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Catalyst is a chemical substance that increases the rate of a chemical reaction without itself being consumed in the process. While enzymes are nature's catalysts, essential for the functioning of all living organisms, most commercial-scale chemical reactions are catalysed by man-made transition metal-based species that assist in breaking and making of chemical bonds. 

Catalysis is the backbone of modern chemical processes 

Catalysis, the increase in the rate of a chemical reaction due to an added catalyst, is highly important to our modern life as the vast majority of commercial synthetic processed are catalysed. In many of these reactions, the catalyst reacts with a small inert molecule and activates it for further transformations. For long, expensive and rare transition metals and their compounds have played a crucial role in mediating and controlling the activation of small molecules. Over the past two decades, reactive main group species consisting entirely of cheap, earth-abundant elements have been extensively examined as an alternative to perform similar transformations. 

Reactive main group compounds are often low-valent and low-coordinate, meaning they have unshared valance electrons and unused coordination sites, respectively. For their reactivity to be utilized, they need to be modified, tamed, with suitable ligands that allow the desired reaction to take place without any unwanted side reactions. This is no simple task as too much stabilisation can lead to no or very little reactivity, whereas too little stabilization often leads to uncontrolled reactivity and a mixture of products.  

“This is an example of the Goldilocks principle in chemistry as everything needs to be “just right” for the desired reactivity to emerge”, explains Annika Lehmann from the Ģ��ֱ��. 

Experimental and computational studies of reactive main group species  

In her thesis work, M.Sc. Annika Lehmann investigated the reactivity of terphenyl-stabilized low-valent aluminium and bismuth compounds towards small molecules and molecules with unsaturated chemical bonds. Another goal of her work was to study the chemistry of coordination compounds of the β-diketiminato ligand with antimony to realize new stable doubly bonded distibenes or rare stibinyl radicals that could be used in subsequent small molecule activation studies. 

“The first part of the project gave important insight into the reactivity of compounds prepared in the group of our collaborator Prof. Philip P. Power at UC Davis, USA. For example, we could demonstrate that the long sought after dialuminene could be stabilized with a very sterically bulky terphenyl ligand, which allowed its characterization, though its reactivity could only be assessed indirectly. Furthermore, we were also able to explain the mechanism of hydrobismuthation, that is, the addition of a bismuth hydride to a multiple bond. This was the first example of such reaction to be reported”, tells Lehmann. 

“In the second part of the project, we showed that with the right choice of ligand, antimony β-diketiminato complexes could be obtained reproducibly and in high yields. These compounds underwent chemical reduction to give a distibane and a persistent stibinyl radical. Unfortunately, the goals of isolating and characterizing a doubly bonded distibene or a stable stibinyl radical could not yet be met, but the studied systems show great potential for reaching them in the future”, Lehmann explains. 

The research project received funding from the European Research Council under the EU’s Horizon 2020 programme (grant #772510 to H.M.T.). The writing of the thesis was funded by the Alfred Kordelin foundation. 

The examination of M.Sc. Annika Lehmann’s doctoral thesis “Experimental and Computational Studies of Reactive Main Group Species: Low-Coordinate Complexes, Multiple Bonding, and Hydrometallation” is held on Friday 11.10.2024 at 12:00 at Ylistönrinne Campus in lecture hall FYS1. The opponent is Associate Prof. Dr. Christine Caputo (University of New Hampshire, USA) and Custos Prof. Dr. Heikki M. Tuononen (Ģ��ֱ��). The event is held in English.  

The dissertation “Experimental and Computational Studies of Reactive Main Group Species: Low-Coordinate Complexes, Multiple Bonding, and Hydrometallation” can be read on the JYX publication archive: .