Under the covers
Our series on the research and artistic inspiration behind journal covers continues with a tale of alchemy, Greek mythology, and gold catalysis.
The field of homogeneous gold catalysis – using gold compounds in solution to facilitate reactions – has grown rapidly over the past 15 years. It is most often used to create ring structures from alkenes and alkynes (molecular structures that include double and triple bonds between carbon atoms).
Gold catalysts can operate under relatively mild conditions, making them particularly useful in the synthesis of a variety of reactions.
In their recent review in Chem Soc Rev, Abdullah Asiri and Stephen Hashmi, of King Abdulaziz University in Saudi Arabia, have provided a comprehensive overview of the fascinating range of reactions and syntheses that have been catalysed by gold in recent years.
The article formed part of a themed collection on the use of coinage metals in organic synthesis.
This review focuses on diynes, molecules containing two triple bonds, also referred to as alkynyl groups.
Stephen Hashmi explains: "Monoalkynes [molecules containing a single triple bond] alone show a broad range of unique reactivity patterns in gold catalysis, but in the case of diynes previously unknown reactivity patterns specific to substrates with two alkynyl groups, i.e. involving both alkynyl groups at the same time, are observed...
"These 'diyne-specific' reactivity patterns have not been summarized yet, thus my colleague Abdullah M. Asiri and I decided to compile this review. A series of interesting mechanisms and conversions are discussed in detail.
"The examples document how these can be utilized in the synthesis of hetero- and carbocycles in both total synthesis of natural products and the synthesis of compounds for material science – often a significant increase of molecular complexity is observed."
Hashmi hopes that the review will provide inspiration for the development of new and more sophisticated reactions.
From the art desk
PhD candidate Svetlana Tsupova from the Hashmi group created the artwork for the cover. She explains her design.
"In classical alchemy, gold is represented by the sun; this was my starting point. Therefore I chose to represent the gold catalyst as Sun chariot. The large shield (inspired by those of the hoplites, citizen-soldiers of ancient greek city-states) both obscures the character and reveals the key element: gold.
"A second purpose to this enormous shield is to hide the human figure (cf. aniconism in Islamic art), leaving only the hand visible, as this review was written under the aegis of King Abdulaziz University.
"Different pantheons have different descriptions of the horses of the chariot, but the Norse mythology has a perfect match. The Sun chariot in drawn by two steeds (Árvakr and Alsviðr), one white and one dark. Therefore in the picture the horses have manes of different colours, one light and one dark. Similar and yet different, just as gold has two modes of action in dual catalysis (σ- and π- activation and bonding).
"They trample underfoot the substrate, with each bringing down a pair of hooves on a separate alkyne bond, and leaving the product in their wake. Dual activation reaction was chosen as example reaction, as it ranks amongst the latest and most progressive ones in the field of gold catalysis which possesses a high potential for materials sciences."