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Molecules 2015, 20(2), 3089-3106; doi:10.3390/molecules20023089

Selective C–C Coupling Reaction of Dimethylphenol to Tetramethyldiphenoquinone Using Molecular Oxygen Catalyzed by Cu Complexes Immobilized in Nanospaces of Structurally-Ordered Materials

1
Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan
2
Research Center for Solar Energy Chemistry, Osaka University, 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan
*
Author to whom correspondence should be addressed.
Academic Editor: Kei Saito
Received: 15 December 2014 / Accepted: 5 February 2015 / Published: 12 February 2015
(This article belongs to the Special Issue Frontier in Green Chemistry Approaches)
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Abstract

Two high-performance Cu catalysts were successfully developed by immobilization of Cu ions in the nanospaces of poly(propylene imine) (PPI) dendrimer and magadiite for the selective C–C coupling of 2,6-dimethylphenol (DMP) to 3,3',5,5'-tetramethyldiphenoquinone (DPQ) with O2 as a green oxidant. The PPI dendrimer encapsulated Cu ions in the internal nanovoids to form adjacent Cu species, which exhibited significantly high catalytic activity for the regioselective coupling reaction of DMP compared to previously reported enzyme and metal complex catalysts. The magadiite-immobilized Cu complex acted as a selective heterogeneous catalyst for the oxidative C–C coupling of DMP to DPQ. This heterogeneous catalyst was recoverable from the reaction mixture by simple filtration, reusable without loss of efficiency, and applicable to a continuous flow reactor system. Detailed characterization using ultraviolet-visible (UV-vis), Fourier transform infrared (FTIR), electronic spin resonance (ESR), and X-ray absorption fine structure (XAFS) spectroscopies and the reaction mechanism investigation revealed that the high catalytic performances of these Cu catalysts were ascribed to the adjacent Cu species generated within the nanospaces of the PPI dendrimer and magadiite. View Full-Text
Keywords: immobilized copper catalyst; poly(propylene imine) dendrimer; magadiite; oxidative coupling; dimethylphenol; diphenoquinone immobilized copper catalyst; poly(propylene imine) dendrimer; magadiite; oxidative coupling; dimethylphenol; diphenoquinone
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Maeno, Z.; Mitsudome, T.; Mizugaki, T.; Jitsukawa, K.; Kaneda, K. Selective C–C Coupling Reaction of Dimethylphenol to Tetramethyldiphenoquinone Using Molecular Oxygen Catalyzed by Cu Complexes Immobilized in Nanospaces of Structurally-Ordered Materials. Molecules 2015, 20, 3089-3106.

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