Palladium with water-soluble phosphines

The linear telomerization reaction of dienes was one of the very first processes catalyzed by water soluble phosphine complexes in aqueous media [7,8]. The reaction itself is the dimerization of a diene coupled with a simultaneous nucleophilic addition of HX (water, alcohols, amines, carboxylic acids, active methylene compounds, etc.) (Scheme 7.3). It is catalyzed by nickel- and palladium complexes of which palladium catalysts are substantially more active. In organic solutions [Pd(OAc)2] + PPhs gives the simplest catalyst combination and Ni/IPPTS and Pd/TPPTS were suggested for mnning the telomerizations in aqueous/organic biphasic systems [7]. An aqueous solvent would seem a straightforward choice for telomerization of dienes with water (the so-called hydrodimerization). In fact, the possibility of separation of the products and the catalyst without a need for distillation is a more important reason in this case, too. 

Likewise, in the case of the oxygenated analogs, the combination of the aqueous medium, the water-soluble phosphine tppts (199), palladium(II) acetate, and cinnamyl acetate plus DBU changed the outcome of the reaction dramatically. Thus, from 214, 219, and 224, only sulfides 218,223 and 226 were formed. The sulfides are the products of kinetic control (see the conversion of 218 into the mixture of N-l, N-3, and N-l/N-3 allylated compounds) they separate from the reaction aqueous medium. And this fact, together with the lower temperature required when working in water/ acetonitrile (17/3), permits isolation of the sulfides instead of the thermodynamically more stable /V-allylated compounds. 

A palladium-based method has been developed for the alkylation of the phenolic oxygen of tyrosine residues. Fig. 5f (61). In this reaction, allylic carbonates, esters, and carbamates are activated by palladium(O) complexes in aqueous solution to form electrophilic pi-allyl complexes. These species react at pH 8-10 with the phenolate anions of tyrosine residues, which results in the formation of an aryl ether and the regeneration of the Pd(0) catalyst. The reaction requires P(m-C6H4S03 )3 as a water-soluble phosphine ligand. Activated pi-allyl complexes that do not react with tyrosine residues undergo P-hydride elimination under the basic conditions to yield diene by-products. A particularly attractive feature of this method is its ability to use substrates with charged groups in the allylic positions. This ability allows hydrophobic substrates, such as lipids, to be solubilized to facilitate protein modification. 

In 1994, Sen and Jiang reported aqueous ethylene/CO copolymerization by cationic palladium(II) catalysts with water-soluble bidentate sulfonated nitrogen- or phosphine-based ligands, such as 1. At 50 °C and 35 bar each of efhylene and CO, moderate activities of up to ca. 10 TO h were observed (with a catalyst prepared in situ from [Pd (NC(d I. ) i (l b )2/bidentalc water-soluble ligand). 

Palladium complexed with a water-soluble phosphine, the sodium salt of triphenylphosphine /n-sulfonic acid, in an aqueous film on silica catalyzed allylation in acetonitrile in 100% conversion (5.8).30 No metal was lost. The catalyst could be recycled. 

In this manner, unprotected nucleosides can be coupled to boronic acids in moderate yields. In the Stille coupling reaction, the palladium catalyst formed in situ from PdCl2 and four equivalents of TPPMS was used effectively to couple various aryl halides with R groups on RSnCl3 (Eq. 3) [16]. The use of this catalyst improved the yield and reproducibility compared to the use of PdCl2 alone. The So-nogashira coupling of alkynes with aryl halides is an additional route for the formation of sp—sp2 bonds. The use of this water-soluble phosphine with Pd(OAc)2... 

A counter phase transfer catalysis effect was observed in reduction of allyl chloride with sodium formate in water/n-heptane systems with water soluble palladium(II) catalysts having phosphine ligands with polyether chains [274] it was demonstrated that the catalyst transported the substrate to the aqueous phase where it reacted with the formate. 

If water-soluble phosphine ligands are applied, extremely mild reaction conditions can be achieved. Especially, Pd(TPPMS)3, which converts 4-iodotoluene, is tolerant of a broad range of functional groups, including those present in unprotected nucleotides and amino acids [6]. Interestingly, even the coupling of a donor-substituted iodoarenes and cyclic olefins can be conducted by palladium acetate with TPPTS at only 25 °C in aqueous acetonitrile. However, the low rates observed require a reaction time of up to 48 h for high conversions [12]. 

Telomerization of 1,4-butadiene with water, alcohols, amines, and acids is an extremely useful reaction since it leads to the formation of practically important products. (179,180). For example, the telomer with water, 2,7-octadiene-l-ol can be further hydrogenated to 1-octanol which is a raw material for plasticizers for poly(vinyl chloride). In fact, this reaction was among the processes disclosed in the first patents on the use of TPPTS in biphasic solvent mixtures (58). The catalyst for such telomerizations usually consists of palladium(O) and an excess of TPPTS, TPPMS, or other water-soluble phosphines (eg, with quaternary ammonium substituents). The telomerization of 1,4-butadiene with water was developed into an industrial process by Kuraray Ind. (Scheme 26). Interestingly, the best ligand was the phosphonium salt shown in (Scheme 26) and the catalyst could be prepared in situ from this ligand and [Pd(OAc)2] (179). It is assumed that under the reaction conditions the corresponding tertiary phosphine can be formed to some extent and coordinates to palladium. In any case with a large excess of... 

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. 

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