Quantum effects in CH activation with [Cu₂O₂]²⁺ complexes.

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Biomimetic Catalysis

Background:

• Enzymes activate strong alkane C-H bonds under mild conditions.
• Dioxo-dicopper complexes ([Cu2O2]2+) mimic these enzymatic catalysts.
• Kinetic isotope effects (KIEs) provide crucial mechanistic insights.

Purpose of the Study:

• To investigate the CH bond activation mechanism by [Cu2O2]2+ complexes.
• To compare the one-step oxo-insertion and two-step radical recombination pathways.
• To elucidate factors influencing reaction rates and KIEs.

Main Methods:

• Density functional theory (DFT) calculations.
• Variational transition-state theory (VTST) with multidimensional tunneling.
• Systematic variation of ligand electrophilicity and substrate chain length.

Main Results:

• Oxo-insertion pathway exhibits lower activation barriers and higher rate coefficients.
• Radical recombination pathway shows larger tunneling contributions.
• Both pathways show excellent agreement with experimental KIEs and Hammett slopes, leaving the preferred mechanism open.

Conclusions:

• Computational methods accurately model C-H activation mechanisms.
• Ligand and substrate properties significantly influence reaction kinetics.
• The study highlights the complexity of C-H activation and the need for further investigation into the dominant pathway.