Search

In this work, we report the assignment of the majority of the ferriheme resonances of high-spin nitrophorins (NPs) 1 and 4 and compare them to those of NP2, published previously. It is found that the structures of the ferriheme complexes of NP1 and NP4, in terms of the orientation of the histidine imidazole ligand, can be described with good accuracy by NMR techniques and that the angle plot proposed previously for the high-spin form of the NPs (Shokhireva, T. Kh.; Shokhirev, N. V.; Walker, F. A. Biochemistry 2003, 42, 679-693) describes the angle of the effective nodal plane of the axial histidine imidazole in solution. There is an equilibrium between the two heme orientations (A and B), which depends on the heme cavity shape, which can be altered by mutation of amino acids with side chains (phenyl vs tyrosyl) near the potential position where a heme vinyl group would be in one of the isomers. The A:B ratio can be much more accurately measured by NMR spectroscopy than by X-ray crystallography. [ABSTRACT FROM AUTHOR]

Presents information on a study which examines the synthesis and characterization of a series of metalated ethene. Methods and materials employed in the study; Results of experiments; Conclusion of the study.

Oxidation of CpCr[(XylNCMe)2CH] (Xyl = 2,6-Me2C6H3) with pyridine N-oxide or air generated the μ-oxo dimer, {CpCr[(XylNCMe)2CH]}2(μ-O). The μ-oxo dimer was converted to paramagnetic Cr(III) CpCr[(XylNCMe)2CH](X) complexes (X = OH, O2CPh, Cl, OTs) via protonolysis reactions. The related Cr(III) alkoxide complexes (X = OCMe3, OCMe2Ph) were prepared by salt metathesis and characterized by single crystal X-ray diffraction. The interconversion of the Cr(III) complexes and their reduction back to Cr(II) with Mn powder were monitored using UV-vis spectroscopy. The related CpCr[(DepNCMe)2CH] (Dep = 2,6-Et2C6H3) Cr(II) complex was studied for catalytic oxygen atom transfer reactions with PPh3 using O2 or air. Both Cr(II) complexes reacted with pyridine N-oxide and γ-terpinene to give the corresponding Cr(III) hydroxide complexes. When CpCr[(DepNCMe)2CH] was treated with pyridine N-oxide in benzene in the absence of hydrogen atom donors, a dimeric Cr(III) hydroxide product was isolated and structurally characterized, apparently resulting from intramolecular hydrogen atom abstraction of a secondary benzylic ligand C-H bond followed by intermolecular C-C bond formation. The use of very bulky hexaisopropylterphenyl ligand substituents did not preclude the formation of the analogous μ-oxo dimer, which was characterized by X-ray diffraction. Attempts to develop a chromium-catalyzed intermolecular hydrogen atom transfer process based on these reactions were unsuccessful. The protonolysis and reduction reactions of the μ-oxo dimer were used to improve the previously reported Cr-catalyzed radical cyclization of a bromoacetal. [ABSTRACT FROM AUTHOR]

In this work we report the assignment of the majority of the ferriheme resonances of low-spin nitrophorins (NP) 1 and 4 and compare them to those of NP2, published previously. It is found that the structure of the ferriheme complexes of NP1 and NP4, in terms of the orientation of the ligand(s), can be determined with good accuracy by NMR techniques in the low-spin forms and that angle plots proposed previously (Shokhirev, N. V.; Walker, F. A. J. Biol. Inorg. Chem. 1998, 3, 581-594) describe the angle of the effective nodal plane of the axial ligands in solution. The effective nodal plane of low-spin NP1, NP4, and NP2 complexes is in all cases of imidazole and histamine complexes quite similar to the average of the His-59 or -57 and the exogenous ligand angles seen in the X-ray crystal structures. For the cyanide complexes of the nitrophorins, however, the effective nodal plane of the axial ligand does not coincide with the actual histidine-imidazole plane orientation. This appears to be a result of the contribution of an additional source of asymmetry, the orientation of one of the zero-ruffling lines of the heme. Probably this effect exists for the imidazole and histamine complexes as well, but because the effect of asymmetry that occurs from planar exogenous axial ligands is much larger than the effect of heme ruffling the effect of the zero-ruffling line can only be detected for the cyanide complexes, where the only ligand plane is that of the proximal histidine. The three-dimensional structures of the three NP-CN complexes, including that of NP2-CN reported herein, confirm the high degree of ruffling of these complexes. There is an equilibrium between the two heme orientations (A and B) that depends on the heme cavity shape and changes somewhat with exogenous axial ligand. The A:B ratio can be much more accurately measured by NMR spectroscopy than by X-ray crystallography. [ABSTRACT FROM AUTHOR]

A series of boron-disubstituted O-BODIPYs were synthesized, and their structures and spectroscopic properties were investigated using both computational and experimental methods. Three methods were investigated for the preparation of 4,4-dimethoxy-BODIPYs bearing electron-donating or electron-withdrawing 8-aryl groups: method A employs refluxing in the presence of NaOMe/MeOH, method B uses AlCl3 in refluxing dichloromethane followed by addition of methanol as nucleophile, and method C involves activation of the BODIPYs using TMSOTf in refluxing toluene followed by addition of methanol. The yields obtained depend on the method used and the structure of the starting BODIPYs; for example, 1a and 3a were most efficiently prepared using method C (98 and 70%, respectively), while 2a was best prepared by method A (50%). Methods B and C were employed for the synthesis of seven new 4,4-dialkoxy-BODIPYs. 4,4-Dipropargyloxy-BODIPY 1e reacted under Cu(I)-catalyzed alkyne-azide Huisgen cycloaddition conditions to produce 4,4-bis(1,2,3-triazole)-BODIPY 4 in 78% yield. The substitution of the fluorides for alkoxy groups on the BODIPYs had no significant effect on the absorption and emission wavelengths but altered their fluorescence quantum yields. Among this series of dialkoxy-BODIPYs, the 4,4-dipropargyloxy 1e and its corresponding bis(1,2,3-triazole) 4 show the largest quantum yields in toluene and THF, respectively. [ABSTRACT FROM AUTHOR]

Electrochemical studies of the oxidation of dodecasubstituted and highly nonplanar nickel porphyrins in a noncoordinating solvent have previously revealed the first nickel(III) porphyrin dication. Herein, we investigate if these nonplanar porphyrins can also be used to detect the so far unobserved copper(III) porphyrin dication. Electrochemical studies of the oxidation of (DPP)Cu and (OETPP)Cu show three processes, the first two of which are macrocycle-centered to give the porphyrin dication followed by a CuII/CuIII process at more positive potential. Support for the assignment of the CuII/CuIII process comes from the linear relationships observed between E1/2 and the third ionization potential of the central metal ions for iron, cobalt, nickel, and copper complexes of (DPP)M and (OETPP)M. In addition, the oxidation behavior of additional nonplanar nickel porphyrins is investigated in a noncoordinating solvent, with nickel meso-tetraalkylporphyrins also being found to form nickel(III) porphyrin dications. Finally, examination of the nickel meso-tetraalkylporphyrins in a coordinating solvent (pyridine) reveals that the first oxidation becomes metal-centered under these conditions, as was previously noted for a range of nominally planar porphyrins. [ABSTRACT FROM AUTHOR]

The phenyl-iron complex of 5,10,15-tritolylcorrole was prepared by reaction of the starting chloro-iron complex with phenylmagnesium bromide in dichloromethane. The organometallic complex was fully characterized by a combination of spectroscopic methods, X-ray crystallography, and density functional theory (DFT) calculations. All of these techniques support the description of the electronic structure of this phenyl-iron derivative as a low-spin iron(IV) coordinated to a closed-shell corrolate trianion and to a phenyl monoanion. Complete assignments of the ¹H and 13C NMR spectra of the phenyl-iron derivative and the starting chloro-iron complex were performed on the basis of the NMR spectra of the regioselectively β-substituted bromo derivatives and the DFT calculations. [ABSTRACT FROM AUTHOR]

