摘要
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, -OCH3 or -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 ratelimiting 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.