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- Biochemie und Chemie (194) (remove)
The title compound, di-μ3-chlorido-tetra-μ2-chlorido-tetrakis(diethyl ether-κO)bis(1,1-dimethylethyl)tetramagnesium, [Mg4(C4H9)2Cl6(C4H10O)4], features an Mg4Cl6 open-cube cluster. The two four-coordinate Mg2+ ions show an almost tetrahedral coordination, whereas the two six-coordinate Mg2+ ions have their ligands in an octahedral environment. The Mg—Cl bond lengths differ depending on the coordination number (2 or 3) of the bridging μ-Cl− ligands. There are few comparable structures deposited in the Cambridge Structural Database.
Synthesis and crystal structure of 2-(2-hydroxyphenyl)-1,3-bis(4-methoxybenzyl)-1,3-diazinan-5-ol
(2022)
The redetermined structure of 2-(2-hydroxyphenyl)-1,3-bis(4-methoxybenzyl)-1,3-diazinan-5-ol, C26H30N2O4, at 173 K has orthorhombic (Pbca) symmetry. It was previously described by Bolte et al. [ Private Communication (refcode EWICEV). CCDC, Cambridge, England]. The title compound resulted from the condensation reaction between 1,3-bis{[(4-methoxyphenyl)methyl]amino}propan-2-ol and 2-hydroxybenzaldehyde in CH3OH. The structure exhibits disorder. One of the 4-methoxybenzyl groups, the hydroxy group bonded to the 1,3-diazinan ring, and the methyl group of the methoxy residue are disordered over two orientations, with occupancies of 0.807 (3)/0.193 (3), 0.642 (5)/0.358 (5), and 0.82 (4)/0.18 (4), respectively. The dihedral angles between the mean planes of the central 1,3-diazinan-5-ol and the 4-methoxyphenyl rings (both occupancy components of the disordered ring) are 88.65 (13), 85.79 (14) and 83.4 (7)°. The crystal packing is sustained by C—H...O and O—H...π interactions, giving rise to infinite chains running along the b-axis direction.
The title compound, C8H16N4·2C11H16O, was synthesized from the corresponding sterically crowded phenol by treatment with the aminal cage polyamine. Single-crystal X-ray diffraction structural analysis revealed the three-molecule aggregate to crystallize in the monoclinic space group P2/c with one half of a 1,3,6,8-tetraaztricyclo[4.4.1.13,8]dodecane (TATD) molecule and one 2-tert-butyl-4-methylphenol molecule per asymmetric unit. The crystal structure features intermolecular O—H...N and C—H...O hydrogen bonds, as well as intermolecular C—H...π interactions.
First crystal structure of a Pigment Red 52 compound: DMSO solvate hydrate of the monosodium salt
(2021)
Pigment Red 52, Na2[C18H11ClN2O6S], is an industrially produced hydrazone-laked pigment. It serves as an intermediate in the synthesis of the corresponding Ca2+ and Mn2+ salts, which are used commercially for printing inks and lacquers. Hitherto, no crystal structure of any salt of Pigment Red 52 is known. Now, single crystals have been obtained of a dimethyl sulfoxide solvate hydrate of the monosodium salt of Pigment Red 52, namely, monosodium 2-[2-(3-carboxy-2-oxo-1,2-dihydronaphthalen-1-ylidene)hydrazin-1-yl]-5-chloro-4-methylbenzenesulfonate dimethyl sulfoxide monosolvate monohydrate, Na+·C18H12ClN2O6S−·H2O·C2H6OS, obtained from in-house synthesized Pigment Red 52. The crystal structure was determined by single-crystal X-ray diffraction at 173 K. In this monosodium salt, the SO3− group is deprotonated, whereas the COOH group is protonated. The residues form chains via ionic interactions and hydrogen bonds. The chains are arranged in polar/non-polar double layers.
