Ruthenium complexes iodides

Figure 38. Decay of PMC transients measured with a TSO -based nanostructured sensitization solar cell (ruthenium complex as sensitizer in the presence of 0.1 M TBAP in propylene carbonate). The transients are significantly affected by additions of iodide.40 (a) no I", (b) 2 mM r, (c) 20 mM r. (d) 200 mMT.

Based on extensive screening of hundreds of ruthenium complexes, it was discovered that the sensitizer s excited state oxidation potential should be negative of at least —0.9 V vs. SCE, in order to inject electrons efficiently into the Ti02 conduction band. The ground state oxidation potential should be about 0.5 V vs. SCE, in order to be regenerated rapidly via electron donation from the electrolyte (iodide/triiodide redox system) or a hole conductor. A significant decrease in electron injection efficiencies will occur if the excited and ground state redox potentials are lower than these values. 

Fig. 23. Scheme showing possible interconversions of ruthenium complexes in an iodide-promoted system during catalysis (191). 

The main methodologies developed until now for enantioselective oxidation of sulfides are effective only in the oxidation of alkyl aryl sulfoxides. Dialkyl sulfoxides on the other hand are generally oxidized with only poor selectivity. In an attempt to solve this problem, Schenk s group69 recently reported a stereoselective oxidation of metal-coordinated thioethers with DMD. The prochiral thioether is first coordinated to a chiral ruthenium complex by reaction with the chloride complexes [CpRu[(S,S)-chiraphos]Cl], 36. Diastereoselective oxygen transfer from DMD produces the corresponding sulfoxides in high yield and selectivity. The chiral sulfoxides 37 are liberated from the complexes by treatment with sodium iodide. Several o.p. aryl methyl sulfoxides have been obtained by this method in moderate to high ee (Scheme 12). 

Two carbonyl complexes K2[Ru(CN)2I2(CO)2] (from ruthenium carbonyl iodide and KCN)4 and [RuC1(CN)(NH3)(CO)(PPh3)2] (4) (from treatment of [RuCl2(CCl2)(CO)(PPh3)2] with ammonia) are known. Reaction of the latter with CO gives [RuCl(CN)(CO)2(PPh3)2] (5).49... 

Methanol is protonated to give an ion pair with a ruthenium carbonyl iodide anion. Dehydration by an 5 2 type process gives a methyl complex which undergoes insertion of carbon monoxide to an acetyl intermediate followed by reduction to an alkoxy derivative. Finafly. ethanol is released via hydrogenation of the alkoxy intermediate. 

When ethanol is produced, methanol is formed in the first step, and is then homologated. Dombek reported that ruthenium complexes are effective for the production of ethylene glycol at 340 atm and below, especially in the presence of iodide (Eq. 11.4) [11]. 

Water-soluble ruthenium complexes RuHCl(tppts)3, RuCl2(tppts)3, RUH2 (tppts)3, or the rhodium complex RhCl(PTA)3, are also effective catalysts for the hydrogenation of the carbonyl function of aldehydes [16], carbohydrates [17], and keto acids [13], provided that the iodide salt Nal is added for ruthenium complexes. 

Ru(Tp)I(Ci6Hi7l)]-0.512 (Fig. 2.80) has been obtained as a cocrystal of an iodine-bearing neutral ruthenium complex and diiodine. The centrosymmetric diiodine molecule links a pair of Ru complexes via halogen bonds to the Ru-bound iodide anions, thus forming a linear I- I-I- I chain.349... 

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