- Synthesis, characterization, and alkyne trimerization catalysis of a heteroleptic two-coordinate FeI complex
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The synthesis of the first heteroleptic, two-coordinate FeI complex IPr-Fe-N(SiMe3)DIPP (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; DIPP = 2,6-iPr2-C6H3) is reported. Protonation of the FeII bis(amido) complex Fe[N(SiMe3)DIPP]2 followed by addition of IPr and reduction by potassium graphite in a one-pot reaction results in good yields of 1. The redox activity of 1 and comparison between 1 and its reduction product by 57Fe M?ssbauer spectroscopy are discussed, and the reduction was found to be metal-based rather than ligand-based. The activity of 1 toward the catalytic cyclotrimerization of terminal and internal alkynes is described.
- Lipschutz, Michael I.,Chantarojsiri, Teera,Dong, Yuyang,Tilley, T. Don
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Read Online
- Synthesis methodology, stability, acidity, and catalytic behavior of the 18 × 10 member ring pores ITQ-33 zeolite
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We used a flexible organic structure-directing agent (OSDA) and high-throughput (HT) synthesis techniques to explore a large composition region. A zeolite with the largest pores reported to date (ITQ-33) was found under very unusual synthesis conditions, together with other known structures. A second HT experimental design allowed, finally synthesizing pure ITQ-33. We studied the thermal and hydrothermal stability and acid properties of the zeolite. We investigated the role of pore diameter on zeolite acid strength by comparing the 18-ring pore (ITQ-33) with a 12-MR pore (ITQ-17) zeolite with the same framework composition. Finally, we compared the catalytic properties of ITQ-33 for reactant molecules of different sizes with those of 12-MR (Beta) and 14-MR (UTD-1) zeolites.
- Moliner, Manuel,Diaz-Cabanas, Maria J.,Fornes, Vicente,Martinez, Cristina,Corma, Avelino
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Read Online
- Detailed kinetic study of cumene isopropylation in a liquid-liquid biphasic system using acidic chloroaluminate ionic liquids
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A kinetic study of cumene isopropylation has been carried out using the acidic ionic liquid 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl)/AlCl3 (molar ratio 1:2) as the catalyst phase in a semi-batch liquid-liquid biphasic reaction system. Kinetic models representing the alkylation reaction network have been established based on reaction temperature and propylene partial pressure variations. By comparing the results of the kinetic models with the measured concentrations in the liquid organic phase, the importance of the different product solubilities in the acidic ionic liquid became evident. Correction of the product concentrations in the organic phase based on a COSMO-RS calculation of the relative product solubilities in the acidic ionic liquid [EMIM][Al2Cl7] gave a remarkably good prediction of the reaction kinetics by the kinetic model. These findings demonstrate the suitability of COSMO-RS to predict the relative solubilities of different aromatic compounds in highly reactive catalytic systems.
- Joni,Schmitt,Schulz,Lotz,Wasserscheid
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Read Online
- Two derivatives of phenylpyridyl-fused boroles with contrasting electronic properties: Decreasing and enhancing the electron accepting ability
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Two derivatives of phenylpyridyl-fused boroles were prepared via functionalization of the pyridyl groups, namely to an electron-rich dihydropyridine moiety (compound 1) and an electron-deficient N-methylpyridinium cation (compound 2). Due to strong conjugation between the dihydropyridine moiety and the boron atom, the reduction potential of compound 1 shifts cathodically. In contrast, compound 2 exhibits three reduction processes with a first reversible reduction potential anodically shifted in comparison to its precursor (TipPBB2) or the non-borylated framework 1-methyl-2-phenylpyridin-1-ium triflate (3). The significantly anodically shifted reduction potential indicates the extreme electron deficiency of compound 2, which also leads to the reversible coordination of THF. Photophysical properties of both compounds in different solvents were investigated. Theoretical studies further support the strong conjugation in the ground state of compound 1 and the electron-deficient property of compound 2.
- He, Jiang,Rauch, Florian,Krummenacher, Ivo,Braunschweig, Holger,Finze, Maik,Marder, Todd B.
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p. 355 - 361
(2021/01/11)
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- Catalytic hydrodebromination of aryl bromides by cobalt tetra-butyl porphyrin complexes with EtOH
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Hydrodebromination of aryl bromides catalyzed by electron rich and sterically unhindered cobalt 5,10,15,20-tetrabutylporphyrin was achieved at mild conditions in good yields employing EtOH as the hydrogen source. The catalytic efficiency was enhanced compared with previously reported by cobalt tetra-aryl porphyrin catalysts. A revised mechanism of single electron transfer was proposed.
