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

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 ; M_n =510 Da) and polystyrene (PS; M_n ≈10 000 Da) are converted into oxygenated monomers, dimers, and oligomers.

Keywords: C−C bond activation; electrocatalysis; plastic upcycling; radical chemistry; redox mediators.