- Trialkylammonium salt degradation: Implications for methylation and cross-coupling
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Trialkylammonium (most notably N,N,N-trimethylanilinium) salts are known to display dual reactivity through both the aryl group and the N-methyl groups. These salts have thus been widely applied in cross-coupling, aryl etherification, fluorine radiolabelling, phase-transfer catalysis, supramolecular recognition, polymer design, and (more recently) methylation. However, their application as electrophilic methylating reagents remains somewhat underexplored, and an understanding of their arylation versus methylation reactivities is lacking. This study presents a mechanistic degradation analysis of N,N,N-trimethylanilinium salts and highlights the implications for synthetic applications of this important class of salts. Kinetic degradation studies, in both solid and solution phases, have delivered insights into the physical and chemical parameters affecting anilinium salt stability. 1H NMR kinetic analysis of salt degradation has evidenced thermal degradation to methyl iodide and the parent aniline, consistent with a closed-shell SN2-centred degradative pathway, and methyl iodide being the key reactive species in applied methylation procedures. Furthermore, the effect of halide and non-nucleophilic counterions on salt degradation has been investigated, along with deuterium isotope and solvent effects. New mechanistic insights have enabled the investigation of the use of trimethylanilinium salts in O-methylation and in improved cross-coupling strategies. Finally, detailed computational studies have helped highlight limitations in the current state-of-the-art of solvation modelling of reaction in which the bulk medium undergoes experimentally observable changes over the reaction timecourse. This journal is
- Assante, Michele,Baillie, Sharon E.,Juba, Vanessa,Leach, Andrew G.,McKinney, David,Reid, Marc,Washington, Jack B.,Yan, Chunhui
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p. 6949 - 6963
(2021/06/02)
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- Copper-Catalyzed Methoxylation of Aryl Bromides with 9-BBN-OMe
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A Cu-catalyzed cross-coupling reaction between aryl bromides and 9-BBN-OMe to provide aryl methyl ethers under mild conditions is reported. The oxalamide ligand BHMPO plays a key role in the transformation. Various functional groups on bromobenzenes are well tolerated, providing the desired anisole products in moderate to high yields.
- Li, Chen,Song, Zhi-Qiang,Wang, Dong-Hui,Wang, Jing-Ru
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supporting information
p. 8450 - 8454
(2021/11/17)
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- Depolymerization of Hydroxylated Polymers via Light-Driven C-C Bond Cleavage
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The accumulation of persistent plastic waste in the environment is widely recognized as an ecological crisis. New chemical technologies are necessary both to recycle existing plastic waste streams into high-value chemical feedstocks and to develop next-generation materials that are degradable by design. Here, we report a catalytic methodology for the depolymerization of a commercial phenoxy resin and high molecular weight hydroxylated polyolefin derivatives upon visible light irradiation near ambient temperature. Proton-coupled electron transfer (PCET) activation of hydroxyl groups periodically spaced along the polymer backbone furnishes reactive alkoxy radicals that promote chain fragmentation through C-C bond β-scission. The depolymerization produces well-defined and isolable product mixtures that are readily diversified to polycondensation monomers. In addition to controlling depolymerization, the hydroxyl group modulates the thermomechanical properties of these polyolefin derivatives, yielding materials with diverse properties. These results demonstrate a new approach to polymer recycling based on light-driven C-C bond cleavage that has the potential to establish new links within a circular polymer economy and influence the development of new degradable-by-design polyolefin materials.
- Nguyen, Suong T.,McLoughlin, Elizabeth A.,Cox, James H.,Fors, Brett P.,Knowles, Robert R.
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p. 12268 - 12277
(2021/08/23)
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- A general palladium-catalyzed cross-coupling of aryl fluorides and organotitanium (IV) reagents
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Pd(OAc)2/1-[2-(di-tert-butylphosphanyl)phenyl]-4-methoxy-piperidine was demonstrated to effectively catalyze cross-coupling of aryl fluoride and aryl(alkyl) titanium reagent. Both electron-deficient and electron-rich aryl fluoride can react effectively with nucleophile and provide extensive functional groups tolerance. 2-Arylated product was realized by selective activation of the C–F bond. Graphic abstract: [Figure not available: see fulltext.].
- He, Xiao-Yun
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p. 823 - 832
(2021/07/19)
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- Site-Specific Alkene Hydromethylation via Protonolysis of Titanacyclobutanes
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Methyl groups are ubiquitous in biologically active molecules. Thus, new tactics to introduce this alkyl fragment into polyfunctional structures are of significant interest. With this goal in mind, a direct method for the Markovnikov hydromethylation of alkenes is reported. This method exploits the degenerate metathesis reaction between the titanium methylidene unveiled from Cp2Ti(μ-Cl)(μ-CH2)AlMe2 (Tebbe's reagent) and unactivated alkenes. Protonolysis of the resulting titanacyclobutanes in situ effects hydromethylation in a chemo-, regio-, and site-selective manner. The broad utility of this method is demonstrated across a series of mono- and di-substituted alkenes containing pendant alcohols, ethers, amides, carbamates, and basic amines.
- Bartfield, Noah M.,Frederich, James H.,Law, James A.
