期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 143, 期 49, 页码 20849-20862出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.1c09280
关键词
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资金
- NSF CAREER award [1654144]
- National Institutes of Health [R35 GM133470]
- University of Chicago
- Department of Defense [00003765]
- Sloan Foundation [FG-2019-11497]
- Division of Chemistry (CHE), National Science Foundation (NSF) [NSF/CHE1346572]
- Division of Materials Research (DMR), National Science Foundation (NSF) [NSF/CHE1346572]
- National Science Foundation [NSF/DMR-1531283]
- U.S. DOE [DEAC02-06CH11357]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1654144] Funding Source: National Science Foundation
This study reports the isolation and characterization of a new terminal Co-III-oxo complex capable of hydroxylation of aliphatic C-H bonds. The experimental and DFT analysis reveal that the reaction is endergonic at the initial C-H activation step but driven by an extremely exergonic radical rebound step, similar to cytochrome P450 enzymes. The rapid C-H hydroxylation reactivity displayed in this well-defined system provides insight into biological systems and synthetic oxidants.
The selective hydroxylation of aliphatic C-H bonds remains a challenging but broadly useful transformation. Nature has evolved systems that excel at this reaction, exemplified by cytochrome P450 enzymes, which use an iron-oxo intermediate to activate aliphatic C-H bonds with k(1) > 1400 s(-1) at 4 degrees C. Many synthetic catalysts have been inspired by these enzymes and are similarly proposed to use transition metal-oxo intermediates. However, most examples of well-characterized transition metal-oxo species are not capable of reacting with strong, aliphatic C-H bonds, resulting in a lack of understanding of what factors facilitate this reactivity. Here, we report the isolation and characterization of a new terminal Co-III-oxo complex, PhB((Ad)Im)(3)(CoO)-O-III. Upon oxidation, a transient Co-IV-oxo intermediate is generated that is capable of hydroxylating aliphatic C-H bonds with an extrapolated k(1) for C-H activation >130 s(-1) at 4 degrees C, comparable to values observed in cytochrome P450 enzymes. Experimental thermodynamic values and DFT analysis demonstrate that, although the initial C-H activation step in this reaction is endergonic, the overall reaction is driven by an extremely exergonic radical rebound step, similar to what has been proposed in cytochrome P450 enzymes. The rapid C-H hydroxylation reactivity displayed in this well-defined system provides insight into how hydroxylation is accomplished by biological systems and similarly potent synthetic oxidants.
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