- ON THE REACTIVITY OF V(η-C6H3Me3-1,3,5)2I
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V(η-C6H3Me3-1,3,5)2I reacts with reducing agents such as MeLi, Na or Na to yield the neutral complex V(η-C6H3Me3-1,3,5)2 in 70-75percent yield.Reaction of V(η-C6H3Me3-1,3,5)2I with compounds containing suitable donor atoms such as THF,
- Aviles, T.,Teuben, J.H.
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- Pentadienyl, Cyclohexadienyl, and Arene Uranium Borohydride Complexes
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The compounds (η-2,4-dimethylpentadienyl)U(BH4)3 (2) and (η-6,6-dimethylcyclohexadienyl)2U(BH4)2 (5) were obtained from the reactions of U(BH4)4 (1) with the corresponding potassium dienyl anions; treatment of (η-2,4-Me2C5H5)3U with TlBH4 gave (η-2,4-Me2C
- Baudry, Denise,Bulot, Emmanuelle,Ephritikhine, Michael
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- Direct α-arylation of ketones: The reaction of cyclic ketone enolates with diphenyliodonium triflate
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Diphenyliodonium triflate 1a reacts with the lithium enolates of cyclic ketones 2 (ring size = 5 - 8), in the presence of stoichiometric quantities of copper cyanide, to afford the corresponding α-phenylated ketones 3 or α,α'-diphenylated ketones 4.
- Ryan, John H.,Stang, Peter J.
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- Catalytic Reduction of Alkyl and Aryl Bromides Using Propan-2-ol
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Milstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan-2-ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin-based conditions for these reductions.
- Haibach, Michael C.,Stoltz, Brian M.,Grubbs, Robert H.
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- The Triflic Acid-Catalysed Deacylation and Decarboxylation of Polymethylbenzenecarbonyl Derivatives under Mild Conditions
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Sterically hindered acylarenes are deacylated to arenes in good yields on heating in boiling 1,2-dichloroethane containing a catalytic amount of triflic acid and water.Hindered arenecarboxylic acids undergo decarboxylation under the same conditions to give arenes in high yields.
- Keumi, Takashi,Morita, Toshio,Ozawa, Yoshihiro,Kitajima, Hidehiko
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- One-Electron Oxidation of Alkylbenzenes in Acetonitrile by Photochemically Produced NO3.: Evidence for an Inner-Sphere Mechanism
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The reaction between NO3. and polyalkylbenzenes was studied using 308-nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the alkylbenzenes in acetonitrile solution.For all benzenes, with the exception of monoalkylbenzenes and o- and m-xylene, the reaction with NO3. was found to yield the corresponding radical cations and to proceed in an apparently straightforward bimolecular manner.For monoalkylbenzenes and o- and m-xylene, radicals were seen which are derived from the parents by formal loss of H. from the side chain of the aromatic.This reaction proceeds via a complex between the aromatic and NO3. with the decomposition of the complex being rate determining at higher concentrations of aromatic (rate constants for decomposition between 6 * 105 and 4 * 107 s-1).In the complex, electron transfer from the aromatic to NO3. is suggested to be concerted with deprotonation of the incipient radical cation.Formation of a complex between NO3. and aromatics is likely even in those cases where radical cations are observed, with the assumption that in these cases the complex decomposition rate is greater than 6 * 107 s-1.
- Giacco, Tiziana Del,Baciocchi, Enrico,Steenken, Steen
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- Accessing Pincer Bis(carbene) Ni(IV) Complexes from Ni(II) via Halogen and Halogen Surrogates
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This communication describes the two-electron oxidation of (DIPPCCC)NiX (DIPPCCC = bis(diisopropylphenyl-benzimidazol-2-ylidene)phenyl); X = Cl or Br) with halogen and halogen surrogates to form (DIPPCCC)NiX3. These complexes represent a rare oxidation state of nickel, as well as an unprecedented reaction pathway to access these species through Br2 and halogen surrogate (benzyltrimethylammonium tribromide). The NiIV complexes have been characterized by a suite of spectroscopic techniques and can readily reduce to the NiII counterpart, allowing for cycling between the NiII/NiIV oxidation states.
- Martinez, Gabriel Espinosa,Ocampo, Cristian,Park, Yun Ji,Fout, Alison R.
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- Selective and Mild Deacylation of Hindered Acylarenes with Aqueous Trifluoroacetic Acid
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Sterically hindered acylarenes are deacylated to arenes in quantitative yields on heating in boiling 85percent trifluoroacetic acid.Hindered arenecarboxylic acids undergo decarboxylation under the same conditions to give arenes in high yields.
- Keumi, Takashi,Morita, Toshio,Inui, Yoko,Teshima, Naomi,Kitajima, Hidehiko
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- Acetone and acetaldehyde oligomerization on TiO2 surfaces
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Acetone undergoes aldol condensation and cyclization reactions on TiO2 to form mesitylene (1,3,5-trimethylbenzene) below 400 K. The reaction rate is slow on pure anatase TiO2, but on Degussa P25, a mixture of anatase and rutile, more than 20% of a monolayer of acetone forms mesitylene during temperature-programmed desorption or hydrogenation. Other C5-C9 hydrocarbon products also form on both oxidized and reduced TiO2, whereas hexene forms only on reduced TiO2. Acetaldehyde undergoes aldol condensation on both types of TiO2; acetaldehyde either desorbs or forms dimeric condensation products on anatase. However, on Degussa P25 TiO2, trimeric condensation products, higher molecular weight compounds, and coke also form. In addition, C5H8, C5H10, C6H10, and C9H14 form as secondary reaction products of aldol condensation. Surface concentrations of acetaldehyde and acetone are higher on Degussa P25 than on anatase TiO2. Degussa P25 has more sites that catalyze aldolization, and it has more acid sites. These condensation reactions, which take place at relatively low temperature, may be partly responsible for deactivation of Degussa P25 during photocatalytic oxidation.
- Luo, Shengcheng,Falconer, John L.
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- Reactivity of 17-, 18-, and 19-Electron Cationic Complexes Generated by the Electrochemical Oxidation of Tricarbonyl(mesitylene)tungsten
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The electrochemical oxidation of (mesitylene)W(CO)3 (W) in MeCN produces the 17-electron complex W+, which reacts very rapidly with solvent (S) or tri-n-butyl phosphite (P) to give 19-electron species (WS+, WP+) that undergo spontaneous further oxidation to the 18-electron analogues (WS2+, WP2+). The identities of WS2+ and WP2+ were established by voltammetric, IR spectroelectrochemical, and NMR experiments. Although the 17-electron ? 19-electron transformation is not directly observable, digital simulation techniques allowed selection of a probable mechanism and semiquantitative determination of the rate and equilibrium parameters describing the interconversion of the 17-, 18-, and 19-electron species: W+ + S ? WS+, k ? 105 M-1 s-1, Keq ? 10-1 M-1; W+ + P ? WP+, k ? 107 M-1 s-1, Keq ? 3 × 103 M-1 at 298 K. The related 18-electron complex WS2+ is quite reactive, but orders of magnitude less so than W+ and WS+. Experiments with (mesitylene)Cr(CO)3 (Cr) suggest that associative attack by MeCN at the 17-electron Cr+ is 104 times slower than attack at the W+ analogue. This study illustrates the power of digital simulation techniques for interpreting complex mechanistic schemes and characterizing important but unobservable reaction intermediates. Electrochemical oxidation of (arene)W(CO)3 occurs without loss of arene or CO ligands, suggesting that the electroactivation of these complexes may have useful synthetic applications; this contrasts sharply with (arene)Cr(CO)3 analogues, which decompose with loss of arene and CO ligands upon oxidation in MeCN.
- Zhang, Yun,Gosser,Rieger,Sweigart
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- Grignard reagents in ionic solvents: Electron transfer reactions and evidence for facile Br-Mg exchange
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Grignard reagents form persistent solutions in phosphonium ionic liquids possessing O-donor anions and these solutions are excellent reaction media for electron transfer processes and transmetallation reactions. The Royal Society of Chemistry.
- Ramnial, Taramatee,Taylor, Stephanie A.,Clyburne, Jason A. C.,Walsby, Charles J.
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- N-heterocyclic carbene bound nickel(I) complexes and their roles in catalysis
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The new paramagnetic complexes NiI(IMes)2X (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) were prepared from the reaction of Ni(IMes)2 with aryl halides. Products that would arise from oxidative addition were not observed. In contrast, NiII(tmiy) 2(X)(Ar) complexes were formed from the oxidative addition of aryl halides to Ni bound by a sterically less hindered NHC ligand, tmiy (tetramethylimidazol-2-ylidene). The paramagnetic NiI(IMes) 2X complexes were compared to known Ni(0) and Ni(II) catalysts for Kumada and Suzuki coupling reactions. Stoichiometric reactions between the NiI(IMes)2X complexes with aryl halides and transmetalating agents were also evaluated.
- Zhang, Kainan,Conda-Sheridan, Martin,R. Cooke, Shayna,Louie, Janis
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- Temperature resolved FTIR spectroscopy of Cr2+/SiO2 catalysts: Acetylene and methylacetylene oligomerisation
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Results related to time-resolved FTIR spectroscopy at variable temperature of acetylene and methylacetylene oligomerization on a model Phillips catalyst were presented. Acetylene and methylacetylene resulted in the immediate formation of benzene and 1,3,5-trimethylbenzene, respectively, without evidence of any measurable intermediate product. This indicated that the active Cr sites were able to coordinate simultaneously three monomers and thus must display a high unsaturative coordination. The results could be an insight of chromium species active in the Phillips catalyst.
