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Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides

1
Laboratory of Organic Chemistry, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu 501–1196, Japan
2
Catalysts Development Center, N.E. Chemcat Corporation, 678 Ipponmatsu, Numazu 410–0314, Japan
3
Department of Chemistry and Biomolecular Science, Gifu University, 1-1 Yanagido, Gifu 501–1193, Japan
*
Author to whom correspondence should be addressed.
Catalysts 2019, 9(5), 461; https://doi.org/10.3390/catal9050461
Received: 30 April 2019 / Revised: 17 May 2019 / Accepted: 17 May 2019 / Published: 19 May 2019
(This article belongs to the Special Issue Catalysts for Suzuki–Miyaura Coupling Reaction)
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Abstract

The catalyst activities of various heterogeneous palladium catalysts supported by anatase-, rutile- and brookite-type titanium oxide for ligand-free Suzuki–Miyaura cross-coupling reactions of aryl chlorides were evaluated. Palladium acetate [Pd(OAc)2], supported on anatase-type titanium oxide (TiO2) via acetonitrile solution impregnation process without reduction [Pd/TiO2 (anatase-type)], demonstrated the highest catalyst activity in comparison to those of other titanium oxide (rutile- or brookite-type) supported Pd(OAc)2 without reduction and reduced Pd/TiO2 (anatase-type) [Pd(red)/TiO2 (anatase-type)]. Various aryl chloride and bromide derivatives were smoothly coupled with arylboronic acids including heteroarylboronic acids in the presence of 5–10 mol% Pd/TiO2 (anatase-type) without the addition of any ligands. Although the fresh Pd/TiO2 (anatase-type) catalyst was surprisingly comprised of ca. 1:2 mixture of palladium(II) and palladium(0) species according to X-ray photoelectron spectroscopy (XPS), in spite of no reduction process, significant further increment of palladium(0) species was observed during the Suzuki–Miyaura coupling reaction, and Pd/TiO2 (anatase-type) was converted into a catalyst, which contained palladium(0) species as the main component [ca. 1:5 mixture of palladium(II) and palladium(0) species]. Therefore, the reduction via the electron donation process to the palladium(II) species may have occurred during the reaction on anatase-type titanium oxide. View Full-Text
Keywords: Suzuki–Miyaura reaction; palladium; heterogeneous catalyst; titanium oxide; anatase titania; aromatic chloride Suzuki–Miyaura reaction; palladium; heterogeneous catalyst; titanium oxide; anatase titania; aromatic chloride
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Yamada, T.; Masuda, H.; Park, K.; Tachikawa, T.; Ito, N.; Ichikawa, T.; Yoshimura, M.; Takagi, Y.; Sawama, Y.; Ohya, Y.; Sajiki, H. Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides. Catalysts 2019, 9, 461.

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