Structure and Reactivity of Copper Complexes Supported by a Bulky Tripodal N ₄4 Ligand: Copper(I)/Dioxygen Reactivity and Formation of a Hydroperoxide Copper(II) Complex

摘要

> A copper(I) complex, [Cu I (TIPT ₂ aped)(CH ₃ CN)]ClO ₄ ( 1 ), and two copper(II) complexes, [Cu II (TIPT ₂ aped)(Cl)]PF ₆ ( 2 ) and [Cu II (TIPT ₂ aped)(ClO ₄ )]ClO ₄ ( 3 ), were synthesized and characterized. The reaction of 1 with dioxygen in acetone at –90 °C gave an end‐on superoxide copper(II) complex 4 . The superoxide copper(II) complex 4 reacted with 2,2,6,6‐tetramethylpiperidin‐1‐ol (TEMPO‐H) and 2,6‐di‐ tert ‐butyl‐4‐methoxyphenol (DTBMP) to generate a hydroperoxide copper(II) complex 6 . These copper‐oxygen adducts were thoroughly characterized by UV/Vis, resonance Raman, EPR, and NMR spectroscopic techniques. Complex 6 was also synthesized from the copper(II) complex 3 in the presence of hydrogen peroxide and triethylamine. The reaction of 4 with TEMPO‐H showed a relatively large kinetic deuterium isotope effect ( k _H / k _D = 5.8) and a largely negative activation enthalpy (Δ H ? ). Based on the kinetic data, the reaction mechanism for the conversion of 4 to 6 is discussed.