Synthesis, spectroscopy, and reactivity of meso-unsubstituted azuliporphyrins and their heteroanalogues. Oxidative ring contractions to carba-, oxacarba-, thiacarba-, and selenacarbaporphyrins

This paper reports the first detailed study on meso-unsubstituted azuliporphyrins, an important family of porphyrin-like molecules where one of the usual pyrrole rings has been replaced by an azulene subunit. Although the azulene moiety introduces an element of cross-conjugation, zwitterionic resonance contributors with tropylium and carbaporphyrin substructures give azuliporphyrins diatropic character that falls midway between true carbaporphyrins and nonaromatic benziporphyrins. Protonation affords an aromatic dication where this type of resonance interaction is favored due to the associated charge delocalization. Two different "3 + 1" syntheses of meso-unsubstituted azuliporphyrins have been developed. Acid-catalyzed reaction of readily available tripyrrane dicarboxylic acids with 1,3-azulenedicarbaldehyde, followed by oxidation with DDQ or FeCl(3), affords good yields of azuliporphyrins. Alternatively, azulene reacted with acetoxymethylpyrroles (2 equiv) in refluxing acetic acid/2-propanol to give tripyrrane analogues, and following a deprotection step, condensation with a pyrrole dialdehyde in TFA-CH(2)Cl(2) gave the azuliporphyrin system. The latter approach was also used to prepare 23-thia- and 23-selenaazuliporphyrins. However, reaction of the azulitripyrrane with 2,5-furandicarbaldehyde produced a mixture of three oxacarbaporphyrins in moderate yield. The free base forms of thia- and selenaazuliporphyrins both showed intermediary aromatic character that was considerably enhanced upon protonation. The UV-vis spectra for azuliporphyrins and their heteroanalogues showed four bands between 350 and 500 nm and broad absorptions at higher wavelengths. Addition of TFA gave dications that showed porphyrin-like spectra with Soret bands between 460 and 500 nm. In the presence of pyrrolidine, azuliporphyrins and their heteroanalogues undergo nucleophilic attack on the seven-membered ring to give carbaporphyrin adducts. These systems also undergo oxidative rearrangements under basic conditions with t-BuOOH to give benzocarbaporphyrins. The selenaazuliporphyrin afforded two benzoselenacarbaporphyrins, a previously unknown core-modified carbaporphyrin system. The proton NMR spectra for these compounds showed strong diatropic ring currents with the internal CH resonance upfield above -5 ppm, while the meso-protons resonated downfield near 10 ppm. The UV-vis spectra were also porphyrin-like and gave strong Soret bands at ca. 440 nm.     

Conjugated macrocycles related to the porphyrins. 21. Synthesis,spectroscopy, electrochemistry,and structural characterization of carbaporphyrins

The "3 + 1" variant of the MacDonald condensation has been shown to be an excellent methodology for synthesizing carbaporphyrins. In particular, 1,3-indenedicarbaldehyde condenses with tripyrranes in the presence of TFA to give, following oxidation with DDQ, a series of benzocarbaporphyrins in excellent yields. Triformylcyclopentadienes also afford carbaporphyrin products, albeit in low yields ranging from 5 to 8%. These hybrid bridged annulene structures have porphyrin-like electronic absorption spectra with strong Soret bands near 420 nm and a series of Q-bands through the visible region. The proton NMR spectrum confirms the presence of a strong diamagnetic ring current, and the meso-protons show up at 10 ppm, while the internal CH is shielded to approximately -7 ppm. Carbaporphyrins undergo reversible protonation with TFA. Initial addition of acid affords a monocation, although mixtures of protonated species are observed in the presence of moderate concentrations of TFA. However, in the presence of 50% TFA a C-protonated dication is generated. The dications relocate the pi-delocalization pathway through the benzo moiety of benzocarbaporphyrins, and these therefore represent bridged benzo[18]annulenes, although they nevertheless retain powerful macrocyclic ring currents. Carbaporphyrins with fused acenaphthylene and phenanthrene rings have been prepared, and the former demonstrated significantly larger bathochromic shifts in UV-vis spectroscopy that parallel previous observations for acenaphthoporphyrins. A diphenyl-substituted benzocarbaporphyrin 19b was also characterized by X-ray crystallography, and these data show that the macrocycle is reasonably planar although the indene subunit is tilted out of the mean macrocyclic plane by 15.5 degrees. The structural data indicates that the preferred tautomer in the solid state has the two NH's flanking the pyrrolene unit in agreement with previous spectroscopic and theoretical studies. Cyclic voltammetry for carbaporphyrin 19a was more complex than for true porphyrins, showing five anodic waves and two quasi-reversible reductive couples.     

