- Electrochemical synthesis of aromatic sulfur compounds in ionic liquids
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Electrochemical properties of ionic liquids (pyridinium and imidazolium salts) and the effect of additives of organic solvents on the electrochemical determination of organic compounds in ionic liquids have been studied. Transformations of aromatic and aliphatic sulfur compounds in ionic liquids in the presence of aromatic substrates are discussed. A new method has been proposed for identification of organic sulfur compounds-gas chromatography on columns with ionic liquid as the active phase.
- Okhlobystina,Okhlobystin,Letichevskaya,Abdulaeva,Movchan,Berberova
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- Efficient phosphine-mediated formal C(sp3)-C(sp3) coupling reactions of alkyl halides in batch and flow
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The construction of C(sp3)-C(sp3) bond is an essential chemical transformation in synthetic chemistry due to its abundance in organic scaffolds. Here we demonstrate a valuable adaptation of the Wittig-type chemical procedure to efficiently facilitate C(sp3)-C(sp3) bond formation utilizing a range of alkyl building blocks. Additionally the method is amenable with flow synthesis to afford coupled products in good to excellent yields without laborious purification process.
- Tran,Hock,Gordon,Koenigs,Nguyen
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- Decamethyltitanocene hydride intermediates in the hydrogenation of the corresponding titanocene-(η2-ethene) or (η2-alkyne) complexes and the effects of bulkier auxiliary ligands
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1H NMR studies of reactions of titanocene [Cp?2Ti] (Cp? = η5-C5Me5) and its derivatives [Cp?(η5:η1-C5Me4CH2)TiMe] and [Cp?2Ti(η2-CH2CH2)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp?2TiH2] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp?2TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp?2Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp?2Ti] in a 2:1 ratio. Hydrogenation of alkyne complexes [Cp?2Ti(η2-R1CCR2)] (R1 = R2 = Me or Et) performed at room temperature afforded alkanes R1CH2CH2R2, and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R1 = Me or Ph, R2 = SiMe3, and R1 = R2 = Ph or SiMe3, successful hydrogenation required the application of increased temperatures (70-80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η5-C5Me4tBu and η5-C5Me4SiMe3 did not hinder the addition of dihydrogen to the corresponding titanocenes [(η5-C5Me4tBu)2Ti] and [(η5-C5Me4SiMe3)2Ti] yielding [(η5-C5Me4tBu)2TiH2] (3) and [(η5-C5Me4SiMe3)2TiH2] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η5-C5Me4tBu)2TiH] (5) and [(η5-C5Me4SiMe3)2TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η5-C5Me4tBu)(η5:η1-C5Me4CMe2CH2)Ti] and [(η5-C5Me4SiMe3)(η5:η1-C5Me4SiMe2CH2)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η1-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp?2Ti(η3-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp?2Ti(η2-H2)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (-132.70 kJ mol-1), 3 (-121.11 kJ mol-1), and 4 (-112.35 kJ mol-1), in accordance with the more facile dihydrogen dissociation.
- Pinkas, Ji?í,Gyepes, Róbert,Císa?ová, Ivana,Kubi?ta, Ji?í,Horá?ek, Michal,Mach, Karel
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- Zeolite as a reagent and as a catalyst: Reduction and isomerization of alkenes by Ca Y
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Depending on the number of Bronsted acid sites present, Ca Y can act either as a reagent and reduce stilbenes to 1,2-diarylethanes or act as a catalyst and isomerize cis-stilbenes to the more stable trans form; Lewis acid sites generated by the activation process yield radical cations from stilbenes but these do not yield any stable products.
- Pitchumani,Joy, Abraham,Prevost, Nicolette,Ramamurthy
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- Development of Carbon-Neutral Cellulose-Supported Heterogeneous Palladium Catalysts for Chemoselective Hydrogenation
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Palladium catalysts immobilized on cellulose particles (Pd/CLP) and on a cellulose-monolith (Pd/CLM) were developed. These composites were applied as hydrogenation catalysts and their catalyst activities were evaluated. Although both catalysts catalyzed the deprotection of benzyloxycarbonyl-protected aromatic amines (Ar-N-Cbz) and aromatic benzyl esters (Ar-CO2Bn), only Pd/CLM could accomplish the hydrogenolysis of aliphatic-N-Cbz and aliphatic-CO2Bn protective groups. The difference in the physical structure of the cellulose supports induced unique chemoselectivity. Aliphatic-N-Cbz and aliphatic-CO2Bn groups were tolerated under the Pd/CLP-catalyzed hydrogenation conditions, while Ar-N-Cbz, Ar-CO2Bn, alkene, alkyne, azido and nitro groups could be smoothly reduced.
- Yamada, Tsuyoshi,Teranishi, Wataru,Park, Kwihwan,Jiang, Jing,Tachikawa, Takumu,Furusato, Shinichi,Sajiki, Hironao
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- Synthesis and hydrogenation activity of iron dialkyl complexes with chiral bidentate phosphines
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The activity of bis(phosphine) iron dialkyl complexes for the asymmetric hydrogenation of alkenes has been evaluated. High-throughput experimentation was used to identify suitable iron-phosphine combinations using the displacement of pyridine from py2Fe(CH2SiMe3)2 for precatalyst formation. Preparative-scale synthesis of a family of bis(phosphine) iron dialkyl complexes was also achieved using both ligand substitution and salt metathesis methods. Each of the isolated organometallic iron complexes was established as a tetrahedral and hence high-spin ferrous compound, as determined by M?ssbauer spectroscopy, magnetic measurements, and, in many cases, X-ray diffraction. One example containing a Josiphos-type ligand, (SL-J212-1)Fe(CH2SiMe3)2, proved more active than other isolated iron dialkyl precatalysts. Filtration experiments and the lack of observed enantioselectivity support dissociation of the phosphine ligand upon activation with dihydrogen and formation of catalytically active heterogeneous iron. The larger six-membered chelate is believed to reduce the coordination affinity of the phosphine for the iron center, enabling metal particle formation.
- Hoyt, Jordan M.,Shevlin, Michael,Margulieux, Grant W.,Krska, Shane W.,Tudge, Matthew T.,Chirik, Paul J.
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- Allenylsilanes fonctionnels II. Synthese par voie organoaluminique du 2-trimethylsilylbuta-2,3-dienal et application a la synthese d'alcools secondaires α-alleniques trimethylsilyles
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The 2-trimethylsilyl-2,3-butadienal is easily prepared, in good yield, by the reaction at -80 deg C between triethylorthoformate and the organoaluminum compound prepared from Me3SiCC-CH2Br.The resulting conjugated aldehyde reacts readily with various organometallic compounds (containing Al, Mg, Zn) to produce alcohols resulting from an 1,2-addition only, but for the saturated or phenylic magnesium derivatives which also give products from 1,4-addition.
- Mesnard, Danielle,Miginiac, Leone
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- Silver-Catalyzed Decarboxylative Couplings of Acids and Anhydrides: An Entry to 1,2-Diketones and Aryl-Substituted Ethanes
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Silver-catalyzed oxidative decarboxylative couplings of carboxylic acids and anhydrides to produce 1,2-diketones and substituted ethanes were developed. This reaction allows the generation of acyl or alkyl radicals by decarboxylation of the corresponding α-keto acids, alkyl acids and anhydrides, which are sequentially coupled to efficiently construct a new C?C bond. This reaction represents a carboxylic acid decarboxylative alternative that employs a radical termination strategy. (Figure presented.).
- Zou, Hua-Xu,Li, Yang,Yang, Yuan,Li, Jin-Heng,Xiang, Jiannan
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- ELECTROCATALYZED CARBOXYLATION OF ORGANIC HALIDES BY COBALT-SALEN COMPLEX.
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The carboxylation of benzylic and allylic chlorides by CO2 in tetrahydrofuran + hexamethylphosphoramide (40percent -60percent) is electrocatalyzed by cobalt Schiff-base complex Co(Salen).The reactions were performed by controlled-potential electrolysis at the R-Co(Salen) reduction potential.The yield of the carboxylic acid formation has been calculated.
- Folest, Jean-Claude,Duprilot, Jean-Marc,Perichon, Jacques,Robin, Yvette,Devynck, Jacques
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- On the Mechanism of Thermal Ring Expansion of 3,3-Dialkyloxindoles
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13C Labelling experiments show that the title reaction takes place by a free radical mechanism which involves (i) homolysis of the C(3)-alkyl bond, (ii) rearrangement of the resulting 3-indolyl radical to a 3-indolylmethyl radical , (iii) ring expansion by competitive neophyl rearrangement or attack at the carbonyl position, and (iv) aromatisation by loss of a hydrogen atom.
- McNab, Hamish
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- Manganese-catalyzed oxidative homo-coupling of aryl Grignard chlorides
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Manganese-catalyzed homo-coupling of aryl magnesium chlorides to give biphenyls was successfully achieved using manganese chloride as catalyst. A variety of aryl magnesium chlorides were efficiently converted into the corresponding symmetrical biaryls using 10 mol% MnCl2 as catalyst in the presence of a stoichiometric amount of 1,2-dichloroethane. Since the aryl chlorides, from which the Grignard reagents were prepared, are cheaper and more readily available that the corresponding bromides and iodides this procedure should become the method of choice for preparing symmetrical biaryls.
- Zhou, Zhiming,Xue, Weizhe
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- Synthesis and catalytic hydrogenation reactivity of a chromium catecholate porous organic polymer
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A single-site chromium catecholate POP (catPOP A2B1) was synthesized and characterized via AT-IR, XAS, and EPR spectroscopy. The well-defined, four-coordinate, 11-electron Cr(III) centers bound to catecholate POP were demonstrated to be active hydrogenation catalysts for nonpolar unsaturated organic substrates under mild conditions (5 mol % of Cr, 200 psi of H2, 60 °C). This material constitutes the first example of a well-defined, supported organometallic chromium hydrogenation precatalyst.
- Camacho-Bunquin, Jeffrey,Siladke, Nathan A.,Zhang, Guanghui,Niklas, Jens,Poluektov, Oleg G.,Nguyen, Sonbinh T.,Miller, Jeffrey T.,Hock, Adam S.
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- Pd/P(t-Bu)3: A mild catalyst for selective reduction of alkenes under transfer-hydrogenation conditions
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A new and efficient mild Pd/P(t-Bu)3 catalyst for selective reduction of various alkenes under transfer-hydrogenation conditions has been developed leading to the corresponding saturated derivatives in chemical yields varying from 65% to 98%. Georg Thieme Verlag Stuttgart.
