Bond cleavage reactions including C−C and/or C−O bonds in the chemical industry and organic chemistry can be a valuable transformation. Especially, performing this chemical transformation under mild conditions (e.g., room temperature, solar light) is beneficial to enhancing the selectivity of the targeted product or preventing the production of unwanted products. The work here reports a facile one-pot C−C/C−O σ-bonds cleavage reaction using the photocatalyst nanoparticles that affords the visible-light-induced cleavage products in excellent yields under mild conditions. We synthesized polypyridyl metal complexes and organic sensitizers as photocatalysts (PCs). Then, the PC was immobilized onto TiO2 substrates or nanoparticles. This system allowed to perform photocatalytic cleavage reactions with lignin model compounds under the solar light illumination. Photophysical studies of PC and TiO2 reveal that the intermolecular energy/electron transfer from the photoexcited PC to TiO2 occurs in acetonitrile solution. Under ambient temperature and aerobic conditions, the photocatalytic reaction with PC/TiO2 NPs afforded the Cα−Cβ/Cβ-O bonds cleavage products in excellent yields. This study successfully performed a C-C/C-O bond cleavage reaction with the one-step process using a heterogeneous photocatalysis system at room temperature and under the solar light illumination without the need of additional mediators or oxidizing/reducing agents. This system can be extended and served as a feasible method for lignin depolymerization under mild conditions.

Photocatalytic selective C-C/C-O bond cleavage of lignin at room temperature

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