Soluble ligand method

Several methods have been described to liberate the hydroxyl groups from 24 to produce the water-soluble, tetrahydroxyl bidentate ligand 25 [52, 53b]. Water-soluble ligands are of interest due to the prospect of recycling the catalyst into an aqueous phase, ideally without loss of performance. The enantiomeric hydrogenation of itaconic acid was performed in aqueous methanol over a range of solvent compositions (MeOH H20, 9 1 to 3 97), with consistently excellent levels of performance (100% conversion, 99% ee, SCR 100, 12 h) [52 b]. Interest-... 

In the following few sections we shall now review the most important water-soluble ligands and the synthetic methods of general importance. It should be noted, that in many cases only a few examples of the numerous products available through a certain synthetic procedure are shown in the tables and the reader is referred to the literature for further details. 

The commercial success of rhodium-trisulfonated triphenylphosphine (TPPTS) catalysts1 has prompted considerable interest in TPPTS and other water-soluble ligands.2 The potential for new applications for the synthesis of both bulk and fine chemicals in water has led to methods for the preparation of a wide variety of sulfonated phosphines including chiral phosphines3 and... 

Epoxides are possibly the most studied of the three-membered heterocycles. While a host methods for the synthesis of epoxides have been developed, work continues, especially in the development of more chemo-, regio-, and stereoselective methods. The development of new metal-based epoxidation catalysts continues to garner significant levels of activity. The use of the Mn-based catalyst, I, with a water-soluble ligand provides excellent yields of the corresponding epoxides <06MI139>. A Mn-salen complex was modified by the addition of phosphonium groups at either end to render it water-soluble. The use of 5 mol% of this catalyst with NalO as the oxidant provided a quantitative yield of cyclohexene oxide from cyclohexene. 

In addition to the copper/molten ligand method, the syntheses of [Cu(4-Xpz)2] (X = Cl, 16, and Br, 17) on treatment of Cu(OH)2 or Cu20 with excess 4-XpzH in refluxing xylene were described (36). Two forms of the 4-ClpzH derivative were obtained, one green and one brown. It was apparent from the X-ray powder diffraction pattern that the two forms are structurally distinct. While details of the structure of the brown form still remain unknown, comparison of its solubility and thermal properties with those of the structurally... 

The hydroxycarbonylations (carboxylations) of alkyl, aryl, benzyl and allyl halides are from a retrosynthetic and mechanistic standpoint closely related. This type of reaction is widely used in organic synthesis [6], although a stoichiometric amount of salt by-product makes these methods less attractive on a large scale. The use of water-soluble catalysts for carbonylation of organic halides was scarcely studied in the past. Up to now palladium, cobalt, and nickel compounds in combination with water-soluble ligands have been used as catalysts for various carboxylations. 

We reported a new method which allows for the rapid parallel solubility measurements for libraries of materials in SCFs [75]. The technique was used to evaluate the solubility of a mixed hbrary of 100 synthetic polymers including polyesters, polycarbonates, and vinyl polymers. It was found that poly(vinyl acetate) (PVAc) showed the highest solubility in CO2 the anomalously high solubility of PVAc has been shown previously [72]. This method is at least 50 times faster than other techniques in terms of the rate of useful information that is obtained and has broad utility in the discovery of novel SCF-soluble ligands, catalysts, biomolecules, dyes, or pharmaceuticals for a wide range of materials applications. 

Further steps to improve the method are actually steps leading back to the well-acclaimed methods of supported catalysis, in which not the solvent but the catalyst itself is bound to a carrier. The use of catalysts with water-soluble ligands, however, permits one to bridge the gap between SAP and canonical supported catalysis, not in one step, but in a series of smaller steps. 

The anhydrous chloride is prepared by standard methods. It is readily soluble in water to give a blue-green solution from which the blue hydrated salt CuClj. 2H2O can be crystallised here, two water molecules replace two of the planar chlorine ligands in the structure given above. Addition of dilute hydrochloric acid to copper(II) hydroxide or carbonate also gives a blue-green solution of the chloride CuClj but addition of concentrated hydrochloric acid (or any source of chloride ion) produces a yellow solution due to formation of chloro-copper(ll) complexes (see below). 

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