Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 50

between the alcohol and (formed reversibly from the oxo
species). There is no direct evidence for the existence of
the isolation of this compound has been claimed (from crystal structure data
on an alcohol solvated species) 66 , but other work has suggested that the
structure reported is that of a species 167 . Nevertheless,
crystals of have been isolated during a synthesis of
and analyzed by X-ray crystallography (see Section
3.5) 164 . Isomerization of to species via proton
migration has been invoked within some non-porphyrin systems 176 .
Studies on the catalytic alcohol oxidation process involved investigation
of the above systems under an atmosphere of air or The initial rate
of production of the ketone product is governed by the rate of formation of
the bis(alkoxy) species, while subsequently the catalysis rate is likely
determined by regeneration of the dioxo species via disproportionation of the
species (see Sections 2 and 3.3.); however, this will depend on the
concentration of which increases as the catalysis proceeds, and indeed
water has been considered to accelerate the disproportionation reaction by
increasing the rate of dioxo formation (eq. 35) 65 . Of note, the Ru-

bis(alkoxide) species are stable in dry benzene under an atmosphere of dry
while in air in wet benzene the species are slowly regenerated
over several hours, with eventual formation of 2 mole equivalents of ketone
(eq. 36); such a reaction suggests the likely involvement of the
bis(alkoxy)species as intermediates in the catalysis 65 . No radical

intermediates were detected during the above alcohol oxidations, and
addition of radical inhibitors such as BHT in small amounts did not
significantly effect the rate of ketone production, although there was some
NMR evidence for reaction of BHT with possibly to form

a bis(phenoxy) species 169 .
The O-atom donor, lutidine- N -oxide, has been used with to
catalyze the room temperature oxidation of alcohols to the corresponding
aldehydes or ketones in ~80% 96,145 . Thus, under Ar, allyl alcohols were
oxidized selectively to aldehydes selectively, and
to was not oxidized. Cyclohexanol and adamantanol
gave the corresponding ketones. The related system,
mentioned in the previous section, catalytically oxidizes cyclohexanol to
cyclohexanone 160 .