title: Direct C-H arene homocoupling over gold nanoparticles supported on metal oxides.
abstract: The direct CH/CH bond coupling of dimethyl phthalate was performed successfully over supported gold nanoparticle catalysts. Gold on reducible metal oxides, such as Co3 O4 , and on inert oxides that have an oxygen-releasing capacity, such as ZrO2 , showed the highest catalytic activity for the production of biphenyl tetracarboxylate using O2 as the sole oxidant. Supported Pd(OH)2 also catalyzed the reaction, but the catalytic activity was inferior to that of gold. Moreover, the gold catalysts exhibited excellent regioselectivity for the synthesis of valuable 3,3',4,4'-tetrasubstituted biphenyls by coupling with each other at the 4-position without the need for additional ligands. Gold catalysts also promoted the oxidative homocoupling of arenes including o-xylene to give symmetrical biaryls with high regioselectivity. X-ray absorption fine structure measurements revealed that the catalytically active species was Au(0) and that the lattice oxygen of Co3 O4 played an important role in the gold-catalyzed oxidative coupling. The results of the kinetic studies were consistent with an electrophilic aromatic substitution pathway. Regioselectivity is not controlled by directing groups or the electronic character of the substituents but by steric hindrance, which suggests that gold nanoparticles not only catalyze the oxidative coupling but also act as bulky ligands to control the regioselectivity.
authors.affiliation: Research Center for Gold Chemistry, School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo 192-0397 (Japan); Department of Chemistry, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan).
authors.forename: Tamao
authors.initials: T
authors.lastname: Ishida
authors.forename: Shohei
authors.initials: S
authors.lastname: Aikawa
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Mise
authors.forename: Ryota
authors.initials: R
authors.lastname: Akebi
authors.forename: Akiyuki
authors.initials: A
authors.lastname: Hamasaki
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Honma
authors.forename: Hironori
authors.initials: H
authors.lastname: Ohashi
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Tsuji
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Miyasaka
authors.forename: Takushi
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Makoto
authors.initials: M
authors.lastname: Tokunaga
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D010795:Phthalic Acids / Q000737:chemistry; D014992:Xylenes / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D010087:Oxides; D010795:Phthalic Acids; D014992:Xylenes; C024629:dimethyl phthalate; D003035:Cobalt; D006046:Gold; D015040:Zirconium; C028541:zirconium oxide; C060728:cobalt oxide; C026114:2-xylene
keywords: gold; heterogeneous catalysis; nanoparticles; oxidation; supported catalysts