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supporting information
p. 14360 - 14364
(2021/05/27)
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- A highly stable all-in-one photocatalyst for aryl etherification: The NiIIembedded covalent organic framework
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The efficient conversion of aryl bromides to the corresponding aryl alkyl ethers by dual nickel/photocatalysis has seen great progress, but difficulties of recycling the photosensitizer or nickel complexes cause problems of sustainability. Here, we report the design of a novel, highly stable vinyl bridge 2D covalent organic framework (COF) containing Ni, which combines the role of photosensitizer and reactive site. The as-prepared sp2c-COFdpy-Ni acts as an efficient heterogeneous photocatalyst for C-O cross coupling. The sp2c-COFdpy-Ni can be completely recovered and used repeatedly without loss of activity, overcoming the limitations of the prior methods. Preliminary studies reveal that strong interlayer electron transfer may facilitate the generation of the proposed intermediate sp2c-COFdpy-NiI in a bimolecular and self-sustained manner. This all-in-one heterogeneous photocatalyst exhibits good compatibility of substrates and tolerance of functional groups. The successful attempt to expand the 2D COFs with this new catalyst into photocatalytic organic transformation opens an avenue for photoredox/transition metal mediated coupling reactions.
- Chen, Hao,Dong, Wenbo,Hu, Jianxiang,Rao, Li,Wang, Pei,Wang, Shengyao,Xiang, Yonggang,Yang, Yi
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p. 5797 - 5805
(2021/08/23)
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- Visible-Light Promoted C–O Bond Formation with an Integrated Carbon Nitride–Nickel Heterogeneous Photocatalyst
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Ni-deposited mesoporous graphitic carbon nitride (Ni-mpg-CNx) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross-coupling reactions. The dual catalytic Ni-mpg-CNx is demonstrated for C–O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good-to-excellent yields (60–92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron-withdrawing, -donating and neutral groups. The heterogeneous Ni-mpg-CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.
- Vijeta, Arjun,Casadevall, Carla,Roy, Souvik,Reisner, Erwin
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supporting information
p. 8494 - 8499
(2021/03/08)
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- Catalytic SNAr Hydroxylation and Alkoxylation of Aryl Fluorides
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Nucleophilic aromatic substitution (SNAr) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron-deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SNAr reactions. The method is applicable to a broad array of electron-rich and neutral aryl fluorides, which are inert under classical SNAr conditions. Although the mechanism of SNAr reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise-like energy profile. Notably, we isolated a rhodium η5-cyclohexadienyl complex intermediate with an sp3-hybridized carbon bearing both a nucleophile and a leaving group.
- Kang, Qi-Kai,Li, Ke,Li, Yuntong,Lin, Yunzhi,Shi, Hang,Xu, Lun
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supporting information
p. 20391 - 20399
(2021/08/13)
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- Efficient Pd-Catalyzed Direct Coupling of Aryl Chlorides with Alkyllithium Reagents
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Organolithium compounds are amongst the most important organometallic reagents and frequently used in difficult metallation reactions. However, their direct use in the formation of C?C bonds is less established. Although remarkable advances in the coupling of aryllithium compounds have been achieved, Csp2?Csp3 coupling reactions are very limited. Herein, we report the first general protocol for the coupling or aryl chlorides with alkyllithium reagents. Palladium catalysts based on ylide-substituted phosphines (YPhos) were found to be excellently suited for this transformation giving high selectivities at room temperature with a variety of aryl chlorides without the need for an additional transmetallation reagent. This is demonstrated in gram-scale synthesis including building blocks for materials chemistry and pharmaceutical industry. Furthermore, the direct coupling of aryllithiums as well as Grignard reagents with aryl chlorides was also easily accomplished at room temperature.
- Dilchert, Katharina,Gessner, Viktoria H.,Gro?johann, Angela,Rodstein, Ilja,Scherpf, Thorsten,Steinert, Henning,Tappen, Jens
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supporting information
p. 20596 - 20603
(2020/09/09)
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- Generation of Alkyl Radical through Direct Excitation of Boracene-Based Alkylborate
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The generation of tertiary, secondary, and primary alkyl radicals has been achieved by the direct visible-light excitation of a boracene-based alkylborate. This system is based on the photophysical properties of the organoboron molecule. The protocol is applicable to decyanoalkylation, Giese addition, and nickel-catalyzed carbon-carbon bond formations such as alkyl-aryl cross-coupling or vicinal alkylarylation of alkenes, enabling the introduction of various C(sp3) fragments to organic molecules.
- Hashizume, Daisuke,Hosoya, Takamitsu,Nakamura, Kei,Ohmiya, Hirohisa,Sato, Yukiya,Sumida, Yuto
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supporting information
p. 9938 - 9943
(2020/06/27)
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- Rational Design of an Iron-Based Catalyst for Suzuki–Miyaura Cross-Couplings Involving Heteroaromatic Boronic Esters and Tertiary Alkyl Electrophiles
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Suzuki–Miyaura cross-coupling reactions between a variety of alkyl halides and unactivated aryl boronic esters using a rationally designed iron-based catalyst supported by β-diketiminate ligands are described. High catalyst activity resulted in a broad substrate scope that included tertiary alkyl halides and heteroaromatic boronic esters. Mechanistic experiments revealed that the iron-based catalyst benefited from the propensity for β-diketiminate ligands to support low-coordinate and highly reducing iron amide intermediates, which are very efficient for effecting the transmetalation step required for the Suzuki–Miyaura cross-coupling reaction.
- Byers, Jeffery A.,Crockett, Michael P.,Li, Bo,Wong, Alexander S.
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supporting information
p. 5392 - 5397
(2020/03/04)
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- Electrophotocatalytic SNAr Reactions of Unactivated Aryl Fluorides at Ambient Temperature and Without Base
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The electrophotocatalytic SNAr reaction of unactivated aryl fluorides at ambient temperature without strong base is demonstrated.
- Huang, He,Lambert, Tristan H.