- Zecchina,Bertarione,Damin,Scarano,Lamberti,Prestipino,Spoto,Bordiga
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- Highly active, well-defined (cyclopentadiene)(N-heterocyclic carbene)palladium chloride complexes for room-temperature Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions of aryl chlorides and deboronation homocoupling of arylboronic acids
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A new class of well-defined N-heterocyclic carbene (NHC)-(cyclopentadiene) palladium chloride complexes such as CpPd(NHC)Cl wasw synthesized from the readily available starting NHC-palladium(II) chloride dimers. These air-stable, coordinatively saturated NHC-Pd complexes bearing the cyclopentadiene (Cp) unit exhibit high catalytic activity in the room temperature Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions involving unactive aryl chlorides as the substrates. In addition, they are found to be extremely efficient catalysts in the deboronation homocoupling of arylboronic acids at room temperature.
- Jin, Zhong,Guo, Su-Xian,Gu, Xiao-Peng,Qiu, Ling-Ling,Song, Hai-Bing,Fang, Jian-Xin
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- Syntheses and reductions of C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes
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Two C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes, 1-(BMes2)-2-R-1,2-C2B10H10 (1, R = H, 2, R = Ph), were synthesised by lithiation of 1,2-dicarba-closo-dodecaborane and 1-phenyl-1,2-dicarba-closo-dodecaborane, respectively, with n-butyllithium and subsequent reaction with fluorodimesitylborane. These novel compounds were structurally characterised by X-ray crystallography. Compounds 1 and 2 are hydrolysed on prolonged exposure to air to give mesitylene and boronic acids 1-(B(OH)2)-2-R-1,2-C2B10H10 (3, R = H, 4, R = Ph respectively). Addition of fluoride anions to 1 and 2 resulted in boryl-carborane bond cleavage to give dimesitylborinic acid HOBMes2. UV absorption bands at 318-333 nm were observed for 1 and 2 corresponding to local π-π-transitions within the dimesitylboryl groups while visible emissions at 541-664 nm with Stokes shifts of 11 920-16 170 cm-1 were attributed to intramolecular charge transfer transitions between the mesityl and cluster groups. Compound 2 was shown by cyclic voltammetry to form a stable dianion on reduction. NMR spectra for the dianion [2]2- were recorded from solutions generated by reductions of 2 with alkali metals and compared with NMR spectra from reductions of 1,2-diphenyl-ortho-carborane 5. On the basis of observed and computed 11B NMR shifts, these nido-dianions contain bowl-shaped cluster geometries. The carborane is viewed as the electron-acceptor and the mesityl group is the electron-donor in C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes.
- Kahlert, Jan,B?hling, Lena,Brockhinke, Andreas,Stammler, Hans-Georg,Neumann, Beate,Rendina, Louis M.,Low, Paul J.,Weber, Lothar,Fox, Mark A.
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- Characterization of the extra-large-pore zeolite UTD-1
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The molecular sieve UTD-1 is investigated using scanning and transmission electron microscopies (TEM), solid-state NMR spectroscopy, electron (ED) and X-ray diffraction (XRD), adsorption studies, and catalytic test reactions. The results confirm that UTD-1 is the first high-silica zeolite to contain a one;dimensional, extra-large 14-ring pore system. TEM and ED show that UTD-1 is faulted along the (002) planes. Simulations of XRD patterns of faulted structures using DIFFaX indicate that the XRD pattern of a framework containing the so-called double crankshaft chains is in better agreement with the experimental pattern than a framework with the narsarsukite chains previously reported. Thermal/hydrothermal stability studies show that UTD-1 has similar stability to other medium- and large-pore, high-silica zeolites. The ratio of isomerization to disproportionation, and the distribution of trimethylbenzene isomers in the m-xylene isomerization test reaction from UTD-1 are similar to those obtained from other large-pore zeolites (zeolites Y or L). However, UTD-1 shows a p-/o-xylene ratio of products below one.The molecular sieve UTD-1 is investigated using scanning and transmission electron microscopies (TEM), solid-state NMR spectroscopy, electron (ED) and X-ray diffraction (XRD), adsorption studies, and catalytic test reactions. The results confirm that UTD-1 is the first high-silica zeolite to contain a one-dimensional, extra-large 14-ring pore system. TEM and ED show that UTD-1 is faulted along the (002) planes. Simulations of XRD patterns of faulted structures using DIFFaX indicate that the XRD pattern of a framework containing the so-called double crankshaft chains is in better agreement with the experimental pattern than a framework with the narsarsukite chains previously reported. Thermal/hydrothermal stability studies show that UTD-1 has similar stability to other medium-and large-pore, high-silica zeolites. The ratio of isomerization to disproportionation, and the distribution of trimethylbenzene isomers in the m-xylene isomerization test reaction from UTD-1 are similar to those obtained from other large-pore zeolites (zeolites Y or L). However, UTD-1 shows a p-/o-xylene ratio of products below one.
- Lobo, Raul F.,Tsapatsis, Michael,Freyhardt, Clemens C.,Khodabandeh, Shervin,Wagner, Paul,Chen, Cong-Yan,Balkus Jr., Kenneth J.,Zones, Stacey I.,Davis, Mark E.
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- B(C6F5)3-Catalyzed Transfer of Dihydrogen from One Unsaturated Hydrocarbon to Another
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A transition-metal-free transfer hydrogenation of 1,1-disubstituted alkenes with cyclohexa-1,4-dienes as the formal source of dihydrogen is reported. The process is initiated by B(C6F5)3-mediated hydride abstraction from the dihydrogen surrogate, forming a Bronsted acidic Wheland complex and [HB(C6F5)3]-. A sequence of proton and hydride transfers onto the alkene substrate then yields the alkane. Although several carbenium ion intermediates are involved, competing reaction channels, such as dihydrogen release and cationic dimerization of reactants, are largely suppressed by the use of a cyclohexa-1,4-diene with methyl groups at the C1 and C5 as well as at the C3 position, the site of hydride abstraction. The alkene concentration is another crucial factor. The various reaction pathways were computationally analyzed, leading to a mechanistic picture that is in full agreement with the experimental observations.
- Chatterjee, Indranil,Qu, Zheng-Wang,Grimme, Stefan,Oestreich, Martin
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- Strategy for Selective Csp2-F and Csp2-Csp2Formations from Organoplatinum Complexes
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By changing the parameters of fluorination reaction of bisaryl-platinum(II) complexes, each possible competitive pathway of Ar-Ar and Ar-F formation can be selectively controlled. It was discovered that steric hindrance, type of fluorinating reagent, and
- Sarkissian, Elin,Golbon Haghighi, Mohsen
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- Cycloaddition of Carbon Dioxide to Propyne over Supported Rh4 and Fe2Rh4 Carbonyl Cluster-derived Catalysts
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Rh4 and Fe2Rh4 carbonyl cluster-derived catalysts supported on selected metal oxides such as TiO2, Al2O3, and ZrO2 exhibit catalytic activity in the formation of 4,6-dimethyl-2-pyrone by the cycloaddition of carbon dioxide to propyne under moderate conditions.
- Pillai, S. Muthukumaru,Ohnishi, Ryuichiro,Ichikawa, Masaru
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- Tailoring the Morphology of MTW Zeolite Mesocrystals: Intertwined Classical/Nonclassical Crystallization
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The morphology and porosity of zeolite play a significant role in the activity and selectivity of catalytic reactions. It is a dream to optionally modulate zeolite morphology by regulating the crystallization process on the basis of comprehensively understanding the mechanisms. Herein, a series of MTW zeolite mesocrystals can be consciously fabricated with morphologies from a dense structure to a loose one of an oriented nanocrystallite aggregate by changing the H2O/SiO2 ratio. Their intertwined classical/nonclassical crystallization processes are investigated comprehensively. The results indicate that the crystallization of MTW zeolite takes place by a chain of events, including the formation of wormlike particles (WLPs), their aggregation, and crystallization of aggregates. MTW with a loose structure mainly crystallizes by an internal reorganization after a fast aggregation of WLPs in a concentrated system. On the other hand, the dense structure of MTW is realized via the co-occurrence of a coalescence of the participating WLPs during its crystal growth with a slower rate in a dilute system. Moreover, the advantages of MTW with a loose structure are confirmed through cumene cracking and 1,2,4-trimethylbenzene transformation. This method could pave the way for the synthesis of other zeolites with diverse morphologies and/or mesoporosities via subtle regulation of the crystallization pathway.