The respiratory chain of Escherichia coli contains two different types of terminal oxidase that are differentially regulated as a response to changing environmental conditions. These oxidoreductases catalyze the reduction of molecular oxygen to water and contribute to the proton motive force. The cytochrome bo3 oxidase (cyt bo3) acts as the primary terminal oxidase under atmospheric oxygen levels, whereas the bd‐type oxidase is most abundant under microaerobic conditions. In E. coli, both types of respiratory terminal oxidase (HCO and bd‐type) use ubiquinol‐8 as electron donor. Here, we assess the inhibitory potential of newly designed and synthesized 3‐alkylated Lawson derivatives through L‐proline‐catalyzed three‐component reductive alkylation (TCRA). The inhibitory effects of these Lawson derivatives on the terminal oxidases of E. coli (cyt bo3 and cyt bd‐I) were tested potentiometrically. Four compounds were able to reduce the oxidoreductase activity of cyt bo3 by more than 50 % without affecting the cyt bd‐I activity. Moreover, two inhibitors for both cyt bo3 and cyt bd‐I oxidase could be identified. Based on molecular‐docking simulations, we propose binding modes of the new Lawson inhibitors. The molecular fragment benzyl enhances the inhibitory potential and selectivity for cyt bo3, whereas heterocycles reduce this effect. This work extends the library of 3‐alkylated Lawson derivatives as selective inhibitors for respiratory oxidases and provides molecular probes for detailed investigations of the mechanisms of respiratory‐chain enzymes of E. coli.
A new pseudopolymorph of perchlorinated neopentasilane: the benzene monosolvate Si(SiCl3)4·C6H6
(2020)
A new pseudopolymorph of dodecachloropentasilane, namely a benzene monosolvate, Si5Cl12·C6H6, is described. There are two half molecules of each kind in the asymmetric unit. Both Si5Cl12 molecules are completed by crystallographic twofold symmetry. One of the benzene molecules is located on a twofold rotation axis with two C—H groups located on this rotation axis. The second benzene molecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional interactions beyond normal van der Waals contacts occur in the crystal.
NHC supersilyl silver complex [Ag(IPr)SitBu3] as a promising agent for substitution reactions
(2020)
The NHC supersilyl silver complex [Ag(IPr)SitBu3] (IPr = NHCIPr) was prepared by treatment of Ag(IPr)Cl with Na(thf)2[SitBu3] in benzene/thf at room temperature. X‐ray quality crystals of the NHC supersilyl silver complex [Ag(IPr)SitBu3] (monoclinic, space group P21/m) were grown from heptane at room temperature. The 29Si NMR spectrum of a solution of [Ag(IPr)SitBu3] in C6D6 revealed two doublets caused by coupling to 107Ag and 109Ag nuclei. We further investigated the possibility of a conversion of triel halides EX3 by treatment with [Ag(IPr)SitBu3]. At ambient temperature the reaction of [Ag(IPr)SitBu3] with an excess of EX3 yielded tBu3SiEX2 (E = B, Al; X = Cl, Br; E = Ga; X = Cl) and IPr·EX3 (EX3 = BCl3, BBr3, AlCl3, AlBr3, GaCl3). The identity of tBu3SiEX2 and IPr·EX3 was confirmed by comparison with authentic samples.
The tetraaryl μ‐hydridodiborane(4) anion [2H]− possesses nucleophilic B−B and B−H bonds. Treatment of K[2H] with the electrophilic 9‐H‐9‐borafluorene (HBFlu) furnishes the B3 cluster K[3], with a triangular boron core linked through two BHB two‐electron, three‐center bonds and one electron‐precise B−B bond, reminiscent of the prominent [B3H8]− anion. Upon heating or prolonged stirring at room temperature, K[3] rearranges to a slightly more stable isomer K[3 a]. The reaction of M[2H] (M+=Li+, K+) with MeI or Me3SiCl leads to equimolar amounts of 9‐R‐9‐borafluorene and HBFlu (R=Me or Me3Si). Thus, [2H]− behaves as a masked [:BFlu]− nucleophile. The HBFlu by‐product was used in situ to establish a tandem substitution‐hydroboration reaction: a 1:1 mixture of M[2H] and allyl bromide gave the 1,3‐propylene‐linked ditopic 9‐borafluorene 5 as sole product. M[2H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R2BFlu].