Porphyrins with exocyclic rings. Part 20: Synthesis and spectroscopic characterization of porphyrins with fused 2,1,3-benzoxadiazole and 2,1,3-benzoselenadiazole moieties

Porphyrins with fused 2,1,3-benzoxadiazole and 2,1,3-benzoselenadiazole units were prepared by the ‘3+1’ MacDonald-type methodology. 4-Nitro-2,1,3-benzoxadiazole, 6-chloro-4-nitro-2,1,3-benzoxadiazole and 4-nitro-2,1,3-benzoselenadiazole condensed with isocyanoacetates in the presence of the non-nucleophilic base DBU to give tricyclic pyrrole derivatives in excellent yields. Further cleavage of the ester moieties and decarboxylation afforded α-unsubstituted pyrroles and these were further condensed with 2 equiv of an acetoxymethylpyrrole tert-butyl ester to give crude preparations of tripyrranes. The tert-butyl ester protective groups were cleaved with TFA and following dilution with dichloromethane, ‘3+1’ condensation with a pyrrole dialdehyde, and oxidation with ferric chloride, the heterocyclic ring fused porphyrins were obtained in moderate yields. The yields were lower than expected because of difficulties in preparing required tripyrranes due to the reduced reactivity of the pyrrolic intermediates. The UV-vis spectra of these new porphyrin systems were highly modified showing broadened split Soret bands. In addition, the nickel(II), copper(II) and zinc complexes gave unusual UV-vis spectra with weakened split Soret bands and strong Q-type absorptions above 600 nm. These modified structures show some potential for applications as photosensitizers in photodynamic therapy.     

Synthesis and reactivity of N-methyl and N-phenyl meso-unsubstituted N-confused porphyrins

Condensations of 1-methyl and 1-phenyl-2,4-pyrroledicarbaldehydes with a tripyrrane in TFA-dichloromethane, followed by oxidation with aqueous FeCl(3), gave novel cross-conjugated meso-unsubstituted N-confused porphyrins (NCPs; 12). These porphyrin analogues showed significant diatropic ring currents that were enhanced upon protonation. Reactions with nickel(II) acetate in refluxing DMF, or palladium(II) acetate in acetonitrile, gave good yields of the corresponding nickel(II) or palladium(II) organometallic derivatives 18 and 19. These complexes were stable and the proton NMR spectra showed slightly increased downfield shifts to the external protons. Addition of TFA resulted in C-protonation at the internal carbon to give aromatic cations that showed the inner CH resonance between -2.5 and -4.0 ppm. The nickel(II) cations 20a and 20b slowly underwent demetalation but the related palladium cations 20c and 20d were quite robust and showed no loss of palladium after 1 week at room temperature. Reaction of NCPs 12 with silver(I) acetate gave silver(III) derivatives 21a and 21b where an oxidation had occurred at C-3 to afford a lactam unit. The silver complexes showed strong diatropic ring currents and porphyrin-like UV-vis spectra with a Soret band near 430 nm. N-Methyl NCP 21a also reacted with gold(III) acetate to give the gold(III) NCP 21c, albeit in low yield, and this species showed similar spectroscopic properties to silver(III) NCP 21a. Syntheses of N-phenyl NCP 12b were accompanied by the formation of the 3-oxo derivative 15b, and the related N-methyl product 16a could also be obtained when the reaction mixtures were oxidized with silver(I) acetate under acidic conditions. The proton NMR spectra for these aromatic NCPs in CDCl(3) show the internal CH shifted upfield to near -6.5 ppm, while the external meso-protons are strongly deshielded giving 4 singlets between 9 and 10 ppm. This study demonstrates that meso-unsubstituted NCPs have unusual reactivity and unique spectroscopic properties, and these results complement and extend the work on the much better known meso-tetraaryl NCPs.     

