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

New mixed‐sandwich ruthenium(II) complexes have been prepared by treatment of either [RuCp(acn) 3 ][PF 6 ] or [RuCp*(acn) 3 ][PF 6 ] (Cp = η 5 ‐cyclopentadienyl; Cp* = η 5 ‐pentamethylcyclopentadienyl, acn = CH 3 CN) with tris(pyrazolyl)methane ( H Tpm) and tris(3,5‐dimethylpyrazolyl)methane ( Me Tpm), respectively. [RuCp( H Tpm)][PF 6 ] ( 1 ), [RuCp*( H Tpm)][PF 6 ] ( 2 ) and [RuCp( Me Tpm)][PF 6 ] ( 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 ( * ) ( R Tpm)] + featuring η 5 ‐cyclopentadienyl and κ 3 N ‐coordinated R Tpm ligands. The air‐sensitive salt [RuCp*(acn)( Me Tpm)][PF 6 ] ( 4 ) exhibits a κ 2 N ‐coordinated Me Tpm and one remaining acetonitrile ligand, presumably due to steric interactions between the sterically more bulky Cp* and Me Tpm ligands. Cyclic voltammetric studies of the symmetric mixed‐sandwich complexes 1 – 3 in acetonitrile show quasi‐reversible oxidation processes centred at E 0 1/2 = +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 R Tpm entities have very little influence.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)