Rare-earth metal complexes with redox-active formazanate ligands.

The synthesis and characterisation of rare-earth metal complexes with redox-active formazanate ligands are described. Deprotonation of the neutral formazan ligand LH (L = PhNNC(Ph)NNPh) with [Ln{N(SiMe)}] (Ln = Y, Sm, Dy) resulted in homoleptic tris(formazanate) complexes with the general formula [(L)Ln] (Ln = Y (1), Sm (2), Dy (3)), in which the central metal atom is coordinated by six N atoms, revealing a propeller-type structure. To generate heteroleptic complexes, a novel formazan ligand LH (L = {PhNNC(4-BuPh)NNPh}) was employed. Salt metathesis by using the trivalent precursors [SmCp*(μ-Cl)K(thf)] (Cp* = η-CMe) or [LnCpCl] (Cp = η-CH, Ln = Dy, Yb) and [LK(thf)] formed mono(formazanate) complexes, [LSmCp*] (4) and [LLnCp] (Ln = Dy (5), Yb (6)), respectively. Unexpectedly, a redox reaction occurred between [LK(thf)] and the divalent ytterbium precursor, [YbI(thf)], generating the trivalent ytterbium complex [(L)Yb] (7). When the neutral formazan ligand (L2H) reacted with [SmCp*(thf)], the oxidised samarium complex 4 was formed. These novel compounds were fully characterised and their electrochemical properties were explored by cyclic voltammetry.