- Trifluoromethylation of organic halides with methyl halodifluoroacetates - a process via difluorocarbene and trifluoromethide intermediates
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Treatment of methyl halodifluoroacetates, XCF2CO2Me (X=Cl, Br, I), with organic halides RY in the presence of KF and CuI at an appropriate temperature in DMF gave the corresponding trifluoromethylated derivatives, RCF3, in moderate to high yields.A process involving difluorocarbene and trifluoromethide intermediates is suggested.
- Duan, Jian-Xing,Su, De-Bao,Chen, Qing-Yun
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- Aryl-CF3 Coupling from Phosphinoferrocene-Ligated Palladium(II) Complexes
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This article describes a detailed investigation of ligand effects on Ph-CF3 coupling from phosphinoferrocene-ligated PdII(Ph)(CF3) complexes. This study reveals that increasing the size of the phosphine substituents results in an enhanced rate of Ph-CF3 coupling, with (DtBPF)Pd(Ph)(CF3) (DtBPF = 1,1′-bis(di-tert-butylphosphino)ferrocene) being the most reactive complex. The mechanism of Ph-CF3 bond formation from both (DtBPF)Pd(Ph)(CF3) and (DiPrPF)Pd(Ph)(CF3) (DiPrPF = 1,1′-bis(diisopropylphosphino)ferrocene) was interrogated experimentally and computationally. These studies implicate a pathway involving concerted Ph-CF3 bond-forming reductive elimination from the four-coordinate PdII centers. An alternative pathway involving α-fluoride elimination and subsequent PhF2C-F coupling from PdII(CF2Ph)(F) intermediates was also evaluated but was ruled out based on DFT as well as the independent synthesis and reactivity studies of (DiPrPF)Pd(CF2Ph)(F).
- Ferguson, Devin M.,Bour, James R.,Canty, Allan J.,Kampf, Jeff W.,Sanford, Melanie S.
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- New Vistas in Transmetalation with Discrete “AgCF3” Species: Implications in Pd-Mediated Trifluoromethylation Reactions
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This work describes the employment of discrete “AgCF3” complexes as efficient transmetalating agents to PdII to surmount overlooked challenges related to the transmetalation step in Pd-catalyzed trifluoromethylation processes. We report the participation of a unique silver ate (Cs)[Ag(CF3)2] complex, under stoichiometric and catalytic conditions, in the unprecedented one-pot formation of PhCF3 using PhI as starting material. Moreover, we show that the transmetalation step, which is often ignored in these transformations, can also determine the success or failure of the coupling process.
- Martínez de Salinas, Sara,Mudarra, ángel L.,Benet-Buchholz, Jordi,Parella, Teodor,Maseras, Feliu,Pérez-Temprano, Mónica H.
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- Application of Visible-to-UV Photon Upconversion to Photoredox Catalysis: The Activation of Aryl Bromides
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The activation of aryl-Br bonds was achieved by sequential combination of a triplet-triplet annihilation process of the organic dyes, butane-2,3-dione and 2,5-diphenyloxazole, with a single-electron-transfer activation of aryl bromides. The photophysical and chemical steps were studied by time-resolved transient fluorescence and absorption spectroscopy with a pulsed laser, quenching experiments, and DFT calculations.
- Majek, Michal,Faltermeier, Uwe,Dick, Bernhard,Pérez-Ruiz, Raúl,JacobivonWangelin, Axel
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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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- 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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- 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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- 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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- 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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- 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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- 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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- Mechanistic Insight into Copper-Mediated Trifluoromethylation of Aryl Halides: The Role of CuI
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The synthesis, characterization, and reactivity of key intermediates [Cu(CF3)(X)]-Q+ (X = CF3 or I, Q = PPh4) in copper-mediated trifluoromethylation of aryl halides were studied. Qualitative and quantitative studies showed [Cu(CF3)2]-Q+ and [Cu(CF3)(I)]-Q+ were not highly reactive. Instead, a much more reactive species, ligandless [CuCF3] or DMF-ligated species [(DMF)CuCF3], was generated in the presence of excess CuI. On the basis of these results, a general mechanistic map for CuI-promoted trifluoromethylation of aryl halides was proposed. Furthermore, on the basis of this mechanistic understanding, a HOAc-promoted protocol for trifluoromethylation of aryl halides with [Ph4P]+[Cu(CF3)2]- was developed.
- Jin, Yuxuan,Leng, Xuebing,Liu, He,Shen, Qilong,Wu, Jian
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supporting information
p. 14367 - 14378
(2021/09/13)
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- Cross-Coupling through Ag(I)/Ag(III) Redox Manifold
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In ample variety of transformations, the presence of silver as an additive or co-catalyst is believed to be innocuous for the efficiency of the operating metal catalyst. Even though Ag additives are required often as coupling partners, oxidants or halide scavengers, its role as a catalytically competent species is widely neglected in cross-coupling reactions. Most likely, this is due to the erroneously assumed incapacity of Ag to undergo 2e? redox steps. Definite proof is herein provided for the required elementary steps to accomplish the oxidative trifluoromethylation of arenes through AgI/AgIII redox catalysis (i. e. CEL coupling), namely: i) easy AgI/AgIII 2e? oxidation mediated by air; ii) bpy/phen ligation to AgIII; iii) boron-to-AgIII aryl transfer; and iv) ulterior reductive elimination of benzotrifluorides from an [aryl-AgIII-CF3] fragment. More precisely, an ultimate entry and full characterization of organosilver(III) compounds [K]+[AgIII(CF3)4]? (K-1), [(bpy)AgIII(CF3)3] (2) and [(phen)AgIII(CF3)3] (3), is described. The utility of 3 in cross-coupling has been showcased unambiguously, and a large variety of arylboron compounds was trifluoromethylated via [AgIII(aryl)(CF3)3]? intermediates. This work breaks with old stereotypes and misconceptions regarding the inability of Ag to undergo cross-coupling by itself.
