Green Chemistry PAPER Cite this: Green Chem., 2013, 15, 1030 Received 7th November 2012, Accepted 10th February 2013 DOI: 10.1039/c3gc36761d www.rsc.org/greenchem Iron-catalyzed cross-coupling reaction: recyclable heterogeneous iron catalyst for selective olefination of aryl iodides in poly(ethylene glycol) medium† Abdol Reza Hajipour* a,b and Ghobad Azizi b An environmentally friendly iron-based catalyst supported on acac-functionalized silica was successfully prepared and evaluated as a heterogeneous catalyst for Mizoroki–Heck reaction of aryl iodides and olefins. Our catalytic system showed good activities that were comparable to that of palladium catalysts. The catalyst was simply recovered from the reaction mixture and recycled five times. Furthermore, the reaction was carried out in poly(ethylene glycol) as a green solvent. Interestingly, using this catalyst, aryl iodides were selectively olefinated in the presence of aryl bromides. Introduction The palladium-catalyzed Mizoroki–Heck cross-coupling reac- tion represents one of the most valuable methods for carbon– carbon bond formation in organic synthesis. 1 Thus, a number of efficient catalytic systems have been developed for this cross-coupling reaction. The catalyst in the standard Heck reaction is a Pd(0) species stabilized by two phosphine ligands. However, phosphine ligands have some drawbacks; they are expensive, toxic, unrecoverable, and sensitive to oxygen and water. 2 On the other hand, due to the high cost of palladium, researchers are also interested in the Heck reactions catalysed by inexpensive transition metals such as Ni, 3,4 Co, 5,6 Cu 7 and Mn. 4 Nevertheless, the stress of modern efficiency criteria has prompted the search for alternative catalysts that address the economic and ecological disadvantages associated with the use of palladium, cobalt and nickel catalysts. In contrast to the above mentioned metals, iron is one of the most abundant metals on earth, and one of the most inex- pensive and environmentally friendly ones. Iron catalysts have recently been introduced to address these economic and eco- logical challenges. Many biological systems rely on the rich chemistry of iron-containing enzymes. It is also a vital metal for life, and thus constitutes an attractive metal for a vast array of chemical synthetic transformations as no severe toxicity and side effects exist. Also, iron(III) catalysts are air and moisture stable and easy to store for long periods under normal labora- tory conditions. In the field of C–C bond formation via Grignard derivatives, 8–12 Suzuki–Miyaura 13,14 and Sonogashira reactions 15–19 a variety of works were accomplished and the iron-catalyzed cross-coupling method is able to compete with the palladium-catalysed one. However, to the best of our knowledge, only one work on iron catalyzed Heck cross-coup- ling reaction has been reported 20 and heterogeneous iron cata- lysts have never been used in Heck reaction. The recent report by Vogel and co-workers 20 on iron-cata- lyzed Heck reaction urges us to present our own studies on this topic. They demonstrated a novel iron-catalysed arylation of styr- enes using a rather large amount of FeCl 2 (20 mol%) along with picolinic acid as ligand (80 mol%) and t- BuOK as base (4 mol%) in DMSO under mild conditions at 60 °C. The presence of strong base resulted in the polymerization of acrylate esters. Here, we report a simple, cost-effective, environmentally benign, recyclable, and efficient covalently silica supported iron(III)-acac catalytic system for the Heck reaction of aromatic iodides and olefins (styrene and acrylates) under ligand-less conditions (Scheme 1). In this work, only a catalytic amount of iron in poly(ethylene glycol) is used as a green solvent. Scheme 1 Iron catalysed Heck reaction. † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3gc36761d a Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan 84156, IR Iran. E-mail: haji@cc.iut.ac.ir; Fax: +98 311 391 2350; Tel: +98 311 391 3262 b Department of Neuroscience, University of Wisconsin, Medical School, 1300 University Avenue, Madison, 53706-1532 WI, USA 1030 | Green Chem., 2013, 15, 1030–1034 This journal is © The Royal Society of Chemistry 2013 Downloaded by University of Aberdeen on 30/03/2013 13:56:33. Published on 11 February 2013 on http://pubs.rsc.org | doi:10.1039/C3GC36761D View Article Online View Journal | View Issue