reduction of different aryldiazonium salts in aqueous solution was studied in this work and it is shown that the aryldiazonium salts are converted to the corresponding aryl radical and aryl anion. The results of this research indicate that the reduction of aryldiazonium salts takes place in two single-electron steps. Our data show that when the substituted group on the phenyl ring is H, Cl, OH, NO2, OCH3or SO3?, the corresponding diazonium salt shows poor adsorption characteristics, but when the substituted group is methyl, the corresponding diazonium salt shows strong adsorption characteristics. In the latter case, the voltammogram exhibits three cathodic peaks. In addition, the effect of various substitutions on the aryldiazonium reduction was studied by Hammett's method. The data are show that with increasing electron withdrawing capacity of the substituent, the reduction of corresponding diazonium salt becomes easier.
- Goljani, Hamed,Nematollahi, Davood,Sepehrmansourie, Hassan,Tavakkoli, Zahra,Zolfigol, Mohammad Ali
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p. 25811 - 25815
(2021/08/09)
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- Heterogeneously Catalyzed Selective Decarbonylation of Aldehydes by CeO2-Supported Highly Dispersed Non-Electron-Rich Ni(0) Nanospecies
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Aldehyde decarbonylation has been extensively investigated, primarily using noble-metal catalysts; however, nonprecious-base-metal-catalyzed aldehyde decarbonylation has been hardly reported. We have established an efficient selective aldehyde decarbonylation reaction with a broad substrate scope and functional group tolerance utilizing a heterogeneous Ni(0) nanospecies catalyst supported on CeO2. The high catalytic performance is attributable to the highly dispersed and non-electron-rich Ni(0) nanospecies, which possibly suppress a side reaction producing esters and adsorbed CO-derived inhibition of the catalytic turnover, according to detailed catalyst characterization and kinetic evaluation.
- Matsuyama, Takehiro,Yatabe, Takafumi,Yabe, Tomohiro,Yamaguchi, Kazuya
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p. 13745 - 13751
(2021/11/17)
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- Radical-mediated alkoxypolyhaloalkylation of styrenes with polyhaloalkanes and alcoholsviaC(sp3)-H bond cleavage
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We have developed a new radical-mediated alkoxypolyhaloalkylation of styrenes with polychloroalkanes and alcohols for the facile synthesis of complex polyhaloalkanes. 4-Methoxybenzenediazonium tetrafluoroborate is a good radical initiator for this transformation. This protocol is well applied to the late-stage functionalization of complex molecules, including vitamin E, estrone and cholesterol derivatives.
- Liang, Yun-Yan,Huang, Jing,Ouyang, Xuan-Hui,Qin, Jing-Hao,Song, Ren-Jie,Li, Jin-Heng
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supporting information
p. 3684 - 3687
(2021/04/16)
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- Non-innocent Radical Ion Intermediates in Photoredox Catalysis: Parallel Reduction Modes Enable Coupling of Diverse Aryl Chlorides
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We describe a photocatalytic system that elicits potent photoreductant activity from conventional photocatalysts by leveraging radical anion intermediates generated in situ. The combination of an isophthalonitrile photocatalyst and sodium formate promotes diverse aryl radical coupling reactions from abundant but difficult to reduce aryl chloride substrates. Mechanistic studies reveal two parallel pathways for substrate reduction both enabled by a key terminal reductant byproduct, carbon dioxide radical anion.
- Chernowsky, Colleen P.,Chmiel, Alyah F.,Wickens, Zachary K.,Williams, Oliver P.,Yeung, Charles S.
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supporting information
p. 10882 - 10889
(2021/07/31)
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- Photoredox-catalyzed reduction of halogenated arenes in water by amphiphilic polymeric nanoparticles
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The use of organic photoredox catalysts provides new ways to perform metal-free reactions controlled by light. While these reactions are usually performed in organic media, the application of these catalysts at ambient temperatures in aqueous media is of considerable interest. We here compare the activity of two established organic photoredox catalysts, one based on 10-phenylphenothiazine (PTH) and one based on an acridinium dye (ACR), in the light-activated dehalogenation of aromatic halides in pure water. Both PTH and ACR were covalently attached to amphiphilic polymers that are designed to form polymeric nanoparticles with hydrodynamic diameter DH ranging between 5 and 11 nm in aqueous solution. Due to the hydrophobic side groups that furnish the interior of these nanoparticles after hydrophobic collapse, water-insoluble reagents can gather within the nanoparticles at high local catalyst and substrate concentrations. We evaluated six different amphiphilic polymeric nanoparticles to assess the effect of polymer length, catalyst loading and nature of the catalyst (PTH or ACR) in the dechlorination of a range of aromatic chlorides. In addition, we investigate the selectivity of both catalysts for reducing different types of aryl-halogen bonds present in one molecule, as well as the activity of the catalysts for C-C cross-coupling reactions. We find that all polymer-based catalysts show high activity for the reduction of electron-poor aromatic compounds. For electron-rich compounds, the ACR-based catalyst is more effective than PTH. In the selective dehalogenation reactions, the order of bond stability is C-Cl > C-Br > C-I irrespective of the catalyst applied. All in all, both water-compatible systems show good activity in water, with ACR-based catalysts being slightly more efficient for more resilient substrates.