- Demonti, Luca,Mézailles, Nicolas,Nebra, Noel,Saffon-Merceron, Nathalie
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supporting information
p. 15396 - 15405
(2021/10/12)
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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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- Aryl dechlorination and defluorination with an organic super-photoreductant
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Direct excitation of the commercially available super-electron donor tetrakis(dimethylamino)ethylene (TDAE) with light-emitting diodes at 440 or 390 nm provides a stoichiometric reductant that is able to reduce aryl chlorides and fluorides. The method is very simple and requires only TDAE, substrate, and solvent at room temperature. The photoactive excited state of TDAE has a lifetime of 17.3 ns in cyclohexane at room temperature and an oxidation potential of ca. -3.4 V vs. SCE. This makes TDAE one of the strongest photoreductants able to operate on the basis of single excitation with visible photons. Direct substrate activation occurs in benzene, but acetone is reduced by photoexcited TDAE and substrate reduction takes place by a previously unexplored solvent radical anion mechanism. Our work shows that solvent can have a leveling effect on the photochemically available redox power, reminiscent of the pH-leveling effect that solvent has in acid-base chemistry.
- Glaser, Felix,Kerzig, Christoph,Larsen, Christopher B.,Wenger, Oliver S.
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p. 1035 - 1041
(2020/08/28)
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- Deoxyfluorination of acyl fluorides to trifluoromethyl compounds by FLUOLEAD/Olah's reagent under solvent-free conditions
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A new protocol enabling the formation of trifluoromethyl compounds from acyl fluorides has been developed. The combination of FLUOLEAD and Olah's reagent in solvent-free conditions at 70 °C initiated the significant deoxyfluorination of the acyl fluorides and resulted in the corresponding trifluoromethyl products with high yields (up to 99%). This strategy showed a great tolerance for various acyl fluorides containing aryloyl, (heteroaryl)oyl, or aliphatic acyl moieties, providing good to excellent yields of the trifluoromethyl products. Synthetic drug-like molecules were also transformed into the corresponding trifluoromethyl compounds under the same reaction conditions. A reaction mechanism is proposed.
- Liang, Yumeng,Taya, Akihito,Zhao, Zhengyu,Saito, Norimichi,Shibata, Norio
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p. 3052 - 3058
(2021/01/15)
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- Method for catalyzing dehalogenation of aromatic halogen-containing organic matter by using supported metal oxide
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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.
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Paragraph 0129-0130
(2020/06/05)
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- Dehalogenation method of covalent organic framework material photocatalytic halogenated aromatic compound
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The invention relates to a dehalogenation method of a halogenated aromatic compound. The method comprises the following steps: removing halogen substituent groups on aromatic rings from the halogenated aromatic compound under the action of a photocatalyst under illumination to obtain the aromatic compound. According to the reaction system, under the action of the photocatalyst, a hydrogen donor and an alkali, the halogenated aromatic compound can be selectively dehalogenated to synthesize the aromatic compound, and the GC yield of the product can reach 92% or above and can reach 99% at most.
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Paragraph 0067-0069
(2021/01/11)
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- Transition metal catalyzed nitro-aromatic denitration method
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The invention provides a transition metal catalyzed nitro-aromatic denitration method, which comprises the following steps: in a nitrogen atmosphere, taking nitro-aromatic as a substrate in an organicsolvent, reacting under the action of alkali and a reducing agent under the action of a transition metal catalyst and a ligand, and carrying out column chromatography separation to obtain an aromaticcompound. The method can directly convert nitro aromatic hydrocarbon into corresponding aromatic hydrocarbon compounds, is high in catalytic efficiency, low in cost and convenient to operate, and canbe compatible with various functional groups. In addition, the directional reduction nitro group, position and number of the nitro group of the polynitro compound are regulated and controlled throughthe proportion and addition amount of the reducing agent and the catalytic system, so that the directional conversion of the polynitro group is realized.
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Paragraph 0027; 0029-0032; 0045-0048
(2020/08/18)
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- Nickel-Catalyzed Electrosynthesis of Aryl and Vinyl Phosphinates
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A mild and useful nickel-catalyzed electrochemical phosphonylation of aryl and vinyl bromides is described. We show that alkyl H-phenylphosphinates can be coupled electrochemically with functionalized aryl and vinyl bromides using very simple conditions (Fe/Ni anode, bench-stable nickel pre-catalyst, undivided cell, galvanostatic electrolysis) to furnish the corresponding aryl and vinyl phosphinates in satisfactory to good yields. Couplings can also be applied to heteroaromatic bromides with some limitations like increased propensity to hydro-dehalogenation.