- Zhao, Yang,Zhang, Hongbin,Wang, Peicheng,Xue, Fangqi,Ye, Zhaoqi,Zhang, Yahong,Tang, Yi
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- Ultrafast Relaxation and Electron Transfer in Optically Prepared "Simple" Ion Pairs
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An extensive investigation of the ultrafast pump-probe spectroscopy of the charge-transfer band of the mesitylene/Br EDA complex and related complexes in various solvents and over a broad range of UV, visible, and near-IR probe wavelangths is described.The data allow for a measurement of the charge-recombination kinetics which exhibits a distribution of rate constants, including an initial very fast component (τca.1 ps),a factor of >1000 slower component, and intermediate-rate processes.The nonexponential kinetics may be associated with a distribution of arene+/Br- acceptor geometries in the initially prepared state of the ion pair.The complex kinetics are discussed in terms of contemporary electron-transfer theory, which indicates that the most likely source of the dramatically nonexponential kinetics is an inner-sphere effect involving specific, configurationally dependent electronic interactions of the donor and acceptor.The reaction kinetics particularly at early times, is not strongly sensitive to solvent polarity or solvation dynamics, further supporting that mainly the donor/acceptor electronic interactions are dominating the kinetics.The data also reveal features due to the local transition on the transient D+ species in the ion pair and evidence of vibrationally unrelaxed absorption due the initially re-formed complex subsequent to charge recombination.
- Hoermann, Aldo,Jarzeba, Wlodzimierz,Barbara, Paul F.
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- Promising process for synthesis of 3,5-xylenol from isophorone
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A thermocatalytic process for the synthesis of 3,5-xylenol from isophorone over a silicon dioxide catalyst promoted by iron oxides was developed. The process holds promise for commercialization. Nauka/Interperiodica 2006.
- Kirichenko,Glazunova,Kirichenko,Dzhemilev
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- Transsulfonylation between Aromatic Sulfones and Arenes.
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Transsulfonylation between various aromatic and arenes catalyzed by triflic acid at 150 deg C are described.The structural requirements for the occurence of the transsulfonylations are shown to be similar to those for the transacylations that were described earlier.However, in view of the inherent differences in the properties of aromatic ketones and sulfones with respect to conjugation of the carbonyl and sulfonyl groups with the aromatic ring, a different rationale for the transsulfonylation reactions is offered.A mechanism is suggested that rationalizes the similar structural requirements for transacylations in terms of steric relief of strain in the reactions of certain ketones and sulfones.
- El-Khawaga, Ahmed M.,Roberts, Royston M.
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- Kinetics of Sulphodeacylation of Dimesityl Ketone: a Dual-path Sequence of First-order Reactions
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The kinetics of the conversion in 89.8percent (w/w) sulphuric acid of 2,2',4,4',6,6'-hexamethylbenzophenone (A) into 2,4,6-trimethylbenzenesulphonic acid (D) were measured, and analysed in terms of the dual-path first-order reaction sequence , where (B) and (C) are, respectively, 2,4,6-trimethylbenzoic acid and 1,3,5-trimethylbenzene.
- Farooqi, Jameel A.,Gore, Peter H.,Saad, Esmat F.,Waters, David N.,Moxon, Gerald F.
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- METAL COMPLEXES WITH ALLYLANILINES. IV. SYNTHESIS AND REACTIVITY OF RHODIUM(I) COMPLEXES WITH 2-ALLYLANILINE AND N-ALLYLANILINE
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The reaction of 2-allylaniline (2aa) with 2 (I) in toluene or benzene at room temperature affords the dimer 2 (II) in which the ligand acts as bidentate, being coordinated to the metal through the N atom and the olefinic group.II in CH2Cl2, isomerizes 2aa to trans-2-propenylaniline.This reaction goes also catalytically.Heating of II in benzene affords 2-methyl-indoline.N-Allylaniline (naa) reacts with I to give the deep violet diamagnetic complex Rh2Cl2(naa)3 (III), which is converted slowly into 2.When III is heated with an excess of naa, the ligand is catalytically transformed into propene, azobenzene, N-n-propylaniline, N-i-propylaniline, N-allylideneaniline and aniline, as the more abundant products.Moreover, III reacts with diphenylacetylene to afford 2,5-dihydro-1,2,3-triphenyl-4-methyl-pyrrole.The reaction of III with methylacetylene follows a more complex path, and products of dimerization and trimerization of the alkyne have been isolated.Carbon dioxide influences the oligomerization reaction.
- Aresta, M.,Fazio, M. De
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- Cyclopropanation by Gold- or Zinc-Catalyzed Retro-Buchner Reaction at Room Temperature
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Through the design of a second generation of more reactive 7-substituted 1,3,5-cycloheptatrienes, a room-temperature gold(I)-catalyzed retro-Buchner-cyclopropanation sequence and the first zinc(II)-catalyzed version of this process, which uses inexpensive
- Mato, Mauro,Herlé, Bart,Echavarren, Antonio M.
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- A new peroxo-route for the synthesis of Mg-Zr mixed oxides catalysts: Application in the gas phase acetone self-condensation
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We propose in this manuscript a new peroxo-mediated procedure for preparing magnesia-zirconia mixed oxides, with Mg/Zr molar ratio between 1 and 3, with enhanced distribution of basic sites. The mixed magnesia-zirconia oxides have been prepared from the gelled complex by Pechini-type method. The MgO-ZrO 2 materials have been characterized and used as catalysts for acetone aldol condensation. The proposed preparation method provides a high degree of molecular homogeneity and favours the formation of magnesia-stabilized zirconia phase. Acetone gas-phase self-condensation was carried out over these catalysts as model reaction requiring the presence of basic sites. The condensation yields diacetone alcohol and mesityl oxide as mean C6 products, and phorones, isophorones and mesitylene as C9 products. In comparison to Mg-Zr oxide prepared by co-precipitation, these new materials present better conversions and higher selectivity to linear dimers and trimers (as mesitylene), whereas the selectivity for isophorones is significantly lower.
- Krivtsov, Igor,Faba, Laura,Díaz, Eva,Ordó?ez, Salvador,Avdin, Viacheslav,Khainakov, Sergei,Garcia, Jose R.
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- Merging visible-light photocatalysis and transition-metal catalysis in the copper-catalyzed trifluoromethylation of boronic acids with CF3I
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This communication describes the development of a mild method for the cross-coupling of arylboronic acids with CF3I via the merger of photoredox and Cu catalysis. This method has been applied to the trifluoromethylation of electronically diverse aromatic and heteroaromatic substrates and tolerates many common functional groups.
- Ye, Yingda,Sanford, Melanie S.
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- Relative Reactivities of Amide, Diphenylphosphide, and Diphenylarsenide Ions toward Aryl Radicals
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Competition experiments have been carried out in liquid ammonia at reflux temperature to determine the relative rate constants for the coupling reactions of amide (NH2-), diphenylphosphide (Ph2P-), and diphenylarsenide (Ph2As-) toward aryl radicals.It is proposed that these nucleophiles react under photostimulation with halo aromatic substrates through an SRN1 mechanism of aromatic substitution.Relative rate constants of NH2- vs.Ph2P- ions toward 2,4,6-trimethylphenyl radicals and Ph2P- vs.Ph2As- ios toward 2-quinolyl radicals have been determined.The results here reported indicate that NH2- (1.00) - (6.4) = Ph2As- (6.4).The fact that there is not a difference in the rate constants of Ph2P- vs.Ph2As- suggests that both nucleophiles react at diffusion-controlled rate.In competition experiments of Ph2P- vs.Ph2As- ions toward phenyl radicals, it was found that Ph2P- (1.00) > Ph2As- (0.44).The decrease of the Ph2As- ion reactivity is attributed to the reversible coupling of this nucleophile with phenyl radicals.
- Alonso, Ruben A.,Bardon, Alicia,Rossi, Roberto A.
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- Reaction of mesitylenetetracobaltnonacarbonyl with 2. Syntheses and structures of the clusters C5H5(CO)2MoCo3(CO)6(μ-CO)3 and (C5H5)2(CO)3Mo2Co2(CO)4(μ-CO)3
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Interaction of (mesitylene)Co4(CO)9 (I) with 2 (II) has been shown to result in a mixture of clusters Cp(CO)2MoCo3(CO)6(μ-CO)3 (III) and Cp2(CO)3Mo2Co2(CO)4(μ-CO)3 (IV).Complexes III and IV have also been obtained by an independent synthesis fr
- Kaganovich, V. S.,Slovokhotov, Yu. L.,Mironov, A. V.,Struchkov, Yu. T.,Rybinskaya, M. I.
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- The dimesitylenevanadium(I) cation
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Hexacarbonylvanadium oxidizes dimesitylenevanadium(0) to the [V(C6H3(CH3)3)2] + cation, the compound [V(C6H3- (CH3)3)2][V(CO)6/s
- Calderazzo, Fausto
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- A new method to prepare functional phosphines through steady-state photolysis of triarylphosphines
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The steady-state photolysis of triarylphosphine, Ar3P, was carried out using a xenon lamp or a high-pressure mercury lamp under an argon atmosphere in a solvent containing a functional group, CH3X. Gas chromatograph-mass spectroscopic analysis on the photolysis showed that a phosphine to which the functional group from the solvent is incorporated, Ar2PCH2X, was formed in a moderate yield, along with tetraaryldiphosphine, Ar2PPAr2. The product, Ar2PCH2CN, from the photolysis in acetonitrile (X=CN) was isolated by column chromatography. In the photolysis in other solvents tried here (ethyl acetate, acetone, 2-butanone, and 3,3-dimethyl-2-butanone), Ar2PCH2X formed in the reaction mixture was so labile on a silica-gel column that it was treated with S8 powder to convert to the corresponding phosphine sulfide, Ar2P(=S)CH2X. The resulting phosphine sulfide was isolated by column chromatography. The isolated products in these reactions, Ar2PCH2CN and Ar2P(=S)CH2X, were characterized by 1H, 13C, and 31P NMR spectroscopy, IR spectroscopy, and elemental analysis or high-resolution mass spectroscopy. The formation of Ar2PCH2X as well as Ar2PPAr2 is explained by homolytic cleavage of a P-C bond of Ar3P in the photoexcited state. This reactivity of Ar3P in the photoexcited state is in sharp contrast to that exerted under aerobic conditions, where Ar3P in the photoexcited state donates readily an electron to oxygen producing the radical cation, Ar3P·+. This photoreaction, which affords a functional phosphine, Ar2PCH2X, in one-pot with generating very small amounts of unidentified side products, has potential for use in preparing functional phosphines.