- Brunel, Jean Michel
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- Heavy cation effect on intersystem crossing between triplet and singlet phenylacyl and benzyl geminate radical pairs within zeolites
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The difference in product selectivity observed between dibenzyl ketones and naphthyl esters in zeolites is due to the difference in spin of the radical pairs formed from these precursors. Heavy cations present in zeolites can enhance intersystem crossing between triplet and singlet geminate radical pairs. (C) 2000 Elsevier Science Ltd.
- Warrier,Turro,Ramamurthy
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- REACTION OF ZIRCONOCENE DICHLORIDE WITH ALKYLLITHIUMS OR ALKYL GRIGNARD REAGENTS AS A CONVENIENT METHOD FOR GENERATING A "ZIRCONOCENE" EQUIVALANT AND ITS USE IN ZIRCONIUM-PROMOTED CYCLIZATION OF ALKENES, ALKYNES, DIENES, ENYNES, AND DIYNES
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Treatment of Cl2ZrCp2 with 2 equiv of alkylmetals (RM) containing Li or Mg, e.g., n-BuLi, in THF produces organozirconium species that act as sources of "ZrCp2," the latter product being a convenient reagent for preparing zirconacycles.
- Negishi, Ei-ichi,Cederbaum, Fredrik E.,Takahashi, Tamotsu
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- Activation of heteroallenes by coordinatively unsaturated nickel(II) alkyl complexes supported by the hydrotris(3-phenyl-5-methyl)pyrazolyl borate (TpPh,Me) ligand
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Activation of sulfur containing heteroallenes by nickel(ii) alkyl complexes supported by the bulky hydrotris(3-phenyl-5-methylpyrazolyl)borate (TpPh,Me) ligand is described. Exposure of TpPh,MeNiCH2Ph (1a) and TpPh,MeNiCH2Si(CH3)3 (1b) to CS2 resulted in formation of the insertion products TpPh,MeNi(η2-CS2)CH2Ph (2a) and TpPh,MeNi(η2-CS2)CH2Si(CH3)3 (2b) in moderate yields. Reaction of 1a and MeNCS produced two species in a 1:1 ratio, identified as TpPh,MeNi(η2-MeNC)CH2Ph (3) and TpPh,MeNi(η2-MeNCS)SCH2Ph (4). Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a-b in the presence of isocyanides (i.e.tBuNC), which resulted in isolation of TpPh,MeNi(η2-tBuNC)CH2Ph (5a) and TpPh,MeNi(η2-tBuNC)CH2Si(CH3)3 (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare example of a Ni(i) carbonyl species TpPh,MeNiCO (6). Alternatively, complex 6 was also formed by exposure of 1a-b to an atmosphere of CO. Isolation of the intermediate species (TpPh,MeNi(η2-CO)CH2TMS (7b) and TpPh,MeNi(CO)(C(O)R, (8a-b) with R = Ph, TMS)) shed light on the formation of such species.
- Abubekerov, Mark,Eymann, Léonard Y. M.,Gianetti, Thomas L.,Arnold, John
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- Synthesis of polymer-attached niobium and tantalum complexes and their applications to the catalysis of olefin hydrogenation, isomerization and ethylene dimerization
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Polymer-attached CpNbCl4, CpNbCl3, CpNbCl2, Cp2Nb(BH4), CpTaCl4, (PhCH2)NbCl4 and (PhCH2)TaCl4 have been prepared. The reduction products of supported niobium and tantalum chlorides are active hydrogenation catalysts for olefins and for diphenylacetylene which was hydrogenated to 1,2-diphenylethane through intermediate stilbene. The similar reduction products have also been employed in catalytic isomerization of allylbenzene which is converted into a mixture of trans- and cis-propenylbenzene. Polymer-attached CpTaCl4, when treated with neopentyllithium, can effect dimerization of ethylene to give 1-butene.
- Chang, Biau-Hung,Lau, Chak-Po,Grubbs, Robert H.,Brubaker Jr., Carl H.
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- HIGH ACTIVITY OF MoO3-SnO2 FOR HYDROCRACKING OF DIPHENYL ETHER AND DIPHENYLMETHANE
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Of four newly synthesized catalysts designed for coal liquefaction, MoO3-SnO2 was superior for use with diphenyl ether and diphenylmethane with either H2 or CO + H2O.This agrees with the results of using these catalysts with a sub-bitumenous coal.Carbon monoxide and H2O is superior to H2 for ether cleavage, whereas H2 is better for hydrocarbon cleavage.
- Stenberg, Virgil I.,Srinivas, V. R.,Tanabe, Kozo,Jin, Tuo,Hattori, Hideshi
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- Mediation of photochemical reactions of 1-naphthyl phenylacylates by polyolefin films. A 'radical clock' to measure rates of radical-pair cage recombinations in 'viscous space'
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The fates of phenylacyl/1-naphthoxy singlet radical pairs generated upon irradiation of 1-naphthyl phenylacetate (1a) and 1-naphthyl 2-phenylpropanoate (1b) in three unstretched and stretched polyethylene films and isotactic and syndiotactic polypropylene films have been investigated. From dynamic fluorescence measurements the primary locus of reactions by 1 is within amorphous regions of the films. The reaction cages afforded by these media inhibit escape of the radical pairs and mediate their reorientational motions leading to photo-Fries and related products. In essence, the cages act as stiff-walled templates. In addition, a method is described to measure the rate constants for the singlet radical pairs. Thus, the rate constants (leading to the keto precursors) of the 2-phenylacyl-1-naphthols from the radical pairs of 1 (> 108 s-1) are >6 times the rate constants for the 4-isomers. Film stretching increases this selectivity but there is no obvious correlation between the rate of the in-cage radical pair recombinations and macroscopic polymer, properties such as degree of crystallinity and frequency of branched chains. By contrast, formation of (the keto precursors of) 2-benzylic-1-naphthols (from in-cage recombinations after phenylacyl decarbonylation) is slower than for the 4-benzyl-1-naphthols. (C) 2000 Elsevier Science Ltd.
- Gu, Weiqiang,Weiss, Richard G.
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- Kinetics of the thermal decomposition reaction of diethylketone cyclic triperoxide in acetone-toluene and acetone-1 -propanol binary solvent mixtures
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The thermal decomposition reaction of diethylketone triperoxide (DEKT) ca. 0.02 M was studied in binary mixtures of acetone-toluene and acetone-1 -propanol at 150°C. Products of DEKT thermolysis in solution, detected by GC analysis, were diethylketone, bi
- Iglesias, Mariangeles,Eyler, Nora,Canizo, Adriana
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- A novel host molecule p-[1-(4-hydroxyphenyl)-1-methylethyl]-calix[8]arene. Synthesis and complexation properties in non-aqueous polar solution
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A novel deep-cavity calixarene, p-[1-(4-hydroxyphenyl)-1-methylethyl]calix[8]arene 1 was synthesized and its complexation with aromatic compounds was examined. Reaction of p-[1-(4-methoxyphenyl)-1-methylethyl]phenol 2 with paraformaldehyde under various conditions only resulted in p-[1-(4-methoxyphenyl)-1-methylethyl]calix[8]arene 3, and no corresponding calix[4]arene and calix[6]arene were detected. Removal of the methyl in the ether groups of 3 afforded 1 in 80% yield. Solubilization, fluorescence and photochemical probe studies demonstrated that 1 forms inclusion complexes with a variety of aromatic compounds in polar non-aqueous solutions.
- Tung, Chen-Ho,Ji, Hai-Feng
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- Transfer semihydrogenation of alkynes catalyzed by a zero-valent palladium N-heterocyclic carbene complex
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(Chemical Equation Presented) Beyond Lindlar and without hydrogen: Transfer hydrogenation of internal alkynes catalyzed by a palladium(0) catalyst containing an N-heterocyclic carbene ligand gives Z alkenes without over-reduction to alkanes (see scheme). Contrary to most transfer hydrogenations, ketones are not reduced. As such, this is the first catalyst that shows excellent stereo- and chemo-selectivity for the semihydrogenation of alkynes without the need for hydrogen gas.
- Hauwert, Peter,Maestri, Giovanni,Sprengers, Jeroen W.,Catellani, Marta,Elsevier, Cornelis J.
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- Additive Effects on the CIDNP, Cage Effect, and Exit Rate of Micellized Radical Pairs
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The effects of additives on the recombination efficiency and exit rates of micellized benzyl radicals have been studied by steady-state CIDNP, steady-state product analysis, and time-resolved optical absorption techniques.The results indicate that the efficiency of triplet geminate pair recombination increases monotonically as the micellar volume increases.Aggregation numbers of SDS micelles were deduced as a function of additive concentration from CIDNP measurements and were found to be consistent with literature values.
- Turro, N. J.,Zimmt, M. B.,Lei, X. G.,Gould, I. R.,Nitsche, K. S.,Cha, Y.
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- Photodecarboxylation of arylacetic acids induced by light-sensitive Hg2F2
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Photolysis of arylacetic acids in argon-saturated acetonitrile in the presence of Hg2F2 gives the corresponding 1,2-diarylethanes as the major product via a radical pathway. This reaction offers an interesting procedure for selective decarboxylation of arylacetic acids with the assistance of a light-sensitive compound.
- Habibi, Mohammad H.,Farhadi, Saeid
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- Highly selective catalysts for liquid-phase hydrogenation of substituted alkynes based on Pd—Cu bimetallic nanoparticles
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Catalytic properties of Pd—Cu bimetallic catalysts supported on SiO2 and Al2O3 were studied in a model reaction of selective hydrogenation of diphenylacetylene. Application of PdCu2(AcO)6 heterobimetallic acetate complex as a precursor made it possible to obtain homogeneous Pd—Cu bimetallic nanoparticles. This result was supported by the data of IR spectroscopy of adsorbed CO. The Pd-Cu catalysts showed considerably higher selectivity than monometallic samples. Moreover, the introduction of copper decreases the hydrogenation rate of diphenylethylene (DPE) to diphenylethane. As a result, the maximum yield of the target product, DPE, increased from 78 to 93% in the presence of Pd—Cu catalysts.
- Mashkovsky,Markov,Bragina,Tkachenko,Yakushev,Kozitsyna, N. Yu.,Vargaftik,Stakheev, A. Yu.
