The Pd(TPPTS) 3 complex (TPPTS is the sodium salt of tris(m-sulfophenyl)phosphine) easily ionizes allyl alcohol in water over a wide range of pH: OH - and TPPTS are released, and [Pd(η 3 - allyl)(TPPTS) 2 ] + is formed. The released TPPTS further reacts with the palladium cationic complex to reversibly produce both the allylphosphonium salt of TPPTS [(allyl)Ar 3 P] + and Pd(TPPTS) 3 , the latter acting as the catalyst of the allylation of TPPTS by allyl alcohol. Primary allylic alcohols, such as butenol (trans-2-buten-1ol), prenol (3-methyl-2-buten-1-ol), geraniol, and cinnamyl alcohol, react with Pd(TPPTS) 3 to produce hydroxide ion, the corresponding hydrosoluble cationic palladium complex, and allylic phosphonium salts. At room temperature, [Pd(η 3 -allyl)(TPPTS) 2 ] + is stable up to pH 12, but beyond this value, palladium precipitates. The temperature has an adverse effect on the complex stability: palladium precipitates at 80 °C, even at pH 7, with the formation of a small amount of propylene. The addition of [(allyl)Ar 3 P] + increases the stability of [Pd(η 3 -allyl)(TPPTS) 2 ] + . Above pH 10, [(allyl)Ar 3 P] + decomposes into OTPPTS and propylene by reaction with OH. At lower pH, [(allyl)Ar 3 P] + is slowly isomerized into [(propenyl)Ar 3 P] + , which further reduces its stability toward pH and temperature. These consecutive reactions of the TPPTS ligand could explain most of the catalyst instability. This study outlines the basis for a better understanding of the instability phenomenon of the catalytic system Pd(0)-TPPTS in reactions with allylic intermediates, e.g. the Tsuji-Trost reaction, and in the reaction of dienes in aqueous media in which palladium often precipitates.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry