Tyrosinase Enzyme-Inspired Cu(I)-Porous Organic Polymer for Selective Oxidation of Biomass-Derived 5-HMF

In biobased PET, terephthalic acid (TPA) can be replaced with biobase alternatives like bioderived 5-diformylfuran (DFF). In this work, we have selectively synthesized DFF from the oxidation of 5-hydroxymethylfurfural (HMF) using our tyrosinase enzyme-inspired catalysts vicinal <i><b>V</b></i><b>-Cu-POP</b> and nonvicinal <i><b>NV</b></i><b>-Cu-POP</b>, respectively. Motivated by the oxygenated form of tyrosinase, we introduced binuclear copper(I) moieties into a porous organic polymer to create enzyme-inspired heterogeneous catalysts for the selective oxidation of HMF. <i><b>V</b></i><b>-Cu-POP</b> can effectively activate O₂ for mild and selective oxidation because the two Cu centers are in close proximity, which is impossible in the case of <i><b>NV</b></i><b>-Cu-POP</b>. For the determination of the coordination environment of the catalytically active site, the X-ray absorption near-edge structure (XANES) studies and the copper(I) state for both the enzyme-inspired catalysts <i><b>V</b></i><b>-Cu-POP</b> and <i><b>NV</b></i><b>-Cu-POP</b> are identified through characteristic features in the absorption spectra. The fitting parameters and EXAFS spectra rule out the formation of the Cu-Cu bond. Further, the key intermediate μ-hydroxy species (Cu (II)-O-O-Cu (II)), which forms during the reaction in the case of the enzyme-inspired catalyst, <i><b>V</b></i><b>-Cu-POP</b> is also confirmed by time-resolved <i>in situ</i> ATR-IR spectroscopy and DFT computational study. This intermediate is not formed in the case of nonvicinal <i><b>NV</b></i><b>-Cu-POP</b>, which is the main reason for lower catalytic activity toward HMF oxidation. <i><b>NV</b></i><b>-Cu-POP</b> still retains the peaks of reactants at the same reaction conditions, which is confirmed by time-resolved <i>in situ</i> ATR-IR spectroscopy. Overall, in this study, we have shown how a tyrosinase enzyme-inspired catalyst exhibits greater catalytic activity toward the oxidation reaction due to the formation of its vicinal conformer compared to the nonvicinal conformer.