Ruthenium TPPTS complex

Hydrogenation of propionaldehyde, catalyzed by various ruthenium-TPPTS complexes, was dramatically influenced by the addition of certain salts [122, 123]. Whereas in the absence of salts there was no reaction at 35 °C and 50 bar H2, in the presence of Nal TOFs of more than 2000 h 1 were determined. This was lowered to 300 h-1 when the sodium cation was selectively sequestered by a cryptant (4,7,13,16,21-pentoxa-l,10-diazabicyclo[5.8.8]tricosane). Obviously, the larger part of the salt effect belonged to the cation. It was concluded that electrophilic assistance by Na+ facilitated C-coordination of the aldehyde and formation of a hydroxy-alkyl intermediate. 

Ir/tppts catalysts exhibit almost the same selectivity as Ru/tppts in the hydrogenation of a,p-unsaturated aldehydes albeit with approximately 70 times lower rates.485 In sharp contrast to the ruthenium and iridium based tppts catalysts, RhJ tppts complexes catalyse the chemoselective hydrogenation of a,fl-unsaturated aldehydes to the corresponding saturated aldehydes (Figure 14, III).54-485... 

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]. 

A ruthenium complex [RuCl2(TPPTS)2]2 was used for regeneration of NADP+ to NADPH withhydrogen. Thus, 2-heptanonewas reduced with alcohol dehydrogenase from Thermoanaerobacter brockii in the presence of the mthenium complex, NAD P, and hydrogen at 60°C to (S)-2-heptanol in 40 % ee. Turnover number was reported to be 18 (Figure 8.6) [5cj. 

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. 

Besides the electrochemical application, the (Cp )Rh(bpy)-complex 9 can also be used to reduce cofactors with hydrogen. In a recent study it was compared with ruthenium complex 13 [RuC12(TPPTS)2]2 (TPPTS tris(w-sulfonatophenyl)-phosphine Scheme 43.5). Both complexes were used to regenerate the cofactors in the reduction of 2-heptanone to (S)-2-heptanol, catalyzed by an ADH from Thermoanaerobium brockii (TfrADH) [46, 47]. The TON for both catalysts was 18. 

The selective hydrogenation of a,/3-unsaturated aldehydes to give the corresponding unsaturated alcohols [Eq. (9)] was investigated with the ruthenium complex catalysts, initially present as [Ru(H)(Cl)(tppts)3] or [Ru(H)2(tppts)4] (91). 

Complexes of ruthenium, [HRu(CO)Cl(tppms)3] 2H20 and [HRu(CO) Cl(tppts)3], were reported to be catalysts for the same hydrogenation reaction (92). The metal complexes were not pure rather, they were used in the presence of the free sulfonated phosphanes and their respective oxides. 

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... 

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. 

One of the most interesting applications of these catalytic systems is the regioselective reduction of a, -unsaturated aldehydes to unsaturated alcohols or saturated aldehydes [18,19]. For example, 3-methyl-2-buten-l-al or prenal was selectively reduced to prenol with a selectivity up to 97% using ruthenium complexes associated with tppts in a mixture of water/toluene at 35 °C and 20 bars hydrogen [Eq. (1)] conversely, the saturated aldehyde was obtained with a selectivity up to 90% using RhCl(tppts)3 as the catalyst at 80 °C and 20 bars hydrogen. The same selectivities were observed for (Ej-cinnamaldehyde,2-buta-nal and citral. 

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-... 

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... 

The first anti-Markovnikov hydration of terminal acetylenes, catalyzed by ruthenium(II)-phosphine complexes, has been described in 1998 [27], As shown on Scheme 9.8, the major products were aldehydes, accompanied by some ketone and alcohol. In addition to TPPTS, the fluorinated phosphine, PPh QFs) also formed catalytically active Ru-complexes in reaction with [ RuC12(C6H6) 2]. 

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] " ... 

Ruthenium complexes of TPPTS and TPPMS [19-22] have been employed as catalysts or catalyst precursors for the hydrogenation of a,y unsaturated carbonyl compounds in biphasic systems [19-23aj c Section 2.4.2. Other ligands 7-13 are known and have been described [20, 23b, cj. 

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