Catalytic Behavior of Mono‐N‐Protected Amino‐Acid Ligands in Ligand‐Accelerated C−H Activation by Palladium(II). (8th April 2020)

• Record Type: Journal Article
• Authors: Salazar, Chase A.; Gair, Joseph J.; Flesch, Kaylin N.; Guzei, Ilia A.; Lewis, Jared C.; Stahl, Shannon S.
• Is Part Of: Angewandte Chemie. Volume 132:Number 27(2020)
• Page Start: 10965
• Page End: 10969
• Publication Date: 2020-04-08
• Subjects: carboxylate ligands -- C−H activation -- homogeneous catalysis -- palladium -- reaction mechanisms; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202002484
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: 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. Abstract : Rapid exchange of mono‐ N ‐protected amino‐acid (MPAA) ligands with other carboxylate ligands plays a key role in the ligand‐accelerated catalysis observed in Pd II ‐catalyzed C−H functionalization reactions. The MPAA ligands are shown to play a catalytic role in Pd II ‐mediated C−H activation.