期刊
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
卷 59, 期 27, 页码 10873-10877出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202002484
关键词
carboxylate ligands; C-H activation; homogeneous catalysis; palladium; reaction mechanisms
Mono-N-protected amino acids (MPAAs) are increasingly common ligands in Pd-catalyzed C-H functionalization reactions. Previous studies have shown how these ligands accelerate catalytic turnover by facilitating the C-H activation step. Here, it is shown that MPAA ligands exhibit a second property commonly associated with ligand-accelerated catalysis: the ability to support catalytic turnover at substoichiometric ligand-to-metal ratios. This catalytic role of the MPAA ligand is characterized in stoichiometric C-H activation and catalytic C-H functionalization reactions. Palladacycle formation with substrates bearing carboxylate and pyridine directing groups exhibit a 50-100-fold increase in rate when only 0.05 equivalents of MPAA are present relative to Pd-II. These and other mechanistic data indicate that facile exchange between MPAAs and anionic ligands coordinated to Pd(II)enables a single MPAA to support C-H activation at multiple Pd(II)centers.
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