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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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Metal and Ligand Effects on Coordinated Methane pKa: Direct Correlation with the Methane Activation Barrier
DFT and coupled cluster methods were used to investigate the impact of 3d metals and ligands upon the acidity and activation of coordinated methane C–H bonds. A strong, direct relationship was established between the pKa of coordinated methane and the free energy barriers (ΔG⧧) to subsequent H3C–H activation. The few outliers to this relationship indicated other salient factors (such as thermodynamic stability of the product and ligand–metal coordination type) that impacted the methane activation barrier. High variations in the activation barriers and pKa values were found with a range of 34.8 kcal/mol for the former and 28.6 pKa units for the latter. Clear trends among specific metals and ligands were also derived; metal ions such as CoI, as well as Lewis acids and π-acids, consistently yielded higher acidity for ligated methane and hence lower ΔG⧧.
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- Award ID(s):
- 1953547
- PAR ID:
- 10269845
- Date Published:
- Journal Name:
- Journal of physical chemistry
- Volume:
- 124
- ISSN:
- 1932-7447
- Page Range / eLocation ID:
- 7283–7289
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1021/acs.jpca.0c04756