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- Nickel atom - ligand reactions: evidence for an unstable η3-benzylnickel species from mixed-ligand cocondensation with nickel atoms
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Detailed studies of nickel atom - benzyl halide cocondensation reactions, with and without a second organic ligand, have been carried out.Benzyl halides (X = Cl, Br) when cocondensed with nickel atoms at -196 deg C give no isolable organonickel product but only bibenzyl and nickel(II) halide, indicative of an initial unstable benzylnickel compound.Allyl chloride/benzyl chloride mixtures do not give the stable η3-allylnickel chloride, but instead a highly-unstable sublimable yellow solid which apparently is the η3-benzylnickel chloride dimer.All of this work indicates complexities in the initial metal atom interactions with the ligands.A further case is reported in which the presence of aluminosilicate insulating wool drastically changes the products obtained.
- Hartman, Stephen J.,Kelusky, Eric C.
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- Formation of Alcohols from Alkenes with TiCl4-NaBH4
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The reaction of alkenes with TiCl4-NaBH4 in 1,2-dimethoxyethane afforded alcohols, the hydroxy group of which was introduced in an anti-Markovnikov direction.
- Kano, Shinzo,Tanaka, Yasuyuki,Hibino, Satoshi
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- Highly Selective Pd–Cu/Α-Al2O3 Catalysts for Liquid-Phase Hydrogenation: The Influence of the Pd: Cu Ratio on the Structure and Catalytic Characteristics
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The structure and catalytic characteristics of a series of Pd–Cu/α-Al2O3 catalysts with Pd: Cu ratio varied from Pd1–Cu0.5 to Pd1–Cu4 were studied. The use of α-Al2O3 with a small surface area (Ssp = 8 m2/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd0 and Cu0 nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.
- Markov,Bragina,Baeva,Rassolov,Mashkovsky,Stakheev, A. Yu.
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- SIZE, SHAPE, AND SITE SELECTIVITIES IN THE PHOTOCHEMICAL REACTIONS OF MOLECULES ADSORBED ON PENTASIL ZEOLITES. EFFECTS OF COADSORBED WATER
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The photochemistry of methylbenzyl benzyl ketones (ACOB) in the presence of pentasil zeolites follows strikingly different pathways due to the location of the adsorbed ketone.The product distribution, in terms of the cage effect (efficiency of geminate radical combination), demonstrates the effects of sorption and diffusion on the radical species produced by photolysis. p-ACOB is readily adsorbed within the pentasil framework and produces p-AB as the primary product.In contrast, the photolysis product distributions of o-ACOB can be dramatically varied depending upon the extent of its adsorption into the framework.By addition of a nonreactive titrant, such as water, after the ketone adsorption, the photolysis product distributions can be systematically varied depending upon the aluminum content of the framework.The observed results are completely described by considerations of (a) the size and shape sorption of the pentasil zeolites, (b) the sorption of water by the hydrophilic sites of the pentasil zeolites (which depend upon the framework aluminum content), and (c) the hydrophobic characteristics of the pentasil channels which do not contain framework aluminum.
- Turro, Nicholas J.,Cheng, Chen-Chih,Abrams, Lloyd,Corbin, David R.
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- Synthesis of Ag nanoparticles/ordered mesoporous carbon as a highly efficient catalyst for the electroreduction of benzyl bromide
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To develop efficient catalysts for the electroreduction of organic halides, a facile one-pot synthesis of Ag nanoparticles/ordered mesoporous carbon electrode materials via the self-assembly of CH3COOAg and resol in the presence of triblock copolymer is proposed. The resultant electrode materials possess uniform mesopore sizes (3.3 nm) and pore volumes (～0.28 cm3 g-1), high specific surface areas (～500 m2 g-1), and uniformly dispersed Ag nanoparticles (12-36 nm) loaded within the carbon matrix. Cyclic voltammetry, measurements of electrochemically active surface area, and electrolysis experiments were conducted to understand the correlations between the catalytic ability and the structural and textural features of the catalysts. Excellent bibenzyl yield (98%) and remarkable reusability were obtained under mild conditions. The results confirm that the prepared nanocomposites show outstanding performance in the electroreduction degradation of PhCH2Br to bibenzyl.
- Zhang, Zhi-Xia,Wang, Shuo,Li, Shi-Ming,Shan, Si-Li,Wang, Huan,Lu, Jia-Xing
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- Catalytic Reduction of Diphenylacetylene by Zinc over Palladium-Carbon Using Viologens as Electron Mediators
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Diphenylacetylene was reduced over palladium-carbon in methanol-water mixture in presence of zinc using N,N'-dialkyl-4,4'-bipyridinium ions (viologens) as mediators giving cis-stilbene as the major product and bibenzyl as the minor one.The reaction involved the direct contact of zinc with the catalyst.
- Shosenji, Hideto,Nakano, Yasuhiro,Yamada, Kimiho
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- Photochemistry of 2,5,7,7-Tetraphenyl-7-boratabicyclohepta-2,4-diene (a Boratanorcaradiene Anion): No Evidence for Diphenylborene Anion
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Irradiation of 2,5,7,7-tetraphenyl-7-boratabicyclohepta-2,4-diene anion (1, a boratanorcaradiene, as its potassium or tetramethylammonium salt) with UV light leads to formation of p-terphenyl in high yield.This observation led us to consider the possibility that diphenylborene anion (Ph2B-, an analogue of diphenylcarbene) might also be formed in this reaction.We designed and carried out a series of spectroscopic and chemical experiments to detect and characterize the borene.None of these experiments provides evidence for the formation of diphenylborene from this reaction.We suggest that the formation of p-terphenyl from the photolysis of 1 is initiated by an electron-transfer (photoionization) process.We also reexamined experiments reported earlier that were claimed to show that diphenylborene is formed from the irraditation or overirradiation of tetraphenylborate.Each of these experiments is ambiguous and cannot be relied upon to demonstrate the formation of the borene by this route.
- Boyatzis, Stamatis,Wilkey, John D.,Schuster, Gary B.
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- Cobalt-Catalyzed Csp3?Csp3Homocoupling
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An efficient and easy method for Csp3?Csp3homocoupling was developed using cobalt bromide as catalyst. A series of functionalized alkyl bromides and alkyl chlorides were coupled in high yields under mild conditions. This reaction seems to involve a radical intermediate. (Figure presented.).
- Cai, Yingxiao,Qian, Xin,Gosmini, Corinne
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- Kinetics and Thermochemistry of the Reversible Combination Reactions of the Allyl and Benzyl Radicals with NO
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The equilibrium kinetics of the reversible additions of NO to the benzyl (C6H5CH2) and allyl (CH2CHCH2) radicals have been studied at atmospheric pressure and over the temperature range 400 1/k-1 and k3/k-3) for the forward and reverse processes: C6H5CH2 + NO + N2 C6H5CH2NO + N2 (reactions 1, -1) and CH2CHCH2 + NO +N2 CH2CHCH2NO + N2 (reactions 3, -3).Thermodynamic treatment of the data by both second law and third law methods of analysis yielded values for the enthalpy and entropy of reaction 1 and 3 which were self consistent and hence the following average values: reaction 1, ΔH0298 = -123 +/- 5 kJ mol-1 (thus ΔH00 = -117 +/- 6 kJ mol-1 and ΔH0f298(C6H5CH2-NO) = 176 +/- 7 kJ mol-1, ΔS0298 = -159 +/- 9 J K-1 mol-1); reaction 3, ΔH0298 = -110 +/- 5 kJ mol-1 (thus ΔH00 = -105 +/- 4 kJ mol-1 and ΔH0f298(CH2CHCH2NO) = 148 +/- 8 kJ mol-1 ΔS0298 = -154 +/- 9 kJ mol-1).The bond dissociation energies for these adducts (= -ΔH0298) are compared and discussed in relation to those for other alkyl nitrosos.Also as part of the study, some measurements of the rate coefficients for the benzyl and ally association reactions with NO (reactions 1 and 3) and their radical self-recombinations (reaction 4, C6H5CH2 + C6H5CH2, and reaction 5, CH2CHCH2 + CH2CHCH2) were made under similar experimental conditions, yielding (in units 1E-11 cm3 molecule-1 s-1): k1(415, 443, 466 K) = 0.91 +/- 0.08, 0.81 +/- 0.05, and 0.62 +/- 0.09, k3(403 K) = 0.71 +/- 0.04, k4(435-519 K) = 2.9 +/- 0.3, k5(403-540 K) = 2.6 +/- 0.2.
- Boyd, A.A.,Noziere, B.,Lesclaux, R.
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- Rapid SmI2-mediated reductions of alkyl halides and electrochemical properties of SmI2/H2O/Amine
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Mixtures of SmI2/H2O/amine have been found to reduce alkyl halides more efficiently than SmI2/ HMPA/alcohol mixtures at room temperature. Alkyl and aryl iodides were quantitatively reduced in 3N in the reduction of 1-chlorodecane showed that the reaction order is one. Water was shown not to participate in the rate-determining step of this reduction. There was a significant change of the UV-vis spectrum and color of SmI2 upon addition of either PMDTA or water, while no effect was observed with the addition of Et3N or TMEDA. Although the combination of SmI2, water, and amines produces a very efficient reducing system, cyclic voltammetric experiments showed that the redox potential is nearly identical with that of SmI2 alone. These results are consistent with precipitation providing the driving force for reduction. Taken together, the results of these experiments show that the combination of SmI2/ H2O/amine provides a fundamentally novel and useful approach to enhance the reactivity of SmI2.
- Dahlen, Anders,Hilmersson, Goeran,Knettle, Brian W.,Flowers II, Robert A.
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- 6,12-Diphenyldibenzo[b,f][1,5]diazocine as an electron-capture agent: Efficient mechanistic probe for SET processes and reagent for the oxidative dimerization of benzylic organometallics
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In the present study, 6,12-diphenyldibenzo[b,f][1,5]diazocine, which X-ray diffraction measurements have now shown to possess a tub-shaped, eight-membered central ring, has been treated with sodium or lithium metal at 25 °C in THF, in an attempt to form the planar, Hueckel-aromatic dianion by the addition of two electrons to the central diazocine. Hydrolysis of such an aromatic dianion should have led to the isomeric 5,12- or 5,6-dihydro derivative of the original diazocine. In actuality, the only product obtained quantitatively upon hydrolytic workup was the interesting quadricyclic transannular reduction product, 4b,9b-diphenyl-4b,5,9b,10-tetrahydroindolo[3,2-b]indole, whose 3D structure has now been confirmed by X-ray crystallography and 13C NMR spectroscopy. Preferential SET transannular reduction of the diazocine to yield the quadricyclic indolo[3,2-b]indole dianion, rather than the planar, Hueckel-aromatic anion, is ascribed to the transannular electronic stabilization operative in the tub-shaped diazocine radical-anion. The quantitative generation of the indolo[3,2-b]indole dianion can be employed for the oxidative dimerization of the organic groups in benzylic lithium reagents. Thus treating one equivalent of the diazocine with two equivalents of benzyllithium, benzhydryllithium, or trityllithium yields quantitatively bibenzyl, 1,1,2,2-tetraphenylethane, or (4-benzhydrylphenyl)triphenylmethane, respectively. This oxidative dimerization is potentially of practical preparative scope, since the hydrolysis byproduct, the indolo[3,2-b]indole, is conveniently reconverted into the starting diazocine reagent by oxidation with chromium trioxide in acetic acid. The formation of the indolo[3,2-b]indole as a byproduct in the carbometalation of the diazocine by various RLi and Grignard reagents offers a clue as to the SET mechanism of carbometalation. Copyright
- Eisch, John J.,Yu, Kun,Rheingold, Arnold L.
