Journal
INORGANIC CHEMISTRY
Volume 57, Issue 15, Pages 8778-8787Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.8b00563
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Funding
- National Natural Science Foundation of China [21672018, 21373023]
- Beijing Municipal Natural Science Foundation [2162029]
- BUCT Fund for Disciplines Construction and Development [XK1527]
- China Scholarship Council [201606880007]
- U.S. National Science Foundation [CHE-1661604]
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The pyridine-based PNN ruthenium pincer complex (PNN)Ru(CO)(H) can catalyze the well-known dehydrogenative amidation reaction, but the mechanism is not fully understood. In this work, we find there exists an alternative metal-substrate cooperation mechanism in this reaction system, which is more favorable than the aromatization-dearomatization mechanism. The possible reaction of the excess base t-BuO- with catalyst species (PNN)Ru(CO)(H) is studied, indicating t-BuO- is able to facilitate the ligand substitution and enhance catalytic activities. With the bifunctional Ru-N moiety, the imine-substituted species (PN)(imine)Ru(CO)(H) 5 could serve as an alternative catalytic species and efficiently facilitate some elementary steps such as the hydrogen transfer, hydrogen elimination, and C-N coupling. Meanwhile, the C-N coupling step proceeds via the split of aldehydic C-H bond across the Ru(II)-imine bond, which results in an amide bond directly. The hemiaminal is uninvolved in the C-N coupling process. Finally, the formation of linear peptides and cyclic dipeptides are unveiled by the newly proposed mechanism. The metal-substrate cooperation could widely exist in transition metal catalyst systems with a large influence on the reaction activity.
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