- Daili, Farah,Ouarti, Abdelhakim,Pinaud, Marine,Kribii, Ibtihal,Sengmany, Stéphane,Le Gall, Erwan,Léonel, Eric
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supporting information
p. 3452 - 3455
(2020/05/25)
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- Continuous flow synthesis of arylhydrazines: via nickel/photoredox coupling of tert -butyl carbazate with aryl halides
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Nickel/photoredox catalyzed C-N couplings of hydrazine-derived nucleophiles provide a powerful alternative to Pd-catalyzed methods. This continuous-flow photochemical protocol, optimized using design of experiments, achieves these couplings in short residence times, with high selectivity. A range of (hetero)aryl bromides and chlorides are compatible and understanding of process stability/reactor fouling has been discerned. This journal is
- Mata, Alejandro,Tran, Duc N.,Weigl, Ulrich,Williams, Jason D.,Kappe, C. Oliver
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supporting information
p. 14621 - 14624
(2020/12/02)
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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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- 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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- Practical Transition-Metal-Free Protodeboronation of Arylboronic Acids in Aqueous Sodium Hypochlorite
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A concise and practical method was developed for the protodeboronation of arylboronic acids under mild conditions in aqueous NaClO at 100 °C. The strategy is low-cost, transition-metal-free, and base-free.
- Li, Minxin,Tang, Yanling,Gao, Jinchun,Rao, Gaoxiong,Mao, Zewei
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p. 2039 - 2042
(2020/10/21)
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- Pt-Pd nanoalloy for the unprecedented activation of carbon-fluorine bond at low temperature
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Carbon-fluorine bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that has hitherto often required harsh conditions. The alloying of Pt with Pd is crucial to promote the overall C-F bond. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond cleavage. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction.
- Dhital, Raghu Nath,Ehara, Masahiro,Haesuwannakij, Setsiri,Nomura, Keigo,Sakurai, Hidehiro,Sato, Yoshinori
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p. 1180 - 1185
(2020/10/18)
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- Catalytic Hydrogenolysis of Aryl C-F Bonds Using a Bimetallic Rhodium-Indium Complex
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A homogeneous rhodium-indium catalyst hydrodefluorinates substrates bearing strong aryl C-F bonds, including difluoro- and fluorobenzene, using 1 atm of H2, alkoxide bases, and moderate temperatures (70-90 °C). Characterization of catalytic intermediates establishes a formal Rh-I/RhI redox cycle. The Rh → In interaction is proposed to enable catalysis by stabilizing the reactive Rh-I species, which is responsible for cleaving the Ar-F bond and is ultimately regenerated using H2 and base.
- Moore, James T.,Lu, Connie C.
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supporting information
p. 11641 - 11646
(2020/07/27)
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- Stoichiometric Studies on the Carbonylative Trifluoromethylation of Aryl Pd(II) Complexes using TMSCF3 as the Trifluoromethyl Source
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We have performed a series of stoichiometric studies in order to identify viable steps for a hypothetical catalytic cycle for the palladium-mediated carbonylative coupling of an aryl bromide with TMSCF3. Our work revealed that benzoyl Pd(II) complexes bearing Xantphos or tBu3P as the phosphine ligands, which are generated from the corresponding PdII(Ph)Br complexes exposed to stoichiometric 13CO from 13COgen, were unable to undergo transmetalation and reductive elimination to trifluoroacetophenone. Instead, in the presence of base and additional CO, these organometallic complexes readily underwent reductive elimination to the acid fluoride. Attempts to determine whether the acid fluoride could represent an intermediate for acetophenone production were unrewarding. Only in the presence of a boronic ester did we observe some formation of the desired product, although the efficiency of transformation was still low. Finally, we investigated the reactivity of four phosphine-ligated PdII(Ph)CF3 complexes (Xantphos, DtBPF, tBu3P, and triphenylphosphine) with carbon monoxide. With the exception of the tBu3P-ligated complex, all other metal complexes led to the facile formation of trifluoroacetophenone. We also determined in the case of triphenylphosphine that CO insertion occurred into the Pd-Ar bond, as trapping of this complex with n-hexylamine led to the formation of n-hexylbenzamide.
- Daasbjerg, Kim,Domino, Katrine,Johansen, Martin B.,Skrydstrup, Troels
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supporting information
(2020/03/04)
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- Palladium Catalyzed C?O Coupling of Amino Alcohols for the Synthesis of Aryl Ethers
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Amine containing aryl ethers are common pharmacophore motifs that continue to emerge from drug discovery efforts. As amino alcohols are readily available building blocks, practical methodologies for incorporating them into more complex structures are highly desirable. We report our efforts to explore the application of Pd-catalyzed C?O coupling methods to the arylation of 1,2- and 1,3-amino alcohols. We established general and reliable conditions, under which we explored the scope and limitations of the transformation. The insights gained have been valuable in employing this methodology within a fast-moving drug discovery environment, which we anticipate will be of general interest to the synthesis and catalysis communities.
- Mikus, Malte S.,Sanchez, Carina,Fridrich, Cary,Larrow, Jay F.
