Gold-Decorated 3D 2,6-Diaminopyridine Network: A Robust Catalyst for the Bromination of Aromatic Compounds Ali Pourjavadi,* ,† Nahid Keshavarzi, † Seyed Hassan Hosseini, ‡ and Firouz Matloubi Moghaddam § † Polymer Research Laboratory, Department of Chemistry, Sharif University of Technology, Tehran, Iran ‡ Department of Chemical Engineering, University of Science and Technology of Mazandaran, Behshahr, Iran § Laboratory of Organic Synthesis and Natural Products, Department of Chemistry, Sharif University of Technology, Tehran, Iran * S Supporting Information ABSTRACT: This article reports the synthesis of a magnetic heterogeneous catalyst through the decoration of gold ions onto the cross-linked polymeric nanocomposite from 2,6-diaminopyridine. The activity of the resulting catalyst was then evaluated in the bromination of aromatic compounds. The nitrogen rich support showed a high affinity to gold ions, and the measured content of Au was 0.76 mmol g -1 . The structure of the catalyst was fully characterized by using Fourier-transform infrared spectroscopy, thermogravimetric analysis, atomic absorption spectroscopy, transmission electron microscopy, scanning electron microscope, energy-dispersive X-ray spectroscopy, Brunauer- Emmett-Teller surface area analysis, a vibrating sample magnetometer, and X-ray diffraction techniques. Various substituted arenes were converted to the corresponding Br-containing aromatic compounds in a good to excellent yield using 300 mg of catalyst. It is worth mentioning, that the catalyst was simply collected from the solution and reused in eight cycles without significant loss of its activity. ■ INTRODUCTION Haloarenes have been used as intermediates in biologically active compounds. These compounds are specifically useful for the synthesis of drugs, pharmaceuticals, agrochemicals, pig- ments, and photographic materials. 1 Aryl bromides are starting materials in several important organic reactions, including Heck, Suzuki, and Sonogashira reactions. 2 The direct method for the bromination of aromatic systems uses Br 2 as a reagent. However, the main problem of this reaction is that the generation of highly corrosive and toxic HBr as a byproduct, which causes serious environmental issues. 3 Different types of protocols have been developed for the bromination of aromatic substrates, but the most commonly used reagent, N-bromosuccinic imide (NBS), possesses easy handling and low toxicity. 4 However, when NBS is used for the bromination of aromatic compounds, a large amount of a strong Lewis or Bronsted acid is usually required as the catalyst in harsh reaction conditions. 5 Wang and co-workers have reported a mild protocol for efficient bromination of various types of arenes by using AuCl 3 as the catalyst. 6 They reported that only a tiny amount of AuCl 3 catalyst enhanced the bromination reaction, and the reaction can be performed at lower temperatures. 7 The mechanism of the reaction showed that a gold atom could create a complex with an aromatic compound and NBS, which enhanced the reactivity of both substrates. 7a In the past several decades, numerous papers have reported the application of Au as catalyst in various organic transformations. 8 Major problems in the Au-catalyzed reactions are the high cost of gold and the difficult recycling of the catalyst, which have limited the widespread industrial application of Au-catalysts. To solve these drawbacks, a versatile approach is the heterogneization of Au. 9 Various types of solid beds have been introduced for immobilization of gold ions, such as magnetic nanoparticles, 10 silica, 11 cross-linked polymers, 12 and alumina. 9f,13 Magnetic nanoparticles have advantages, such as easy separation, high surface area, good dispersibility, and excellent stability in various conditions, compared to those of mesoporous silica compounds for the immobilization of gold. 15 In spite of the several advantages of heterogeneous catalytic systems, the remaining problem is the low loading amount of the active spices (gold). In the recent decade, use of three- dimensional (3D) polymeric networks for the immobilization of active catalysts has been developed as an ideal way to increase the loading amount of metal ions. 14 The main reasons for choosing the 3D polymeric networks as metal supports are the porosity and the presence of numerous chelating sites. 14g Since each polymeric chain is composed of several coordinating monomers, the final 3D polymeric network can carry a large number of metal ions. The decoration of magnetic nanoparticles into the 3D polymeric network resulted in the Received: March 16, 2018 Revised: June 22, 2018 Accepted: June 26, 2018 Article pubs.acs.org/IECR Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.iecr.8b01179 Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX Ind. Eng. Chem. Res. Downloaded from pubs.acs.org by UNIV OF NEW ENGLAND on 07/13/18. For personal use only.