Magnetite and Metal‐Impregnated Magnetite Catalysts in Organic Synthesis: A Very Old Concept with New Promising Perspectives

Abstract

Magnetite is a well-known material, with the impregnation of transition metals onto its surface being a very old protocol for preparing catalysts. However, only recently, the combination of both, magnetite and impregnation protocols, have been recognized as a powerful methodology to prepare catalysts. The impregnation protocol, of nearly all transition metals in the magnetite surface, has rendered the first generation of catalysts. These simple catalysts have been used in a very broad range of organic transformations. Thus, simple imine derivative formation or unknown reactions such as the direct cross β-alkylation of primary alcohols, through dehydrogenation, oxidation, addition, hydrogen autotransfer and multicomponent reactions has been accomplished using these catalysts. In most cases, these catalysts could be just isolated by magnetic decantation and reused several times without a detrimental effect on the initial results. In some cases, the study of the surface of the catalyst by means of several surface characterization techniques has permitted to determine the real species involved in the process and their structural changes within the reaction cycles. Furthermore, the post-modification of the catalysts by reduction or oxidation of the immobilized metal, or by the addition of ligands, has enlarged the applicability of this type of catalysts.

Palladium on Polydopamine: Its True Potential in Catalytic Transfer Hydrogenations and Heck Coupling Reactions

“…One option is to use ac entrifuge to separate the solid catalyst from the reactionm ixture, however,b yt aking advantage of the universal adhesiveness of the forming PDA, am ore attractive option is its deposition on magnetic nanoparticles prior to Pd deposition. Magnetic nanoparticles (MNPs) are currently among the most used materials aiding the recycling process of heterogeneous nanoscale catalysts [43][44][45] andh ave been used in combination with PDA-based materials also. [18,19] Therefore, we encapsulatedM NPs with aP DA layer,f ollowed by the deposition of Pd on the surface of the resulting Fe 3 O 4 @PDA particles (see the Supporting Informationf or furtherd etails).…”

Solid-Supported Palladium Catalysts in Sonogashira Reactions: Recent Developments

“…Thus, they can be easily separated from the reaction medium just by using a magnet (the so-called magnetic purification or magnetic decantation), avoiding the tedious recovery of catalyst from colloidal mixtures by filtration and/or centrifugation strategies, typically used for other heterogeneous supports. In this field, magnetite, an iron(II) and (III) oxide in a cubic inverse spinel structure, is the most used support [9], although other related materials employed recently will also be presented. There are different methodologies to incorporate palladium species, to the support, such as impregnation, coating, grafting, and coating-grafting.…”

New bis(N‐heterocyclic carbene) palladium complex immobilized on magnetic nanoparticles: as a magnetic reusable catalyst in Suzuki‐Miyaura cross coupling reaction

“…This class of supports can be magnetized in the presence of an external magnet and thus can be separated from the reaction mixture using an external magnetic field. Recent reports show that magnetic nanoparticles are efficient supports and can facilitate the isolation and recycling of expensive catalysts from the reaction media …”