Water-soluble Ru complexes

Cyclopropanation is an important synthetic method, and enantioselective catalytic reactions of olefins and diazoacetates provide access to valuable products with biological activity. In general, these reactions are conducted in anhydrous solvents and in several cases water was found to diminish the rate or selectivity (or both) of a given process. Therefore it came as a surprise, that the Cyclopropanation of styrene with (+)- or (-)-menthyl diazoacetates, catalyzed by a water-soluble Ru-complex with a chiral bis(hydroxymethyldihydrooxazolyl)pyridine (hm-pybox) ligand proceeded not only faster but with much Wgher enantioselectivity (up to 97 % e.e.) than the analogous reactions in neat THF or toluene(8-28 % e.e.) (Scheme 6.34) [72]. The fine yields and enantioselectivities may be the results of an accidental favourable match of the steric and electronic properties of hm-pybox and those of the menthyl-dizaoacetates, since the hydroxyethyl or isopropyl derivatives of the ligand proved to be inferior to the hydroxymethyl compound. Nevertheless, this is the first catalytic aqueous cyclopropanation which may open the way to other similar reactions in aqueous media. 

In this system RuO, powders were coated with the water insoluble polymer complex (i8) and used as suspensions. Ru02 colloids were stabilized by the water soluble Ru complex prepared from poly(Vbpy) and used (see also Sect. 3.4). 

Sodium or ammonium formates are also suitable as hydride donors for the hydrogenation of a, 0-unsaturated and aromatic aldehydes with water-soluble Ru complexes [88, 93], With [RuCl2(TPPMS)2], both the catalyst and the formate are in the aqueous phase the phase-transfer problem associated with catalysts not soluble in water and aqueous formate solutions does not arise [93, 94]. These systems olfer interesting theoretical aspects [87, 95, 186]. 

Scheme 2 Selective reduction of unsaturated aldehydes to alcohols, catalyzed by water-soluble Ru complexes.

RUO4 was shown to oxidize PCBs in water [21]. Water-soluble Ru complexes, such as [Ru(H20)2(dmso)4], were effective catalysts for the KHSO5 oxidation of a number of polychlorobenzenes and polychlorophenols, mainly converted into HCl and CO2 [22]. Replacement of the dmso- solvated ruthenium by RuPcS resulted... 

Monflier et al. (1997) have suggested Pd catalysed hydrocarboxylation of higher alpha olefins in which chemically modified P-cyclodextrin (especially dimethyl P-cyclodextrin) is u.sed in water in preference to a co-solvent like methanol, acetone, acetic acid, acetonitrile, etc. Here, quantitative recycling of the aqueous phase is possible due to easy phase separation without emulsions. A similar strategy has been adopted by Monflier et al. (1998) for biphasic hydrogenations for water-in.soluble aldehydes like undecenal using a water-soluble Ru/triphenylphosphine trisulphonate complex with a. suitably modified p-cyclodextrin. 

In some ca.ses the use of a two-phase system may allow a change in the selectivity. Thus, Joo et al. (1998) have shown that water-soluble Ru hydrides (sulphanatophenylphosphine Ru complexes) give different products in the hydrogenation of cinnamaldehyde with variation in the pH of the aqueous media. At a pH greater than 7.2, cinnamyl alcohol is formed and at a pH less than 5 saturated aldehyde is formed. 

The use of chiral ruthenium catalysts can hydrogenate ketones asymmetrically in water. The introduction of surfactants into a water-soluble Ru(II)-catalyzed asymmetric transfer hydrogenation of ketones led to an increase of the catalytic activity and reusability compared to the catalytic systems without surfactants.8 Water-soluble chiral ruthenium complexes with a (i-cyclodextrin unit can catalyze the reduction of aliphatic ketones with high enantiomeric excess and in good-to-excellent yields in the presence of sodium formate (Eq. 8.3).9 The high level of enantioselectivity observed was attributed to the preorganization of the substrates in the hydrophobic cavity of (t-cyclodextrin. 

Krakovjak MG, Anufrieva EV, Anan eva TD, Nekrasova TN (2005a) Water-soluble fullerene complexes with n-vinylcaprolactam homo- and copolymers and a method for preparation of these complexes. Russian patent RU 2 264 415 10.02.2005... 

