Hydrogen atoms on supported metal nanoparticles (NPs) play a significant role in heterogeneous catalysis. Despite the extensive previous research, however, the adsorption of hydrogen onto practical supported NP catalysts is still unclear especially in the atmospheric pressure conditions. In this study, adsorption/desorption isotherms of hydrogen on Pt NPs supported on alumina (Al 2 O 3 ) were obtained in gas-flow conditions using the analysis of the difference spectra of Pt L III -edge X-ray absorption spectroscopy (XAS) at 303 K. From the analysis of extended X-ray absorption fine structure (EXAFS), a positive linear relationship was observed between the hydrogen coverage and PtÀ Pt bond distance. Additionally, the re-adsorption experiment of hydrogen after the first adsorption/desorption cycle and the transient change of dispersive XAS spectra in the hydrogen adsorption suggests that the hydrogen adsorption induces the surface reconstruction of Pt NPs on Al 2 O 3 at around room temperature and atmospheric pressure.
Herein, we report the stereospecific Sonogashira coupling
of a
chiral α-bromocarboxamide possessing a tert-alkyl moiety and an alkyne; this reaction produces a chiral tert-alkylated alkyne in a stereoretentive manner. In this
reaction, both the CuBr/bathophen catalyst system and carboxamide
directing group are essential for achieving the high enantiospecificities
of the couplings. Mechanistic studies of this reaction revealed that
the alkynyl copper species is the key intermediate that coordinates
to the carboxamide group of chiral α-bromocarboxamide.
The Suzuki-Miyaura coupling is extremely useful to construct Csp2-Csp2 carbon bonds. On the other hand, Csp2-Csp3 coupling reactions are do not work well, and tert-alkylative Suzuki-Miyaura coupling is particularly challenging due to problematic oxidative addition and beta-hydride elimination side reactions. In this short review, we will introduce recent examples of tert-alkylative Suzuki-Miyaura couplings with tert-alkyl electrophiles or -boron reagents. The review will mainly focus on catalyst and product structures and the proposed mechanisms .
There is significant interest in the development of process routes for active pharmaceutical ingredients using C−H arylation methodology. An efficient and practical synthetic route for febuxostat (1), which is the first non-purine-type xanthine oxidase inhibitor, was established via palladium-and coppercatalyzed C−H arylation of thiazole with aryl bromide. The catalyst loading was reduced to 0.1 mol % for the intermolecular C−H arylation, and a three-step synthesis produced febuxostat in 89% overall yield with excellent selectivity.
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