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.
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.
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.