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supporting information
p. 658 - 662
(2019/11/28)
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- 1,4-Dehydrogenation with a Two-Coordinate Cyclic (Alkyl)(amino)silylene
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Cyclic (alkyl)(amino)silylene (CAASi) 1 has been found to successfully dehydrogenate 1,4-dihydroaromatic compounds containing various substituents to afford the corresponding aromatic compounds. The observed high substrate generality proves 1 to be a potential 1,4-dehydrogenation reagent for organic compounds. For the reaction with 9,10-dimethyl-9,10-dihydroanthracene, silylene 1 activated not only benzylic C?H bonds but also aromatic C?H bonds to yield a silaacenaphthene derivative, which is an unprecedented reaction of silylenes. The results of the experimental and computational study of the reaction of CAASi 1 with 9,10-dihydroanthracene and 1,4-cyclohexadiene are consistent with the notion that 1,4-dehydrogenation with CAASi 1 proceeds mainly through a stepwise hydrogen-abstraction mechanism.
- Koike, Taichi,Kosai, Tomoyuki,Iwamoto, Takeaki
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supporting information
p. 9295 - 9302
(2019/07/04)
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- Method for methylation reaction
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The invention relates to a method for a methylation reaction. The method is characterized in that a reaction substrate is reacted in an organic solvent in the presence of an alkali with methyl trifluoroacetate as a methylation reagent to obtain a corresponding methylated product. The method is a new methylation method, and has the advantages of cheapness, easiness in operation, mild reaction conditions, wide application range of the substrate, avoiding of dimethyl sulfate, iodomethane and other highly toxic methylation reagents, and obtaining of the methylated product with a high yield.
- -
-
Paragraph 0013
(2019/01/21)
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- An Additive-Free, Base-Catalyzed Protodesilylation of Organosilanes
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We report an additive-free, base-catalyzed C-, N-, O-, and S-Si bond cleavage of various organosilanes in mild conditions. The novel catalyst system exhibits high efficiency and good functional group compatibility, providing the corresponding products in good to excellent yields with low catalyst loadings. Overall, this transition-metal-free process may offer a convenient and general alternative to current employing excess bases, strong acids, or metal-catalyzed systems for the protodesilylation of organosilanes.
- Yao, Wubing,Li, Rongrong,Jiang, Huajiang,Han, Deman
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p. 2250 - 2255
(2018/02/23)
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- Active Molybdenum-Based Anode for Dehydrogenative Coupling Reactions
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A new and powerful active anode system that can be operated in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been discovered. In HFIP the molybdenum anode forms a compact, conductive, and electroactive layer of higher-valent molybdenum species. This system can replace powerful but stoichiometrically required MoV reagents for the dehydrogenative coupling of aryls. This electrolytic reaction is more sustainable and allows the conversion of a broad scope of activated arenes.
- Beil, Sebastian B.,Müller, Timo,Sillart, Sydney B.,Franzmann, Peter,Bomm, Alexander,Holtkamp, Michael,Karst, Uwe,Schade, Wolfgang,Waldvogel, Siegfried R.
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supporting information
p. 2450 - 2454
(2018/02/09)
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- Synthesis and catalytic activity of rhenium carbonyl complexes containing alkyl-substituted tetramethylcyclopentadienyl ligands
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A series of six alkyl-substituted tetramethylcyclopentadienyl mononuclear metal carbonyl complexes [(η5-C5Me4R)Re(CO)3] [R?=?allyl (1), i-Pr (2), n-butyl (3), t-butyl (4), benzyl (5), CH(CH2)4 (6)] have been synthesized by treating the corresponding ligands (C5Me4R) [R?=?allyl, i-Pr, n-butyl, t-butyl, benzyl, CH(CH2)4] with Re2(CO)10 in refluxing xylene. The six new complexes were characterized by elemental analysis, IR, 1H NMR and 13C NMR spectroscopy. The crystal structures of all six complexes were determined by X-ray crystal diffraction analysis, showing that they have similar molecular structures, being mononuclear carbonyl complexes. In each of these complexes, the Re atom is η5-coordinated to the cyclopentadienyl ring. Complexes 1–5 have significant catalytic activity in Friedel–Crafts reactions of aromatic compounds with alkylation reagents. Compared with traditional catalysts, these mononuclear rhenium carbonyl complexes have obvious advantages such as lower amounts of catalyst, mild reaction conditions and environmentally friendly chemistry.
- Li, Zhan-Wei,Ma, Zhi-Hong,Li, Su-Zhen,Han, Zhan-Gang,Zheng, Xue-Zhong,Lin, Jin
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p. 137 - 144
(2017/02/23)
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- Syntheses, structures and catalytic activity for Friedel-Crafts reactions of substituted indenyl rhenium carbonyl complexes
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The complexes [(η5-C9H6R)Re(CO)3] [R?=?nBu (8), tBu (9), CH(CH2)4 (10), Ph (11), Bz (12), 4-methoxyphenyl (13), 4-chlorophenyl (14)] were synthesized by refluxing substituted indenyl ligands [C9H7R] [R?=?nBu (1), tBu (2), CH(CH2)4 (3), Ph (4), Bz (5), 4-methoxyphenyl (6), 4-chlorophenyl (7)], and Re2(CO)10 in decalin. The molecular structures of 9, 10, 12, and 13 were determined by X-ray diffraction analysis. These four crystals have similar molecular structures of the mononuclear carbonyl complex. In each of these molecules, Re is η5-coordinated to the five-membered ring of the indenyl group. Complexes 8–14 have catalytic activity for Friedel-Crafts reactions of aromatic compounds with a variety of alkylation and acylation reagents. Compared with traditional catalysts, these mononuclear metal carbonyl complexes have obvious advantages such as high activities, mild reaction conditions, high selectivity, and environmentally friendly chemistry.
