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Fe(III)/Pyridine N-oxide LMCT Photocatalysis for Unactivated C(sp3)-H Functionalizations
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DOI：10.1021/acscatal.6c00581.png)
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Abstract
En 中文
Heteroatom-centered radical-mediated hydrogen-atom transfer (HAT) has emerged as a powerful tool for C-H functionalization, yet selective activation of unactivated C(sp(3))-H bonds, especially at the primary sites, remains a significant challenge. Here, we report an Fe(III)/pyridine N-oxide (PNO) catalytic system that harnesses ligand-to-metal charge transfer (LMCT) excitation to access highly electrophilic cationic N-oxy radicals from readily available PNOs, enabling diverse HAT-mediated functionalization of unactivated C(sp(3))-H bonds. This LMCT system enables the catalytic generation of reactive cationic N-oxy radicals, such as the pentachloropyridine N-oxy radical, which are inaccessible by conventional outer-sphere photoredox catalysis. The synthetic application of the Fe(III)/PNO LMCT system was highlighted by using pentachloropyridine N-oxide as a selective HAT agent for primary C(sp(3))-H bonds, affording up to 20:1 regioselectivity in hydrazination of alkanes, aliphatic ketones/esters/nitriles, protected amines/alcohols, and amino acids. Computational and kinetic studies were performed to elucidate the reaction mechanisms, revealing that HAT by cationic N-oxy radicals is highly facile and reversible, effectively leveling the intrinsic energy barrier among various C-H bonds.
Keywords:
pyridine N-oxide
LMCT
C-H functionalization
iron
site-selectivity
cationic N-oxy radical
Journal
IF:
13.1
Papers:
1.6W
Citations:
15.0W