New class of potent catalysts of O2.-dismutation. Mn(III) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

Three new Mn(III) porphyrin catalysts of O2.-dismutation (superoxide dismutase mimics), bearing ether oxygen atoms within their side chains, were synthesized and characterized: Mn(III) 5,10,15,20-tetrakis[N-(2-methoxyethyl)pyridinium-2-yl]porphyrin (MnTMOE-2-PyP(5+)), Mn(III)5,10,15,20-tetrakis[N-methyl-N'-(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTM,MOE-2-ImP(5+)) and Mn(III) 5,10,15,20-tetrakis[N,N'-di(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTDMOE-2-ImP(5+)). Their catalytic rate constants for O2.-dismutation (disproportionation) and the related metal-centered redox potentials vs. NHE are: log k(cat)= 8.04 (E(1/2)=+251 mV) for MnTMOE-2-PyP(5+), log k(cat)= 7.98 (E(1/2)=+356 mV) for MnTM,MOE-2-ImP(5+) and log k(cat)= 7.59 (E(1/2)=+365 mV) for MnTDMOE-2-ImP(5+). The new porphyrins were compared to the previously described SOD mimics Mn(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)), Mn(III) 5,10,15,20-tetrakis(N-n-butylpyridinium-2-yl)porphyrin (MnTnBu-2-PyP(5+)) and Mn(III) 5,10,15,20-tetrakis(N,N'-diethylimidazolium-2-yl)porphyrin (MnTDE-2-ImP(5+)). MnTMOE-2-PyP(5+) has side chains of the same length and the same E(1/2), as MnTnBu-2-PyP(5+)(k(cat)= 7.25, E(1/2)=+ 254 mV), yet it is 6-fold more potent a catalyst of O2.-dismutation , presumably due to the presence of the ether oxygen. The log k(cat)vs. E(1/2) relationship for all Mn porphyrin-based SOD mimics thus far studied is discussed. None of the new compounds were toxic to Escherichia coli in the concentration range studied (up to 30 microM), and protected SOD-deficient E. coli in a concentration-dependent manner. At 3 microM levels, the MnTDMOE-2-ImP(5+), bearing an oxygen atom within each of the eight side chains, was the most effective and offered much higher protection than MnTE-2-PyP(5+), while MnTDE-2-ImP(5+) was of very low efficacy.     

New PEG-ylated Mn(III) porphyrins approaching catalytic activity of SOD enzyme

Two new tri(ethyleneglycol)-derivatized Mn(III) porphyrins were synthesized with the aim of increasing their bioavailability, and blood-circulating half-life. These are Mn(III) tetrakis(N-(1-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)pyridinium-2-yl)porphyrin, MnTTEG-2-PyP5+ and Mn(III) tetrakis(N,N'-di(1-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)imidazolium-2-yl)porphyrin, MnTDTEG-2-ImP5+. Both porphyrins have ortho pyridyl or di-ortho imidazolyl electron-withdrawing substituents at meso positions of the porphyrin ring that assure highly positive metal centered redox potentials, E1/2 = +250 mV vs. NHE for MnTTEG-2-PyP5+ and E1/2 = + 412 mV vs. NHE for MnTDTEG-2-ImP5+. As expected, from established E1/2 vs. log kcat(O2 *-) structure-activity relationships for metalloporphyrins (Batinic-Haberle et al., Inorg. Chem., 1999, 38, 4011), both compounds exhibit higher SOD-like activity than any meso-substituted Mn(III) porphyrins-based SOD mimic thus far, log kcat = 8.11 (MnTTEG-2-PyP5+) and log kcat = 8.55 (MnTDTEG-2-ImP5+), the former being only a few-fold less potent in disproportionating O2*- than the SOD enzyme itself. The new porphyrins are stable to both acid and EDTA, and non toxic to E. coli. Despite elongated substituents, which could potentially lower their ability to cross the cell wall, MnTTEG-2-PyP5+ and MnTDTEG-2-ImP5+ exhibit similar protection of SOD-deficient E. coli as their much smaller ethyl analogues MnTE-2-PyP5+ and MnTDE-2-ImP5+, respectively. Consequently, with anticipated increased blood-circulating half-life, these new Mn(III) porphyrins may be more effective in ameliorating oxidative stress injuries than ethyl analogues that have been already successfully explored in vivo.     

Methoxy-derivatization of alkyl chains increases the in vivo efficacy of cationic Mn porphyrins. Synthesis, characterization, SOD-like activity, and SOD-deficient E. coli study of meta Mn(III) N-methoxyalkylpyridylporphyrins

Cationic Mn(III) N-alkylpyridylporphyrins (MnPs) are potent SOD mimics and peroxynitrite scavengers and diminish oxidative stress in a variety of animal models of central nervous system (CNS) injuries, cancer, radiation, diabetes, etc. Recently, properties other than antioxidant potency, such as lipophilicity, size, shape, and bulkiness, which influence the bioavailability and the toxicity of MnPs, have been addressed as they affect their in vivo efficacy and therapeutic utility. Porphyrin bearing longer alkyl substituents at pyridyl ring, MnTnHex-2-PyP(5+), is more lipophilic, thus more efficacious in vivo, particularly in CNS injuries, than the shorter alkyl-chained analog, MnTE-2-PyP(5+). Its enhanced lipophilicity allows it to accumulate in mitochondria (relative to cytosol) and to cross the blood-brain barrier to a much higher extent than MnTE-2-PyP(5+). Mn(III) N-alkylpyridylporphyrins of longer alkyl chains, however, bear micellar character, and when used at higher levels, become toxic. Recently we showed that meta isomers are ～10-fold more lipophilic than ortho species, which enhances their cellular accumulation, and thus reportedly compensates for their somewhat inferior SOD-like activity. Herein, we modified the alkyl chains of the lipophilic meta compound, MnTnHex-3-PyP(5+) via introduction of a methoxy group, to diminish its toxicity (and/or enhance its efficacy), while maintaining high SOD-like activity and lipophilicity. We compared the lipophilic Mn(III) meso-tetrakis(N-(6'-methoxyhexyl)pyridinium-3-yl)porphyrin, MnTMOHex-3-PyP(5+), to a hydrophilic Mn(III) meso-tetrakis(N-(2'-methoxyethyl)pyridinium-3-yl)porphyrin, MnTMOE-3-PyP(5+). The compounds were characterized by uv-vis spectroscopy, mass spectrometry, elemental analysis, electrochemistry, and ability to dismute O(2)˙(-). Also, the lipophilicity was characterized by thin-layer chromatographic retention factor, R(f). The SOD-like activities and metal-centered reduction potentials for the Mn(III)P/Mn(II)P redox couple were similar-to-identical to those of N-alkylpyridyl analogs: log k(cat) = 6.78, and E(1/2) = +68 mV vs. NHE (MnTMOHex-3-PyP(5+)), and log k(cat) = 6.72, and E(1/2) = +64 mV vs. NHE (MnTMOE-3-PyP(5+)). The compounds were tested in a superoxide-specific in vivo model: aerobic growth of SOD-deficient E. coli, JI132. Both MnTMOHex-3-PyP(5+) and MnTMOE-3-PyP(5+) were more efficacious than their alkyl analogs. MnTMOE-3-PyP(5+) is further significantly more efficacious than the most explored compound in vivo, MnTE-2-PyP(5+). Such a beneficial effect of MnTMOE-3-PyP(5+) on diminished toxicity, improved efficacy and transport across the cell wall may originate from the favorable interplay of the size, length of pyridyl substituents, rotational flexibility (the ortho isomer, MnTE-2-PyP(5+), is more rigid, while MnTMOE-3-PyP(5+) is a more flexible meta isomer), bulkiness and presence of oxygen.     

