Carbon-13 nuclear magnetic resonance studies on high spin iron(III) porphyrins

Carbon-13 NMR studies on a series of high spin iron(III) porphyrins, namely tetraphenylporphyrin iron(III) halides [Fe(TPP) X, X=Cl, Br, I] in CDCl₃ solution are reported. As expected the¹³C shifts are found to be an order of magnitude larger than the corresponding proton shifts. The dipolar contribution, which is quite important for the proton NMR, becomes much less significant for the¹³C shifts. No systematic variation in the¹³C shift across the series is observed, except for the meso-carbon which shows a small but gradual decrease in going from the chloro to the iodo complex. The¹³C shift for the various carbon atoms of the porphyrin ligand shows interesting pattern which is discussed in terms of spin delocalisation mechanisms.     

Spectral properties and solution behavior of gold(III) coordination compounds with water-soluble porphyrins

Gold(III) coordination compounds with three water-soluble porphyrins―5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H₂TSPP^4–), 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (H₂TMPyP⁴⁺), and 5,10,15,20-tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin (H₂TTMAPP⁴⁺)―have been studied. Complex [Au(TTMAPP)]⁵⁺ has been prepared for the first time. The analysis of coordination-induced shifts of proton signals in NMR spectra and intensities of Q bands in absorption spectra indicates the high degree of bond covalence in the studied metal porphyrins and a partial transfer of electron density from porphyrin to gold ion. The cationic complexes [Au(TMPyP)]⁵⁺ and [Au(TTMAPP)]⁵⁺ in aqueous solutions has been found to exist in monomeric form, while anionic complex [Au(TSPP)]^3– undergoes dimerization upon growth of concentration and solution ionic strength. Equilibrium constant for dimerization has been calculated, the constant has been found to decrease when temperature rises. Thermodynamic parameters of dimerization process have been determined: ΔH° =–31.8 kJ/mol and ΔS° =–13.8 J/mol K.     

Magnetic behaviour of spin-mixed iron(III) porphyrins

Detailed average magnetic susceptibility (295-4.2 K) and average magnetisation (20-2 K, 50-10 kOe) are reported for two novel spin-mixed iron(III) porphyrins, namely Fe(TPP)ClO4 and Fe(OEP)ClO4. The results confirm an S = 3/2 ground state substantially spin-mixed with a low-lying S = 5/2 state, but do not agree in detail with the crystal-field model of Maltempo.     

Six-coordinate nitrato complexes of iron(III) porphyrins

The interaction of tetrahydrofuran (THF) with thin films of the nitrato complexes Fe(III)(Por)(eta(2)-O(2)NO) [Por = meso-tetraphenylporphyrinato (TPP) and meso-tetratolylporphyrinato (TTP) dianion] at low temperature leads to the formation of the six-coordinate nitrato complex Fe(Por)(THF)(NO(3)), which was characterized by IR and UV-visible spectroscopies. Formation of the THF adduct was accompanied by nitrate linkage isomerization from bidentate to monodentate coordination. The iron(III) center remains in a high spin state in contrast with the previously observed low-spin nitratonitrosyl complex Fe(TPP)(NO)(eta(10-ONO(2)). Upon warming, THF dissociates to restore the initial five-coordinate bidentate nitrato complex.     

Monooxygenase activity of immobilized iron(III) porphyrins

New silica-immobilized iron(III) porphyrin systems possessing monooxygenase activity in aniline oxidation to p-aminophenol, have been found. The catalytic activity depends on both the porphyrin structure and coordination by an axial ligand. The maximum activity in this reaction is observed for imidazol-coordinated hemin. The hydroxylation in the above system is shown to follow a non-radical mechanism.

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This term refers to catalysis with the formation of monooxygenated products using dioxygen oxidants     

Spectral and thermal features of some novel iron(III) chelates with substituted 2-hydroxyaryloximes

The reaction products of five substituted 2-hydroxyaryloximes with Fe(III) ion were obtained and characterized by means of elemental analysis, conductometric measurements, magnetic moment determinations and spectroscopic data (IR and electronic absorption).The thermal stability and mode of decomposition were studied in air atmosphere by using TG-DTA. Kinetic analysis of the TG data was performed with the Coats-Redfern method to determine the apparent activation energies and the pre-exponential factor of the Arrhenius equation. Mass spectrometry was also used, and possible fragmentation patterns are given and discussed.Thanks are due to Tekkosha Hellas, Thessaloniki, for making available the thermogravimetric analysis facilities.     