Synthesis of indenoporphyrins, highly modified porphyrins with reduced diatropic characteristics

Indene-fused porphyrins have been synthesized starting from 2-indanone. Knorr-type reaction of oximes derived from benzyl or tert-butyl acetoacetate with 2-indanone and zinc dust in propionic acid gave good yields of indenopyrroles. Treatment with N-chlorosuccinimide then gave 8-chloro derivatives, and these reacted with 5-unsubstituted pyrroles to give dipyrroles incorporating the fused indene unit. Hydrogenolysis of the benzyl ester protective groups afforded the related dicarboxylic acids, but condensation with a dipyrrylmethane dialdehyde under MacDonald "2 + 2" reaction conditions gave poor yields of the targeted indenoporphyrins. However, when an indene-fused dipyrrole was converted into the corresponding dialdehyde with TFA-trimethyl orthoformate and then reacted with a dipyrrylmethane dicarboxylic acid, an indenoporphyrin was isolated in 26% yield. The porphyrin gave a highly modified UV-vis absorption spectrum with three strong bands showing up in the Soret region and a series of Q bands that extended beyond 700 nm. The proton NMR spectrum also showed a significantly reduced diamagnetic ring current where the meso-protons gave resonances near 9.3 ppm instead of typical porphyrin values of 10 ppm. Nickel(II), copper(II), and zinc complexes were also prepared, and these exhibited unusual UV-vis absorption spectra with bathochromically shifted Soret and Q absorptions. The diamagnetic nickel(II) and zinc complexes also showed reduced diatropic character compared to typical nickel(II) and zinc porphyrins.     

Porphyrins with exocyclic rings. 16. Synthesis and spectroscopic characterization of fluoranthoporphyrins, a new class of highly conjugated porphyrin chromophores

Porphyrins with fused aromatic rings are under detailed investigation due to their unique spectroscopic properties. To gain more insights into the effects due to ring annealation on the porphyrin chromophore, a series of fluoranthoporphyrins have been synthesized. Reaction of 3-nitrofluoranthene with isocyanoacetate esters in the presence of a phosphazene base afforded good yields of the fluorantho[2,3-c]pyrrole esters 8. Cleavage of the ester moiety with KOH in ethylene glycol afforded the parent heterocycle 9, and this condensed with 2 equiv of acetoxymethylpyrroles 10 in refluxing acetic acid-2-propanol to afford tripyrranes 11. Following cleavage of the tert-butyl ester protective groups with TFA, "3 + 1" condensation with pyrrole dialdehyde 12 gave the fluoranthoporphyrins 13 in good overall yields. In addition, reaction of tripyrrane 11 with acenaphthopyrrole dialdehyde 16 gave the mixed acenaphthofluoranthoporphyrin 17 in excellent yields. A difluoranthoporphyrin 18 was also prepared via a "2 + 2" MacDonald condensation. Reaction of fluoranthopyrrole 8a with dimethoxymethane in the presence of p-toluenesulfonic acid gave the symmetrical dipyrrylmethane 19, and following ester saponification, this was condensed with a dipyrrylmethane dialdehyde to afford the adj-difluoranthoporphyrin 18. The UV--vis spectra for these fluoranthoporphyrins gave a series of three broadened absorptions in the Soret band region, although the Q-bands were little effected by ring fusion. The nickel(II), copper(II), and zinc chelates were more unusual, showing strong absorptions near 600 nm. Difluoranthoporphyrin 18 showed many of the same spectroscopic features, although the presence of two ring fusions gave rise to an increase in the spectroscopic shifts. The mixed system 17 gave spectra that showed larger red shifts due to the acenaphthylene unit combined with the features due to the fluoranthene rings. This work further demonstrates the utility of aromatic ring fusion in altering the properties of porphyrinoid systems.     

