Skeletal Rearrangement of Twisted Thia‐Norhexaphyrin: Multiply Annulated Polypyrrolic Aromatic Macrocycles

A hybrid thia‐norhexaphyrin comprising a directly linked N‐confused pyrrole and thiophene unit ( 1 ) revealed unique macrocycle transformations to afford multiply inner‐annulated aromatic macrocycles. Oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone triggered a cleavage of the C?S bond of the thiophene unit, accompanied with skeletal rearrangement to afford unique π‐conjugated products: a thiopyrrolo‐pentaphyrin embedded with a pyrrolo[1,2]isothiazole ( 2 ), a sulfur‐free pentaphyrin incorporating an indolizine moiety ( 3 ), and a thiopyranyltriphyrinoid containing a 2H‐thiopyran unit ( 4 ). Furthermore, 2 underwent desulfurization reactions to afford a fused pentaphyrin containing a pyrrolizine moiety ( 5 ) under mild conditions. Using expanded porphyrin scaffolds, oxidative thiophene cleavage and desulfurization of the hitherto unknown N‐confused core‐modified macrocycles would be a practical approach for developing unique polypyrrolic aromatic macrocycles.     

meso-Trifluoromethyl-substituted expanded porphyrins

A series of meso-trifluoromethyl-substituted expanded porphyrins, including N-fused [24]pentaphyrin 3, [28]hexaphyrin 4, [32]heptaphyrin 5, [46]decaphyrin 6, and [56]dodecaphyrin 7, were synthesized by means of an acid-catalyzed one-pot condensation reaction of 2-(2,2,2-trifluoro-1-hydroxyethyl)pyrrole (1) as the first examples bearing meso-alkyl substituents. Besides these products, porphyrin 2 and two calix[5]phyrins 8 and 9 were also obtained. [28]Hexaphyrin 4 was quantitatively oxidized to [26]hexaphyrin 14 with MnO(2). These expanded porphyrins have been characterized by mass spectrometry, (1)H and (19)F NMR spectroscopy, and UV/Vis spectroscopy. The single-crystal structures have been determined for 3, 4, 6, 7, and 14. The N-fused [24]pentaphyrin 3 displays a distorted structure containing a tricyclic fused moiety that is similar to those of meso-aryl-substituted counterparts, whereas 8 and 9 are indicated to take roughly planar conformations with an inverted pyrrole opposite to the sp(3)-hybridized meso-carbon atom. Both [28]- and [26]hexaphyrins 4 and 14 have figure-of-eight structures. Solid-state structures of the decaphyrin 6 and dodecaphyrin 7 are remarkable, exhibiting a crescent conformation and an intramolecular two-pitch helical conformation, respectively.     

Doubly N‐Fused [24]Pentaphyrin Silicon Complex and Its Fluorosilicate: Enhanced Möbius Aromaticity in the Fluorosilicate

Treatment of nonaromatic N‐fused [24]pentaphyrin with trichloromethylsilane in the presence of a base afforded doubly N‐fused [24]pentaphyrin and its silicon complex. Addition of fluoride ion to the silicon complex led to the formation of its fluorosilicate as an unprecedented monoanionic six‐coordinated Si^IV complex of porphyrinoid. Treatment of the fluorosilicate with acid led to the recovery of the silicon complex. The doubly N‐fused pentaphyrin, the silicon complex, and the fluorosilicate were all characterized as distinct Möbius aromatic molecules by spectroscopic measurements and X‐ray crystallographic analyses. Importantly, the second N‐fusion reaction, Si‐incorporation and fluoride addition to the Si‐atom enhanced the aromaticity of doubly N‐fused [24]pentaphyrins in this order. Tamao–Fleming oxidation of the silicon complex gave β‐keto doubly N‐fused pentaphyrin and triply fused [24]pentaphyrin, which were nonaromatic and Hückel anti‐aromatic, respectively.     

