Cu(II) Coordination\nPolymers for the Selective Oxidation\nof Biomass-Derived Veratryl Alcohol in Green Solvents: A Sustainable\nCatalytic Approach

Four\nair-stable one-dimensional copper(II) coordination\npolymers\n(<b>CP1</b>–<b>CP4</b>) with azide linkers were\nsynthesized using tridentate NNS and NNN ligands. Single-crystal X-ray\ndiffraction (XRD) analysis confirmed the molecular structures of <b>CP1</b>, <b>CP3</b>, and <b>CP4</b>. In the presence\nof TEMPO, all four coordination polymers demonstrated effective catalytic\nactivity for the selective aerobic oxidation of veratryl alcohol,\na biomass model compound, under base-free conditions. <b>CP4</b> exhibited the best catalytic efficiency. Oxidations were conducted\nat ambient temperature (40 °C) utilizing air as a sustainable\noxidant. Selective oxidation of veratryl alcohol to veratraldehyde\nwas also conducted in the presence of a catalytic amount of base (5\nmol %), and enhanced reactivity was observed. The green solvents,\nacetone, and water, were used to maximize sustainability. The optimized\nreaction conditions were applied to broaden the substrate scope of\nvarious lignin model alcohols and substituted benzylic alcohols with\nwide electronic variability. <b>CP4</b> exhibited high recyclability,\nconsistently providing quantitative yields even after ten consecutive\nruns. The catalytic protocol demonstrated sustainability and environmental\ncompatibility, as evidenced by a low <i>E</i>-factor (4.29)\nand a high Eco-scale score (90). Based on experimental evidence and\ntheoretical calculations, a plausible catalytic cycle was proposed.\nFinally, the sustainability credentials of the different optimized\nreaction protocols were evaluated using the CHEM21 green metrics toolkit.