4920-95-0Relevant articles and documents
Palladium-Catalyzed Cross-Dehydrogenative Coupling of o-Xylene: Evidence of a New Rate-Limiting Step in the Search for Industrially Relevant Conditions
álvarez-Casao, Yolanda,van Slagmaat, Christian A. M. R.,Verzijl, Gerard K. M.,Lefort, Laurent,Alsters, Paul L.,Fernández-Ibá?ez, M. ángeles
, p. 2620 - 2626 (2018)
An efficient cross-dehydrogenative coupling of o-xylene under neat conditions, which brings important industrial benefits towards the synthesis of a monomer used in polyimide resins, is reported. The catalyst based on the combination of Pd/N ligand/carboxylate=1:1:2 does not require a Cu cocatalyst and proceeds at 11 bar of O2 pressure. Evaluation of the deuterium kinetic isotope effect (KIE) provides evidence for three different rate-determining steps, which depend on the reaction conditions (medium, temperature). Under the reported neat conditions, the dissociation of a carboxylate-bridged dimer to generate a more reactive monometallic Pd species is proposed to be the rate-limiting step.
Aerobic oxidative coupling of o-xylene: Discovery of 2-fluoropyridine as a ligand to support selective Pd-catalyzed C-H functionalization
Izawa, Yusuke,Stahl, Shannon S.
, p. 3223 - 3229 (2010)
An improved method for the direct oxidative coupling of o-xylene could provide streamlined access to an important monomer used in polyimide resins. The use of 2-fluoropyridine as a ligand has been found to enable unprecedented levels of chemo- and regioselectivity in this palladium-catalyzed aerobic oxidative coupling reaction. Preliminary insights have been obtained into the origin of the effectiveness of 2-fluoropyridine as a ligand. Copyright
Single-site metal-organic framework catalysts for the oxidative coupling of arenes: Via C-H/C-H activation
Van Velthoven, Niels,Waitschat, Steve,Chavan, Sachin M.,Liu, Pei,Smolders, Simon,Vercammen, Jannick,Bueken, Bart,Bals, Sara,Lillerud, Karl Petter,Stock, Norbert,De Vos, Dirk E.
, p. 3616 - 3622 (2019)
C-H activation reactions are generally associated with relatively low turnover numbers (TONs) and high catalyst concentrations due to a combination of low catalyst stability and activity, highlighting the need for recyclable heterogeneous catalysts with stable single-atom active sites. In this work, several palladium loaded metal-organic frameworks (MOFs) were tested as single-site catalysts for the oxidative coupling of arenes (e.g. o-xylene) via C-H/C-H activation. Isolation of the palladium active sites on the MOF supports reduced Pd(0) aggregate formation and thus catalyst deactivation, resulting in higher turnover numbers (TONs) compared to the homogeneous benchmark reaction. Notably, a threefold higher TON could be achieved for palladium loaded MOF-808 due to increased catalyst stability and the heterogeneous catalyst could efficiently be reused, resulting in a cumulative TON of 1218 after three runs. Additionally, the palladium single-atom active sites on MOF-808 were successfully identified by Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
Discovery and mechanistic investigation of Pt-catalyzed oxidative homocoupling of benzene with PhI(OAc)2
Abu-Omar, Mahdi M.,Nabavizadeh, S. Masoud,Niroomand Hosseini, Fatemeh,Park, Chan,Wu, Guang
supporting information, p. 2477 - 2486 (2020/03/05)
We present a Pt-catalyzed direct coupling of benzene to biphenyl. This catalytic reaction employs a cyclometalated platinum(ii) complex [PtMe(bhq)(SMe2)] (bhq = benzo[h]quinolate) with PhI(OAc)2 as an oxidant and does not require an acid, a co-catalyst or a solvent. The reaction kinetics and characterization of potential catalytic species are reported. The reaction is first-order in Pt and second-order in benzene, which implicates the second C-H activation step as rate-determining. A Pt(ii)/Pt(iv) catalytic cycle is suggested. The reaction commences by oxidation of the Pt(ii) complex to give the platinum(iv) species [Pt(bhq)(SMe2)(OAc)2](OAc) followed by C-H activation of benzene to afford the intermediate [PtPh(bhq)(SMe2)(OAc)](OAc) concurrently with the release of HOAc. A second benzene molecule reacts similarly to give the diphenyl intermediate [PtPh2(bhq)(SMe2)](OAc). C-C bond forming reductive elimination ensues to regenerate Pt(ii) and complete the catalytic cycle. The proposed mechanism has been examined by DFT computations, which provide support to experimental findings.
A method for preparing four methyl biphenyl
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Paragraph 0079; 0080, (2017/01/26)
The invention provides a preparation method of tetramethyl biphenyl, which comprises the following steps: mixing halogenated o-xylene, magnesium metal, iodine, ether and transition metal catalyst, and reacting to obtain the tetramethyl biphenyl, wherein the mol ratio of ether to magnesium metal is (0.5-3):1. Compared with the prior art of synthesizing tetramethyl biphenyl from halogenated o-xylene, the invention has the following advantages: by using the raw material halogenated o-xylene as the solvent, the preparation of the format reagent and the coupling reaction are carried out in the initial raw material, so that the addition of abundant anhydrous solvent as the reaction medium is not needed, thereby lowering the reaction cost and simplifying the production technique; the magnesium metal is directly added into the halogenated o-xylene to obtain the format reagent, so the process is simple and the conditions are mild and controllable; and the raw material, the concentration of which in the reaction system is high, is used as the solvent and participates in the oxidation-reduction process in the coupling reaction, no oxidizer is needed, so the reaction conditions are mild and controllable.