Isolation, Purification and Spectral Characteristics of Soluble Guanylate Cyclase from Bovine Lung *

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New riches in carbaporphyrin chemistry: silver and gold organometallic complexes of benzocarbaporphyrins

The NH-N-NH-N core of the porphyrin system represents one of the best studied and most versatile platforms for coordination chemistry. However, the replacement of one or more of the interior nitrogens with carbon atoms would be expected to diminish the ability of these systems to form metallo derivatives considerably. Despite this expectation, carbaporphyrinoid systems have been shown to form stable organometallic derivatives. Although azuliporphyrins and benziporphyrins act as dianionic ligands, benzocarbaporphyrins are trianionic ligands. Treatment of five different meso unsubstituted benzocarbaporphyrins and two different meso tetraarylbenzocarbaporphyrins with excess silver(I) acetate afforded 65-97% yields of the corresponding silver(III) organometallic derivatives. The insertion of silver metal was confirmed by mass spectrometry and X-ray crystallography. The UV-vis spectra showed a strong Soret band at wavelengths between 437 and 451 nm, together with a series of Q-type bands at longer wavelengths. The new metallo carbaporphyrins demonstrate the presence of a strong diatropic ring current in their proton NMR spectra, and carbon-13 NMR spectroscopy indicates that the derivatives retain a plane of symmetry. The reaction of meso tetraaryl carbaporphyrins with gold(III) acetate afforded the related gold(III) complexes, and these also showed strongly porphyrin-like aromatic characteristics. The UV-vis spectra for the gold complexes again showed a strong Soret band between 437-439 nm, but a secondary band near 400 nm is somewhat intensified for the gold species compared to the spectra for the related silver(III) meso tetrasubstituted carbaporphyrins. The ring currents observed for the gold(III) complexes by proton NMR spectroscopy were comparable to those of the silver(III) derivatives, implying that both series have similar macrocyclic conformations. Cyclic voltammetry was performed on two different carbaporphyrins, their silver(III) derivatives, and a gold(III) complex. The silver complexes display a reversible cathodic wave that is assigned to the Ag(III/II) couple. However, the gold porphyrinoid gave a value for the reductive wave that could be due to a gold(III/II) couple or a ligand-based process.     

Tropiporphyrins, cycloheptatrienyl analogues of the porphyrins: synthesis, spectroscopy, chemistry, and structural characterization of a silver(III) derivative

Tripyrranes were condensed with 1,3,5-cycloheptriene-1,6-dicarbaldehyde in TFA-CH(2)Cl(2) to give, following oxidation with 0.1% aqueous ferric chloride solutions, a series of tropiporphyrins 9. These cycloheptatrienyl analogues of the porphyrins show strong diatropic ring currents by proton NMR spectroscopy where the internal CH gives a resonance at -7.3 ppm, although the meso-protons are not shifted as far downfield as most aromatic porphyrinoid systems. These data indicate that the seven-membered ring distorts the porphyrinoid macrocycle and decreases the overall diatropicity in tropiporphyrins. Addition of trace amounts of TFA to solutions of 9 affords the corresponding aromatic monocations, and at higher acid concentrations a nonaromatic dication is generated. The dication has undergone C-protonation at one of the meso-bridges and has lost the plane of symmetry present in the parent system. This species shows significant downfield shifts to the cycloheptatrienyl protons, indicating that this unit has taken on tropylium character. Tropiporphyrin 9a underwent a Diels-Alder cycloaddition with dimethyl acetylenedicarboxylate in refluxing xylenes to give modest yields of the related adduct. The Diels-Alder adduct 17 showed an increased diatropic ring current where the internal proton shifted beyond -9 ppm, and this indicates that the [18]annulene substructure has flattened out compared to 9a. Diimide reduction of 9a afforded a dihydrotropiporphyrin that also showed a stronger ring current. Tropiporphyrins 9 were also shown to react with silver(I) acetate in the presence of DBU in refluxing pyridine to give the corresponding silver(III) organometallic derivatives. The meso-protons for these metal complexes give proton NMR chemical shift values similar to those for the parent tropiporphyrins, indicating that the macrocycle is still distorted, but the external olefinic protons are shifted downfield compared to 9. A diphenyl-substituted silver(III) derivative 18b was further characterized by X-ray crystallography. This shows that the cycloheptatriene unit takes on a highly twisted geometry that distorts the overall conformation of the porphyrinoid macrocycle.     