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

The four expanded p‐benziporphyrins A,C‐di‐p‐benzi[24]pentaphyrin(1.1.1.1.1), N‐fused A‐p‐benzi[24]pentaphyrin, A,D ‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1), and A,C‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1) were obtained in three‐component Lindsey‐type macrocyclizations. These compounds were explored as macrocyclic ligands and as potential aromaticity switches. A BODIPY‐like difluoroboron complex was obtained from the A,C‐di‐p‐benzi[24]pentaphyrin, whereas A,C‐di‐p‐benzi[28]hexaphyrin yielded a Möbius‐aromatic Pd^II complex containing fused pyrrole and phenylene subunits. Conformational behavior, tautomerism, and acid‐base chemistry of the new macrocycles were characterized by means of NMR spectroscopy and DFT calculations. Free base N‐fused A‐p‐benzi[24]pentaphyrin showed temperature‐dependent Hückel–Möbius aromaticity switching, whereas the A,C‐di‐p‐benzi[28]hexaphyrin formed a Möbius‐aromatic dication.     

N-fused pentaphyrins and their rhodium complexes: oxidation-induced rhodium rearrangement

meso-Aryl-substituted pentaphyrins were isolated in the modified Rothemund-Lindsey porphyrin synthesis as a 22-pi-electron N-fused pentaphyrin ([22]NFP5) and a 24-pi-electron N-fused pentaphyrin ([24]NFP5), which were reversibly interconvertible by means of two-electron reduction with NaBH4 or two-electron oxidation with dichlorodicyanobenzoquinone (DDQ). Judging from 1H NMR data, [22]NFP5 is aromatic and possesses a diatropic ring current, while [24]NFP5 exhibits partial anti-aromatic character. Metalation of [22]NFP5 1 with a rhodium(I) salt led to isolation of rhodium complexes 9 and 10, whose structures were unambiguously characterized by X-ray diffraction analyses and were assigned as conjugated 24-pi and 22-pi electronic systems, respectively. In the rhodium(I) metalation of 1, the complex 9 was a major product at 20 degrees C, but the complex 10 became preferential at 55 degrees C. Upon treatment with DDQ, compound 9 was converted to 10 with an unprecedented rearrangement of the rhodium atom.     

meso-Alkylidene (m-benzi)pentaphyrin: a modified pentaphyrin bearing exocyclic double bonds at meso-positions

meso-Alkylidene (m-benzi)pentaphyrin containing exocyclic C=C double bonds at two meso-positions is synthesized and fully characterized for the first time. The single crystal X-ray crystallographic analysis shows a concave conformation with two pyrrole rings inverted. The first protonation occurs exclusively at core nitrogen. The synthesized compound displays concentration dependent chromogenic responses for fluoride anion in organic solvent.     

Nonlinear optical properties as a guide to aromaticity in congeneric pentapyrrolic expanded porphyrins: pentaphyrin, sapphyrin, isosmaragdyrin, and orangarin

On the basis of two-photon absorption and time-resolved spectroscopic measurements, as supported by theoretical calculations of quantitative aromaticity, a relationship between the nonlinear optical properties and aromaticity index has been established for a series of four fully conjugated pentapyrrolic expanded porphyrins, namely pentaphyrin (1.1.1.1.1), sapphyrin (1.1.1.1.0), isosmaragdyrin (1.1.1.0.0), and orangarin (1.0.1.0.0), all of which proved amenable to study in dichloromethane.     

Neo‐Fused Hexaphyrin: A Molecular Puzzle Containing an N‐Linked Pentaphyrin

The first neo‐confused hexaphyrin(1.1.1.1.1.0) was synthesized by oxidative ring closure of a hexapyrrane bearing two terminal “confused” pyrroles. The new compound displays a folded conformation with a short interpyrrolic C???N distance of 3.102 Å, and thus it readily underwent ring fusion to afford a neo‐fused hexaphyrin with an unprecedented 5,5,5,7‐tetracyclic ring structure. Furthermore, coordination of Cu^II triggered a ring opening/contracting reaction to afford a Cu^II complex of an N‐linked pentaphyrin derivative. The roles of reactive N? C bonds in the porphyrinoid macrocycles were demonstrated.     

Contracted and expanded meso-alkynyl porphyrinoids: from triphyrin to hexaphyrin

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H(3)4, porphyrin H(2)2, [24]pentaphyrin(1.1.1.1.1) H(4)5, [28]hexaphyrin(1.1.1.1.1.1) H(4)6, and two linear tripyrromethenes H(2)7 and H(2)8. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H(2)2 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H(4)6, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This C=C bond makes an eta(2)-interaction with the zinc center in ZnCl3 with C-Zn distances of 2.863 and 3.025 A. The porphyrin H(2)2 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H(4)6 adopts a figure-of-eight conformation with virtual C(2) symmetry in the solid state and C(2) symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate.     