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supporting information
p. 430 - 436
(2019/12/27)
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- Silylation of Aryl Chlorides by Bimetallic Catalysis of Palladium and Gold on Alloy Nanoparticles
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Supported palladium-gold alloy-catalyzed cross-coupling of aryl chlorides and hydrosilanes enabled the selective formation of aryl-silicon bonds. Whereas a monometallic palladium catalyst predominantly promoted the hydrodechlorination of aryl chlorides and gold nanoparticles showed no catalytic activity, gold-rich palladium-gold alloy nanoparticles efficiently catalyzed the title reaction to give arylsilanes with high selectivity. A wide array of aryl chlorides and hydrosilanes participated in the heterogeneously-catalyzed reaction to furnish the corresponding arylsilanes in 34–80% yields. A detailed mechanistic investigation revealed that palladium and gold atoms on the surface of alloy nanoparticles independently functioned as active sites for the formation of aryl nucleophiles and silyl electrophiles, respectively, which indicates that palladium and gold atoms on alloy nanoparticles work together to enable the selective formation of aryl-silicon bonds. (Figure presented.).
- Miura, Hiroki,Masaki, Yosuke,Fukuta, Yohei,Shishido, Tetsuya
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supporting information
p. 2642 - 2650
(2020/04/22)
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- Nickel-Mediated Trifluoromethylation of Phenol Derivatives by Aryl C?O Bond Activation
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The increasing pharmaceutical importance of trifluoromethylarenes has stimulated the development of more efficient trifluoromethylation reactions. Tremendous efforts have focused on copper- and palladium-mediated/catalyzed trifluoromethylation of aryl halides. In contrast, no general method exists for the conversion of widely available inert electrophiles, such as phenol derivatives, into the corresponding trifluoromethylated arenes. Reported herein is a practical nickel-mediated trifluoromethylation of phenol derivatives with readily available trimethyl(trifluoromethyl)silane (TMSCF3). The strategy relies on PMe3-promoted oxidative addition and transmetalation, and CCl3CN-induced reductive elimination. The broad utility of this transformation has been demonstrated through the direct incorporation of trifluoromethyl into aromatic and heteroaromatic systems, including biorelevant compounds.
- Hu, Wei-Qiang,Pan, Shen,Qing, Feng-Ling,Vicic, David A.,Xu, Xiu-Hua
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supporting information
p. 16076 - 16082
(2020/07/04)
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- Mechanistic study of visible light-driven CdS or g-C3N4-catalyzed C–H direct trifluoromethylation of (hetero)arenes using CF3SO2Na as the trifluoromethyl source
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The mild and sustainable methods for C–H direct trifluoromethylation of (hetero)arenes without any base or strong oxidants are in extremely high demand. Here, we report that the photo-generated electron-hole pairs of classical semiconductors (CdS or g-C3N4) under visible light excitation are effective to drive C–H trifluoromethylation of (hetero)arenes with stable and inexpensive CF3SO2Na as the trifluoromethyl (TFM) source via radical pathway. Either CdS or g-C3N4 propagated reaction can efficiently transform CF3SO2Na to [rad]CF3 radical and further afford the desired benzotrifluoride derivatives in moderate to good yields. After visible light initiated photocatalytic process, the key elements (such as F, S and C) derived from the starting TFM source of CF3SO2Na exhibited differential chemical forms as compared to those in other oxidative reactions. The photogenerated electron was trapped by chemisorbed O2 on photocatalysts to form superoxide radical anion (O2[rad]?) which will further attack [rad]CF3 radical with the generation of inorganic product F? and CO2. This resulted in a low utilization efficiency of [rad]CF3 (3SO2Na served as the starting materials in inert atmosphere, the photoexcited electrons can be directed to reduce the nitro group to amino group rather than being trapped by O2. Meanwhile, the photogenerated holes oxidize SO2CF3? into [rad]CF3. Both the photogenerated electrons and holes were engaged in reductive and oxidative paths, respectively. The desired product, trifluoromethylated aniline, was obtained successfully via one-pot free-radical synthesis.
- Fu, Xianzhi,Gao, Li,Liu, Ming,Lu, Chenggang,Ma, Xiongfeng,Qin, Nanfang,Qiu, Wenzhao,Sa, Rongjian,Wang, Lele,Wei, Yingcong,Xu, Chunwang,Yuan, Rusheng,Zha, Wenying
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p. 533 - 543
(2020/07/23)
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- Oxidatively Induced Aryl-CF3 Coupling at Diphosphine Nickel Complexes
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This communication describes the synthesis of a series of diphosphine NiII(Ph)(CF3) complexes and studies of their reactivity toward oxidatively induced Ph-CF3 bond-forming reductive elimination. Treatment of these complexes with the one-electron outer-sphere oxidant ferrocenium hexafluorophosphate (FcPF6) affords benzotrifluoride, but the yield varies dramatically as a function of diphosphine ligand. Diphosphines with bite angles of less than 92° afforded 3. In contrast, those with bite angles between 95 and 102° formed PhCF3 in yields ranging from 62 to 77%.
- Bour, James R.,Roy, Pronay,Canty, Allan J.,Kampf, Jeff W.,Sanford, Melanie S.
