Synthesis, Crystal Structures and Redox Properties of Mixed‐Sandwich Complexes of Ruthenium(II) with Cyclopentadienyl and Tris(pyrazolyl)methane Ligands

Abstract

AbstractNew mixed‐sandwich ruthenium(II) complexes have been prepared by treatment of either [RuCp(acn)3][PF6] or [RuCp*(acn)3][PF6] (Cp = η5‐cyclopentadienyl; Cp* = η5‐pentamethylcyclopentadienyl, acn = CH3CN) with tris(pyrazolyl)methane (HTpm) and tris(3,5‐dimethylpyrazolyl)methane (MeTpm), respectively. [RuCp(HTpm)][PF6] (1), [RuCp*(HTpm)][PF6] (2) and [RuCp(MeTpm)][PF6] (3) have been examined by single‐crystal X‐ray diffraction (1, 2) and 2D NMR experiments, which reveal discrete units of cationic mixed‐sandwich complexes of the composition [RuCp(*)(RTpm)]+ featuring η5‐cyclopentadienyl and κ3N‐coordinated RTpm ligands. The air‐sensitive salt [RuCp*(acn)(MeTpm)][PF6] (4) exhibits a κ2N‐coordinated MeTpm and one remaining acetonitrile ligand, presumably due to steric interactions between the sterically more bulky Cp* and MeTpm ligands. Cyclic voltammetric studies of the symmetric mixed‐sandwich complexes 1–3 in acetonitrile show quasi‐reversible oxidation processes centred at E01/2 = +0.38 (1), +0.15 V (2) and +0.35 V (3) vs. Fc/Fc+. These values are mainly affected by the different nature of the Cp ligands; the differently substituted RTpm entities have very little influence.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)