Chemistry Reference
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the 2-equiv. reducing power of phosphines in the presence of (eqs. 21,
22); the overall oxidation (reactions 12, 20-22) is catalytic in Ru,
and That the oxidation proceeds faster than substitution of (e.g. by
CO) supports the outer-sphere process, while EPR data on the system
(eq. 12) showed formation of a mixture of the hydrated superoxide (g = 2.00,
2.10) and a low spin Ru(III) species (g = 1.98, 2.30)
57
.
In principle, any substrate that is oxidizable by can be oxidized
stoichiometrically by a metal complex that allows for outer-sphere
generation of and a catalytic process results if an appropriate
reducing agent, preferably the substrate itself, is present to generate the
lower-valent metal complex - in this case a Ru(II)-porphyrin. A related
system (see Section 3.2) using with leads to catalytic
oxidation of thioethers to sulfoxides, where the reaction corresponding to eq.
12 is photo-assisted
78
. The system gave non-reproducible kinetic data
57
,
and it is possible that a photochemical pathway contributes to the reaction.
The
species (cf. eq. 18) can be reduced by excess
to
generate
and thus can be used as a catalyst precursor for
catalytic
of at least under the outer-sphere conditions.
can oxidize 2 moles of
(or
stoichiometrically, and a 3rd mole of
can subsequently coordinate,
according to eq. 23
in the presence of
catalytic oxidation of
the phosphine can be readily effected at ambient conditions
61,63,64,80
. Initially,
the detectable (
13
) was written without the axial ligand
61,64
, but
kinetic data for the stoichiometric reaction point to the oxide being
coordinated
63
. and were determined
for the first O-atom transfer to (step a) by stopped-flow kinetics, as
well as corresponding data for other phosphines; X = OMe,
Me, F, Cl, values increase with increasing electron-withdrawing
power of the
p-
substituent position, consistent with electrophilic attack of a
Ru=O moiety on the lone-pair of the phosphine. The negative
values
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