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supporting information
p. 3 - 7
(2020/01/03)
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- Delayed fluorescence from a zirconium(iv) photosensitizer with ligand-to-metal charge-transfer excited states
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Advances in chemical control of the photophysical properties of transition-metal complexes are revolutionizing a wide range of technologies, particularly photocatalysis and light-emitting diodes, but they rely heavily on molecules containing precious metals such as ruthenium and iridium. Although the application of earth-abundant ‘early’ transition metals in photosensitizers is clearly advantageous, a detailed understanding of excited states with ligand-to-metal charge transfer (LMCT) character is paramount to account for their distinct electron configurations. Here we report an air- and moisture-stable, visible light-absorbing Zr(iv) photosensitizer, Zr(MesPDPPh)2, where [MesPDPPh]2? is the doubly deprotonated form of [2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine]. This molecule has an exceptionally long-lived triplet LMCT excited state (τ = 350 μs), featuring highly efficient photoluminescence emission (Ф = 0.45) due to thermally activated delayed fluorescence emanating from the higher-lying singlet configuration with significant LMCT contributions. Zr(MesPDPPh)2 engages in numerous photoredox catalytic processes and triplet energy transfer. Our investigation provides a blueprint for future photosensitizer development featuring early transition metals and excited states with significant LMCT contributions. [Figure not available: see fulltext.]
- Castellano, Felix N.,Favale, Joseph M.,Leary, Dylan C.,Lee, Tia S.,Milsmann, Carsten,Petersen, Jeffrey L.,Scholes, Gregory D.,Zhang, Yu
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- Palladium–Borane Cooperation: Evidence for an Anionic Pathway and Its Application to Catalytic Hydro-/Deutero-dechlorination
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Metal–Lewis acid cooperation provides new opportunities in catalysis. In this work, we report a new type of palladium–borane cooperation involving anionic Pd0 species. The air-stable DPB palladium complex 1 (DPB=diphosphine-borane) was prepared and reacted with KH to give the Pd0 borohydride 2, the first monomeric anionic Pd0 species to be structurally characterized. The boron moiety acts as an acceptor towards Pd in 1 via Pd→B interaction, but as a donor in 2 thanks to B-H-Pd bridging. This enables the activation of C?Cl bonds and the system is amenable to catalysis, as demonstrated by the hydro-/deutero-dehalogenation of a variety of (hetero)aryl chlorides (20 examples, average yield 85 %).
- Kameo, Hajime,Yamamoto, Jun,Asada, Ayaka,Nakazawa, Hiroshi,Matsuzaka, Hiroyuki,Bourissou, Didier
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supporting information
p. 18783 - 18787
(2019/11/19)
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- Hydrogen bonding promoted simple and clean photo-induced reduction of C-X bond with isopropanol
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We herein report a simple and clean photo-induced metal-free reduction of C-X bond under an atmosphere of air at room temperature. Isopropanol is used as both the reducing reagent and solvent. Various functional groups (acids, esters, alcohols, anilines, phenols, indoles, pyridines, cyano and trifluoromethyl groups) and other heterocyclic compounds are tolerated. Different organic halides (including C-I, C-Br and C-Cl bonds) can be dehalogenated with moderate to excellent yields. Polyhalides are also reduced chemoselectively and efficiently. DFT calculation suggests a six-membered ring transition state via C-X H-O hydrogen bonding to decrease the activation energy.
- Cao, Dawei,Yan, Chaoxian,Zhou, Panpan,Zeng, Huiying,Li, Chao-Jun
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supporting information
p. 767 - 770
(2019/01/21)
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- Cathodic C-H Trifluoromethylation of Arenes and Heteroarenes Enabled by an in Situ-Generated Triflyltriethylammonium Complex
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While several trifluoromethylation reactions involving the electrochemical generation of CF3 radicals via anodic oxidation have been reported, the alternative cathodic, reductive radical generation has remained elusive. Herein, the first cathodic trifluoromethylation of arenes and heteroarenes is reported. The method is based on the electrochemical reduction of an unstable triflyltriethylammonium complex generated in situ from inexpensive triflyl chloride and triethylamine, which produces CF3 radicals that are trapped by the arenes on the cathode surface.
- Cantillo, David,Jud, Wolfgang,Kappe, C. Oliver,Maljuric, Snjezana
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supporting information
(2019/10/08)
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- Implementing Hydrogen Atom Transfer (HAT) Catalysis for Rapid and Selective Reductive Photoredox Transformations in Continuous Flow
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The reductive transformation of aryl halides and carbonyl compounds is a key step in many photoredox transformations. By combining a highly reducing organic photocatalyst with a thiol hydrogen atom transfer (HAT) catalyst, we showcase rapid and highly selective reactions of these synthetically important starting materials in continuous flow. The fast reduction of aryl iodides, bromides and chlorides has been demonstrated with residence times in some cases below one minute. Selectivity between mono- and di-dehalogenation could also be achieved in some cases. Aryl ketones, aldehydes and imines were shown to undergo facile pinacol couplings, and the coupling of an aryl chloride with a styrene was also successful.