Oxybenziporphyrins, oxypyriporphyrins, benzocarbaporphyrins, and their 23-oxa and 23-thia analogues: synthesis, spectroscopic characterization, metalation, and structural characterization of a palladium(II) organometallic derivative

A series of nine porphyrin analogues have been synthesized using the "3 + 1" variant on the MacDonald condensation. Tripyrrane-type systems with a centrally unsubstituted pyrrole, furan, or thiophene ring were prepared using conventional methods, and these were condensed with indene-1,3-dicarbaldehyde, 5-formylsalicylaldehyde, or 3-hydroxy-2,6-pyridinedicarbaldehyde in the presence of TFA to generate benzocarba-, oxybenzi-, and oxypyriporphyrins, respectively. The furan-containing analogues proved to be highly basic and could only be isolated as the corresponding hydrochloride salts. All nine analogue systems showed porphyrin-like UV-vis spectra with one or two Soret absorptions near 400 nm and a series of weaker bands at longer wavelengths. These systems also showed large diatropic ring currents by proton NMR spectroscopy that were comparable to true porphyrins. In the presence of trace amounts of TFA, benzocarbaporphyrin 12 formed a monocation, and in 50% TFA a C-protonated dication was generated. The 23-oxacarbaporphyrin 14 gave a monocation in chloroform, although the free base was generated in 5% Et(3)N-chloroform. In 50% TFA-CHCl(3), 14 afforded a mixture of mono- and diprotonated species. Thiacarbaporphyrin 15 also formed a monocation in the presence of TFA, but C-protonation was relatively disfavored for this system. Nonetheless, in the presence of TFA-d, 12, 14, and 15 all showed rapid exchange of the internal NH and CH protons. Carbaporphyrin 12 also showed slow exchange at the meso-positions, but this process was not observed for its heteroanalogues 14 and 15. Protonation studies were also conducted for oxybenziporphyrins and oxypyriporphyrins 16-21. Oxacarbaporphyrin 14 was shown to be a superior organometallic ligand and afforded good yields of the related nickel(II) and palladium(II) derivatives under mild conditions. A low yield of the platinum(II) complex could also be isolated. All three complexes retained their aromatic character, although the Pd(II) derivative appeared to possess a slightly larger diatropic ring current. The palladium(II) complex 27 was further characterized by X-ray crystallography. The macrocyclic core was shown to be highly planar where the dihedral angles of the component pyrrole, furan and indene rings relative to the mean [18]annulene plane were all 相似文献   

Adaptation of the Rothemund reaction for carbaporphyrin synthesis: preparation of meso-tetraphenylazuliporphyrin and related benzocarbaporphyrins

Electrophilic substitution of azulene has recently been shown to provide the means by which carbon-carbon bonds can be generated to form novel macrocyclic systems such as calixazulenes. These studies inspired us to develop a "one-pot" Rothemund-type synthesis of meso-tetraphenylazuliporphyrin. Azuliporphyrins, a group of cross-conjugated carbaporphyrinoids that exhibit intriguing chemistry and metallation properties, have previously only been available by multistep syntheses. In this work, azulene, pyrrole and benzaldehyde were shown to react in a 1:3:4 ratio in the presence of boron trifluoride etherate to give meso-tetraphenylazuliporphyrin 7a. The free base shows only a minor diatropic ring current, but addition of TFA generates the related dication which shows greatly enhanced diatropicity where the internal CH shifts from delta = +3.35 to -0.5 ppm. Addition of pyrrolidine to 7a gave rise to a carbaporphyrin adduct which showed a porphyrin-like UV/Vis spectrum and the internal CH shifted further upfield to give a resonance near delta = -5.7 ppm. Treatment of 7a with tertbutyl hydroperoxide in the presence of potassium hydroxide afforded a mixture of benzocarbaporphyrins 9a-c. These tetraphenylcarbaporphyrins were fully aromatic by NMR spectroscopy and gave typical porphyrin-type UV/Vis spectra with a strong Soret band near 446 nm. This new methodology makes these important porphyrin analogues readily available for further study.     

Sur la transformation du β-nitrostyrène sous l'action du chlorure d'acétyle en présence d'un chlorure métallique

While β-nitrostyrene yields only hydroxymic or hydroxamic acid derivatives by treatment with acetyl chloride in the presence of zinc, tin, titanium or aluminium chloride, it also gives 3-chloro 2-indolinone and a 5-acetyl derivative of the latter, when the reaction is carried out with ferric chloride. The procedures of this reaction are examined, and a mechanism is suggested.     

A Soret marker band for four-coordinate ferric heme proteins from absorption spectra of isolated Fe(III)-Heme+ and Fe(III)-Heme+(His) ions in vacuo

In this work, we report the absorption spectra in the Soret band region of isolated Fe(III)-heme+ and Fe(III)-heme+(His) ions in vacuo from action spectroscopy. Fe(III)-heme+ refers to iron(III) coordinated by the dianion of protoporphyrin IX. We find that the absorption of the five-coordinate complex is similar to that of pentacoordinate metmyoglobin variants with hydrophobic binding pockets except for an overall blueshift of about 16 nm. In the case of four-coordinate iron(III), the Soret band is similar to that of five-coordinate iron(III) but much narrower. These spectra serve as a benchmark for theoretical modeling and also serve to identify the coordination state of ferric heme proteins. To our knowledge this is the first unequivocal spectroscopic characterization of isolated 4c ferric heme in the gas phase.     

Preparation of new nitrogen-bridged heterocycles. 53. Syntheses of 3-(benzylthio)thieno[3,4-b]indolizine derivatives and their intramolecular arene-arene interactions

Various ethyl 1-arylcarbonyl-3-[(un)substituted methylthio]thieno[3,4-b]indolizine-9-carboxylates were synthesized in good yields by a novel methodology in which the S-alkylation of 5-arylcarbonyl-4-ethoxycarbonylmethyl-3-(1-pyridinio)thiophene-2-thiolates with alkyl or benzyl halides, the 1,5-dipolar cyclization of the resulting pyridinium salts in the presence of a base, and the aromatization were performed. In the X-ray analyses of some 3-(benzylthio)thieno[3,4-b]indolizine-9-carboxylates, a gauche and two anti conformers in relation to the exocyclic sulfide linkage were found. Interestingly, all of the 3-(benzylthio)thieno[3,4-b]indolizine derivatives showed significant high-field shifts (delta up to 0.3 ppm) for the 5- and 6-proton signals compared with those of the 3-methylthio derivatives in the (1)H-NMR spectra and exhibited a definite absorption band near 425 nm in their UV spectra, indicating an intramolecular arene-arene interaction between the thieno[3,4-b]indolizine and the phenyl ring.     

Optochemical sensing of hydrogen chloride gas using meso-tetramesitylporphyrin deposited glass plate

Meso-tetramesitylporphyrin (MTMP) deposited glass plate (solid state sensor) was used to sense hydrogen chloride (HCl) gas based on optochemical method. Exposure of the solid state sensor to HCl vapor results in the formation of protonated meso-tetramesitylporphyrin (PMTMP). UV-vis and fluorescence spectral techniques were used to study the protonation of MTMP in dichloromethane-methanol mixture. The optical spectra of MTMP show an intense Soret band at 418 nm with a 14 nm red shift upon protonation by HCl. Ab-initio calculations were carried out to visualize the effect of protonation on planarity and stability of the porphyrin ring. The solid state sensor was characterized by UV-vis spectral technique. The sensor exhibits characteristic Soret and Q bands for the deposited MTMP with slight red shift when compared to MTMP in dichloromethane. The concentration of gaseous HCl was monitored from the changes in the absorbance of Soret band of PMTMP at 452 nm. The detection limit of the solid state sensor towards gaseous HCl was found to be 0.03 ppm. The present solid state sensor was highly stable for several months.     

