Reuben Hudson

Fe3O4 Nanoparticle-Supported Copper(I) Pybox Catalyst: Magnetically Recoverable Catalyst for Enantioselective Direct-Addition of Terminal Alkynes to Imines

An Fe(3)O(4) nanoparticle-supported copper(I) pybox catalyst, which exhibits excellent reactivity and yields products with good enantioselectivity, was developed. As a proof of concept, six optically active propargyl amines were obtained in excellent yields. The catalyst can be magnetically removed and recycled easily six times without a decrease in activity or enantioselectivity.

Magnetic copper–iron nanoparticles as simple heterogeneous catalysts for the azide–alkyne click reaction in water

The development of a novel bimetallic copper–iron nanoparticle synthesis provides a recoverable heterogeneous catalyst for the azide–alkyne “click” reaction in water. The nanoparticles catalyze the production of a diverse range of triazoles, while separation and reuse proved to be easy.

Bare magnetic nanoparticles: sustainable synthesis and applications in catalytic organic transformations

Magnetic nanoparticles have become increasingly attractive in the field of catalysis over the last decade as they combine interesting reactivity with an easy, economical and environmentally benign mode of recovery. Early strategies focused on the use of such nanoparticles as a vehicle for supporting other catalytic nanomaterials or molecules to facilitate recovery. More recently, research has shown that bare magnetic nanoparticles may serve the dual role of a catalyst and a magnetically recoverable entity. At the same time, emerging sustainability concepts emphasize the utility of earth abundant and less toxic resources, especially iron. Herein, we review the recent progress made in the assembly of such systems and their direct application in catalysis. Examples of such bare nanoparticles include iron oxide (Fe2O3 and Fe3O4), metal ferrites (MFe2O4, M = Cu, Co and Ni), Fe(0), Co(0), Ni(0), and multi-component nanoparticles. Features such as reactivity, recoverability and leaching are discussed in a critical fashion.

Iron-iron oxide core–shell nanoparticles are active and magnetically recyclable olefin and alkyne hydrogenation catalysts in protic and aqueous media

We report for the first time the use of iron-iron oxide core-shell nanoparticles for the hydrogenation of olefins and alkynes under mild conditions in ethanol and in an aqueous medium. This catalyst proves robust towards the presence of oxidants, such as oxygen and water, is magnetically recoverable and shows selectivity towards the less activated double bonds.

Highly efficient iron(0) nanoparticle-catalyzed hydrogenation in water in flow

Highly efficient catalytic hydrogenations are achieved by using amphiphilic polymer-stabilized Fe(0) nanoparticle (Fe NP) catalysts in ethanol or water in a flow reactor. Alkenes, alkynes, aromatic imines and aldehydes were hydrogenated nearly quantitatively in most cases. Aliphatic amines and aldehydes, ketone, ester, arene, nitro, and aryl halide functionalities are not affected, which provides an interesting chemoselectivity. The Fe NPs used in this system are stabilized and protected by an amphiphilic polymer resin, providing a unique system that combines long-term stability and high activity. The NPs were characterized by TEM of microtomed resin, which established that iron remains in the zero-valent form despite exposure to water and oxygen. The amphiphilic resin-supported Fe(0) nanoparticles in water and in flow provide a novel, robust, cheap and environmentally benign catalyst system for chemoselective hydrogenations.

Reversing aggregation: direct synthesis of nanocatalysts from bulk metal. Cellulose nanocrystals as active support to access efficient hydrogenation silver nanocatalysts

A highly atom-economical synthetic method to access nanocatalysts from bulk metal is described. A water suspension of cellulose nanocrystals was exposed to an Ag wire, under air and light exposure. In 2 weeks, Ag nanoparticles of size 1.3 nm ± 0.3 nm were deposited onto the biopolymer. These species were active for the hydrogenation of aldehydes, 4-nitrophenol, alkenes and alkynes.

Jacinto Sa and Anna Srebowata (eds): Hydrogenation with low-cost transition metals

Many sectors of the chemical industry including textiles, food, fine chemicals, and bulk chemicals rely on catalytic hydrogenation. Highly active, yet precious and toxic metals such as platinum, palladium, and ruthenium have long dominated research spheres where investigators seek to showcase novel reactivity, selectivity, and performance. Concurrently, the overwhelming scale of hydrogenation in commercial production continues to drive the pursuit of less toxic, inexpensive transition metal catalysts. With their new book, Hydrogenation with Low-Cost Transition Metals (CRC Press, 2015, 203 pages, ISBN: 9781498730532), Jacinto Sa and Anna Srebowata effectively capture this shift toward more benign and inexpensive catalysts. On the homogeneous end of the metal catalyst spectrum, advances with low-cost transition metals have been enabled by novel ligand architectures, while on the heterogeneous end, similar gains have been made under the evolving precision of nanoparticle fabrication. The authors quickly narrow the focus of the book to heterogeneous catalysis with a specific emphasis on applications toward fine chemical production. In a useful introduction for the rest of the book, the authors lay a foundation for catalytic hydrogenation. Topics of typical reducing agents (H2, formic acid, or isopropanol) are seamlessly interwoven with fundamental discussions of highly dispersed metals, semihydrogenation (partial reduction, alkyne ? alkene) and asymmetric hydrogenation, alongside a historical jaunt through the hydrogenation of oils, the Haber–Bosch process, and the evolution of pressure reactors to provide context to maintain readers’ interest. The narrative in the introduction specifically draws the reader toward important qualities for any heterogeneous hydrogenation catalyst (activity, selectivity, filtration rate, and recycling). Other in-depth introductory discussions include explanations of alkyne partial reductions, wherein hydrogenation of the alkene proceeds faster than the alkyne, but the alkyne binds more strongly to the surface of the catalyst, so as long as some alkyne starting material remains, selectivity for the partial reduction can be achieved—an explanation most never received in their undergraduate introduction to Lindlar’s catalyst. Specific chapters on hydrogenation with nickel, copper, iron, and silver follow, while future editions may save space for cobalt. Each of these individual-metal-focused chapters serves mostly as a stand-alone reference with similar backgrounds and examples. The authors often delve into specifics of chemoselectivity; a favorite topic appears to be the industrially relevant selective hydrogenation of the C=O double bond over the C=C double bond in a,bunsaturated aldehydes, which most chapters showcase. Nanoparticle supports such as montmorillonite clay, silica, zeolite, alumina, carbon nanotubes, and others are highlighted in each chapter, as are various methods for nanoparticle preparation, such as the sol–gel, reduction, microemulsion, thermal decomposition, electrodeposition, polyol, and hydrothermal as well as solvothermal methods, among others.