Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 105

square planar geometry. When the compound formed from
the reaction of the Cu(I) complex with at -78 °C, is
warmed to 25 °C and kept under an atmosphere of for 20 h, benzylic
hydroxylation of the phenylethyl group occurs in 46% yield, close to that of
the maximum 50% yield observed in the PY2Phe system (Scheme 9). The
authors suggest that the ligand hydroxylation may occur via the abstraction of
a benzylic hydrogen atom by the core followed by the
rebinding of a hydroxyl group (rebound mechanism) or through a concerted
mechanism.

Using RPY2 ligands similar to our PY2Bz, Reglier and co-
workers 111,112 have reported on model systems that can hydroxylate aliphatic
C-H bonds in a stereospecific manner. While one of these systems, IndPY2,
contains an indane moiety with a benzylic C-H bond, two other systems,
n -propyl and

cyclopentyl moieties, respectively) which are hydroxylated stereospecifically.
Similar to Itoh's PY2Phe system, hydroxylation of the benzylic position in
IndPY2 can either take place via reaction of the copper(I) complex with
for ~50% hydroxylation yield or by reducing the copper(II) complex with
benzoin/triethylamine under Ar and then exposing the unidentified reduced
species to for ~100% hydroxylation. The stereoselective hydroxylation of
the cyclopentyl and the n -propyl moieties in n PrPY2 and c PtPY2 are more
complicated, however. For instance, when the Cu(I) complexes
and react with and the resulting copper(II)
complexes were demetallated, the starting ligands n PrPY2 and c PtPY2 were
recovered with no products resulting from oxygenation of the ligand. Only
treatment of Cu(II) compounds

PrPY2 and c PtPY2, have non-activated C-H bonds (with n

and