Electrochemical Activation of C-C Bonds via Mediated Hydrogen Atom Transfer Reactions

Bing Yan, Changxia Shi, Gregg T Beckham, Eugene Chen, Yuriy Roman

Abstract: Activating inert sp3–sp3 carbon-carbon (C−C) bonds remains a major bottleneck in the chemical upcycling of recalcitrant polyolefin waste. In this study, redox mediators are used to activate the inert C−C bonds. Specifically, N-hydroxyphthalimide (NHPI) is used as the redox mediator, which is oxidized to phthalimide-N-oxyl (PINO) radical to initiate hydrogen atom transfer (HAT) reactions with benzylic C−H bonds. The resulting carbon radical is readily captured by molecular oxygen to form a peroxide that decomposes into oxygenated C−C bond-scission fragments. This indirect approach reduces the oxidation potential by >1.2 V compared to the direct oxidation of the substrate. Studies with model compounds reveal that the selectivity of C−C bond cleavage increases with decreasing C−C bond dissociation energy. With NHPI-mediated oxidation, oligomeric styrene (OS510; Mn=510 Da) and polystyrene (PS; Mn≈10 000 Da) are converted into oxygenated monomers, dimers, and oligomers.