- Eisenreich, Fabian,Kuster, Tom H. R.,Palmans, Anja R. A.,van Krimpen, David
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supporting information
(2021/10/05)
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- Metal-Free Photoredox-Catalyzed Hydrodefluorination of Fluoroarenes Utilizing Amide Solvent as Reductant
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A metal-free photoredox-catalyzed hydrodefluorination of fluoroarenes was achieved by using N,N,N’,N’-tetramethyl-para-phenylenediamine (1) as a strong photoreduction catalyst. This reaction was applicable not only to electron-rich monofluoroarenes but also to polyfluoroarenes to afford non-fluorinated arenes. The experimental mechanistic studies indicated that the amide solvent NMP plays an important role for regeneration of the photocatalyst, enabling additive-free photoreduction catalysis.
- Toriumi, Naoyuki,Yamashita, Kazuya,Iwasawa, Nobuharu
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supporting information
p. 12635 - 12641
(2021/08/03)
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- Iodine-catalyzed tandem oxidative aromatization for the synthesis of meta-substituted alkoxybenzenes
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A rapid method for the synthesis of meta-substituted alkoxybenzenes is achieved by oxidation of cyclohexenones. This one-pot transformation is catalyzed by molecular iodine with DDQ as an oxidant in the presence of alcohols. Diverse cyclohexenones with aryl or alkyl substitutes are well tolerated to the mild oxidative conditions affording desired products in up to 92% yield. These oxidizing processes were applicable to the efficient synthesis of useful meta-substituted phenolic products which are difficult to obtain by traditional electrophilic substitutions.
- Jiang, Dahong,Jia, Xicheng,Zhang, Shuhua,Zhang, Zhihua,Li, Lei,Qiao, Yanhui
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- Method for preparing anisole from phenol and methanol
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The invention discloses a method for preparing anisole from phenol and methanol. The method is characterized in that a fixed bed reactor is adopted, and active components such as sodium acetate, potassium acetate, calcium acetate, magnesium acetate or ammonium acetate modified gamma-Al2O3 loaded ammonium fluoride, sodium fluoride, potassium fluoride, ferric fluoride, magnesium fluoride, calcium fluoride and the like are used as catalysts to catalyze phenol and methanol to prepare anisole. The modification of the ferric fluoride, the magnesium fluoride and the calcium fluoride is prepared by dipping corresponding nitrate and ammonium fluoride on gamma-Al2O3 for two times. Efficient synthesis of anisole is achieved, the phenol conversion rate is high, anisole selectivity is high, the catalyst is simple in preparation process, low in cost, high in stability and long in service life, and the application requirement of an industrial catalyst is met.
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Paragraph 0022-0045
(2021/08/11)
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- Selective O-Methylation of Phenol with Dimethyl Carbonate over Catalysts Supported on CaO
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Abstract: In this work CaO-based catalysts were found to be efficient heterogeneous catalysts for the methylation of phenol with dimethyl carbonate (DMC) in a closed high pressure reactor. The optimization experiments have been carried out to obtain best phenol conversion and the results showed that CaO catalyst modified with KCl had the best catalytic performance. When the reaction was carried out at 200°C, with phenol to dimethyl carbonate molar ratio of 1 : 2, 15% KCl/CaO catalyst dosage of 3%, reaction time 9 h, 100% conversion of phenol and 95% selectivity towards anisole have been achieved. The structure and properties of the materials were thoroughly characterized by Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET). The close correlation was found between surface basicity of the catalysts and their catalytic performance for phenol conversion and anisole selectivity.
- Chen, Shijun,Li, Shaoying,Tang, Ying,Xu, Zhongying,Zhang, Zhifang
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p. 496 - 506
(2021/08/23)
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- Methylation with Dimethyl Carbonate/Dimethyl Sulfide Mixtures: An Integrated Process without Addition of Acid/Base and Formation of Residual Salts
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Dimethyl sulfide, a major byproduct of the Kraft pulping process, was used as an inexpensive and sustainable catalyst/co-reagent (methyl donor) for various methylations with dimethyl carbonate (as both reagent and solvent), which afforded excellent yields of O-methylated phenols and benzoic acids, and mono-C-methylated arylacetonitriles. Furthermore, these products could be isolated using a remarkably straightforward workup and purification procedure, realized by dimethyl sulfide‘s neutral and distillable nature and the absence of residual salts. The likely mechanisms of these methylations were elucidated using experimental and theoretical methods, which revealed that the key step involves the generation of a highly reactive trimethylsulfonium methylcarbonate intermediate. The phenol methylation process represents a rare example of a Williamson-type reaction that occurs without the addition of a Br?nsted base.
