Synthesis and crystal structure of an unexpected anionic trinuclear cobalt(III) complex with ferrocenyl-containing tridentate ONO donor Schiff base ligands

Abstract

The tridentate ONO-donor Schiff base ligand derived from the condensation of 1-ferrocenyl-1,3-butanedione and 2-aminophenol, generated in situ and treated further with potassium tert-butoxide, reacted in THF with Co(NO3)2·6H2O in the presence of pyridine to afford the ionic complex [{(η5-C5H5)Fe(η5-C5H4)-C(O)CH=C(CH3)N-C6H4-2-O}2Co(III)]-[K(HOCH2CH3)2]+ (1, 50% yield). Compound 1 was characterized by elemental analysis, FT-IR, and multidimensional 1H and 13C NMR spectroscopy. Single-crystal X-ray diffraction reveals that the two metalloligands are meridionally coordinated to a Co(III) ion that adopts a slightly distorted octahedral geometry. The doubly solvated potassium counter-ion is asymmetrically positioned with respect to the two metalloligands. Such an arrangement allows the observation by 1H NMR of restricted rotation of the ferrocenyl units and the splitting of both carbonyl and imine carbons, thus suggesting that the structure observed in the solid state is retained in solution. Complex 1 exhibits in its cyclic voltammetry curve two anodic reversible waves attributed to the oxidation of Co(III)-phenolates into Co(III)-phenoxyl radical and that of the ferrocenyl fragment into its ferrocenium counterpart.