[Show abstract][Hide abstract] ABSTRACT: The title compound, C
Si, crystallizes in a tetragonal space group and exists as an N—H...N hydrogen-bonded tetramer, formed around the crystallographic fourfold rotoinversion axis. The molecular identity is clearly the 5-trimethylsilyl-3-methyl-1
-pyrazole tautomer and the structure is isomorphous with that of 5-
-pyrazole [Foces-Foces & Trofimenko (2001).
[Show abstract][Hide abstract] ABSTRACT: Structural differences in [V2Te2O10]n(2n-) chain metrics are directly ascribed to variations in noncovalent interactions in a series of organically templated vanadium tellurites, including [C6H17N3][V2Te2O10]·H2O, [C5H16N2][V2Te2O10], and [C4H14N2][V2Te2O10]. The noncovalent interaction (NCI) method was used to locate, quantify, and visualize intermolecular interactions in [C4H14N2][V2Te2O10] and [C5H16N2][V2Te2O10]. Variations in the van der Waals attractions between [1,4-diaminobutaneH2](2+) and [1,5-diaminopentaneH2](2+) result in divergent packing motifs for these cations, which causes a reorganization of N-H···O hydrogen bonding and variances in the [V2Te2O10]n(2n-) chain metrics. The application of the NCI method to this type of solid-state structure provides a direct method to elucidate the structural effects of weak noncovalent interactions.
[Show abstract][Hide abstract] ABSTRACT: Dimethoxybenzitripyrranes were prepared in excellent yields by reacting benzene dicarbinols with BF3.Et2O and excess pyrrole in refluxing 1,2-dichloroethane. Reaction with a pyrrole dialdehyde in the presence of TFA, followed by oxidation with DDQ, afforded good yields of meso-diphenyldimethoxybenziporphyrins. These dimethoxyporphyrinoids exhibited weakly diatropic properties that were enhanced upon protonation. The dimethoxybenzitripyrranes also reacted with a thiophene dicarbinol to give dimethoxythiabenziporphyrins, and the nonplanar nature of this system was demonstrated by X-ray crystallography. The dimethoxybenziporphyrins reacted with palladium(II) acetate to give the related organometallic derivatives, but the thiabenziporphyrins underwent a demethylation to afford palladium(II) thiaoxybenziporphyrins. Related palladium(II) complexes were also prepared from previously reported thiacarbaporphyrinoids. The X-ray structure for one of the complexes showed that the six-membered ring is very distorted and the thiophene ring is strongly tilted out of the plane of the macrocycle. The dimethoxybenzitripyrranes also reacted with dimethoxybenzene dicarbinols to give the first examples of dibenziporphyrins, thereby further demonstrating the versatility of this synthetic methodology.
The Journal of Organic Chemistry 10/2014; 79(22). DOI:10.1021/jo502063w · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An adj-dicarbaporphyrin was prepared by carrying out a base-catalyzed MacDonald reaction between bis(3-indenyl)methane and a dipyrrylmethane dialdehyde. The porphyrinoid system exhibited highly diatropic characteristics and the proton NMR spectrum gave resonances at -5.74 and -6.24 ppm for the internal NH and CH protons, respectively. The UV-vis spectrum was also porphyrin-like, giving a Soret band at 455 nm and a series of Q bands at longer wavelengths. Addition of TFA gave a C-protonated monocation and at higher acid concentrations a dicationic species was observed. Addition of DBU afforded a mono-deprotonated porphyrinoid anion. All of these species retained highly diatropic characteristics. DFT calculations showed that a nonplanar tautomer with four internal hydrogens was favored, in agreement with the spectroscopic data. NICS calculations also confirmed the aromatic characteristics of the free base, cationic and anionic structures. The dicarbaporphyrin reacted with palladium(II) acetate in refluxing acetonitrile to give an unusual tripalladium sandwich complex. The complex consists of two dianionic palladium(II) dicarbaporphyrin units surrounding a palladium(IV) cation with unique η5-interactions that involve meso-carbon atoms.
