Heterolytic Splitting of Allylic Alcohols with Palladium(0)−TPPTS in Water. Stabilities of the Allylphosphonium Salt of TPPTS and of the Ionic Complex [Pd(η³-allyl)(TPPTS)₂]⁺

Abstract

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(η3-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)Ar3P]+ 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-1-ol), 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(η3-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)Ar3P]+ increases the stability of [Pd(η3-allyl)(TPPTS)2]+. Above pH 10, [(allyl)Ar3P]+ decomposes into OTPPTS and propylene by reaction with OH−. At lower pH, [(allyl)Ar3P]+ is slowly isomerized into [(propenyl)Ar3P]+, 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.

Cationic Ruthenium‐Cyclopentadienyl‐Diphosphine Complexes as Catalysts for the Allylation of Phenols with Allyl Alcohol; Relation between Structure and Catalytic Performance in O‐ vs. C‐Allylation

“…It has been reported that oxidative addition of allyl alcohol in the absence of acid does take place, the reaction medium becoming more basic, [25] which supports our theory on initial hydroxyl anion formation.…”

N‐Benzylation/Benzylic CH Amidation Cascade by the (η3‐Benzyl)palladium System in Aqueous Media: An Effective Pathway for the Direct Construction of 3‐Phenyl‐3,4‐dihydro‐ (2H)‐1,2,4‐benzothiadiazine 1,1‐Dioxides

“…Basset and co-workers reported that the p-allyl palladium intermediate was unstable under basic conditions. [10] Since our results were consistent with these reports on the palladiumcatalyzed allylation with allylic alcohols, (h 3 -benzyl)-palladium was proposed to be an intermediate here in analogy to the allylic substitution reaction.…”

Mechanistic Studies for Synthesis of Bis(indolyl)methanes: Pd-Catalyzed C–H Activation of Indole–Carboxylic Acids with Benzyl Alcohols in Water

“…In our previous work, benzylation of anthranilic acid did not occur at 120 °C in 1 M NaOH aq [28]. Thus, the (η 3 -benzyl)palladium intermediate might be unstable under high temperature and strong basic conditions [34].…”