Electrochemistry of [(TMpyP)M(II)]4+ (X-)4 (X- = Cl- or BPh4-) and [(TMpyP)M(III)Cl]4+ (Cl-)4 in N,N-dimethylformamide where M is one of 15 different metal ions

The electrochemistry of 16 different water-soluble porphyrins of the type [(TMpyP)M(II)]4+ (X-)4 or [(TMpyP)M(III)Cl]4+ (Cl-)4 is reported in nonaqueous media where TMpyP is the dianion of meso-tetrakis(N-methylpyridiniumyl)porphyrin and X- = Cl- or BPh4-. These studies were carried out to examine the effect of the metal ion and porphyrin counterion (X-) on the electrochemical properties of the TMpyP complexes with a special emphasis being given to the overall number of electrons added and the number of electrode processes upon reduction. All of the investigated compounds with electroinactive central metal ions undergo an overall addition of six electrons. This occurs for most compounds via three two-electron-transfer steps, but more than three processes are observed for porphyrins having metal ions with a low electronegativity (e.g., Cd(II)). The first reduction of each porphyrin having an M(II) ion or an electroinactive M(III) ion yields a porphyrin dianion which is characterized by an intense band located close to 800 nm, and this reversible reduction is followed by further reductions of the 1-methyl-4-pyridyl groups at more negative potentials. Four of the compounds with electroactive central metal ions, [(TMpyP)M(III)Cl]4+(Cl-)4 (M = Co, Fe, Mn, or Au), undergo an additional reversible M(III)/M(II) process prior to reactions involving the porphyrin pi-ring system and the 1-methyl-4-pyridyl substituents.     

Discrimination of nitroxyl and nitric oxide by water-soluble Mn(III) porphyrins

The water-soluble manganese(III) meso-tetrakis (N-ethylpyridinium-2-yl) porphyrin (Mn(III)TEPyP) and manganese(III) meso-(tetrakis(4-sulfonato-phenyl)) porphyrinate (Mn(III)TPPS) are able to chemically distinguish between HNO and NO donors, reacting with the former in a fast, efficient, and selective manner with concomitant formation of the {MnNO}(7) complex (k(on(HNO)) approximately equal to 10(5) M(-1) s(-1)), while they are inert or react very slowly with NO donors. DFT calculations and kinetic data suggest that HNO trapping is operative at least in the case of Mn(III)TPPS, while catalytic decomposition of the HNO donors (sodium trioxodinitrate and toluene sulfohydroxamic acid) seems to be the main pathway for Mn(III)TEPyP. In the presence of oxygen, the product Mn(II)TEPyP(NO) oxidizes back to Mn(III)TEPyP, making it possible to process large ratios of nitroxyl donor with small amounts of porphyrin.     

Reduction and adduct formation from electrosprayed solutions of porphyrin salts

The solutions of four meso-tetrakis(N-alkylpyridinium-4-yl)porphyrin salts and of the p-toluenesulfonate salt of meso-tetrakis(4-trimethylammoniumphenyl)porphyrin, in methanol, were studied by electrospray mass spectrometry, in order to investigate the influence of the type of counter ion, the length of the substituent N-alkyl groups of the four (N-alkylpyridinium-4-yl)porphyrins and the presence of an aromatic (alkylpyridinium) or aliphatic (trimethylammonium) nitrogen, in ion formation.In our experimental conditions, adducts with the counter ions were formed only for the meso-tetrakis(4-trimethylammoniumphenyl)porphyrin and were not observed for the other porphyrins, even when the counter ion was the same. In contrast, formation of reduced species, such as the [M(4+) + e(-)]3+, [M(4+) + 2e(-)]2+, [M(4+) + 4e(-) + 2H(+)]2+, and [M(4+) + 5e(-) + 2H(+)]+ ions was observed only for the (N-alkylpyridinium-4-yl)porphyrins and the appearance of these species is apparently solvent related and may occur via counter ion/solvent adducts.     

