Water-soluble palladium catalyst

The reaction is performed in a biphasic aqueous-organic medium using a water-soluble palladium catalyst (see later). 

The importance of water as a solvent has led to the development of water-soluble phosphines. This has been achieved by the incorporation of hydrophilic substituents into the phosphine stmcture. The choice of substituents, whether anionic, cationic, or neutral, depends on the exigencies of the end use. The anionic species [Ph2P(3-C6H4S03)l Na+ has been used to afford a water-soluble palladium catalyst (37) by Du Pont workers. ... 

The cross-coupling reactions of various aryl halides and triflates with vinyl- or arylboronic acids and esters (Suzuki cross-coupling reaction) was also carried out in water in the presence of tetrabutylammonium bromide and a base such as Na2C03, using a phosphine-free palladium catalyst to give biaryl derivatives [Eq. 18)1 [108,109]. More recently, Casalnuovo [101] and Gen t [102,110] have performed this reaction using water-soluble palladium catalysts PdCla (tppms)2 and Pd(OAc)2/tppts in water/acetonitrile. 

Although the first aim of the use of a water-soluble palladium catalyst in allylic alkylation in a two-phase system was the recycling of the catalyst, this methodology finds quite interesting applications in the deprotection of peptides as well as in the selective alkylation of uracils and thiouracils. More recently, the effective use of supported aqueous-phase catalysis as well as asymmetric alkylation in water in the presence of surfactants or amphiphilic resin-supported phosphines open new applications and developments for the future. 

A new, water soluble palladium catalyst was used in the Sonogashira reaction (Pd(OAc)2 triphenylphosphine-trisulfonate sodium salt) [131], and several groups adapted the Sonogashira coupling and subsequent cyclization to the solid-phase synthesis of indoles. Bedeschi and coworkers used this method to prepare a series of 2-substituted-5-indolecarboxylic acids [132], CoUini and Ellingboe extended the technique to l,2,3-trisubstituted-6-indolecarboxylic acids [133]. Zhang and... 

The reaction of4-bromoacetophenone with N-mefhylanilme in water using NaOH as the base and the aforementioned catalyst afforded the tertiary amine in 36% yield. By adding co-solvents, such as methanol, the yield can be increased to 91%. In conclusion, the advantages are the facile catalyst/product separation, the reusability of the water-soluble palladium catalyst, and the use of NaOH instead of the expensive NaOBu as the base. 

The reactivity of water-soluble palladium catalyst, Pd(QS)2 (palladium di(sodirmi) alizarine monosulfonate) has been examined in multilamellar dispersions of unsaturated phospholipids [4]. With substrates of dioleoylphosphatidylcholine there is a transient appearance of trans co9 but no cis double bonds were observed when the trans 9 derivative of phosphatidylcholine was used as substrate. 

Method H includes the green-chemistry approach by using water as the only reaction solvent. The water-soluble palladium-catalyst from phosphine 243, derived from D-glucono-1,5-lactone, in only 0.1 mol%, affects clean cross-coupling reactions of aryl iodides, bromides, as well as chlorides and triflates [38]. Thus 2-bromo... 

The synthesis of poly(p-phenylene) via the homocoupling of p-hro-mophenylboronic acids was first reported by the Max Planck Institut. After this discovery, various new poly(p-phenylenes) were synthesized. A rigid-rod poIy(p-phenylene) was prepared by cross-coupling a biphenyl diboronic ester and a dibromide in aqueous DMF in the presence of a water soluble palladium catalyst (Eq. 78). The... 

Pd-catalyzed allylic substitution reactions can also be performed using water-soluble phosphine ligands, including TPPTS 132, as shown by the reaction of nitroester 48 with allyl acetate 133 to give the substitution product 134 (Scheme 24). The use of water-soluble palladium catalysts has been the subject of a review.t Water-soluble catalysts have also been applied to supported Uquid phase reactions. A silica bead supports a thin film of polar solvent in which the palladium complex resides.t The substrates and product reside in the bulk organic phase and can be decanted from the glass bead catalyst at the end of the reaction. 

This reaction could be successfully achieved with low to moderate degrees of substitutions (DS = 0.04-0.52) depending on experimental conditions. For example, using 0.3 mol% of the water soluble palladium catalyst (Pd/TPPTS), the reaction occurred in zPrOH/NaOH 0.1 N solvent mixture, even at 50 °C and after 3 h reaction, the DS reached 0.08. Unfortunately, these conditions did not preserve the granular aspect of starch, which is a key factor for an industrial aqueous process. After optimization, a system based on [(7i-allyl)Pd(TPPTS)2Cl]/Na2S04 in dimethylisosorbide as cosolvent allowed to obtain high conversions of butadiene (93%) without degradation of the starch texture. 

The hydrogenation of phospholipid-bound unsaturated fatty acids by a homogeneous, water-soluble, palladium catalyst, Biochim.Biophys.Acta 92 1 (1987) 167-174... 

Hummel, W., and Groger, H. (2012) Combination of a Suzuki cross-coupling reaction using a water-soluble palladium catalyst with an asymmetric enzymatic reduction towards a one-pot process in aqueous medium at room temperature. J. Mol. Catal. B Enzym., 84, 89-93. 

---