meso‐3,5‐Bis(trifluoromethyl)phenyl‐Substituted Expanded Porphyrins: Synthesis,Characterization, and Optical,Electrochemical, and Photophysical Properties

Trifluoroacetic acid‐catalyzed condensation of pyrrole with electron‐deficient and sterically hindered 3,5‐bis(trifluoromethyl)benzaldehyde results in the unexpected production of a series of meso‐3,5‐bis(trifluoromethyl)phenyl‐substituted expanded porphyrins including [22]sapphyrin 2 , N‐fused [22]pentaphyrin 3 , [26]hexaphyrin 4 , and intact [32]heptaphyrin 5 together with the conventional 5,10,15,20‐tetrakis(3,5‐bis(trifluoromethyl)phenyl)porphyrin 1 . These expanded porphyrins are characterized by mass spectrometry, ¹H NMR spectroscopy, UV/Vis/NIR absorption spectroscopy, and fluorescence spectroscopy. The optical and electrochemical measurements reveal a decrease in the HOMO–LUMO gap with increasing size of the conjugated macrocycles, and in accordance with the trend, the deactivation of the excited singlet state to the ground state is enhanced.     

Fabrication and electron transport properties of epitaxial films of electron-doped 12CaO·7Al2O3 and 12SrO·7Al2O3

Epitaxial growth and electron doping of 12CaO·7Al₂O₃ (C12A7) and 12SrO·7Al₂O₃ (S12A7) are reported. The C12A7 films were prepared on Y₃Al₅O₁₂ (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 || (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 films provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands.     

Modified expanded corrole-ferrocene conjugates: syntheses, structure and properties

Syntheses, characterization and properties of expanded corrole-ferrocene conjugates are reported. Ferrocenyl group are covalently linked to the corrole macrocycle through three different spacers groups. The synthetic strategy involved prior insertion of ferrocene with spacers to the dipyrromethane unit followed by a "3+2" acid-catalyzed oxidative coupling methodology. The optical and emission data of the expanded corrole-ferrocene conjugates depend on the nature and length of the spacer groups and the maximum effects are seen where ferrocene is directly linked to the meso carbon of macrocycle. The single crystal X-ray structure of two expanded corrole-ferrocene conjugates; [22]pentaphyrin (1.1.0.1.0) with different meso substituents, clearly reveal shortening of the C-C bond length linking the meso carbon and the aryl substituent containing the ferrocene moiety relative to meso aryl substituents without ferrocene. The results suggest that an electronic interaction between the two pi systems. Electrochemical data reveal harder oxidation for the ferrocene unit in the conjugates relative to free ferrocene; this suggests the electron donating nature of the ferrocene. The first corrole ring oxidation shows easier oxidation relative to 1 and the magnitude of shifts in potential is inversely proportional to the length of spacer. The molecular first hyperpolarizabilities (beta) measured at 1064 nm by HRS method vary in the range 20-32x10(-30) esu and imply that the beta values can be increased by enhancing the number of mobile electrons in the conjugation. The conjugates form 1:1 metal complex with the Rh(I) where rhodium is coordinated to one amino and one imino nitrogen of the dipyrromethane unit.     

Spectroscopic characterization of the oxidation control of the iso-pentaphyrin/pentaphyrin system

We have recently described the synthesis of two porphyrogenic macrocycles: 20-phenyl-2,13-dimethyl-3,7,8,12-tetraethyl-[24]iso-pentaphyrin (1) and 20-phenyl-2,13-dimethyl-3,7,8,12-tetraethyl-[22]pentaphyrin (2) (J. Med. Chem.2006, 49, 196-204). We found that the structure of iso-pentaphyrin is influenced by the acidity of the medium. By adjusting the TFA concentration, we solved two isomers of iso-pentaphyrin: 1 and 1A. At high TFA concentration iso-pentaphyrin is present only as 1, which is slowly oxidized into the aromatic macrocycle 2 upon exposure to air. The correlation between acidic conditions, isomer structures, and oxidation is discussed.     

