Oxo-Centred Trimetallic Clusters Supported by Electron-Withdrawing Carboxylates: Highly Inert Character in Ligand Exchange Kinetics of the Dichloroacetate-Bridged Complex [Ru3(µ3-O)(µ-CHCl2COO)6(pyridine)3

Abstract

Two new oxo-centred trinuclear ruthenium clusters supported by six dichloroacetate ligands, [Ru3(μ3-O)(μ-CHCl2COO)6(CH3OH)3]CHCl2COO (1) and [Ru3(μ3-O)(μ-CHCl2COO)6(pyridine)3] (2), have been synthesised and characterised by spectroscopic methods, electrospray ionisation mass spectrometry, single-crystal X-ray diffraction, and cyclic voltammetry. Due to the strong inductive effect of the dichloroacetate ligands, the redox potential of 2 was shifted to the positive side (~1.0 V or more) relative to the acetate analogue [Ru3(μ3-O)(μ-CH3COO)6(pyridine)3], and also the rate of pyridine/pyridine-d5 exchange reaction of 2 in CD3CN was retarded with the rate constant of kex298 K = 1.9 × 10–8 s–1 which is 105-fold smaller than the value for [Ru3(μ3-O)(μ-CH3COO)6(pyridine)3]. Highly positive activation parameters obtained for 2, ΔH‡ = 138 ± 7 kJ mol–1 and ΔS‡ = 71 ± 20 J K–1 mol–1, illustrate a dissociative activation pathway in which rupture of the Ru–N(pyridine) bond is involved in the rate-determining step.