In search for chelating TAMLs (tetraamido macrocyclic ligands) with peripheral bidentate donor centers: a cobalt(III) complex of the 3,3′-(2,2′-bipyridindiyl)-tailed TAML

The synthesis of 1,2-C6H4(NHCOCMe2NHCO)2-3,3′-(2,2′-bpy) (3), a TAML (tetraamido macrocyclic ligand) incorporating the peripheral 2,2′-bipyridine unit, is described. Its geometry after optimization by density functional theory (DFT) indicated a rather unfavorable conformation of four N–H amide units for forming macrocyclic transition metal complexes. This explains why the iron(III) derivative of 3 could not be obtained even after deprotonation of the N–H bonds by n-BuLi. Nevertheless, the macrocyclic complex of CoIII was synthesized in moderate yield, characterized, and explored by DFT. Our data suggest a strongly distorted square-planar geometry of the macrocyclic complex between CoIII and 3. The dihedral angle between the pyridine rings equals 80° ruling out the possibility of metal chelation by the bipyridine unit.