Three new Ru-aqua complexes containing a mixed carbene and pyridylic ligands with general formulas [Ru(CNC)(bpy)(H2O)](PF6)2 (1) (CNC is 2,6-bis(butylimidazol-2-ylidene)pyridine; bpy is 2,2'-bipyridine) and cis-/trans-[Ru(CNC)(nBu-CN)(H2O)](PF6)2 (cis-2 and trans-2) (nBu-CN is 2-(butylimidazol-2-ylidene)pyridine) have been prepared and structurally characterized both in the solid state (monocrystal X-ray diffraction analysis for 1 and for the related complex trans-[Ru(Br)(CNC)(nBu-CN)](PF6)) and in solution (for all of them) through NMR. The electrochemical properties of these three Ru-aqua complexes have been investigated by cyclic voltammetry, differential pulse voltammetry and Coulombimetric techniques. It is found that, for complex 1 at pH 7, the difference between the IV/III and the III/II redox couples (DeltaE1/2) is 50 mV, which is the smallest ever reported for this type of complex. On the other hand, for complexes cis-2 and trans-2, the oxidation state III is unstable with respect to disproportionation to II and IV. The reactivity of their Ru=O species has been tested toward cis-beta-methylstyrene oxidation, and it has been compared to [Ru(O)(trpy)(bpy)]2+. An inverse correlation between the degree of cis/trans-epoxide isomerization and DeltaE1/2 is found. In particular, for complexes cis-2 and trans-2, which have a DeltaE1/2 < 0, the epoxidation is highly stereoselective, yielding only cis-epoxide.
New triolefinic macrocyclic ligands of the type (E,E,E)-1,6,11-tris(arenesulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-triene (aryl: a = ferrocenyl, b = 4-pyrrol-1-ylphenyl, c = 4-methylphenyl) and their Pd 0 complexes (1aab, 1abb and 1bcc) have been prepared and characterized. Further structural characterization in the solid state has also been performed by means of X-ray diffraction analysis for the complex 1bcc. The redox properties of both the ligands and their Pd complexes have been studied using cyclic voltammetric and coulombimetric techniques. In particular, complexes and ligands containing the pyrrole group do polymerize upon exposure to
A family of new ruthenium complexes containing a combination of polypyridyl and carbene ligands has been prepared and characterized from structural, spectroscopic, and redox viewpoints both experimentally and computationally. Interestingly, a correlation between ΔE1/2, defined as the difference between E1/2(RuIV/III) and E1/2(RuIII/II), and the activity and selectivity of some catalytic oxidation processes has been clearly established. A density functional theory study on the synthesized species has been carried out revealing a correlation between the number of carbene ligands and ΔE1/2, and consequently with the RuIII disproportionation. The reactivity of these complexes has been tested with regard to the electrocatalytic oxidation of benzyl alcohol.
The cover picture shows a general cartoon of heterogeneous catalytic processes performed on Suzuki-type cross-coupling reactions. The submerged gear represents the hub in the system, holding the active sites of the catalysts which are triazatriolefinic palladium(0) complexes. The catalysts are anchored through oxidative electropolymerization of the pyrrole groups contained in their structures, and can be monitored through the electroactivity of additional ferrocene entities also present. Details are discussed in the article by A. Llobet, A. Roglans et al. on p. 1601 ff.
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