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 L 1 H (L 1 = PhNNC(Ph)NNPh) with [Ln{N(SiMe 3 ) 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 L 2 H (L 2 = {PhNNC(4- t BuPh)NNPh}) was employed. Salt metathesis by using the trivalent precursors [SmCp* 2 (μ-Cl) 2 K(thf)] (Cp* = η 5 -C 5 Me 5 ) or [LnCp 2 Cl] 2 (Cp = η 5 -C 5 H 5 , Ln = Dy, Yb) and [L 2 K(thf)] formed mono(formazanate) complexes, [L 2 SmCp* 2 ] (4) and [L 2 LnCp 2 ] (Ln = Dy (5), Yb (6)), respectively. Unexpectedly, a redox reaction occurred between [L 2 K(thf)] and the divalent ytterbium precursor, [YbI 2 (thf) 2 ], generating the trivalent ytterbium complex [(L 2 ) 3 Yb] (7). When the neutral formazan ligand (L2H) 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.