Pyrrol-Based Ligands as Salen Relatives: Complex Synthesis, Characterization and Comparison

Schiff bases like the mixed N, O donor ligands of the salen (Bis(salicyliden)ethylendiamin) family are frequently chosen systems for complexation studies. Advantageous is their ability to stabilize a large number of metals including actinides, as well as their tuneable electronical and sterical properties.1–4 Pyrrol-based ligands are salen’s structural relatives, but only exhibit N-donor functionalities. This provides the possibility to investigate and compare the binding situation between early actinides and N atoms in different environments.
In this study a complex series from Th to Pu with the pyrrol-based ligands 1,2-ethylenediamine-N,N’-bis(1H-pyrrol-2-yl)methylene (pyrenH2) L¹ H₂ and 1,2-benzenediamine-N,N’-bis(1H-pyrrol-2-yl)methylene (pyrophenH2) L² H₂ was synthesized. Characterization in solution (NMR) and solid state (SC-XRD) in combination with quantum chemical calculations reveal the different binding situations to the different N donors at the electronic level, which leads to unique paramagnetic behavior in solution.

1 B. E. Klamm et al., Chem. Commun., 2018, 54, 8634–8636.
2 A. N. Dame et al., Eur. J. Inorg. Chem., 2015, 2015, 2996–3005.
3 B. E. Klamm et al., Inorg. Chem., 2018, 57, 15389–15398.
4 T. Radoske et al., Chem. – Eur. J., 2020, 26, 16853–16859.