Fábio S. Vinhado

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 2 O 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 2 O 2 and Mn(III) porphyrins was confirmed. The characterisation of supported metalloporphyrins by UV–VIS spectroscopy is reported too.

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

Abstract 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(III) ([Fe{T(4- N -MePy)MPFP}] 4+ ) and 5,10,15-tris(pentafluorophenyl)-20-(3-sulfonatophenyl)porphyrin iron(III) ([Fe{M(3-SO 3 P)TPFP}]) immobilised on silica gel (SiO 2 ) and modified silica with sulfonatophenyl (SiSO 3 − ), propylimidazole (IPG), sulfonatophenyl plus propylimidazole (SiSO 3 − (IPG)), propyltrimethylammonium (SiN + ) and propyltrimethylammonium plus propylimidazole (SiN + (IPG)) were studied in the epoxidation of ( Z )-cyclooctene by H 2 O 2 . The better yields of product, cis -epoxycyclooctane, were achieved with the catalytic systems, [Fe{M(4- N -MePy)TPFP}]-SiSO 3 (IPG), [Fe{M(3-SO 3 P)TPFP}]-IPG and [Fe{M(3-SO 3 P)TPFP}]-SiO 2 , 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.

Characterization and catalytic activity of iron(III) mono(4-n-methyl pyridyl)-tris(halophenyl) porphyrins in homogeneous and heterogeneous systems

Abstract The synthesis, characterization and catalytic activity of the cationic iron porphyrins Fe[M(4-N-MePy)TDCPP]Cl2 and Fe[M(4-N-MePy)TFPP]Cl2 in the epoxidation of (Z)-cyclooctene by PhIO in homogeneous solution and supported on silica gel (SG), imidazole propyl gel (IPG) or SG modified with 2-(4-sulfonatophenyl)ethyl groups (SiSO3) have been accomplished. When supported on IPG, both cationic FeP bind to the support via Fe–imidazole coordination. Fe[M(4-N-MePy)TDCPP]IPG contains a mixture of low-spin bis-coordinated FeIIIP and high-spin mono-coordinated FeIIIP species, whereas Fe[M(4-N-MePy)TFPP]IPG only contains high-spin mono-coordinated FeIIIP. These FePIPG catalysts also contain FeIIP species, whose presence was confirmed by EPR spectroscopy using NO as a paramagnetic probe. Both cationic FePs coordinate to SG through Fe–O ligation and they are present as high-spin FeIIIP species. The cationic FePs supported on SiSO3− are also high-spin FeIIIP species and they bind to the support via electrostatic interaction between the 4-N-methylpyridyl groups and the SO3− groups present on the matrix. In homogeneous solution, both Fe[M(4-N-MePy)TDCPP]Cl2 and Fe[M(4-N-MePy)TFPP]Cl2 have similar catalytic activity to Fe(TDCPP)Cl and Fe(TFPP)Cl, leading to cis-epoxycyclooctane yields of 92%. When supported on inorganic matrices, both FePs lead to epoxide yields comparable to their homogeneous analogues and their anchoring enables catalyst recovery and re-use. Recycling of Fe[M(4-N-MePy)TDCPP]SiSO3− shows that this FeP maintains its activity in a second reaction.

A novel chlorin derivative of Meso-tris(pentafluorophenyl)-4-pyridylporphyrin: synthesis, photophysics and photochemical properties

Photodynamic therapy (PDT) is based on the accumulation of a photosensitizer, such as a porphyrin or a chlorin, in a malignant tissue after its administration. Chlorins exhibit photophysical properties similar to those of the porphyrin macrocycles, but with intensified and red-shifted Q bands, making chlorin-containing systems even better candidates for PDT. In this contribution, we report the synthesis of 5,10,15-tris(pentafluorophenyl)-20-(4-pyridyl)porphyrin, (2) and its transformation to the novel chlorin derivatives 4, (5,10,20-tris(pentafluorophenyl)-15-(4-pyridyl)-tetrahydro-1H- N-methyl-pyrrolo [3,4-b]porphyrin and 5, (5,10,15-tris(pentafluorophenyl)-20-(4-pyridyl)-tetrahydro-1H- N-methyl-pyrrolo[3,4-b]porphyrin) by 1,3-dipolar cycloaddition with an azomethine ylide. The new products have been characterized by UV-Vis, 1H NMR and FAB-MS. The photophysics, photochemical and photobleaching properties of chlorin 4 have been evaluated. Its quantum yield of photobleaching (fPb, mol Einstein-1) was 0.047±0.014. In order to demonstrate the production of 1O2 when 4 is used as a photosensitizer, uric acid tests have been carried out. The results indicate that chlorin 4 can be considered a promising photosensitizer in PDT.