Synthesis,structure, properties,and phosphatase-like activity of the first heterodinuclear Fe(III)Mn(II) complex with the unsymmetric ligand H(2)BPBPMP as a model for the PAP in sweet potato

The new heterodinuclear mixed valence complex [Fe(III)Mn(II)(BPBPMP)(OAc)(2)]ClO(4) (1) with the unsymmetrical N(5)O(2) donor ligand 2-bis[((2-pyridylmethyl)-aminomethyl)-6-((2-hydroxybenzyl)(2-pyridylmethyl))-aminomethyl]-4-methylphenol (H(2)BPBPMP) has been synthesized and characterized. Compound 1 crystallizes in the monoclinic system, space group P2(1)/c, and has an Fe(III)Mn(II)(mu-phenoxo)-bis(mu-carboxylato) core. Two quasireversible electron transfers at -870 and +440 mV versus Fc/Fc(+) corresponding to the Fe(II)Mn(II)/Fe(III)Mn(II) and Fe(III)Mn(II)/Fe(III)Mn(III) couples, respectively, appear in the cyclic voltammogram. The dinuclear Fe(III)Mn(II) center has weakly antiferromagnetic coupling with J = -6.8 cm(-1) and g = 1.93. The (57)Fe M?ssbauer spectrum exhibits a single doublet, delta = 0.48 mm s(-1) and DeltaE(Q) = 1.04 mm s(-1) for the high spin Fe(III) ion. Phosphatase-like activity at pH 6.7 with the substrate 2,4-bis(dinitrophenyl)phosphate reveals saturation kinetics with the following Michaelis-Menten constants: K(m) = 2.103 mM, V(max) = 1.803 x 10(-5) mM s(-1), and k(cat) = 4.51 x 10(-4) s(-1).     

Synthesis,Redox Behavior,Sensitizer Activity,and Oxygen Transfer of Covalently Bound Polymeric Porphyrins

Metal complexes of covalently bound porphyrins are used as sensitive probes for several investigations. Substituted derivatives of tetraphenyl-porphin, phthalocyanine, and naphthalocyanine are synthesized at positively and negatively charged as well as uncharged polymers. The photo-redox activities were studied under irradiation with visible light in the presence of a donor and an acceptor. The triplet life times of covalently bound porphyrin moieties are strongly enhanced compared with the analogous monomeric porphyrins. In addition, the polymer binding results in higher photocatalytic activity. The electron-transfer reactions of Mn(III)-containing porphyrins using the reducing agent dithionite are strongly influenced by the polymer environment. In contrast to monomeric Mn(III)-porphyrins, the porphyrins containing polymers exhibit a two-step reduction which may be due to the change of the conformation of the polymer coil. The catalytic epoxidation of 2,5-dihydrofuran with hypochlorite with formation of 3,4-epoxytetrahydrofuran occurs with water-soluble porphyrins in water. No influence of the polymer environment exists. The different reactions require reaction times from milliseconds up to hours.     

High-frequency and field EPR investigation of (8,12-diethyl-2,3,7,13,17,18-hexamethylcorrolato)manganese(III)

High-field and frequency electron paramagnetic resonance (HFEPR) of solid (8,12-diethyl-2,3,7,13,17,18-hexamethylcorrolato)manganese(III), 1, shows that in the solid state it is well described as an S = 2 (high-spin) Mn(III) complex of a trianionic ligand, [Mn(III)C(3)(-)], just as Mn(III) porphyrins are described as [Mn(III)P(2)(-)](+). Comparison among the structural data and spin Hamiltonian parameters reported for 1, Mn(III) porphyrins, and a different Mn(III) corrole, [(tpfc)Mn(OPPh(3))], previously studied by HFEPR (Bendix, J.; Gray, H. B.; Golubkov, G.; Gross, Z. J. Chem. Soc., Chem. Commun. 2000, 1957-1958), shows that despite the molecular asymmetry of the corrole macrocycle, the electronic structure of the Mn(III) ion is roughly axial. However, in corroles, the S = 1 (intermediate-spin) state is much lower in energy than in porphyrins, regardless of axial ligand. HFEPR of 1 measured at 4.2 K in pyridine solution shows that the S = 2 [Mn(III)C(3)(-)] system is maintained, with slight changes in electronic parameters that are likely the consequence of axial pyridine ligand coordination. The present result is the first example of the detection by HFEPR of a Mn(III) complex in solution. Over a period of hours in pyridine solution at ambient temperature, however, the S = 2 Mn(III) spectrum gradually disappears leaving a signal with g = 2 and (55)Mn hyperfine splitting. Analysis of this signal, also observable by conventional EPR, leads to its assignment to a manganese species that could arise from decomposition of the original complex. The low-temperature S = 2 [Mn(III)C(3)(-)] state is in contrast to that at room temperature, which is described as a S = 1 system deriving from antiferromagnetic coupling between an S = (3/2) Mn(II) ion and a corrole-centered radical cation: [Mn(II)C(*)(2-)] (Licoccia, S.; Morgante, E.; Paolesse, R.; Polizio, F.; Senge, M. O.; Tondello, E.; Boschi, T. Inorg. Chem. 1997, 36, 1564-1570). This temperature-dependent valence state isomerization has been observed for other metallotetrapyrroles.     