- Chen, Chen,Zuo, Huiping,Chan, Kin Shing
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p. 510 - 517
(2019/01/04)
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- Hydrodehalogenation of Aryl Halides through Direct Electrolysis
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A catalyst- and metal-free electrochemical hydrodehalogenation of aryl halides is disclosed. Our reaction by a flexible protocol is operated in an undivided cell equipped with an inexpensive graphite rod anode and cathode. Trialkylamines nBu3N/Et3N behave as effective reductants and hydrogen atom donors for this electrochemical reductive reaction. Various aryl and heteroaryl bromides worked effectively. The typically less reactive aryl chlorides and fluorides can also be smoothly converted. The utility of our method is demonstrated by detoxification of harmful pesticides and hydrodebromination of a dibrominated biphenyl (analogues of flame-retardants) in gram scale.
- Ke, Jie,Wang, Hongling,Zhou, Liejin,Mou, Chengli,Zhang, Jingjie,Pan, Lutai,Chi, Yonggui Robin
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supporting information
p. 6911 - 6914
(2019/05/10)
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- Nickel(I) Aryl Species: Synthesis, Properties, and Catalytic Activity
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In this work, Ni(I) aryl species that are directly relevant to cross-coupling have been synthesized. Transmetalation of (dppf)NiIX (dppf = 1,1′-bis(diphenylphosphino)-ferrocene, X = Cl, Br) with aryl Grignard reagents or aryl boronic acids in t
- Mohadjer Beromi, Megan,Banerjee, Gourab,Brudvig, Gary W.,Hazari, Nilay,Mercado, Brandon Q.
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p. 2526 - 2533
(2018/03/13)
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- Isolation and Reactivity of a Digerma Analogue of Vinyllithiums: A Lithium Digermenide
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The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the Si=Si moiety. The corresponding germanium analogue, digermenide Tip2Ge=Ge(Tip)Li·dme2 (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip2GeCl2 with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at -70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the Ge=Ge motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip2Ge=Ge(Tip)SiR3.
- Nieder, David,Klemmer, Lukas,Kaiser, Yvonne,Huch, Volker,Scheschkewitz, David
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supporting information
p. 632 - 635
(2018/03/21)
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- Dual Roles for Potassium Hydride in Haloarene Reduction: CSNAr and Single Electron Transfer Reduction via Organic Electron Donors Formed in Benzene
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Potassium hydride behaves uniquely and differently than sodium hydride toward aryl halides. Its reactions with a range of haloarenes, including designed 2,6-dialkylhaloarenes, were studied in THF and in benzene. In THF, evidence supports concerted nucleophilic aromatic substitution, CSNAr, and the mechanism originally proposed by Pierre et al. is now validated through DFT studies. In benzene, besides this pathway, strong evidence for single electron transfer chemistry is reported. Experimental observations and DFT studies lead us to propose organic super electron donor generation to initiate BHAS (base-promoted homolytic aromatic substitution) cycles. Organic donor formation originates from deprotonation of benzene by KH; attack on benzene by the resulting phenylpotassium generates phenylcyclohexadienylpotassium that can undergo (i) deprotonation to form an organic super electron donor or (ii) hydride loss to afford biphenyl. Until now, BHAS reactions have been triggered by reaction of a base, MOtBu (M = K, Na), with many different types of organic additive, all containing heteroatoms (N or O or S) that enhance their acidity and place them within range of MOtBu as a base. This paper shows that with the stronger base, KH, even a hydrocarbon (benzene) can be converted into an electron-donating initiator.
- Barham, Joshua P.,Dalton, Samuel E.,Allison, Mark,Nocera, Giuseppe,Young, Allan,John, Matthew P.,McGuire, Thomas,Campos, Sebastien,Tuttle, Tell,Murphy, John A.
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supporting information
p. 11510 - 11518
(2018/09/12)
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- Formal Nucleophilic Silyl Substitution of Aryl Halides with Silyllithium Reagents via Halogenophilic Attack of Silyl Nucleophiles
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A new reaction has been developed for the formal nucleophilic silyl substitution of aryl halides with silyllithium or silylpotassium reagents. Dimethylphenylsilyllithium reacted with various aryl halides to form the corresponding arylsilanes in moderate to good yields with concomitant formation of the disilanes under the optimized reaction conditions. Mechanistic studies indicated that this silyl substitution reaction progresses through polar halogenophilic attack of silyl nucleophiles.
- Yamamoto, Eiji,Ukigai, Satoshi,Ito, Hajime
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p. 2460 - 2464
(2017/10/06)
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- Facile routes to abnormal-NHC-cobalt(II) complexes
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Deprotonation of [IPrPh]I (1) with Co{N(SiMe3)2}2 readily affords the abnormal N-heterocyclic carbene (aNHC) complex (aIPrPh)2CoI2 (2) (aIPrPh = 1,3-bis(2,6-iPr2C6H3)-2-phenyl-imidazol-4-ylidene). Treatment of 1 with NaHBEt3 yields (aIPrPh)BEt3 (3) that serves as an aNHC-transfer agent and yields (aIPrPh)Co{N(SiMe3)2}2 (4) on reaction with Co{N(SiMe3)2}2.