- Ma, Zhihong,Zhang, Xinli,Wang, Hong,Han, Zhangang,Zheng, Xuezhong,Lin, Jin
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p. 709 - 721
(2017/02/05)
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- Distyrylbenzene-based segmented conjugated polymers: Synthesis, thin film morphology and chemosensing of hydrophobic and hydrophilic nitroaromatics in aqueous media
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Two new segmented conjugated polymers bearing distyrylbenzene chromophoric units and their model compounds were synthesized. The tendency of the model compounds to form H- and J-type aggregates in the amorphous matrix was greatly diminished by the twisted polymeric architecture. Fluorescence anisotropy measurements indicated good exciton mobilities in condensed phase. Fluorescence quenching by nitroaromatic aqueous solutions was fast, complete, selective and reversible pointing to a rapid diffusion of analytes into the films. The quenching response to nitrophenols was superior to that against nitrotoluenes. The increase of the electron-donating capabilities by diethoxy-substitution was detrimental to the amorphous morphology and it did not increase sensitivity to NACs. Quenching efficiencies of polymers were not modified when MeOH was used instead of water. The solubility parameter distances, Ra. indicate that the sensing materials show higher responses when their affinity with the analytes is lower. This observation could help in the designing of fluorescent sensors.
- Almassio, Marcela F.,Romagnoli, Maria J.,Del Rosso, Pablo G.,Schvval, Ana Belén,Garay, Raúl O.
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p. 167 - 179
(2017/03/02)
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- Synthesis and catalytic activity of monobridged bis(cyclopentadienyl)rhenium carbonyl complexes
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Thermal treatment of three monobridged biscyclopentadienes (C5H5)R(C5H5) [R?=?C(CH3)2 (1), C(CH2)5 (2), Si(CH3)2 (3)] with Re2(CO)10 in refluxing mesitylene gave the corresponding complexes [(η5-C5H4)2R][Re(CO)3]2 [R?=?C(CH3)2 (4), C(C5H10) (5), Si(CH3)2 (6)], which were separated by chromatography, and characterized by elemental analysis, IR, and 1H NMR spectroscopy. The molecular structures of complexes 5 and 6 were characterized by X-ray crystal diffraction analysis and show that both are monobridged bis(cyclopentadienyl)rhenium carbonyl complexes in which the molecule consists of two [(η5-C5H4)Re(CO)3] moieties linked by a single bridge, in which each of the two Re(CO)3 units is coordinated to the cyclopentadienyl ring in an η5 mode. All three of these monobridged bis(cyclopentadienyl)rhenium carbonyl complexes have good catalytic activities in Friedel–Crafts alkylation reactions.
- Li, Zhen,Ma, Zhi-Hong,Wang, Hong,Han, Zhan-Gang,Zheng, Xue-Zhong,Lin, Jin
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p. 647 - 653
(2016/07/29)
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- Synthesis and catalytic reactivity of mononuclear substituted tetramethylcyclopentadienyl molybdenum carbonyl complexes
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The reactions of five dinuclear carbonyl complexes [(η 5-C5Me4R)Mo(CO)3]2 [R = allyl, n Bu, t Bu, Ph, Bz] with I2 in chloroform solution gave the corresponding mononuclear substituted tetramethylcyclopentadienyl molybdenum carbonyl complexes [(η 5-C5Me4R)MoI(CO)3] [R = allyl (1), n Bu (2), t Bu (3), Ph (4), Bz (5)]. The molecular structures of complexes 2, 3 and 5 were determined by X-ray diffraction analysis. The results show that the substituent in the ring can directly affect the Mo-I bond distances; the more sterically hindered the substituent, the longer the Mo-I bond. Friedel-Crafts reactions of aromatic compounds with a variety of alkylation reagents catalyzed by the complexes showed that all of these mononuclear molybdenum carbonyl complexes have catalytic activity in Friedel-Crafts alkylation reactions. Indeed, compared with traditional catalysts, these mononuclear metal carbonyl complexes have obvious advantages such as higher activities, mild reaction conditions, high selectivity, simple post-processing, and environmentally friendly chemistry.
- Ma, Zhi-Hong,Lv, Lin-Qian,Wang, Hong,Han, Zhan-Gang,Zheng, Xue-Zhong,Lin, Jin
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p. 225 - 233
(2016/02/20)
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- An N-heterocyclic carbene-based nickel catalyst for the Kumada–Tamao–Corriu coupling of aryl bromides and tertiary alkyl Grignard reagents
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In this study, nickel-catalyzed coupling reactions between arylhalides and tert-alkyl Grignard reagents were developed. Our original bicyclic NHC ligands reduced the formation of isomerized products, and we found that NMP as a co-solvent suppressed the reduction process. Under the optimal conditions we developed, the catalyst loading was lowered to 0.5?mol?%, and catalyst loading using ortho-substituted aryl bromides was also applicable at the level of 2.0?mol?%.