Aggregation and solution behavior of 5-(1-(4-carboxybutyl) pyridinum-4-yl) 10,15,20-tris (1-methylpyridinium-4-yl) porphyrin: A resonance light scattering, fluorescence and absorption spectroscopic study

Aggregation behavior of water soluble porphyrins, 5-(1-(4-carboxybutyl) pyridinum-4-yl) 10,15,20-tris (1-methylpyridinium-4-yl) porphyrin (5-CBPyP) in the presence of various concentrations of calf thymus DNA (ct-DNA) and sodium chloride were studied in comparison with meso-tetrakis (4-N-methyl pyridinum) porphyrin (TMPyP), by optical absorption, fluorescence and resonance light scattering (RLS) spectroscopies. Both porphyrins obey Beer’s law in extended range of concentration. Optical absorption and RLS measurements demonstrated nonaggregation for both porphyrins under increasing concentration of ct-DNA and NaCl. However, in comparison, 5-CBPyP had less tendency for aggregation that may be taken as an advantage for its probable application in photodynamic therapy of cancer. The trend of changes in absorption spectra of both porphyrins in the presence of ct-DNA indicates the homogeneous intercalation binding mode. The values of (2.81 ± 0.28) × 10⁶ M^?1 and (0.95 ± 0.09) × 10⁶ M^?1 were obtained for apparent binding constant of TMPyP and 5-CBPyP from analysis of optical absorption data, respectively. This indicates the less affinity of 5-CBPyP to ct-DNA in comparison with TMPyP. The binding of both porphyrins to ct-DNA quenches fluorescence emission of Ethidium bromide (EB) that is bound to ct-DNA. The quenching process obeys linear Stern-Volmer relationship indicating the displacement of EB from its binding sites by these porphyrins. The results of this technique also represent the intercalation mode of binding for both porphyrins and higher binding affinity of TMPyP compared with 5-CBPyP.     

Fast nitroxyl trapping by ferric porphyrins

Iron(II) porphyrin nitrosyl complexes are obtained in high yields from the reaction of iron(III) porphyrins with the nitroxyl donors sodium trioxodinitrate and toluensulfohydroxamic acid. The reaction was found to proceed both in organic solvents and in aqueous media from iron(III) (meso-tetraphenyl) porphyrinate ([FeIII(TPP)]+) and iron(III) meso-tetrakis (4-sulfonatophenyl) porphyrinate ([FeIII(TPPS)]3-) or iron(III) protoporphyrin IX, respectively. The kinetic rate constant for the reaction of ([FeIII(TPPS)]3-) with sodium trioxodinitrate (kon) was estimated to be 1.00 +/- 0.04 x 107 M-1 s-1. As well as resulting in a versatile method for obtaining ferrous nitrosyl porphyrins, the reaction points at ferric porphyrins as efficient nitroxyl traps and provides a tool to model nitroxyl reactivity toward hemeproteins.     

