Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 35

porphyrin systems 14,153 . The Ru(porp)(CO)(EtOH) complexes (porp =
TCPP 150 and TDCPP 151 ) were successfully encapsulated into the channels of
mesoporous material MCM-41 154 , modified by treatment

with 3-

(aminopropyl)triethoxysilane M-41( ); the ligand exchange reaction utilized

is shown in Figure 13 150,151 . Ru(TCPP)(CO)/M-41( m ) containing 8.3 wt.%
Ru showed good catalytic activity for alkene epoxidation using

m

as

oxidant in under at r.t. 150 . A higher catalytic activity at lower Ru
content was attributed to efficient site isolation, coupled with diffusion
reaction pathways, conditions that precluded formation of stable,
catalytically inactive species. Total turnovers of 9000 were achieved
with 0.1 wt.% of Ru for oxidation of norbornene to give 53% exo -epoxide
(yield based on consumption of TBHP), in comparison with only 216
turnovers using the 8.3 wt.% Ru catalyst; 230 turnovers were achieved with
Ru(TCPP)(CO)(EtOH) as a homogeneous catalyst in In general, the
turnovers were 20-40 times higher with the supported catalyst, which was
stable under the oxidation conditions, with activities not changing after 2
days of reaction. Although the turnover numbers are reasonable, the
chemoselectivity for the supported catalyst is poor. Thus, styrene gave only
11.0% of styrene oxide with benzaldehyde being the co-product (26.5%);
cyclohexene gave 2.2% epoxide, cyclohex-2-en-l-ol (7%) and cyclohex-2-
en-l-one (12.3%); cis- and trans -stilbene gave trans- stilbene oxide as the
major product for both isomers (8.6 and 9.35%, respectively), with cis -oxide
(1.4 and 0.18%) and benzaldehyde (0.94 and 0.27%) being the other co-
products 150 .
Ru(TDCPP)(CO)/M-41( m ) also catalyzed selective alkene epoxidation
using as an O-donor in the presence of HC1 151 . Aromatic and
aliphatic alkenes gave epoxides in good yields (up to 98%, based on the
amount of substrate consumed) with complete selectivities, styrene, cis-
stilbene, norbornene and octene-
1 giving only cis -products; trans -stilbene was not oxidized. Of note, the
formation of cis -oxides from cis -alkenes here is quite different from the
preferred formation of trans -oxides from cis- or trans -stilbene catalyzed by