Detailed assignment of the magnetic circular dichroism and UV-vis spectra of five-coordinate high-spin ferric [Fe(TPP)(Cl)

High-spin (hs) ferric heme centers occur in the catalytic or redox cycles of many metalloproteins and exhibit very complicated magnetic circular dichroism (MCD) and UV-vis absorption spectra. Therefore, detailed assignments of the MCD spectra of these species are missing. In this study, the electronic spectra (MCD and UV-vis) of the five-coordinate hs ferric model complex [Fe(TPP)(Cl)] are analyzed and assigned for the first time. A correlated fit of the absorption and low-temperature MCD spectra of [Fe(TPP)(Cl)] lead to the identification of at least 20 different electronic transitions. The assignments of these spectra are based on the following: (a) variable temperature and variable field saturation data, (b) time-dependent density functional theory calculations, (c) MCD pseudo A-terms, and (d) correlation to resonance Raman (rRaman) data to validate the assignments. From these results, a number of puzzling questions about the electronic spectra of [Fe(TPP)(Cl)] are answered. The Soret band in [Fe(TPP)(Cl)] is split into three components because one of its components is mixed with the porphyrin A2u72-->Eg82/83 (pi-->pi*) transition. The broad, intense absorption feature at higher energy from the Soret band is due to one of the Soret components and a mixed sigma and pi chloro to iron CT transition. The high-temperature MCD data allow for the identification of the Q v band at 20 202 cm(-1), which corresponds to the C-term feature at 20 150 cm(-1). Q is not observed but can be localized by correlation to rRaman data published before. Finally, the low energy absorption band around 650 nm is assigned to two P-->Fe charge transfer transitions, one being the long sought after A1u(HOMO)-->d pi transition.     

Gas‐Phase Spectroscopy of Ferric Heme?NO Complexes

Weakly bound complexes between ferric heme cations and NO were synthesised in the gas phase from ion–molecule reactions, and their absorption measured based on photodissociation yields. The Soret band, which serves as an important marker band for heme‐protein spectroscopy, is maximal at 357±5 nm and significantly blue‐shifted compared to ferric heme nitrosyl proteins (maxima between 408 and 422 nm). This is in stark contrast to the Q‐band absorption where the protein microenvironment is nearly innocent in perturbing the electronic structure of the porphyrin macrocycle. Photodissociation is primarily through loss of NO. In contrast to the Q‐band region, two‐photon absorption was seen in the Soret band despite NO loss only requiring ～1 eV. A model based on intersystem crossing to a long‐lived triplet state where a barrier has to be surmounted is suggested. Finally, we summarise the measured absorption maxima of heme and its complexes with amino acids and NO.     

Circular dichroism and theoretical calculations of pinacyanol dimer inclusion in γ-cyclodextrin

Aggregation of pinacyanol chloride is strongly enhanced through inclusion into γ-cyclodextrin, which was studied using both UV/Visible, derivative and Circular Dichroism (CD) spectroscopy. The intensities at 546 and at 507 nm were increased with the growing ratio of γ-cyclodextrin to dye. Both aggregates were shown to be optically active. CD spectra with two and three oppositely signed excitonic bands were shown. The structures of the aggregates have been analysed and discussed in terms of qualitative H-type aggregation and quantitative based on OSCI program. Applying eight different parameter sets aggregates of pinacyanol chloride ranging in size from 2 to 20 dye molecules were considered. The calculated energy splitting was adjusted, via the transition dipole length, to the experimentally observed band shift. Rotational strengths associated with the CD absorptions were calculated and used to obtain an estimate of the inherent twist of the dimer aggregate inside the γ-cyclodextrin cavity.     