Functionalization of the &bgr;-pyrrolic positions of the corroie macrocycle with --NO2 groups Is limited at present to metallocorrolates due to the instability exhibited by corroie free bases under oxidizing conditions. A careful choice of the oxidant can limit the transformation of corroles into decomposition products or isocorroie species, preserving the corroie aromatidty, and thus allowing the insertion of nitro groups onto the corroie framework Here we report results obtained by reacting 5,10,lS-tritolylcorroIe (TTCorrH3) with the AgNO2/NaNO2 system, to give mono- and dinitrocorrole derivatives when stoichiometry is carefully controlled. Reactions were found to be regioselective, affording the 3-NO2TTCorrH3 and 3,17-(NO2)2TTCorrH3 isomers as the main products in the case of mono- and disubstitution, in 53 and 20% yields, respectively. In both cases, traces of other mono- and disubstituted isomers were detected, which were structurally characterized by X-ray crystallography. The influence of the &bgr;-nitro substituants on the corroie properties is studied in detail by UV--visible, electrochemical, and spectroelectrochemical characterization of these fimctionalized corroies. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of the ground and excited state properties of these &bgr;-nitrocorrole derivatives also afforded significant information, dosely matching the experimental observations. It is found that the &bgr;-NO2 substituents conjugate with the Ä-aromatic system of the macrocycle, which initiates significant changes in both the spectroscopic and redox properties of the so fimctionalized corroies. This effect is more pronounced when the nitro group is introduced at the 2-position, because in this case the conjugation is, for steric reasons, more efficient than in the 3-nitro isomer. [ABSTRACT FROM AUTHOR]

Two different methods for the regioselective nitration of different mesatriarylcorroles leading to the corresponding β-substituted nitrocorrole iron complexes have been developed. A two-step procedure affords three Fe(III) nitrosyl products-the unsubstituted corrole, the β-nitrocorrole, and the 3,17-dinitrocorrole. In contrast, a one-pot synthetic approach drives the reaction almost exclusively to formation of the iron nitrosyl 3,17 dinitrocorrole. Electron-releasing substituents on the meso-aryl groups of the triarylcorroles induce higher yields and longer reaction times than what is observed for the synthesis of similar triarylcorroles with electron-withdrawing functionalities, and these results can be confidently attributed to the Ihcile formation and stabilization of an intermediate iron corrole sr-cation radical. Electron-withdrawing substituents on the meso-aryl groups of triarylcorrole also seem to labilize the axial nitrosyl group which, in the case of the pentafluorophenylcorrole derivative, results in the direct formation of a disubstituted iron μ-oxo dimer complex. The influence of meso-aryl substituents on the progress and products of the nitration reaction was investigated. In addition, to elucidate the most important factors which influence the redox reactivity of these different iron nitrosyl complexes, selected compounds were examined by cyclic voltammetry and thin-layer UV-visible or PTIR spectroelectrochemistry in CH2CI2. [ABSTRACT FROM AUTHOR]

Copper and germanium complexes of β-substituted nitrocorroles were reacted with 4-amino-4H-1,2,4-triazole to give the corresponding β-amino-β-nitro derivatives, in moderate to good yields. This is the first successful example of a vicarious nucleophilic substitution performed on corrole derivatives, because the same reaction carried out on silver complexes afforded the corresponding 6-azahemiporphycenes by way of corrole ring expansion. The first step of this work is related to the modification of a synthetic protocol for preparation of the β-substituted nitro corroles. The nitration reaction was carried out on a copper corrole using NaNO2 as the primary source of NO2- coupled with AgNO2 used as oxidant. By variation of the molar ratio of the reagents it was possible to direct the product distribution toward mono- and dinitro derivatives. The reaction between mono- and dinitro derivatives of (TtBuCorrCu) with 4-amino-4H-1,2,4-triazole gave good results, leading to the isolation of 2-(NH2)-3-(NO2)-TtBuCorrCu and 2,18-(NH2)2-3,17-(NO2)2-TtBuCorrCu in moderate yields. To elucidate factors that influence the reaction, and to highlight the different behavior observed for different metal complex substrates, the electrochemistry of three copper complexes, TtBuPCorrCu, (NO2)TtBuPCorrCu, and (NO2)2TtBuPCorrCu, was studied by cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry. The nitro groups on (NO2)xTtBuPCorrCu are highly electron-withdrawing, which leads not only to a substantial positive shift of all redox potentials but also to a unique redox behavior and UV-vis spectrum of the singly reduced product as compared to the parent compound, TtBuPCorrCu. Finally, the amination reaction was carried out on a Ge(IV) nitrocorrolate, giving in good yield the 2-amino-3-nitroderivative, which was structurally characterized by single crystal X-ray crystallography. [ABSTRACT FROM AUTHOR]

