New synthetic precursors for CO‐coordinated, oxo‐centred triruthenium(II,III,III) complexes with varied carboxylato groups [Ru3O(RCO2)6(CO)(solvent)2] where R = C2H5, CH3 and C6H5 have been prepared and characterised. Among the series, the propionato‐bridged complex [Ru3O(C2H5CO2)6(CO)(THF)2] (1) was structurally determined by single‐crystal X‐ray crystallography. Cyclic voltammetry revealed thatthe benzoato‐bridged complex [Ru3O(C6H5CO2)6(CO)(C2H5OH)2] in 0.1 mol dm–3 nBu4NPF6/DMF undergoes two consecutive one‐electron processes assignable to the redox of the Ru3(μ3‐O) core, the redox potentials of which are highly dependent on the electron‐donating/accepting nature of the carboxylato groups. UV‐light excitation of the compounds in CH3CN resulted in the dissociation of CO to form the tris(CH3CN) compounds [Ru3O(RCO2)6(CH3CN)3] (R = C2H5, CH3 and C6H5). These compounds are highly useful as synthetic precursors to a wide range of μ3‐oxo‐triruthenium derivatives with well‐defined redox responses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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This paper reports the synthesis and characterization of a novel series of chain-like compounds where oxo-centered triruthenium cluster moieties are bridged by 4,4'-bipyridine (4,4'-bpy) spacers. A reaction of solvent-coordinated triruthenium "monomer" precursor [Ru(3)O(CH(3)CO(2))(6)(CO)(CH(3)OH)(2)] with a 0.1 equimolar amount of 4,4'-bpy in CH(3)OH gave mixture of chain-like compounds containing "dimers" to "tetramers" which were cleanly separated by column chromatography and characterized by spectroscopic and electrochemical methods. Cyclic voltammetry revealed that all chain-like compounds exhibit reversible and stepwise redox processes in solution with very weak intramolecular coupling between the triruthenium components across the 4,4'-bpy bridge. Photo-induced dissociation of CO from the compounds and electrode surface binding were also investigated.

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.

At the right places: Owing to substitution-lability difference in disparate metal centers, an oxo-centered heterometallic trinuclear acetato complex [Ru2MgO(CH3COO)6(py)3] (py = pyridine; see picture) undergoes site-selective substitution of propionates and ferrocenycarboxylates in a stepwise manner. The new substituted families have been successfully separated by chromatography and fully characterized.