- Ghadwal, Rajendra S.,Lamm, Jan-Hendrik,Rottsch?fer, Dennis,Schürmann, Christian J.,Demeshko, Serhiy
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supporting information
p. 7664 - 7667
(2017/07/11)
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- Gold-Catalyzed Proto- and Deuterodeboronation
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A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in "green" solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific ipso-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B-C bond cleavage and facile protonolysis of a Au-σ-phenyl intermediate.
- Barker, Graeme,Webster, Stacey,Johnson, David G.,Curley, Rachel,Andrews, Matthew,Young, Paul C.,MacGregor, Stuart A.,Lee, Ai-Lan
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p. 9807 - 9816
(2015/11/03)
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- Iminoborylene complexes: evaluation of synthetic routes towards BN-allenylidenes and unexpected reactivity towards carbodiimides
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The synthetic and reaction chemistries of cationic iminoborylene complexes [LnM=B=N=CR2]+, which feature a unique heterocumulene structure, have been systematically investigated. Precursors of the type CpFe(CO)2B(Cl)NCAr2 (Ar = p-Tol/Mes, 5c/d) have been generated by B-centred substitution chemistry using CpFe(CO)2BCl2 and suitable lithiated ketimines - a reaction which is found to be highly sensitive to the steric bulk at both the metal fragment and the ketimino group. Carbonyl/phosphine exchange (using PCy3 or PPh3), followed by halide abstraction allows for the generation of the cationic iminoborylenes [CpFe(PR3)(CO)(BNCAr2)]+[BArX 4]- (R = Cy, Ar = p-Tol/Mes, 12c/d; R = Ph, Ar = Mes, 13d; ArX = 3,5-X2C6H3 where X = Cl, CF3) which have been characterized spectroscopically and by X-ray crystallography. The reactivity of these iminoborylene systems towards a range of nucleophiles and unsaturated substrates has been investigated. The latter includes the first examples of M=B metathesis reactivity with a carbodiimide, and results in Fe=B cleavage and formation of the isonitrile complexes [CpFe(PCy3)(CO)(CNR)]+[BArCl 4]- (R = iPr/Cy, 16/17).
- Niemeyer,Kelly,Riddlestone,Vidovic,Aldridge
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supporting information
p. 11294 - 11305
(2015/06/25)
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- Application of cooperative iron/copper catalysis to a palladium-free borylation of aryl bromides with pinacolborane
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A new cooperative copper/iron catalysis for the borylation of various aryl bromides with pinacolborane, at -10 °C, is reported. Use of the toxic, precious metal Pd is avoided. The mechanism of the protodebromination side reaction is discussed.
- Labre, Flavien,Gimbert, Yves,Bannwarth, Pierre,Olivero, Sandra,Dunach, Elisabet,Chavant, Pierre Y.
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supporting information
p. 2366 - 2369
(2014/05/20)
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- Enantioselective organocatalytic fluorination-induced Wagner-Meerwein rearrangement
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Cracked under strain: Strained allylic cyclobutanols and cyclopropanols readily undergo a ring expansion described by the title rearrangement. This reaction is promoted by catalytic amounts of 1 and displays high tolerance with respect to the substrate scope. The corresponding β-fluoro spiroketone products are isolated in high yields and with excellent stereoselectivities. EDG=electron-donating group, EWG=electron-withdrawing group. Copyright
- Romanov-Michailidis, Fedor,Guénée, Laure,Alexakis, Alexandre
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supporting information
p. 9266 - 9270
(2013/09/12)
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- An efficient approach to the cyclotrimerisation of alkynes: Solvent-free synthesis of 1,3,5-trisubstituted benzenes using p-toluenesulfonic acid monohydrate
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An environmentally friendly, efficient method for transforming alkynes into substituted benzenes catalyzed by p-toluenesulfonic acid monohydrate (p-TsOH·H2O) under solvent-free conditions has been developed, which conforms to the principles of "green" chemistry and overcomes the shortcomings of previous methods for the synthesis of substituted benzenes. The reaction is quite general and provides good to excellent yields. ARKAT-USA, Inc.
- Gao, Qi,Bao, Fang-Ping,Feng, Xiao-Jing,Pan, Ying-Ming,Wang, Heng-Shan,Li, Dian-Peng
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- The palladium-catalyzed desulfitative cyanation of arenesulfonyl chlorides and sodium sulfinates
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A palladium-catalyzed desulfitative cyanation of arenesulfonyl chlorides and sodium sulfinates has been developed, providing aryl nitriles in moderate to excellent yields. It represents a facile procedure to access aryl nitriles.
- Chen, Jianbin,Sun, Yang,Liu, Bin,Liu, Dongfang,Cheng, Jiang
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experimental part
p. 449 - 451
(2012/01/05)
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- Ti(O-i-Pr)4/Me3SiCl/Mg-mediated reductive cleavage of sulfonamides and sulfonates to amines and alcohols
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A low-valent titanium generated in situ from Ti(O-i-Pr)4, Me3SiCl, and Mg powder in THF reacted with aryl- and alkyl-sulfonamides of aryl and alkyl amines in a reductive N-S/S-O/S-C bond cleaving pathway to provide the corresponding amines and hydrocarbons (and thiols) derived from the sulfonyl moiety. The reagent could also cleave sulfonates to the corresponding alcohols.
