Applied Catalysis A: General 406 (2011) 124–132 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General jo u r n al hom epage: www.elsevier.com/locate/apcata Pd nanoparticles immobilized on PAMAM-grafted MWCNTs hybrid materials as new recyclable catalyst for Mizoraki–Heck cross-coupling reactions Mohammad Reza Nabid ∗ , Yasamin Bide, Seyed Jamal Tabatabaei Rezaei Department of Chemistry, Shahid Beheshti University, G.C., P.O. Box 1983963113 Tehran, Iran a r t i c l e i n f o Article history: Received 21 May 2011 Received in revised form 10 August 2011 Accepted 16 August 2011 Available online 24 August 2011 Keywords: Dendrimer Palladium nanoparticles Carbon nanotubes Supported catalysis Heck reaction a b s t r a c t Polyamidoamine (PAMAM) dendrimers up to the third generation (G) were grown onto the surface of functionalized multiwall carbon nanotubes (MWCNTs-NH 2 ) by a divergent method, the PAMAM-grafted- MWCNTs (PAMAM-g-MWCNTs) hybrid materials were obtained. Because of the surface modification of the multiwall carbon nanotubes with PAMAM dendrimers, these hybrid materials are not only soluble in aqueous medium but also are able to trap water soluble metal ions such as Pd 2+ via complex formation of PAMAM dendrimer with metal ions. The reduction of trapped palladium ions in the dendritic shell of PAMAM-g-MWCNTs by sodium borohydride led to immobilized palladium nanoparticles on the surface of MWCNTs. Thus, palladium nanoparticles were immobilized by PAMAM-g-MWCNTs hybrid materials (PdNs-PAMAM-g-MWCNTs) and their application as a new nanocatalyst toward Heck reaction in different conditions was investigated. The G3 and G2 hybrid materials were found to be very active in cross- coupling reactions of aryl iodides, bromides and also chlorides with olefinic compounds in Heck reactions with short reaction time duration and high yields. The catalyst can be recycled several times without loss in activity. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Since their discovery by Iijima [1], carbon nanotubes (CNTs) have attracted great interest in the most fields of science due to their unique physical and chemical properties [2,3]. Owing to their unique structure and interesting properties such as large sur- face area, CNTs are excellent supporting materials for catalysts, especially in heterogeneous catalysis [4,5]. Although CNTs sup- ported metal nanoparticles exhibit greater catalytic efficiency than their bulk counterparts, because of high surface-to-volume ratio [6], there are some difficulties in dispersing metal nanoparticles on the surface of pristine CNTs due to their hydrophobic nature as well as their tendency for agglomeration. In order to over- come these problems and to favor a high loading of nanoparticles, grafting well-defined polymers known as dendrimers can act as macromolecular coupling agents carrying multiple binding sites [7–16]. Dendrimers are nanosized, highly branched molecules, with very well-defined chemical structures, engineered precisely to carry molecules encapsulated in their interior void spaces or attached to their surface. These unique abilities of dendrimers led to the design of novel dendritic materials for a variety of advance applications [17]. Chemical attachment of dendrimers to ∗ Corresponding author. Tel.: +98 21 29902800; fax: +98 21 22431586. E-mail address: m-nabid@sbu.ac.ir (M.R. Nabid). the surface of CNTs can be performed by either “convergent” or “divergent” methods. In convergent method prefabricated den- drimers are connected to functionalize CNTs through chemical reaction. The convergent synthesis strategy is characterized by low grafting density because of the hindrance of the dendrimer branches which react with CNTs [18–20]. The divergent method involves the growth of dendrimers from the surface of CNTs by first covalently attaching of appropriate functional groups. In contrast to convergent route this method leads to the higher grafting den- sity and control over the dendrimer growth with the possibility of designable structures [21,22]. Palladium has been recognized as an indispensable catalyst for carbon–carbon and carbon-heteroatom bond forming reac- tions and there is a great deal of literature on its properties in many reactions [23–31]. Recently, palladium nanoparticles sup- ported on insoluble solids have received considerable attention as a new generation of heterogeneous catalysts in various sci- entific fields because of their superior catalytic performance, good stability, ease of separation and satisfactory reusability in comparison to the traditional homogeneous Pd(OAc) 2 , PdCl 2 catalysts [32–57]. Because of these reasons and also as a part of our ongoing research program on the application of cata- lysts for the development of useful new synthetic methodologies [58–61], herein, we report the synthesis of a heterogeneous palladium nanocatalyst supported on PAMAM-grafted-MWCNTs and its efficiency in the promotion of the Heck coupling reaction. 0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2011.08.021