Synthesis, properties and molecular structure of [Ru(tpm)(bpy) (CH 3CN)](PF6)2 (tpm = tris(1-pyrazolyl)methane, bpy = 2,2′-bipyridine) - Another example of nitrile hydrolysis promoted by ruthenium(II)

Abstract

The synthesis and isolation of [Ru(tpm)(bpy)(CH3CN)](PF 6)2 (tpm = tris(1-pyrazolyl)methane; bpy = 2,2′-bipyridine) in good yield is described. This new RuII complex has been spectroscopically (IR, UV/Vis, emission) and electrochemically (cyclic voltammetry) characterized. Its solid-state structure has been solved by means of X-ray diffraction analysis and shows a distorted octahedral geometry where, as expected, the tpm ligand occupies three facial coordination sites, the bpy ligand chelates two further sites, and the CH3CN ligand saturates the coordination sphere of the Ru metal center. Electrochemical and spectroscopic results indicate that the CH3CN ligand acts as a moderately strong π-acceptor. The capacity of the coordinated CH 3CN ligand to undergo basic hydrolysis is also described. A second-order rate constant kobs = 1.3 × 10-3 M -1 s-1 (T = 25°C) has been obtained by following the UV/Vis absorption changes over time; the activation parameters obtained over the temperature range 17.0-40.0°C are: ΔH‡ = 74 ± 4 kJ mol-1 and ΔS‡ = -54 ± 12 J mol-1 K-1. These results are compared and discussed with regard to related complexes described in the literature that are also capable of carrying out this reaction. The results presented here make it possible to characterize the electronic and steric factors further and understand how they influence the basic hydrolysis of the coordinated CH 3CN ligand. © Wiley-VCH Verlag GmbH & Co. KGaA, 2005.