Analogously, the SAPC catalyzed hydroformylation reaction was carried out using other water-soluble metal complexes of Pt and Co. Pt complexes in the presence of an Sn co-catalyst underwent hydrolysis of the Pt-Sn bond, which led to lower reaction selectivity. With the corresponding Co catalyst, good hydroformylation selectivities and conversions could be achieved, provided excess phosphine was used. Other authors performed hydrogenation of a,(3-unsaturated aldehydes using SAPC, and Ru and Ir water-soluble complexes. 

The water-soluble Ru(II) complex [Ru(i76-C6H6)(CH3CN)3](BF4)2 catalyzed the biphasic hydrogenation of alkenes and ketones with retention of the catalyst in the aqueous phase (87). However, the ruthenium complex moved to the organic phase when benzaldehyde was hydrogenated. In a benzene-D20 system, H-D exchange was observed between H2 and D20. Both monohydridic pathway and a dihydridic pathway are possible for hydrogen activation, and these two different catalytic cycles influence the yield and product distribution. 

Water-soluble transition metal complexes, which are effective catalysts in other hydrogenation processes, were found to be effective catalysts in C02 hydrogenation. The first report disclosed the application of Rh complexes with water-soluble phosphine ligands in water-amine mixtures to afford formic acid.122 Water-soluble Ru-phosphine121,123,124 and Rh-phosphine123 124 complexes were used in aqueous solution to hydrogenate C02 or HCO3 to formic acid or HCOO-, respectively. 

Bicontinuous microemulsions consisting of cationic surfactant AUTMAB (30-40 wt%), MMA (30-40 wt%), and 20-40 wt% of an aqueous 50 pM solution of water-soluble metal complexes such as Ru(dip)3Cl2 (dip=4,7-diphenyl-1,10-phenanthroline) have been investigated [98]. After polymerization, the microemulsion transformed into a transparent polymer film which showed a remarkable enhancement in lirminescence intensity. The emission hfetime also... 

Water-soluble Ru-EDTA complexes are active carbonylation eatalysts for the conversion of amines to amides [158]. TPPTS (and other water-soluble ligands, other additives included) have been used for special carbonylations [159, 203, 238]. For other types of carbonylation and Heck reaction, see Sections 2.1.2.3 and 3.1.6. 

Thiourea reacts with Ru(III) in a hot acidic medium to form a water-soluble blue complex Ru(NH2 CS NH2)6. The method based on this reaction [42,43] is rather insensitive (e = 2.5-10 at 620 nm). Ref 42a is cited later, but not here. Please adjust or correct. 

Hydrated electrons react with certain water-soluble metalloporphyrin complexes, reducing the porphyrin ligands to pi-radical species. When the metal centers are Zn(II), Pd(II), Ag(II), Cd(II), Cu(II), Sn(IV), and Pb(II), the radical complexes are produced at diffusion-controlled rates and decay with second-order kinetics.188 Fe(III) porphyrins, on the other hand, yield Fe(II) porphyrins.189 Rather different behavior is seen in the reaction of e (aq) with [Ru(bpy)3]3 + here, parallel paths generate the well-known luminescent excited-state [ Ru(bpy)3]2 + and another reduced intermediate, both of which decay to the ground-state [Ru(bpy)3]2+, 190 In a direct demonstration of the chemical mechanism of inner-sphere electron transfer, [Coni(NH3)5L]2+ complexes where L = nitrobenzoate and dinitrobenzoate react with e (aq) to form Co(III)-ligand radical intermediates, which then undergo intramolecular electron transfer to yield Co(II) and L.191... 

Ruthenium tetroxide was shown to oxidize PCBs in water [20], Water-soluble ruthenium complexes, such as [Ru(H20)2(DMS0)4]2+, are effective catalysts for the KHSO5 deep oxidation of a number of chloroaliphatics, of a-chlorinated al-kenes, polychlorobenzenes, and polychlorophenols. When the reactions are carried out in water in the presence of surfactant agents, degradation of the substrates is definitely faster. Aromatic substrates are mainly converted into HC1 and C02, polychlorophenols being more sensitive to oxidation than substituted benzenes [21]. Replacement of the DMSO- solvated ruthenium by RuPcS results in a definite improvement of the reaction course with hydrogen peroxide, since dismutation of... 

Synthesis of the first water-soluble catalyst complexes was reported in 1973 [3] and was based on the use of sulfonated triphenylphosphine to replace TPP. The sulfonated derivative was found to stabilize the lower oxidation states of a number of transition metals such as Rh, Ru, Ir, Pt, Ni, and Cu in aqueous systems and these water-soluble catalysts facilitated hydrogenation of soluble substrates like pyruvic acid. 

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