- Yasui, Shinro,Ando, Taro,Ozaki, Masashi,Ogawa, Yuya,Shioji, Kosei
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- SOME CATALYTIC PROPERTIES OF Rh(diphos)(η-BPh4)
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The covalent complex Rh(diphos)(η-BPh4) (I) reacts with CO in polar solvents to afford the cationic dicarbonyl cis-(BPh4).I is an effective catalyst for methylacetylene oligomerization and allene polymerization.In the presence of CO2 and methylacetylene, I affords 4,6-dimethyl-2-pyrone.
- Albano, P.,Aresta, M.
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- Infrared and Raman spectra, ab initio calculations and conformational studies of ethyl iodosilane
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Ethyl iodosilane (CH3CH2-SiH2I) was synthesized for the first time. Infrared spectra were recorded in the vapour, amorphous and crystalline solid phases in MIR and FIR regions. Additional MIR spectra of the compound isolated in argon and nitrogen matrices were obtained at 5 K. Raman spectra of the liquid, excited by argon and by Nd3+ YAG lasers, were recorded at room temperature including polarization measurements. The spectra were studied in an extended temperature range 173-353 K and a ΔH value of 1.2 ± 0.3 kJ mol-1 was obtained with gauche being the low energy conformer. Spectra of the amorphous and crystalline solids were obtained at liquid nitrogen temperature. Ethyl iodosilane exists in an equilibrium between anti and gauche conformers, in the vapour, liquid and amorphous states. After careful annealing the amorphous solid on a cold Cu finger (Raman) or on a CsI or Si window (infrared) to 160 K a partly crystalline solid was formed. A number of IR and Raman bands were reduced in intensity after annealing, although they did not vanish completely. From comparison between the observed and calculated vibrational modes it was apparent that the gauche conformer was present in the crystal. The sample was mixed with argon and nitrogen in a ratio 1:1000, deposited on a window at 5 or 10 K and annealed to temperatures between 5 and 36 K (argon) and 5-30 K (nitrogen). IR bands attributed to the anti and gauche conformers were reduced and increased in intensities, respectively. Thus, the gauche conformer was the low energy conformer in the matrices and probably also in the vapour phase. Ab initio calculations were performed at the RHF/3-21 G* and 6-311G* B3LYPs and gave optimized geometries, IR and Raman intensities and vibrational frequencies for the anti and gauche conformers. An enthalpy difference of 0.9 kJ mol-1 was obtained from the calculations with gauche being the low energy conformer. After scaling, a reasonably good agreement between the experimental and calculated wavenumbers for the anti and gauche conformer was obtained. The spectra of ethyl iodosilane were closely related to those of the corresponding ethyl fluoro, ethyl chloro and ethyl bromosilane.
- Aleksa, Valdemaras,Powell, David L.,Gruodis, Alytis,Hassler, Karl,Hummeltenberg, Reinhard,Herzog, Klaus,Salzer, Reiner,Klaeboe, Peter,Nielsen, Claus J.
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- Nickel-catalyzed cross-coupling of anisole derivatives with trimethylaluminum through the cleavage of carbonoxygen bonds
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Nickel-catalyzed cross-coupling of methoxyarenes with trimethylaluminum is described. The use of 1,3-dicyclohexylimidazol-2-ylidene as a ligand and NaO'Bu as a base promotes the methylation of anisole derivatives via the cleavage of normally unreactive aryl carbonoxygen bonds.
- Morioka, Toshifumi,Nishizawa, Akihiro,Nakamura, Keisuke,Tobisu, Mamoru,Chatani, Naoto
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- Perfluoroalkylated Main-Group Element Lewis Acids as Catalysts in Transfer Hydrogenation
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Transfer hydrogenation plays an important part in organic chemistry. Recently, strong Lewis acids like B(C6F5)3 have been introduced as a catalyst for these reactions. We successfully employed the Lewis acid (C2F5)3PF2 as a catalyst in the transfer hydrogenation between 1,3,5-trimethylcyclohexa-1,4-diene and 1,1-diphenylethylene. Surprisingly, the treatment of the diene alone with a catalytic amount of (C2F5)3PF2 led to a quantitative dismutation to mesitylene and 1,3,5-trimethylcyclohexane. With B(C6F5)3, there was a solvent-dependency: in CH2Cl2 mainly the dismutation products were obtained, while in toluene the evolution of H2 was observed. Additionally, the catalytic activity of various perfluoroalkylated germanes and silanes was tested.
- Bader, Julia,Maier, Alexander F. G.,Paradies, Jan,Hoge, Berthold
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- Reaction of Methanol and Acetone over Metal Ion-Exchanged Forms of Fluoro Tetrasilicic Mica to Form Methyl Vinyl Ketone
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Methyl vinyl ketone was obtained at 30-40percent selectivity by the reaction of methanol and acetone at 350 deg.C over Ti(IV)-, Cr(III)-, Mn(II)-, and Sn(IV)-exchanged forms of fluoro tetrasilicic mica (TSM).The addition of oxygen into the feed increased the conversion of acetone and the reaction over Ti(IV)-TSM converted 11percent of acetone fed into methyl vinyl ketone at 85percent selectivity.
- Wang, Fey-long,Ueda, Wataru,Morikawa, Yutaka,Ikawa, Tsuneo
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- Phosphoric acid-modified commercial kieselguhr supported palladium nanoparticles as efficient catalysts for low-temperature hydrodeoxygenation of lignin derivatives in water
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Efficient production of high value-added chemicals and biofuels via low-temperature chemoselective HDO of lignin derivatives in water is still a challenge. Here, we construct a low-cost, active and stable Pd/PCE catalyst using phosphoric acid-modified commercial Celite (PCE) as the support, and this catalyst exhibits excellent activity in low-temperature HDO of vanillin as well as other lignin derivatives in water. The superior catalytic performance is due to the presence of P species on the surface of Pd/PCE, accelerating the selective conversion of the intermediate into the final product. Detailed experimental and mechanistic studies reveal that the rapid conversion of the intermediate to the final product proceeds via a free-radical process in an interfacial microenvironment created by intimate interacting between the P species and Pd NPs. The insights of this work provide a new low-cost catalytic system for efficient production of valuable chemicals and future biofuels from lignin derivatives. This journal is
- Cui, Yuntong,Liu, Zhaohui,Ran, Jiansu,Wang, Jianjian,Yangcheng, Ruixue
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p. 1570 - 1577
(2022/03/14)
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- Protodesilylation of Arylsilanes by Visible-Light Photocatalysis
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The first visible-light-mediated photocatalytic, metal- and base-free protodesilylation of arylsilanes is presented. The C(sp2)-Si bond cleavage process is catalyzed by a 5 mol % loading of a commercially available acridinium salt upon blue-light irradiation. Two simple approaches have been identified employing either aerobic or hydrogen atom transfer cocatalytic conditions, which enable the efficient and selective desilylation of a broad variety of simple and complex arylsilanes under mild conditions.
- García Manche?o, Olga,Kuhlmann, Jan H.,Uygur, Mustafa
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supporting information
p. 1689 - 1694
(2022/03/14)
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- Metal-Free Heterogeneous Semiconductor for Visible-Light Photocatalytic Decarboxylation of Carboxylic Acids
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A suitable protocol for the photocatalytic decarboxylation of carboxylic acids was developed with metal-free ceramic boron carbon nitrides (BCN). With visible light irradiation, BCN oxidize carboxylic acids to give carbon-centered radicals, which were trapped by hydrogen atom donors or employed in the construction of the carbon-carbon bond. In this system, both (hetero)aromatic and aliphatic acids proceed the decarboxylation smoothly, and C-H, C-D, and C-C bonds are formed in moderate to high yields (35 examples, yield up to 93%). Control experiments support a radical process, and isotopic experiments show that methanol is employed as the hydrogen atom donor. Recycle tests and gram-scale reaction elucidate the practicability of the heterogeneous ceramic BCN photoredox system. It provides an alternative to homogeneous catalysts in the valuable carbon radical intermediates formation. Moreover, the metal-free system is also applicable to late-stage functionalization of anti-inflammatory drugs, such as naproxen and ibuprofen, which enrich the chemical toolbox.