Journal of the American Chemical Society 04/2014; 136(18). DOI:10.1021/ja502795x · 11.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neo-confused porphyrins represent a unique family of porphyrin isomers that retain overall aromatic characteristics by virtue of a 17-atom 18pi electron delocalization pathway. These porphyrin analogues have a pyrrolic subunit connected in a 1,3-fashion so that a nitrogen atom is directly connected to a meso-bridging carbon. Pyrrole-3-carbaldehydes were shown to react with sodium hydride and 5-acetoxymethylpyrrole-2-carbaldehydes in DMF to give the crucial neo-confused dipyrrolic dialdehyde intermediates. MacDonald "2 + 2" condensation of the dialdehydes with a dipyrrylmethane afforded a dihydroporphyrinoid, and subsequent oxidation with 0.2% aqueous ferric chloride generated a series of fully conjugated neo-confused porphyrins. Unusual dihydroporphyrin by-products were also identified. Reaction of neo-confused porphyrins with nickel(II) or palladium(II) acetate in refluxing acetonitrile gave excellent yields of the corresponding organometallic derivatives. Proton NMR spectroscopy demonstrate that the diatropic character of this system is diminished compared to regular porphyrins, although neo-confused porphyrins retain porphyrin-like UV-vis spectra. Protonation led to the sequential formation of mono- and dicationic species. Proton NMR spectra for the dications showed the presence of enhanced diamagnetic ring currents.
The Journal of Organic Chemistry 04/2014; 79(9). DOI:10.1021/jo500580e · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The inclusion of Ln(III) ions into the 12-MC-4 framework generates the first heterotrimetallic complexes of this molecular class. The controllable and deliberate preparations of these compounds are demonstrated through 12 crystal structures of the Ln(III)M(I)(OAc)4[12-MCMn(III)(N)shi-4](H2O)4·6DMF complex, where OAc(-) is acetate, shi(3-) is salicylhydroximate, and DMF is N,N-dimethylformamide. Compounds 1-12 have M(I) as Na(I), and Ln(III) can be Pr(III) (1), Nd(III) (2), Sm(III) (3), Eu(III) (4), Gd(III) (5), Tb(III) (6), Dy(III) (7), Ho(III) (8), Er(III) (9), Tm(III) (10), Yb(III) (11), and Y(III) (12). An example with M(I) = K(I) and Ln(III) = Dy(III) is also reported (Dy(III)K(OAc)4[12-MCMn(III)(N)shi-4](DMF)4·DMF (14)). When La(III), Ce(III), or Lu(III) is used as the Ln(III) ions to prepare the Ln(III)Na(I)(OAc)4[12-MCMn(III)(N)shi-4] complex, the compound Na2(OAc)2[12-MCMn(III)(N)shi-4](DMF)6·2DMF·1.60H2O (13) results. For compounds 1-12, the identity of the Ln(III) ion affects the 12-MCMn(III)(N)shi-4 framework as the largest Ln(III), Pr(III), causes an expansion of the 12-MCMn(III)(N)shi-4 framework as demonstrated by the largest metallacrown cavity radius (0.58 Å for 1 to 0.54 Å for 11), and the Pr(III) causes the 12-MCMn(III)(N)shi-4 framework to be the most domed structure as evident in the largest average angle about the axial coordination of the ring Mn(III) ions (103.95° for 1 to 101.69° for 11). For 14, the substitution of K(I) for Na(I) does not significantly affect the 12-MCMn(III)(N)shi-4 framework as many of the structural parameters such as the metallacrown cavity radius (0.56 Å) fall within the range of compounds 1-12. However, the use of the larger K(I) ion does cause the 12-MCMn(III)(N)shi-4 framework to become more planar as evident in a smaller average angle about the axial coordination of the ring Mn(III) ions (101.35°) compared to the analogous Dy(III)/Na(I) (7) complex (102.40°). In addition to broadening the range of structures available through the metallacrown analogy, these complexes allow for the mixing and matching of a diverse range of metals that might permit the fine-tuning of molecular properties where one day they may be exploited as magnetic materials or luminescent agents.
