Water-soluble ruthenium-TPPTS complexes

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. 

Water-soluble rhodium(I) complexes with TPPTS, TPPMS, and PTA ligands, such as [RhCl(TPPTS)3], are capable of hydrogenating aldehydes, although their catalytic activity is inferior to the ruthenium complexes discussed above [116]. In sharp contrast to the ruthenium(II)-based catalysts, in reactions of unsaturated al-... 

More recently, catalytic hydrogenations of alkenes by other catalysts in water have been explored. For example, water-soluble ruthenium complex RuCl2(TPPTS)3 has been used for the catalytic hydrogenation of unsaturated alkenes (and benzene). Hydrogenation of nonactivated alkenes catalyzed by water-soluble ruthenium carbonyl clusters was reported in a biphasic system. The tri-nuclear clusters undergo transformation during reaction but can be reused repeatedly without loss of activity. The organometallic aqua complex [Cp Ir (H20)3] " ... 

Several water-soluble ruthenium complexes, with P = TPPMS, TPPTS, or PTA ligands (cf. Section 2.2.3.2), catalyze the selective reduction of crotonaldehyde, 3-methyl-2-butenal (prenal), and trans-cinnamaldehyde to the corresponding unsaturated alcohols (Scheme 2) [33—36]. Chemical yields are often close to quantitative in reasonable times and the selectivity toward the aUyhc alcohol is very high (> 95%). The selectivity of the reactions is critically influenced by the pH of the aqueous phase [11] as well as by the H2 pressure [37]. The hydrogenation of propionaldehyde, catalyzed by Ru(II)/TPPTS complexes, was dramatically accelerated by the addition of inorganic salts [38], too. In sharp contrast to the Ru(II)-based catalysts, in hydrogenation of unsaturated aldehydes rhodium(I) complexes preferentially promote the reaction of the C=C double bond, although with incomplete selectivity [33, 39]. 

It has been shown previously how water-soluble rhodium Rh-TPPTS catalysts allow for efficient aldehyde reduction, although chemoselectivity favors the olefmic bond in the case of unsaturated aldehydes [17]. The analogous ruthenium complex shows selectivity towards the unsaturated alcohol in the case of crotonaldehyde and cinnamaldehyde [31]. 

The use of water-soluble ligands was referred to previously for both ruthenium and rhodium complexes. As in the case of ruthenium complexes, the use of an aqueous biphasic system leads to a clear enhancement of selectivity towards the unsaturated alcohol [34]. Among the series of systems tested, the most convenient catalysts were obtained from mixtures of OsCl3 3H20 with TPPMS (or better still TPPTS) as they are easily prepared and provide reasonable activities and modest selectivities. As with their ruthenium and rhodium analogues, the main advantage is the ease of catalyst recycling with no loss of activity or selectivity. However, the ruthenium-based catalysts are far superior. 

If cobalt, rhodium and ruthenium complexes are the most frequently used in hydroformylation reactions, most carbonylation reactions employ palladium catalysts. The active water-soluble complex Pd(TPPTS)3 is easily prepared by reducing in situ PdCl2/TPPTS with CO in water at room temperature. The carbonylation of alcohols and olefins (Scheme 1.24) requires the presence... 

The remaining two examples of metathesis chemistry in water are related to the synthesis of polymers. In the first case, the solubility and stability of the ruthenium catalysts in water is exploited in the emulsion polymerization of norbor-nenes and cyclooctadiene. In emulsion polymerization, a water-soluble initiator is required. Claverie [58] used complex 11 or the related complex RuC12-(TPPTS)2(=CHC02Et) (where TPPTS = tris(3-sulfonatophenyl)phosphine, sodium salt). These two complexes were used with standard surfactants to product well... 

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