- Chan, Bun,Lui, Matthew Y.,Lui, Yuen Wai
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- O-Methylation of Phenol for High Selective Synthesis of Anisole over Calcium Oxide Catalyst
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Abstract: In this article, a CaO-based catalyst was prepared by impregnating potassium salt on CaO to develop a highly efficient heterogeneous catalyst for highly selective synthesis of anisole (AN) from phenol and dimethyl carbonate by a O-methylation. KF/CaO catalysts are highly active and selective towards formation of anisole via methylation of phenol with the highest yield of 97.48% AN was obtained at 200°C. Various reaction parameters including KF loading, the amount of catalyst and the calcination temperature on the catalytic activity were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), BET, CO2?TPD and thermogravimetric (TG) were used to characterize the prepared catalyst. It was found that the high catalytic activity of CaO after modification with KF is associated with the structural aspects and the amount of basicity of the catalyst. Temperature programmed desorption of CO2 and XRD studies revealed the K2O species, a strong basic site formed by the substitution of the Ca2+ in CaO lattice by K+, might have great contribution for the high conversion of phenol and good selectivity of anisole.
- Zhifang Zhang,Xu, Zhongying,Li, Shaoying,Li, Zhaoyi,Zhang, Jie,Tang, Ying
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p. 596 - 603
(2021/04/16)
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- Ni-catalyzed reductive decyanation of nitriles with ethanol as the reductant
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A nickel-catalyzed reductive decyanation of aromatic nitriles has been developed, in which the readily available and abundant ethanol was applied as the hydride donor. Various functional groups on the aromatic rings, such as alkoxyl, amino, imino and amide, were compatible in this catalytic protocol. Heteroaryl, benzylic and alkenyl nitriles were also tolerated. Mechanistic investigation indicated that ethanol provided hydride efficientlyviaβ-hydride elimination in this reductive decyanation.
- Wu, Ke,Ling, Yichen,Sun, Nan,Hu, Baoxiang,Shen, Zhenlu,Jin, Liqun,Hu, Xinquan
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supporting information
p. 2273 - 2276
(2021/03/09)
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- Exploiting a silver-bismuth hybrid material as heterogeneous noble metal catalyst for decarboxylations and decarboxylative deuterations of carboxylic acids under batch and continuous flow conditions
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Herein, we report novel catalytic methodologies for protodecarboxylations and decarboxylative deuterations of carboxylic acids utilizing a silver-containing hybrid material as a heterogeneous noble metal catalyst. After an initial batch method development, a chemically intensified continuous flow process was established in a simple packed-bed system which enabled gram-scale protodecarboxlyations without detectable structural degradation of the catalyst. The scope and applicability of the batch and flow processes were demonstrated through decarboxylations of a diverse set of aromatic carboxylic acids. Catalytic decarboxylative deuterations were achieved on the basis of the reaction conditions developed for the protodecarboxylations using D2O as a readily available deuterium source.
- ?tv?s, Sándor B.,Fül?p, Ferenc,Kónya, Zoltán,Kukovecz, ákos,Márton, András,Mészáros, Rebeka,Pálinkó, István,Szabados, Márton,Varga, Gábor
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p. 4685 - 4696
(2021/07/12)
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- H2-Free Selective Dehydroxymethylation of Primary Alcohols over Palladium Nanoparticle Catalysts
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The dehydroxymethylation of primary alcohols is a promising strategy to transform biomass-derived oxygenates into hydrocarbon fuels. In this study, a novel, highly efficient, and reusable heterogeneous catalyst system was established for the H2-free dehydroxymethylation of primary alcohol using cerium oxide-supported palladium nanoparticles (Pd/CeO2). A wide range of aliphatic and aromatic alcohols including biomass-derived alcohols were converted into the corresponding one-carbon shorter hydrocarbons in high yields in the absence of any additives, accompanied by the production of H2 and CO. Pd/CeO2 was easily recovered from the reaction mixture and reused, retaining its high activity, thus, providing a simple and sustainable methodology to produce hydrocarbon fuels from biomass-derived oxygenates.
