The Influence of Dynamic Coordination Spheres in Metal-Based Homogeneous Catalysis

The role of supporting ligands in controlling the catalytic efficacy of metal complexes cannot be overstated. A balance between developing high denticity ligands that are able to effectively stabilise catalytic intermediates, and low coordination numbers that leave vacant coordination sites for substrate binding, can be challenging. We have recently discovered that the catalytic efficacy of main group metals can be increased by employing high denticity ligands by exploiting the inherent lability of these closed shell metal ions.

This catalyst design strategy is exemplified by the aluminium-catalysed trimerization of isocyanates with a 5-coordinate ligand that contains a hemi-labile pyridyl donor. The pyridyl is able to de-coordinate, and by so doing disfavours the backwards reaction that would lead to slower reaction kinetics; this catalyst is much more active than its pyridyl-free counterpart. The aim of this project is to probe the scope of this effect with other main group metals, and with other catalytic transformations. These metals are expected to cover Group 13 but could also extend into the s-block and early d block. We also envisage probing the effectiveness for this reaction in polymerisation and co-polymerisation reactions.
Polymerisation reactions are expected to focus primarily on epoxide/anhydride co-polymers, which contain ester linkages and are therefore biodegradable / hydrolysable. There are > 100,000 different monomer combinations, which means that they can be prepared with greater property scope than traditional polymers; for example, we have prepared flame-retardant derivatives with no toxic additives. Most co-polymerisation catalysts are based upon salen-type ligands; the lack of extensive studies with alternative ligand environments is an inherent limitation to further exploitation of these co-polymers. We are particularly interested to determine if a dynamic coordination sphere could be exploited to increase efficiency in preparing alternating co-polymers.

While polymerisation remains the primary focus, there is scope for exploring the influence of complexes exhibiting dyanamic coordination behaviour in the activation of other small molecules such as H2 and CO which leads into hydrogenation and/or carbonylation catalysis.
New ligand leads and complexes will derive from initial studies and continually inform subsequent studies.

Catalysis is crucially important to the UK economy, with products and services reliant on catalytic processes amounting to 21% of GDP and 15% of all exports. The UK is scientifically strong and internationally recognised in the field, but the science base is fragmented and becoming increasingly specialised. The EPSRC Centre for Doctoral Training in Catalysis will overcome these problems by acting as beacon for excellent postgraduate training in Catalysis and Reaction Engineering with a programme that will develop an advanced knowledge base of traditional and emerging catalysis disciplines, understanding of industry and global contexts, and research and professional skills tailored to the needs of the catalysis researcher.

Although the chemical sector is an immensely successful and important part of the overall UK economy, this sector is not the only end-user of catalysis. Through its training and its research portfolio the Centre will, therefore, impact on a broad range of technologies, processes and markets. It will:
(a) provide UK industry with the underpinning science and the personnel from which to develop and commercially leverage innovative future technologies for the global marketplace;
(b) allow the UK to maintain its position as a world leader in the high-technology area of catalysis and reactor engineering;
(c) consolidate and establish the UK as the centre for catalysis expertise.

Likewise, society will benefit from the human and intellectual resource that the Centre will supply. The skills and technologies that will be developed within the Centre will be highly applicable to the fields of sustainable manufacture, efficient and clean energy generation, and the protection of the environment through the clean-up of air and water - allowing some of the biggest societal challenges to be addressed.