Magnetic, electrochemical and spectroscopic properties of iron(III) amine-bis(phenolate) halide complexes

Eight new iron(III) amine-bis(phenolate) complexes are reported. The reaction of anhydrous FeX(3) salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L1, 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L2, and 2-methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L3, 2-methoxyethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L4 produces the trigonal bipyramidal iron(III) complexes, L1FeCl (1a), L1FeBr (1b), L2FeCl (2a), L2FeBr (2b), L3FeCl (3a), L3FeBr (3b), L4FeCl (4a), and L4FeBr (4b). All complexes have been characterized using electronic absorption spectroscopy, cyclic voltammetry and room temperature magnetic measurements. Variable temperature magnetic data were acquired for complexes 2b, 3a and 4b. Variable temperature M?ssbauer spectra were obtained for 2b, 3a and 4b. Single crystal X-ray molecular structures have been determined for proligand H(2)L4 and complexes 1b, 2b, and 4b.     

New iron(III) phosphate phases: crystal structure and electrochemical and magnetic properties

Two new iron(III) phosphates, FePO(4), have been synthesized from the dehydration of hydrothermally prepared monoclinic and orthorhombic hydrated phosphates FePO(4).2H(2)O. The structures of both hydrates were redetermined from single crystal data. On dehydration, a topotactic reaction takes place with only those bonds associated with the water molecules being broken, so that both FePO(4) phases have essentially the same Fe-P backbone frameworks as the corresponding hydrates. They are, respectively, monoclinic FePO(4), space group P2(1)/n, a= 5.480(1) A, b = 7.480(1) A, c= 8.054(1) A, beta = 95.71(1) degrees, and Z = 4; and orthorhombic FePO(4), space group Pbca, a = 9.171(1) A, 9.456(1) A, c = 8.675(1) A, and Z = 8. Both of these phases are thermally unstable relative to the trigonal quartz-like FePO(4). The electrochemical studies find that the orthorhombic iron phosphate is more active than the monoclinic phase, while both are more active than trigonal FePO(4). Both phases approach Curie-Weiss behavior at room temperature, with the monoclinic phase exhibiting stronger antiferromagnetic interactions due to Fe-O-Fe interactions. The electrochemical and magnetic data are consistent with the structures of these two compounds. The properties of these new iron phosphate structures are compared with other iron phosphate phases.     

Studies on iron(III) and manganese(III) derivatives of new meso-aryl substituted and brominated porphyrins

A series of Fe^III and Mn^III porphyrins with various tolyl and naphthyl substituents at the meso positions, and their perbromoderivatives with Br substituents at the -pyrrole positions, have been synthesised and investigated. As seen in the case of the free-base porphyrins, both Fe^III and Mn^III derivatives of the Br-substituted porphyrins also exhibit pronounced red-shifts in both B and Q bands compared to their nonbrominated analogues. This is attributed to the electron-withdrawing ability of eight Br substituents at -pyrrole positions and is also due to distortion brought about in the -framework by the bulky substituents including those at the meso positions. The naphthyl groups seem to be making mesomeric contributions for both nonbrominated and brominated porphyrins of these metal ions as is evident from the higher wavelength absorption of the B band as compared to the tolyl derivatives. While the meso-substituent do not exhibit any isomer dependent change on the electronic properties of Fe^III porphyrins, they show a noticeable effect in the Mn^III derivatives. During the metallation of meso-tetratolylporphyrins by Fe^III ions -oxo dimeric compounds are formed, while the naphthyl porphyrins and the bromoderivatives do not form such dimeric species. The presence of bulky groups at the meso positions and heavy bromines on the -pyrrole positions can be considered to prevent the formation of catalytically inert -oxo dimers.     

Synthesis and photophysical properties of porphyrins with fluorenyl pendant arms

Symmetrical-A₄-porphyrins bearing four fluorene donor moieties TOFP (5,10,15,20-tetra(4-(2 methyloxyfluorenyl)phenyl)porphyrin) as well as eight fluorene arms OOFP (5,10,15,20-octa(3,5-(2-methyloxyfluorenyl)phenyl)porphyrin) were synthesized and characterized. Preliminary photophysical properties are reported. In comparison to the reference tetraphenylporphyrin TPP, the luminescence properties are slightly improved. The fluorescence quantum yields of tetrafluorenylporphyrin TOFP (1) and octafluorenylporphyrin OOFP (2) are 0.10 and 0.13, respectively.     

Magnetic properties and electronic structure of manganese(III) porphyrins

The average magnetic susceptibility (1.2-100 K) and magnetisation (100–15000 Oe at 4.2 K) of two perchlorato manganese(III) porphyrins establish them to be high-spin, in contrast to the “anomalous” behaviour of analogous iron(III) porphyrins. An explanation of the origin of the zero-field splitting in high-spin manganese(III) porphyrins is presented.     