- Yamaguchi, Sho,Kondo, Hiroki,Uesugi, Kohei,Sakoda, Katsumasa,Jitsukawa, Koichiro,Mitsudome, Takato,Mizugaki, Tomoo
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p. 1135 - 1139
(2020/12/29)
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- Electrochemical Thiolation and Borylation of Arylazo Sulfones with Thiols and B2pin2
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An efficient electrochemical synthesis approach of various unsymmetrical thioethers and arylboronates has been developed. Bench stable arylazo sulfones were used as radical precursors for carbon-heteroatom bond formation under electrochemical conditions. Moreover, the scalability of this approach was evaluated by performing the electrochemical thiolation and borylation of arylazo sulfones with thiols and B2pin2 on a gram scale. This protocol not only avoided the use of stoichiometric oxidants, metal catalysts, activating agents and even added bases, but also exhibited favorable functional group tolerance. (Figure presented.).
- Wang, Rongkang,Chen, Fangming,Jiang, Lvqi,Yi, Wenbin
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supporting information
p. 1904 - 1911
(2021/02/12)
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- Direct bromodeboronation of arylboronic acids with CuBr2 in water
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An efficient and practical method has been developed for the preparation of aryl bromides via the direct bromodeboronation of arylboronic acids with CuBr2 in water. This strategy provides several advantages, such as being ligand-free, base-free, high yielding, and functional group tolerant.
- Tang, Yan-Ling,Xia, Xian-Song,Gao, Jin-Chun,Li, Min-Xin,Mao, Ze-Wei
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- Electrophotocatalytic C?H Heterofunctionalization of Arenes
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The electrophotocatalytic heterofunctionalization of arenes is described. Using 2,3-dichloro-5,6-dicyanoquinone (DDQ) under a mild electrochemical potential with visible-light irradiation, arenes undergo oxidant-free hydroxylation, alkoxylation, and amination with high chemoselectivity. In addition to batch reactions, an electrophotocatalytic recirculating flow process is demonstrated, enabling the conversion of benzene to phenol on a gram scale.
- Huang, He,Lambert, Tristan H.
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supporting information
p. 11163 - 11167
(2021/04/19)
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- Engaging Ag(0) single atoms in silver(I) salts-mediated C-B and C-S coupling under visible light irradiation
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Silver(I) salts were found active in the borylation and sulfenylation of aryl iodides under visible light irradiation. The optimized borylation protocol using AgF did not need any additive, operated under very mild conditions, and well tolerated a broad scope of substrates and boron sources. Formation of Ag(0) single atoms (AgSAs) during the borylation reactions was examined using high-angle annular dark field aberration-corrected scanning transmission electron microscope (HAADF AC-STEM) and electron paramagnetic resonance (EPR). The activities of the silver(I) salts were affected by the anions and could be associated with their abilities in formation of AgSAs during the reactions. Kinetic studies showed that the deiodination rate was linearly correlated with the loading of AgSAs, and hence AgSAs were the true catalytic centers for the 1e?-reduction of the C-I moieties. The oxidation state of AgSAs kept 0 in both the resting and the working states. A “work-in-tandem” mechanism involving AgSAs as the catalytic centers and AgNPs as the light absorber to achieve the borylation of aryl iodides under visible light irradiation is proposed. The current approach not only provides an alternative system for borylation and sulfenylation of aryl iodides, but also reveals a new activity of silver(I) salts involving AgSAs under visible light irradiation.
- Cui, Enxin,Guo, Lirong,Li, Haibin,Qiao, Dan,Tung, Chen-Ho,Wang, Yifeng
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p. 255 - 263
(2021/09/06)
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- Iron-Catalyzed C-C Single-Bond Cleavage of Alcohols
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An iron-catalyzed deconstruction/hydrogenation reaction of alcohols through C-C bond cleavage is developed through photocatalysis, to produce ketones or aldehydes as the products. Tertiary, secondary, and primary alcohols bearing a wide range of substituents are suitable substrates. Complex natural alcohols can also perform the transformation selectively. A investigation of the mechanism reveals a procedure that involves chlorine radical improved O-H homolysis, with the assistance of 2,4,6-collidine.
- Liu, Wei,Wu, Qiang,Wang, Miao,Huang, Yahao,Hu, Peng
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supporting information
p. 8413 - 8418
(2021/11/01)
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- Method for preparing aldehyde/ketone by breaking C-C key
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The invention discloses a method for preparing aldehyde/ketone by breaking C-C bonds, and the method comprises the following steps of anaerobic condition. In an organic solvent system, an alcohol is used as a reaction raw material, and the C-C bond is selectively broken under the common action of an iron catalyst, an organic base and an additive to obtain aldehyde/ketone. The method is low in cost, easy to obtain, wide in substrate range, simple and product in post-treatment and high in purity, a new synthetic route and a method are developed for an aldehyde ketone compound, and the method has good application potential and research value.
- -
-
Paragraph 0099-0102
(2021/11/19)
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- Method for reducing aromatic C-N/Cl C/I bond to aromatic-H / D
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A method of reducing C an aromatic-N C/Cl/I bond to an aromatic-H / D, the process being a stable aromatic quaternary ammonium salt. After addition of the base and the solvent, the aromatic compound or the deuterated aromatic compound can be efficiently prepared by irradiation with visible light or ultraviolet light. The method can efficiently convert stable aromatic-N/I chemical bonds into aromatic-H / D bonds by visible light or ultraviolet light in a cheap and easily available solvent or deuterated solvent without using a catalyst or a transition metal compound C C. The whole production process is green, environment-friendly, low in cost, wide in substrate applicability, high in yield, high in deuterated rate, simple and convenient to operate, free of explosion risk and remarkable in advantage compared with the conventional production process.
- -
-
Paragraph 0039-0040
(2021/09/08)
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- Separation of Anisole and Valuable Byproducts from Liquid Reaction Mixtures by Solvent Extraction and Multicomponent Distillation
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Anisole (methoxybenzene) is a widely used organic intermediate that can be synthesized via vapor-phase alkylation of phenol by methanol in the presence of a commercial NaX zeolite as a catalyst (SiO2:Al2O3 ratio of 2.6:3). The indigenously synthesized anisole is then separated from the multicomponent liquid reaction mixture, consisting of o-cresol, p-cresol and p-xylen, along with unreacted methanol and phenol. The separated anisole has substantial demand for applications in the chemical, pharmaceutical, plastics and pesticides industries. Separation of individual components from the reaction mixture requires identification of techniques that could be scaled up. Distillation is one of the most dependable techniques for the separation of multicomponent liquid mixtures. The novelty of the present study is the synthesis and separation of anisole along with individual components of methanol, phenol and o-cresol from its reaction mixture using a single distillation column under atmospheric and vacuum conditions, respectively. Through this process, the purity of the resulting methanol, anisole and phenol were found to be 99.99, 99.80 and 98.29% by simple distillation, whereas 91.0% pure o-cresol was separated by vacuum distillation due to its high boiling point. The experimental results were used to calculate the material, individual component and energy balances, whereas the PRO/II process simulation was performed to scale-up the process. On the other hand, anisole recovery from a synthetic multicomponent liquid mixture was also successfully conducted using solvent extraction. The overall observations found the integration of solvent extraction with distillation to be an effective, economical and dependable solution for the isolation of anisole and other important by-products.
- Vani, Bukke,Pabba, Manideep,Kalyani, Swayampakula,Sridhar, Sundergopal
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p. 160 - 177
(2021/01/29)
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- Catalytic role of metals supported on SBA-16 in hydrodeoxygenation of chemical compounds derived from biomass processing
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Hydrodeoxygenation (HDO) carried out at high temperatures and high hydrogen pressures is one of the alternative methods of upgrading pyrolytic oils from biomass, leading to high quality biofuels. To save energy, it is important to carry out catalytic proc
- Szczyglewska, Paulina,Feliczak-Guzik, Agnieszka,Jaroniec, Mietek,Nowak, Izabela
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p. 9505 - 9517
(2021/03/16)
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- Aluminum Metal-Organic Framework-Ligated Single-Site Nickel(II)-Hydride for Heterogeneous Chemoselective Catalysis
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The development of chemoselective and heterogeneous earth-abundant metal catalysts is essential for environmentally friendly chemical synthesis. We report a highly efficient, chemoselective, and reusable single-site nickel(II) hydride catalyst based on robust and porous aluminum metal-organic frameworks (MOFs) (DUT-5) for hydrogenation of nitro and nitrile compounds to the corresponding amines and hydrogenolysis of aryl ethers under mild conditions. The nickel-hydride catalyst was prepared by the metalation of aluminum hydroxide secondary building units (SBUs) of DUT-5 having the formula of Al(μ2-OH)(bpdc) (bpdc = 4,4′-biphenyldicarboxylate) with NiBr2 followed by a reaction with NaEt3BH. DUT-5-NiH has a broad substrate scope with excellent functional group tolerance in the hydrogenation of aromatic and aliphatic nitro and nitrile compounds under 1 bar H2 and could be recycled and reused at least 10 times. By changing the reaction conditions of the hydrogenation of nitriles, symmetric or unsymmetric secondary amines were also afforded selectively. The experimental and computational studies suggested reversible nitrile coordination to nickel followed by 1,2-insertion of coordinated nitrile into the nickel-hydride bond occurring in the turnover-limiting step. In addition, DUT-5-NiH is also an active catalyst for chemoselective hydrogenolysis of carbon-oxygen bonds in aryl ethers to afford hydrocarbons under atmospheric hydrogen in the absence of any base, which is important for the generation of fuels from biomass. This work highlights the potential of MOF-based single-site earth-abundant metal catalysts for practical and eco-friendly production of chemical feedstocks and biofuels.
- Antil, Neha,Kumar, Ajay,Akhtar, Naved,Newar, Rajashree,Begum, Wahida,Dwivedi, Ashutosh,Manna, Kuntal
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p. 3943 - 3957
(2021/04/12)
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- Photo-induced thiolate catalytic activation of inert Caryl-hetero bonds for radical borylation
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Substantial effort is currently being devoted to obtaining photoredox catalysts with high redox power. Yet, it remains challenging to apply the currently established methods to the activation of bonds with high bond dissociation energy and to substrates with high reduction potentials. Herein, we introduce a novel photocatalytic strategy for the activation of inert substituted arenes for aryl borylation by using thiolate as a catalyst. This catalytic system exhibits strong reducing ability and engages non-activated Caryl–F, Caryl–X, Caryl–O, Caryl–N, and Caryl–S bonds in productive radical borylation reactions, thus expanding the available aryl radical precursor scope. Despite its high reducing power, the method has a broad substrate scope and good functional-group tolerance. Spectroscopic investigations and control experiments suggest the formation of a charge-transfer complex as the key step to activate the substrates.
- K?nig, Burkhard,Wang, Hua,Wang, Shun
-
supporting information
p. 1653 - 1665
(2021/06/17)
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- Boronic Acid Pairs for Sequential Bioconjugation
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Boronic acids can play diverse roles when applied in biological environments, and employing boronic acid structures in tandem could provide new tools for multifunctional probes. This Letter describes a pair of boronic acid functional groups, 2-nitro-arylboronic acid (NAB) and (E)-alkenylboronic acid (EAB), that enable sequential cross-coupling through stepwise nickel- and copper-catalyzed processes. The selective coupling of NAB groups enables the preparation of stapled peptides, protein-protein conjugates, and other bioconjugates.
- Ball, Zachary T.,Ding, Yuxuan,Miller, Mary K.,Swierczynski, Michael J.
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supporting information
p. 5334 - 5338
(2021/07/26)
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- The Effect of Sulfonate Groups in the Structure of Porous Aromatic Frameworks on the Activity of Platinum Catalysts Towards Hydrodeoxygenation of Biofuel Components
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Abstract: Platinum catalysts based on porous aromatic frameworks (PAF-30 and PAF-30–SO3H) have been synthesized. Properties of the obtained catalysts have been assessed via hydrogenation of guaiacol, veratrole, and pyrocatechol at 250°С and hydrogen pressure 3.0 MPa in isopropanol medium. It has been shown that the presence of acidic sites in the catalyst significantly increases the yield of deoxygenation products. The effect of the substrate structure on the rate of its hydrodeoxygenation and the mechanism of the occurring processes have been studied. [Figure not available: see fulltext.]
- Kalinina,Kulikov,Cherednichenko,Maximov,Karakhanov
-
p. 1061 - 1070
(2021/09/06)
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- Electrochemical Activation of Diverse Conventional Photoredox Catalysts Induces Potent Photoreductant Activity**
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Herein, we disclose that electrochemical stimulation induces new photocatalytic activity from a range of structurally diverse conventional photocatalysts. These studies uncover a new electron-primed photoredox catalyst capable of promoting the reductive cleavage of strong C(sp2)?N and C(sp2)?O bonds. We illustrate several examples of the synthetic utility of these deeply reducing but otherwise safe and mild catalytic conditions. Finally, we employ electrochemical current measurements to perform a reaction progress kinetic analysis. This technique reveals that the improved activity of this new system is a consequence of an enhanced catalyst stability profile.
- Chernowsky, Colleen P.,Chmiel, Alyah F.,Wickens, Zachary K.
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supporting information
p. 21418 - 21425
(2021/08/25)
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- Continuous Flow Acylation of (Hetero)aryllithiums with Polyfunctional N,N-Dimethylamides and Tetramethylurea in Toluene
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The continuous flow reaction of various aryl or heteroaryl bromides in toluene in the presence of THF (1.0 equiv) with sec-BuLi (1.1 equiv) provided at 25 °C within 40 sec the corresponding aryllithiums which were acylated with various functionalized N,N-
- Djukanovic, Dimitrije,Filipponi, Paolo,Heinz, Benjamin,Knochel, Paul,Mandrelli, Francesca,Martin, Benjamin,Mostarda, Serena
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supporting information
p. 13977 - 13981
(2021/09/13)
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- Removal of Alkyl Sulfonates Using DABCO
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During the route development of a midstage clinical candidate, we were challenged with a presence of alkyl sulfonates, which were identified as potential genotoxic impurities in our active pharmaceutical ingredient (API). As a result, we initiated a development effort to identify a method to remove the alkyl sulfonates that would be amenable for scale-up. Herein, we report our effort toward the development of a general approach using DABCO (1,4-diazabicyclo[2.2.2]octane) to remove alkyl sulfonates that is both efficient and convenient from the bench to scale-up.