[Show abstract][Hide abstract] ABSTRACT: A series of hetero-azuliporphyrins have been prepared by the "3 + 1" variant on the MacDonald condensation. Azulitripyrranes with tert-butyl and phenyl substituents reacted with thiophene or selenophene dialdehydes in the presence of TFA to give, following an oxidation step, thia- and selena-azuliporphyrins in 45-55% yield. Two of these compounds gave crystals suitable for X-ray crystallographic analysis and the data were consistent with the presence of a 17-atom delocalization pathway. The hetero-azuliporphyrins have significant diatropic character that is enhanced by the presence of an electron-donating tert-butyl substituent. The aromatic character is further increased in polar solvents such as DMSO, which are believed to stabilize dipolar resonance contributors with 18π electron delocalization pathways. Protonation also greatly increases the diatropic characteristics of these macrocycles. The porphyrinoids underwent an oxidative ring contraction with t-BuOOH-KOH to give moderate yields of benzoheterocarbaporphyrins. Reaction of azulitripyrranes with 2,5-furandicarbaldehyde afforded oxa-azuliporphyrins, a class of carbaporphyrinoids that had previously been inaccessible. These "missing links" in the study of heteroazuliporphyrins were isolated as the dihydrochloride salts. Protonated oxa-azuliporphyrins are stable aromatic compounds, but the free base forms underwent rapid decomposition in solution.
[Show abstract][Hide abstract] ABSTRACT: A set of formation principles governing organically templated vanadium selenite oxalates are described in the context of nine new compounds. The compositions of the reaction mixture dictate the form of the secondary building units from which [(VO)2(C2O4)(SeO3)2]n2n– layers are constructed. The strength of hydrogen-bonding interactions is maximized in these compounds, directly affecting the orientations of the organic ammonium cations and enabling amine packing efficiency to affect layer tessellation. The orientations of selenite stereoactive lone pairs are driven by the minimization of internal void space. Compound symmetry can be directed to chiral space groups through the use of chiral components, with the use of either (R)-2-methylpiperazine or (S)-2-methylpiperazine, resulting in noncentrosymmetric, polar, chiral structures that crystallize in the space group P21 (No. 4).
[Show abstract][Hide abstract] ABSTRACT: Studies directed toward the isoindolinone core of muironolide A are described. An initial plan to implement an intramolecular Diels-Alder cycloaddition was thwarted by an undesired conjugate addition during the attempted preparation of the Diels-Alder substrate. A revised retrosynthetic analysis revealed a direct, albeit challenging, intermolecular Diels-Alder disconnection. Toward this end, a sterically hindered and electronically deactivated diene was utilized with N-phenylmaleimide to achieve a Diels-Alder cycloaddition.
[Show abstract][Hide abstract] ABSTRACT: Benzitripyrranes were prepared by reacting diphenyl benzenedicarbinols with excess pyrrole in the presence of BF3.Et2O. These dipyrrolic compounds underwent acid catalyzed condensations with a pyrrole dialdehyde to afford good yields of diphenylbenziporphyrins, and further reaction with palladium(II) acetate gave stable organometallic derivatives. The X-ray crystal structure of a palladium(II) benziporphyrin showed that the system deviates significantly from planarity. Although the benzitripyrranes failed to give stable macrocyclic products with furan or thiophene dialdehydes, they afforded tetraphenyl heterobenziporphyrins upon reaction with diphenyl furan or thiophene dicarbinols and BF3.Et2O. Benziporphyrins and their heteroanalogues showed no indication of a diamagnetic ring current by proton NMR spectroscopy, but addition of TFA gave rise to the formation of weakly diatropic dications.
The Journal of Organic Chemistry 08/2013; 78(18). DOI:10.1021/jo401365p · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: MacDonald "2 + 2" condensation of a 1,2'-dipyrrylmethane dialdehyde with a 2,2'-dipyrrylmethane afforded a neo-confused porphyrin in 55% yield. In addition, a novel dihydroporphyrin with two appended pyrrolic units was isolated and structurally characterized.
Chemical Communications 07/2013; 49(68). DOI:10.1039/c3cc44248a · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The title compound, CHO, is a phenyl-subsituted dihydro-pyran-dione in which the heterocycle adopts a boat conformation with the phenyl substituent canted 72.14 (5)° relative to the mean plane of the heterocycle.
