Hérica C Sacco

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.

Factors which affect the catalytic activity of iron(III) meso tetrakis(2,6-dichlorophenyl) porphyrin chloride in homogeneous system

An optimization study of the reaction conditions of Fe(TDCPP)Cl when it is used as catalyst in the hydroxylation of cyclohexane by iodosylbenzene (PhIO) has been carried out. It was found that Fe(TDCPP)Cl follows the classical PhIO mechanism described for Fe(TPP)Cl, which involves the monomeric active species FeIV(O)P+ (I). In the optimized condition ([Fe(TDCPP) = 3.0 × 10−4 mol l−1 in 1,2-dichloroethane (DCE); ultrasound stirring at 0°C; PhIOFeP molar ratio = 100), this FeP led to a yield of cyclohexanol (C-ol) of 96% and a turnover number of 96. Therefore, Fe(TDCPP)Cl may be considered a good biomimetic model and a very stable, resistant and selective catalyst, which yields C-ol as the sole product. DCE showed to be a better solvent than dichloromethane (DCM), 1 DCE:1 MeOH mixture or acetonitrile (ACN). Since the FeIV(O)P+ is capable of abstracting hydrogen atom from DCM, MeOH or ACN, the solvent competes with the substrate. Presence of O2 lowers the yield of C-ol, as it can further oxidize this alcohol to carboxylic acid in the presence of radicals. Presence of H2O also causes a decrease in the yield, since it converts the active species I into FeIV(OH)P, which cannot oxidize cyclohexane. Addition of excess imidazole or OH− to the system results in a decrease in the yield of C-ol, due to the formation of the hexaccordinated complexes Fe(TDCPP)Im+2 (low-spin, β2 = 2.5 × 108 mol−2 l2) and Fe(TDCPP)(OH)−2 (high-spin, β2 = 6.3 × 107 mol−2 l2). The formation of both Fe(TDCPP)Im+2 and Fe(TDCPP)(OH)−2 complexes were confirmed by EPR studies. The catalytic activities of Fe(TDCPP)Cl and Fe(TFPP)Cl were compared. The unusually high yields of C-ol with Fe(TFPP)Cl obtained when ultrasound, DCM and O2 atmosphere were used, suggest that a parallel mechanism involving the μ-oxo dimer form, O2 and radicals may also be occurring with this FeP, besides the PhIO mechanism.

Meso-aryl substituted metalloporphyrins supported on imidazole propyl gel (IPG). Catalytic activity in the oxidation of cyclohexane and characterization of iron porphyrin—IPG systems

Abstract In this work, the catalytic activity of Fe and Mn porphyrins with meso-aryl electron withdrawing substituents in the hydroxylation of cyclohexane using iodosylbenzene as the oxygen donor were compared. The catalysts were used in three ways: in solution, supported on imidazole propyl gel (IPG) and supported on silica gel (SG). Mn-porphyrin-IPG systems are better catalysts: Mn(TDCPP)-IPG gives 67% of cyclohexanol yield, while the corresponding solution system gives 17%. With the Fe(TDCPP)-IPG system, there is a decrease in the catalytic activity (25%), when compared to the solution system. It was possible to understand, through UV-Vis and EPR spectra characterization, that an excess of imidazole in the iron (III) porphyrin-IPG systems promotes partial catalyst deactivation due to the bis-imidazolyl coordination and reduction to iron(II). If the imidazole/ Fe(TDCPP) ratio decreases in the Fe(TDCPP)-IPG, the yield increases to 60%. It was possible to recycle Mn(TDCPP)-IPG, Fe(TDCPP)-IPG and Fe(TFPP)IPG up to 5 times without leaching of the supported catalyst, which results in very efficient systems with high turnovers.

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.

Polymeric organic-inorganic hybrid material containing iron(III) porphyrin using sol-gel process

Abstract Here we describe the preparation of iron(III) porphyrinosilica in a simple one-pot reaction, where the –SO 2 Cl groups present in the phenyl rings of FeTDCSPP + react with 3-aminopropyltriethoxysilane and tetraethoxysilane in the presence of a nitrogenous base, leading to iron(III) porphyrinosilica. In this same procedure, molecular cavities containing regularly spaced functional groups are created through the molecular imprinting technique, in which the nitrogenous base coordinated to the iron(III) porphyrin serves as a template. The removal of such template in a Soxhlet extractor leads to a cavity with the same shape and size as the nitrogenous base, enabling the construction of shape-selective catalysts mimicking cytochrome P-450. Five different imprinting molecules have been used: imidazole, 1-methylimidazole, 2-methylbenzimidazole, 4-phenylimidazole and miconazole and ultra-violet/visible absorption spectroscopy, thermogravimetric analysis and electron paramagnetic resonance carried out.

Synthesis of hybrid silicates containing porphyrins incorporated by a sol–gel process and their properties

Abstract Porphyrin was incorporated in a silicate network, via a covalent bond, by grafting a functional group with 3-aminopropyltriethoxysilane, using a sol–gel process. We have carried out the synthesis and measured the absorption spectra, nuclear magnetic resonance spectra, infrared (IR) spectra, luminescence spectra and lifetime of these hybrid silicates, porphyrinosilicas. These samples contained the following free-base porphyrins: meso-tetrakis- p -chlorobenzoylporphyrin, meso-tetrakis-2,6-dichloro-3-chlorosulfonylphenylporphyrin. The obtained porphyrinosilicas have similar absorption and luminescence spectra to the free base porphyrins in solution. IR spectra confirm the formation of monomeric species. Lifetime measurement for porphyrinosilica reveals that 32%xa0±xa02% of porphyrin is covalently bonded to the silica network.