- Shohji, Noriaki,Kawaji, Tsuyoshi,Okamoto, Sentaro
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supporting information; experimental part
p. 2626 - 2629
(2011/07/08)
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- Regioselective synthesis of 1,3,5-substituted benzenes via the InCl 3/2-iodophenol-catalyzed cyclotrimerization of alkynes
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A novel indium(III)-catalyzed cyclotrimerization of alkynes in the presence of 2-iodophenol gave 1,3,5-substituted benzenes in excellent yields with complete regioselectivity. The reaction condition is tolerant to air, and atom economical, in accordance with the concept of modern green chemistry. This method provides a rapid and efficient access to 1,3,5-substituted benzenes.
- Xu, Yan-Li,Pan, Ying-Ming,Wu, Qiang,Wang, Heng-Shan,Liu, Pei-Zhen
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experimental part
p. 8472 - 8476
(2011/12/04)
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- Mesoporous mordenites obtained by sequential acid and alkaline treatments - Catalysts for cumene production with enhanced accessibility
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Two commercially available mordenites, obtained from Zeolyst (Si/Al = 10 at/at) and BASF (Si/Al = 8 at/at), were subjected to post-synthesis treatments. The impact of acid treatment, alkaline treatment (desilication) and a combination of both on porosity,
- Van Laak, Adri N.C.,Sagala, Sophia L.,Zecevic, Jovana,Friedrich, Heiner,De Jongh, Petra E.,De Jong, Krijn P.
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experimental part
p. 170 - 180
(2011/02/23)
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- Controlling the charge transfer in phenylene-bridged borylene-amine π-conjugated systems
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Image Presented Novel boron-nitrogen-containing π-conjugated compounds 3,3′- and 4,4′-((2,4,6-triisopropylphenyl)borylene)bis(N, N-diarylbenzenamine) (1-2), m- and p-phenylene bridged to the boron center, respectively, have been synthesized and characterized. Optical studies by means of UV-vis absorption and emission measurements as well as DFT calculations reveal a different charge transfer behavior between the para series and the meta series at ground and excited states.
- Pron, Agnieszka,Zhou, Gang,Norouzi-Arasi, Hassan,Baumgarten, Martin,Muellen, Klaus
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supporting information; experimental part
p. 3550 - 3553
(2011/02/22)
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- Selective alkylation of aromatic hydrocarbons
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A method for increasing selectivity of alkylation to monoalkylation comprising: providing a feedstream consisting essentially of alkylating agent and a stoichiometric excess of benzene, the alkylating agent consisting essentially of a molar blend of propylene and one or more linear butene(s); and, contacting the feedstream with a catalytically effective amount of zeolite beta under alkylation reaction conditions which increase selectivity of the alkylation to monoalkylation compared to predicted selectivity to monoalkylation based on the concentration of the alkylating agent and on the molar blend of propylene and one or more linear butene(s).
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Page/Page column 6; 7
(2008/06/13)
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- A mixed naphthyl-phenyl phosphine ligand motif for Suzuki, Heck, and hydrodehalogenation reactions
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Nap-Phos, representing a new naphthyl-phenyl biaryl-type phosphine ligand class and available by a short synthesis (4 steps, 71% overall yield), effectively catalyzes the Suzuki-Miyaura (including highly hindered cases), hydrodehalogenation, and Heck reactions. Georg Thieme Verlag Stuttgart.
- Demchuk, Oleg M.,Yoruk, Bilge,Blackburn, Tom,Snieckus, Victor
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p. 2908 - 2913
(2008/02/12)
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- An efficient catalyst system for palladium-catalyzed borylation of aryl halides with pinacolborane
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The combination of Pd(dba)2 and bis(2-di-tert-butyl- phosphinophenyl)ether has proven to be efficient for the cross-coupling of pinacolborane with aryl bromides and chlorides. The substrate scope is broad and the present system enables the synthesis of ortho-, meta-, and para-substituted electron-rich and -deficient arylboronates. Georg Thieme Verlag Stuttgart.
- Murata, Miki,Sambommatsu, Tomoko,Watanabe, Shinji,Masuda, Yuzuru
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p. 1867 - 1870
(2008/02/08)
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- Process for synthesizing diisopropylbenzene
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This invention relates to a process for synthesizing para-diisopropylbenzene utilizing only cumene and propylene as raw materials. This synthesis technique offers the advantage of eliminating benzene as a raw material used in the process. The elimination of benzene is beneficial because it simplifies the process and eliminates the need to purchase and store benzene for use in the synthesis. The elimination of benzene from the synthesis is of particular value since the use of benzene in industrial applications has been under attack on the basis of environmental, safety, and health concerns. The present invention discloses a process for producing para-diisopropylbenzene from cumene and propylene, said process comprising the steps of (1) introducing a feed stream into an alkylation zone wherein said feed stream is comprised of cumene and propylene, and wherein said alkylation zone contains an alkylation catalyst; (2) allowing the cumene and propylene in the feed stream to react together to produce a first mixture of para-diisopropylbenzene and meta-diisopropylbenzene; (3) fractionally distilling the mixture of para-diisopropylbenzene and meta-diisopropylbenzene in a fractional distillation step to separate the meta-diisopropylbenzene from the para-diisopropylbenzene; (4) isomerizing the meta-diisopropylbenzene in the presence of a transalkylation catalyst to produce a second mixture of para-diisopropylbenzene and meta-diisopropylbenzene; (5) recycling the second mixture of para-diisopropylbenzene and meta-diisopropylbenzene recovered from the transalkylation step to the fractional distillation step; and (6) recovering the para-diisopropylbenzene that was separated from the meta-diisopropylbenzene by the fractional distillation step.
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Page/Page column 4-6
(2008/06/13)
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- Reduction of dinitrogen to ammonia at a well-protected reaction site in a molybdenum triamidoamine complex
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We have synthesized a triamidoamine ligand ([(RNCH2CH2)3N]3-) in which R is 3,5-(2,4,6-i-Pr3C6H2)2C6H3 (HexaIsoPropylTerphenyl or HIPT). The reaction between MoCl4(THF)2 and H3[HIPTN3N] in THF followed by 3.1 equiv of LiN(SiMe3)2 led to formation of orange [HIPTN3N]MoCl. Reduction of [HIPTN3N]MoCl with magnesium in THF under dinitrogen led to formation of salts that contain the {[HIPTN3N]Mo(N2)}- ion. The {[HIPTN3N]Mo(N2)}- ion can be oxidized by zinc chloride to give [HIPTN3N]Mo(N2) or protonated to give [HIPTN3N]Mo-N=N-H. Other relevant compounds that have been prepared include {[HIPTN3N]Mo-N=NH2}+, [HIPTN3N]Mo≡N, {[HIPTN3N]Mo=NH}+, and {[HIPTN3N]Mo(NH3)}+. (The anion is usually {B(3,5-(CF3)2C6H3)4}- = {BAr'4}-.) Reduction of [HIPTN3N]Mo(N2) with CoCp2 in the presence of {2,6-lutidinium}BAr'4 in benzene leads to formation of ammonia and {[HIPTN3N]Mo(NH3)}+. Preliminary X-ray studies suggest that the HIPT substituent creates a deep, three-fold symmetric cavity that protects a variety of dinitrogen reduction products against bimolecular decomposition reactions, while at the same time the metal is left relatively open toward reactions near the equatorial amido ligands. Copyright
- Yandulov, Dmitry V.,Schrock, Richard R.
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p. 6252 - 6253
(2007/10/03)
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- Thermolysis of free-radical initiators: tert-butylazocumene and its 1,3- and 1,4-bisazo and 1,3,5-trisazo analogues
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Four tert-butylazocumenes (4-7) were prepared from the corresponding cyanobenzenes, and their nitrogen evolution kinetics and products were analyzed. In combination with TEMPO, the simplest compound, tert-butylazocumene (4), shows promise as a "one-radical" initiator of styrene polymerization. The ABNO-trapped cumyl radical 29 is a particularly stable trialkylhydroxylamine, whose thermolysis half-life is 2.1 h at 150 °C. Taking advantage of this stability, we trapped the cumyl radical centers from 7 to afford tris adduct 32a. While the behavior of the meta bisazoalkane 6 can be mostly predicted from that of 4, the para isomer 5 exhibits both unusual products and kinetics, attributed to the formation of quinodimethane 33 via azo-containing radical 34. In fact, flash vacuum pyrolysis of 5 allowed observation of the 1H and 13C NMR spectra of 33, whose persistence even at ambient temperature showed that this quinodimethane is far more stable than the parent 36. Finally, evidence is presented that 7 is an initiator of star polymerization.
- Engel,Pan,Ying,Alemany
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p. 3706 - 3715
(2007/10/03)
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- Diverging effects of steric congestion on the reaction of tributylstannyl radicals with areneselenols and aryl bromides and their mechanistic implications
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The effects of bulky ortho,ortho' groups on the reactions of aryl bromides and areneselenols with tributylstannane have been studied. Bulky ortho,ortho' groups accelerate the reaction of the bromides with the stannane but retard the reactions of the selenols. On the other hand, ab initio and force field calculations show that introducing bulky ortho substituents into selenols causes a greater increase in strain than in the corresponding bromides. Two possible explanations for the divergent reactivity patterns are advanced. On one hand, it is possible that bromine abstraction by stannyl radicals from aryl bromides proceeds in a single step through a linear transition state whereas the abstraction of sell from the selenols involves a T-shaped, hypervalent intermediate. Alternatively, it may be that both reactions are concerted with the bromine abstraction having a late transition state and the sell abstraction an early one. Approximate second-order rate constants for the reaction of tributylstannane with a range of hindered aryl bromides are derived from competition reactions. 2,4,6-Tri-tert- butylbenzeneselenol is able to function moderately well as a catalyst for the stannane-mediated reactions of vinyl bromides. The X-ray crystal structure of bis(2,4,6-triisopropylphenyl) diselenide is presented.