- Ando, Shin,Mawatari, Mai,Matsunaga, Hirofumi,Ishizuka, Tadao
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supporting information
p. 3287 - 3290
(2016/07/11)
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- Synthesis of mixed silylene-carbene chelate ligands from nheterocyclic silylcarbenes mediated by nickel
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The NiII -mediated tautomerization of the N-heterocyclic hydrosilylcarbene L2Si(H)(CH2)NHC1, where L2 = CH(C=CH2)(CMe)(NAr)2, Ar = 2,6-iPr2C6H3 ; NHC = 3,4,5-trimethylimidazol-2-yliden-6-yl, leads to the first N-heterocyclic silylene (NHSi)-carbene (NHC) chelate ligand in the dibromo nickel(II) complex [L1SiD(CH2)(NHC)NiBr2]2 (L1 = CH(MeC=NAr)2). Reduction of 2 with KC8 in the presence of PMe3 as an auxiliary ligand afforded, depending on the reaction time, the N-heterocyclic silyl-NHC bromo NiII complex [L2Si(CH2)NHCNiBr(PMe3)] 3 and the unique Ni0 complex [h2(Si-H){L2Si(H)(CH2)NHC}Ni(PMe3)2] ,inf>4 featuring an agostic Si-H→!Ni bonding interaction. When 1,2-bis(dimethylphosphino)ethane (DMPE) was employed as an exogenous ligand, the first NHSi-NHC chelate-ligand-stabilized Ni0 complex [L1SiD(CH2)NHCNi(dmpe)] 5 could be isolated. Moreover, the dicarbonyl Ni0 complex 6, [L1SiD-(CH2)NHCNi(CO)2], is easily accessible by the reduction of 2 with K(BHEt3) under a CO atmosphere. The complexes were spectroscopically and structurally characterized. Furthermore, complex 2 can serve as an efficient precatalyst for Kumada-Corriu-type cross-coupling reactions.
- Tan, Gengwen,Enthaler, Stephan,Inoue, Shigeyoshi,Blom, Burgert,Driess, Matthias
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supporting information
p. 2214 - 2218
(2015/02/19)
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- Synthesis of Ni(II) complexes with unsymmetric [O,N,O′]-pincer ligands and their use as precatalysts in carbon-carbon bond formations to access diarylmethanes
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1-Acetyl-[1a,3,5-CF3,1-C(=O)CH3] and 1-benzoyl-5-hydroxypyrazolines [1b, 3,5-CF3, 1-C(=O)C 6H5] have been synthesized and reacted with Ni(OAc) 2·4H2O in the presence of PPh3 to form square planar nickel complexes, which revealed a O,N,O′-coordination. An additional coordination site on the nickel center is occupied by one triphenylphosphane ligand. After having investigated the properties of the complexes, catalytic experiments have been carried out to synthesize diarylmethanes. Applying the complexes in the nickel-catalyzed carbon-carbon cross coupling of aryl halides with benzylzinc bromide excellent yields and selectivities of the corresponding diarylmethane have been obtained. Moreover, various experiments have been performed to shed light on the underlying reaction mechanism.
- Someya, Chika I.,Irran, Elisabeth,Enthaler, Stephan
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p. 136 - 144
(2014/07/08)
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- Metal-free arylations via photochemical activation of the Ar-OSO 2R bond in aryl nonaflates
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The photolysis of electron-rich aryl nonaflates (ArONfs) in protic media was investigated and heterolysis of the Ar-OS bond (from 3ArONf) took place. The reaction generated a triplet phenyl cation that added to π-bond nucleophiles. This metal-free arylation method was made further useful by adopting in situ preparation of ArONf from the corresponding phenol.
- Raviola, Carlotta,Canevari, Veronica,Protti, Stefano,Albini, Angelo,Fagnoni, Maurizio
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supporting information
p. 2704 - 2708
(2013/10/08)
-
- Amino acid intercalated layered double hydroxide catalyzed chemoselective methylation of phenols and thiophenols with dimethyl carbonate
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Sixteen different amino acids are intercalated into Mg-Al layered double hydroxides (LDHs) by the reconstruction method and are characterized by powder XRD and FT-IR. The intercalated amino acid-LDHs (AA-LDHs) are used as catalysts for chemoselective O-methylation of phenol and S-methylation of thiophenol with dimethyl carbonate (DMC) as a green methylating agent. The intercalation behavior of various amino acids is influenced by various structural features of amino acids, namely, carbon chain length, structure, and physicochemical properties. In particular, amino acids possessing a hydrophobic side-chain show higher catalytic activity. A suitable reaction mechanism is proposed. The catalyst can also be recycled.
- Subramanian, Thirumeni,Dhakshinamoorthy, Amarajothi,Pitchumani, Kasi
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p. 7167 - 7170
(2013/12/04)
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- Indium(III) triflate - A catalyst for greener aromatic alkylation reactions
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An environmentally friendly method for alkylating aromatic compounds with simple alcohols in the presence of a catalytic amount of indium(III) triflate is reported. Ionic liquids are used as solvents and energy-efficient heating is provided by microwave radiation. Good yields are obtained with benzyl, secondary, and tertiary alcohols. Simple primary alcohols are not effective alkylating agents under these conditions. With tertiary alcohols, activated aromatic compounds such as toluene and anisole must be used to obtain good yields. The catalyst, which is immobilized in a water-insoluble ionic liquid, can be easily recycled without significant loss of activity.
- Mack, Ryan,Askins, Grant,Lowry, Jacob,Hurley, Nathan,Reeves, Perry C.
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p. 1262 - 1265
(2014/01/06)
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- Mild and general palladium-catalyzed synthesis of methyl aryl ethers enabled by the use of a palladacycle precatalyst
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A general method for the Pd-catalyzed coupling of methanol with (hetero)aryl halides is described. The reactions proceed under mild conditions with a wide range of aryl and heteroaryl halides to give methyl aryl ethers in high yield.
- Cheung, Chi Wai,Buchwald, Stephen L.
