Ca2Mg5GeN6 – A Layered Nitridomagnesogermanate

The nitridomagnesogermanate Ca₂Mg₅GeN₆ was synthesized at 780 °C using a sodium flux in sealed tantalum ampules. Pure metals were used as starting materials and sodium azide NaN₃ was added as nitrogen source. Ca₂Mg₅GeN₆ was obtained as a byproduct in the form of colorless platelet‐like crystals. Solution and refinement of the crystal structure [space group P6₃/mmc (no. 194), Z = 1, a = 3.453(2), c = 17.506(13) Å and V = 180.8(2) ų] were performed on the basis of single‐crystal X‐ray diffraction data. Ca₂Mg₅GeN₆ represents the first layered nitridogermanate. Its structure is made up of corner‐sharing (Mg/Ge)N₄ tetrahedra and corner‐sharing trigonal planar (Mg/Ge)N₃ units with mixed occupancy of Mg and Ge. Ca²⁺ ions are located in between the sheets. The crystal structure is closely related to that of the nitridomagnesoaluminate CaMg₂AlN₃ as well as to the carbides ScAl₃C₃ and UAl₃C₃.     

A–π–D–π–A Electron‐Donating Small Molecules for Solution‐Processed Organic Solar Cells: A Review

Organic solar cells based on semiconducting polymers and small molecules have attracted considerable attention in the last two decades. Moreover, the power conversion efficiencies for solution‐processed solar cells containing A–π–D–π–A‐type small molecules and fullerenes have reached 11%. However, the method for designing high‐performance, photovoltaic small molecules still remains unclear. In this review, recent studies on A–π–D–π–A electron‐donating small molecules for organic solar cells are introduced. Moreover, the relationships between molecular properties and device performances are summarized, from which inspiration for the future design of high performance organic solar cells may be obtained.     

Spectroscopical UV–Vis implications of an intramolecular η2–Mg coordination in bacteriochlorophyll–a from the Fenna–Matthews–Olson complex

Chlorophylls and their related compounds prominently feature a Mg²⁺ ion in the center of a porphyrine, with an intermolecular fifth coordination usually observed to place the ion out of the macrocyclic plane. Herein, we assess the role of a potential intramolecular η²–(C = C)Mg interaction and compare it to the intermolecular coordination from the Hystidine groupt to Mg²⁺ for Bacterichlorophyll–a (Bchl–a), the main photosynthetic pigment in the Fenna–Matthews–Olson complex present in green and purple bacteria. The influence of this fifth coordination on the UV‐Vis spectroscopy (CAM‐B3LYP/cc‐pVDZ), and the concomitant change in geometry around Mg in Bchl–a from planar to pyramidal is assessed by the quantum theory of atoms in molecules based non–covalent interactions scheme and through energetic analysis via natural bond orbital population methods at the M06‐2X/cc‐pVDZ and compared to the reference multi–hapto compound, magnesocene, Cp₂Mg.     

A Highly Efficient Friedel–Crafts Reaction of 3‐Hydroxyoxindoles and Aromatic Compounds to 3,3‐Diaryl and 3‐Alkyl‐3‐aryloxindoles Catalyzed by Hg(ClO4)2⋅3 H2O

We report a highly efficient Friedel–Crafts reaction of 3‐alkyl or 3‐aryl 3‐hydroxyoxindoles with a variety of aromatic and heteroaromatic compounds to unsymmetrical 3,3‐diaryloxindoles or 3‐alkyl‐3‐aryloxindoles, which are interesting medicinal targets and useful building blocks for the synthesis of natural products. Hg(ClO₄)₂ ? 3 H₂O was identified as a powerful catalyst for this reaction, and is significantly more efficient than other screened metal perchlorate hydrates and Brønsted acids such as HOTf and HClO₄. The high catalytic property of Hg(ClO₄)₂ ? 3 H₂O originates from the unprecedented dual activation effects of aromatic mercuration, which could generate a strong protic acid to facilitate the generation of a carbocation at the C3‐position of oxindoles and simultaneously form the more reactive nucleophilic reaction partner.     

