Light-Driven Depolymerization of Native Lignin Enabled by Proton Coupled Electron Transfer

Here, we report a catalytic, light-driven method for the redox-neutral depolymerization of native lignin biomass at ambient temperature. This transformation proceeds via a proton-coupled electron-transfer (PCET) activation of an alcohol O-H bond to generate a key alkoxy radical intermediate, which then facilitates the beta-scission of a vicinal C-C bond. Notably, this single-step depolymerization is driven solely by visible-light irradiation, requires no stoichiometric chemical reagents, and produces no stoichiometric waste. This method exhibits good efficiency and excellent selectivity for the activation and fragmentation of the beta-O-4 linkage in the polymer backbone, even in the presence of numerous other PCET-active functional groups. The feasibility of this protocol in enabling the cleavage of the beta-1 linkage in model lignin dimers was also demonstrated. These results provide further evidence that visible-light photocatalysis can serve as a viable method for the direct conversion of lignin biomass into valuable arene feedstocks.