Vicinally diiodinated polycyclic aromatic hydrocarbons (I2‐PAHs) are accessible from the corresponding diborylated B2‐PAHs through boron/iodine exchange. The B2‐PAHs have been prepared via twofold electrophilic borylation reactions templated by a vicinally disilylated benzene. Our protocol is applicable to fluorenes, acenes, annulated acenes, oligoaryls, and even [5]helicene. Using B2‐naphthalene as the example, we have shown that the reaction scope can, in principle, be expanded to include the synthesis of vicinally dibrominated and dihydroxylated PAHs. The usefulness of the building blocks provided by our method in the field of optoelectronic materials was demonstrated by the successful conversion of I2‐fluoranthene to the analogous doubly alkynylated fluoranthene emitter.
[1,3-Bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene]triiodoborane benzene hemisolvate
(2020)
Remote control of the synthesis of a [2]rotaxane and its shuttling via metal‐ion translocation
(2019)
Remote control in an eight‐component network commanded both the synthesis and shuttling of a [2]rotaxane via metal‐ion translocation, the latter being easily monitored by distinct colorimetric and fluorimetric signals. Addition of zinc(II) ions to the red colored copper‐ion relay station rapidly liberated copper(I) ions and afforded the corresponding zinc complex that was visualized by a bright sky blue fluorescence at 460 nm. In a mixture of all eight components of the network, the liberated copper(I) ions were translocated to a macrocycle that catalyzed formation of a rotaxane by a double‐click reaction of acetylenic and diazide compounds. The shuttling frequency in the copper‐loaded [2]rotaxane was determined to k298=30 kHz (ΔH≠=62.3±0.6 kJ mol−1, ΔS≠=50.1±5.1 J mol−1 K−1, ΔG≠298=47.4 kJ mol−1). Removal of zinc(II) ions from the mixture reversed the system back generating the metal‐free rotaxane. Further alternate addition and removal of Zn2+ reversibly controlled the shuttling mode of the rotaxane in this eight‐component network where the ion translocation status was monitored by the naked eye.
A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ‐bonds and five continuous stereogenic centers are formed in this one‐pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E‐ or a Z‐configured enamide.
We have encountered two polymorphs of the title compound, C24H16B2OS2, both of which display almost the same unit-cell parameters. Compound (I) crystallizes in the non-centrosymmetric space group P21 with four molecules in the asymmetric unit. These molecules are related by pseudosymmetry. As a result, the space group looks like P21/c, but the structure cannot be refined successfully in that space group. Compound (II) on the other hand crystallizes in the centrosymmetric space group P21/c with only two molecules in the asymmetric unit. The crystals studied for (I) and (II) were both non-merohedral twins.
Iodo(triphenyl)silane
(2019)
The molecular structure of the title compound, C18H15ISi, which crystallizes in the space group C2/c, does not exhibit any unusual features. Two weak C—H⋯π interactions may help to consolidate the packing. The present structure is not isostructural with the known Ph3SiX (X = F, Cl or Br) compounds.
The title co-crystal, 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane (HMTA, 1)–4-fluorophenol (4-FP) (1/1), C6H12N4·C6H5FO, shows an unusual asymmetric unit that comprises eight independent molecules (Z′′ = 8), four for each component, with four formula units per asymmetric unit (Z′ = 4). In the molecular packing, each HMTA molecule bridges one 4-FP molecule via an O−H···N hydrogen bond to form a two-molecule aggregate. Differences can be observed between the bond lengths and angles of the independent HMTA and 4-FP molecules and those of the molecules in the aggregate. The C−N bonds exhibit different bond lengths in the tetrahedral cage-like structure of the HMTA molecules, but the largest differences between the molecular aggregates are in the bond lengths in the 4-fluorophenol ring. In the crystal, the HMTA and 4-FP molecules form two hydrogen-bonded (O−H···N, C−H···F and C−H···O) dimers of HMTA and 4-FP molecules, A···D and B···C inversion dimers, which generate enlarged R88(34) ring motifs in both supramolecular structures. In both structures, the crystal packing also features additional C−H···F and C−H···O interactions. The A···D and B···C dimers are linked by additional C−H···F and C−H···O hydrogen bonds, forming columns along the a and b axes, respectively. The importance of the C−H···F interaction to the structure and crystal packing has been demonstrated.