- Steiner, Alexander,Williams, Jason D.,Rincón, Juan A,de Frutos, Oscar,Mateos, Carlos,Kappe, C. Oliver
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supporting information
p. 5807 - 5811
(2019/08/01)
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- Catalytic Transfer Hydrodebenzylation with Low Palladium Loading
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A highly-efficient catalytic system for hydrodebenzylation reaction is described. The cleavage of O-benzyl and N-benzyl protecting groups was performed using an uncommonly low palladium loading (0.02–0.3 mol%; TON up to 5000) in a relatively short reaction time. The approach was used for a variety of substrates including pharmaceutically important precursors, and gram-scale deprotection reaction was shown. Transfer conditions together with easy-to-make Pd/C catalyst are the key features of this debenzylation scheme. (Figure presented.).
- Yakukhnov, Sergey A.,Ananikov, Valentine P.
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supporting information
p. 4781 - 4789
(2019/09/16)
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- Involving Single-Atom Silver(0) in Selective Dehalogenation by AgF under Visible-Light Irradiation
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The dehalogenation-arylation and the hydrodehalogenation of various types of organic halides are selectively realized using AgF and visible light without any organic additives under mild conditions. Single-atom silver(0) (denoted as SAAg) serves as the catalytically active center, and the TOF of SAAg reaches 6000 h-1. This elusive activity of Ag is beyond that expected from its ionic, nano, or bulk forms.
- Wu, Wenli,Cui, Enxin,Zhang, Yun,Zhang, Chen,Zhu, Feng,Tung, Chen-Ho,Wang, Yifeng
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p. 6335 - 6341
(2019/07/04)
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- Competing dehalogenation versus borylation of aryl iodides and bromides under transition-metal-free basic conditions
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In this work, selectivity-controllable base-promoted transition-metal-free borylation and dehalogenation of aryl halides are described. Under the conditions of borylation, the dehalogenation which emerges as a competitive side reaction has been well-controlled by carefully controlling the borylation conditions. On the other hand, the dehalogenation using benzaldehyde as a hydrogen source has also been accomplished. The applications of direct radical borylation and dehalogenation of aryl halides demonstrate their synthetic practicability in pharmaceutical-oriented organic synthesis. Based on the experimental evidences, the tBuOK/1,10-Phen-triggered radical nature of both competitive reactions has been revealed.
- Niu, Yi-Jie,Sui, Guo-Hui,Zheng, Hong-Xing,Shan, Xiang-Huan,Tie, Lin,Fu, Jia-Le,Qu, Jian-Ping,Kang, Yan-Biao
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p. 10805 - 10813
(2019/09/30)
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- Au@ZnO Core-Shell: Scalable Photocatalytic Trifluoromethylation Using CF3CO2Na as an Inexpensive Reagent under Visible Light Irradiation
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Trifluoromethylation is of significant importance for the synthesis of many small molecules vital for medicinal and agrochemical research. The importance of the CF3 group as well as the related synthetic challenges is so evident that many reagents have been reported for the synthesis of trifluoromethylated compounds, but these typical reagents are expensive and the methods for preparing them are difficult. Here, we report a new scalable and operationally simple trifluoromethylation reaction using sodium trifluoroacetate as a reagent and Au-modified ZnO as a photocatalyst under visible light irradiation. The reaction proceeds via trifluoromethylation of a broad range of aryl halides, arylboronic acids, and arene and heteroarene substrates. Some pharmaceutical and agrochemical compounds have been trifluoromethylated directly to demonstrate the applicability of the method.
- Bazyar, Zahra,Hosseini-Sarvari, Mona
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supporting information
p. 2345 - 2353
(2019/10/16)
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- Visible-light photocatalytic trifluoromethylation of arenes using graphene oxide as a metal-free photocatalyst
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Photocatalytic trifluoromethylation has been considered as an efficient method to introduce trifluoromethyl groups into organic substances. However, the relatively high cost and toxic feature of the metal-based photocatalysts have become major obstacles for their further applications in this area. In this work, graphene oxide sheets have been successfully utilized as a kind of metal-free photocatalyst for the trifluoromethylation of arenes, using inexpensive CF3SO2Na as the CF3 radical source. It is shown that graphene oxide sheets exhibit suitable bandgaps under visible light irradiation to photocatalyse the oxide CF3SO2Na to form the electrophilic radical CF3, which efficiently induces the trifluoromethylation of typical benzene molecules and some of their derivatives.
- Tong, Ying,Pan, Hao,Huang, Weichao,Qiu, Wenzhao,Ding, Zhengxin,Xu, Chao,Yuan, Rusheng
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p. 8741 - 8745
(2019/06/14)
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- Ligand-free trifluoromethylation of iodoarenes by use of 2-Aryl-2-trifluoromethylbenzimidazoline as new trifluoromethylating reagent
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N-Methyl 2-aryl-2-trifluoromethylbenzimidazolines were synthesized and utilized in the trifluoromethylation reaction of iodoarenes in the presence of copper(I) salt and base. Iodoarenes bearing electron-donating and electron-withdrawing groups were tolerant to this reaction in the absence of a ligand and gave trifluorotoluene derivatives in good to high yields.