Bromo-substituted Mn(II) and Mn(III)-tetraarylporphyrins: synthesis and properties

Abstract

Mono-, tetra-, and octa-bromo substituted Mn(II)- and Mn(III)-tetraarylporphyrins were synthesized by reactions of manganese(II) chloride with corresponding porphyrin ligands or their Cd(II)-complexes in DMF. With the use of the metal exchange reaction, the time of the Mn-porphyrins formation is significantly reduced with increase in yield of final products in comparison with the complexation reaction. Mn(III)-tetraarylporphyrins reduce to the Mn(II)-porphyrins in DMF in the presence of NaOH and in pure DMF. The obtained compounds were identified using UV–vis and ¹H NMR spectroscopy, mass-spectrometry, and elemental analysis.     

meso-四(烷氧基苯基)卟啉及其金属络合物的波谱研究

采用^1H NMR、MS、IR、UV、元素分析等分析测试表征手段确证了所合成的10个系列卟啉及其金属络合物的结构,研究了不同位置、不同链长烷氧基四苯基卟啉和不同金属离子卟啉络合物的结构与^1HNMR、IR和UV等波谱之间的关系,总结了卟啉配体及其金属络合物的^1H NMR、IR和UV判据,报道和解释了meso-四(烷氧基苯基)卟啉铜、锰络合物和meso-四(邻烷氧基苯基)卟啉钴络合物的^1H NMR研究结果,通过MS、^1H NMR、IR、UV、元素分析确证了我们所合成的铁卟啉为μ-氧桥联夹心二聚体结构,且存在两种典型构象,导致同系列络合物有四种类型^1H NMR谱图。     

Laser flash photolysis generation and kinetic studies of porphyrin-manganese-oxo intermediates. Rate constants for oxidations effected by porphyrin-Mn(V)-oxo species and apparent disproportionation equilibrium constants for porphyrin-Mn(IV)-oxo species

Porphyrin-manganese(V)-oxo and porphyrin-manganese(IV)-oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrin-manganese(III) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15,20-tetrakis(4-methylpyridinium)porphyrin (TMPyP). The order of reactivity for (porphyrin)Mn(V)(O) derivatives in self-decay reactions in acetonitrile and in oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)Mn(V)(O) in acetonitrile are k = 6.1 x 10(5) M(-1) s(-1) for cis-stilbene and k = 1.4 x 10(5) M(-1) s(-1) for diphenylmethane, and the kinetic isotope effect in oxidation of ethylbenzene and ethylbenzene-d(10) is k(H)/k(D) = 2.3. Competitive oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found in the LFP studies of (porphyrin)Mn(V)(O) derivatives. The apparent rate constants for reactions of (porphyrin)Mn(IV)(O) species show inverted reactivity order with (TPFPP) < (TMPyP) < (TPP) in reactions with cis-stilbene, triphenylamine, and triphenylphosphine. The inverted reactivity results because (porphyrin)Mn(IV)(O) disproportionates to (porphyrin)Mn(III)X and (porphyrin)Mn(V)(O), which is the primary oxidant, and the equilibrium constants for disproportionation of (porphyrin)Mn(IV)(O) are in the order (TPFPP) < (TMPyP) < (TPP). The fast comproportionation reaction of (TPFPP)Mn(V)(O) with (TPFPP)Mn(III)Cl to give (TPFPP)Mn(IV)(O) (k = 5 x 10(8) M(-1) s(-1)) and disproportionation reaction of (TPP)Mn(IV)(O) to give (TPP)Mn(V)(O) and (TPP)Mn(III)X (k approximately 2.5 x 10(9) M(-1) s(-1)) were observed. The relative populations of (porphyrin)Mn(V)(O) and (porphyrin)Mn(IV)(O) were determined from the ratios of observed rate constants for self-decay reactions in acetonitrile and oxidation reactions of cis-stilbene by the two oxo derivatives, and apparent disproportionation equilibrium constants for the three systems in acetonitrile were estimated. A model for oxidations under catalytic conditions is presented.     

