Benzene Hydroxylation by Bioinspired Copper(II) Complexes: Coordination Geometry versus Reactivity.

Area of Science:

• Coordination Chemistry
• Catalysis
• Bioinorganic Chemistry

Background:

• Investigated bioinspired copper(II) complexes with N4-tripodal and diazepane-based ligands.
• Explored their catalytic activity in aromatic C-H bond functionalization.

Purpose of the Study:

• To synthesize and characterize novel copper(II) complexes.
• To evaluate their catalytic efficiency in benzene hydroxylation.
• To elucidate the role of coordination geometry in catalytic activity.

Main Methods:

• Synthesis and characterization of copper(II) complexes.
• Spectroscopic studies (UV-Vis, EPR) and electrochemical analysis.
• Catalytic testing for benzene hydroxylation using H2O2.
• Mechanistic studies including electrospray ionization mass spectrometry, kinetic isotope effect, and 18O-labeling.
• Density functional theory (DFT) calculations.

Main Results:

• Trigonal-bipyramidal (TBP) copper(II) complexes showed higher catalytic activity (37% phenol, 98% selectivity) than square-pyramidal (SP) complexes (29% phenol).
• Evidence for a Cu(II)-OOH intermediate was established through various spectroscopic and kinetic methods.
• H2O2 was confirmed as the oxygen source, with 92% 18O incorporation into phenol.
• DFT calculations supported the proposed reaction mechanism and intermediate structures.

Conclusions:

• Coordination geometry of copper(II) complexes is a critical factor in determining catalytic efficiency for C-H hydroxylation.
• The TBP geometry facilitates superior catalytic performance compared to SP geometry.
• The study provides insights into the mechanism of copper-catalyzed aromatic hydroxylation.