- Miyagawa, Masamichi,Ishikawa, Taisuke,Shinkai, Kota,Akiyama, Takahiko
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supporting information
p. 29 - 31
(2019/01/04)
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- Chemoselective Hydrodeoxygenation of Carboxylic Acids to Hydrocarbons over Nitrogen-Doped Carbon-Alumina Hybrid Supported Iron Catalysts
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The establishment of catalyst systems for the chemoselective hydrodeoxygenation (HDO) of carboxylic acids to hydrocarbons, such as the HDO of long-chain fatty acids to alkanes, is important for biomass to biofuel conversion. As the most abundant and probably the cheapest transition metal on the earth, iron is a promising non-noble-metal alternative to precious metals for large-scale conversion of biomass. However, it usually suffers from unsatisfactory activity. In this work, a nitrogen-doped carbon-alumina hybrid supported iron (Fe-N-C@Al2O3) catalyst is established for chemoselective HDO of carboxylic acids to hydrocarbons. By using stearic acid HDO as the model reaction, n-octadecane and n-heptadecane are produced with yields of 91.9% and 6.0%, respectively. Triglycerides can also be converted into liquid alkanes with a total molar yield of >92%. In addition, the iron catalyst can chemoselectively catalyze the HDO of the carboxylic acid group in the presence of other functional groups such as an aromatic ring. This chemoselectivity has rarely been seen before because the aromatic ring is usually more easily hydrogenated in comparison to HDO of the carboxylic acid group. The characterization results showed that both the formation of a nitrogen-doped carbon-alumina hybrid and the iron loading are important for the Lewis basicity of these catalysts, in order to adsorb the acid substrates. The addition of melamine as the nitrogen precursor during pyrolysis eliminates undesired reactions between the iron precursor and alumina support to form an inactive hercynite phase, leading to the formation of an Fe3C active phase for the hydrogenation of -COOH to -CH2OH and the hybrid of N-C and alumina for the HDO of -CH2OH to -CH3.
- Li, Jiang,Zhang, Junjie,Wang, Shuai,Xu, Guangyue,Wang, Hao,Vlachos, Dionisios G.
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p. 1564 - 1577
(2019/02/03)
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- Mechanism of Photoredox-Initiated C-C and C-N Bond Formation by Arylation of IPrAu(I)-CF3 and IPrAu(I)-Succinimide
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Herein, we report on the photoredox-initiated gold-mediated C(sp2)-CF3 and C(sp2)-N coupling reactions. By adopting gold as a platform for probing metallaphotoredox catalysis, we demonstrate that cationic gold(III) complexes are the key intermediates of the C-C and C-N coupling reactions. The high-valent gold(III) intermediates are accessed by virtue of photoredox catalysis through a radical chain process. In addition, the bond-forming step of the coupling reactions is the reductive elimination from cationic gold(III) intermediates, which is supported by isolation and crystallographic characterization of key Au(III) intermediates.
- Kim, Suhong,Toste, F. Dean
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supporting information
p. 4308 - 4315
(2019/01/25)
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- Catalytic reduction of aryl trialkylammonium salts to aryl silanes and arenes
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A new approach for the reduction of aryl ammonium salts to arenes or aryl silanes using nickel catalysis is reported. This method displays excellent ligand-controlled selectivity based on the N-heterocyclic carbene (NHC) ligand employed. Utilizing a large NHC in non-polar solvents generates aryl silanes, while small NHCs in polar solvents promote reduction to arenes. Several classes of aryl silanes can be accessed from simple aniline building blocks, including those useful for cross-couplings, oxidations, and halogenations. The reaction conditions are mild, functional group tolerant, and provide efficient access to a variety of benzene derivatives.
- Rand, Alexander W.,Montgomery, John
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p. 5338 - 5344
(2019/05/29)
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- M?C Bond Homolysis in Coinage-Metal [M(CF3)4]? Derivatives
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A comparative study of the homoleptic [M(CF3)4]? complexes of all three coinage metals (M=Cu, Ag, Au) reveals that homolytic M?C bond cleavage is favoured in every case upon excitation in the gas phase (CID-MS2). Homolysis also occurs in solution by photochemical excitation. Transfer of the photogenerated CF3. radicals to both aryl and alkyl carbon atoms was also confirmed. The observed behaviour was rationalized by considering the electronic structure of the involved species, which all show ligand-field inversion. Moreover, the homolytic pathway constitutes experimental evidence for the marked covalent character of the M?C bond. The relative stability of these M?C bonds was evaluated by energy-resolved mass spectrometry (ERMS) and follows the order CuAg?Au. The qualitatively similar and rather uniform behaviour experimentally observed for all three coinage metals gives no ground to suggest variation in the metal oxidation state along the group.
- Baya, Miguel,Joven-Sancho, Daniel,Alonso, Pablo J.,Orduna, Jesús,Menjón, Babil
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supporting information
p. 9954 - 9958
(2019/06/24)
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- Semi-heterogeneous Dual Nickel/Photocatalysis using Carbon Nitrides: Esterification of Carboxylic Acids with Aryl Halides
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Cross-coupling reactions mediated by dual nickel/photocatalysis are synthetically attractive but rely mainly on expensive, non-recyclable noble-metal complexes as photocatalysts. Heterogeneous semiconductors, which are commonly used for artificial photosynthesis and wastewater treatment, are a sustainable alternative. Graphitic carbon nitrides, a class of metal-free polymers that can be easily prepared from bulk chemicals, are heterogeneous semiconductors with high potential for photocatalytic organic transformations. Here, we demonstrate that graphitic carbon nitrides in combination with nickel catalysis can induce selective C?O cross-couplings of carboxylic acids with aryl halides, yielding the respective aryl esters in excellent yield and selectivity. The heterogeneous organic photocatalyst exhibits a broad substrate scope, is able to harvest green light, and can be recycled multiple times. In situ FTIR was used to track the reaction progress to study this transformation at different irradiation wavelengths and reaction scales.
