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Title: Photocatalytic C–H activation and the subtle role of chlorine radical complexation in reactivity

The functionalization of methane, ethane, and other alkanes derived from fossil fuels is a central goal in the chemical enterprise. Recently, a photocatalytic system comprising [CeIVCl5(OR)]2−[CeIV, cerium(IV); OR, –OCH3or –OCCl2CH3] was disclosed. The system was reportedly capable of alkane activation by alkoxy radicals (RO•) formed by CeIV–OR bond photolysis. In this work, we present evidence that the reported carbon-hydrogen (C–H) activation of alkanes is instead mediated by the photocatalyst [NEt4]2[CeCl6] (NEt4+, tetraethylammonium), and RO• are not intermediates. Spectroscopic analyses and kinetics were investigated for C–H activation to identify chlorine radical (Cl•) generation as the rate-limiting step. Density functional theory calculations support the formation of [Cl•][alcohol] adducts when alcohols are present, which can manifest a masked RO• character. This result serves as an important cautionary note for interpretation of radical trapping experiments.

 
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Award ID(s):
1902509
NSF-PAR ID:
10230250
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  
Publisher / Repository:
American Association for the Advancement of Science (AAAS)
Date Published:
Journal Name:
Science
Volume:
372
Issue:
6544
ISSN:
0036-8075
Page Range / eLocation ID:
p. 847-852
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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