Sulfonated phosphine ligands

When water-miscible ionic liquids are used as solvents, and when the products are partly or totally soluble in these ionic liquids, the addition of polar solvents, such as water, in a separation step after the reaction can make the ionic liquid more hydrophilic and facilitate the separation of the products from the ionic liquid/water mixture (Table 5.3-2, case e). This concept has been developed by Union Carbide for the hydroformylation of higher alkenes catalyzed by Rh-sulfonated phosphine ligand in the N-methylpyrrolidone (NMP)/water system. Thanks to the presence of NMP, the reaction is performed in one homogeneous phase. After the reaction. 

Considerable work has been conducted on a water-soluble catalyst using sulfonated phosphine-modified rhodium. Details of this chemistry will be described in Chapter 5. The general concept (Figure 2.3) is to make the catalyst water soluble, then after product formation, decant the product. In order for the water-soluble catalyst to be effective, the alkene must dissolve in the aqueous layer. This has been demonstrated on a commercial basis using propene. The low solubility of higher alkenes in the aqueous catalyst layer has proven problematic. The desirable characteristic of the ligand, water solubility, is needed in the separation step but is a disadvantage in the reaction step. 

The problems associated with the in situ approaches can be avoided by using a discrete catalyst. The presumed structure of the monometallic palladium catalyst contains the sulfonated phosphine ligand chelated to the palladium and a palladium-carbon bond (polymer), most probably in cis geometry with respect to the phosphorous (Fig. 8). 

The sulfonated phosphine ligand is chelated to the metal center... 

Water-soluble transition-metal complexes have been used recently for transfer hydrogenolysis of halocarbons. Paetzold and Oehme [110] have realized the reductive dehaiogenation of allyl or benzyl halides in the presence of [(phosphine) 2PdCl2] complexes with sulfonated phosphines as ligands (e.g., Ph2P(CH2)3S03K) by... 

Figure 5.6 Some examples of sulfonated phosphine ligands widely used in aqueous-organic biphasic catalysis [19]...

The solubility of these phosphine ligands in water can be extraordinarily high. The sodium salt of the ira-sulfonated triphenylphosphine (tppts) has a solubility in water of 1.1 kg 1 1 [20], Apart from high solubility, these sulfonated phosphines are widely used for several reasons including ... 

In contrast to the free-radical polymerizations, there have been relatively few studies on transition metal catalysed polymerization reactions in water. This is largely due to the fact that the early transition metal catalysts used commercially for the polymerization of olefins tend to be very water-sensitive. However, with the development of late transition metal catalysts for olefin polymerizations, water is beginning to be exploited as a medium for this type of polymerization reaction. For example, cationic Pd(II)-bisphosphine complexes have been found to be active catalysts for olefin-CO copolymerization [21]. Solubility of the catalyst in water is achieved by using a sulfonated phosphine ligand (Figure 10.5) as described in Chapter 5. 

The synthesis of aldehydes via hydroformylation of alkenes is an important industrial process used to produce in the region of 6 million tonnes a year of aldehydes. These compounds are used as intermediates in the manufacture of plasticizers, soaps, detergents and pharmaceutical products [7], While the majority of aldehydes prepared from alkene hydroformylation are done so in organic solvents, some research in 1975 showed that rhodium complexes with sulfonated phosphine ligands immobilized in water were able to hydroformylate propene with virtually complete retention of rhodium in the aqueous phase [8], Since catalyst loss is a major problem in the production of bulk chemicals of this nature, the process was scaled up, culminating in the Ruhrchemie-Rhone-Poulenc process for hydroformylation of propene, initially on a 120000 tonne per year scale [9], The development of this biphasic process represents one of the major transitions since the discovery of the hydroformylation reaction. The key transitions in this field include [10] ... 

Due to these reasons both in the early attempts in academic research and in the first successful industrial process in AOC sulfonated phosphines were used as ligands (TPPMS and TPPTS, respectively). A detailed survey of the sulfonated ligands is contained in Table 1 and in Figures 1-5. 

Table I. Selected examples of sulfonated phosphine ligands for aqueous organometallic catalysis (see Figure 1 for general structure)... 

Mono- or biphasic systems in which the anion of the ionic liquid acts as a ligand for the homogeneous catalyst, e.g. a sulfonated phosphine ligand (see later). 

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... 

Alkyl ethers of sucrose have been prepared by reaction with long-chain alkyl halides to provide mixtures of regioisomers and products of different degree of substitution.82,83 A similar reaction with chloromethyl ethers of fatty alcohols provides formaldehyde acetals.84,85 Alkenyl ethers of various carbohydrates, and notably of sucrose, can also be obtained by palladium-catalyzed telomerization of butadiene (Scheme 6).86 88 Despite a low-selectivity control, this simple and clean alternative to other reactions can be carried out in aqueous medium when sulfonated phosphines are used as water-soluble ligands. 

Water soluble ligands greatly facilitate catalyst separation. Examples are (22-XLI)174 and (22-XLII),175 which are used in hydroformylations and hydrogenation catalysis, respectively. Rhodium complexes of the sulfonated phosphine (22-XLI) are used in the production of butyraldehyde, a large-scale process developed by Ruhrchemie/Rhone-Poulenc.174... 

Chiral-sulfonated phosphines have also been synthesized and used in the preparation of water-soluble late transition-metal complexes. These complexes, like their analogs in nonaqueous solution, can be used as homogeneous catalysts for the hydrogenation of prochiral alkenes. When the phosphine ligand has a chiral center, the alkane product can potentially be obtained in enantiomeric excess. A variety of different approaches have been used to prepare chiral phosphines that are soluble in aqueous... 

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