Ruthenium complexes oxygen

Fuel cells essentially reverse the electrolytic process. Two separated platinum electrodes immersed in an electrolyte generate a voltage when hydrogen is passed over one and oxygen over the other (forming H30+ and OH-, respectively). Ruthenium complexes are used as catalysts for the electrolytic breakdown of water using solar energy (section 1.8.1). 

Klimant I., Wolfbeis O.S., Oxygen-sensitive materials based on silicone-soluble ruthenium complexes, Anal. Chem. 1995 67 3160-3166. 

McEvoy A.K., McDonagh C.M., MacCraith B.D., Development of a fiber opic dissolved oxygen sensor based on quenching of a ruthenium complex entrapped in a porous sol-gel film, SPIEProc. 2508, 190-198, (1995). 

Figure 6.2 A bifurcated optical fibre is used to carry light to a probe. The hose tip consists of a thin layer of hydrophobic sol-gel material doped with a ruthenium complex which senses oxygen and reveals its content. (Image courtesy of Ocean Optics.)...

A.K. McEvoy, C.M. McDonagh and B.D. MacCraith, Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive ruthenium complexes immobilized in sol-gel-derived porous silica coatings, Analyst, 121(6) (1996) 785-788. 

Cyclizations of dihydroxystilbene 256 using 4 mol % of chiral ruthenium complexes under photolytic conditions were investigated by Katsuki et al. (Scheme 65) [167]. Coordination of alcohols/phenols to Ru(IV) species generates a cation radical with concomitant reduction of metal to Ru(III). Cycli-zation of this oxygen radical followed by another cyclization provides the product 257. Catalyst 259 provided 81% ee of the product in chlorobenzene solvent. Optimization of the solvent polarity led to a mixture of toluene and f-butanol in 2 3 ratio as the ideal solvent. Substituents on the phenyl rings led to a decrease in selectivity. Low yields were due to the by-product 258. 

I. Klimant and M. J. P. Leiner, Recent investigations in optical oxygen sensing The behavior of ruthenium complexes in silicone matrices, in Abstracts, 1st European Conference on Optical Chemical Sensors and Biosensors, Graz, Austria, April 12-15, 131 (1992). 

We reported the use of an indenyl ruthenium complex 2 as a racemization catalyst which did not produce ketones as the byproducts [17]. The metal catalyst requires a weak base like triethylamine and molecular oxygen to be activated. The DKR with 2 in combination with an immobilized PCL was carried out at a lower temperature (60°C) to afford good yields and high optical purities (Scheme 1.15). It is noteworthy that 2 does not require ketone as hydrogen mediator for racemization. 

Ruthenium complexes catalyse the two main oxidative reactions for alkenes those in which oxygen atoms or hydroxyl groups span the erstwhile double bond without C=C rupture (e.g. epoxidation, ctT-dihydroxylation, ketohydroxylation), and cleavage reactions in which the C=C bond is broken. Although RuO has recently been shown to be effective for c/x-dihydroxylation and ketohdroxylation, epoxidations are in general effected by Ru complexes of lower oxidation states, while RuO excels at cleavage reactions. 

The stoichiometric interaction of an enyne and [RuCl(PCy3)(pcymene)]B(Ar )4 XVIIIa containing a bulky non-coordinating anion B(ArF)4 showed by NMR at —30 ° C the formation of the alkenyl alkylidene ruthenium complex and acrolein. This formation could be understood by the initial formation of a vinylidene intermediate and transfer of a hydride from the oxygen a-carbon atom to the electrophilic vinylidene carbon, as a retroene reaction step (Scheme 8.13) [54]. 

Similarities between [Ru(bpy),]2+ (discussed in Chapter 13) and [Pt,(pop)J4 are apparent. Reactive excited states are produced in each when it is subjected to visible light. The excited state ruthenium cation, [Ru(bpy)3]" +, can catalytically convert water to hydrogen and oxygen. The excited slate platinum anion, [Pt,(pop)J 4-, can catalytically convert secondary alcohols to hydrogen and ketones. An important difference, however, is that the ruthenium excited stale species results from (he transfer of an electron from the metal to a bpy ligand, while in the platinum excited state species the two unpaired electrons are metal centered. As a consequence, platinum reactions can occur by inner sphere mechanisms (an axial coordination site is available), a mode of reaction rot readily available to the 18-clectron ruthenium complex.-03... 

O Neal DP, Meledeo MA, Davis JR, Ibey BL, Gant VA, Pishko MV, Cote GL (2004), Oxygen sensor based on the fluorescence quenching of a ruthenium complex immobilized in a biocompatible polyethylene glycol) hydrogel, IEEE Sensors Journal 4 728 - 734. 

Fig. 3 Oscilloscope traces showing emission of light at nm by the photoexcited ruthenium complex (left) and its bleaching recovery at 452 nm (right), a, b Ru (II) -tris (2, 2 -bipyridine) alone c a + oxygen d a + semicarbazide. The concentrations used were Ru(II)tris (2, 2 -bipyridine), 50 pM oxygen, 1.26 mM semicarbazide, 20 mM. All solutions were in 1 MNaOH.

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