108818-39-9Relevant academic research and scientific papers
Mechanisms of double and single carbonylation reactions of aryl iodides catalyzed by palladium complexes to give α-keto esters and esters
Ozawa, Fumiyuki,Kawasaki, Nobuo,Okamoto, Hidekazu,Yamamoto, Takakazu,Yamamoto, Akio
, p. 1640 - 1651 (2008/10/08)
Various aryl iodides are converted into α-keto esters and esters on reactions with alcohols and Et3N under CO pressure in the presence of catalytic amounts of palladium complexes. Detailed examination of factors controlling the selectivity for α-keto ester formation revealed the following characteristics of the reactions. (a) Use of palladium catalysts having bulkier tertiary phosphine ligands increases the selectivity for α-keto ester formation. (b) Secondary alcohols of moderate bulkiness and high basicity gave α-keto esters in high selectivity. (c) Addition of less polar solvents such as benzene and dichloromethane to the system improves the selectivity for α-keto ester formation. (d) Higher CO pressure is required to obtain α-keto esters in higher yields. NMR examination of the catalytic system containing PhI, alcohol, Et3N, and PdCl2(PPh3)2 revealed the presence of an aroylpalladium(II) complex as the predominant species. Model studies of the reactions of isolated phenyl- and benzoylpalladium(II) complexes toward alcohols, Et3N, and carbon monoxide indicate that an aroylpalladium(II) intermediate generated by a rapid CO insertion into an arylpalladium(II) complex is responsible for both the ester and α-keto ester formations in the catalytic reactions. Alcohols of higher basicity show higher reactivity in the α-keto ester formation whereas more acidic alcohols give esters at higher reaction rates. A kinetic study on the ester formation indicates that the ester formation proceeds predominantly through a mechanism involving predissociation of a tertiary phosphine ligand. On the basis of the experimental results a mechanism comprising two catalytic cycles to produce α-keto ester and ester is proposed.