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supporting information
p. 3998 - 4001
(2013/09/02)
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- Properties and reactivity of zinc-folded sheet mesoporous materials
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Mesoporous material incorporating zinc with different Si/Zn ratios = 95, 65, and 20 have been synthesized by intercalating kanemite using cetyltrimethylammonium bromide as the intercalating agent and zinc nitrate. The resulting materials were characterized by different techniques such as: inductively coupled plasma technique, XRD, Brunauer-Emmett-Teller, and a temperature-programmed-desorption of pyridine. The catalytic performance was studied in the vapor phase tert-butylation of anisole with tert-butanol at different temperatures under atmospheric pressure. The results indicate that Zn-FSM-16 (20) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA).
- Laribi,Chenouf,Bachari,Hamani
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p. 1771 - 1780
(2013/07/05)
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- Kinetic and spectroscopic studies of aerobic copper(II)-catalyzed methoxylation of arylboronic esters and insights into aryl transmetalation to copper(II)
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We previously reported a preliminary mechanistic study of aerobic Cu(OAc)2-catalyzed methoxylation of 4-tolylboronic ester (King et al. J. Am. Chem. Soc., 2009, 131, 5044-5045), which revealed that aryl transmetalation from the boronic ester to CuII is the turnover-limiting step. In the present study, more thorough kinetic and spectroscopic studies provide additional insights into the transmetalation pathway and identity of the CuII catalyst resting state(s). EPR spectroscopic studies show that at least two copper(II) species are present under catalytic conditions, and their relative populations vary as a function of reaction time and acidity of the arylboronic ester and are influenced by addition of acetic acid or acetate to the reaction mixture. Analysis of kinetic data and 11B NMR and EPR spectra under diverse reaction conditions suggests that aryl transmetalation occurs from a tetracoordinate, anionic boronate to a cationic CuII species, mediated by a methoxide bridge.
- King, Amanda E.,Ryland, Bradford L.,Brunold, Thomas C.,Stahl, Shannon S.
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p. 7948 - 7957
(2013/01/16)
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- Carbon-based leaving group in substitution reactions: Functionalization of sp3-hybridized quaternary and tertiary benzylic carbon centers
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Lewis acid promoted substitution reactions employing Meldrum's acid and 5-methyl Meldrum's acid as carbon-based leaving groups are described which transform unstrained quaternary and tertiary benzylic Csp 3-Csp3 bonds into Csp3-X bonds (X = C, H, N). Importantly, this reaction has a broad scope in terms of both suitable substrates and nucleophiles with good to excellent yields obtained (typically >90%).
- Mahoney, Stuart J.,Lou, Tiantong,Bondarenko, Ganna,Fillion, Eric
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p. 3474 - 3477
(2012/09/05)
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- Cross-coupling of non-activated chloroalkanes with aryl grignard reagents in the presence of iron/N-heterocyclic carbene catalysts
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An efficient and high-yielding cross-coupling reaction of various primary, secondary, and tertiary alkyl chlorides with aryl Grignard reagents was achieved by using catalytic amounts of N-heterocyclic carbene ligands and iron salts. This reaction is a simple and efficient arylation method having applicability to a wide range of industrially abundant chloroalkanes, including polychloroalkanes, which are challenging substrates under conventional cross-coupling conditions.
- Ghorai, Sujit K.,Jin, Masayoshi,Hatakeyama, Takuji,Nakamura, Masaharu
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supporting information; experimental part
p. 1066 - 1069
(2012/04/10)
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- Microwave-assisted methylation of phenols with DMF-DMA
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We evaluated the potential of N,N-dimethylformamide dimethylacetal (DMF-DMA) as a methylating agent for a library of para-substituted phenols under microwave irradiation. The rate of reaction was dictated by the electronic nature of the para-substituent. With an electron-withdrawing group the reaction was completed within 30 min. For electron-donating groups, the reaction times were 60 min. Esterification and enamino-ketone formation was also observed with carboxylic acid and ketone functional groups, respectively.
- Belov, Pavel,Campanella, Veronica L.,Smith, Alison W.,Priefer, Ronny
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experimental part
p. 2776 - 2779
(2011/06/19)
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- Cationic and radical intermediates in the acid photorelease from aryl sulfonates and phosphates
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The irradiation of a series of phenyl sulfonates and phosphates leads to the quantitative release of acidity with a reasonable quantum yield (≈0.2). Products characterization, ion chromatography analysis and potentiometric titration are consistent with the intervening of two different paths in this reaction, viz. cationic with phosphates and (mainly) radical with sulfonates. The Royal Society of Chemistry and Owner Societies 2011.
- Terpolilli, Marco,Merli, Daniele,Protti, Stefano,Dichiarante, Valentina,Fagnoni, Maurizio,Albini, Angelo
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experimental part
p. 123 - 127
(2012/01/03)
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- Nickel-catalyzed Kumada cross-coupling reactions of tertiary alkylmagnesium halides and aryl bromides/triflates
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We report a Ni-catalyzed process for the cross-coupling of tertiary alkyl nucleophiles and aryl bromides. This process is extremely general for a wide range of electrophiles and generally occurs with a ratio of retention to isomerization >30:1. The same procedure also accommodates the use of aryl triflates, vinyl chlorides, and vinyl bromides as the electrophilic component.
- Joshi-Pangu, Amruta,Wang, Chao-Yuan,Biscoe, Mark R.
