Pyrrole and Carbazole Ligands

Pyrrole ligands can form both Ln-N or-bonds and tjs-n-Ln bonds. r-Bonds have bran observed in heteroleptic lanthanide(III) complexes with sterically less crowded pyrrole ligands [195]. The introduction of sterically demanding groups in a-position as in 2,5-di-fert-butylpyrrole led to a shielding of the nitrogen and subsequent -coordination to the lanthanide center [196]. Additionally, rj1-coordination to a sodium atom is observed in the obtained ate complex. 

In lanthanide(II) carbazole complexes of type Ln(cbz)2(solvent)4 Ln-N c-bonds can even stabilize samarium(II) [197,198]. 

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