Preparation of new nitrogen-bridged heterocycles. 58. Syntheses and intramolecular arene-pi interactions of 3-(allylthio)- and 3-(propargylthio)thieno[3,4-b]indolizine derivatives

Various thieno indolizine derivatives having an allylthio or propargylthio group at the 3-position were prepared and their intramolecular arene-pi interactions were investigated. Their 1H-NMR spectra showed significant low-field shifts (delta 0.10-0.34 ppm) to the 5-proton on the thieno indolizine ring, and this effect was the reverse to that observed in 3-(arylmethylthio)thieno indolizines. However, their UV spectra exhibited a characteristic absorption band due to the arene-pi interaction near 430 nm and these values were almost similar to those for arene-arene interaction of 3-arylmethylthio derivatives though their molar extinction coefficients were largely varied by the 3-substituents. Furthermore, both types of gauche conformations in which the intramolecular arene-pi interactions are possible in one form and impossible in the other were confirmed by X-ray analyses of some compounds.     

Reactions of nickel(II) 2,21-dimethyl-2-aza-21-carbaporphyrin with phenyl Grignard reagents, phenyllithium, and n-butyllithium

Addition of a phenyl Grignard reagent to a toluene solution of the nickel(II) chloride complex of a dimethylated inverted porphyrin, (2-NCH3-21-CH3CTPP)NiIICl (1), at 203 K results in the formation of a rare paramagnetic (sigma-phenyl)nickel(II) species, (2-NCH3-21-CH3CTPP)NiIIPh (2). The coordination of the sigma-phenyl in 2 is determined by a unique pattern of three sigma-phenyl resonances (ortho 375.0 ppm; meta 108.94 ppm; para 35.68 ppm (at 283 K)) in the 1H NMR and 2H NMR spectra. The (sigma-phenyl)nickel(II) compound 2 is in the high-spin ground electronic state (dxy)2(dxz)2(dyz)2(dz2)1(dx2-y2)1, as confirmed by similarity of the NMR spectra of the equatorial ligand in 1 and 2. Titration of 1 with phenyllithium produces (2-NCH3-21-CH3CTPP)NiIIPh (2). One-electron reduction with excess PhLi yields [(2-NCH3-21-CH3CTPP)NiIIPh]- (3), which can be also generated by independent routes, e.g., by reduction of (2-NCH3-21-CH3CTPP)NiIIPh using lithium triethylborohydride or tetrabutylammonium borohydride. The spectroscopic data indicate that (2-NCH3-21-CH3CTPP)NiIIPh (2) undergoes one-electron reduction without a substantial disruption of the molecular geometry. The presence of two paramagnetic centers in 3, i.e., the high-spin nickel(II) and the carbaporphyrin anion radical, produces remarkable variations in a spectral patterns, such as the upfield and downfield positions of pyrrole resonances (103.78, 96.66, -25.35, -50.97, -92.15, -114.83 ppm (at 253 K)) and sign alternations of the meso-phenyl resonances (ortho -77.81, -79.34 ppm; meta 48.77, 48.04 ppm; para -85.65, -86.46 ppm (at 253 K)). A single species, 4, is detected in the 1H NMR titration of 1 with n-butyllithium. The formation of one- or two-electron-reduced species, [(2-NCH3-21-CH3CTPP)NiBu]- or [(2-NCH3-21-CH3CTPP)NiBu]2-, respectively, is considered to account for the spectroscopic properties of 4 (pyrrole 17.33, 15.45, -5.79, -7.74, -14.62, -58.14 ppm; 21-CH3 3 ppm (at 203 K)). The temperature dependence of the hyperfine shifts of 4 demonstrates pronounced anti-Curie behavior, interpreted in terms of a temperature-dependent spin equilibrium between diamagnetic and paramagnetic states with diamagnetic properties approached as the temperature is lowered. Warming of 2-4 results in complete decomposition via homolytic/heterolytic cleavage of an axial nickel-apical carbon bond. In the case of 2 or 3, the process yields a mixture of two compounds, 5 and 6, which are detected by EPR spectroscopy, demonstrating the anisotropy of the g tensor (5, g1 = 2.237, g2 = 2.092, g3 = 2.090; 6, g1 = 2.115, g2 = 2.030, g3 = 1.940 (in frozen toluene solution at 77 K)).