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- Couplings of benzylic halides mediated by titanocene chloride: Synthesis of bibenzyl derivatives
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Titanocene monochloride catalyzes the homocoupling of benzylic halides and benzylic gem-dibromides to give the corresponding bibenzyl and stilbenyl systems. Exposure of benzylic bromides to Ti(III) in the presence of aldehydes gave rise to the Barbier-type products. Examples of the utility of the herein described processes are included.
- Barrero, Alejandro F.,Herrador, M. Mar,Del Moral, Jose F. Quilez,Arteaga, Pilar,Akssira, Mohammed,El Hanbali, Fadwa,Arteaga, Jesus F.,Dieguez, Horacio R.,Sanchez, Elena M.
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- Synthesis and catalytic activity of iron complexes with bidentate NHC ligands
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A family of well-defined FeII complexes of the type {BnN(N-CH2(CH2)n-N′-tert-butyl-imidazole- 2-ylidene)2}FeCl2 (Bn = benzyl; n = 1 (1) or 2 (2)), {BnN(N-CH2(CH2)n-N′-methylbenzimidazole- 2-ylidene)2}FeCl2 (n = 1 (3) or 2 (4)) and {BnN(N-CH 2CH2CH2-N′-methylbenzimidazole-2-ylidene) 2}FeBr2 (5) has been synthesized. These complexes are rare examples of Fe species supported by bidentate NHC ligands. Complexes 2, 3, 4 and 5 were characterized by X-ray crystallography and in all cases a distorted tetrahedral geometry is observed around the Fe center. The magnetic data is consistent with the complexes containing non interacting high spin Fe II centers (S = 2) and indicates that a large zero-field splitting (D) is present. The new complexes are highly active pre-catalysts for the homo-coupling of Grignard reagents.
- Wu, Jianguo,Dai, Wei,Farnaby, Joy H.,Hazari, Nilay,Le Roy, Jennifer J.,Mereacre, Valeriu,Murugesu, Muralee,Powell, Annie K.,Takase, Michael K.
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- Heterobimetallic Pd/Mn and Pd/Co complexes as efficient and stereoselective catalysts for sequential Cu-free Sonogashira coupling–alkyne semi-hydrogenation reactions
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A series of heterobimetallic PdII/MII complexes (MII = Mn, Co) were synthesised and tested as precatalysts for sequential Sonogashira coupling–alkyne semi-hydrogenation reactions to form Z-aryl alkenes. The carbometalated heterobimetallic PdII/CoII complex CoPdL3′ demonstrated an apparent cooperative effect compared to the corresponding monometallic counterparts. This compound was identified as a potent single-molecule catalyst for the one-pot Cu-free Sonogashira coupling of aryl bromides with terminal alkynes followed by chemo- and stereoselective semi-hydrogenation of the alkyne intermediate using NH3·BH3 as a hydrogen source. Furthermore, different aromatic substrates have been tested to show the generality of the reaction for the synthesis of Z-alkenes, including biologically active combretastatin A-4. In addition, the homogeneous nature of the catalytically active species was demonstrated.
- Baweja, Saral,Clauss, Reike,Gelman, Dmitri,Hey-Hawkins, Evamarie
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p. 1344 - 1356
(2022/02/03)
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- Sustainable System for Hydrogenation Exploiting Energy Derived from Solar Light
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Herein described is a sustainable system for hydrogenation that uses solar light as the ultimate source of energy. The system consists of two steps. Solar energy is captured and chemically stored in the first step; exposure of a solution of azaxanthone in ethanol to solar light causes an energy storing dimerization of the ketone to produce a sterically strained 1,2-diol. In the second step, the chemical energy stored in the vicinal diol is released and used for hydrogenation; the diol offers hydrogen onto alkenes and splits back to azaxanthone, which is easily recovered and reused repeatedly for capturing solar energy.
- Ishida, Naoki,Kamae, Yoshiki,Ishizu, Keigo,Kamino, Yuka,Naruse, Hiroshi,Murakami, Masahiro
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supporting information
p. 2217 - 2220
(2021/02/16)
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- Silylene-Bridged Tetranuclear Palladium Cluster as a Catalyst for Hydrogenation of Alkenes and Alkynes
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A planar tetranuclear palladium cluster was obtained from the reaction of a cyclotetrasilane with [Pd(CNtBu)2]3. Single-crystal X-ray diffraction analysis and DFT calculations revealed that the tetranuclear framework of the cluster was supported effectively by the bridging organosilylene ligand. Although [Pd(CNtBu)2]3 as well as mononuclear palladium bis(silyl) complex, cis-Pd(SiMePh2)2(CNtBu)2, do not act as the effective catalyst, the planar tetranuclear palladium cluster acts as an efficient catalyst for the hydrogenation of alkenes and alkynes including sterically hindered tri- and tetra-substituted alkenes.
- Yanagisawa, Chikako,Yamazoe, Seiji,Sunada, Yusuke
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p. 169 - 173
(2020/10/29)
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- Ambient Hydrogenation and Deuteration of Alkenes Using a Nanostructured Ni-Core–Shell Catalyst
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A general protocol for the selective hydrogenation and deuteration of a variety of alkenes is presented. Key to success for these reactions is the use of a specific nickel-graphitic shell-based core–shell-structured catalyst, which is conveniently prepared by impregnation and subsequent calcination of nickel nitrate on carbon at 450 °C under argon. Applying this nanostructured catalyst, both terminal and internal alkenes, which are of industrial and commercial importance, were selectively hydrogenated and deuterated at ambient conditions (room temperature, using 1 bar hydrogen or 1 bar deuterium), giving access to the corresponding alkanes and deuterium-labeled alkanes in good to excellent yields. The synthetic utility and practicability of this Ni-based hydrogenation protocol is demonstrated by gram-scale reactions as well as efficient catalyst recycling experiments.
- Beller, Matthias,Feng, Lu,Gao, Jie,Jackstell, Ralf,Jagadeesh, Rajenahally V.,Liu, Yuefeng,Ma, Rui
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supporting information
p. 18591 - 18598
(2021/06/28)
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- Method for continuously preparing bibenzyl by using microchannel reaction device
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The invention provides a method for continuously preparing bibenzyl by using a microchannel reaction device, wherein the method comprises the steps: by taking toluene as a reaction raw material, carrying out continuous reaction in the micro-channel reaction device in the presence of a catalyst, an oxidant and a solvent, and carrying out free radical self-coupling reaction to obtain bibenzyl II. The method provides a novel bibenzyl preparation method; the method has the advantages of simple process operation, safety, high efficiency and mild reaction conditions. The reaction process is shown as a reaction formula defined in the specification.
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Paragraph 0026-0066
(2021/06/02)
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- Pd/C-Catalyzed H2 Evolution from Tetrahydroxydiboron Hydrolysis
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The production of H2 from non-fossil sources is a key research challenge to contributing solving the forthcoming energy problem. Aqueous solutions of tetrahydroxydiboron have very recently appeared as a H2 source, from which both hydrogen atoms are provided by water, in the presence of highly sophisticated nanocatalysts. Herein, commercial and cheap Pd/C is shown to be an efficient and recyclable catalyst for H2 evolution upon tetrahydroxydiboron hydrolysis. Graphic Abstract: [Figure not available: see fulltext.]
- Zhou, Junjie,Huang, Yu,Shen, Jialu,Liu, Xiang
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p. 3004 - 3010
(2021/02/12)
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- Acid- and Base-Catalyzed Hydrolytic Hydrogen Evolution from Diboronic Acid
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The efficient production of H2 from hydrogen-rich sources, particularly from water, is a crucial task and a great challenge, both as a sustainable energy source and on the laboratory scale for hydrogenation reactions. Herein, a facile and effective synthesis of H2 and D2 from only acid- or base-catalyzed metal-free hydrolysis of B2(OH)4, a current borylation reagent, has been developed without any transition metal or ligand. Acid-catalyzed H2 evolution was completed in 4 min, whereas the base-catalyzed process needed 6 min. The large kinetic isotopic effects for this reaction with D2O, deuteration experiments and mechanistic studies have confirmed that both H atoms of H2 originate from water using either of these reactions. This new, metal-free catalytic system holds several advantages, such as high efficiency, simplicity of operation, sustainability, economy, and potential further use.
- Wang, Yi,Shen, Jialu,Huang, Yu,Liu, Xiang,Zhao, Qiuxia,Astruc, Didier
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supporting information
p. 3013 - 3018
(2021/03/26)
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- Microwave-Assisted Nickel-Catalyzed Rapid Reductive Coupling of Ethyl 3-iodopropionate to Adipic Acid
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Abstract: 3-iodopropionic acid (3-IPA) can be efficiently synthesized from the glycerol derivative glyceric acid (GA), which is a potential biomaterial-based platform molecule. In this report, ethyl 3-iodopropionate was rapidly dimerized to diethyl adipate in a microwave reactor using NiCl2·6H2O as a catalyst, co-catalyzed by Mn and the 1, 10-Phenanthroline monohydrate ligand. Under the optimum reaction conditions, diethyl adipate can be obtained with 84% yield at 90?°C in just 5?min. Diethyl adipate was hydrolyzed to obtain the adipic acid (AA) in 89% yield with an acid catalyst. AA is an important chemical and a monomer for producing a wide range of high-performance polymeric substances. This rapid coupling method is also applicable to other alkyl halides. Graphic Abstract: [Figure not available: see fulltext.]
