A new dinuclear Ru-Hbpp based water oxidation catalyst with a trans-disposition of the Ru-OH

Departament de Química and Serveis Tècnics de Recerca (STR), Universitat de Girona, Campus de Montilivi, E-17071, Girona, Spain.
Dalton Transactions (Impact Factor: 4.2). 03/2011; 40(14):3640-6. DOI: 10.1039/c0dt00964d
Source: PubMed


The bis(2-pyridyl)ethylamine (bpea) ligand has been used as a starting material for the synthesis of dinuclear Ru complexes of general formula trans,fac-{[Ru(n)X(bpea)](2)(μ-bpp)}(m+) (for X = Cl, n = II, m = 1, trans-Ru(II)-Cl, 1(+); for X = OH, n = III, m = 3, trans-Ru(III)-OH, 2(3+)) where the 3,5-bis(2-pyridyl)pyrazolate anionic ligand (bpp) acts as bridging dinucleating ligand, the bpea ligand coordinates in a facial manner and the monodentate ligands X are situated in a trans fashion with regard to one another. These complexes have been characterized in solution by 1D and 2D NMR spectroscopy, UV-vis and electrochemical techniques and in the solid state by X-ray diffraction analysis. The reaction of 1(PF(6)) with Ag(+) generates the corresponding solvated complex where the Cl ligand has been removed as insoluble AgCl, followed by the oxidation of Ru(II) to Ru(III) to generate the corresponding dinuclear complex trans-Ru(III)-OH, 2(PF(6))(3). The latter has been shown to catalytically oxidize water to molecular dioxygen using Ce(IV) as oxidant. Quantitative gas evolution as a function of time has been monitored on line by both manometry and mass spectroscopy (MS) techniques. Relative initial velocities of oxygen formation together with structural considerations rule out an intramolecular O-O bond formation pathway.

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  • No preview · Chapter · Jan 2012
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    ABSTRACT: The synthesis of new dinuclear complexes of the general formula in,in-{[Ru(II)(trpy)(L)](μ-bpp)[Ru(II)(trpy)(L')]}(3+) [bpp(-) is the bis(2-pyridyl)-3,5-pyrazolate anionic ligand; trpy is the 2,2':6',2″-terpyridine neutral meridional ligand, and L and L' are monodentate ligands; L = L' = MeCN, 3a(3+); L = L' = 3,5-lutidine (Me(2)-py), 3c(3+); L = MeCN, L' = pyridine (py), 4(3+)], have been prepared and thoroughly characterized. Further, the preparation and isolation of dinuclear complexes containing dinitrile bridging ligands of the general formula in,in-{[Ru(II)(trpy)](2)(μ-bpp)(μ-L-L)}(3+) [μ-L-L = 1,4-dicyanobutane (adiponitrile, adip), 6a(3+); 1,3-dicyanopropane (glutaronitrile, glut), 6b(3+); 1,2-dicyanoethane (succinonitrile; succ), 6c(3+)] have also been carried out. In addition, a number of homologous dinuclear complexes previously described, containing the anionic bis(pyridyl)indazolate (bid(-)) tridentate meridional ligand in lieu of trpy, have also been prepared for comparative purposes. In the solid state, six complexes have been characterized by X-ray crystallography, and in solution, all of them have been spectroscopically characterized by NMR and UV-vis spectroscopy. In addition, their redox properties have also been investigated by means of cyclic voltammetry and differential pulse voltammetry and show the existence of two one-electron waves assigned to the formation of the II,III and III,III species. Dinitrile complexes 6a(3+), 6b(3+), and 6c(3+) display a dynamic behavior involving their enantiomeric interconversion. The energy barrier for this interconversion can be controlled by the number of methylenic units between the dinitrile ligand. On the other hand, pyridyl complexes in,in-{[Ru(II)(T)(py)](2)(μ-bpp)}(n+) (T = trpy, n = 3, 3b(3+); T = bid(-), n = 1, 3b'(+)) and 3c(3+) undergo two consecutive substitution reactions of their monodentate ligands by MeCN.The substitution kinetics have been monitored by (1)H NMR and UV-vis spectroscopy and follow first-order behavior with regard to the initial ruthenium complex. For the case of 3b(3+), the first-order rate constant k(1) = (2.9 ± 0.3) × 10(-5) s(-1), whereas for the second substitution, the k obtained is k(2) = (1.7 ± 0.7) × 10(-6) s(-1), both measured at 313 K. Their energies of activation at 298 K are 114.7 and 144.3 kJ mol(-1), respectively. Density functional theory (DFT) calculations have been performed for two consecutive substitution reactions, giving insight into the nature of the intermediates. Furthermore, the energetics obtained by DFT calculations of the two consecutive substitution reactions agree with the experimental values obtained. The kinetic properties of the two consecutive substitution reactions are rationalized in terms of steric crowding and also in terms of through-space interactions.
    No preview · Article · Feb 2012 · Inorganic Chemistry
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    ABSTRACT: A bis(ruthenium-bipyridine) complex bridged by 1,8-bis(2,2':6',2''-terpyrid-4'-yl)anthracene (btpyan), [Ru(2)(μ-Cl)(bpy)(2)(btpyan)](BF(4))(3) ([1](BF(4))(3); bpy = 2,2'-bipyridine), was prepared. The cyclic voltammogram of [1](BF(4))(3) in water at pH 1.0 displayed two reversible [Ru(II),Ru(II)](3+)/[Ru(II),Ru(III)](4+) and [Ru(II),Ru(III)](4+)/[Ru(III),Ru(III)](5+) redox couples at E(1/2)(1) = +0.61 and E(1/2)(2) = +0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E = +1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [1](3+) ions at E = +1.60 V in water at pH 2.6 (buffered with H(3)PO(4)/NaH(2)PO(4)) catalytically evolved dioxygen. Immediately after the electrolysis of the [1](3+) ion in H(2)(16)O at E = +1.40 V, the resultant solution displayed two resonance Raman bands at nu = 442 and 824 cm(-1). These bands shifted to nu = 426 and 780 cm(-1), respectively, when the same electrolysis was conducted in H(2)(18)O. The chemical oxidation of the [1](3+) ion by using a Ce(IV) species in H(2)(16)O and H(2)(18)O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δnu = 16 and 44 cm(-1)) fully fit the calculated ones based on the Ru-O and O-O stretching modes, respectively. The first successful identification of the metal-O-O-metal stretching band in the oxidation of water indicates that the oxygen-oxygen bond at the stage prior to the evolution of O(2) is formed through the intramolecular coupling of two Ru-oxo groups derived from the [1](3+) ion.
    No preview · Article · Feb 2012 · Chemistry - A European Journal
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