Supported iron(III)porphyrins pentafluorophenyl-derivatives as catalysts in epoxidation reactions by H2O2:: the role of the silica-support and sulfonatophenyl residues in the activation of the peroxidic bond

Ionic Fe(III)porphyrins pentafluorophenyl-derivatives: 5,10,15-tris(pentafluorophenyl)-20-(4-N-methylpyridyl)porphyrin iron(III) ([Fe{M(4-N-MePy)TPFP}](2+)), 5,10,15-tris(4-N-methylpyridyl)-20- pentafluorophenyl)porphyrin iron(HI) ([Fe {T(4-N-MePy)MPFP}](4+)) and 5,10,15-tris(pentafluorophenyl)-20-(3-sulfonatophenyl)porphyrin iron(III) ([Fe{M(3-SO3P) TPFP}]) immobilised on silica get (SiO2) and modified silica with sulfonatophenyl (SiSO3-), propylimidazole (IPG), sulfonatophenyl plus propylimidazole (SiSO3- (IPG)), propyltrimethylammonium (SiN+) and propyltrimethylammonium Plus propylimidazole (SiN+(IPG)) were studied in the epoxidation of (Z)-cyclooctene by H2O2. The better yields of product, cis-epoxycyclooctane, were achieved with the catalytic systems, [Fe{M(4-N-MePy)TPFP}]-SiSO3(IPG), [Fe{M(3-SO3P) TPFP}]-IPG and [Fe{M(3-SO3P)TPFP}]-SiO2, where is more probable to have available sulfonatophenyl groups. That is, where there is no ionic binding Fe(III)porphyrin-support via sulfonatophenyl. A charge effect supplied by the available sulfonatophenyl residues and a more polar microenvironment provided by the silica-support promote the heterolytic cleavage of the O-O bond, which is essential to obtain high yields of products in oxidation reactions. Effects of general acid-base catalysis, as occurs in enzymes, and higher reduction potential provided by electron-withdrawing groups, present on porphyrin ring or axial ligand, as recently reported by Nam and coworkers for homogeneous Fe(III)porphyrins, to promote the heterolysis of the O-O bond are ruled out. (C) 2002 Elsevier Science B.V. All rights reserved.