Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 46

phenol to give ( 24 ). The disproportionation of to and
(see Sections 2 and 3.3) is thought to be a competing pathway for the
reaction with water, and this would give rise to the observed
which was also formed during the anaerobic reaction of
with excess phenol. Under anaerobic conditions, the kinetic
dependence on phenol for loss of the reactant becomes > 1 because
of the faster reaction of the p -hydroquinone than phenol. The selective attack
of at the para-position of the phenol is presumably imposed by the
steric restraints of the TMP ligand. The mechanism of the net O-atom
insertion into C-H bond could involve either sequential electron and H-atom
transfer processes as suggested for the reaction between phenol and trans-
or something akin to the oxygen-rebound
mechanism 76,101 with initial H-atom abstraction from the phenol at a Ru=O
site. Effective catalytic hydroxylation/oxidation of phenol to give p-
hydroquinone and or p -quinone has yet to realized using these Ru porphyrin

systems.
N,N -Dimethylaniline is marginally catalytically oxidized by 3.3 x 10 -3
mM benzene solutions of under aerobic conditions at 50°C
perhaps to the p -hydroxy-derivative; the turnover of 2.1 after 30 h, was
limited by decomposition of the catalyst to Ru(TMP)CO via a
decarbonylation process, presumably of the phenolic product 65 . The
preliminary findings could be consistent with initial attack of an electrophilic
oxo moiety at the para-position of the aniline, as suggested for the phenol
oxidation (see above), or attack at the moiety (see Section 3.7). Of
note, methoxybenzene, toluene, chlorobenzene, bromobenzene and
nitrobenzene were not oxidized by
The Ru(porp)CO/HX/2,6-Cl 2 pyNO systems (porp = TMP, TPP; X =
Cl, Br; see Sections 3.3 and 3.4) can, however, convert alkoxyarenes
eventually to the p -benzoquinone derivatives selectively, as exemplified in
Fig. 23 l66 . The yields of 11-97% varied with the structure of the substrates,
but the most electron-rich C-atom was preferentially attacked by an