- Zhang, Linfeng,Zheng, Jing,Zou, Wenya,Shu, Yongqi,Yang, Weiran
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p. 2339 - 2345
(2021/01/04)
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- Reductive C(sp3)-C(sp3) homo-coupling of benzyl or allyl halides with H2using a water-soluble electron storage catalyst
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This paper reports the first example of a reductive C(sp3)-C(sp3) homo-coupling of benzyl/allyl halides in aqueous solution by using H2as an electron source {turnover numbers (TONs) = 0.5-2.3 for 12 h}. This homo-coupling reaction, promoted by visible light, is catalysed by a water-soluble electron storage catalyst (ESC). The reaction mechanism, and four requirements to make it possible, are also described.
- Futakuchi, Sayaka,Miyazawa, Keishi,Nakai, Hidetaka,Ogo, Seiji,Shimauchi, Daiki,Takahashi, Yukina,Yatabe, Takeshi,Yoon, Ki-Seok
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p. 39450 - 39454
(2021/12/27)
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- Alkali Metal Adducts of an Iron(0) Complex and Their Synergistic FLP-Type Activation of Aliphatic C-X Bonds
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We report the formation and full characterization of weak adducts between Li+ and Na+ cations and a neutral iron(0) complex, [Fe(CO)3(PMe3)2] (1), supported by weakly coordinating [BArF20] anions, [1·M][BArF20] (M = Li, Na). The adducts are found to synergistically activate aliphatic C-X bonds (X = F, Cl, Br, I, OMs, OTf), leading to the formation of iron(II) organyl compounds of the type [FeR(CO)3(PMe3)2][BArF20], of which several were isolated and fully characterized. Stoichiometric reactions with the resulting iron(II) organyl compounds show that this system can be utilized for homocoupling and cross-coupling reactions and the formation of new C-E bonds (E = C, H, O, N, S). Further, we utilize [1·M][BArF20] as a catalyst in a simple hydrodehalogenation reaction under mild conditions to showcase its potential use in catalytic reactions. Finally, the mechanism of activation is probed using DFT and kinetic experiments that reveal that the alkali metal and iron(0) center cooperate to cleave C-X via a mechanism closely related to intramolecular FLP activation.
- Tinnermann, Hendrik,Sung, Simon,Csókás, Dániel,Toh, Zhi Hao,Fraser, Craig,Young, Rowan D.
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supporting information
p. 10700 - 10708
(2021/07/31)
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- Reactions of benzyltriphenylphosphonium salts under photoredox catalysis
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The development of benzyltriphenylphosphonium salts as alkyl radical precursors using photoredox catalysis is described. Depending on substituents, the benzylic radicals may couple to form C-C bonds or abstract a hydrogen atom to form C-H bonds. A natural product, brittonin A, was also synthesized using this method.
- Boldt, Andrew M.,Dickinson, Sidney I.,Ramirez, Jonathan R.,Benz-Weeden, Anna M.,Wilson, David S.,Stevenson, Susan M.
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p. 7810 - 7815
(2021/09/28)
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- Monovalent Nickel-Mediated Radical Formation: A Concerted Halogen-Atom Dissociation Pathway Determined by Electroanalytical Studies
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The recent success of nickel catalysts in stereoconvergent cross-coupling and cross-electrophile coupling reactions partly stems from the ability of monovalent nickel species to activate C(sp3) electrophiles and generate radical intermediates. This electroanalytical study of the commonly applied (bpy)Ni catalyst elucidates the mechanism of this critical step. Data rule out outer-sphere electron transfer and two-electron oxidative addition pathways. The linear free energy relationship between rates and the bond-dissociation free energies, the electronic and steric effects of the nickel complexes and the electrophiles, and DFT calculations support a variant of the halogen-atom abstraction pathway, the inner-sphere electron transfer concerted with halogen-atom dissociation. This mechanism accounts for the observed reactivity of different electrophiles in cross-coupling reactions and provides a mechanistic rationale for the chemoselectivity obtained in cross-electrophile coupling over homocoupling.
- Diao, Tianning,Fu, Yue,Lin, Qiao,Liu, Peng
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supporting information
p. 14196 - 14206
(2021/09/13)
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- Electro-mediated PhotoRedox Catalysis for Selective C(sp3)–O Cleavages of Phosphinated Alcohols to Carbanions
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We report a novel example of electro-mediated photoredox catalysis (e-PRC) in the reductive cleavage of C(sp3)?O bonds of phosphinated alcohols to alkyl carbanions. As well as deoxygenations, olefinations are reported which are E-selective and can be made Z-selective in a tandem reduction/photosensitization process where both steps are photoelectrochemically promoted. Spectroscopy, computation, and catalyst structural variations reveal that our new naphthalene monoimide-type catalyst allows for an intimate dispersive precomplexation of its radical anion form with the phosphinate substrate, facilitating a reactivity-determining C(sp3)?O cleavage. Surprisingly and in contrast to previously reported photoexcited radical anion chemistries, our conditions tolerate aryl chlorides/bromides and do not give rise to Birch-type reductions.
- Barham, Joshua P.,K?nig, Burkhard,Karl, Tobias A.,Reiter, Sebastian,Tian, Xianhai,Yakubov, Shahboz,de Vivie-Riedle, Regina
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p. 20817 - 20825
(2021/08/18)
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- Reductive activation and hydrofunctionalization of olefins by multiphoton tandem photoredox catalysis
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The conversion of olefin feedstocks to architecturally complex alkanes represents an important strategy in the expedient generation of valuable molecules for the chemical and life sciences. Synthetic approaches are reliant on the electrophilic activation of unactivated olefins, necessitating functionalization with nucleophiles. However, the reductive functionalization of unactivated and less activated olefins with electrophiles remains an ongoing challenge in synthetic chemistry. Here, we report the nucleophilic activation of inert styrenes through a photoinduced direct single electron reduction to the corresponding nucleophilic radical anion. Central to this approach is the multiphoton tandem photoredox cycle of the iridium photocatalyst [Ir(ppy)2(dtbbpy)] PF6, which triggers in situ formation of a high-energy photoreductant that selectively reduces styrene olefinic π bonds to radical anions without stoichiometric reductants or dissolving metals. This mild strategy enables the chemoselective reduction and hydrofunctionalization of styrenes to furnish valuable alkane and tertiary alcohol derivatives. Mechanistic studies support the formation of a styrene olefinic radical anion intermediate and a Birch-type reduction involving two sequential single electron transfers. Overall, this complementary mode of olefin activation achieves the hydrofunctionalization of less activated alkenes with electrophiles, adding value to abundant olefins as valuable building blocks in modern synthetic protocols.
- Czyz, Milena L.,Taylor, Mitchell S.,Horngren, Tyra H.,Polyzos, Anastasios
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p. 5472 - 5480
(2021/06/01)
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- ZnBr2-Catalyzed Dehydrogenative Borylation of Terminal Alkynes
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The simple, commercially available ZnBr2 has been successfully employed as a highly efficient and chemoselective catalyst for the dehydrogenative borylation of terminal alkynes with HBpin under mild conditions. It shows a good tolerance toward various functional groups such as aryl, alkyl, heteroaryl, etc. The plausible reaction mechanism has been investigated based on the corresponding stoichiometric experiments and DFT calculations.
- Luo, Man,Qin, Yi,Chen, Xi,Xiao, Qian,Zhao, Binlin,Yao, Weiwei,Ma, Mengtao
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p. 16666 - 16674
(2021/11/18)
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- Highly Selective Hydrogenation of C═C Bonds Catalyzed by a Rhodium Hydride
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Under mild conditions (room temperature, 80 psi of H2) Cp*Rh(2-(2-pyridyl)phenyl)H catalyzes the selective hydrogenation of the C═C bond in α,β-unsaturated carbonyl compounds, including natural product precursors with bulky substituents in the β position and substrates possessing an array of additional functional groups. It also catalyzes the hydrogenation of many isolated double bonds. Mechanistic studies reveal that no radical intermediates are involved, and the catalyst appears to be homogeneous, thereby affording important complementarity to existing protocols for similar hydrogenation processes.
- Gu, Yiting,Lisnyak, Vladislav G.,Norton, Jack R.,Salahi, Farbod,Snyder, Scott A.,Zhou, Zhiyao
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supporting information
p. 9657 - 9663
(2021/07/19)
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- Ligand-enabled and magnesium-activated hydrogenation with earth-abundant cobalt catalysts
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Replacing expensive noble metals like Pt, Pd, Ir, Ru, and Rh with inexpensive earth-abundant metals like cobalt (Co) is attracting wider research interest in catalysis. Cobalt catalysts are now undergoing a renaissance in hydrogenation reactions. Herein, we describe a hydrogenation method for polycyclic aromatic hydrocarbons (PAHs) and olefins with a magnesium-activated earth-abundant Co catalyst. When diketimine was used as a ligand, simple and inexpensive metal salts of CoBr2in combination with magnesium showed high catalytic activity in the site-selective hydrogenation of challenging PAHs under mild conditions. Co-catalyzed hydrogenation enabled the reduction of two side aromatics of PAHs. A wide range of PAHs can be hydrogenated in a site-selective manner, which provides a cost-effective, clean, and selective strategy to prepare partially reduced polycyclic hydrocarbon motifs that are otherwise difficult to prepare by common methods. The use of well-defined diketimine-ligated Co complexes as precatalysts for selective hydrogenation of PAHs and olefins is also demonstrated.
- Han, Bo,Jiao, Hongmei,Ma, Haojie,Wang, Jijiang,Zhang, Miaomiao,Zhang, Yuqi
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p. 39934 - 39939
(2021/12/31)
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- Designing of Highly Active and Sustainable Encapsulated Stabilized Palladium Nanoclusters as well as Real Exploitation for Catalytic Hydrogenation in Water
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Abstract: Encapsulated nanoclusters based on palladium, 12-tunstophosphoric acid and silica was designed by simple wet impregnation methodology. The catalyst was found to be very efficient towards cyclohexene hydrogenation up to five catalytic runs with substrate/catalyst ratio of 4377/1 at 50?°C as well as for alkene, aldehyde, nitro and halogen compounds. Graphic Abstract: Silica encapsulated Pd nanoclusters stabilized by 12-tungstophosphoric acid is proved to be sustainable and excellent for water mediated hydrogenation reaction with very high catalyst to substrate ratio as well as TON.[Figure not available: see fulltext.]