Spectral and M?ssbauer studies of some iron(III) high spin complexes

Some new iron(III) complexes of triazene 1-oxides are synthesised and characterised by analysis, magnetic, electronic and M?ssbauer spectra. They are found to be high spin Fe³⁺ systems.     

Polynuclear iron(III) pivalates

The formation of magnetically active polynuclear Fe^III pivalates in the FeSO₄·7H₂O-KOOCCMe₃ system was studied. The reaction of FeSO₄·7H₂O (1) with KOOCCMe₃ in EtOH in air afforded the antiferromagnetic trinuclear complex [Fe₃O(OOCCMe₃)₆(H₂O)₃]⁺[OOCCMe₃]^–·3EtOH. A change of the solvent (EtOH) in this system to a 40:1 benzene—THF mixture resulted in the formation of the antiferromagnetic hexanuclear cluster [Fe₆(O)₂(OH)₂(OOCCMe₃)₁₂(HOOCCMe₃)(THF)]·1.5C₆H₆. The addition of trimethylacetic acid to EtOH and recrystallization from hexane gave rise to the antiferromagnetic coordination polymer [K₂Fe₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(H₂O)₂]_n (7). Recrystallization of the latter from acetonitrile afforded the antiferromagnetic tetranuclear complex K₂Fe₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(MeCN)₂. The structures of these compounds were established by X-ray diffraction analysis, and their magnetic susceptibilities and thermal decomposition were investigated.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2403–2413, November, 2004.     

Study of the catalytic behavior of montmorillonite/iron(III) and Mn(III) cationic porphyrins

Two samples of montmorillonite (one of Brazilian origin, BNC1 clay, and the other STX-1, supplied by the Clay Mineral Society Repository (University of Missouri, USA) were allowed to react with biomimetic metalloporphyrins of Fe(III) and Mn(III) in cationic form. The compounds were characterized by several techniques, showing that the metalloporphyrins molecules were adsorbed at the surface of the clay platelet crystals. The catalytic activities of the intercalated complexes for the oxidation of alkane were dependent upon the concentration of the porphyrin immobilized in the clay and factors such as the metal ion species in the porphyrins, choice of solvent, and concentration of the iodosylbenzene oxidant. Good selectivity to cyclohexanol instead of cyclohexanone was observed for the catalytic oxidation of cyclohexane by iodosylbenzene.     

Some novel manganese(III) porphyrins with catalytic properties

Abstract

A series of manganese(III) porphyrins with 4-methylimidazole have been prepared. These are high-spin complexes having general formula [Mn^III(THMPP)X(4-MeIm)], where THMP?=?5,10,15,20-tetra(4-hydroxy-3-methoxyphenyl)porphine ligand, X?=?Cl^?, Br^?, NCS^?, or N₃^? and 4-MeIm?=?4-methylimidazole. All the complexes have been characterized by UV-visible, FT-IR, ESI-MS spectra, elemental analyses and magnetic susceptibility measurements. These manganese(III) porphyrins oxidize aromatic alcohols to aldehydes. The oxidation reactions have been carried out at room temperature in the presence of oxidants such as NaIO₄, H₂O₂, and NaOCl. The comparative studies proved that NaIO₄ behaves as the most efficient oxidant in these oxidative transformation reactions.     

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

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 Fe^IIIP and high-spin mono-coordinated Fe^IIIP species, whereas Fe[M(4-N-MePy)TFPP]IPG only contains high-spin mono-coordinated Fe^IIIP. These FePIPG catalysts also contain Fe^IIP 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 Fe^IIIP species. The cationic FePs supported on SiSO₃⁻ are also high-spin Fe^IIIP 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.     

Synthesis and reactions of meso-(p-nitrophenyl)porphyrins

An improved methodology is reported for the regioselective nitration of the phenyl groups of meso-tetraphenylporphyrin 1, using NaNO₂ and TFA. The degree of nitration is easily controlled by the equivalent amount of NaNO₂ used and the reaction time. The nitroporphyrins are reduced to the corresponding aminoporphyrins under standard SnCl₂/HCl conditions. Reaction of tri-aminoporphyrin 9 with 1-formyl-o-carborane followed by reduction using NaBH₄ gave a novel tri-carboranylporphyrin bearing amine linkages between the porphyrin and the carborane groups.     

二氯二茂钛的制备及催化二聚环戊二烯开环易位聚合——推荐一个无水无氧综合化学实验

将有工业应用背景的特色科研成果提炼成综合化学实验，拓展了专业实验的知识面，使学生能在较高层次上了解化学实验领域中的特殊研究方法及手段。     

Built-in axial base binding on phenanthroline-strapped zinc(II) and iron(III) porphyrins

In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions.