Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 44

on the pro- S face versus pro- R face during an O-atom rebound step, resulting
from the fit of the substrate in the chiral cavity (see Fig. 10). Chiral
induction via radical intermediates is a remarkable result. Under catalytic
conditions (5 ml benzene, 25°C, alkane : : catalyst = 0.5 mmol :
0.55 mmol : ), effectively oxidizes the
substrates to alcohols in 28 to 72% yields, with ee values of 12-76% ( S ) .
Use of the system 138 (see Fig. 10) for
hydroxylation of the tertiary alkanes ( rac -2-phenylbutane and -2-phenyl-
hexane) under catalytic conditions ( of Ru, oxidant and 1
mmol alkane, 48% aq. HBr, 50 mg of 4A molecular sieves in 1 ml
benzene under Ar at 25°C) results in tertiary alcohols with modest
enantioselectivity and yields, again remarkable considering the possible
radical nature of the process (see above). Hydroxylation of the alkanes gave

PhC(Me)(R)OH (16% ee, 41% yield, 103 TON for R = Bu; 27% ee, 54%
yield, 135 TON for R = Et). The highest ee (38%) was obtained for
hydroxylation of the 2-phenylbutane at 10°C; some kinetic resolution of the
unreacted alkane (up to 8%) was evident 138 . This is the first report of
catalytic enantioselective hydroxylation of tertiary alkanes.

3.5 Oxidative-dehydrogenation of phenols and other

arenes

Preliminary studies had suggested that benzene solutions of
react stoichiometrically with phenol under 1 atm to give
the paramagnetic species ( 23 ), via a detected
species, according to eq. 32, and data were given for
the second-order rate constant Evidence for ( 23 ) included data,