Hierarchical porous metal-organic polyhedra for efficient oxidative cleavage of β-O-4 bonds in lignin model compound

Catalytic cleavage of β-O-4 linkages is an essential but challenging step in the depolymerisation of lignin. Here, we report the templated electrosynthesis of a hydrophobic metal-organic polyhedral catalyst (Cu-MOP-e), which exhibits excellent hydrothermal stability and exceptional activity for this reaction. The oxidative cleavage of 2-phenoxyacetophenone, 1, a lignin model compound, over Cu-MOP-e at 90 oC for 1 h affords full conversion with yields of the monomer products phenol and benzoic acid of 99%. The reusability of Cu-MOP-e has been confirmed by carrying out ten cycles of reaction. The mechanism of catalyst-substrate binding has been investigated by high resolution synchrotron X-ray powder diffraction, in situ X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy and density functional theory calculations. The combination of optimal porosity and active Cu(II) sites provides confined binding of 2-phenoxyacetophenone, thus promoting the cleavage of β-O-4 linkage under relatively mild conditions.