High-frequency and -field EPR investigation of a manganese(III) N-confused porphyrin complex, [Mn(NCTPP)(py)2

We report the first high-frequency and -field electron paramagnetic resonance (HFEPR) study of a Mn(III) N-confused porphyrin (NCP) complex (NCP is also known as inverted porphyrin or 2-aza-21-carbaporphyrin). We have found a striking variation in the electronic properties of the S = 2 Mn(III) ion coordinated by NCP compared to other Mn(III) porphyrinoid complexes. Thus, inversion of a single pyrrole ring greatly changes the equatorial ligand field exerted and leads to large magnitudes of both the axial and rhombic zero-field splitting [respectively, D = -3.084(3) cm(-1), E = -0.608(3) cm(-1)], which are unprecedented in other Mn(III) porphyrinoids.     

Reactivity of dioxoosmium(VI) porphyrins toward arylhydrazine. Isolation of hydrazidoosmium and amidoosmium porphyrins

Reactions of dioxoosmium(VI) porphyrins [Os(VI)(Por)O(2)] with excess 1,1-diphenylhydrazine in tetrahydrofuran at ca. 55 degrees C for 15 min afforded bis(hydrazido(1-))osmium(IV) porphyrins [Os(IV)(Por)(NHNPh(2))(2)] (1a, Por = TPP (meso-tetraphenylporphyrinato dianion); 1b, Por = TTP (meso-tetrakis(p-tolyl)porphyrinato dianion)), hydroxo(amido)osmium(IV) porphyrins [Os(IV)(Por)(NPh(2))(OH)] (2a, Por = TPP; 2b, Por = TTP), and bis(hydrazido(2-))osmium(VI) porphyrin [Os(VI)(Por)(NNPh(2))(2)] (3c, Por = TMP (meso-tetramesitylporphyrinato dianion)). The same reaction under harsher conditions (in refluxing tetrahydrofuran for ca. 1 h) gave a nitridoosmium(VI) porphyrin, [Os(VI)(Por)(N)(OH)] (4b, Por = TTP). Oxidation of 1a,b with bromine in dichloromethane afforded bis(hydrazido(2-)) complexes [Os(VI)(TPP)(NNPh(2))(2)] (3a) and [Os(VI)(TTP)(NNPh(2))(2)] (3b), respectively. All the new osmium porphyrins were identified by (1)H NMR, IR, and UV-vis spectroscopy and mass spectrometry; the structure of 2b was determined by X-ray crystallography (Os-NPh(2) = 1.944(6) A, Os-OH = 1.952(5) A).     

Synthesis of Vinylene-Co,N-Linked Multi(porphyrin)s by the Addition of Free-Base Porphyrins to a C(2)H(2) Complex of Cobalt(III) Porphyrin and Their Oxidative Rearrangement to Vinylene-N,N'-Linked Multi(porphyrin)s

The nucleophilic addition reaction of a pyrrole nitrogen of free-base porphyrins to a pi-complexed acetylene ligand in a cationic Co(III) porphyrin intermediate afforded good yields of vinylene-Co,N'-linked bis(porphyrin)s, (Por)Co(III)-CH=CH-(N-Por)H(2). N-substituted porphyrin free bases are N-vinylated regioselectively at the pyrrole adjacent to the original N-substituted pyrrole in this reaction. Tris- and tetrakis(porphyrin)s have been prepared by reacting a vinylene-N,N'-linked bis(meso-tetraarylporphyrin) with (OEP)Co(III)(H(2)O)(2)ClO(4) (OEP: octaethylporphyrin dianion) and acetylene. The tetrakis(porphyrin) proved to be a 1:1 mixture of C(i)()- and C(2)-symmetric regioisomers. These organometallic Co(III) complexes underwent facile oxidative migration of the Co-bound vinyl group to a porphyrin pyrrole nitrogen when treated with Fe(III) salts or HClO(4) to provide moderate to good yields of Co(II) vinylene-N,N'-linked multi(porphyrin) complexes. (Vinylene-N,N')bis(porphyrin) free bases with combinations of different porphyrins have been obtained by this procedure. The homobinuclear (2Co(II), 2Cu(II), and 2Zn(II)) and heterobinuclear (Co(II)Cu(II) and Co(II)Zn(II)) complexes have been prepared and characterized spectroscopically. The single-crystal X-ray analysis of (CH=CH-N,N')[(OEP)Co(II)Cl][(TPP)Zn(II)Cl] (TPP: meso-tetraphenylporphyrin dianion) showed a face-to-face structure with an average inter-ring separation of 4.39 ? (triclinic P&onemacr;; Z = 2; a = 14.806(4), b = 18.703(10), c = 13.796(3) ?, alpha = 97.69(3), beta = 99.57(2), gamma = 96.74(3) degrees ).     

