Bis(acetylacetonato)bis(pyrazolato)ruthenate(iii) as a redox-active scorpionate ligand

Abstract

The potential of a new anionic octahedral metal complex [Ru^III(acac)₂(pz)₂]⁻ (1⁻) (pzH = pyrazole) as a ligand with a scorpionate coordination behaviour like tris(pyrazolyl)borate (tp) and reversible redox activity is presented. Trinuclear metal complexes, [Ru^III₂Zn^II(acac)₄(pz)₄] (2) and [Ru^IIRu^III₂(acac)₄(pz)₄] (3), were each synthesized by the reaction of ZnCl₂ or Ru₃(CO)₁₂ with [Ru^III(acac)₂(pz)(pzH)] (1H) that is in situ deprotonated and acts as a precursor of 1⁻. Single-crystal X-ray diffraction studies clarified that 1⁻ acts as a scorpionate ligand; two 1⁻ units in 2 and one unit in 3 function as bidentate ligands with two pyrazolates as pincers, while another 1⁻ unit in 3 functions as a tridentate ligand with one oxygen atom as a tail in addition to the two pyrazolate pincers. Moreover, 2 and 3 showed reversible multi-stage redox behaviours based on the Ru^II/Ru^III and Ru^III/Ru^IV couples of the 1⁻ units in the cyclic voltammetry (CV) measurements. Based on the X-ray, IR, and CV measurements and the comparison with other Ru(II) complexes with tp derivatives, the 1⁻ unit was found to act as a redox-active scorpionate with electron withdrawing properties compared to the tp.