Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 93

2.2 Recent Further Advances in Copper-Dioxygen Complex

Generation

Biomimetic copper-dioxygen chemistry has advanced considerably
since the first structurally-characterized copper-dioxgygen adduct. However,
it has been difficult to simulate the room-temperature stability of hemocyanin
in these model complexes due to the fact that unlike the enzyme active sites,
these models usually do not possess protective environments which can help
stabilize potentially reactive copper-dioxygen species. Recently, two room-
temperature stable copper-dioxygen complexes have been synthesized which
come closer to the goal of mimicking the dioxygen carrier hemocyanin.
Using 1,2-bis[2-(bis(6-methyl-2-pyridyl)methyl)-6-pyridyl]ethane
(Scheme 4), a ligand with two sterically hindered tripyridylmethane units
tethered by an ethylene spacer, Kodera and co-workers 90 were able to
reversibly generate a peroxo complex with a half-life of
25.5 h at 25 °C in dichloromethane. The peroxo compound
(Scheme 4) which has been characterized by x-ray crystal analysis, can be
synthesized either by the reaction of the copper(I) precursor with or by
treating the complex with As the crystal
structure shows, the core of sits in a protective
environment surrounded by the methyl moieties of the pyridine rings and by
the ethylene linker (Scheme 4). This may explain in part the stability of the
peroxo compound

Gorun and co-workers 91 also reported on the synthesis of a room-
temperature stable copper-dioxygen adduct, by replacing
C-H bonds in the vicinity of the core with C-F bonds. The ligand, 3-
trifluoromethyl-5-methyl-1-pyrazolyl borate

is analogous to the