Counter Phase Transfer Catalysis by Water-Soluble Phosphine Complexes

Abstract

The phase transfer catalysis is one of the big subjects in the latter half of the 20th century, and a large number of studies have been reported. The phase transfer catalysts,which are crown ethers or onium salts, transport anions from aqueous phase into organic phase, and accelerate reactions of organic substrates with the anions. Hypothetically, it is possible to exist a functional molecule capable of transferring lipophilic molecules from organic phase into aqueous phase. However, such a molecule was not reported until recently. In 1986, Mathias et al. and we reported the first examples of such functional molecules. Mathias et al. [1] reported that 4-dimethylaminopyridine reacts with acid halides in organic phase to form pyridinium salts, which transfer into aqueous phase and react with amino acids in the aqueous phase to give amides. This catalysis was named “inverse phase transfer catalysis”. We found that water-soluble palladium complexes, reacting with allyl halides in organic phase, transport them ino aqueous phase, and catalyze the reduction of the allyl compounds with sodium formate in the aqueous phase [2]. We called this catalysis “counter phase transfer catalysis”.