Cationic manganese(III) porphyrins bound to a novel bis-functionalised silica as catalysts for hydrocarbons oxygenation by iodosylbenzene and hydrogen peroxide

Abstract

The cationic manganese porphyrins: manganese(III) 5,10,15-tris(2,6-dichlorophenyl)-20-(4- N-methylpyridyl)porphyrin ([Mn{M(4- N-MePy)TDCPP}] 2+), 5,10,15,20-tetra(2,3,5,6-tetrafluoro-4-trimethylammoniumphenyl)porphyrin ([Mn(TF4TMAPP)] 5+) and 5,10,15,20-tetra(4- N-methylpyridyl)porphyrin ([Mn{T(4- N-MePy)P}] 5+) supported on silica modified with propylimidazole (IPG), sulfonatophenyl (SiSO 3 −) and both propylimidazole and sulfonatophenyl (SiSO 3 −(IPG)) have been studied as catalysts in the epoxidation of ( Z)-cyclooctene and oxidation of cyclohexane. High yields of products were obtained using PhIO as oxidant without leaching, except for the IPG, of the catalyst from the surface of the support. The catalysts also have been used with H 2O 2 in the epoxidation of ( Z)-cyclooctene with and without a co-catalyst (imidazole or ammonium acetate). The best catalyst [Mn{T(F4TMAPP)}]-SiSO 3(IPG) achieved almost 200 turnovers of the product cis-epoxycyclooctane using ammonium acetate as co-catalyst. The analogous homogeneous systems have been studied for comparison, but they did not reach the same efficiency . With these studies the two-fold role of imidazole in oxygenations of hydrocarbons by H 2O 2 and Mn(III) porphyrins was confirmed. The characterisation of supported metalloporphyrins by UV–VIS spectroscopy is reported too.