Impact of nature and length of linker on the catecholase activity of a covalently immobilized copper(II) complex in continuous flow catalysis

• A copper(II) complex covalently grafted on graphite felt support.
• Influence of the chain nature and length on the catalytic activity.
• Increasing catecholase activity with chain length of linkers.
• Higher catecholase activity with linkers containing polyoxoethylene units.

The catecholase activity of four immobilized mononuclear copper(II) catalysts with chains of different nature and length used as linkers is studied in continuous flow catalysis. The graphite felt support was first derivatized by cathodic reduction of 4-carboxymethyl-benzenediazonium salts. Complexes with different chains were then covalently immobilized on the functionalized porous support by esterification reaction. The successful achievement of the immobilization process is attested by the presence of the CuII/I reversible system in cyclic voltammetry. Volume concentrations around 10−8 mol cm−3 of immobilized catalysts are estimated by integration of the redox peak. Comparison of the catecholase activity of the immobilized complexes allows to conclude on the effect of the chain nature and length. First, high chain length positively influences the catalytic activity. Second, the presence of oxygen atoms in the linker significantly enhances the catecholase activity of the catalyst. A possible explanation is the chain hydrophilicity, making easier the access of the catalytic center by H2O molecules.

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