Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 57

More generally, Ru(porp)-bis(imido) and -oxo(imido) species, products
of oxidative-dehydrogenation of bis(amine) complexes, are of considerable
interest as metalloporphyrin imido complexes have been postulated in the
nitrite reductase cycle 209 , and can be used as models for metabolism of
natural amines 201 . Further, the imido ligand is isoelectronic with the oxo
ligand, and transition metal imido complexes, including metalloporphyrin
derivatives, are the key reagents or intermediates in reactions such a
oxyamination 210 ,

s

amination 211-215 aziridination 201b,207,208,213,214,216

and of

olefins. Outside of Ru species, metalloporphyrin complexes with imido
ligands are well demonstrated and include those of Ti 217 , Cr 218 ,Mn 216 , Fe 201 ,
and Os 68,200,206,219 . Well characterized complexes are the p-
tolylsulfonyl derivatives (porp = TPP, TTP, 4-C1-TPP, 4-
MeO-TPP, OEP, TMP, prepared by Che's group via reaction of
Ru(porp)(CO)(MeOH) with PhINTs 207,208,213 ; these tosylimido complexes are
stable in the solid state for a few days at -15°C, but in at r. t. they
decompose after a few hours, and are not very reactive toward water. They
readily react with to yield the bis(phosphine) complexes 208 .
Formation of species with other substituents on the N
atom and has been proposed in oxidation of
and oxidation of primary amine by (see
above). has been isolated 200 , but it quickly hydrolyzes in air
to give oxo(imido) and species 68,196,200 . In comparison,
complexes are more stable and have been characterized by
X-ray analysis 200 .
A mono(imido) complex where X = Me,
H, Cl, I) (analogous to has been prepared via reaction
with This mono(imido) species can react with
tertiary phosphines to yield phosphinimines and complexes
(Fig. 28); the imido transfer reaction for the system obeys the rate
law = showing standard saturation
kinetics behavior 199 . The electron-deficient arylimide systems were more
reactive than the electron-rich analogues [ k = 39.5 (X = I), 16.0 (X = H),
13.6 (X = Cl), 25.0°C, in toluene]; and the more
reactive the imido complex, the lower its affinity for the phosphine [ K = 1.15
(X = I), 13.6 (X = H), 2.39 (X = Cl), . The proposed
mechanism involves reversible binding of phosphine to and subsequent
rate-limiting irreversible intramolecular imido-group transfer (Figure 28).
Unfortunately, no spectroscopic evidence was given for species ( 29 )(or

( 30 )) under conditions where they should be present.