A series of free-base and metalated isocorroles represented as (TT-n-iso-Cor)H2 and (TT-n-iso-Cor)MII, where n = 5 or 10 and M = Ni or Cu, were synthesized and characterized by electrochemistry and spectroelectrochemistry in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate. The metalation of the free-base macrocycles with CoII, MnIII, or ZnII was also attempted but was unsuccessful. Six isocorroles were isolated and shown to undergo two stepwise oxidations to give p-cation radicals and dications in CH2Cl2, with the most stable products being obtained in the case of the 10-substituted derivatives. The same isocorroles could also be reduced by one or two electrons, but the initial one-electron addition products are unstable and undergo a rapid chemical reaction giving a reduced corrole or corrole-like product, which could be reoxidized to the corresponding (TTCor)M at a controlled positive potential. This series of reactions effectively illustrates an isocorrole to corrole conversion upon reduction and reoxidation and was monitored by both electrochemistry and thin-layer spectroelectrochemistry. [ABSTRACT FROM AUTHOR]

The reaction of 5,10,15-triarylcorrole with 4-amino-4H-1,2,4-titazole provides another example of corrole ring expansion to give the corresponding 6-azahemiporphycene, a novel porphyrin analogue. The facile oxidation of the corrole ring is a required step for the ring expansion and for this reason the reaction fails in the ease of corroles bearing meso-phenyl groups carrying electron-withdrawing substituents. Steric requirements also limited the scope of the reaction, which is not successful in the ease of 2,6-disubstituted meso-aryl corroles. The occurrence of an initial oxidation is further supported by formation of the 6-azahemiporphycene derivative when the reaction is carried out under the same conditions, using a 5- or a lO-isocorrole as starting material. 1H NMR spectra and X-ray crystal characterization of 6-azahemiporphycene evidenced the presence of an intramolecular N—H ⋯ N hydrogen bond in the inner core of the macrocycle, while photophysical characterization confirmed the aromatic character of the novel macrocycle, showing an intense Soret-like band around 410 nm in the absorption spectrum. The fluorescence emission is very modest, and 6-azahemiporphycene showed higher photostability than the corresponding corrole species. Different metal complexes of 6-azahemiporphycene were prepared following synthetic protocols usually exploited for the preparation of metalloporphyrins, demonstrating good coordination properties for the macrocycte. Both the free-base and metal derivatives were characterized by cyclic voltammetry and spectroelectrochemistry in dichioromethane and benzonitrite. To further detail the behavior of this novel macrocycle, density functional theory (DFT) calculations were carried out on the basic structure of 6-azahemiporphycene with the aim of assessing aromaticity and tautomerism, as well as calculating its stability with respect to the 5-aza isomer. [ABSTRACT FROM AUTHOR]

