resumo
The chiral Mn(III) salen complex (C1) was immobilised onto a natural clay (BEN) and a porous clay heterostructure (PCH) functionalised with 3-aminopropyltriethoxysilane (APTES). FTIR, XPS and Mn chemical analysis confirm the C1 anchorage in both materials, but with higher efficiency in BEN_APTES clay. The catalytic activity of C1@BEN_APTES and C1@PCH_APTES, was assessed in the epoxidation of styrene (sty) and ae-methylstyrene (ae-Mesty) using NaOCl and m-chloroperoxybenzoic acid (m-CPBA)/N-methylmorpholine-N-oxide (NMO). Both materials behave as moderate catalysts, show high epoxide selectivity but low enantiomeric excesses. In the case of sty epoxidation with m-CBPA/NMO the C1@PCH_APTES catalyst showed the highest catalytic activity, whereas in ae-Mesty epoxidation, the C1@PCH_APTES catalyst, although leading to lower substrate conversion than the BEN analogue, presented the lowest complex leaching. In all cases, the oxidant NaOCl had some destructive effect in the hybrid catalysts, highlighting the importance of a careful choice of catalyst and oxidant system.
palavras-chave
ALUMINUM PILLARED CLAYS; ASYMMETRIC EPOXIDATION; ENANTIOSELECTIVE EPOXIDATION; MESOPOROUS MATERIALS; MN(SALEN) COMPLEXES; NONFUNCTIONALIZED ALKENES; PROBE MOLECULES; MODIFIED MCM-41; SILICA; ADSORPTION
categoria
Chemistry
autores
Kuzniarska-Biernacka, I; Silva, AR; Carvalho, AP; Pires, J; Freire, C
nossos autores
Ana Rosa Silva
Investigador PrincipalGrupos
agradecimentos
This work was funded by Fundacao para a Ciencia e a Tecnologia (FCT) and FEDER, through project ref. PPCDT/CTM/56192/2004. IKB thanks FCT for a Post-Doctoral fellowship.