Water-based reactions anionic phosphines

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. 

Imidazolium-styrene copolymers were prepared by copolymerization of 1-vi-nyl-3-butylimidazolinm-based ionic liquids ([VBImJX, X=C1 , BF ", and PFg) with styrene, which were used as polymeric supports to immobilize Pd(OAc)2 using a method of alcohol reduction [22]. It was demonstrated that Pd existed in the form of Pd nanoparticles (NPs) on these imidazolium-styrene copolymers. Using the [VBIm]Cl-styiene copolymer as a support, Pd NPs of less than 6 nm were formed, which was particularly interesting, as usually only a Pd carbene complex was formed when Pd(OAc)2 was treated with 1,3-dialkyimidazolium ionic liquids containing a halide anion. The copolymer-supported Pd catalysts were found to be efficient and reusable catalysts for the Heck reaction in water in the absence of a phosphine ligand and phase-transfer catalyst. 

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