Nonionic phosphines

In 2003 Jin and coworkers [13] reported on the synthesis of a novel nonionic water-soluble phosphine 3 by a two-step ethoxylation of 2-(diphenyl-phosphinojphenylamine. In this new family of nonionic phosphines the polyoxyethylene moieties are introduced into the amino group of organo-phosphines. 

The nonionic phosphine 7 was used in the rhodium-catalyzed hydro-formylation of 1-dodecene under thermoregulated phase-separable conditions. Phosphine 7 is soluble in toluene at higher temperatures, but can be... 

The thermoregulated phase-transfer function of nonionic phosphines has been proved by means of the aqueous-phase hydrogenation of sodium cinnamate in the presence of Rh/6 (N =32, R = n-CsHu) complex as the catalyst [16]. As outlined in Figure 2, an unusual inversely temperature-dependent catalytic behavior has been observed. Such an anti-Arrhenius kinetic behavior could only be attributed to the loss of catalytic activity of the rhodium complex when it precipitates from the aqueous phase on heating to its cloud point. Moreover, the reactivity of the catalyst could be restored since the phase separation process is reversible on cooling to a temperature lower than the cloud point. 

Fig. 2 Atmospheric-pressure hydrogenation of sodium cinnamate using Rh/6 (N = 32, R = n-CsH,) as the catalyst in water at different temperatures. The cloud point of the catalyst is 64 °C. Anti-Arrhenius kinetic behavior results due to the inversely temperature-dependent water-solubility of the nonionic phosphine [16].

Thermoregulated phase-transfer catalysis, however, could be successfully put into effect for the hydroformylation of higher olefins in aqueous/organic two-phase media [11], As shown in Table 2, various olefins have been converted to the corresponding aldehydes in the presence of nonionic phosphine-modified rhodium complexes as catalysts. An average turnover frequency (TOF) of 250 h-1 for 1-do-decene and 470 Ir1 for styrene have been achieved. Even the hydroformylation of oleyl alcohol, an extremely hydrophobic internal olefin, would give a yield of 72% aldehyde [19]. In comparison, no reaction occurred if Rh/TPPTS complex was used as the catalyst under the same conditions. 

Tab. 2 Two-phase hydroformylation of olefins catalyzed by nonionic phosphine-modified rhodium complexes [10, 19],...

The concept of TRPTC provides a reasonable explanation for the satisfactory catalytic reactivity of Rh/nonionic phosphine complexes in the case of the two-phase hydroformylation of higher olefins. At a temperature lower than the cloud point, a nonionic phosphine-modified rhodium catalyst would remain in the aqueous phase since the partition of the catalyst between water and a nonpolar aprotic organic solvent strongly favors the aqueous phase. On heating to a temperature higher than the cloud point, however, the catalyst loses its hydrate shell, transfers into the organic phase and then catalyzes the transformation of alkenes to aide-... 

The strategy of TPSC (using nonionic phosphines with the property of CST as ligand to separate, recover and reuse a homogeneous catalyst) was firstly applied in the hydroformylation of higher olefins [30] (Table 3). 

More recently, the application scope of thermoregulated phase-separable transition metal complex with nonionic phosphine ligand has been expanded from hy-droformylation to hydrogenation, and the central metal varied from Rh to Ru. The first experimental study is the hydrogenation of styrene catalyzed by thermoregulated phase-separable Ru3(CO)12/PETPP complex catalyst. Under the conditions of Ph2 = 2.0 MPa, T=90°C, catalyst/substrate (mol/mol) = 1/1000, 3 hours, the Ru3(CO)12/PETPP complex catalyst exhibited good activity (Table 5). Compared with other catalysts, Ru3(CO)12/PETPP complex showed the same catalytic activity compared to the lipophilic Ru3(CO)9(TPP)3, while the hydrophilic Ru3(CO)9-(TPPTS)3 and Ru3(CO)9(TPPMS)3 are less active (Table 6). 

Furthermore, the combination of palladium(II) salts with tetrabutylammonium halide additives, called Jeffery conditions , is an efficient system for Heck-type reactions [7a], but the mechanistic implications are unknown. Also, nonionic phosphine ligands, such as triphenylphosphine which yields Pd(PPh3)4, are applied in water-miscible organic solvents, like DMF and acetonitrile. In these cases, the application of water is of crucial importance, but the role is often not well investigated. 

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-... 

Rhodium complexes generated from the polyethylene glycol)-functionalized phosphine 9 (n = 1, x = 0, R = Me, Bu), which should behave as a nonionic surfactant and be able to induce micelle formation, have been used as catalysts in the hydroformylation of 1-dodecene in an aqueous/organic two-phase system [31]. The conversion of 1-dodecene was 80% and the n/iso ratio 60 40, with no carryover of the rhodium catalyst into the organic phase. The Rh/9 (n = 1, x = 0, R = Me, Bu) catalyst remained active after one recycle step [31],... 

Whitesides and co-workers [40] synthesized the nonionic surfactant phosphines 9 (n = 2 x = 0 m = 12, 16 R = Me), 12, 13, 14 and used them as ligands in rhodium-catalyzed hydrogenation of water-immiscible starting materials such as cyclohexene in a two-phase system. 

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). 

Some other C—C bond coupling reactions in micellar systems should be mentioned here. Monflier et al. [72] described, in both papers and patents, the telome-rization of 1,3-butadiene into octadienol in a micellar system by means of a palladium-phosphine catalyst. Water-soluble and amphiphilic phosphines have been used and the surfactants were widely varied. The authors have shown that the promoting effect of surfactants appeared above the CMCs of the surfactants, and they conclude that micellar aggregates were present in the reaction mixture. Cationic, anionic, and nonionic surfactants gave this micellar effect but the combination of the highly water-soluble TPPTS and the surfactant dodecyldimethylamine hydrocarbonate was found to be best. A speculation about the location of reactants shows that the reaction probably occurs in the interface between the micellar pseudophase and water. 

Thermoregulated Phase-transfer Catalysis with Nonionic Water-soluble Phosphines... 

Tab. 1 Cloud [11.13]- points of nonionic water-soluble phosphines with polyoxyethylene moieties ...

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