- Patel, Anish,Patel, Anjali
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p. 803 - 820
(2020/08/12)
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- Boosting homogeneous chemoselective hydrogenation of olefins mediated by a bis(silylenyl)terphenyl-nickel(0) pre-catalyst
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The isolable chelating bis(N-heterocyclic silylenyl)-substituted terphenyl ligand [SiII(Terp)SiII] as well as its bis(phosphine) analogue [PIII(Terp)PIII] have been synthesised and fully characterised. Their reaction with Ni(cod)2(cod = cycloocta-1,5-diene) affords the corresponding 16 VE nickel(0) complexes with an intramolecularη2-arene coordination of Ni, [E(Terp)E]Ni(η2-arene) (E = PIII, SiII; arene = phenylene spacer). Due to a strong cooperativity of the Si and Ni sites in H2activation and H atom transfer, [SiII(Terp)SiII]Ni(η2-arene) mediates very effectively and chemoselectively the homogeneously catalysed hydrogenation of olefins bearing functional groups at 1 bar H2pressure and room temperature; in contrast, the bis(phosphine) analogous complex shows only poor activity. Catalytic and stoichiometric experiments revealed the important role of the η2-coordination of the Ni(0) site by the intramolecular phenylene with respect to the hydrogenation activity of [SiII(Terp)SiII]Ni(η2-arene). The mechanism has been established by kinetic measurements, including kinetic isotope effect (KIE) and Hammet-plot correlation. With this system, the currently highest performance of a homogeneous nickel-based hydrogenation catalyst of olefins (TON = 9800, TOF = 6800 h?1) could be realised.
- Lücke, Marcel-Philip,Yao, Shenglai,Driess, Matthias
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p. 2909 - 2915
(2021/03/14)
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- Photoredox-Catalyzed Simultaneous Olefin Hydrogenation and Alcohol Oxidation over Crystalline Porous Polymeric Carbon Nitride
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Booming of photocatalytic water splitting technology (PWST) opens a new avenue for the sustainable synthesis of high-value-added hydrogenated and oxidized fine chemicals, in which the design of efficient semiconductors for the in-situ and synergistic utilization of photogenerated redox centers are key roles. Herein, a porous polymeric carbon nitride (PPCN) with a crystalline backbone was constructed for visible light-induced photocatalytic hydrogen generation by photoexcited electrons, followed by in-situ utilization for olefin hydrogenation. Simultaneously, various alcohols were selectively transformed to valuable aldehydes or ketones by photoexcited holes. The porosity of PPCN provided it with a large surface area and a short transfer path for photogenerated carriers from the bulk to the surface, and the crystalline structure facilitated photogenerated charge transfer and separation, thus enhancing the overall photocatalytic performance. High reactivity and selectivity, good functionality tolerance, and broad reaction scope were achieved by this concerted photocatalysis system. The results contribute to the development of highly efficient semiconductor photocatalysts and synergistic redox reaction systems based on PWST for high-value-added fine chemical production.
- Qiu, Chuntian,Sun, Yangyang,Xu, Yangsen,Zhang, Bing,Zhang, Xu,Yu, Lei,Su, Chenliang
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p. 3344 - 3350
(2021/07/26)
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- Nuclearity expansion in Pd clusters triggered by the migration of a phenyl group in cyclooligosilanes
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Heptanuclear palladium clusters with six palladium atoms in a planar arrangement were obtained from the reaction of [Pd(CNtBu)2]3with Ph-substituted cyclotetrasilane or cyclopentasilaneviathe migration of a phenyl group. The molecular structures of these clusters as well as those of two possible intermediates were determined by single-crystal X-ray diffraction analyses.
- Shimamoto, Kento,Sunada, Yusuke
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supporting information
p. 7649 - 7652
(2021/08/09)
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- Highly Reusable and Active Nanometal?Silicon-Nanowire Array Hybrid Catalysts for Hydrogenation
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Highly reusable and active silicon-nanowire-array-stabilized metal-nanoparticle (SiNA-MNP) catalysts are prepared for effective hydrogenation under mild conditions. Monometallic Pd (SiNA-Pd), platinum (SiNA-Pt), and rhodium (SiNA-Rh) nanoparticles are pre
- Baek, Heeyoel,Sato, Takuma,Uozumi, Yasuhiro,Yamada, Yoichi M. A.
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supporting information
p. 708 - 712
(2021/02/16)
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- C-Methylenation of anilines and indoles with CO2and hydrosilane using a pentanuclear zinc complex catalyst
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The one-stepC-methylenation of anilines and indoles with CO2and phenylsilane was catalyzed by a pentanuclear ZnIIcomplex to give diarylmethanesviageminal C-H and C-C bond formation. It is proposed that the zinc-hydride complex generatedin situis a catalytically active species and that bis(silyl)acetal is a key intermediate. When aniline was used as a substrate, both theC-methylenation andN-methylation proceeded.
- Ema, Tadashi,Kosugi, Hiroyasu,Nishimura, Ritsuki,Takaishi, Kazuto,Yamada, Yuya
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supporting information
p. 8083 - 8086
(2021/08/20)
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- Chemoselective Hydrogenation of Olefins Using a Nanostructured Nickel Catalyst
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The selective hydrogenation of functionalized olefins is of great importance in the chemical and pharmaceutical industry. Here, we report on a nanostructured nickel catalyst that enables the selective hydrogenation of purely aliphatic and functionalized olefins under mild conditions. The earth-abundant metal catalyst allows the selective hydrogenation of sterically protected olefins and further tolerates functional groups such as carbonyls, esters, ethers and nitriles. The characterization of our catalyst revealed the formation of surface oxidized metallic nickel nanoparticles stabilized by a N-doped carbon layer on the active carbon support.
- Klarner, Mara,Bieger, Sandra,Drechsler, Markus,Kempe, Rhett
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supporting information
p. 2157 - 2161
(2021/05/21)
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- Metal-Organic Framework-Confined Single-Site Base-Metal Catalyst for Chemoselective Hydrodeoxygenation of Carbonyls and Alcohols
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Chemoselective deoxygenation of carbonyls and alcohols using hydrogen by heterogeneous base-metal catalysts is crucial for the sustainable production of fine chemicals and biofuels. We report an aluminum metal-organic framework (DUT-5) node support cobalt(II) hydride, which is a highly chemoselective and recyclable heterogeneous catalyst for deoxygenation of a range of aromatic and aliphatic ketones, aldehydes, and primary and secondary alcohols, including biomass-derived substrates under 1 bar H2. The single-site cobalt catalyst (DUT-5-CoH) was easily prepared by postsynthetic metalation of the secondary building units (SBUs) of DUT-5 with CoCl2 followed by the reaction of NaEt3BH. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) indicated the presence of CoII and AlIII centers in DUT-5-CoH and DUT-5-Co after catalysis. The coordination environment of the cobalt center of DUT-5-Co before and after catalysis was established by extended X-ray fine structure spectroscopy (EXAFS) and density functional theory. The kinetic and computational data suggest reversible carbonyl coordination to cobalt preceding the turnover-limiting step, which involves 1,2-insertion of the coordinated carbonyl into the cobalt-hydride bond. The unique coordination environment of the cobalt ion ligated by oxo-nodes within the porous framework and the rate independency on the pressure of H2 allow the deoxygenation reactions chemoselectively under ambient hydrogen pressure.
- Antil, Neha,Kumar, Ajay,Akhtar, Naved,Newar, Rajashree,Begum, Wahida,Manna, Kuntal
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supporting information
p. 9029 - 9039
(2021/06/28)
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- Lewis Basic Salt-Promoted Organosilane Coupling Reactions with Aromatic Electrophiles
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Lewis basic salts promote benzyltrimethylsilane coupling with (hetero)aryl nitriles, sulfones, and chlorides as a new route to 1,1-diarylalkanes. This method combines the substrate modularity and selectivity characteristic of cross-coupling with the practicality of a base-promoted protocol. In addition, a Lewis base strategy enables a complementary scope to existing methods, employs stable and easily prepared organosilanes, and achieves selective arylation in the presence of acidic functional groups. The utility of this method is demonstrated by the synthesis of pharmaceutical analogues and its use in multicomponent reactions.
- Bandar, Jeffrey S.,Reidl, Tyler W.
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supporting information
p. 11939 - 11945
(2021/08/20)
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- Remarkable catalytic activity of polymeric membranes containing gel-trapped palladium nanoparticles for hydrogenation reactions
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Polymeric flat-sheet membranes and hollow fibers were prepared via UV photo-initiated polymerization of acrylic acid at the surface of commercial polyether sulfones (PES) membranes. These polymeric materials permitted to immobilize efficiently palladium nanoparticles (PdNP), which exhibited a mean diameter in the range of 4?6 nm. These materials were synthesized by chemical reduction of Pd(II) precursors in the presence of the corresponding support. We successfully applied the as-prepared catalytic materials in hydrogenation reactions under continuous flow conditions. Flat sheet membranes were more active than hollow fibers due to the flow configuration and defavorable operating conditions. Actually, various functional groups (i.e. C[dbnd]C, C[tbnd]C and NO2) were reduced in flow-through configuration, under mild conditions (between 1.4 and 2.2 bar H2 at 60 °C, using 3.2 mol% of Pd loading), archiving high conversions in short reaction times (12?24 s).
- López-Viveros, Melissa,Favier, Isabelle,Gómez, Montserrat,Lahitte, Jean-Fran?ois,Remigy, Jean-Christophe
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p. 263 - 269
(2020/05/13)
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- Introducing the Dihydro-1,3-azaboroles: Convenient Entry by a Three-Component Reaction, Synthetic and Photophysical Application
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The (Fmes)BH2·SMe2 reagent (7) reacts sequentially with an acetylene and, e.g., xylylisonitrile in a convenient three-component reaction to give a series of unprecedented dihydro-1,3-azaborole derivatives 16. The tolane-derived example 16a was deprotonated and used as a ligand in organometallic chemistry. Compounds 16 served as the starting materials for the straightforward synthesis of various dihydro-1,3-azaborinine derivatives by treatment with an isonitrile. Several diaryldihydro-1,3-azaboroles showed interesting photophysical properties such as aggregation-induced emission and high fluorescence quantum yields.