Several procedures for the demetalation of silver(III) corrolates have been tested. Acidic conditions induce removal of the silver ion but they can also promote concomitant oxidation of the corrole nucleus to an isocorrole species, the degree of which will depend upon the specific acidic media. This oxidation cannot be completely avoided by addition of hydrazine, particularly in the case of 3-NO2 substituted complexes which are quantitatively converted into the corresponding 3-NO2, 5-hydroxy isocorroles upon silver ion removal. Several β-nitro isocorrole products were isolated, and one was structurally characterized. Electrochemical and chemical reductive methods for silver(III) corrolates demetalation were then tested with the aim to avoid the formation of isocorroles. While reaction with sodium borohydride was shown to be quite effective to demetalate unsubstituted silver corrolates this was not the case for the β-nitro derivatives where the peripheral nitro group is reduced by borohydride giving the corresponding 3-amino free base corrole species. For the β-nitro corrole silver complexes, a successful approach was obtained using DBU/THF solutions which afforded the 3-NO2 corrole free-base compound as a single reaction product in good yield. These conditions were also effective for unsubstituted corroles although longer reaction times were necessary in this case. To study in greater detail the corrole demetalation behavior, selected Ag(III) derivatives were characterized by cyclic voltammetry in pyridine, and the demetalation products spectrally characterized after controlled potential reduction in a thin-layer spectroelectrochemical cell. Electrochemical and chemical reductive methods are effective for silver(III) corrolate demetalations, avoiding both a decomposition of the starting complex and the formation of isocorrole species, observed in acidic conditions. For β-nitro corrole silver complexes the successful approach is obtained using DBU/THF solutions because the corresponding 3-amino free base corrole species is obtained in the reductive conditions. Selected Ag(III) derivatives have been characterized by cyclic voltammetry in pyridine, and the demetalation products spectrally characterized. [ABSTRACT FROM AUTHOR]

The reaction between germanium(IV) meso-triphenylcorrolates and nitrate salts affords the corresponding β-nitro substituted corroles in good yield. Chromatographic separation of the crude reaction mixtures enables isolation of a μ-oxo dimer along with the corresponding monomers bearing a hydroxy or methoxy group at an axial position of the germanium central metal ion. Depending on the reaction conditions, mono- or dinitro substituted complexes can be obtained. The substitution is highly regioselective in each case, giving only the 3-nitro or 3,17-dinitro derivative among the different possible isomers. Five of the synthesized complexes were examined by cyclic voltammetry and UV-visible spectroelectrochemistry in dichloromethane, and the dinitro μ-oxo dimer is structurally characterized. [ABSTRACT FROM AUTHOR]

The reaction of meso-triarylcorroles with AgNO2 proceeds with concomitant metalation and peripheral substitution to give the corresponding nitro-substituted silver(III) corrole complex. The substitution is highly regioselective, giving only the corresponding 3-nitro derivative, among the different possible isomers. The results obtained indicate that the reaction intermediate is the π-cation radical of the complex, which is then attacked by nitrite ion. This was proven by the reaction of the copper corrole complexes with NaNO2: in this case, the nitration reaction proceeded without the addition of an oxidant, because of the π-cation radical character of the copper complex. The reaction is also successful in the case of 2,3,17,18-tetraethyl-8,12-diacetoxymethyl-7,13-dimethylcorrole (AMC0rH3), with the formation of the meso-substituted silver corrole derivative (NO2)3AMCorAg (fully characterized by X-ray crystallography), the first of its kind to be reported. Two of the corroles are characterized by cyclic voltammetry and spectroelectrochemistry in dichloromethane, and the site of electron transfer is elucidated. [ABSTRACT FROM AUTHOR]

β,β′-Fused monoruthenocenylporphyrins, Cp*Ru(III)[1,2-[M(II)-5, 10,1 5,20-tetrakis(3,5-di-tert-butylphenyl)-porphyrinato]-3-methyl-cyclopentadienide] (M = Ni (20), Cu (21), Zn (22)), and bisferrocenoporphyrins, Fe(II) bis[1,2-[M(II)-5,10,15,20-tetraphenylporphyrinato]-3-methyl-cyclopentadienide] (M Ni (24), Cu (25), Zn (26)), were synthesized and characterized. A novel synthetic approach to β,β′-fused porphyrins through Pd(0)-catalyzed [3 + 2] cycloaddition was implemented in this work. UV-vis spectra of these compounds show largely broadened and red-shifted bands (relative to their precursors) indicating potential electronic communication between the attached organometallic moiety and the porphyrin core. The electrochemistry of these molecules suggests significant electronic interactions between the metallocene and metalloporphyrin in molecules 20 and 24. The crystal structure of the bisferrocenoporphyrin 26, Fe(II) bis[1,2-[Zn(II)-5,10,1 5,20-tetraphenylporphyrinato]-3-methyl-cyclopentadienide], was determined: {Cp2Fe[ZnTPP(THF)]2}{Cp2Fe[ZnTPP(THF)ZnTPP(MeOH)]}•3MeOH•6THF, M = 3804.35, monoclinic, space group P21/c, a = 33.327(5) Å, b = 19.145(3) Å, c 29.603(5) Å, β = 106.309(2)°, V = 18128(5) ų, z = 4. In this molecule, one porphyrin ring is rotated by about 72° with respect to the other in the 5-fold axis of the Cp ring. [ABSTRACT FROM AUTHOR]

The high-yield preparation of metallo-benzoylbiliverdins 9, 10, and 11 from either oxidation of dodeca-substituted porphyrin 6 in the presence of NaNO2/TFA and air followed by metalation or by reaction of the Ni(II) or Cu(II) complexes of 6 with m-chloroperoxybenzoic acid in pyridine under air is reported. The X-ray structures of complexes 9 and 10 and the electrochemistry and spectroelectrochemistry of metallo-benzoylbiliverdins 9–11 are presented and discussed. [ABSTRACT FROM AUTHOR]

Examines the relationship between the aryl-porphyrin rotational barrier and the core substituent M in some novel dodecaarylporphyrins and octaphenylphorphyrins, where steric crowding of the peripheral groups always results in a very nonplanar macrocycle. Differences in the nonplanar conformation of the macrocycle as a function of M; Deformability of the macrocycle along a nonplanar distortion mode.

Examines the electrochemistry of 29 nickel(II) porphyrins in dichloromethane in order to determine the electronic and structural factors which govern electron-transfer processes in porphyrins. Reversible half-wave potentials for the reduction and oxidation of the porphyrins; Effect of substituents on the redox behavior of the porphyrin ring; Electronic and structural effects on half-wave potentials.

Examines the luminescence properties of gallium-metal cofacial anthracene-bridged diporphyrins. Molecular structure of cofacial nature of prophyrin macrocycles and axial methoxyl ligands bound on unhindered porphyrin faces; Ultraviolet-visible spectrum of gallium and ruthenium derivatives and free bases; Absorption and fluorescence spectra in ethanol.

Compares factors that affect the stabilization of open-shell cyclopentadienyl-molybdenum(II) complexes through a density functional study. Bond dissociation energies; Pi donation from ligand lone pairs; Extent of the stabilization; Steric interactions.

Analysis the effect of the symmetry of the substitution pattern and subsequent orientations on the out-of-plane and in-plane distortions of the prophyrin macrocycle. Methodology used in the analysis; Details on the significant nonplanar distortions of the porphyrin macrocycle; Implications of the findings.

Presents a study which investigated the influence of metal size on the macrocyclic conformation of a series of 5,15-disubstituted metalloporphyrins, using X-ray crystallography molecular mechanics and resonance Raman spectrocopy. Examination of the molecular simulations and crystal structures; Materials used to study the synthesis of the 5,15-disubtituted metalloporphyrins; Findings of the study.

Provides information on an experimental study reporting on the electrochemistry of nine different manganese(III) dodecaphenylporphyrins containing halogen or CF3 groups on the phenyl rings of the porphyrin macrocycle. Methodology used to conduct the study; Information on the X-ray structural determination of (DPPF20)MNCl; Results of the study; Discussion on the results.

Analyzes the conformations of symmetrically and asymmetrically deca- and undecasubstituted porphyrins bearing meso-alkyl or -aryl groups. Out of plane distortion in sterically crowded decasubstituted free-base porphyrins; Amount on in-plane distortion.

The reaction of 2,2'-bipyridine (bpy) with monomeric chromium(II) precursors was used to prepare the S = 1 complexes Cr(tBu-acac)2(bpy) (1) and (Ã5-Cp)(η¹-Cp)Cr(bpy) (3), as well as the S = 2 compound Cr[N(SiMe3)2]2(bpy) (4). The crystallographically determined bond lengths indicate that die bpy ligands in 1 and 3 are best regarded as radical anions, while 4 shows no structural evidence for electron transfer from Cr11 to the neutral bpy ligand. [ABSTRACT FROM AUTHOR]