[Show abstract][Hide abstract] ABSTRACT: Azuliporphyrins were reacted with [Ir(COD)Cl](2) in refluxing o- or p-xylene to give novel iridium(iii) derivatives that regioselectively incorporated an oxidized solvent molecule. The iridium(iii) is inserted within the porphyrinoid macrocycle and possesses an additional apical acyl unit.
Chemical Communications 10/2012; 48(96). DOI:10.1039/c2cc37104a · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Porphyrin ohne N: Bilin‐Analoga und verwandte aromatische Dicarbaporphyrinoide wurden ausgehend von Bis(3‐indenyl)methan hergestellt. Obwohl alle vier Pyrrolringe des Porphyrinmakrocyclus ersetzt wurden (durch je zwei Furan‐ und Inden‐Einheiten), präsentiert das System Porphyrin‐ähnliche UV/Vis‐Spektren und hoch diatrope Charakteristika.
[Show abstract][Hide abstract] ABSTRACT: Porphyrin without N: Bilin analogues and related aromatic dicarbaporphyrinoids have been prepared from bis(3‐indenyl)methane. Even though all four pyrrole rings from the porphyrin macrocycle have been replaced by two furan and two indene subunits, the system retains porphyrin‐like UV/Vis spectra and highly diatropic characteristics.
[Show abstract][Hide abstract] ABSTRACT: Invertiert und doch diatrop: Ein neuer Typ von Porphyrin-Isomeren wird beschrieben, in denen ein Pyrrol-Stickstoffatom an eine der meso-Brücken gebunden ist. Das System behält die typischen Charakteristika der Porphyrine und bildet mit Nickel(II)-acetat einen stabilen metallorganischen Komplex.
[Show abstract][Hide abstract] ABSTRACT: Tripyrrane analogues were prepared by reacting resorcinol or 2-methylresorcinol with 2 equiv of an acetoxymethylpyrrole in the presence of p-toluenesulfonic acid and calcium chloride. Following removal of the benzyl ester protective groups, the resorcinol-derived benzitripyrrane was reacted with a pyrrole dialdehyde to give an aromatic hydroxyoxybenziporphyrin. However, furan and thiophene dialdehydes gave highly insoluble products that could not be fully characterized. The methylresorcinol-derived tripyrrane analogue reacted with pyrrole, furan, thiophene, and selenophene dialdehydes to give unstable porphyrinoids that were further oxidized with [bis(trifluoroacetoxy)iodo]benzene to give stable benziporphyrin derivatives. These oxidized benziporphyrins showed strongly diatropic properties by proton NMR spectroscopy where the differences in chemical shifts (Δδ) were >18 ppm in some cases. The selenophene-derived system was further characterized by X-ray crystallography, and these results showed that one of the pyrrole subunits in this crowded structure was tilted by 21° relative to the mean macrocyclic plane. The tripyrrolic system reacted with silver(I) acetate to give the corresponding silver(III) organometallic complex. Regioselective alkylation with methyl or ethyl iodide and potassium carbonate gave diastereomeric mixtures of N-alkyl derivatives, and the N-ethyl substitution products showed highly diastereotopic characteristics.