A method for preparing four methyl biphenyl
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Paragraph 0039; 0042; 0043, (2017/01/12)
The invention provides a preparation method of tetramethyl biphenyl, which comprises the following steps: mixing o-xylene, oxidizer, additive and metal catalyst, and reacting to obtain the tetramethyl biphenyl, wherein the additive is organic acid and/or organic acid anhydride, and the oxidizer is inorganic oxidizer and/or organic oxidizer containing metal cation. Compared with the prior art of synthesizing tetramethyl biphenyl from halogenated o-xylene, the invention uses the o-xylene for direct coupling to obtain the tetramethyl biphenyl. The raw material o-xylene is cheap and accessible, and the preparation of the halogenated o-xylene is not needed, so the invention lowers the production cost, is simple to operate and has the advantages of mild reaction conditions and low facility request; and under the action of the catalyst, the o-xylene is directly coupled to prepare the tetramethyl biphenyl, and all the carbon atom frameworks of the o-xylene enter the product, so the invention also has the advantage of high economical efficiency of atoms.
PROCESS FOR THE PRODUCTION OF BIARYL COMPOUNDS
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Page/Page column 14; 15, (2016/02/10)
Process for producing biaryl compounds by aerobic cross dehydrogenative coupling (CDC) of two arene groups comprising at least one aryl carbon-hydrogen bond, in the presence of a catalyst system comprising a palladium salt comprising at least one non-cyclopalladatable carboxylate anion and one or more non-beta-eliminatable, non-cyclopalladatable ligands comprising at least one N-donor atom, the one or more ligands having a 0.5/1 - 1.5/1 molar ratio of N-donor atoms relative to the Pd atoms.
Kinetics and mechanism of heterogeneous palladium-catalyzed coupling reactions of chloroaryls in water
Mukhopadhyay, Sudip,Rothenberg, Gadi,Gitis, Diana,Wiener, Harold,Sasson, Yoel
, p. 2481 - 2484 (2007/10/03)
Coupling reactions of substituted chlorobenzenes to biphenyls catalyzed by palladium on carbon are performed in water using sodium hydroxide and sodium formate in the presence of a surface active agent. Thus, chlorobenzene, p-chloro-o-xylene, p-chloro-1,1,1-trifluorotoluene, p-chloroanisole, and p-chlorotoluene are coupled under moderate conditions to the respective biaryls. A competing reduction process occurs (e.g. chlorobenzene is reduced to benzene), which can be minimized by altering conditions. The relationship of product selectivity to reaction temperature, formate concentration, base concentration, and surfactant type is examined. The roles of formate, Pd catalyst, and surfactant are discussed. It is proposed that the reduction is dependent on the participation of palladium hydride [Pd2+(H-)2], while the coupling occurs via single electron-transfer from Pd0 to the substrate, with subsequent decomposition of the chloroaryl radical anions to obtain aryl radicals and chloride anions. This mechanism is supported by experiments with stoichiometric and sub-stoichiometric amounts of palladium which indicate that selective coupling can occur also in the absence of hydrogen (providing that reduced palladium Pd0, is present in sufficient amount), and by kinetic investigations which indicate that the coupling is actually a first-order reaction, for which the rate-determining step may be the dissociation of the chloroaryl radical anion.
Palladium-catalyzed aryl-aryl coupling in water using molecular hydrogen: Kinetics and process optimization of a solid-liquid-gas system
Mukhopadhyay, Sudip,Rothenberg, Gadi,Wiener, Harold,Sasson, Yoel
, p. 14763 - 14768 (2007/10/03)
Coupling of substituted chlorobenzenes to the respective biphenyls is effected in water, using hydrogen gas and NaOH in the presence of catalytic PEG-400 and Pd/C. The catalyst can be efficiently recycled. The competing reduction process (e.g. of chlorobenzene to benzene) can be minimized by altering reaction conditions. The roles of the hydrogen, the hydroxide, the Pd catalyst, and the PEG are discussed.
Regiospecific Synthesis of 2,3,6,7,10,11-Hexasubstituted Triphenylenes by Oxidative Photocyclisation of 3,3'',4,4',4'',5'-Hexasubstituted 1,1':2'1''-Terphenyls
Bushby, Richard J.,Hardy, Cristopher
, p. 721 - 724 (2007/10/02)
Photolysis of 4',5'-dimethoxy-1,1':2',1''-terphenyl (3) in the presence of iodine gives 2,3-dimethoxy-triphenylene (4) (72percent).A similar photolysis of either 3,4-dimethoxy-3'',4',4'',5'-tetramethyl-1,1':2',1''-terphenyl (5) or 4',5'-dimethoxy-3,3'',4,4''-tetramethyl-1,1':2',1''-terphenyl (7) gives 2,3-dimethoxy-6,7,10,11-tetramethyltriphenylene (6).The regiospecificity of these photocyclisation reactions makes this the best route to asymmetrical 2,3,6,7,10,11-hexasubstituted derivatives of triphenylene.