低温区CsI掺杂的12CaO·7Al2O3型发射材料负离子的发射特性

本文利用潮湿浸渍法将碘化铯(CsI)掺杂至12CaO·7Al2O3(C12A7)型负离子存储发射材料的表面并对其的结构与存储特性进行了X射线衍射和电子顺磁共振的表征,与此同时还对该材料的发射特性、离子发射分支比以及温度对发射强度的影响等方面进行了研究和分析。将实验和表征结果与未掺杂的C12A7进行对比后发现,C12A7表面上CsI的掺入很大程度上改善了该材料的发射特性。掺杂CsI后,在800 V·cm-1的引出场下,发射温度由570℃降低至470℃,与此同时,在同样的发射条件下,其发射强度也明显增强。低温区(<500℃)氧负离子O-的发射纯度接近100%。以上结果表明掺杂CsI至C12A7表面是一种在低温下获得氧负离子O-源的有效途径。     

C12A7-O-纳米材料的制备及抗菌活性

利用溶胶-凝胶法制备了C12A7-O-{[Ca24Al28O64]4+·4(O-)}纳米材料. 采用X射线衍射、电子顺磁共振及透射电子显微镜等手段对制备的材料进行了表征. 结果表明, 在最佳焙烧条件(1150 ℃, 6 h)下制备的材料平均粒径为74 nm, 并具有晶胞参数为(1.199±0.004) nm的C12A7(Ca12Al14O33)笼状结构, 材料内包含浓度高达1.2×1020 cm-3的氧负离子(O-). 初步研究结果表明, 合成的C12A7-O-纳米材料具有良好的广谱抗菌作用.     

Substituent effects in benz[a]anthracene carbocations: a stable ion, electrophilic substitution (nitration, bromination), and DFT study

A series of novel carbocations were generated from isomeric monoalkylated and dialkylated benz[a]anthracenes (BAs) by low-temperature protonation in FSO(3)H/SO(2)ClF. With the monoalkyl derivatives (5-methyl, 6-methyl, 7-methyl, and 7-ethyl) as well as the D-ring methylated analogues (9-methyl, 10-methyl, and 11-methyl), the C-7 or the C-12 protonated carbocations were observed (as the sole or major carbocation) in all cases. Protonation of the 12-methyl derivative (9) gave the C-7 protonated carbocation (9H+) as the kinetic species and the ipso-protonated carbocation (9aH+) as the thermodynamic cation. With the 12-ethyl derivative (10), relief of steric strain in the bay-region greatly favors ipso-protonation (10aH+). With 3,9-dimethyl (14), C-7 protonation (14H+) is strongly favored (with <10% protonation at C-12), and with 1,12-dimethyl (15) the sole species observed is the C-7 protonated carbocation (15H+). For 7-methyl-12-ethyl, 7-ethyl-12-methyl, and 7,12-diethyl derivatives (16, 17, and 18), two ipso-protonated carbocations were initially formed (C-7/C-12), rearranging in time to give the C-12 protonated carbocations exclusively (16aH+, 17aH+, and 18aH+). Protonation outcomes are compared with the computed relative energies by DFT. Charge delocalization paths in the resulting carbocations were deduced based on the magnitude of Deltadelta13C values. For the thermodynamically more stable C-12 protonated carbocations, the charge delocalization path is analogous to those derived based on computed NPA charges for the benzylic carbocations formed by 1,2-epoxide (bay-region) and 5,6-epoxide (K-region) ring opening. Nitration (and bromination) of the 4-methyl, 7-methyl, 7-ethyl, 3,9-dimethyl, and 1,12-dimethyl derivatives resulted in isolation and characterization of several novel derivatives. Excellent agreement is found between low-temperature protonation selectivities and the regioselectivities observed in model substitution reactions.     

7-Decarboxymethyl-cobyrinates: vitamin B12-derivatives that lack the c-side chain

The synthesis of cobyrinic acid derivatives by reduction of dehydrocobyrinates is largely unexplored. It is, however, a rational path to B(12) analogues that lack specific substituents of the corrin moiety of natural B(12) derivatives. The partial syntheses of four epimeric 7-decarboxymethyl-cobyrinates is described, which is achieved by reduction of Δ7-dehydro-7-de[carboxymethyl]-cobyrinate with zinc or with the 'prebiotic' reducing agent formic acid. A direct and remarkably efficient route was found to 7-decarboxymethyl-cobyrinates, which are cobyrinic acid derivatives in which the c-side chain at ring B of vitamin B(12) is missing. The structures of the hexamethyl-7-decarboxymethyl-cobyrinates were characterized and the stereochemical and conformational properties at their newly saturated ring B were analyzed. The stereochemical outcome of the reduction was found to depend strongly on the reaction conditions. In 7-decarboxymethyl-cobyrinates, both peripheral carbon centres of ring B carry a hydrogen atom, and the characteristic quaternary carbon centre at C7 of the cobyrinic acid moiety of vitamin B(12) is lacking. The still highly substituted 7-decarboxymethyl-cobyrinates are readily dehydrogenated in the presence of dioxygen, furnishing 7-de[carboxymethyl]-Δ(7)-dehydro-cobyrinate as the common, unsaturated oxidation product. The noted stability of vitamin B(12) and of other Co(III)-cobyrinates in the presence of air is a consequence of their highly substituted corrin macrocycle, a finding of interest in the context of chemical rationalizations of the B(12) structure.     