- Corazzata, Kaitlyn,Langston, Alexander,Lee, Elaine C.,Mo, Shunyan,Rose, Peter J.,Snodgrass, Joseph
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supporting information
(2021/11/30)
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- A General Approach to O-Sulfation by a Sulfur(VI) Fluoride Exchange Reaction
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O-sulfation is an important chemical code widely existing in bioactive molecules, but the scalable and facile synthesis of complex bioactive molecules carrying O-sulfates remains challenging. Reported here is a general approach to O-sulfation by the sulfur(VI) fluoride exchange (SuFEx) reaction between aryl fluorosulfates and silylated hydroxy groups. Efficient sulfate diester formation was achieved through systematic optimization of the electronic properties of aryl fluorosulfates. The versatility of this O-sulfation strategy was demonstrated in the scalable syntheses of a variety of complex molecules carrying sulfate diesters at various positions, including monosaccharides, disaccharides, an amino acid, and a steroid. Selective hydrolytic and hydrogenolytic removal of the aryl masking groups from sulfate diesters yielded the corresponding O-sulfate products in excellent yields. This strategy provides a powerful tool for the synthesis of O-sulfate bioactive compounds.
- Ferraro, Samantha L.,Flynn, James P.,Hwang, Seung,Liu, Chao,Niu, Jia,Yang, Cangjie
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p. 18435 - 18441
(2020/08/25)
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- Discovery and characterization of an acridine radical photoreductant
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Photoinduced electron transfer (PET) is a phenomenon whereby the absorption of light by a chemical species provides an energetic driving force for an electron-transfer reaction1–4. This mechanism is relevant in many areas of chemistry, including the study of natural and artificial photosynthesis, photovoltaics and photosensitive materials. In recent years, research in the area of photoredox catalysis has enabled the use of PET for the catalytic generation of both neutral and charged organic free-radical species. These technologies have enabled previously inaccessible chemical transformations and have been widely used in both academic and industrial settings. Such reactions are often catalysed by visible-light-absorbing organic molecules or transition-metal complexes of ruthenium, iridium, chromium or copper5,6. Although various closed-shell organic molecules have been shown to behave as competent electron-transfer catalysts in photoredox reactions, there are only limited reports of PET reactions involving neutral organic radicals as excited-state donors or acceptors. This is unsurprising because the lifetimes of doublet excited states of neutral organic radicals are typically several orders of magnitude shorter than the singlet lifetimes of known transition-metal photoredox catalysts7–11. Here we document the discovery, characterization and reactivity of a neutral acridine radical with a maximum excited-state oxidation potential of ?3.36 volts versus a saturated calomel electrode, which is similarly reducing to elemental lithium, making this radical one of the most potent chemical reductants reported12. Spectroscopic, computational and chemical studies indicate that the formation of a twisted intramolecular charge-transfer species enables the population of higher-energy doublet excited states, leading to the observed potent photoreducing behaviour. We demonstrate that this catalytically generated PET catalyst facilitates several chemical reactions that typically require alkali metal reductants and can be used in other organic transformations that require dissolving metal reductants.
- MacKenzie, Ian A.,Wang, Leifeng,Onuska, Nicholas P. R.,Williams, Olivia F.,Begam, Khadiza,Moran, Andrew M.,Dunietz, Barry D.,Nicewicz, David A.
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- Method for catalyzing dehalogenation of aromatic halogen-containing organic matter by using supported metal oxide
-
The invention relates to a hydrodehalogenation catalyst, and aims to provide a method for catalyzing dehalogenation of an aromatic halogen-containing organic matter by using a supported metal oxide. The method comprises the following steps: adding an organic solvent, the aromatic halogen-containing organic matter, a neutralizer and a catalyst material into a sealable reaction container, and uniformly mixing; introducing hydrogen until the pressure is 0.1-3.0 MPa, and performing a reaction at 25-180 DEG C for 0.1-24 h; catalyzing dehalogenation through the catalyst in the reaction process to finally obtain a dehalogenated organic matter. The selectivity of the product in the dehalogenation process of the aromatic halogen-containing organic matter can be effectively regulated, and efficientdehalogenation can still be performed even if the halogen-containing organic matter contains two or more reducible functional groups, so that important compounds in chemical and agricultural processesare efficiently prepared. In the dehalogenation process, the catalyst is stable and can be recycled, no toxic or harmful byproduct is generated in the whole reaction process, and the method is environmentally friendly and has industrial application prospects.