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supporting information; experimental part
p. 8478 - 8481
(2011/06/25)
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- Nickel-catalyzed cross-coupling of aryl bromides with tertiary grignard reagents utilizing donor-functionalized N-heterocyclic carbenes (NHCs)
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Metal-catalyzed cross-coupling reactions are among the most important transformations in organic synthesis, allowing the efficient construction of complex structures from simpler, readily available building blocks.Many applications in large and small-scale synthesis can be found in different areas such as agrochemicals, pharmaceuticals and supramolecular chemistry. Whereas the coupling of sp2-hybridized carbon atoms in either reaction partner is well established, the use of CACHTUNGTRENUNG(sp3)-hybridized substrates presents some challenges. Catalytic cross-coupling of sterically hindered tertiary alkyl substrates is especially difficult, generally resulting in low yields, and thus, only few reports exist.[27] A big challenge in this field is not only to get the required level of reactivity, but also to overcome competing pathways like β-hydride elimination, hydrodehalogenation or isomerization
- Lohre, Claudia,Droege, Thomas,Wang, Congyang,Glorius, Frank
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scheme or table
p. 6052 - 6055
(2011/06/25)
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- Use of diethoxymethane as a solvent for phase transfer-catalyzed O -alkylation of phenols
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The effectiveness of diethoxymethane (DEM) as a solvent for O-alkylation of a variety of phenols under phase transfer conditions has been examined and evaluated. The reaction between 4-methoxy phenol and benzyl chloride was selected to compare reaction rates in various solvents and the efficiency of various PTCs. This reaction was further studied to develop a commercially amenable process complete with recycle streams and efficient product isolation. DEM is a good solvent for these types of phase transfer-catalyzed reactions and can be considered as an alternative solvent for dichloromethane and toluene.
- Coleman, M. Todd,Leblanc, Gabriel
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experimental part
p. 732 - 736
(2011/07/07)
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- Non-catalytic conversion of C-F bonds of benzotrifluorides to C-C bonds using organoaluminium reagents
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A facile method for the conversion of C-F bonds of benzotrifluorides to C-C bonds has been developed using aluminium reagents in the absence of catalysts.
- Terao, Jun,Nakamura, Misaki,Kambe, Nobuaki
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supporting information; experimental part
p. 6011 - 6013
(2010/11/16)
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- Methylation of phenolic hydroxyl group and demethylation of anisoles
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A mild methylation of phenolic hydroxyl groups with iodomethane was enabled in the presence of sodium bis(trimethylsilyl)amide at room temperature. The reverse reaction, namely demethylation of methyl phenyl ethers, was easily achieved by microwave heating with neat iodotrimethylsilane.
- Sato, Nobuhiro,Endo, Hiroyuki
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experimental part
p. 229 - 230
(2009/12/03)
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- Streamlined synthesis of the bippyphos family of ligands and cross-coupling applications
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We describe the efficient preparation of Bippyphos, 1. The key precursor to Bippyphos, 5, was prepared via a one-pot bromination of diketone 2 followed by alkylation with pyrazole and condensation with phenylhydrazine. Lithiation of 5 and trapping with ditert-butylchlorophosphine afforded Bippyphos, 1. Using this approach we have prepared several derivatives of Bippyphos to probe the structure and activity relationships of this family of phosphine ligands. We also demonstrate the utility of these ligands in Pdcatalyzed amination reactions and other cross-coupling reactions.
- Withbroe, Gregory J.,Singer, Robert A.,Sieser, Janice E.
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p. 480 - 489
(2013/01/03)
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- Study on the electronic effect on coordinating donors in heptacoordinate trichlorogermanes
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Trichloro[tris(2,5-dimethoxyphenyl)methyl]germane (1a), trichloro[tris(3-fluoro-6-methoxyphenyl)methyl]germane (1b), and trichloro[tris(2-methoxy-5-trifluoromethylphenyl)methyl]germane (1c) were synthesized. X-ray crystallographic analyses of 1a-c revealed their heptacoordinate geometries around the germanium atoms. The interatomic distances between the oxygen atoms and the central germanium atoms in the crystalline state were not significantly affected by change of functional groups on the benzene rings, while the optimized structures by theoretical calculations and Atoms in Molecules (AIM) analysis indicated linear relationship between the donating ability of functional groups and the O?Ge interatomic interactions.
- Iwanaga, Kohei,Kobayashi, Junji,Kawashima, Takayuki
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p. 10127 - 10132
(2008/02/13)
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- Diastereoselective Synthesis of 2-Alkoxy-5-tert-butylmandelic Acid
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Lewis acid catalyzed addition of N-glyoxyloyl-(2R)-bornane-10,2-sultam to O-protected 4-tert-butylphenols is presented. The reactions proceed with excellent diastereoselectivities. The products of the addition are hydrolyzed with LiOH·H2O yielding optically pure α- hydroxycarboxylic acids.
- Bauer, Tomasz,Gajewiak, Joanna
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- Tetrakis(2-hydroxyphenyl)ethene and derivatives. A structurally preorganized tetradentate ligand system for polymetallic coordination chemistry and catalysis
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A topologically unique, conformationally constrained tetradentate ligand system for polymetallic coordination chemistry has been developed: tetrakis(2-hydroxyphenyl)ethene (1a) and substituted derivatives. The design exploits the planarity of the tetraphenylethylene core to impart rigidity to the roughly square oxygen binding array, while maintaining a degree of conformational mobility associated with rotation about the aryl-ethylene carbon-carbon bonds. Tetrakis(2-hydroxyphenyl)ethene derivatives are designed to promote multiple metal bridging over chelating coordination modes. The ligand is synthesized from anisole or 4-tert-butylanisole in four steps via the 2,2-dimethoxybenzophenone hydrazones 4a,b. The sterically hindered ortho-substituted tetraphenylethylene core is produced in high yield by acid-catalyzed decomposition of the corresponding diaryl diazomethane prepared in situ by oxidation of the hydrazone using nickel peroxide. Deprotection of the methyl ethers using boron tribromide gives tetrakis(2-hydroxyphenyl)ethene (1a), characterized by X-ray crystallography, and tetrakis(5-tert-butyl-2-hydroxyphenyl)ethene (1b). Sterically isolating substituents in the 3-position can be installed via Claisen rearrangement/hydrogenation, providing tetrakis(3-n-propyl-2-hydroxyphenyl)ethene (6) efficiently. To illustrate potential applications of this unprecedented ligand class, two coordination complexes are reported, including tetrakis(2-diethylaluminoxyphenyl)ethene (8), a structurally robust eight-membered-ring aluminum/oxygen crown complex characterized both in solution and in the solid state. Copyright
- Verkerk, Udo,Fujita, Megumi,Dzwiniel, Trevor L.,McDonald, Robert,Stryker, Jeffrey M.
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p. 9988 - 9989
(2007/10/03)
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- Rhenium complexes-catalyzed alkylation of arenes with alkyl halides
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Rhenium complexes have been shown to catalyze the alkylation of arenes with alkyl halides. When arenes were reacted with an alkyl chloride in the presence of a catalytic amount of rhenium complexes, such as bromopentacarbonylrhenium(I) [ReBr(CO)5], tricarbonylcyclopentadienylrhenium(I) [Re(C5H5)(CO)3] and decacarbonyldirhenium [Re2(CO)10], alkylation of the arenes proceeded under mild conditions to give a mixture of mono- and dialkyl substituted arenes in moderate-to-good yields.
- Nishiyama,Kakushou,Sonoda
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p. 2779 - 2782
(2007/10/03)
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- Electrophilic Aromatic Alkylation by Hydroperoxides. Competition between Ionic and Radical Mechanisms with Phenols
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Tertiary hydroperoxides have been utilized for the electrophilic alkylation of activated aromatic substrates, particularly phenols and phenol ethers. Cumyl (1) and tert-butyl (2) hydroperoxides have shown a greatly different behavior as concerns the catalysis and the regioselectivity. The best catalyst for 1 is TiCl4, which is completely inactive with 2. With the latter an effective catalyst is FeCl3, which, however, can give rise to a combination of electrophilic and radical reactions with alkyl phenols. 2,2′-Dihydroxy-3,3′-di-tert-butyl-5,5′-dimethyldiphenyl is obtained in high yields from p-cresol.
- Liguori, Lucia,Bjorsvik, Hans-Rene,Fontana, Francesca,Bosco, Dino,Galimberti, Laura,Minisci, Francesco
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p. 8812 - 8815
(2007/10/03)
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- Comparison between SiMe2 and CMe2 spacers as σ-bridges for photoinduced charge transfer
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The potential of dimethylsilylene and isopropylidene σ-spacers as bridges for photoinduced charge transfer (CT) in 4-cyano-4'-(dimethylamino)- and 4-cyano-4'-methoxy-substituted diphenyldimethylsilanes and 2,2-diphenylpropanes was studied. Fluorescence solvatochromism and time-resolved microwave conductivity measurements show that upon photoexcitation a charge separated state (D.+σA.-)* is populated in all compounds. Excited state dipole moments for a given donor-acceptor combination are, irrespective of the bridge, equal. The CT states of the silanes are however lying at lower energies, implying that the presence of silicon thermodynamically facilitates the CT process. Cyclic voltammetry data of model compounds show that this is a consequence of the lowering of the acceptor reduction potential by the silicon bridge. It was however inferred from radiative decay rates that the electronic coupling between the CT and locally excited states as well as the coupling between the ground and CT state is larger for the carbon-bridged compounds. As shown by both solution and solid state electronic spectra and radiative decay rates, the photophysics of the DσA compounds are dominated by intensity borrowing of the CT transitions from transitions localized in the Dσ and σA chromophores.
- Van Walree, Cornelis A.,Roest, Martin R.,Schuddeboom, Wouter,Jenneskens, Leonardus W.,Verhoeven, Jan W.,Warman, John M.,Kooijman, Huub,Spek, Anthony L.
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p. 8395 - 8407
(2007/10/03)
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- Facile synthesis of alkyl phenyl ethers using cesium carbonate
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A highly efficient alkylation method of phenols using alkyl halide/cesium carbonate/acetonitrile system is described.
- Lee,Yuk,Cho
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p. 1367 - 1370
(2007/10/02)
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- Method of manufacturing alkylphenyl alkyl ethers or alkylphenyl alkyl thioethers
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Alkylphenyl alkyl ethers or alkylphenyl alkyl thioethers, of the formula STR1 where U represents O or S; and R1 -R6 each independently represent an alkyl or aryl group with 1-6 C atoms, but R1 -R5 may each independently represent a functional group other than these, particularly --COOR (R=C1-4 alkyl), --NO2, --NH2, --O--CH2 --CH2 --OH, --OH, --CHO, --H, or -halogen; R1 -R5 may be bridged by suitable bifunctional substituents, such as, e.g., --(CH2)x --, or --(CH2)x --Z--(CH2)y -- (where Z represents a hetero atom; x=0-7 and y=0-7), or by unsaturated substituents or anellated ring systems; may be produced in high space-time yield by reacting the corresponding phenol or thiophenol with a arylalkyl carbonate at a temperature of 70°-300° C. under elevated or normal pressure, in the presence of a monocyclic, bicyclic, polycyclic, or acyclic amidine as a catalyst.
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