Poly(benzyl ether) Dendrimers Functionalized at the Core with Palladium Bis(N-Heterocyclic Carbene) Complexes as Catalysts for the Heck Coupling Reaction

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• 作者：Alba M. Ortiz ; Alberto Sánchez-Méndez ; Ernesto de Jesús ; Juan C. Flores ; Pilar Gómez-Sal ; Francisco Mendicuti
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：February 1, 2016
• 年：2016
• 卷：55
• 期：3
• 页码：1304-1314
• 全文大小：652K
• ISSN：1520-510X

文摘

Bis(imidazolylidene)palladium complexes 9–12 containing a sterically hindered aryl group (mesityl or 2,6-diisopropylphenyl) and a poly(benzyl ether) dendron as N-substituents of the NHC ligand are accessible up to the third generation by transmetalation of the corresponding silver complexes. Complexes 9–12 are soluble, active, and very stable catalysts under Heck reaction conditions. The NHC ligand appears to be stably coordinated to the Pd during catalysis. The catalytic activity increases with generation number, although irregularly. The palladium site is not significantly congested in the reaction solvent by the increasing size of the dendritic substituents, as corroborated by X-ray diffraction, fluorescence and DOSY-NMR spectroscopy, and MD simulation studies. This is a consequence of the conformational semiflexibility of the poly(benzyl ether) dendrons and the benzylic link between these dendrons and the N-heterocyclic ligands.