Metalloporphyrins as chemical shift reagents: the unambiguous NMR characterization of the cis- and trans-isomers of meso-(bis)-4′-pyridyl-(bis)-4′-carboxymethylphenylporphyrins

The condensation of pyrrole with 4-pyridylcarboxyaldehyde and methyl 4-formyl benzoate under Adler-Longo conditions yielded the series of meso-(4′-pyridyl)/(4′-carboxymethylphenyl)porphyrins as a mixture. Careful column chromatography afforded each isomer in pure form. In this paper we focus on the two bis-substituted isomeric meso-porphyrins, 5,10-bis(4′-pyridyl)-15,20-bis(4′-carboxymethylphenyl)porphyrin and 5,15-bis(4′-pyridyl)-10,20-bis(4′-carboxymethylphenyl)porphyrin, respectively, 4′-cis and 4′-transDPyDMeP. The assignment of the geometry of the two isomers was performed by ¹H NMR spectroscopy on the trinuclear adducts [(4′-cisDPyDMeP){Ru(TPP)(CO)}₂] and [(4′-transDPyDMeP){Ru(TPP)(CO)}₂], obtained by selective coordination of [Ru(TPP)(CO)(EtOH)] (TPP=tetraphenylporphyrin) to the peripheral nitrogen atoms. The axially bound ruthenium porphyrins act as chemical shift reagents on the central porphyrin, allowing a clear distinction of the pyrrole proton resonances and consequent unambiguous assignment of the geometry of each isomer based upon symmetry considerations.     

Synthesis, characterization, and reactivities of manganese(V)-oxo porphyrin complexes

The reactions of manganese(III) porphyrin complexes with terminal oxidants, such as m-chloroperbenzoic acid, iodosylarenes, and H(2)O(2), produced high-valent manganese(V)-oxo porphyrins in the presence of base in organic solvents at room temperature. The manganese(V)-oxo porphyrins have been characterized with various spectroscopic techniques, including UV-vis, EPR, 1H and 19F NMR, resonance Raman, and X-ray absorption spectroscopy. The combined spectroscopic results indicate that the manganese(V)-oxo porphyrins are diamagnetic low-spin (S = 0) species with a longer, weaker Mn-O bond than in previously reported Mn(V)-oxo complexes of non-porphyrin ligands. This is indicative of double-bond character between the manganese(V) ion and the oxygen atom and may be attributed to the presence of a trans axial ligand. The [(Porp)Mn(V)=O](+) species are stable in the presence of base at room temperature. The stability of the intermediates is dependent on base concentration. In the absence of base, (Porp)Mn(IV)=O is generated instead of the [(Porp)Mn(V)=O](+) species. The stability of the [(Porp)Mn(V)=O](+) species also depends on the electronic nature of the porphyrin ligands: [(Porp)Mn(V)=O](+) complexes bearing electron-deficient porphyrin ligands are more stable than those bearing electron-rich porphyrins. Reactivity studies of manganese(V)-oxo porphyrins revealed that the intermediates are capable of oxygenating PPh(3) and thioanisoles, but not olefins and alkanes at room temperature. These results indicate that the oxidizing power of [(Porp)Mn(V)=O](+) is low in the presence of base. However, when the [(Porp)Mn(V)=O](+) complexes were associated with iodosylbenzene in the presence of olefins and alkanes, high yields of oxygenated products were obtained in the catalytic olefin epoxidation and alkane hydroxylation reactions. Mechanistic aspects, such as oxygen exchange between [(Porp)Mn(V)=16O](+) and H(2)(18)O, are also discussed.