The effect of high pressure on the Heck reaction - A contribution to a deeper understanding of the mechanism

被引:23
作者
Buback, M
Perkovic, T
Redlich, S
de Meijere, A
机构
[1] Univ Gottingen, Inst Organ Chem, D-37077 Gottingen, Germany
[2] Univ Gottingen, Inst Phys Chem, D-37077 Gottingen, Germany
关键词
catalysis; Heck reaction; IR spectroscopy; kinetics; palladium;
D O I
10.1002/ejoc.200200720
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The influence of high pressure on the Heck reactions of iodobenzene with methyl, ethyl and tert-butyl acrylate, and of both 4-nitrophenyl iodide and 4-nitrophenyl triflate with methyl acrylate, has been studied for the first time by quantitative on-line FT-IR spectroscopy. Reaction rates and activation parameters (DeltaH(double dagger), DeltaS(double dagger), DeltaV(double dagger)) were determined at temperatures between 50 and 120 degreesC and pressures up to 3000 bar. A clear influence on the kinetics of the reactions was observed by the nature of the leaving group and by the steric and electronic features of the acrylate. tert-Butyl acrylate, which is more electron-rich than methyl acrylate according to PES measurements, was found to react 1.4-times faster on average than methyl acrylate and, at elevated pressures, triflate turned out to be a better leaving group than iodide. Thus, the observed activation volume for the reaction of iodobenzene with tert-butyl acrylate (DeltaV(double dagger) = -12cm(3) mol(-1)) is more negative than that of the reaction of iodobenzene with ethyl acrylate (DeltaV(double dagger) = -7 cm(3) mol(-1)) or methyl acrylate (DeltaV(double dagger) = -5 cm(3) mol(-1)). For the variation of the leaving group in 4-nitrophenyl iodide and 4-nitrophenyl triflate, the activation volumes for the reaction of each with methyl acrylate are -9 and -37 cm(3) mol(-1), respectively. The results suggest that the rate-determining step of the overall reaction is not the oxidative addition, but is either the alkene coordination or the subsequent carbopalladation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).
引用
收藏
页码:2375 / 2382
页数:8
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