- Crich, David,Hwang, Jae-Taeg,Gastaldi, Stephane,Recupero, Francesco,Wink, Donald J.
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p. 2877 - 2882
(2007/10/03)
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- Contributions of enthalpy and entropy factors to isomerization equilibrium of isopropyl- and cyclohexylbenzenes
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Experimental and theoretical data on the liquid-phase equilibrium of the positional isomerization of isopropyl- and cyclohexylbenzenes are analyzed in detail. Contributions of the enthalpy and entropy factors to the equilibrium constants of the ortho-meta and para-meta transformations are estimated.
- Nesterova,Pimerzin,Krasnykh
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p. 1884 - 1890
(2007/10/03)
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- Friedel-crafts alkylation and acylation in the absence of solvent
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A short and efficient synthetic route, for alkylation and acylation of aromatic compounds in the absence of solvent is developed. According to the reaction system and conditions used, different alkyl-, and acyl arenes are obtained in moderate to good yields. The structures are assigned by 1H and 13C NMR spectroscopy.
- Ghiaci,Asghari
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p. 2213 - 2220
(2007/10/03)
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- Flash photolysis study of a Friedel-Crafts alkylation. Reaction of the photogenerated 9-fluorenyl cation with aromatic compounds
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A combination of flash photolysis and product analysis is employed to investigate the reaction of aromatic compounds (ArH) with the 9-fluorenyl cation (Fl+) photogenerated from 9-fluorenol in 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP).The availability of the photochemical route to Fl+ means that the reaction of benzylic-type cation with ArH can be directly followed by flash photolysis.An additional feature with electron-rich ArH is that the cyclohexadienyl cation is observed to grow as Fl+ decays.Thus both cationic intermediates of a Friedel-Crafts alkylation are observed in the same experiment.The formation of the cyclohexadienyl cation is demonstrated to be reversible, or at least quasi-reversible, with the kinetic analysis furnishing absolute rate constants for the formation of this cation as well as for its loss of H+ and Fl+.Values of kH:kD for benzene:benzene and toluene:toluene are ca. 1.5 and demonstrate that Fl+ addition is at least partly reversible with these compounds as well.The Hammett ρ+ value obtained for a series of the less electron-rich ArH is -8, indicative of a transition state with considerable cyclohexadienyl cation character.Anisole shows a negative deviation from from Hammett correlation line, explained by the addition of Fl+ to ArH becoming encounter-controlled.This behaviour is dramatically illustrated in a comparison of data for Fl+ and Br2.For the less electron-rich ArH, rate constants for the two electrophiles are parallel.However, from m-xylene through pentamethylbenzene, the rate with Fl+ is unchanged, while the rate with Br2 increases over 1000-fold.The concept of encounter control with Fl+ is strongly supported by the absolute rate constants, which for the electron-rich ArH are all in the range 1-2 E9 dm3 mol-1 s-1, a magnitude typical of diffusion-controlled reactions.The electron-rich ArH also show no intermolecular selectivity since their reactions are encounter-controlled, but have a high intramolecular selectivity.It is suggested that a factor influencing the latter is the reversibility of formation of the cyclohexadienyl cation from the encounter complex.
- McClelland, Robert A.,Cozens, Frances L.,Li, Jianhui,Steenken, Steen
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p. 1531 - 1544
(2007/10/03)
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- Hemicarcerands that encapsulate hydrocarbons with molecular weights greater than two hundred
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Syntheses are reported for the globe-shaped hemicarcerands 1 and 2 composed of two rigid bowl-like units (polar caps) attached to one another at their rims through four OCH2C≡CC≡CCH2O units (equatorial spacers). Eight pendant CH3(CH2)4 groups in 1 and C6H5CH2CH2 groups in 2 attached in assemblies of four to each polar cap render the hosts soluble in organic solvents. The important shell-closing reactions 2Ar(OCH2C≡CH)4 + [O] → Ar(OCH2C≡CC≡CCH2O)4Ar went in 5-8% yields in pyridine-O2-Cu(OAc)2 to give a hemicarcerand free of pyridine. The higher solubility of 1 (compared to that of 2) in organic solvents led to an examination of its binding properties. By heating 1 dissolved either in potential guests or in 1,3,5-[(CH3)3C]3C6H3 (too large to enter 1) containing dissolved potential guests at 80-140 °C for 2-7 days, 1:1 hemicarceplexes mixed with the empty host were isolated in those cases when the potential guests were just small enough to enter the host's portals at high temperatures but large enough not to depart during isolation as stable solids. Thus, constrictive bonding played a large role in kinetic stabilization of the hemicarceplexes. The 1H NMR spectra of both the host and the guest were markedly modified upon complexation. The half-lives in hours of representative complexes dissolved in CDCl3 at 25 °C were as follows: 1·1,3,5-[(CH3)2CH]3C6H 3, 1628; 1·1,3,5-Et3C6H3, 960; 1·4-Et[2.2]paracyclophane, 24; 1·1,3-dimethyladamantane, 13.5; 1-[3.3]paracyclophane, 13; 1·tetradehydro[2.2]paracyclophane, 11; 1·[2.2]paracyclophane, 5; 1·4,12-dihydroxy[2.2]paracyclophane, 4; and 1·[2.3]paracyclphane, 0.5. Complexes of smaller guests such as CHCl3, ferrocene, adamantane, and 1,3,5-trimethylbenzene were unstable to room-temperature isolation conditions. Larger guests such as [3.4]paracyclophane and 4,12-dinitro[2.2]paracyclophane did not enter the portals of 1 at temperatures under which host 1 was stable, whereas smaller guests such as CH2Cl2 and pyridine entered and departed the host at 25 °C rapidly on the NMR time scale. Catalytic reduction (H2, PdC) of the eight acetylenic bonds of 1 produced an empty host of much more flexible structure, 3, whose binding properties have not yet been examined.
