Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 43

considered rate-determining under conditions when there was a zero-order
dependence on substrate. At lower [substrate], the reaction of ( 21 ) with the
hydrocarbon became rate-determining, when kinetic deuterium isotopic
effects for hydroxylation of adamantane and cis-
decalin were measured 162 . It is clear that the dioxo
species, does not participate in these systems using
pyridine oxides as an O-atom donor. Some rate data had suggested that the
HCl/HBr acids may also accelerate deoxygenation of the N-oxide by the Ru-
porphyrin Total turnovers up to 18,800 were reached for
adamantane oxidation and, for the TDCPP system, a high turnover of
was attained 160 .
An example of enantioselective hydroxylation of a benzylic C-H bond
using or complexes (see Fig. 10)
has been reported by Che's group 163 . The stoichiometric oxidation of
substituted ethylbenzenes, 2-ethylnaphthalene, indane and dehydronaphtha-
lene by in containing pyrazole at r.t., led to the
corresponding alcohols (27-48% yield) and ketones (24-34% yield), with ee
values of 9-58% ( S ) for the alcohols. The second-order rate constant
determined for oxidation, for example, of ethylbenzene was
at 25°C with a kinetic isotope effect for of
8.9 at 40°C and 11.2 at 25°C. A dual-parameter Hammett correlation with
data for 4-substituted ethylbenzenes was considered consistent with a rate-
limiting step involving C-H bond cleavage (Fig. 21). Preferential formation
of the S -isomer was explained by preferential collapse of the benzylic radical