Na7Sn12: a binary Zintl phase with a two-dimensional covalently bonded tin framework

Na(7)Sn(12) was synthesized by quenching of stoichiometric amounts of the elements (700 degrees C) in a sealed niobium ampule and further thermal treatment at 270 degrees C for 40 days. Single crystals of Na(7)Sn(12) were obtained from a mixture with the composition Na(6)SrSn(16). The structure of Na(7)Sn(12) consists of two-dimensional polyanions 2 (infinity) [Sn(12)(7-)], which are separated by Na atoms. Bonding Sn-Sn contacts in the polyanion vary between 2.827(2) and 3.088(2) A. Crystal data: monoclinic, P2/n, Z = 4, a = 13.375(3) A, b = 9.239(2) A, c = 17.976(4) A, gamma = 90.15(3) degrees, V = 2243.0(8) A(3), mu = 13.22 mm(-1), d(calc) = 4.694 g cm(-3), R1(F) = 6.1% (for all reflections). Extended-Hückel tight-binding calculations with the implementation the electron localization function (ELF) reveal that Na(7)Sn(12) can be viewed as an intermetallic compound with exclusively localized bonding and nonbonding regions as expected from the 8 - N rule. Thus Na(7)Sn(12) is a Zintl phase with the formula (Na(+))(7)[(2b)Sn(2)(-)](1)[(3b)Sn(-)](5)[(4b)Sn(0)](6).     

Six new dammarane-type triterpene saponins from the leaves of Panax ginseng

Six new minor saponins, together with known ginsenosides, were isolated from the leaves of Panax ginseng. The new saponins were named as ginsenoside-Rh5, -Rh6, -Rh7 -Rh8, -Rh9 and -Rg7, and their structures were elucidated on the basis of chemical and physicochemical evidence to be as follows: ginsenoside-Rh5: 3beta,6alpha,12beta,24zeta-tetrahydroxy-dammar-20(22),25-diene 6-O-beta-D-glucopyranoside (1), -Rh6: 3beta,6alpha12beta,20(S)-tetrahydroxy-25-hydroperoxy-dammar-23-ene 20-O-beta-D-glucopyranoside (2), -Rh7: 3beta,7beta,12beta,20(S)-tetrahydroxy-dammar-5,24-diene 20-O-beta-D-glucopyranoside (3), -Rh8: 3beta,6alpha,20(S)-trihydroxy-dammar-24-ene-12-one 20-O-beta-D-glucopyranoside (4), -Rh9: 3beta,6alpha,20(S)-trihydroxy-12beta,23-epoxy-dammar-24-ene 20-O-beta-D-glucopyranoside (5) and -Rg7: 3-O-beta-D-glucopyranosyl 3beta,12beta,20(S),24(R)-tetrahydroxy-dammar-25-ene 20-O-beta-D-glucopyranoside (6).     

Effect of Positions of Methyl Substituents in the Complexation Kinetics of Macrocyclic Tetraamines with Copper(II) in Strongly Basic Aqueous Media

The complexation kinetics of the reaction of copper(II) with isomeric tetraamine macrocyclic ligands, C-rac-5, 7, 7, 12, 12, 14-hexamethyl-l, 4, 8, 11-tetraazacyclotetradecane (tet c), C-meso-5, 7, 7, 12, 12, 14-hexamethyl-l, 4, 8, 11-tetraazacyclotetradecane (tet d), and C-meso-5, 5, 7, 12, 12, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradecane (tet a) in strongly basic aqueous media have been examined at 25.0 ± 0.1°C by means of the stopped-flow technique. The variation in the values of the resulting rate constants indicates that the positions of the methyl substituents play a significant role in these reactions. These reactions exhibit associative character and second-bond formation is proposed as the rate-determining step.