Sergio Dovidauskas

Monomeric and extended oxo-centered triruthenium clusters

Abstract The chemistry of μ-oxo-centered trinuclear ruthenium-carboxylate clusters, of general formula [Ru 3 O(RCO 2 ) 6 L 3 ] n , has been dealt with special emphasis on their spectroscopic and electrochemical properties, as well as their capability to form ligand-bridged oligomeric structures exhibiting pronounced electronic delocalization. Mixed systems containing trinuclear ruthenium clusters attached to transition metal complexes and porphyrins are also focused upon in this review article, from the point of view of cooperative interactions and supramolecular chemistry. The role of the trinuclear clusters as electron donor/acceptor groups, and their relevance in biomimetic systems, redox catalysis and molecular devices have been discussed.

A new highly efficient tetra-electronic catalyst based on a cobalt porphyrin bound to four μ3-oxo-ruthenium acetate clusters

A meso-tetra(4-pyridyl)cobaltporphyrin modified with four [μ3-O-Ru3(Ac)6(py)2]+ clusters (CoTCP=cobalt tetraclusterporphyrin) has been synthesized and characterized by 1H-NMR and UV–Vis spectroscopy, electrochemistry and spectroelectrochemistry. The facility of CoTCP to form adherent and durable films on a glassy carbon surface has been exploited in the preparation of modified electrodes exhibiting outstanding catalytic activity in the tetraelectronic reduction of dioxygen to water. This finding has been confirmed from the linear behavior and the slope of the Levich plots up to 4000 rpm, as well as from the high current densities, e.g. up to 2.8 mA cm−2 obtained for the modified electrodes. The enhanced activity has been interpreted in terms of the electronic activation of the cobalt porphyrin by the peripheral triangular ruthenium cluster complexes, as supported by detailed spectroelectrochemical data confirming a significant electronic coupling between the cobalt porphyrin and [μ3-O-Ru3(Ac)6]+ groups.

(5,10,15,20-Tetra(4-pyridil)porphinato)manganese(III) acetate modified by four μ3-oxo-triruthenium acetate clusters: synthesis, characterization, electrochemical behavior and catalytic activity

Abstract A novel supermolecule constituted by four μ 3 -oxo-triruthenium acetate clusters coordinated to manganese(III)- meso -tetra(4-pyridil)porphyrin acetate ([MnTPyP]CH 3 COO) has been synthesized. Characterization has been performed by UV–Vis and 1 H NMR spectroscopy. The electrochemical behavior (cyclic voltammetry and spectroelectrochemistry) in N , N ′-dimethylformamide has been analyzed in terms of five redox processes: three related to peripheral clusters (Ru IV,III,III /Ru III,III,III /Ru III,III,II /Ru III,II,II ) and two centered on the Mn–porphyrin core (Mn III P/Mn II P/Mn II P 2− ). A direct comparison has been performed between MnTCP and MnTPyP as catalysts for the cyclooctene and cyclohexane oxidation reactions. The improved selectivity exhibited by the supramolecular catalyst for cyclohexane oxidation has been ascribed to electronic effects on the oxomanganese(V) porphyrin species induced by the four peripheral clusters, in the formal Ru IV Ru III Ru III oxidation state.

Extended Electronic Interactions in a Triangular μ‐Oxotriruthenium Acetate Cluster Containing Nitric Oxide

The binding of NO to the trinuclear cluster [Ru3O(CH3CO2)6(py)2]+ (py = pyridine) leads to a stable, diamagnetic [Ru3O(CH3CO2)6(py)2(NO)]+ complex, displaying extended electronic interactions which arise from the coupling of the unpaired π* electron of NO and the unpaired electron in the π-orbitals of the Ru3O unit. This complex has been isolated and its spectroscopic characterization (EPR, 1H and 13C NMR, IR, UV/Vis) and electrochemical/spectroelectrochemical properties are reported in this paper. The NO0 character in the complex is supported by spectroscopic and electrochemical results, as well as by semi-empirical theoretical calculations carried out for the complex. A remarkable point in this system is the dramatic changes in the Ru−NO electronic interactions accompanying the several successive redox states of the triangular Ru3O center. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Electrochemical and binding properties of a meso‐tetra(4‐pyridyl)porphyrinatozinc supermolecule containing four µ3‐oxo‐triruthenium acetate clusters

The synthesis and characterization of a zinc meso-tetra(4-pyridyl)porphyrin containing four coordinated μ3-oxo-triruthenium acetate cluster complexes, ZnTCP, are reported. The coordination of four ruthenium acetate clusters to the zinc porphyrin has been confirmed by 1H and 13C NMR spectroscopy, including COSY and HETCOR bidimensional correlation techniques. Cyclic voltammetry and spectroelectrochemistry studies have revealed the presence of seven redox processes in the −1.5 to 2.5 V range, four of them attributed to cluster-centered (RuIV,IV,III/RuIV,III,III/RuIII,III,III/RuIII,III,II/RuIII,II,II) and three to porphyrin ring-centered (ZnP+/ZnP/ZnP.−/ZnP2−) redox reactions. The axial coordination reaction has been monitored by spectrophotometric titrations in dichloromethane and acetonitrile, in the 380–480 nm range, using pyridine, imidazole, water and acetonitrile as ligands. The influence of the peripheral ruthenium complexes on the electronic properties of the porphyrin ring has been assayed by measuring the axial coordination properties of the zinc ion. The calculated equilibrium constants for axial coordination of pyridine and imidazole to ZnTCP in dichloromethane are respectively one and two orders of magnitude higher than for meso-tetraphenylporphyrinatozinc, showing a regular increase as a function of the basicity of the ligands. The results have demonstrated that the Ru(III,III,III) species act as electron-withdrawing groups, decreasing significantly the electronic density on the porphyrin ring.

13C NMR spectra of triangular μ-oxoruthenium acetate clusters revisited: HETCOR study of two pyridine and 4,4′-bipyridine derivative

The previous assignment of the 13C NMR spectra of triangular [Ru3O(CH3CO2 )6L3]+ clusters (L=pyridine derivatives) has been revised based on 1H–13C HETCOR and HMBC analysis. ©1999

Propriedades e aplicações de clusters trinucleares de carboxilatos de rutênio

A review with 94 references focusing on m3-oxo-triruthenium carboxylate clusters is presented. The electronic, magnetic, electrochemical, and catalytic properties of these compounds are discussed. Main synthetic routes and structural characteristics, including their use as building blocks in supramolecular systems are described.

Syntheses, electrochemistry and photophysical properties of a series of meso-pyridylpentafluorophenylporphyrins

This work presents the synthesis and characterization of a series of substituted pyridylpentafluroporphyrins, including the separation of the cis- and trans-isomers, the latter being characterized by X-ray crystallography. The spectroscopic and electrochemical properties of the series are dependent on the number of electron withdrawing pentafluorophenyl substituent, but they do not depend on the symmetry of the molecule. Ongoing from the monosubstituted to the more substituted pentafluorophenyl porphyrin H2(MPyTFPP) derivative, the Soret bands are slightly red-shifted and their quantum fluorescence yields range from 0.035 to 0.046, consistent with the value of 0.045 for the fully substituted 5,10,15,20-tetrapentafluorophenylporphyrin (dichloromethane solutions). The redox potentials of the reductive processes of monoanion and dianion formation are also sensitive to the number of pentafluoro substituents, shifting 180 mV to more positive values for the P0/P-1 process ongoing from the monopentafluoro to the tris-pentafluorophenyl substituted derivative.