Ion- and atom-leaching mechanisms from palladium nanoparticles in cross-coupling reactions

被引:222
作者
Gaikwad, Anil V.
Holuigue, Alexandre
Thathagar, Mehul B.
ten Elshof, Johan E.
Rothenberg, Gadi
机构
[1] Univ Amsterdam, Vant Hoff Inst Mol Sci, NL-1018 WV Amsterdam, Netherlands
[2] DSM Pharma Chem, NL-6160 MD Geleen, Netherlands
[3] Univ Twente, MESA Inst Nanotechnol, NL-7500 AE Enschede, Netherlands
关键词
catalysis; cross-coupling; Heck reaction; membranes nanoparticles;
D O I
10.1002/chem.200700105
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Leaching of palladium species from Pd nanoparticles under C-C coupling conditions was observed for both Heck and Suzuki reactions by using a special membrane reactor. The membrane allows the passage of palladium atoms and ions, but not of species larger than 5 nm. Three possible mechanistic scenarios for palladium leaching were investigated with the aim of identifying the true catalytic species. Firstly, we examined whether or not palladium(0) atoms could leach from clusters under non-oxidising conditions. By using our membrane reactor, we proved that this indeed happens. We then investigated whether or not small palladium(0) clusters could in fact be the active catalytic species by analysing the reaction composition and the palladium species that diffused through the membrane. Neither TEM nor ICP analysis supported this scenario. Finally, we tested whether or not palladium(II) ions could be leached in the presence of Phi by oxidative addition and the formation of [(PdArI)-Ar-II] complexes. Using mass spectrometry, UV-visible spectroscopy and (CNMR)-C-13 spectroscopy, we observed and monitored the formation and diffusion of these complexes, which showed that the first and the third mechanistic scenarios were both possible, and were likely to occur simultaneously. Based on these findings, we maintain that palladium nanoparticles are not the true catalysts in C-C coupling reactions. Instead, catalysis is carried out by either palladium(0) atoms or palladium(II) ions that leach into solution.
引用
收藏
页码:6908 / 6913
页数:6
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