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Abstract Herein, we report the first systematic study of the oxidative addition of aryl bromides to a PdIcenter to generate organometallic PdIIIcomplexes. These isolable PdIIIcomplexes stabilized by tetradentate macrocyclic pyridinophane ligands exhibit distinct UV–vis and EPR spectroscopic signatures that allowed for the monitoring of their generation in situ. These ligand scaffolds were sterically and electronically tuned using a modular synthetic approach to probe the kinetic properties and activation parameters of the oxidative addition reaction, and a combination of UV–vis and cryo stopped‐flow spectroscopic studies reveal a rapid oxidative addition step occurring at a PdIcenter. In addition, these results are in strong agreement with our recent reactivity studies, which demonstrated that mononuclear PdIsystems are competent catalysts in Kumada cross‐coupling reactions, and thus set the stage for an improved understanding of potential catalytic applications for odd‐electron Pd systems.
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Catalytic Behavior of Mono‐ N ‐Protected Amino‐Acid Ligands in Ligand‐Accelerated C−H Activation by Palladium(II)
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 PdII. These and other mechanistic data indicate that facile exchange between MPAAs and anionic ligands coordinated to PdIIenables a single MPAA to support C−H activation at multiple PdIIcenters.
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- Award ID(s):
- 1700982
- PAR ID:
- 10143681
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 27
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 10873-10877
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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