- Shi, Jiale,Yuan, Tao,Zheng, Meifang,Wang, Xinchen
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p. 3040 - 3047
(2021/03/09)
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- Ceramic boron carbonitrides for unlocking organic halides with visible light
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Photochemistry provides a sustainable pathway for organic transformations by inducing radical intermediates from substrates through electron transfer process. However, progress is limited by heterogeneous photocatalysts that are required to be efficient, stable, and inexpensive for long-term operation with easy recyclability and product separation. Here, we report that boron carbonitride (BCN) ceramics are such a system and can reduce organic halides, including (het)aryl and alkyl halides, with visible light irradiation. Cross-coupling of halides to afford new C-H, C-C, and C-S bonds can proceed at ambient reaction conditions. Hydrogen, (het)aryl, and sulfonyl groups were introduced into the arenes and heteroarenes at the designed positions by means of mesolytic C-X (carbon-halogen) bond cleavage in the absence of any metal-based catalysts or ligands. BCN can be used not only for half reactions, like reduction reactions with a sacrificial agent, but also redox reactions through oxidative and reductive interfacial electron transfer. The BCN photocatalyst shows tolerance to different substituents and conserved activity after five recycles. The apparent metal-free system opens new opportunities for a wide range of organic catalysts using light energy and sustainable materials, which are metal-free, inexpensive and stable. This journal is
- Yuan, Tao,Zheng, Meifang,Antonietti, Markus,Wang, Xinchen
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p. 6323 - 6332
(2021/05/19)
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- Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers
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Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylationviaradical-mediated pathways, with optimized conditions that only require the photocatalyst and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.
- Shon, Jong-Hwa,Kim, Dooyoung,Rathnayake, Manjula D.,Sittel, Steven,Weaver, Jimmie,Teets, Thomas S.
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p. 4069 - 4078
(2021/04/06)
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- Metal-Free Photoredox-Catalyzed Hydrodefluorination of Fluoroarenes Utilizing Amide Solvent as Reductant
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A metal-free photoredox-catalyzed hydrodefluorination of fluoroarenes was achieved by using N,N,N’,N’-tetramethyl-para-phenylenediamine (1) as a strong photoreduction catalyst. This reaction was applicable not only to electron-rich monofluoroarenes but also to polyfluoroarenes to afford non-fluorinated arenes. The experimental mechanistic studies indicated that the amide solvent NMP plays an important role for regeneration of the photocatalyst, enabling additive-free photoreduction catalysis.
- Toriumi, Naoyuki,Yamashita, Kazuya,Iwasawa, Nobuharu
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supporting information
p. 12635 - 12641
(2021/08/03)
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- Visible-Light-Induced, Base-Promoted Transition-Metal-Free Dehalogenation of Aryl Fluorides, Chlorides, Bromides, and Iodides
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We report a simple and efficient visible-light-induced transition-metal-free hydrogenation of aryl halides. The combined visible light and base system is used to initiate the desired radical-mediated hydrogenation. A variety of aryl fluorides, chlorides, bromides, and iodides could be reduced to the corresponding (hetero)arenes with excellent yields under mild conditions. Various functional groups and other heterocyclic compounds are tolerated.
- Ding, Ting-Hui,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 3084 - 3088
(2020/04/10)
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- Discovery and characterization of an acridine radical photoreductant
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Photoinduced electron transfer (PET) is a phenomenon whereby the absorption of light by a chemical species provides an energetic driving force for an electron-transfer reaction1–4. This mechanism is relevant in many areas of chemistry, including the study of natural and artificial photosynthesis, photovoltaics and photosensitive materials. In recent years, research in the area of photoredox catalysis has enabled the use of PET for the catalytic generation of both neutral and charged organic free-radical species. These technologies have enabled previously inaccessible chemical transformations and have been widely used in both academic and industrial settings. Such reactions are often catalysed by visible-light-absorbing organic molecules or transition-metal complexes of ruthenium, iridium, chromium or copper5,6. Although various closed-shell organic molecules have been shown to behave as competent electron-transfer catalysts in photoredox reactions, there are only limited reports of PET reactions involving neutral organic radicals as excited-state donors or acceptors. This is unsurprising because the lifetimes of doublet excited states of neutral organic radicals are typically several orders of magnitude shorter than the singlet lifetimes of known transition-metal photoredox catalysts7–11. Here we document the discovery, characterization and reactivity of a neutral acridine radical with a maximum excited-state oxidation potential of ?3.36 volts versus a saturated calomel electrode, which is similarly reducing to elemental lithium, making this radical one of the most potent chemical reductants reported12. Spectroscopic, computational and chemical studies indicate that the formation of a twisted intramolecular charge-transfer species enables the population of higher-energy doublet excited states, leading to the observed potent photoreducing behaviour. We demonstrate that this catalytically generated PET catalyst facilitates several chemical reactions that typically require alkali metal reductants and can be used in other organic transformations that require dissolving metal reductants.
- MacKenzie, Ian A.,Wang, Leifeng,Onuska, Nicholas P. R.,Williams, Olivia F.,Begam, Khadiza,Moran, Andrew M.,Dunietz, Barry D.,Nicewicz, David A.
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- Exploiting the radical reactivity of diazaphosphinanes in hydrodehalogenations and cascade cyclizations
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The remarkable reducibility of diazaphosphinanes has been extensively applied in various hydrogenations, based on and yet limited by their well-known hydridic reactivity. Here we exploited their unprecedented radical reactivity to implement hydrodehalogenations and cascade cyclizations originally inaccessible by hydride transfer. These reactions feature a broad substrate scope, high efficiency and simplicity of manipulation. Mechanistic studies suggested a radical chain process in which a phosphinyl radical is generated in a catalytic cycle via hydrogen-atom transfer from diazaphosphinanes. The radical reactivity of diazaphosphinanes disclosed here differs from their well-established hydridic reactivity, and hence, opens a new avenue for diazaphosphinane applications in organic syntheses.
- Cheng, Jin-Pei,Yang, Jin-Dong,Zhang, Jingjing
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p. 4786 - 4790
(2020/06/18)
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- Effects of steam on toluene hydrogenation over a Ni catalyst
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The catalytic toluene hydrogenation over Ni/SiO2 was carried out using H2 or a H2/H2O mixture. The toluene conversion and MCH selectivity were evaluated under partial steam pressures 0?10 kPa, at H2/t
- Atsumi, Ryosuke,Kobayashi, Keisuke,Xieli, Cui,Nanba, Tetsuya,Matsumoto, Hideyuki,Matsuda, Keigo,Tsujimura, Taku
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- Mechanistic Interrogation of Alkyne Hydroarylations Catalyzed by Highly Reduced, Single-Component Cobalt Complexes
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Highly reactive catalysts for ortho-hydroarylations of alkynes have previously been reported to result from activation of CoBr2 by Grignard reagents, but the operative mechanism and identity of the active cobalt species have been undefined. A mechanistic analysis of a related system, involving hydroarylations of a (N-aryl)aryl ethanimine with diphenylacetylene, was performed using isolable reduced Co complexes. Studies of the stoichiometric reaction of Co(I) or Co(II) precursors with CyMgCl implicated catalyst initiation via a β-H elimination/deprotonation pathway. The resulting single-component Co(-I) complex is proposed as the direct pre-catalyst. Michaelis-Menten enzyme kinetic studies provide mechanistic details regarding the catalytic dependence on substrate. The (N-aryl)aryl ethanimine substrate exhibited saturation-like behavior, whereas alkyne demonstrated a complex dependency; rate inhibition and promotion depend on the relative concentration of alkyne to imine. Activation of the aryl C-H bond occurred only in the presence of coordinated alkyne, which suggests operation of a concerted metalation-deprotonation (CMD) mechanism. Small primary isotope effects are consistent with a rate-determining C-H cleavage. Off-cycle olefin isomerization catalyzed by the same Co(-I) active species appears to be responsible for the observed Z-selectivity.
- Suslick, Benjamin A.,Tilley, T. Don
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supporting information
p. 11203 - 11218
(2020/07/08)
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- Visible-Light-Induced Ni-Catalyzed Radical Borylation of Chloroarenes
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A highly selective and general photoinduced C-Cl borylation protocol that employs [Ni(IMes)2] (IMes = 1,3-dimesitylimidazoline-2-ylidene) for the radical borylation of chloroarenes is reported. This photoinduced system operates with visible light (400 nm) and achieves borylation of a wide range of chloroarenes with B2pin2 at room temperature in excellent yields and with high selectivity, thereby demonstrating its broad utility and functional group tolerance. Mechanistic investigations suggest that the borylation reactions proceed via a radical process. EPR studies demonstrate that [Ni(IMes)2] undergoes very fast chlorine atom abstraction from aryl chlorides to give [NiI(IMes)2Cl] and aryl radicals. Control experiments indicate that light promotes the reaction of [NiI(IMes)2Cl] with aryl chlorides generating additional aryl radicals and [NiII(IMes)2Cl2]. The aryl radicals react with an anionic sp2-sp3 diborane [B2pin2(OMe)]- formed from B2pin2 and KOMe to yield the corresponding borylation product and the [Bpin(OMe)]?- radical anion, which reduces [NiII(IMes)2Cl2] under irradiation to regenerate [NiI(IMes)2Cl] and [Ni(IMes)2] for the next catalytic cycle.
- Tian, Ya-Ming,Guo, Xiao-Ning,Krummenacher, Ivo,Wu, Zhu,Nitsch, J?rn,Braunschweig, Holger,Radius, Udo,Marder, Todd B.
