Tenside phosphines

Thermoregulated Phase Transfer Catalysis - A conceptual advance in the field of biphasic hydroformylation of higher olefins is the use of rhodium catalysts generated from nonionic tenside phosphines, such as ethoxylated tris(4-... 

A particularly elegant approach to circumventing the solubility problem is to generate transition metal complexes from tenside phosphines which combine both the inherent properties of a ligand (appropriate steric and electronic environment) and a surfactant in one molecule, and to use them as catalysts in micellar systems. 

In order to rationalize the effect whereby the activity in the Rh/2-catalyzed hydroformylation of 1-tetradecene goes through a maximum as a function of the tail length of the surfactant 2, the model of simplified spherical (Hartley) ionic micelle [9a-c] (Figure 1) was proposed [14, 15], The core of the micelle is probably composed of the hydrophobic tail of the tenside phosphine 2 where 1-tetradecene is solubilized (Figure 1, stippled part). 

The inverse temperature dependence of the water-solubility of nonionic tenside phosphines at the Tp was applied by Bergbreiter et al. [41] in the hydrogenation of allyl alcohol using water-soluble rhodium catalysts modified with the smart ligand 15 in aqueous media. In this case, on heating the sample to 40-50°C the reaction stopped but on cooling to 0 °C hydrogenation was resumed in the aqueous phase (cf. Section 4.6.3). 

The tenside phosphines 38 (n = 1, 2, 3) containing amino and phosphonate moieties were used as ligands to impart surfactant properties to Pd catalysts for the carbonylation (cf. Section 6.5) of benzyl chloride to phenylacetic acid under aqueous-biphase conditions [66], The recovery of the Pd/38 catalyst after the carbonylation reaction, however, was only 85-92%. 

Dror and Manassen hydrogenated a- and cyclic olefins such as 1-octene, 1 -dodecene and cyclohexene in micellar systems using rhodium catalysts modified with water-insoluble carboxylated tenside phosphines 45 (Table 3 n=3,5,7,9,l 1) in the presence of conventional tensides such as sodium dodecylsulfate (SDS) or cetyltrimethylammonium bromide (CTAB) and cosolvents e.g. dimethyl sulfoxide. Linear olefins were more reactive than cyclic olefins. Maximum efficiency was observed in the presence of the anionic surfactant SDS when 45 contained a chain of 5-7 carbon atoms. In contrast, using the cationic tenside CTAB the ligand 45 with 5 C atoms was almost inactive but became active again with dodecyl trimethylammonium bromide. 

The first water-soluble system specifically designed to combine both functions of a ligand and a surfactant in one molecule and applied in transition-metal-cata-lyzed conversions of highly water-insoluble substrates in micellar systems is the zwitterionic tenside trisulfoalkylated tris(2-pyridyl)phosphine, 2 (n = 0, 3, 5, 7, 9, 11) [4, 14, 72, 74]. Turnover frequencies (TOF) up to 340 h-1 were achieved in the micellar hydroformylation of 1-tetradecene to pentadecanals, according to Eq. (1), using Rh/2 catalysts at 125 °C, by fine tuning of the hydrophilic/lipophilic properties of the tenside system 2 [4, 14]. In sharp contrast, Rh/TPPTS catalysts gave only traces of pentadecanals under the same biphasic conditions. 

Rhodium complexes modified with the tenside chiral phosphine 5 were used as catalysts in the hydroformylation of styrene, according to Eq. 2, in an aqueous/organic two-phase system [19, 26], The TOFs achieved with the surfactant catalyst Rh/5 were higher (245 h-1) compared with the Rh/TPPTS system (100 Ir1) [26]. The n/iso ratios of the aldehydes were about 0.6 with Rh/TPPTS and ca. 0.4 with the Rh/5 system. Although the phosphine 5 is chiral, virtually no optical activity was observed in the phenylisopropanal product. HQ... 

The surfactant phosphines containing poly(ethyleneoxide) 31, sulfonate 47, amine 34 (with R7R2/R3 = H/H/—CH2—N[(CH2)2—NEt2]2, sulfate 36, and phospho-nate 37 moieties were used as tenside ligands to modify Rh catalysts for the hydroformylation of higher alkenes such as 1-hexene, 1-octene, 1-decene, and 1-dode-cene in aqueous/organic two-phase systems [58, 62-65],... 

Rhodium complexes generated from the water-insoluble carboxylated surfactant phosphine 17 (n = 3, 5, 7, 9, 11) were used as catalysts in the micellar hydrogenation of a- and cyclic olefins, such as 1-octene, 1-dodecene, and cyclohexene, in the presence of conventional cationic or anionic tensides such as cetyltrimethylammo-nium bromide (CTAB) or SDS and co-solvents, e.g., dimethyl sulfoxide [15], After the reaction the catalyst was separated from the organic products by decantation and recycled without loss in activity. There is a critical relationship between the length of the hydrocarbon chain of the ligand 17 and the length and nature of the added conventional surfactant, for obtaining maximum reactivity. For example,... 

The most severe dra wback in homogeneous catalysis is the separation of the catalyst from the reaction mixture. The industrial success of the aqueous two-phase hydroformylation ofpropene to n-butanal [1] in Ruhrchemie AG in 1984 represents the considerable progress in this field. However, aqueous/organic biphasic catalysis has its limitations when the water solubility of the starting materials proves too low, as in hydroformylation of higher olefins (see Chapter 1). To solve this issue, a variety of approaches have been attempted. Additions of co-solvents [2] or surfactants [3, 4] to the system or application of tenside ligands [5, 6] and amphiphilic phosphines [7, 8] are ways to increase the reaction rates. Other approaches such as fluorous biphase system (FBS see Chapter 4) [9], supported aqueous phase catalysis (SAPC see Section 2.6) [10], supercritical CO2 (cf. Chapter 6) [11] and ionic liquids (cf Chapter 5) [12] have also been introduced to deal with this problem. 

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