Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 56

was usually selective. Thus, oxidation of rac -valine ester (10 equiv.) yielded
the bis(amino ester) complex with 66% ee ; ee values for esters of alanine,
leucine and phenylalanine were 10, 26, and 0%, respectively 203 .
There are clearly several complications to the simplified scheme
proposed for the oxidation of amines (see Fig. 26),
although the essential feature of a disproportionation of to
and likely remains. The can react with imine as well as amine, and
oxo-imido or bis(imido) species have also been identified within certain
amine systems, and the concentrations of the dehydrogenated amine species
and co-product water, which increase as the stoichiometric or catalytic
reactions proceed, will certainly effect the behavior of the system (see
Section 3.6.).
Reactions of other complexes with excess of primary or
secondary amines have been reported 195,196,205 ; with the porp = TPP, TTP, 4-
Cl-TPP, 3,5-Cl-TPP and 3,4,5-MeO-TPP, and with R = H,
cyclohexyl, n -octyl, and n -dodecyl, and (R = Me, Et), the
complexes are formed, and X-ray structures of
and were solved; however, no
information was given on the amine dehydrogenation products that must
result from consumption of the oxo ligands.
Of interest, Ru(IV)-bis(amido) complexes have been isolated when the
secondary amine was used as reactant, and the stability of these
complexes was strongly dependent on the substituent on the phenyl groups
of TPP: and
were isolated presumably via the stoichiometry of eq. 42, although this was
not established 196 ; the bis(amido) species can be reoxidized back to the dioxo
complex using

-chloroperbenzoic acid 170 . Other porphyrinato ligand
systems generated a mixture of products 196 , in contrast with corresponding

meta

chemistry of the complexes that cleanly gave the
bis(amido) products 206 . The only X-ray structures of Ru(porp) mixed amido
complexes were obtained for Ru(porp)(NHTs)(pz) (porp = TPP 207 , OEP 208 ),
which were isolated during some reactions of with alkene in
the presence of pyrazine (see below). Somewhat analogous to eq. 42,
reaction of (porp =TTP, 3,4,5-MeO-TPP) with the imine
leads to formation of the corresponding methyleneamido

complexes of which the trimethoxy derivative was

structurally characterized.