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supporting information
p. 18231 - 18242
(2020/11/02)
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- Highly-chemoselective step-down reduction of carboxylic acids to aromatic hydrocarbons: Via palladium catalysis
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Aryl carboxylic acids are among the most abundant substrates in chemical synthesis and represent a perfect example of a traceless directing group that is central to many processes in the preparation of pharmaceuticals, natural products and polymers. Herein, we describe a highly selective method for the direct step-down reduction of carboxylic acids to arenes, proceeding via well-defined Pd(0)/(ii) catalytic cycle. The method shows a remarkably broad substrate scope, enabling to direct the classical acyl reduction towards selective decarbonylation by a redox-neutral mechanism. The utility of this reaction is highlighted in the direct defunctionalization of pharmaceuticals and natural products, and further emphasized in a range of traceless processes using removable carboxylic acids under mild, redox-neutral conditions orthogonal to protodecarboxylation. Extensive DFT computations were conducted to demonstrate preferred selectivity for the reversible oxidative addition and indicated that a versatile hydrogen atom transfer (HAT) pathway is operable.
- Liu, Chengwei,Qin, Zhi-Xin,Ji, Chong-Lei,Hong, Xin,Szostak, Michal
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p. 5736 - 5742
(2019/06/18)
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- The Tandem Photoredox Catalysis Mechanism of [Ir(ppy)2(dtb-bpy)]+ Enabling Access to Energy Demanding Organic Substrates
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We report the discovery of a tandem catalytic process to reduce energy demanding substrates, using the [Ir(ppy)2(dtb-bpy)]+ (1+) photocatalyst. The immediate products of photoinitiated electron transfer (PET) between 1+ and triethylamine (TEA) undergo subsequent reactions to generate a previously unknown, highly reducing species (2). Formation of 2 occurs via reduction and semisaturation of the ancillary dtb-bpy ligand, where the TEA radical cation serves as an effective hydrogen atom donor, confirmed by nuclear magnetic resonance, mass spectrometry, and deuterium labeling experiments. Steady-state and time-resolved luminescence and absorption studies reveal that upon irradiation, 2 undergoes electron transfer or proton-coupled electron transfer (PCET) with a representative acceptor (N-(diphenylmethylene)-1-phenylmethanamine; S). Turnover of this new photocatalytic cycle occurs along with the reformation of 1+. We rationalize our observations by proposing the first example of a mechanistic pathway where two distinct yet interconnected photoredox cycles provide access to an extended reduction potential window capable of engaging a wide range of energy demanding and synthetically relevant organic substrates including aryl halides.
- Connell, Timothy U.,Fraser, Catherine L.,Czyz, Milena L.,Smith, Zoe M.,Hayne, David J.,Doeven, Egan H.,Agugiaro, Johnny,Wilson, David J. D.,Adcock, Jacqui L.,Scully, Andrew D.,Gómez, Daniel E.,Barnett, Neil W.,Polyzos, Anastasios,Francis, Paul S.
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p. 17646 - 17658
(2019/11/11)
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- Hydrogen bonding promoted simple and clean photo-induced reduction of C-X bond with isopropanol
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We herein report a simple and clean photo-induced metal-free reduction of C-X bond under an atmosphere of air at room temperature. Isopropanol is used as both the reducing reagent and solvent. Various functional groups (acids, esters, alcohols, anilines, phenols, indoles, pyridines, cyano and trifluoromethyl groups) and other heterocyclic compounds are tolerated. Different organic halides (including C-I, C-Br and C-Cl bonds) can be dehalogenated with moderate to excellent yields. Polyhalides are also reduced chemoselectively and efficiently. DFT calculation suggests a six-membered ring transition state via C-X H-O hydrogen bonding to decrease the activation energy.
- Cao, Dawei,Yan, Chaoxian,Zhou, Panpan,Zeng, Huiying,Li, Chao-Jun
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supporting information
p. 767 - 770
(2019/01/21)
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- Synthesis and Characterization of Strong Cyclometalated Iridium Photoreductants for Application in Photocatalytic Aryl Bromide Hydrodebromination
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A series of potent bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands is described. Structure-property analysis reveals that substituent modification of the NacNac ligands has a large effect on the ground-state IrIV/IrIII potential, which shifts cathodically as the NacNac is made more electron-rich. In addition, the excited-state IrIV/?IrIII potentials are ca. 300-500 mV more negative than that of fac-Ir(ppy)3 (ppy = 2-phenylpyridine), indicating that these compounds have much more reducing excited states. Rate constants for excited-state electron transfer between these photosensitizers and benzophenone are -2-3 times faster than fac-Ir(ppy)3, demonstrating that these complexes are both kinetically and thermodynamically more potent for excited-state electron transfer. We use these photosensitizers to optimize a simple reaction procedure for photocatalytic debromination of aryl bromide substrates, which requires only the photosensitizer, blue light, and an amine base, without silanes or other additives that are used in previously reported methods.
- Shon, Jong-Hwa,Sittel, Steven,Teets, Thomas S.
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p. 8646 - 8658
(2019/09/12)
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- Surface Modification of a Supported Pt Catalyst Using Ionic Liquids for Selective Hydrodeoxygenation of Phenols into Arenes under Mild Conditions
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The selective and efficient removal of oxygenated groups from lignin-derived phenols is a critical challenge to utilize lignin as a source for renewable aromatic chemicals. This report describes how surface modification of a zeolite-supported Pt catalyst using ionic liquids (ILs) remarkably increases selectivity for the hydrodeoxygenation (HDO) of phenols into arenes under mild reaction conditions using atmospheric pressure H2. Unmodified Pt/H-ZSM-5 converts phenols into aliphatic species as the major products along with a slight amount of arenes (10 % selectivity). In contrast, the catalyst modified with an IL, 1-butyl-3-methylimidazolium triflate, keeps up to 76 % selectivity for arenes even at a nearly complete conversion of phenols. The IL on the surface of Pt catalyst may offer the adsorption of phenols in an edge-to-face manner onto the surface, thus accelerating the HDO without the ring hydrogenation.
- Ohta, Hidetoshi,Tobayashi, Kanako,Kuroo, Akihiro,Nakatsuka, Mao,Kobayashi, Hirokazu,Fukuoka, Atsushi,Hamasaka, Go,Uozumi, Yasuhiro,Murayama, Haruno,Tokunaga, Makoto,Hayashi, Minoru
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supporting information
p. 14762 - 14766
(2019/11/13)
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- Halogenoborane mediated allene cyclooligomerization
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The halogenoboranes XB(C6F5)2 (X: Cl, Br) react with allene to give a mixture of the cyclotrimer 1,3,5-trimethylenecyclohexane (1) and the related halogenoborylated cyclotetramerization products 3a and 3b. Alkyl-substituted allenes were catalytically cyclotrimerized metal-free by XB(C6F5)2 (X: Cl, Br) to give cis,trans-2,4,6-trialkyl-1,3,5-trimethylenecyclohexanes under mild conditions.
- Tao, Xin,W?lke, Christian,Daniliuc, Constantin G.,Kehr, Gerald,Erker, Gerhard
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p. 2478 - 2482
(2019/02/28)
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- Chemical Imaging of the Binder-Dependent Coke Formation in Zeolite-Based Catalyst Bodies During the Transalkylation of Aromatics
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The choice of binder material, added to a zeolite-based catalyst body, can significantly influence the catalyst performance during a reaction, i. e. its deactivation and selectivity. In this work the influence of the binder in catalyst extrudates on the formation of hydrocarbon deposits was explored during the transalkylation of toluene with 1,2,4-trimethylbenzene (1,2,4-TMB). Using in situ UV-vis micro-spectroscopy and ex situ confocal fluorescence microscopy approach, coke species were revealed to predominantly form on the rim of zeolite crystals within Al2O3-bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al2O3-binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4-TMB in the SiO2-bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals.
- Verkleij, Suzanna P.,Whiting, Gareth T.,Pieper, Denise,Parres Esclapez, Sonia,Li, Shiwen,Mertens, Machteld M.,Janssen, Marcel,Bons, Anton-Jan,Burgers, Martijn,Weckhuysen, Bert M.
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p. 4788 - 4796
(2019/09/17)
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- PROCESS FOR CO-PRODUCTION OF MIXED XYLENES AND HIGH OCTANE C9+ AROMATICS
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Disclosed is a process for producing mixed xylenes and C9+ hydrocarbons in which an aromatic hydrocarbon feedstock comprising benzene and/or toluene is contacted with an alkylating agent comprising methanol and/or dimethyl ether under alkylation conditions in the presence of an alkylation catalyst to produce an alkylated aromatic product stream comprising the mixed xylenes and C9+ hydrocarbons. The mixed xylenes are subsequently converted to para-xylene, and the C9+ hydrocarbons and its components may be supplied as motor fuels blending components. The alkylation catalyst comprises a molecular sieve having a Constraint Index in the range from greater than zero up to about 3. The molar ratio of aromatic hydrocarbon to alkylating agent is in the range of greater than 1:1 to less than 4:1.
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Paragraph 0067-0072
(2019/10/23)
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- Decarbonylation of Aromatic Aldehydes and Dehalogenation of Aryl Halides Using Maghemite-Supported Palladium Catalyst
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A facile decarbonylation reaction of a variety of aromatic and heteroaromatic aldehydes using maghemite-supported palladium catalyst has been developed. The magnetic properties of catalyst facilitated an easy and efficient recovery of the catalyst from the reaction mixture using an external magnet. It was found that the catalyst could be reused up to four consecutive catalytic runs without a significant change in activity. In addition, the catalyst was also very effective in the dehalogenation of aryl halides. This is the first report on efficient utilization of directly immobilized Pd on maghemite in decarbonylation and dehalogenation reactions.
