Article

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: 4.1). 03/2011; 40(14):3640-6. DOI: 10.1039/c0dt00964d
Source: PubMed

ABSTRACT 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.

0 Followers
 · 
114 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a systematic electrochemical and spectroelectrochemical study of the catalytic activity for water oxidation of an iridium-N-dimethylimidazolin-2-ylidene (Ir-NHC-Me2) complex adsorbed on a polycrystalline gold electrode. The work aims to understand the effect of the electrolyte properties (anions and acidity) on the activity of the molecular catalyst and check its stability towards decomposition. Our results show that the iridium complex displays a very strong dependence on the electrolyte properties such that large enhancements in catalytic activity may be obtained by adequately choosing pH and anions in the electrolyte. The stability of the adsorbed compound was investigated in situ by Surface Enhanced Raman Spectroscopy and Online Electrochemical Mass Spectrometry showing that the immobilized catalyst exhibits good stability under anodic conditions, with no observable evidence for the decomposition to iridium oxide.
    Journal of the American Chemical Society 06/2014; 136(29). DOI:10.1021/ja504460w · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Water‐oxidation catalysts (WOCs) can potentially be improved by installing pendant electron‐donor groups that may also be proton donors or acceptors. We have modified one of the most well‐studied WOCs with alkoxy or hydroxy substituents on the bidentate bipyridine ligand (N,N), thereby forming [(terpy)RuII(N,N)X] (X = Cl, H2O; terpy = 2,2′;6′,2"‐terpyridine). A combination of NMR spectroscopy (particularly 15N chemical‐shift data), UV/Vis spectroscopy, X‐ray diffraction, and oxygen evolution data point to interesting and beneficial effects of an oxygenated group proximal to X. A methoxy group on the 2,2′‐bipyridyl (bipy) ring cis to X = Cl is shown to facilitate ionization of the chloride ligand in aqueous acetone, perhaps by acceptance of a hydrogen bond from the aquo ligand. Hydrogen‐bond donation of a proximal hydroxy group to a bound aquo ligand is shown by X‐ray diffraction. Distinct differences in pK a values for the 4,4′‐ and 6,6′‐dihydroxy bipy complexes are seen. In water oxidation driven by ceric ammonium nitrate, the 6,6′‐dimethoxy species is somewhat faster and longer‐lived than the analogue that lacks the oxygenated groups [a turnover number (TON) of 215 instead of 138 in 10 h, and a turnover frequency (TOF) of 0.36 min–1 instead of 0.23 over the same time period]. Taken together, oxygenated groups near the WOC active site are promising electron or proton donors and/or hydrogen‐bond acceptors, and are the subject of further scrutiny. Oxygenated substituents (protic OH and aprotic OMe) are compared at positions near to (figure, left) and far from (figure, right) the active site of water‐oxidation catalysts. Facile aquation promoted by a proximal substituent, hydrogen bonding, and pH‐sensitive redox and UV/Vis spectra are seen, along with either enhanced or reduced catalytic rates.
    European Journal of Inorganic Chemistry 02/2014; 2014(4):676. DOI:10.1002/ejic.201300826 · 2.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Two new diiridium–triazolylidene complexes were prepared as bimetallic analogues of established mononuclear water oxidation catalysts. Both complexes are efficient catalyst precursors in the presence of cerium ammonium nitrate (CAN) as sacrificial oxidant. Up to 20000:1 ratios of CAN/complex, the turnover limitation is the availability of CAN and not the catalyst stability. The water oxidation activity of the bimetallic complexes is not better than the monometallic species at 0.6 mM catalyst concentration. Under dilute conditions (0.03 mM), the bimetallic complexes double their activity, whereas the monometallic complexes show an opposite trend and display markedly reduced rates, thereby suggesting a benefit of the close proximity of two metal centers in this low concentration regime. The high dependence of catalyst activity on reaction conditions indicates that caution is required when catalysts are compared by their turnover frequencies only. Ditopic triazolylidene–iridium complexes were evaluated as water oxidation catalysts; the bimetallic arrangement enhances the maximum turnover frequency considerably in catalytic experiments that use low catalyst loadings.
    European Journal of Inorganic Chemistry 02/2014; 2014(4). DOI:10.1002/ejic.201300843 · 2.97 Impact Factor