- Pieber, Bartholom?us,Malik, Jamal A.,Cavedon, Cristian,Gisbertz, Sebastian,Savateev, Aleksandr,Cruz, Daniel,Heil, Tobias,Zhang, Guigang,Seeberger, Peter H.
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supporting information
p. 9575 - 9580
(2019/06/25)
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- Arene-Free Ruthenium(II/IV)-Catalyzed Bifurcated Arylation for Oxidative C?H/C?H Functionalizations
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Experimental and computational studies provide detailed insight into the selectivity- and reactivity-controlling factors in bifurcated ruthenium-catalyzed direct C?H arylations and dehydrogenative C?H/C?H functionalizations. Thorough investigations revealed the importance of arene-ligand-free complexes for the formation of biscyclometalated intermediates within a ruthenium(II/IV/II) mechanistic manifold.
- Rogge, Torben,Ackermann, Lutz
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supporting information
p. 15640 - 15645
(2019/10/28)
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- Metal- and oxidant-free photoinduced aromatic trifluoromethylation performed in aerated gel media: Determining the effects on yield and selectivity
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In this work we have investigated the potential benefits of using supramolecular gel networks as reaction media to carry out air-sensitive metal-free light-induced trifluoromethylation of six-membered (hetero)arenes under aerobic conditions. This reaction was performed at room temperature (RT) using sodium triflinate (CF3SO2Na, Langlois' reagent) as a source of radicals and diacetyl as electron donor. The effects of confinement in gel media, concentration of reactants, and type of light source on yield and product distribution were evaluated and compared to the results obtained in homogeneous solution. Four different low molecular weight (LMW) gelators were employed in this study. The results confirmed the blocking effect of the gel medium against reaction quenching by external oxygen, as well as a certain control on the kinetics and selectivity.
- Abramov, Alex,Vernickel, Hendrik,Saldías, César,Díaz, David Díaz
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- A Predictive Model for the Decarboxylation of Silver Benzoate Complexes Relevant to Decarboxylative Coupling Reactions
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Decarboxylative coupling reactions offer an attractive route to generate functionalized arenes from simple and readily available carboxylic acid coupling partners, yet they are underutilized due to limitations in the scope of carboxylic acid coupling partner. Here we report that the field effect parameter (F) has a substantial influence on the rate of decarboxylation of well-defined silver benzoate complexes. This finding provides the opportunity to surpass current substrate limitations associated with decarboxylation and to enable widespread utilization of decarboxylative coupling reactions.
- Crovak, Robert A.,Hoover, Jessica M.
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p. 2434 - 2437
(2018/02/28)
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- Synthesis of NHC Pincer Hydrido Nickel Complexes and Their Catalytic Applications in Hydrodehalogenation
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The C(carbene)N(amino)N(amine)-pincer nickel(II) bromides 1a-c were hydrogenated to the corresponding nickel(II) hydrides 2a-c by (EtO)3SiH/NaOtBu or NaBH4. These nickel(II) hydrides 2a-c were characterized by NMR and IR spectroscopy as well as X-ray diffraction. The catalytic performance of complex 2b for hydrodehalogenation reactions was explored. With a combination of 3 mol % catalyst loading, (EtO)3SiH/NaOtBu/toluene/80 °C and different reaction times, organic halides were successfully reduced to the related alkanes. A catalytic radical mechanism is proposed and partially verified by experiments.
- Wang, Zijing,Li, Xiaoyan,Sun, Hongjian,Fuhr, Olaf,Fenske, Dieter
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p. 539 - 544
(2018/03/08)
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- Palladium-mediated radical homocoupling reactions: A surface catalytic insight
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In this contribution, we report a palladium nanoparticle-promoted reductive homocoupling of haloarenes that proceeds efficiently to produce corresponding bis-aryls in moderate to excellent yields using relatively low catalyst loading (1 mol%), and exhibits broad functional group tolerance. This work sheds light on how the surface state of Pd(0) nanoparticles plays a crucial role in the reactivity of catalytic systems. Notably, the appropriate choice of palladium salts for the preparation of the preformed nanocatalysts was a key parameter having a major impact on the catalytic activity; thus, the effect of halide anions on the reactivity of the as-prepared palladium nanoparticles could be assessed, with iodide anions being capable of inhibiting the corresponding homocoupling reaction. The homocoupling reaction mechanism has been further studied by means of radical trap and electron paramagnetic resonance (EPR) experiments, revealing that the reaction proceeds via radical intermediates. Taking into account these data, a plausible reaction mechanism based on single-electron transfer processes on the palladium nanoparticle surface is discussed.
- Favier, Isabelle,Toro, Marie-Lou,Lecante, Pierre,Pla, Daniel,Gómez, Montserrat
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p. 4766 - 4773
(2018/09/29)
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