Polly Arnold

 The rare-earth elements, comprising group 3 and the 4f row, contains many elements that are essential to energy technologies. They were labelled as ‘rare earths’ as they are hard to separate from each other; a better fundamental understanding of their differences in electronic structure and bonding is needed to find new ways to separate and recycle them.

I will discuss our most recent work, studying the reactions of f-block complexes with N2, a molecule that would traditionally not be expected to bind to f-block cations. Dinitrogen, 78 % of the earth’s atmosphere, holds a unique position amongst small molecules, in that there is only one industrial process that uses it as a feedstock, the Haber Bosch process. Chemists have spent more than a century trying to make catalysts that can convert N2 under mild conditions to useful products such as fertilizers or energy carrier replacements for fossil fuels. Small scale conversions of N2 that operate under ambient conditions could offer food and energy justice to remote populations.

The few homogeneous catalysts for N2 conversion to ammonia or tris(silyl)amine focused entirely on electron rich metals inspired by nature such as molybdenum until recently. We will discuss a new system, using electron deficient, and earth abundant metals formed into a metallacyclic cage with aromatic ligands, that traps dinitrogen, and funnels electrons and electrophiles to the N atoms, both demonstrating the first nitrogen reduction catalysis by f-block complexes, and enabling the first selective formation of bis(functionalized)amines by any catalyst.

New catalyses like these suggest that we have previously overlooked many possibilities for these metals, and that more opportunities exist down at the bottom of the table to create a better environment.

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