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CH Bond Activation (ch + bond_activation)
Selected AbstractsSpecific Processes and Scrambling in the Dehydrogenation of Ethane and the Degenerate Hydrogen Exchange in the Gas-Phase Ion Chemistry of the Ni(C,H3,O)+/C2H6 CoupleHELVETICA CHIMICA ACTA, Issue 5 2007Maria Schlangen Abstract A mechanistically unprecedented situation characterizes the gas-phase ion chemistry of Ni(C,H3,O)+ when reacted under thermal, single-collision conditions with ethane. A dehydrogenation channel leading to Ni(C3,H7,O)+ is to 90% preceded by a complete loss of positional identity of all nine H-atoms of the encounter complex (,scrambling'), whereas ca. 10% of the reaction exhibit a selective CH bond activation of the alkane. In addition, a degenerate H exchange between ethane and the (C,H3,O) unit occurs as a side reaction, the mechanistic details of which remain unknown for the time being. [source] Regioselective C-2 or C-5 Direct Arylation of Pyrroles with Aryl Bromides using a Ligand-Free Palladium CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Julien Roger Abstract A simple and atom-economical procedure for the regioselective C-2 or C-5 arylation of pyrroles via a CH bond activation is reported. Only 0.5,0.01 mol% of commercially available and air-stable ligand-free palladium(II) acetate [Pd(OAc)2] was employed as the catalyst. The presence of electron-withdrawing substituents such as formyl, acetyl or ester at the C-2 position of the pyrrole is tolerated. This environmentally attractive procedure has also been found to be tolerant to a very wide variety of functional groups on the aryl bromides such as formyl, acetyl, propionyl, ester, nitrile, nitro, fluoro, methoxy, amino or trifluoromethyl. [source] Palladium-Catalyzed Direct C-4 Arylation of 2,5-Disubstituted Furans with Aryl BromidesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2008Aditya Abstract A simple and atom-economic procedure for the selective C-4 arylation of 2,5-disubstituted furans via CH bond activation using electron-deficient aryl bromides is reported. Only 0.5 mol% of the commercially available dimeric (allene)palladium chloride, [Pd(C3H5)Cl]2, was employed as catalyst. This environmentally attractive procedure has been found to be tolerant to a variety of functional groups on the aryl bromide such as carbonyl, nitrile, nitro, fluoro, ester or trifluoromethyl. [source] A Versatile Catalyst for Intermolecular Direct Arylation of Indoles with Benzoic Acids as Arylating ReagentsCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2010Jun Zhou Coupled together: With a versatile catalyst system (Pd(TFA)2/Ag2CO3/propionic acid) both electron-rich and -deficient benzoic acids serve as arylating reagents for the direct functionalization of a wide rage of indoles by a combination of decarboxylation and CH bond activation. Depending on the nature of the benzoic acids, the reaction occurs selectively at either the C2- or C3-position of indoles, which may arise from two different catalytic pathways (see scheme; TFA=trifluoroacetate). [source] Competitive Hydrogen-Atom Abstraction versus Oxygen-Atom and Electron Transfers in Gas-Phase Reactions of [X4O10].+ (X=P, V) with C2H4CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2010Nicolas Dietl Dipl.-Chem. Why so different? The comparison of the reaction of "bare" [P4O10].+ and [V4O10].+ with ethene by mass-spectrometric and computational studies permits insight into mechanistic aspects of the competition between CH bond activation and oxygen-atom and electron transfers. Whereas [P4O10].+ reacts by homolytic CH bond cleavage and electron transfer, the isostructural [V4O10].+ shows only oxygen-atom transfer (see picture). [source] Tertiary Carbinamine Synthesis by Rhodium-Catalyzed [3+2] Annulation of N-Unsubstituted Aromatic Ketimines and AlkynesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Zhong-Ming Sun Dr. Abstract A convenient and waste-free synthesis of indene-based tertiary carbinamines by rhodium-catalyzed imine/alkyne [3+2] annulation is described. Under the optimized conditions of 0.5,2.5,mol,% [{(cod)Rh(OH)}2] (cod=1,5-cyclooctadiene) catalyst, 1,3-bis(diphenylphosphanyl)propane (DPPP) ligand, in toluene at 120,°C, N-unsubstituted aromatic ketimines and internal alkynes were coupled in a 1:1 ratio to form tertiary 1H -inden-1-amines in good yields and with high selectivities over isoquinoline products. A plausible catalytic cycle involves sequential imine-directed aromatic CH bond activation, alkyne insertion, and a rare example of intramolecular ketimine insertion into a RhI,alkenyl linkage. [source] Palladium-Catalyzed Formation of Highly Substituted Naphthalenes from Arene and Alkyne HydrocarbonsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2008Yao-Ting Wu Prof. Abstract Several highly substituted naphthalenes 3 have been synthesized in a one-pot reaction by treatment of arenes 1 with alkynes 2 in the presence of palladium acetate and silver acetate. In this Pd-catalyzed protocol, an arene provides a benzo source for the construction of a naphthalene core through twofold aryl CH bond activation. Reaction of triphenylphosphine with diphenylethyne (2,a) under the catalysis of PdIV complexes produced 1,2,3,4-tetraphenylnaphthalene (3,ba) in 62,% yield. Here, triphenylphosphine undergoes one aryl CP bond cleavage and one aryl CH bond activation to serve as a benzo moiety. Crystal structures of cycloadducts 3,ea, 3,ga, and 3,ac have been analyzed. The twisted naphthalenes arise not only from the overcrowded substituents but also from the contribution of the CH3,, interaction. [source] Conformational Control of [26]Hexaphyrins(1.1.1.1.1.1) by meso -Thienyl SubstituentsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007Masaaki Suzuki Abstract Conformational preference and chemical stability of meso -aryl-substituted [26]hexaphyrins(1.1.1.1.1.1) ([26]ArH) depend upon meso -aryl substituents. Although only a planar and rectangular conformation (type-II conformation) has been identified for [26]ArH so far, we have demonstrated here that a different conformation with all the pyrroles pointing inward (type-I conformation) is preferred for [26]ArH (7 and 11 -I) bearing small 2-thienyl or 3-thineyl substituents at 15- and 30-positions. Both type-I and type-II [26]ArH exhibit diatropic ring currents, reflecting aromatic character. Type-I [26]ArH, such as 7 and 11 -I, have been shown to serve as an effective ligand for PdII ions to provide bis-PdII complexes 12 and 13 with N3C1 coordination through facile CH bond activation. [source] |