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Dioxygen (and CO) react reversibly with dicopper(I) complexes
producing
(PY = 2-pyridyl)
which are
(or
stable at -80 °C in solution.
77
A recent resonance Raman study confirms that
possess side-on ligation, and the
variation in UV-Vis (i.e., shift in a 400-500 nm CT absorption) and
values (765, 751, for N3, N4 and N5 complexes, respectively) are
ascribed to distortions of the
moiety from planarity, probably due to
ligand constraints.
79
Mononucleating ligands RPY2 (R = Me, Ph, ) can
also be utilized to generate similar complexes, where for example
reacts with
65-67
giving
In
fact, this exists as a mixture of both side-on peroxo and
species, both in solution and in the solid state.
67
Further
discussion of this interconversion or equilibrium is given below. It is notable
that the value for the peroxodicopper(II) solution species,
, is lower than observed for
The kinetics of formation of these dioxygen adducts have
recently been compared;
80
all Nn species show relatively similar tendencies,
but the bridged peroxo adducts form expectedly faster for the intramolecular
process in
ligands, compared to the intermolecular reaction
for
A special case
of these
ligands
and their
-xylyl moiety (in XYL-H; diagram),
leading to a monooxygenase model system, discussed below.
Others have shown that species also
form with tris(1-R-4-R'-imidazolyl)phosphines
69-71
or trisubstituted
triazacyclononane (TACN) ligands. For the latter case, Tolman and co-
workers
72-75
discovered important new chemistry, Scheme 3. Oxygenation of
4a
can give both
chemistry occurs when the linker is a
m
adducts
5b
or
5
(Scheme 3 & Chart 2). For R =
i
Pr in
solvent at low temperatures,
5b
is formed reversibly. When the oxygenation is carried out in
tetrahydrofuran solvent,
5
is obtained.
Its properties include UV-Vis features
at 324 and 448 nm, and
The
(580 using
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