Organic syntheses by microwave selective heating of novel metal/CMC catalysts – The Suzuki–Miyaura coupling reaction in toluene and the dehydrogenation of tetralin in solvent-free media Satoshi Horikoshi a,⇑ , Yindee Suttisawat a , Atsushi Osawa a,b , Chiemi Takayama a , Xiuqin Chen b , Shaoming Yang b , Hideki Sakai b , Masahiko Abe b , Nick Serpone c,⇑ a Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyodaku, Tokyo 102-8554, Japan b Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan c Gruppo Fotochimico, Dipartimento di Chimica, Universita di Pavia, via Taramelli 10, Pavia 27100, Italy article info Article history: Received 25 January 2012 Revised 27 February 2012 Accepted 28 February 2012 Available online 28 March 2012 Keywords: Carbon microcoils Activated carbon Hot spots Microplasma Microwaves Suzuki–Miyaura coupling reaction Tetralin dehydrogenation reaction abstract The present study examines carbon microcoils (CMCs) as a novel support for Pt and Pd nanocatalysts and compares it with activated carbon nanoparticles as support for Pt and Pd metal deposits in two model microwave-assisted organic syntheses: (i) the Suzuki–Miyaura coupling reaction between phenylboronic acid and 1-bromo-4-methylbenzene in toluene solvent to produce 4-methyl-biphenyl and (ii) the dehy- drogenation of tetralin (1,2,3,4-tetrahydronaphthalene) in solvent-free conditions. The microwave absorption capacity of the CMCs was more effective than the ACs support from the viewpoint of dielectric parameters (dielectric constant, dielectric loss, and loss tangent). Possible generation of microplasma (i.e., hot spots) on both supports that can impact on the progress of the reactions was monitored visually and photographed with a high-speed camera. Conventional heating (oil bath or heating mantles) of the Pd(Pt)/CMCs and Pd(Pt)/ACs system led to significantly lower product yields. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Carbon microcoils (CMCs) present unique physical characteris- tics, electric properties, electromagnetic properties, chemical prop- erties, and bio-activation properties as expected of innovative materials [1]. As such, CMCs are good candidates as absorbers of electromagnetic waves, as field emitters, as microsensors, as hydro- gen storage materials, and as electrode materials, among others. CMCs look like microsized springs made of carbon that has attracted considerable attention in the stealth technology of the military establishment owing to its high absorption of radio-waves. Particularly significant, these carbon microcoils display a double 3D-helix chiral structure with a coil diameter typically 1–10-lm and a 0.1–10-mm coil length. CMCs can effectively absorb electro- magnetic waves in the 2–18 GHz microwave regions [2]. Recent studies on heterogeneous metal catalyst reactions have shown that microwave radiation as the heating source is particu- larly advantageous in many processes [3]. Microwave heating uti- lizes the polarization ability of molecules to transform electromagnetic energy into thermal energy. As such, in a hetero- geneous catalyzed reaction system in a nonpolar solvent, it is pos- sible to heat selectively only the catalysts by microwave irradiation [4]. Therefore, in the construct of the reaction system, the micro- waves must interact solely with the solid catalyst, a feature that cannot be attained by existing conventional heating methods. To attain such a microwave/catalyst reaction system requires that the catalyst be supported on a material that is a strong absorber of microwave radiation. Activated carbon (AC) has proven in the past to be a good catalyst support and a useful microwave absorber. In the present study, we examine the carbon microcoils as a microwave absorber and as a possible catalyst support. Features of the heat developed on microwave irradiation of CMCs are com- pared with those of the conventional activated carbon support. Pal- ladium nanoparticles used as the metal catalysts were deposited on the CMC surface and used in the Suzuki–Miyaura coupling reac- tion as a model of an organic synthesis in toluene solvent; this sol- vent is a poor microwave absorber. As well, platinum nanoparticle deposits on the CMCs were examined in the dehydrogenation of tetralin as another model reaction and compared with the same deposits on activated carbon; tetralin is also a poor microwave absorber. Interestingly, in the hydrogen storage field, tetralin has been considered as a sort of cycloalkane material for hydrogen storage [5]. 0021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcat.2012.02.019 ⇑ Corresponding authors. E-mail addresses: horikosi@sophia.ac.jp (S. Horikoshi), nick.serpone@unipv.it, nickser@alcor.concordia.ca (N. Serpone). Journal of Catalysis 289 (2012) 266–271 Contents lists available at SciVerse ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat