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)-H-1 (L-1 = PhNNC(Ph)NNPh) with [Ln{N(SiMe3)(2)}(3)] (Ln = Y, Sm, Dy) resulted in homoleptic tris(formazanate) complexes with the general formula [(L-1)(3)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)-H-2 (L-2 = {PhNNC(4-tBuPh)NNPh}) was employed. Salt metathesis by using the trivalent precursors [SmCp*(2)(mu-Cl)(2)K(thf)] (Cp* = eta(5)-C5Me5) or [LnCp(2)Cl](2) (Cp = eta(5)-C5H5, Ln = Dy, Yb) and [(LK)-K-2(thf)] formed mono(formazanate) complexes, [(LSmCp)-Sm-2*(2)] (4) and [L(2)LnCp(2)] (Ln = Dy (5), Yb (6)), respectively. Unexpectedly, a redox reaction occurred between [(LK)-K-2(thf)] and the divalent ytterbium precursor, [YbI2(thf)(2)], generating the trivalent ytterbium complex [(L-2)(3)Yb] (7). When the neutral formazan ligand ((LH)-H-2) reacted with [SmCp*(2)(thf)(2)], the oxidised samarium complex 4 was formed. These novel compounds were fully characterised and their electrochemical properties were explored by cyclic voltammetry.