- Li, Jun,Daniliuc, Constantin G.,Kartha, Kalathil K.,Fernández, Gustavo,Kehr, Gerald,Erker, Gerhard
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supporting information
p. 2059 - 2067
(2021/02/06)
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- Ligand-free (: Z)-selective transfer semihydrogenation of alkynes catalyzed by in situ generated oxidizable copper nanoparticles
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Herein, we present (Z)-selective transfer semihydrogenation of alkynes based on in situ generated CuNPs in the presence of hydrogen donors, such as ammonia-borane and a green protic solvent. This environmentally friendly method is characterized by operational simplicity combined with high stereo- and chemoselectivity and functional group compatibility. Auto-oxidation of CuNPs after the completion of a semihydrogenation reaction results in the formation of a water-soluble ammonia complex, so that the catalyst may be reused several times by simple phase-separation with no need for any special regeneration processes. Formed NH4B(OR)4 can be easily transformed back into ammonia-borane or into boric acid. In addition, a one-pot tandem sequence involving a Suzuki reaction followed by semihydrogenation was presented, which allows minimization of chemical waste production.
- Grela, Karol,Kusy, Rafa?
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supporting information
p. 5494 - 5502
(2021/08/16)
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- Ruthenium-Catalyzed E-Selective Partial Hydrogenation of Alkynes under Transfer-Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source
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E-alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium-catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer-hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer-hydrogenation of alkynes. Optimization reactions showed the best results for the commercially available binuclear [Ru(p-cymene)Cl2]2 complex as pre-catalyst in combination with 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BINAP) as ligand (1 : 1 ratio per Ru monomer to ligand). Mechanistic investigations showed that the origin of E-selectivity in this reaction is the fast Z to E isomerization of the formed alkenes. Mild reaction conditions plus the use of cheap, easily available and safe materials as well as simple setup and inexpensive catalyst turn this protocol into a feasible and promising stereo complementary procedure to the well-known Z-selective Lindlar reduction in late-stage syntheses. This procedure can also be used for the production of deuterated alkenes simply using d2-paraformaldehyde and D2O mixtures.
- Fetzer, Marcus N. A.,Tavakoli, Ghazal,Klein, Axel,Prechtl, Martin H. G.
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p. 1317 - 1325
(2021/02/11)
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- Cobalt Complexes of Bulky PNP Ligand: H2Activation and Catalytic Two-Electron Reactivity in Hydrogenation of Alkenes and Alkynes
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The reactivity of cobalt pincer complexes supported by the bulky tetramethylated PNP ligands Me4PNPR(R = iPr, tBu) has been investigated. In these ligands, the undesired H atom loss reactivity observed earlier in some classical CH2-arm PNP cobalt complexes is blocked, allowing them to be utilized for promoting two-electron catalytic transformations at the cobalt center. Accordingly, reaction of the formally CoIMe complex 3 with H2 under ambient pressure and temperature afforded the CoIII trihydride 4-H, in a reaction cascade reasoned to proceed by two-electron oxidative addition and reductive eliminations. This mechanistic proposal, alongside the observance of alkene insertion and ethane production upon sequential exposure of 3 to ethylene and H2, prompted an exploration into 3 as a catalyst for hydrogenation. Complex 4-H, formed in situ from 3 under H2, was found to be active in the catalytic hydrogenation of alkenes and alkynes. The proposed two-electron mechanism is reminiscent of the platinum group metals and demonstrates the utility of the bulky redox-innocent Me4PNPR ligand in the avoidance of one-electron reactivity, a concept that may show broad applicability in expanding the scope of earth-abundant first-row transition-metal catalysis.
- Fayzullin, Robert R.,Gallagher, James M.,Khaskin, Eugene,Khusnutdinova, Julia R.,Lapointe, Sébastien,Osborne, James,Pandey, Dilip K.
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supporting information
p. 3617 - 3626
(2021/11/16)
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- Visible light enables catalytic formation of weak chemical bonds with molecular hydrogen
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The synthesis of weak chemical bonds at or near thermodynamic potential is a fundamental challenge in chemistry, with applications ranging from catalysis to biology to energy science. Proton-coupled electron transfer using molecular hydrogen is an attractive strategy for synthesizing weak element–hydrogen bonds, but the intrinsic thermodynamics presents a challenge for reactivity. Here we describe the direct photocatalytic synthesis of extremely weak element–hydrogen bonds of metal amido and metal imido complexes, as well as organic compounds with bond dissociation free energies as low as 31 kcal mol?1. Key to this approach is the bifunctional behaviour of the chromophoric iridium hydride photocatalyst. Activation of molecular hydrogen occurs in the ground state and the resulting iridium hydride harvests visible light to enable spontaneous formation of weak chemical bonds near thermodynamic potential with no by-products. Photophysical and mechanistic studies corroborate radical-based reaction pathways and highlight the uniqueness of this photodriven approach in promoting new catalytic chemistry. [Figure not available: see fulltext.].
- Park, Yoonsu,Kim, Sangmin,Tian, Lei,Zhong, Hongyu,Scholes, Gregory D.,Chirik, Paul J.
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p. 969 - 976
(2021/07/25)
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- Kinetics of liquid-phase diphenylacetylene hydrogenation on “single-atom alloy” Pd-Ag catalyst: Experimental study and kinetic analysis
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Catalytic performance of Pd1Ag3/Al2O3 single-atom alloy (SAA) catalyst was studied in liquid-phase hydrogenation of diphenylacetylene (DPA) and compared with the performance of the reference monometallic Pd/Al2O3. Formation of SAA structure in Pd1Ag3/Al2O3 was confirmed by FTIR CO technique. It was found that Pd1Ag3/Al2O3 single-atom alloy catalyst exhibits excellent selectivity in diphenylethene (stilbene) (ca. 98 %), which remains constant over a wide range of DPA conversions (0–95%), while over Pd/Al2O3 selectivity decreases steadily with the increase in DPA conversion. It is remarkable that the selectivity of Pd1Ag3/Al2O3 depends neither on hydrogen pressure (5–15 bar), nor on DPA concentration (0.0262 – 0.159 mol/l). In contrast, over the reference Pd/Al2O3 selectivity tends to decrease with increasing P(H2) and decreasing DPA concentration. The proposed reaction network comprises hydrogenation of DPA in a parallel formation of cis and trans-stilbene with following hydrogenation to bibenzyl and direct formation of the latter from the initial DPA. The calculations clearly shows the capability of the kinetic model to describe the experimental dependencies for Pd1Ag3 single-atom catalyst in an excellent way with the degree of explanation equal to ca. 99 %.
- Rassolov, Alexander V.,Mashkovsky, Igor S.,Bragina, Galina O.,Baeva, Galina N.,Markov, Pavel V.,Smirnova, Nadezhda S.,W?rn?, Johan,Stakheev, Alexander Yu.,Murzin, Dmitry Yu.
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- Heterometallic Mg?Ba Hydride Clusters in Hydrogenation Catalysis
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Reaction of a MgN“2/BaN”2 mixture (N“=N(SiMe3)2) with PhSiH3 gave three unique heterometallic Mg/Ba hydride clusters: Mg5Ba4H11N”7 ? (benzene)2 (1), Mg4Ba7H13N“9 ? (toluene)2 (2) and Mg7Ba12H26N”12 (3). Product formation is controlled by the Mg/Ba ratio and temperature. Crystal structures are described. While 3 is fully insoluble, clusters 1 and 2 retain their structures in aromatic solvents. DFT calculations and AIM analyses indicate highly ionic bonding with Mg?H and Ba?H bond paths. Also unusual H????H? bond paths are observed. Catalytic hydrogenation with MgN“2, BaN”2 and the mixture MgN“2/BaN”2 has been studied. Whereas MgN“2 is only active in imine hydrogenation, alkene and alkyne hydrogenation needs the presence of Ba. The catalytic activity of the MgN”2/BaN“2 mixture lies in general between that of its individual components and strong cooperative effects are not evident.
- Wiesinger, Michael,Knüpfer, Christian,Elsen, Holger,Mai, Jonathan,Langer, Jens,Harder, Sjoerd
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p. 4567 - 4577
(2021/09/09)
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- Synthesis of Dibenzyls by Nickel-Catalyzed Homocoupling of Benzyl Alcohols
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Dibenzyls are essential building blocks that are widely used in organic synthesis, and they are typically prepared by the homocoupling of halides, organometallics, and ethers. Herein, we report an approach to this class of compounds using alcohols, which are more stable and readily available. The reaction proceeds via nickel-catalyzed and dimethyl oxalate assisted dynamic kinetic homocoupling of benzyl alcohols. Both primary and secondary alcohols are tolerated.
- Pan, Feng-Feng,Guo, Peng,Huang, Xiaochuang,Shu, Xing-Zhong
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p. 3094 - 3100
(2021/04/23)
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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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- Visible-Light-Promoted Cross-Coupling of N-Alkylpyridinium Salts and Nitrostyrenes
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A stereoselective, denitrative cross-coupling of β-nitrostyrenes with N-alkylpyridinium salts for the preparation of functionalized styrenes has been developed. The visible-light-induced reaction proceeds without any catalyst at ambient temperature. Broad in scope and tolerant to multiple functional groups, the moderately yielding transformation is orthogonal to several traditional metal-catalyzed cross-couplings.
- Ferko, Branislav,Mar?eková, Michaela,Detková, Katarína Ráchel,Doháňo?ová, Jana,Berke?, Du?an,Jakubec, Pavol
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supporting information
p. 8705 - 8710
(2021/11/20)
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- Hydromagnesiation of 1,3-Enynes by Magnesium Hydride for Synthesis of Tri- and Tetra-substituted Allenes
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A protocol for regio-controlled hydromagnesiation of 1,3-enynes was developed using magnesium hydride that is generated in situ by solvothermal treatment of sodium hydride (NaH) and magnesium iodide (MgI2) in THF. The resulting allenylmagnesium species could be converted into tri- and tetra-substituted allenes by subsequent treatment with various carbon- and silicon-based electrophiles with the aid of CuCN as a catalyst.
- Chiba, Shunsuke,Li, Yihang,Pang, Jia Hao,Takita, Ryo,Wang, Bin,Watanabe, Kohei
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supporting information
p. 217 - 221
(2020/11/30)
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- Ni-catalyzed reductive decyanation of nitriles with ethanol as the reductant
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A nickel-catalyzed reductive decyanation of aromatic nitriles has been developed, in which the readily available and abundant ethanol was applied as the hydride donor. Various functional groups on the aromatic rings, such as alkoxyl, amino, imino and amide, were compatible in this catalytic protocol. Heteroaryl, benzylic and alkenyl nitriles were also tolerated. Mechanistic investigation indicated that ethanol provided hydride efficientlyviaβ-hydride elimination in this reductive decyanation.
- Wu, Ke,Ling, Yichen,Sun, Nan,Hu, Baoxiang,Shen, Zhenlu,Jin, Liqun,Hu, Xinquan
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supporting information
p. 2273 - 2276
(2021/03/09)
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- A simple and efficientin situgenerated copper nanocatalyst for stereoselective semihydrogenation of alkynes
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Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generatedin situsimply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl-aryl, aryl-alkyl, and aliphatic alkynes were selectively reduced to (Z)-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.
