Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 1

Chapter 1

Catalytic oxidations using ruthenium porphyrins

Maria B. Ezhova and Brian R. James
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T
1Z1, Canada

Abstract: The major goal of the Chapter is to review developments in
the use of Ru-porphyrin complexes as homogeneous (or matrix-supported)
catalysts for oxygenation and oxidation processes. The subject was given
impetus with the discovery of a remarkable reaction in which a Ru(II)
porphyrin complex reacted with -dioxo-Ru(VI) species.

Such species, which can be formed from a wide range of O-atom donors,
were shown subsequently to be capable of acting as a bis(monooxygenase)
in transferring both the coordinated oxo ligands (as O-atoms) to olefinic
substrates, saturated hydrocarbons, phosphines, and thioethers, and the
processes become catalytic in the presence of excess of the O-atom donor.
Further, the dioxo species can also exhibit oxidase-like activity, and effect
stoichiometric or catalytic oxidative-dehydrogenation of phenols,
alkoxyarenes, alcohols, and amines. Use of chiral porphyrins has led to
catalytic, asymmetric epoxidation and hydroxylations, even though radical
intermediates are invoked, as well as oxygenation of racemic substrates
(phosphines and more interestingly tertiary alkanes) to yield chiral products
by kinetic resolution processes. The reaction mechanisms invoked range
from genuine O-atom transfer (from or species, where the
disproportionation reaction is important),
to free-radical induced processes, particularly when the porphyrin ligands
are extensively halogenated, as Ru complexes generally of such porphyrins
are extremely active in radical-type decomposition of hydroperoxides, often
present as trace impurities in hydrocarbon substrates.

to give a trans