Immobilization of β halogenated ironporphyrin in the silica matrix by the sol-gel process

We present the synthesis and characterization of a hybrid organic–inorganic material using robust metalloporphyrins halogenated in both meso and b-position: the iron complex (5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin and (2,3,7,8,12,13,17,18-octa-b-bromo-5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin, which stabilize the porphyrins against oxidative degradation. The immobilization was developed by the sol–gel process using pyridine and imidazole as template. Electron paramagnetic resonance (EPR) spectra of (2,3,7,8,12,13,17,18-octa-b-bromo5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin show that the entrapment of ironporphyrin is in a higher symmetry compared to the systems in solution. A reduction of iron was observed in the presence of imidazole, determined by the absence of an EPR spectrum. The addition of chloridric acid vapor induced an oxidation of iron and a small quantity of iron in a high spin state was detected by a component with axial symmetry. The ironporphyrins were active as catalysts for cyclooctene using iodozylbenzene and hydrogen peroxide as oxygen donors. The perhalogenated porphyrins immobilized had a smaller activity due to their iron oxidation and spin states. 2002 Elsevier Science B.V. All rights reserved.

Modified silicas covalently bounded to 5,10,15,20-tetrakis(2-hydroxy-5-nitrophenyl)porphyrinato iron(III): synthesis, spectroscopic and EPR characterization. Catalytic studies

In this work we have studied cyclooctene epoxidation with PhIO, using a new iron porphyrin, 5,10,15,20-tetrakis(2-hydroxy-5-nitrophenyl)porphyrinato iron(III), supported on silica matrices via eletrostatic interaction and / or covalent bonds as catalyst. These catalysts were obtained and immobilized on the solid supports propyltrimethylammonium silica (SiN+); propyltrimethylammonium and propylimidazole silica [SiN+(IPG)] and chloropropylsilica (CPS) via elestrostatic interactions and covalent binding. Characterization of the supported catalysts by UV-Vis spectroscopy and EPR (Electron paramagnetic resonance) indicated the presence of a mixture of FeII and FeIII species in all of the three obtained catalysts. In the case of (Z)-cyclooctene epoxidation by PhIO the yields observed for cis-epoxycyclooctane were satisfactory for the reactions catalyzed by the three materials (ranging from 68% to 85%). Such results indicate that immobilization of metalloporphyrins onto solid supports via groups localized on the ortho positions of their mesophenyl rings can lead to efficient catalysts for epoxidation reactions. The catalyst 1-CPS is less active than 1-SiN and 1-SiN(IPG), this argues in favour of the immobilization of this metalloporphyrin onto solids via electrostatic interactions, which is easier to achieve and results in more active oxidation catalysts. Interestingly, the activity of the supported catalysts remained the same even after three successive recyclings; therefore, they are stable under the oxidizing conditions.

Síntese, caracterização e estudos de transferencia de energia do complexo dimérico constituído por Zn e Mn porfirina

Porphyrins have revealed that factors as the energy transfer distance, molecular geometry and the difference of electronic potential, are important in a well defined electronic transfer. Porphyrin- containing donor-acceptor systems have been usefully employed to test various theoretical descriptions of electron transfer. The objective of this paper consists on the synthesis, purification and characterization by UV/Vis spectroscopy, 1H and 19F NMR, luminescence and lifetime of new molecular models, allowing the investigation of energy transfer parameters. This study was accomplished using the dimer Zn,Mn(TPPF4)2pip and its monomers ZnTPPF4pipH and MnF5TPP. The dimer characterization, Zn,Mn(TPPF4)2pip, was difficult due to the presence of Mn3+. The strong overlap between dp orbitals of manganese and the porphyrin p system increases the interaction manganese-porphyrin in changing the UV/Vis electronic spectrum and distorting the 1H and 19F NMR signals of dimer. The presence of Mn3+ shifts the reduction potential of E1/2 of the porphyrin ring to more negatives values, what results in more difficult reductions, disabling the transfer of energy from Zincporphyrin to Manganeseporphyrin.