- Cram, Donald J.,Jaeger, Ralf,Deshayes, Kurt
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p. 10111 - 10116
(2007/10/02)
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- Cleavage of an Aryl Carbon-Sulphur Bond in Hydride-Thiolate Complexes of Molybdenum(IV); X-Ray Crystal Structure of i3-2,4,6)(OMe)(PMePh2)>2(μ-S)2>
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The complexes 1 (R = Me or Pri; R' = Me or Et) in THF-MeOH decompose via cleavage of an aryl carbon-sulphur bond to give C6H3R3-2,4,6 and complexes 2(μ-S)2, 3 one of which (R = Prs
- Burrow, Timothy E.,Hills, Adrian,Hughes, David L.,Lane, Janette D.,Lazarowych, Natalie J.,et al.
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p. 1757 - 1759
(2007/10/02)
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- MECHANISM OF THE ALKYLATION OF BENZENE WITH PROPYLENE IN THE PRESENCE OF AN ALUMINOSILICATE CATALYST MODIFIED BY REACTION OF ALUMINUM CHLORIDE WITH AROMATIC HYDROCARBONS. CATALYST PROMOTION.
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Investigation of the kinetics of alkylation of benzene with propylene in the presence of an aluminum chloride-isopropylbenzene complex, an aluminosilicate catalyst, and modified aluminosilicate catalysts has established that catalyst activity is enhanced
- Kolesnikov,Zaitseva
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p. 754 - 760
(2007/10/02)
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- UTILIZATION OF SUPERCRITICAL FLUID SOLVENT-EFFECTS IN HETEROGENEOUS CATALYSIS.
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Comparative studies on fixed-bed catalytic isomerization of 1-hexene and disproportionation of 1,4-diisopropylbenzene were performed under liquid, gaseous or supercritical conditions. The kinetic measurements show that by variation of pressure in the different fluid states catalytic surface reactions as well as mass transfer effects between catalyst and fluid phase and/or transport processes inside porous catalysts can be influenced in a very sensitive way. Conclusions are drawn in view of new possibilities for the direction of yield and selectivity of multiple reactions, for the prolongation of catalyst lifetime, and the study of deactivation mechanisms on heterogeneous catalysts.
- Tiltscher,Wolf,Schelschshorn
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p. 897 - 900
(2007/10/02)
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- Studies on the Occurence of Hydrogen Transfer. 65. The Significance of Solvents and Solvent Mixtures in the Reductive Cleavage of Compounds of the Type ArSO2Y (Y= OR, Ar', Cl) with Alkali Amalgams
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The dependence of the yields of the reductive fission of hexyl benzenesulfonate and mesitylphenyl sulfone with alkali-metal amalgams (primarily lithium amalgam) was studied under standard conditions in toluene using a series of eight aprotic and six protic solvents as cosolvents.Yields about 5percent were measured in toluene, but addition of equimolar amounts (w.r.t. ester or sulfone) of the alcohols methanol, ethanol, isopropyl alcohol or tert-butyl alcohol as co-solvent raised the yields to 80 - 100percent (Fig. 1).In toluene, portion-wise addition of substoichiometric amounts (w.r.t ester) of the cosolvent DMF, THF, dioxane and isopropyl alcohol resulted in the values recorded in Fig. 2.The observed effects are attributed to the different solubilities of Li+-solutions (of unknown composition) in toluene.A reaction mechanism for the reductive fission of ArSO2Y (Y = OR, Ar', Cl) with alkali-metal amalgams is proposed.
