abstract
New compounds based on the association of polyoxometalates and cationic porphyrins or metalloporphyrins were prepared with the aim of obtaining new bi-functional catalysts. A combined study on the syntheses, characterization and catalytic activity of these compounds was performed. The new compounds have the general formula (porphyrin)xHy[XM12O40](.)z solv, x=0.75 or 1, X=P or Si and M=W or Mo. The porphyrins used were 5. 10, 1 5,20-tetrakis(4-pyridyl)porphyrin, 5,10,15,20-tetrakis(1 -methyl-4-pyridinio)porphyrin, 5,10,15-tris(2,6dichorophenyl)-20-(4-pyridyl)porphyrin, and 5,10,15 -tris (2,6-di chlorophenyl)-20-(1 -methyl -4-pyridinio)porphyrin, either as free bases or complexed with Mn-III (one case with Zn-II). A few compounds with metal substituted Keggin anions ([PW11Y(H2O)O-39](n-,) Y=Mn, Fe, Ni, Zn) were also prepared. All compounds were characterized by spectroscopic and analytical techniques. The oxidation of cis-cyclooetene, geraniol and (+)-3-carene by hydrogen peroxide catalysedby the polyoxometalate/Mn(III)porphyrin associations and co-catalysed by ammonium acetate was examined. Some of the associations significantly increased the percentage of conversion of the substrates relatively to the respective metalloporphyrin alone. However, the regio-, chemo- and stereoselectivity of the oxidation reactions catalysed by metalloporphyrins were alobally preserved: cis-cyclooctene was selectively epoxidised to epoxycyclooctane; geraniol gave 6,7-epoxygeraniol as the major product and (+)-3-carene was preferably oxidised to the alpha-3,4-epoxycarane. In the conditions studied, the polyoxoanions seem to contribute mainly to stabilise the metalloporphyrin against deactivation during catalytic cycles. (c) 2004 Elsevier B.V.. All rights reserved.
keywords
BY-LAYER METHOD; HYDROGEN-PEROXIDE; OXOMANGANESE(V) PORPHYRIN; SELECTIVE OXIDATION; DIOXYGEN REDUCTION; CRYSTAL-STRUCTURE; SILICA-SUPPORT; HYBRID FILM; COMPLEXES; METAL
subject category
Chemistry
authors
Santo, ICMS; Rebelo, SLH; Balula, MSS; Martins, RRL; Pereira, MMMS; Simoes, MMQ; Neves, MGPMS; Cavaleiro, JAS; Cavaleiro, AMV
our authors
Ana Maria Vieira Silva Viana Cavaleiro
Full professor