Structural and vibrational studies have been carried out for the most stable conformer of 3,3′-ethane-1,2-diyl-bis-1,3,5-triazabicyclo[3.2.1]octane (ETABOC) at the DFT/B3LYP/6-31G(dp) level using the Gaussian 03 software. In light of the computed vibrational parameters, the observed IR Bolhmann bands for the C2V, C2, and Ci symmetrical structures of ETABOC have been analyzed. Hyperconjugative interaction was done by Natural Bond Orbital Analysis. Interpretation of hyperconjugative interaction involving the lone pairs on the bridgehead nitrogen atoms with the neighboring C–N and C–C bonds defines the conformational preference of the title compound. The recorded X-ray diffraction bond parameters were compared with theoretical values calculated at B3LYP/6-31G(d,p) and HF/6-31G(d,p) level of theory showed that ETABOC adopts a chair conformation and possesses an inversion center.
The synthesis and single crystal structure of a new cocrystal, which is composed of OHphenolic∙∙∙OHphenolic∙∙∙Naminalic supramolecular heterosynthons assembled from 4-tert-butylphenol and the macrocyclic aminal TATU, is presented. This cocrystal was prepared by solvent-free assisted grinding, which is a commonly used mechanochemical method. Crystal structure, supramolecular assembly through hydrogen bonding interactions as well as the physical and spectroscopic properties of the title cocrystal are presented in this paper.
Organoboranes are among the most versatile and widely used reagents in synthetic chemistry. A significant further expansion of their application spectrum would be achievable if boron-containing reactive intermediates capable of inserting into C–H bonds or performing nucleophilic substitution reactions were readily available. However, current progress in the field is still hampered by a lack of universal design concepts and mechanistic understanding. Herein we report that the doubly arylene-bridged diborane(6) 1H2 and its B[double bond, length as m-dash]B-bonded formal deprotonation product Li2[1] can activate the particularly inert C(sp3)–H bonds of added H3CLi and H3CCl, respectively. The first case involves the attack of [H3C]− on a Lewis-acidic boron center, whereas the second case follows a polarity-inverted pathway with nucleophilic attack of the B[double bond, length as m-dash]B double bond on H3CCl. Mechanistic details were elucidated by means of deuterium-labeled reagents, a radical clock, α,ω-dihaloalkane substrates, the experimental identification of key intermediates, and quantum-chemical calculations. It turned out that both systems, H3CLi/1H2 and H3CCl/Li2[1], ultimately funnel into the same reaction pathway, which likely proceeds past a borylene-type intermediate and requires the cooperative interaction of both boron atoms.
In the title compound, C17H18N2O, the central carbon atom with the OH substituent and one of the (E)-benzylideneamino substituents are disordered over two sets of sites with occupancies of 0.851 (4) and 0.149 (4). The relative positions of the two disorder components is equivalent to a rotation of approximately 60° about the C—N single bond. In the crystal, the molecules are held together by O—H...N hydrogen bonds, forming simple C(5) chains along the b-axis direction. In addition, pairs of the chains are further aggregated by weak C—H...π interactions.
The asymmetric unit of the title compound, C21H28N4O, consists of two unique molecules linked by an O—H⋯N hydrogen bond. The conformation of both C=N bonds is E and the azomethine functional groups lie close to the plane of their associated benzene rings in each of the independent molecules. The dihedral angles between the two benzene rings are 83.14 (4) and 75.45 (4)°. The plane of the one of the N(CH3)2 units is twisted away from the benzene ring by 18.8 (2)°, indicating loss of conjugation between the lone electron pair and the benzene ring. In the crystal structure, O—H⋯N hydrogen bonds together with C—H⋯O hydrogen bonds link neighbouring supramolecular dimers into a three-dimensional network.