- -
-
Paragraph 0127-0128; 0137-0138
(2020/06/05)
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- Tailorable carbazolyl cyanobenzene-based photocatalysts for visible light-induced reduction of aryl halides
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Herein, a series of carbazolyl cyanobenzene (CCB)-based organic photocatalysts with a broad range of photoredox capabilities were designed and synthesized, allowing precise control of the photocatalytic reactivity for the controllable reduction of aryl halides via a metal-free process. The screened-out CCB (5CzBN), a metal-free, low-cost, scalable and sustainable photocatalyst with both strong oxidative and reductive ability, exhibits superior performance for both dehalogenation and C[sbnd]C bond-forming arylation reactions.
- Ou, Wei,Zou, Ru,Han, Mengting,Yu, Lei,Su, Chenliang
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supporting information
p. 1899 - 1902
(2019/12/27)
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- Effects of Ligand Substitution on the Optical and Electrochemical Properties of (Pyridinedipyrrolide)zirconium Photosensitizers
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A series of seven bis(pyridinedipyrrolide)zirconium complexes, Zr(R1PDPR2)2, where [R1PDPR2]2- is the doubly deprotonated form of [2,6-bis(5-R1-3-R2-1H-pyrrol-2-yl)pyridine], were prepared and characterized in solution by NMR, UV/vis absorption, and emission spectroscopy and cyclic voltammetry. The molecular structures were determined by single-crystal X-ray crystallography. All complexes exhibit remarkably long emission lifetimes (τ = 190-576 μs) with high quantum efficiencies (φPL = 0.10-0.38) upon excitation with visible light in a benzene solution. The substituents on the pyrrolide rings were shown to have significant effects on the photoluminescence and electrochemical properties of these compounds. The R2 substituents (R2 = H, Me, Ph, or C6F5) show only limited effects on the absorption and emission profiles of the complexes but allow systematic tuning of the ground- and excited-state redox potentials over a range of almost 600 mV. The R1 substituents (R1 = H, Me, Ph, or 2,4,6-Me3Ph) influence both the optical and electrochemical properties through electronic effects. Additionally, the R1 substituents have profound consequences for the structural flexibility and overall stability of the compounds. Distortions of the Zr(PDP)2 core from idealized D2d symmetry in the solid state can be traced to the steric profiles of the R1 substituents and correlate with the observed Stokes shifts for each compound. The complex with the smallest ligand system, Zr(HPDPH)2, coordinates two additional solvent molecules in a tetrahydrofuran (THF) solution, which allowed the isolation of photoluminescent, eight-coordinate Zr(HPDPH)2(THF)2. The photoredox catalytic dehalogenation of aryl iodides and aryl chlorides using the most reducing derivative, Zr(MePDPMe)2, highlights the potential of Zr(PDP)2 photosensitizers to promote challenging reductive transformations under mild conditions upon excitation with green light.
- Belldina, Anne M.,Leary, Dylan C.,Milsmann, Carsten,Petersen, Jeffrey L.,Zhang, Yu
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supporting information
p. 14716 - 14730
(2020/11/02)
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- Visible-Light-Induced, Base-Promoted Transition-Metal-Free Dehalogenation of Aryl Fluorides, Chlorides, Bromides, and Iodides
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We report a simple and efficient visible-light-induced transition-metal-free hydrogenation of aryl halides. The combined visible light and base system is used to initiate the desired radical-mediated hydrogenation. A variety of aryl fluorides, chlorides, bromides, and iodides could be reduced to the corresponding (hetero)arenes with excellent yields under mild conditions. Various functional groups and other heterocyclic compounds are tolerated.
- Ding, Ting-Hui,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 3084 - 3088
(2020/04/10)
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- Cobalt-Catalyzed Reductive Carboxylation of Aryl Bromides with Carbon Dioxide
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Cobalt-catalyzed reductive carboxylation of aryl bromides with carbon dioxide has been developed. The reaction proceeded under one atm pressure of CO2 at 40 °C in the presence of cobalt iodide/2,2′-bipyridine catalysts and zinc dust as a reducing reagent. Various aryl bromides could be converted to the corresponding carboxylic acids in good to high yields. Preliminary mechanistic experiments ruled out intervention of intermediate organozinc species for carboxylation with CO2, thus suggesting a direct CO2 insertion into the corresponding ArCoBr species. (Figure presented.).
- Hang, Wei,Yi, Yaping,Xi, Chanjuan
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p. 2337 - 2341
(2020/04/30)
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