- Ajda?i?, Vladimir,Nikoli?, Andrea,Simi?, Stefan,Manojlovi?, Dragan,Stojanovi?, Zoran,Nikodinovic-Runic, Jasmina,Opsenica, Igor M.
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p. 119 - 126
(2017/12/27)
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- Low Temperature Direct Conversion of Methane using a Solid Superacid
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The direct conversion of methane to higher hydrocarbons and hydrogen can be catalyzed using “superacids”: nCH4→CnHm+xH2. The first report of catalytic oligomerization of methane using superacids was that of Olah et al., who demonstrated the superacidity of FSO3H?SbF5, which is a liquid. More recently, Vasireddy et al. showed that gas-phase HBr/AlBr3 was an active superacid. The only reported solid superacid for methane oligomerization is sulfated zirconia (SZ). Here, we report a new class of Br-based solid superacids, AlBrx/H-ZSM-5 (“ABZ-5”, x=1 or 2). ABZ-5 is based on gas-phase HBr/AlBr3, with the objective of synthesizing a heterogeneous analogue of the gas-phase superacid HBr/AlBr3. The results show that ABZ-5 is significantly more active than SZ. Perhaps more significantly, results here show methane conversions of ～1 % at 300 °C using ABZ-5. By comparison with SZ, 350 °C is the lowest temperature reported in the literature at which measurable conversions are shown, and the corresponding methane conversions were a solid superacid catalyst, AlBrx/H-ZSM-5. This solid catalyst is synthesized using a vapor-phase process in which AlBr3 vapor is grafted on to solid H-SZM-5. This catalyst is characterized using NH3-TPD, XRD, and DRIFTS. Hydrocarbon products observed in the temperature range of 200–400 °C include both C2–C6 hydrocarbons and aromatics.
- Kanitkar, Swarom,Carter, James H.,Hutchings, Graham J.,Ding, Kunlun,Spivey, James J.
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p. 5033 - 5038
(2018/10/24)
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- Standard and rapid scan infrared spectroscopic studies of: O -xylene transformations in terms of pore arrangement of 10-ring zeolites-2D COS analysis
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This study attempts to offer an insight into o-xylene isomerization process in terms of steric constraints of 10-ring zeolites. The zeolites under investigation, i.e. ZSM-5, IM-5 and TNU-9, have purely microporous structures and crystals with the same shape and offer comparable protonic functionality, both in manner of amount and strength of Si(OH)Al groups. Under these conditions, micropore topology is recognised to deliver differentiated catalytic performance of each zeolitic structure. Moreover, 10-ring zeolites of reduced dimensionality, i.e. TNU-10 and ZSM-22, are chosen as reference materials. The 2D COS analysis of IR spectra reveal that interaction and catalytic activity in o-xylene isomerization process are strongly influenced by diffusion of reagents in rigid microporous environment and the formation of intermediate species is characterised by IR bands at 1485 and 1455 cm-1. With a prolonged time of the reaction (15 min), the formation of the latter species is observed for zeolite IM-5 characterised by limited 3-dimensionality. Rapid scan experiments show that in a shorter reaction time (4 min), these intermediate moieties are present for all the structure studied. The intermediate species are believed to originate from arenium ions such as methylbenzenium CH3-C6H5+-CH3 and/or methyl-substituted cycloheptatrienyl ions CH3-C7H7+. Their amount is strictly related to the rigidity of the microporous system: the most spacious environment for o-xylene transformation, e.g. TNU-9, is characterised by the lowest population of intermediates, whereas structures offering sufficiently tight geometry, e.g. TNU-10, can accommodate intermediate species in higher quantities, finally leading to the production of p-xylene with high selectivity.
- Go?bek, Kinga,Tarach, Karolina A.,Góra-Marek, Kinga
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p. 9934 - 9950
(2017/08/10)
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- Stannylated Vinylic addition polynorbornene: Probing a reagent for friendly tin-mediated radical processes
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Vinylic addition polynorbornenes (VA-PNB) with stannyl functional groups have been prepared and used in tinmediated radical dehalogenation reactions. The aliphatic and robust scaffold of VA-PNB is well suited for a support in radical processes. VA-PNB-(CH2)nSnHBu2 can be used as a stoichiometric reagent and VA-PNB-(CH2)nSnBu2Cl as a catalyst in the presence of a hydride donor for the reduction of RBr. The mixture KF (aq.)/polymethylhydrosiloxane (PMHS) is the most convenient hydride source to generate VA-PNB-(CH2)nSnHBu2 in situ. Al-though quite popular in this context, boron hydrides, being a source of radicals themselves, are not adequate to correctly evaluate the performance of the anchored organotin group. VAPNB-(CH2)4SnBu2Cl can be recycled and, even if it loses activity upon reuse, it is still useful after ten cycles. The stannylated VAPNB can be separated from the products by simple filtration, and it leads to very low tin contamination (at least 250 times lower than that with use of conventional separation methods).
- García-Loma, Rodrigo,Alb é Niz, Ana C.
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supporting information
p. 4247 - 4254
(2018/08/24)
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- Hydrodehalogenation of Haloarenes by a Sodium Hydride–Iodide Composite
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A simple protocol for hydrodebromination and -deiodination of halo(hetero)arenes was enabled by sodium hydride (NaH) in the presence of lithium iodide (LiI). Mechanistic studies showed that an unusual concerted nucleophilic aromatic substitution operates in the present process.
- Ong, Derek Yiren,Tejo, Ciputra,Xu, Kai,Hirao, Hajime,Chiba, Shunsuke
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supporting information
p. 1840 - 1844
(2017/02/05)
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- Palladium-Catalyzed Deformylation Reactions with Detailed Experimental and in Silico Mechanistic Studies
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A facile, efficient, and general deformylation reaction with a wide-ranging functional group compatibility has been developed with palladium acetate as a precatalyst under exogenous ligand-free conditions. The mechanistic details of the palladium-catalyzed deformylation reaction have been outlined on the basis of a combination of experimental and computational studies. The heterogeneous pathway is predominant for the deformylation, and homogeneous catalysis occurs to a lesser extent. This ligand-free catalytic cycle is proposed to undergo oxidative addition, migratory extrusion, and reductive elimination as the key steps. Kinetic studies reveal a first-order rate dependency with respect to the aldehyde. Furthermore, kinetic isotope effects, competition experiments, and Hammett studies suggest that the migratory extrusion step is the rate-determining step. For the homogeneous pathway, the experimental findings are also supported by DFT studies.
- Modak, Atanu,Rana, Sujoy,Phukan, Ashwini K.,Maiti, Debabrata
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supporting information
p. 4168 - 4174
(2017/08/07)
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- Insight into forced hydrogen re-arrangement and altered reaction pathways in a protocol for CO2 catalytic processing of oleic acid into C8-C15 alkanes
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A new vision of using carbon dioxide (CO2) catalytic processing of oleic acid into C8-C15 alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO2 atmosphere. The yield of C8-C15 ingredients reaches 73.10 mol% in a CO2 atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H2) atmosphere. In the absence of an external H2 source, products which are similar to aviation fuel are generated where aromatization of propene (C3H6) oxidative dehydrogenation (ODH) involving CO2 and propane (C3H8) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO2 atmosphere is significantly different from that in the H2 atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H2 spillover is observed in the H2 atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H2. The CO2 processing of oleic acid described in this paper will significantly contribute to future CO2 utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel.
- Xing, Shiyou,Lv, Pengmei,Yuan, Haoran,Yang, Lingmei,Wang, Zhongming,Yuan, Zhenhong,Chen, Yong
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supporting information
p. 4157 - 4168
(2017/09/07)
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- Quantitative infrared spectroscopic studies and 2D COS analysis of xylenes isomerization over hierarchical zeolites
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The microporous and hierarchical ZSM-5 zeolites were studied with respect to their interaction with o-, m- and p-xylene molecules as well as the catalytic activity in xylenes isomerization process followed by 2D COS analysis of IR spectra. The aspects of mechanism of xylene isomerization reaction have been discussed in the light of the results of 2D COS analysis of IR spectra and catalytic performance of studied zeolites. The ZSM-5 zeolites were characterized by different Si/Al ratio and by various types of generated mesoporosity. This selection assured ability to follow properly the changes in the catalytic performance related not only to acidic properties but also to porosity of the samples. It was shown that the microporous character of zeolites was crucial for high selectivity to the most desired product i.e. p-xylene. In the case of hierarchical zeolites it was confirmed that the formation of by-products as mesitylene and toluene occurred during ortho-xylene isomerization. Furthermore, for hierarchical zeolites the high amount of silanols groups prompted to the coke formation on highly developed external surface.
- Tarach, Karolina A.,Go??bek, Kinga,Choi, Minkee,Góra-Marek, Kinga
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p. 158 - 171
(2017/01/06)
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- Reduction of Aryl Halides into Arenes with 2-Propanol Promoted by a Substoichiometric Amount of a tert-Butoxy Radical Source
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Aryl halides are reduced into the corresponding arenes in high yields, using 2-propanol, cesium carbonate, and di-tert-butyl peroxide (or di-tert-butyl hyponitrite) as a reductant/solvent, a base, and a radical initiator, respectively. This simple system reduces a wide variety of aryl bromides, chlorides, and iodides through single-electron-transfer mechanism with high functional-group tolerance.
