Ethylene glycol palladium catalysts

Another biphasic Heck reaction was described by Beller et al. [25]. The medium consisted of xylene and ethylene glycol. The catalyst was a palladium complex with a carbohydrate-substituted triphenylphosphine (9 and 10). Aryl bromide (15 mmol), styrene (22.5 mmol), and NaOAc (16.5 mmol) were suspended in 10 mL of xylene and 10 mL of ethylene glycol. The catalyst precursor (Pd(OAc)2) and ligand (Pd/ ligand ratio 1 3) were added and the mixture was heated to 130 °C for 20 h. Both ligands A and B showed better results than the TPPTS ligand (cf Section 2.2.3.2) in the case of activated aryl bromides (for instance, p-nitrobromobenzene). However, for deactivated aryl bromides (for instance, 2-bromo-6-methoxynaphthalene) TPPTS proved to generate a more stable and thus more productive catalyst system. 

Scheme 7.121 Heck couplings utilizing an oligo(ethylene glycol)-bound SCS-palladium(ll) complex as catalyst.

Catalysis experiments were performed to investigate the telomerization of butadiene with ethylene glycol in selected TMS systems (e.g. si toluene DMF 1 5 4 or sl 2-octanol DMSO 1.35 3 5.2). With Pd/TPPTS as the catalyst a maximum yield of only 10% of the desired products could be achieved. With Pd/TPPMS the yield increased up to 43% in the TMS system si toluene isopropyl alcohol, but additional water had to be added to obtain a phase split after the reaction. The catalyst leaching is very high and 29% of the palladium used is lost to the product phase. 

Wang X, Yang H, Feng B et al (2009) Functionalized polyethylene glycol)-stabilized palladium nanoparticles as an efficient catalyst for aerobic oxidation of alcohols in supercritical carbon dioxide/poly(ethylene glycol) biphasic solvent system. Catal Lett 132 34-40... 

Ethylene glycol (EG) may be obtained from cellulose by many ways, for instance, by the catalytic conversion over carbide catalysts [71], It is the simplest linear polyol available and often serves as a model for more complex substrates. Many reports are therefore available on the telomerization of EG. The possible telomer products are shown in Scheme 14, the linear mono-telomer typically being the desired compound. The mono-telomer can be used, after saturation of the double bonds, as a plasticizer alcohol in polyvinylchloride production, whereas application in cosmetics and surfactants has also been indicated [72]. Early examples include the work of Dzhemilev et al., who first reported on the telomerization of butadiene with EG in 1980, yielding a mixture of the mono- and di-telomers and butadiene dimers using a palladium catalyst activated by AlEt3 [73]. Kaneda also reported the use of EG in... 

Behr A, Urschey M (2003) Palladium-catalyzed telomerization of butadiene with ethylene glycol in liquid single phase and biphasic systems control of selectivity and catalyst... 

Some positional isomers of coralyne have been synthesized and examined for antileukaemic activity,82 and the distribution of salts of coralyne after they have been administered to rodents has been studied.83 Dehydrogenation of canadine to berberrubine (59) can be accomplished in ethylene glycol and hydrochloric acid with palladium or with tris(triphenylphosphinyl)rhodium chloride, the reaction proceeding faster at low temperatures with the latter catalyst.84 Derivatives of 13-methylberberrubine and its analogues have been synthesized, so that they might be screened to find their potential as antitumour agents.85... 

Some of the most widely studied organic reactions at this time are palladium catalysed carbon-carbon cross coupling reactions, which have been extensively investigated in water. For example, palladium catalysed Suzuki reactions can be performed in water in the presence of poly (ethylene glycol) (PEG). It should be noted that the PEG may be playing the role of a surfactant (PTC) and/or a support for the metal catalyst in water. Interestingly, in this example, no phosphine is needed and the products are easily separated and the catalyst phase reused. Unfortunately, diethyl ether was used to extract the product and as this solvent is hazardous (low flash point and potential peroxide formation), the overall process would be greener if an alternative solvent could be used. 

The hydrogenation of n-botyl oxalate into ethylene glycol and n-butyl alcohol, jointly developed by Union Carbide and Ube Industries. Oxalate is obtained by oxidative carbo-nylation of n-butanoi on the liquid phase, by using a palladium based catalyst and an accelerator (nitric acid, n-butyl nitrite, ), at about 70TC and 6.106 Pa absolute <... 

The cationic palladium(II) complex [Pd(24a)3Cl]+ of the para-isomer of 24a (M = Na) catalyzes the carbonylation of benzyl chloride in basic medium to give phenyl-acetic acid in high yields. The Pd(0) complex [Pd(24a)3], formed by reduction of [Pd(24a)3Cl]+ with CO, is asumed to be the catalytic species [93] (see Scheme 1). Palladium complexes of ligands related to 24a (M = Na) have also been employed in aqueous ethylene glycol phases as catalysts for Suzuki-type C—C cross-coupling reactions for the syntheses of substituted biphenyls (cf. Section 6.6) [97]. 

Although isomerization of alkenes occurs simultaneously with the oxidation, rhodium and ruthenium complexes can also be used instead of palladium for the oxidation of terminal alkene [15]. With these catalysts, symmetrical quaternary ammonium salts such as tetrabutylammonium hydrogensulfate are effective. Interestingly, the rate of palladium-catalyzed oxidation of terminal alkenes can be improved by using poly(ethylene glycol) (PEG) instead of quaternary ammonium salts [16]. Thus, the rates of PEG-400-induced oxidation of 1-decene are up three times faster than those observed with cetyltrimethylammonium bromide under the same conditions. Interestingly, internal alkenes can be efficiently oxidized in this polyethylene glycol/water mixture. 

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