Association of Keggin-type anions with cationic meso-substituted porphyrins: synthesis, characterization and oxidative catalytic studies

• Published in: Journal of molecular catalysis. A, Chemical Vol. 231; no. 1; pp. 35 - 45
• Main Authors: Santos, Isabel C.M.S., Rebelo, Susana L.H., Balula, M. Salete S., Martins, Rosália R.L., Pereira, M. Manuela M.S., Simões, Mário M.Q., Neves, M. Graça P.M.S., Cavaleiro, José A.S., Cavaleiro, Ana M.V.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 20.04.2005; Elsevier
• Subjects: Catalysis; Cationic porphyrins; Chemistry; Cyclooctene; Exact sciences and technology; General and physical chemistry; Hydrogen peroxide; Manganese(III); Metalloporphyrins; Monoterpenes; Oxidation; Polyoxometalates; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Polyoxometalates; Cyclooctene; Hydrogen peroxide; Manganese(III); Oxidation; Monoterpenes; Cationic porphyrins; Metalloporphyrins; Heteropolysalt; Catalytic reaction; Nitrogen heterocycle; Manganese Complexes; Organic ligand; Transition metal Complexes; Hydrogen Peroxides; Characterization; Association; Synthesis; Porphyrin; Monoterpene; Metalloporphyrin; Geraniol
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2004.12.021

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) x H y [XM 12O 40]· z solv, x = 0.75 or 1, X = P or Si and M = W or Mo. The porphyrins used were 5,10,15,20-tetrakis(4-pyridyl)porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin, 5,10,15-tris(2,6-dichorophenyl)-20-(4-pyridyl)porphyrin, and 5,10,15-tris(2,6-dichlorophenyl)-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 ([PW 11Y(H 2O)O 39] n− , Y = Mn, Fe, Ni, Zn) were also prepared. All compounds were characterized by spectroscopic and analytical techniques. The oxidation of cis-cyclooctene, geraniol and (+)-3-carene by hydrogen peroxide catalysed by the polyoxometalate/Mn IIIporphyrin 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 globally preserved: c is-cyclooctene was selectively epoxidised to epoxycyclooctane; geraniol gave 6,7-epoxygeraniol as the major product and (+)-3-carene was preferably oxidised to the α-3,4-epoxycarane. In the conditions studied, the polyoxoanions seem to contribute mainly to stabilise the metalloporphyrin against deactivation during catalytic cycles. The preparation, characterization and catalytic application of new organic/inorganic hybrids with polyoxometalates and cationic porphyrins or metalloporphyrins are described. At 60 °C, some of the new compounds catalysed the epoxidation with H 2O 2 of cis-cyclooctene, geraniol and (+)-3-carene with higher conversions than the corresponding metalloporphyrins alone. The polyoxometalates contributed, in general, to the stabilization of the metalloporphyrins in catalytic conditions. ▪