Nitrogen Chemistry with Alkaline-Earth Metals

NITRO-EARTH is aiming to investigate the hardly explored nitrogen chemistry of the alkaline-earth metals (Ae) in order to disclose new reactivity and catalysis.

In the biogeochemical nitrogen cycle oxidized (NOx), neutral (N2) and reduced (NH3) forms of N are interconverted by a complicated network of processes. In contrast, manipulation of N in industry is challenging and often needs brute-force methods.

The Haber-Bosch process for N2-to-NH3 conversion is, despite being metal-catalysed, one of the most energy consuming industrial processes.

This proposal focusses on the organometallic chemistry of imido [RN(2ˉ)] and nitrido [N(3ˉ)] complexes of the alkaline-earth metals, in particular Mg and Ca.

While the amide (R2Nˉ) chemistry of the Ae metals is well-established, Ae-imido complexes are rare and Ae-nitrido compounds solely exist as insoluble salts, e.g. Mg3N2.

Given the importance of imido and nitrido ligands in transition metal chemistry, access to soluble Ae=NR and Ae≡N complexes promises a rich reactivity and is the prelude of new catalytic processes based on abundant, generally biocompatible, alkaline-earth metals.

The various pathways to reach the target include utilization of recently introduced, highly reducing Mg(0) complexes by HARDER and nitreones which have been investigated by PATEL. Also HARDER’s recently discovered N2 fixation with Ca will play a role in the synthetic approach.

Owing to the highly ionic character and negative charge on N in Ae=NR or Ae≡N complexes, these novel complexes will be extremely potent nucleophiles or deprotonating reagents.

This will be strongly dependent on nuclearity and aggregation which will be controlled by a library of bulky ligands currently available in the HARDER group. The work will be heavily supported by ab initio calculations.

The project ultimately leads to the generation of a new class of alkaline-earth metal catalysts which may provide sustainable alternative for transition metal based catalysts.