Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 12

dimetallic centre contains a single bridging-OH and 3 terminal histidines on
each Cu 48 .
Oxidase mechanisms are not well understood in detail, but those
presented here generally function via an electron transfer chain from the
substrate to the various Cu centres through to which may or may not be
coordinated to the metal. Studies on models for ascorbate oxidase have
invoked reactivity via a ternary species, as well as
oxidation by “free” essentially, the oxidizes the reduced metal and the
ascorbate via its anionic, semiquinone radical 1c .

2. REACTIONS OF RUTHENIUM PORPHYRIN

COMPLEXES WITH AND OTHER

OXIDANTS

Before detailing the catalytic oxygenations/oxidations that have been
effected by Ru-porphyrin species, it is instructive to consider the reactions of
these complexes with various oxidants in the absence of the substrates to be
oxidized; clearly any such Ru products must be considered as catalysts or, at
least, catalyst precursors.
Studies on Ru-porphyrins in the laboratories here were initiated in the
mid-1970s, with the aim of mimicking biological oxygenation/oxidation
processes, especially those effected by their 1st-row, often naturally

occurring Fe-based analogues 8,15,49-53 .
In polar, aprotic solvents such as DMF, DMA ( N,N'-
dimethylacetamide) or pyrrole, complexes of the type (L =
solvent; porp = an anion of OEP or TPP) bind reversibly at ambient
conditions to yield complexes 50 , but such species are readily
converted in the presence of trace water to dinuclear Ru(IV) species of the
type In toluene, under
undergoes a slow irreversible oxidation to a species 50 , which is the
usual oxidation product of Ru(II) “non hindered” porphyrin complexes using
or an O-atom donor as oxidant 8,53 . The reaction of
TPP complexes with in DMF at ~0°C is 1st-order in both
metalloporphyrin and and the findings, particularly a Hammett plot, were
rationalized in terms of formation of a Ru(IV), peroxo species 54 .
Of note, myoglobin, which has been reconstituted with Ru(II)-
mesoporphyrin IX, is 6-coordinate low spin and undergoes, like