- Ueno, Ryota,Shimizu, Takashi,Shirakawa, Eiji
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supporting information
p. 741 - 744
(2016/03/12)
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- Formation of weak and strong Br?nsted acid sites during alkaline treatment on MOR zeolite
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Aluminum rich mordenite zeolite (Si/Al?=?10) was hierarchized by using mild (0.2?M NaOH and 70?°C) and severe (0.4?M NaOH and 85?°C) alkaline treatments. The textural characterization was made by nitrogen adsorption. Acidic properties, i.e. nature (N), concentration (C), strength (S), accessibility (A) and location (L), were drawn from adsorption of two probes molecules followed by infrared spectroscopy: pyridine for N, C, L and S properties while CO for N and S properties. The catalytic model reaction of m-xylene transformation was also used to determine C, S and L properties. The severe alkaline treatment promoted (i) silicon extraction of zeolite framework, without considerable loss of crystallinity, (ii) creation of intra-crystal mesopore and widening of micropore diameter due to formation of interconnection between main canals, and (iii) accessibility of Br?nsted acid sites (BAS) located in side pockets. The silicon removal is inevitably followed by formation of extraframework aluminum species (EFAL) that leads to formations of Lewis acid sites, weak extraframework BAS and very strong BAS due to interaction between EFAL with the bridged hydroxyl, evidenced by a correlation between turnover frequency in m-xylene transformation and concentration of LAS.
- Chaouati,Soualah,Hussein,Comparot, J-D.,Pinard
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- Catalytic reactions of dimethyl disulfide with thiophene and benzene
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The gas-phase reaction of dimethyl disulfide with thiophene proceeds under the action of acid catalysts under atmospheric pressure at 160-350°C and a residence time of τ = 0.6-21 s to form thioalkylation and alkylation products. Dimethyl disulfide reacts with benzene to form only alkylation products. Catalysts containing both strong protic and Lewis acid sites, as well as basic sites of moderate strength, are the most active ones.
- Mashkina,Khairulina
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- Encapsulating Palladium Nanoparticles Inside Mesoporous MFI Zeolite Nanocrystals for Shape-Selective Catalysis
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Pd nanoparticles were successfully encapsulated inside mesoporous silicalite-1 nanocrystals (Pd@mnc-S1) by a one-pot method. The as-synthesized Pd@mnc-S1 with excellent stability functioned as an active and reusable heterogeneous catalyst. The unique porosity and nanostructure of silicalite-1 crystals endowed the Pd@mnc-S1 material general shape-selectivity for various catalytic reactions, including selective hydrogenation, oxidation, and carbon–carbon coupling reactions.
- Cui, Tian-Lu,Ke, Wen-Yu,Zhang, Wen-Bei,Wang, Hong-Hui,Li, Xin-Hao,Chen, Jie-Sheng
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supporting information
p. 9178 - 9182
(2016/08/03)
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- A stable but highly reactive phosphine-coordinated borenium: Metal-free dihydrogen activation and alkyne 1,2-carboboration
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Borenium cations have been found to be valuable analogues of boranes as a result of their cationic character which imparts high electrophilicity. Herein, we report the synthesis, characterization, and reactivity of a new type of borenium cation employing a naphthyl bridge and a strong intramolecular P→B interaction. The cation reacts with H2 in the presence of PtBu3 (frustrated Lewis pair (FLP) approach) but also on its own. The mechanism of the reaction between the borenium cation and H2 in the absence of PtBu3 has been investigated using deuterium-labeling experiments and DFT calculations. Both experiments and calculations imply the side-on coordination of H2 to the B center, followed by heterolytic splitting and B-C bond cleavage. An uncommon syn 1,2-carboboration has also been observed upon reaction of the borenium ion with 3-hexyne. Versatile reactivity: A new type of borenium cation is reported in which a naphthyl bridge supports a strong P→B interaction. Borenium reacts with H2 through side-on coordination of H2 to boron, heterolytic splitting, and concomitant cleavage of the B-Mes bond. The molecule also reacts with 3-hexyne through a syn 1,2-carboboration reaction. NTf2-=triflimide.
- Devillard, Marc,Bouhadir, Ghenwa,Bourissou, Didier,Brousses, Rmy,Miqueu, Karinne
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p. 5722 - 5726
(2015/09/08)
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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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- Efficient synthesis of sterically hindered arenes bearing acyclic secondary alkyl groups by suzuki-miyaura cross-couplings
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Bulky P,P-O ligands were designed to inhibit isomerization and reduction side reactions during the cross coupling between sterically hindered aryl halides and alkylboronic acids. Suzuki-Miyaura cross-couplings between di-ortho-substituted aryl bromides and acyclic secondary alkylboronic acids have been achieved with high yields. The method has also enabled the preparation of ortho-alkoxy di-ortho-substituted arenes bearing isopropyl groups in excellent yields. The utility of the synthetic method has been demonstrated in a late-stage modification of estrone and in the application to a new synthetic route toward gossypol. No side reaction: The shown bulky P,P-O ligands (right) successfully inhibit isomerization and reduction side reactions of the cross-coupling of sterically hindered substrates such as di-ortho-substituted aryl bromides with acyclic secondary alkylboronic acids. The method also allows the preparation of ortho-alkoxy di-ortho-substituted isopropyl arenes in excellent yields.
- Li, Chengxi,Chen, Tianyu,Li, Bowen,Xiao, Guolan,Tang, Wenjun
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supporting information
p. 3792 - 3796
(2015/03/18)
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- Catalytic conversion of isophorone to jet-fuel range aromatic hydrocarbons over a MoOx/SiO2 catalyst
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For the first time, jet fuel range C8-C9 aromatic hydrocarbons were synthesized in high carbon yield (～80%) by the catalytic conversion of isophorone over MoOx/SiO2 at atmospheric pressure. A possible reaction pathway was proposed according to the control experiments and the intermediates generated during the reaction.
- Chen, Fang,Li, Ning,Wang, Wentao,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
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supporting information
p. 11876 - 11879
(2015/07/15)
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- Intramolecular B/N frustrated Lewis pairs and the hydrogenation of carbon dioxide
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The FLP species 1-BR2-2-NMe2-C6H4 (R = 2,4,6-Me3C6H21, 2,4,5-Me3C6H22) reacts with H2 in sequential hydrogen activation and protodeborylation reactions to give (1-BH2-2-NMe2-C6H4)23. While 1 reacts with H2/CO2 to give formyl, acetal and methoxy-derivatives, 2 reacts with H2/CO2 to give C6H4(NMe2)(B(2,4,5-Me3C6H2)O)2CH24. The mechanism of CO2 reduction is considered.
- Courtemanche, Marc-André,Pulis, Alexander P.,Rochette, étienne,Légaré, Marc-André,Stephan, Douglas W.,Fontaine, Frédéric-Georges
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supporting information
p. 9797 - 9800
(2015/06/16)
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- Methylbenzene hydrocarbon pool in methanol-to-olefins conversion over zeolite H-ZSM-5
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The formation and reactivity of a methylbenzenes (MBs) hydrocarbon pool in the induction period of the methanol-to-olefins (MTO) reaction over zeolite H-ZSM-5 was investigated and the mechanistic link of MBs to ethene and propene was revealed. Time evolution analysis of the formed MBs and 12C/13C methanol-switching experiments indicate that in the induction period bulkier compounds such as tetraMB and pentaMB have higher reactivity than their lighter counterparts such as p/m-diMB and triMB. By correlating the distribution of MBs trapped on H-ZSM-5 with ethene and propene, we found that tetraMB and pentaMB favor the formation of propene, while p/m-diMB and triMB mainly contribute to the formation of ethene. On the basis of this relationship, the olefin (ethene and propene) selectivity can be controlled by regulating the distribution of trapped MBs by varying the silicon-to-aluminum ratio of ZSM-5, reaction temperature, and space velocity. The reactivity of MBs and the correlation of MBs with olefins were also verified under steady-state conditions. By observation of key cyclopentenyl and pentamethylbenzenium cation intermediates using in situ solid-state NMR spectroscopy, a paring mechanism was proposed to link MBs with ethene and propene. P/M-diMB and triMB produce ethylcyclopentenyl cations followed by splitting off of ethene, while tetraMB and pentaMB generate propyl-attached intermediates, which eventually produce propene. This work provides new insight into the MBs hydrocarbon pool in MTO chemistry.
- Wang, Chao,Xu, Jun,Qi, Guodong,Gong, Yanjun,Wang, Weiyu,Gao, Pan,Wang, Qiang,Feng, Ningdong,Liu, Xiaolong,Deng, Feng
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p. 127 - 137
(2015/11/09)
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- Methylation of benzene with dimethyl disulfide
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Dimethyl disulfide reacts with benzene at 250-350°C over a period of 1-20 s in the presence of catalysts containing strong Br?nsted and Lewis acid centers to give a mixture of methylbenzenes, viz. toluene, isomeric xylenes, mesitylene, and durene.
- Mashkina,Khairulina
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p. 1729 - 1732
(2016/02/03)
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