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|Titolo:||Switching between K2 and K3 Bis(pyrazol-1-yl)acetate Ligands by Tuning Reaction Conditions: Synthesis, Spectral, Electrochemical, Structural, and Theoretical Studies on Arene-Ru(II) Derivatives of Bis(azol-1-yl)acetate Ligands|
|Autori interni:||MARCHETTI, Fabio|
|Data di pubblicazione:||2009|
|Abstract:||New (arene)ruthenium(II) derivatives containing neutral HL or anionic L− ligands (arene = p-cymene or benzene, HL in general, in particular HL1 = bis(pyrazol-1-yl)acetic acid and HL2 = bis(3,5-dimethylpyrazol-1-yl)acetic acid) have been synthesized and analytically and spectrally characterized. The ligands in neutral form coordinate ruthenium in a chelating κ2-N,N′-bidentate fashion affording 1:1 derivatives of formula [Ru(arene)(HL)Cl]Cl, where the inner Cl can be replaced by a phosphine. These derivatives show very high conductance values in water, due to the contribution of H3O+ produced by deprotonation of the −COOH fragment in HL ligands and consequent formation of 1:2 electrolytes such as [Ru(arene)(κ3-N,N′,O-L)]Cl2 species. However, the remaining derivatives contain monoanion L− ligands coordinating in the tripodal κ3-N,N′,O-tridentate fashion. The solid-state X-ray structure of the complex [Ru(η6-p-cymene)(κ3-N,N′,O-L1)]PF6 confirmed such behavior. The redox properties of those compounds have been investigated by cyclic voltammetry and controlled potential electrolysis, which, on the basis of their measured RuII/III oxidation potentials, have allowed for the ordering of the HL and L− ligands according to their electron-donor character. This is accounted for by DFT calculations, which show a relevant contribution of L ligand orbitals to the highest occupied molecular orbitals (HOMOs) when they are coordinated in the monoanionic tridentate form, while for derivatives containing neutral HL ligands, the main contribution to the HOMOs comes from orbitals of the metal and chlorine atoms, the overall contribution from the bidentate HL ligand orbitals being small. Values of the Lever electrochemical EL ligand parameter (a measure of the net electron donor character of a ligand) have been estimated for the above and related acylpyrazolonate ligands, as well as for the η6-coordinated benzene and cymene.|
|Appare nelle tipologie:||Articolo|
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