Bioinspired copper(I) complexes that exhibit monooxygenase and catechol dioxygenase activity

Area of Science:

• Coordination Chemistry
• Catalysis
• Organic Synthesis

Background:

• Tripodal N-donor ligands are crucial in coordination chemistry for stabilizing metal centers.
• Copper complexes are increasingly explored as catalysts for oxidation reactions.
• Phenol oxidation is a key transformation in organic synthesis and environmental remediation.

Purpose of the Study:

• To synthesize and characterize a new tripodal ligand (L2) with pyridyl/imidazolyl donors.
• To investigate the copper(I) complexation of the new ligand L2.
• To evaluate the catalytic activity of copper complexes with ligands L1, L2, and L3 in phenol oxidation.

Main Methods:

• Synthesis of a novel tripodal ligand L2 featuring pyridyl and imidazolyl units.
• Preparation and characterization of copper(I) complexes [(L2)Cu]OTf, [(L1)Cu]OTf, and [(L3)Cu]OTf.
• Catalytic oxidation of sodium 2,4-di-tert-butylphenolate (NaDTBP) using O2 with the copper complexes.

Main Results:

• The synthesized ligand L2 successfully formed a copper(I) complex.
• Copper complexes 1(OTf), 2(OTf), and 3(OTf) effectively mediated the oxidation of NaDTBP to catecholate and quinone.
• Catalytic oxidation was achieved when protons were present; stoichiometric oxidations revealed sequential monooxygenase and catechol dioxygenase activity.

Conclusions:

• The new tripodal ligand L2 forms active copper catalysts for phenol oxidation.
• The investigated copper complexes exhibit dual catalytic activity: monooxygenase and catechol dioxygenase.
• Ligand structure variations (presence or absence of a phenylene spacer) did not lead to significant differences in catalytic performance.