- Park, Byoung Yong,Lim, Taeho,Han, Min Su
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p. 6891 - 6894
(2021/07/19)
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- Regio- And Stereoselective (S N2) N -, O -, C - And S -Alkylation Using Trialkyl Phosphates
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Bimolecular nucleophilic substitution (S N 2) is one of the most well-known fundamental reactions in organic chemistry to generate new molecules from two molecules. In principle, a nucleophile attacks from the back side of an alkylating agent having a suitable leaving group, most commonly a halide. However, alkyl halides are expensive, very harmful, toxic and not so stable, which makes them problematic for laboratory use. In contrast, trialkyl phosphates are inexpensive, readily accessible and stable at room temperature, under air, and are easy to handle, but rarely used as alkylating agents in organic synthesis. Here, we describe a mild, straightforward and powerful method for nucleophilic alkylation of various N -, O -, C - and S -nucleophiles using readily available trialkyl phosphates. The reaction proceeds smoothly in excellent yield, and quantitative yield in many cases, and covers a wide range of substrates. Further, the rare stereoselective transfer of secondary alkyl groups has been achieved with inversion of configuration of chiral centers (up to 98% ee).
- Banerjee, Amit,Hattori, Tomohiro,Yamamoto, Hisashi
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- C-H Alkylation of Aldehydes by Merging TBADT Hydrogen Atom Transfer with Nickel Catalysis
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Catalyst controlled site-selective C-H functionalization is a challenging but powerful tool in organic synthesis. Polarity-matched and sterically controlled hydrogen atom transfer (HAT) provides an excellent opportunity for site-selective functionalization. As such, the dual Ni/photoredox system was successfully employed to generate acyl radicals from aldehydes via selective formyl C-H activation and subsequently cross-coupled to generate ketones, a ubiquitous structural motif present in the vast majority of natural and bioactive molecules. However, only a handful of examples that are constrained to the use of aryl halides are developed. Given the wide availability of amines, we developed a cross-coupling reaction via C-N bond cleavage using the economic nickel and TBADT catalyst for the first time. A range of alkyl and aryl aldehydes were cross-coupled with benzylic and allylic pyridinium salts to afford ketones with a broad spectrum of functional group tolerance. High regioselectivity toward formyl C-H bonds even in the presence of α-methylene carbonyl or α-amino/oxy methylene was obtained.
- Murugesan, Vetrivelan,Ganguly, Anirban,Karthika, Ardra,Rasappan, Ramesh
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supporting information
p. 5389 - 5393
(2021/07/21)
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- The Formal Cross-Coupling of Amines and Carboxylic Acids to Form sp3–sp3 Carbon–Carbon Bonds
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We have developed a deaminative–decarboxylative protocol to form new carbon(sp3)–carbon(sp3) bonds from activated amines and carboxylic acids. Amines and carboxylic acids are ubiquitous building blocks, available in broad chemical diversity and at lower cost than typical C?C coupling partners. To leverage amines and acids for C?C coupling, we developed a reductive nickel-catalyzed cross-coupling utilizing building block activation as pyridinium salts and redox-active esters, respectively. Miniaturized high-throughput experimentation studies were critical to our reaction optimization, with subtle experimental changes such as order of reagent addition, composition of a binary solvent system, and ligand identity having a significant impact on reaction performance. The developed protocol is used in the late-stage diversification of pharmaceuticals while more than one thousand systematically captured and machine-readable reaction datapoints are reposited.
- Cernak, Tim,Zhang, Zirong
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supporting information
p. 27293 - 27298
(2021/11/22)
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- Stereoselective Synthesis of Highly Substituted 1,3-Dienes via “à la carte” Multifunctionalization of Borylated Dendralenes
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Despite the high relevance of 1,3-dienes, stereoselective methods to access tetrasubstituted conjugated dienes are still scarce. We here report an efficient and modular approach that provides access to multifunctional tetrasubstituted 1,3-dienes with excellent levels of regio- and stereoselectivity. This methodology is based on a tetracomponent reaction between a borylated dendralene, an organolithium reagent and two different electrophiles. Mechanistic studies reveal that this transformation proceeds through a regio- and stereoselective carbolithiation/electrophilic trapping of an in situ formed dendralenic boron-ate complex, followed by a stereoretentive halodeborylation. The ease in which complex structural dienes can be accessed and their synthetic versatility highlight the importance and utility of this method.
- Rivera-Chao, Eva,Fa?anás-Mastral, Martín
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p. 16922 - 16927
(2021/07/02)
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- Cu-catalyzed cross-coupling of benzylboronic esters and epoxides
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A reaction between epoxides and benzylboronic acid pinacol esters is described. CuI was found to be an effective catalyst of this transformation upon activation of the benzylboronic ester with an alkyllithium reagent. The reaction was very efficient and a variety of substituted epoxides were found to be good substrates with good regioselectivity for substitution at the less substituted side of the epoxide. A reaction using an enantioenriched secondary benzylboronic ester was found to not be stereospecific.
- Gierszal, Sophia G.,Barker, Timothy J.
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supporting information
(2021/09/20)
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- Dinuclear cobalt complex-catalyzed stereodivergent semireduction of alkynes: Switchable selectivities controlled by H2O
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Catalytic semireduction of internal alkynes to alkenes is very important for organic synthesis. Although great success has been achieved in this area, switchable Z/E stereoselectivity based on a single catalyst for the semireduction of internal alkynes is a longstanding challenge due to the multichemo- and stereoselectivity, especially based on less-expensive earth-abundant metals. Herein, we describe a switchable semireduction of alkynes to (Z)- or (E)-alkenes catalyzed by a dinuclear cobalt complex supported by a macrocyclic bis pyridyl diimine (PDI) ligand. It was found that cis-reduction of the alkyne occurs first and the Z-E alkene stereoisomerization process is formally controlled by the amount of H2O, since the concentration of H2O may influence the catalytic activity of the catalyst for isomerization. Therefore, this protocol provides a facile way to switch to either the (Z)- or (E)-olefin isomer in a single transformation by adjusting the amount of water.
- Chen, Ke,Zhu, Hongdan,Li, Yuling,Peng, Qian,Guo, Yinlong,Wang, Xiaoming
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p. 13696 - 13705
(2021/11/16)
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- Mixed Alkyl/Aryl Diphos Ligands for Iron-Catalyzed Negishi and Kumada Cross Coupling Towards the Synthesis of Diarylmethane
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Mixed alkyl/aryl diphos ligands have been prepared and their application in iron-catalyzed cross coupling of benzylic chlorides with diaryl zinc (Negishi) or aryl Grignard reagents (Kumada) towards the synthesis of diarylmethane has been evaluated. The iron?diphos catalytic system exhibited the enhanced activity and selectivity in the two coupling reactions. The electron-rich mixed PPh2/PCy2 ligands outperformed their symmetrical PPh2 congeners, and led to decreased homocoupling byproduct formation. It indicates that the electronic effect of the ligands plays an important role in the catalytic performance. The Fe catalyst supported by L8 bearing an electron-rich PCy2 substituent and a sterically demanding tert-butyl on ethene backbone exhibited the best catalytic performance and good functional group tolerance in the two cross coupling reactions.
- Ma, Xufeng,Wang, Han,Liu, Yao,Zhao, Xing,Zhang, Jun
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p. 5134 - 5140
(2021/11/16)
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- Electronic structure analysis and reactivity of the bimetallic bis-titanocene vinylcarboxylate complex, [(Cp2Ti)2(O2C3TMS2)]
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Multimetallic redox cooperativity features heavily in both bioinorganic and synthetic reactions. Here, the electronic structure of the bimetallic Ti/Ti complex 11, [(Cp2Ti)2(O2C3TMS2)] has been revisited with EPR, confirming a predominantly TiIII/TiIII electronic structure. Reactions of 11 with 2,6-dimethylphenyl isocyanide (CNXyl), TMSCl, MeI, and BnCl were explored, revealing differential redox chemistry of the bimetallic core. In reactions with CNXyl and TMSCl, the metallacyclic TiIII center remained unperturbed, with reactions taking place at the pendent κ2(O,O)-titanocene fragment, while reaction with MeI resulted in remote oxidation of the metallacyclic Ti center, indicative of a cooperative redox process. All structures were studied via X-ray diffraction and EPR spectroscopic analysis, and their electronic structures are discussed in the context of the covalent bond classification (CBC) electron counting method.
- Huh, Daniel N.,Maity, Asim,Powers, David C.,Schley, Nathan D.,Tonks, Ian A.,Van Trieste, Gerard P.
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- Decarboxylative Radical Addition to Methylideneoxazolidinones for Stereocontrolled Synthesis of Selectively Protected Diamino Diacids
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Syntheses of stereochemically pure and selectively protected diamino diacids can be achieved by redox decarboxylation of distal N-hydroxyphthalimide esters of protected aspartic, glutamic or α-aminoadipic acids via radical addition to methylideneoxazolidinones. The products are useful for solid-supported syntheses of robust bioactive carbocyclic peptide analogs. Yields of reactive primary radical addition are superior to those of more stabilized radicals, and the reaction fails if the alkylideneoxazolidinone has a methyl substituent on its terminus (i.e., 13a/13b).
- Annadate, Ritesh,Beadle, Jonathan,Hsiao, Yu-Ting,Pascoe, Cameron,Vederas, John C.
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supporting information
p. 7270 - 7273
(2021/10/01)
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- Pd-catalyzed sp-sp3cross-coupling of benzyl bromides using lithium acetylides
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Organolithium-based cross-coupling reactions have emerged as an indispensable method to construct C-C bonds. These transformations have proven particularly useful for the direct and fast coupling of various organolithium reagents (sp, sp2, and sp3) with aromatic (pseudo) halides (sp2). Here we present an efficient method for the cross-coupling of benzyl bromides (sp3) with lithium acetylides (sp). The reaction proceeds within 10 min at room temperature and can be performed in the presence of organolithium-sensitive functional groups such as esters, nitriles, amides and boronic esters. The potential application of the methodology is demonstrated in the preparation of key intermediates used in pharmaceuticals, chemical biology and natural products.
- Buter, Jeffrey,Doze, Anna M.,Feringa, Ben L.,Mondal, Anirban,Visser, Paco
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supporting information
p. 7529 - 7532
(2021/08/05)
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