The Journal of Organic Chemistry 06/2011; 76(15):6295-308. DOI:10.1021/jo201098c · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Benziporphyrins, cross-conjugated porphyrin analogues with a benzene ring in place of one of the usual pyrrole units, have varying degrees of macrocyclic aromaticity because the 6π electron arene needs to give up its aromatic characteristics to facilitate conjugation over the entire system. As naphthalene would lose less resonance stabilization energy in giving up one of its benzene units, it was proposed that naphthiporphyrins would exhibit enhanced diatropicity compared to the related benziporphyrins. A naphthiporphyrin was prepared using the "3 + 1" variant of the MacDonald condensation by reacting 1,3-naphthalenedicarbaldehyde with a tripyrrane in the presence of TFA, followed by oxidation with DDQ. Although the free base form of naphthiporphyrin showed no overall diatropicity, the corresponding dication in TFA-CDCl(3) demonstrated a significant diatropic ring current where the internal CH shifted upfield to between 4.0 and 4.6 ppm. Naphthiporphyrin was converted to the corresponding palladium(II) complexes by reaction with Pd(OAc)(2) in acetonitrile, and the complex was further characterized by X-ray crystallography. Oxynaphthiporphyrins were similarly prepared by the "3 + 1" methodology from 4-methoxy-1,3-naphthalene-dicarbaldehyde, and these showed slightly enhanced diatropic character compared to oxybenziporphyrins. Reaction of oxybenziporphyrins or oxynaphthiporphyrins with silver(I) acetate afforded the corresponding silver(III) organometallic derivatives. A meso-tetraphenyl naphthiporphyrin was also synthesized in 4% yield by reacting a 1,4-naphthalene dicarbinol with 2 equiv of benzaldehyde and 3 equiv of pyrrole in the presence of BF(3).Et(2)O, followed by oxidation with DDQ. However, this 1,4-naphthiporphyrin showed reduced diatropic character compared to the corresponding p-benziporphyrin system. The NMR spectra for the 1,4-naphthiporphyrin show that the naphthalene unit pivots over the macrocycle and this presumably leads to further steric interactions that reduce the planarity of the macrocycle. These results demonstrate that while naphthiporphyrins can show enhanced aromatic properties as predicted, other factors may overwhelm this effect.
The Journal of Organic Chemistry 06/2011; 76(14):5636-51. DOI:10.1021/jo200622s · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Parts 1 and 2 of this series described the educational value of experimental three-dimensional (3D) chemical structures determined by X-ray crystallography and retrieved from the crystallographic databases. In part 1, we described the information content of the Cambridge Structural Database (CSD) and discussed a representative teaching subset of ca. 500 CSD structures that have been selected for their educational relevance. In part 2, we exemplified the value of the CSD teaching subset by describing four worked examples of their use in a teaching context.Although the CSD teaching subset and its associated learning modules provide a major resource for chemical educators, there are many cases where the full CSD System is essential to make an educational point. In part 3, we describe the complete CSD System and its associated software and highlight the extended range of discovery-based learning opportunities this affords. Here, we illustrate a number of teaching examples that take advantage of the massive structural information content of the complete CSD System to broaden and enhance the chemical education experience, including, for example, studies of mean molecular dimensions, stereochemistry and conformations, metal coordination sphere geometries, hydrogen bonding and other supramolecular phenomena, and reaction pathways.Keywords: First-Year Undergraduate/General; Graduate Education/Research; Second-Year Undergraduate; Upper-Division Undergraduate; Chemoinformatics; Computer-Based Learning; Inquiry-Based/Discovery Learning; Internet/Web-Based Learning; X-ray Crystallography
Journal of chemical education 05/2011; 88(7). DOI:10.1021/ed1011025 · 1.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Parts 1 and 2 of this series described the educational value of experimental three-dimensional (3D) chemical structures determined by X-ray crystallography and retrieved from the crystallographic databases. In part 1, we described the information content of the Cambridge Structural Database (CSD) and discussed a representative teaching subset of ca. 500 CSD structures that have been selected for their educational relevance. In part 2, we exemplified the value of the CSD teaching subset by describing four worked examples of their use in a teaching context.Although the CSD teaching subset and its associated learning modules provide a major resource for chemical educators, there are many cases where the full CSD System, now covering more than 500,000 crystal structures, is essential to make an educational point. This is particularly true when introducing students to variance in real experimental observations, for example, where many hundreds of observations are required to generate statistically meaningful trends from the structural data or simply to introducing students to the search and manipulation of data that are commonly available in large chemical and biochemical databases. Here, we describe the complete CSD System and its associated software and highlight the extended range of discovery-based learning opportunities this affords.Keywords: First-Year Undergraduate/General; Graduate Education/Research; Second-Year Undergraduate; Upper-Division Undergraduate; Chemoinformatics; Computer-Based Learning; Inquiry-Based/Discovery Learning; Internet/Web-Based Learning; X-ray Crystallography
Journal of chemical education 05/2011; 88(7). DOI:10.1021/ed1011019 · 1.00 Impact Factor