- Horner, Leopold,Schmitt, Rolf-Erhard
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p. 469 - 474
(2007/10/02)
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- Superacid catalyzed preparation of resorcinol from meta-diisopropylbenzene
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Resorcinol is prepared in high yield and purity by an improved process through superacid (such as perfluorinated alkanesulfonic acids of one to eighteen carbon atoms or polymeric perfluorinated resinsulfonic acids, such as acidified Nafion-H, catalyzed cleavage-rearrangement reaction of meta-bis(2-hydroperoxy-2-propyl)-benzene (meta-diisopropylbenzene dihydroperoxide). Part of the process is the preparation of needed meta-diisopropylbenzene in high purity (98-100%) substantially free of other isomers by treating any mixture of diisopropylbenzenes with an excess of anhydrous hydrogen fluoride or a perfluorinated alkanesulfonic acid of one to six carbon atoms and a Lewis acid fluoride, or by alkylating (transalkylating) cumene with a propyl alkylating agent in the aforementioned superacid systems.
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- STUDIEN ZUM VORGANG DER WASSERSTOFFUEBERTRAGUNG 64. ELECTROREDUCTIVE SPALTUNG VON ARYLSULFONSAEUREDERIVATEN UND ARYLSULFONEN MIT ALKALI-AMALGAMEN
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Arylsulfonylchlorides, n-hexylarylsulfonates and di-aryl sulfones (ArSO2Y; Y=Cl, OC6H13, Ar') were cleaved under standard conditions by alkali metal amalgams (M/Hg; M=Li, Na, K) to the corresponding sulfinate salts (ArSO2M) and MY, as shown in Eq. 1.The substrates ArSO2Y in toluene were not cleaved by Li/Hg alone; first on addition of an equimolar amount of i-propanol could conversions of almost 100percent be achieved. (Tables I,II,III).A series of six n-hexylarylsulfonates were studied under standard conditions, to establish the influence of the reaction medium and the amalgam on the course of reaction, (Table II).The sterically hindered arylsulfonates ArSO2OC6H13, (Ar= mesityl, 2,4,6-tri-isopropyl) were "anomalous", i.e. underwent fission at the ring/sulfur bond , as shown by Eq. 2.Table III describes the reductive fission of mesityl-phenylsulfone and dimesitylsulfone.
- Horner, Leopold,Schmitt, Rolf-Erhard
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p. 301 - 308
(2007/10/02)
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- Electrochemical Oxidation of Allenic Hydrocarbons in Acetonitrile
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The anodic oxidation of a variety of alkyl-substituted allenes, terminal and internal ones, has been investigated in acetonitrile. All compounds studied were found to undergo 2e(-) oxidation followed by nucleophilic attack by acetonitrile and water molecules, to form products containing at least two of the following functional groups, C=C, NHCOCH3, C=O, and OH.The effect of various parameters (concentration, electrolyte, oxidation potential, temperature, and anode material) on the electro-oxidation of a model compound (nona-1,2-diene) has been studied and a general mechanistic scheme is presented and discussed.
- Becker, James Y.,Zinger, Baruch
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p. 395 - 402
(2007/10/02)
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- Formylation and Acylation Reactions Catalysed by Trifluoromethanesulphonic Acid
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Regioselective formylation of toluene, m- and p-xylene, and mesitylene has been achieved by carbonylation in trifluoromethanesulphonic acid at CO pressures of 90-125 atm.In the case of cumene, the formylation reaction is in competition with disproportionation to form di- and tri-isopropylbenzenes, leading to a complex product mixture.Slow addition of cyclohexene or cyclopentene to a mixture of benzene and CF3SO3H under a high CO pressure affords 4-cyclohexylbenzaldehyde and 4-cyclopentylbenzaldehyde in 34percent and 33percent yieds, respectively, while 2-methylbut-1-ene gives 2,2,3-trimethylindanone (39percent) under similar conditions.When cyclohexene is mixed with the acid under carbon monoxide (120 atm) before addition of benzene the major products are cyclohexyl phenyl ketone and cyclohexenyl cyclohexyl ketones.
- Booth, Brian L.,El-Fekky, Teymour A.,Noori, Ghazi F. M.
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p. 181 - 186
(2007/10/02)
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- Electrophilic additions to allenes. VI. The role of steric versus electronic effects in the reactions of arenesulphenyl halides with allenes
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The role of steric and electronic effects during the rate and product determining steps for the addition of arenesulphenyl chlorides to 1,3-disubstituted allenes has been briefly examined.Both effects appear to be generally of minimal importance during the rate determinig step.The available rate data indicate the presence of little, if any, build up of positive charge on sulphur.These results are interpreted in terms of an SN2 attack on bivalent sulphur leading to an alkylidenethiiranium ion intermediate.Steric effects are of greater importance in the product determinig step, particularly when the sulphenyl chlorides possess two bulky ortho substituents, as in the case of 2,4,6-triisopropylbenzenesulphenyl chloride.
- Garratt, Dennis G.,Beaulieu, Pierre L.
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p. 2738 - 2744
(2007/10/02)
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