Seeking New Chemocatalytic and Biocatalytic Solutions

Advances in palladium-catalysed hydrogenation, visible-light photocatalysis and improved chemocatalytic approaches for making heterocyclic compounds are some recent industry developments.
May 01, 2012

Patricia Van Arnum
Catalysis plays a crucial role in the synthesis of pharmaceutical intermediates and APIs. Catalysts can enable more efficient chemical transformations, improve reaction conditions, better product yields and produce greater enantioselectivity. Some key recent developments involve palladiumcatalysed hydrogenation, visiblelight photocatalysis, chemocatalytic approaches for making heterocyclic compounds and advances in biocatalysis.

Palladium-catalysed hydrogenation

Palladium-catalysed hydrogenation reactions are important in industrial chemistry and fine-chemicals manufacture, but precious metal catalysts, such as palladium, are costly. Researchers at the Tufts University's School of Arts and Sciences and School of Engineering in Medford, Massachusetts (US) recently reported on the arrangement of individual atoms in a metal alloy and their ability to catalyse hydrogenation reactions.

Hydrogenation requires the presence of a catalyst, usually a metal or an alloy of both precious and common metals, which allows the hydrogen atoms to bind with other molecules. It is difficult to produce alloys that are selective hydrogenation catalysts and able to attach the hydrogen atoms to specific sites of another molecule. Tufts chemists and chemical engineers reported that when single atoms of palladium were added to copper, which is much cheaper and readily available, the resulting "single atom alloy" became active and selective for hydrogenation reactions, according to a Tufts University press release.

The Tufts scientists scattered single atoms of palladium less than half a nanometer wide onto a copper support. For this research, the Tufts team heated small amounts of palladium to almost 1000 °C. At that temperature, individual atoms embedded themselves on the copper surface. A scanning tunneling microscope enabled the team to see how these single atoms dispersed in the copper and how molecular hydrogen could then dissociate at individual, isolated palladium sites and spill over onto the copper surface layer.

Specifically, the researchers used desorption measurements in combination with high-resolution scanning tunneling microscopy to show that the individual, isolated palladium atoms in a copper surface substantially lowered the energy barrier to both hydrogen uptake on and subsequent desorption from the copper metal surface. The hydrogen dissociation at the palladium atom sites and weak binding to copper allowed for very selective hydrogenation of styrene and acetylene, as compared with pure copper or palladium metal alone (1).

Visible-light photocatalysis

A team of University of Arkansas (US) researchers reported on using visible-light photocatalysis with a ruthenium catalyst to produce a building block for in pharmaceutical synthesis. Specifically, the researchers reported on a visible-light-mediated intermolecular [3+2] cycloaddition of mono- and bicyclic cyclopropylamines with olefins catalysed by [Ru(bpz)3](PF6)2 {2 H2 O to produce aminocyclopentane derivatives in good yields. Saturated 5,5- and 6,5fused heterocycles were obtained in synthetically useful yields and diastereoselectivity (2).

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