Synthesis of fluorinated metalloporphyrinosilica imprinted with templates through sol-gel process

Abstract We present the synthesis of a hybrid material containing fluorinated iron porphyrins through hydrolysis and polycondensation of iron porphyrin bearing a trifluorosilyl function with tetraethoxysilane in the presence of nitrogen bases acting as template molecules. The presence of metalloporphyrin Soret band is detected in the ultraviolet–visible absorption spectra of all metalloporphyrinosilica-templates. Thermogravimetric analysis and electron paramagnetic resonance of the materials also confirm the presence of metalloporphyrin in a silica network. Electron spectroscopy imaging was that of a non-crystalline microstructure. The iron and silicon distribution are homogeneous for the elements in all particle sites. The iron porphyrinosilicas-template were active as catalysts for cyclooctene epoxidation using iodozylbenzene as oxygen donor. In general, the epoxidation yield is larger for iron porphyrinosilicas-template than for manganese porphyrinosilicas-template. The manganese porphyrinosilicas-template had a smaller activity due to their manganese oxidation state. The largest catalytic yield were obtained with the iron porphyrinosilica-pyridine (85%).

Characterization and catalytic activity of 2,6-dichlorophenyl substituted iron(III) porphyrin supported on silica gel and imidazole propyl gel

Abstract In this work we have made use of the study of the interaction between Fe(TDCPP)+ and the axial ligands OH− and imidazole in order to help characterize the heterogenized catalysts Fe(TDCPP)SG and Fe(TDCPP)IPG through UV–VIS and EPR spectroscopies and thus, better understand their different catalytic activity in the oxidation of cyclohexane by PhIO. We have found out that in Fe(TDCPP)SG (containing 1.2×10−6 mol Fe(TDCPP)+/g of support), the FeP bis-coordinates to silica gel through Fe–O coordination and it is high-spin FeIIIP species. In Fe(TDCPP)IPG 1 (containing 1.1×10−6 mol Fe(TDCPP)+ and 2.2×10−4 mol imidazole/g of support), the FeP is bis-ligated to imidazole propyl gel through Fe-imidazole coordination and using NO as a paramagnetic probe, we present evidence that Fe(TDCPP)+ is present as a mixture of low-spin FeIIIP and FeIIP species. This catalyst led to a relative low yield of cyclohexanol (25%) because the bis-coordination of the FeIIIP to the support partially blocks the reaction between Fe(TDCPP)+ and PhIO, thus leading to the formation of only a small amount of the active species FeIV(O)P·+, while the FeIIP species do not react with the oxygen donor. Increasing the amount of Fe(TDCPP)+ and decreasing the amount of imidazole in the support led to the obtention of high-spin FeIIIP EPR signals in the spectra of Fe(TDCPP)IPG 5 (containing 4.4×10−6 mol Fe(TDCPP)+ and 2.2×10−5 mol imidazole/g of IPG), together with low-spin FeIIIP species. This latter catalyst led to better cyclohexanol yields (67%) than Fe(TDCPP)IPG 1. Fe(TDCPP)IPG 5 was further used in a study of the optimization of its catalytic activity and in recycling experiments in the optimized conditions. Recycling oxidation reactions of Fe(TDCPP)IPG 5 led to a total turnover number of 201 and total cyclohexanol yield of 201%, which could not be attained with Fe(TDCPP)Cl in homogeneous solution (turnover=96) due to the difficulty in recovering and reusing it.

Synthesis of manganese porphyrinosilica imprinted with templates using the sol-gel process

Abstract The optimized conditions for the preparation of a new manganese porphyrinosilica-template material are reported. The manganese porphyrinosilica-template was prepared by the sol–gel process, by the reaction of –SO 2 Cl groups present in the phenyl rings of MnTDC(SO 2 Cl)PPCl with 3-aminopropyltriethoxysilane. The reaction produces a precursor porphyrinopropylsilyl species, which were then polymerized with tetraethoxysilane. The presence of manganese porphyrin on xerogel is confirmed by ultraviolet visible absorption spectroscopy and thermogravimetric analysis (TGA). The prepared materials have surface areas between 19 and 674 m 2 g −1 . Electron spectroscopy imaging of the materials show that manganese distribution in the xerogel is uniform. Both manganese(III) porphyrinosilica-template and a similar iron(III) porphyrinosilica-template can catalyze the epoxidation of cyclooctene using iodozylbenzene as oxygen donor. The metalloporphyrinosilica-template presents catalytic activity similar to that of metaloporphyrin in solution.

Ironporphyrins trapped sol–gel glasses: a chemometric approach

Abstract The optimised conditions for preparation of ironporphyrin (FeP)-template trapped silica obtained by the sol–gel process are analysed by fractional factorial design. The FeP iron 5,10,15,20-tetrakis(pentafluorophenyl)-porphyrin (FeTFPPCl), iron 5,10,15,20-tetrakis(2,6-dichlorophenyl-3-sulphonatophenyl)-porphyrin (FeTDCSPP(Na)4Cl), iron 5,10,15,20-tetrakis-p-carboxyphenylporphyrin (FeTCPP(Na)4Cl) and iron 5,10,15,20-tetrakis-p-methylpyridilporphyrin (FeTMPyP(Cl)5) were used. Pyridine or 4-phenylimidazole was used as template. Scanning electron microscopy (SEM) shows that the use of different porphyrins and conditions in the preparation of xerogel produce different product morphologies. The prepared materials have surface areas, between 300 and 1000 m2/g. The electron paramagnetic resonance spectra of trapped materials have characteristic signal of FeIII high spin, the presence of porphyrin species in a rhombic symmetry and porphyrin aggregates were also observed.