ORIGINAL PAPER Modification of silica using piperazine for immobilization of palladium nanoparticles: a study of its catalytic activity as an efficient heterogeneous catalyst for Heck and Suzuki reactions Khodabakhsh Niknam • Maryam Sadeghi Habibabad • Abdollah Deris • Farhad Panahi • Mohammad Reza Hormozi Nezhad Received: 9 August 2012 / Accepted: 8 November 2012 / Published online: 4 December 2012 Ó Iranian Chemical Society 2012 Abstract An efficient heterogeneous palladium catalyst system has been developed based on immobilization of Pd nanoparticles on silica-bonded N-propylpiperazine (SBNPP) substrate. SBNPP substrate can stabilize the Pd nanoparticles effectively so that it can improve their sta- bility against aggregation. Also, grafted piperazine species onto the silica backbone prevents the removing of Pd nanoparticles from the substrate surface. It seems that the high recyclable capability of Pd-SBNPP catalysts is resulted from these two characteristics. Transmission electron microscopy (TEM) of catalyst is shown the size of Pd nanoparticles in Pd-SBNPP average of 20 nm. Fur- thermore, X-ray photoelectron spectroscopy (XPS) of Pd- SBNPP is shown the presence of Pd(0) in the structure of this catalyst. Overall, TEM, XPS and XRD experiments strongly suggested that Pd nanoparticles were formed and immobilized on silica-functionalized piperazine. The cat- alytic activity of this catalyst was investigated in the Heck and Suzuki reactions. The catalyst could be recycled sev- eral times without appreciable loss in catalytic activity. Keywords Heterogeneous palladium nanoparticles Á Silica-bonded N-propylpiperazine Á Heck reaction Á Suzuki reaction Á Aryl halides Á Alkenes Introduction The wide application of metal-catalyzed reactions in aca- demic studies and in the industry piqued the interest of many researchers to improve the synthetic methods for excellent performing of these processes [1–4]. Among many different existing metal-catalyzed strategies for C–C bond formations, palladium catalyzed protocols are mostly considered due to the unique characteristics of palladium [5–10]. Considering the importance of palladium reactions and the cost of palladium metal, different homogeneous and heterogeneous palladium catalyst systems have been developed [11–13]. In respect to the homogeneous cata- lysts, two different types of Pd catalytic systems are reported: (i) using palladium salt with ligands to be formed in in situ Pd-complex in reaction condition, and (ii) using a pre-prepared complex of Pd. It is noteworthy that, in both systems often phosphorous and nitrogen-containing ligands have been used [14]. However, homogenous systems have two major problems; first, they cannot be reused and, therefore, they are not economical. Second, many ligands are toxic and air sensitive, so it is not a green and stable system [15]. In order to have the ability to recover homogeneous catalysts, a complex of palladium metal with the related ligands is deposited onto the surface of solid supports, thus forming heterogeneous catalysts [16, 17]. In the recent years, there is considerable attention on preparation of heterogeneous palladium catalyst based on nanometer scale palladium species [18, 19]. Palladium nanoparticles on a suitable support have the ability to be Electronic supplementary material The online version of this article (doi:10.1007/s13738-012-0188-y) contains supplementary material, which is available to authorized users. K. Niknam (&) Á M. S. Habibabad Á A. Deris Á F. Panahi Department of Chemistry, Faculty of Sciences, Persian Gulf University, 75169 Bushehr, Iran e-mail: khniknam@gmail.com; niknam@pgu.ac.ir M. Reza Hormozi Nezhad Department of Chemistry, Sharif University of Technology, 11155-9516 Tehran, Iran M. Reza Hormozi Nezhad Institute for Nanoscience and Nanotechnology (INST), Sharif University of Technology, 9161 Tehran, Iran 123 J IRAN CHEM SOC (2013) 10:527–534 DOI 10.1007/s13738-012-0188-y