Palladium Supported on a Polyionic Resin as an Efficient, Ligand-Free, and Recyclable Catalyst for Heck, Suzuki-Miyaura, and Sonogashira Reactions

Abstract

Polyionic Amberlite resin formate (ARF), derived from commercially available Amberlite resin chloride by simple rinsing with aqueous formic acid, could be soaked with palladium(0) from palladium salts, the formate counteranion being the reducing source. The resulting Amberlite resin formate supported with palladium(0), ARF-Pd, showed excellent catalytic activity in Heck, Suzuki-Miyaura, and Sonogashira couplings with a range of substrates. The catalyst may be recovered easily and quantitatively without leaching and recycled; it was tested for five runs without any significant loss of activity.Transition-metal-catalyzed organic reactions constitute the central part of contemporary organic synthesis. In particular, palladium-catalyzed C-C bond-forming processes are foremost in the arena of organic process development. 1 The Heck, Suzuki-Miyaura, and Sonogashira reactions are excellent tools for C-C coupling reactions between aryl halides or triflates and suitable partners. 1d Over the last decade, commendable research has been performed and significant developments have been made and practical methodologies have been established. Widespread uses of palladium-catalyzed coupling reactions are found in modern organic synthesis, because the resulting coupled products often find good applications in the preparation of materials, 2 pharmaceuticals, 3 and other bioactive compounds. 4Since the common facet of these C-C coupling reactions is the palladium, which acts as the catalyst, numerous attempts have been made to employ it as either a soluble homogeneous 5 or an immobilized heterogeneous catalyst. 6 Soluble homogeneous palladium catalysts are found to have significant activity in various coupling reactions, but there are drawbacks, such as less active or inactive colloidal species, the catalyst is unrecoverable, the possibility of product contamination, and cost, that are often encountered in the course of such reactions. 7 Consequently, several approaches have been explored utilizing various immobilization techniques on solid or colloidal supports, 8 with the aim of efficient recovery and reuse of the active catalysts. The major thrust for achieving success in designing and developing polymer-supported metal catalysts broadly include: improved stability within the polymer matrix, increased selectivity for reactions, enhanced regioselectivity, phosphine-free, reusable for several runs, and superior asymmetric induction due to sitespecific chiral catalysts. In the past few years, several attempts have been made to surmount the problems pertaining to high reaction temperatures, separation of pure products, and recovery and reuse of palladium complexes by the use of heterogeneous palladium systems. Palladium-on-carbon, 9a carbon nanotubes, 9b and palladium on different metal oxides, 9 silica gel and modified silica gel, 10 fluorous silica, 10e,f zeolites, 11 molecular sieves, 12 hydrotalcite, 13 and sepiolites 14 were found to be suitable catalysts for some reactions. Several groups have examined the use of polymer/dend...

Polymer-templated synthesis of hollow Pd–CeO2nanocomposite spheres and their catalytic activity and thermal stability

“…A fraction of Pd atoms located at the Pd-CeO 2 interface are exposed and the electron exchange between Pd atoms and CeO 2 matrix leads to the formation of ionic Pd species. Besides, the previous researches showed that the Pd 2+ ions could not be completely reduced and minor Pd 2+ component might exist on the surface of Pd NPs [41,42] . Thus, on the basis of XPS data and the Pd-CeO 2 interface observed in Figure 1d, we can consider that the chemical state of surface Pd in the hollow Pd-CeO 2 NCSs is mainly ionic Pd 2+ but not in the form of PdO, which probably results from the strong metal-support interaction caused by the treatment at high temperature, and forming the solid solution-like…”

Solid-Phase Organic Synthesis and Catalysis: Some Recent Strategies Using Alumina, Silica, and Polyionic Resins

“…Using the ARF-Pd, the reaction of 3-iodoanisole and 1-ethynyl-4-methylbenzene carried out in the presence of Et 3 N as the base in acetonitrile solvent at 80 ∘ C for 6 h afforded the desired cross-coupled product in excellent yield (Scheme 20). Similar coupling reactions with other iodoarenes and acetylenes are also found to be successful [237].…”

“…Reactions. Excellent activity, high selectivity, and reusability of the ARF-Pd as potential reductive system have prompted to explore it as a viable heterogeneous Pd catalyst in various C-C coupling reactions (Scheme 20) [237]. One of the key questions on which the researchers have focused is "how can minimization of catalyst cost and catalyst contamination of the product be best achieved?"…”

Fe3O4@OA–Pd and Mo10V2@NSiO2 nanoparticles: an efficient and reusable catalytic system for Heck reaction under ligand free conditions

“…Palladium-catalyzed cross-coupling of aryl halides with olefins, known as Heck coupling, has contributed greatly to the straightforward and facile construction of carbon-carbon bonds [1][2][3][4][5][6][7][8][9][10]. This reaction is generally considered to be a homogeneous reaction most commonly catalyzed by soluble Pd(II) species with a variety of ligands, such as palladium-phosphine complexes [2], oxime palladacycles [3], palladium-salen complexes [4], and palladium-N-heterocyclic carbine complexes [5].…”

“…Thus, heterogeneous catalysts are highly desirable, especially in large-scale synthesis, from both environmental and economic aspects. Much effort has been paid to developing heterogeneous catalytic systems that can be efficiently reused [6,9,10]. Original ways have been found in the elaboration of magnetic catalysts that can be easily removed using external magnets, and in the use of supported forms of catalytic systems without practical loss.…”