An Optimised Small‐Molecule Stabiliser of the 14‐3‐3–PMA2 Protein–Protein Interaction

Modulation of protein–protein interactions (PPIs) is a highly demanding, but also a very promising approach in chemical biology and targeted drug discovery. In contrast to inhibiting PPIs with small, chemically tractable molecules, stabilisation of these interactions can only be achieved with complex natural products, like rapamycin, FK506, taxol, forskolin, brefeldin and fusicoccin. Fusicoccin stabilises the activatory complex of the plant H⁺‐ATPase PMA2 and 14‐3‐3 proteins. Recently, we have shown that the stabilising effect of fusicoccin could be mimicked by a trisubstituted pyrrolinone (pyrrolidone1, 1 ). Here, we report the synthesis, functional activity and crystal structure of derivatives of 1 that stabilise the 14‐3‐3–PMA2 complex. With a limited compound collection three modifications that are important for activity enhancement could be determined: 1) conversion of the pyrrolinone scaffold into a pyrazole, 2) introduction of a tetrazole moiety to the phenyl ring that contacts PMA2, and 3) addition of a bromine to the phenyl ring that exclusively contacts the 14‐3‐3 protein. The crystal structure of a pyrazole derivative of 1 in complex with 14‐3‐3 and PMA2 revealed that the more rigid core of this molecule positions the stabiliser deeper into the rim of the interface, enlarging especially the contact surface to PMA2. Combination of the aforementioned features gave rise to a molecule ( 37 ) that displays a threefold increase in stabilising the 14‐3‐3–PMA2 complex over 1 . Compound 37 and the other active derivatives show no effect on two other important 14‐3‐3 protein–protein interactions, that is, with CRaf and p53. This is the first study that describes the successful optimisation of a PPI stabiliser identified by screening.     

MgAuGa and MgAu2Ga: first representatives of the Mg–Au–Ga system

MgAuGa (magnesium gold gallium), the first ternary representative of the Mg–Au–Ga system, crystallizes in the space group P2m and adopts the Fe₂P structure type (Pearson symbol hP9). Various phases with the general composition AB₂ have been reported in the surrounding binary systems, viz. Mg₂Ga (hP18), MgGa₂ (hP6; CaIn₂ type), AuGa₂ (cF12; CaF₂ type), Au₂Ga (oS24; Pd₂As type) and Mg₂Au (oP12; Co₂Si type). In principle, MgAuGa can be obtained from each of them by partial replacement of the major element with the missing element. In fact, the structure of MgAuGa closely resembles hexagonal Mg₂Ga through a direct group–subgroup relationship. MgAu₂Ga (magnesium digold gallium) also crystallizes hexagonally in the space group P6₃/mmc and is isotypic with Na₃As. It adopts the structure of another binary compound, viz. Mg₃Au (hP8), but shows an unexpected distribution of Mg, Au, and Ga among the atomic positions of the asymmetric unit. Both MgAuGa and MgAu₂Ga can be described as formally anionic Au/Ga frameworks, with pseudo‐hexagonal tunnels around Mg in MgAuGa or cages in MgAu₂Ga.     

Umsetzungen der Dielementverbindungen R2E–ER2 [E = Ga,In; R = CH(SiMe3)2] mit Lithium‐phenylethinid – Bildung von Addukten unter Erhalt der E–E‐Bindungen

Reactions of the Dielement Compounds R₂E–ER₂ [E = Ga, In; R = CH(SiMe₃)₂] with Lithium Phenylethynide – Formation of Adducts by Retention of the E–E Bonds Lithium phenylethynide reacted with the dielement compounds tetrakis[bis(trimethylsilyl)methyl]digallane(4) ( 2 ) and diindane(4) ( 3 ) as a Lewis‐base and gave by the addition of one ethynido ligand to one of the Lewis‐acidic central atoms the anionic adducts 4 and 5 with intact Ga–Ga and In–In single bonds. Thus, compounds were formed, in which tricoordinated, coordinatively unsaturated Ga or In atoms are neighbored to tetracoordinated, coordinatively saturated ones. The E–E bonds [255.83 pm in 4 (Ga–Ga) and 285.24 pm in 5 (In–In)] are only slightly lengthened compared to those of the starting compounds 2 and 3 . A dynamic behavior with a fast change of the position of the ethynido ligand was observed for both compounds in solution at room temperature.     

Enhanced epoxidation of soybean oil by novel Al2O3–ZrO2–TiO2 solid acid catalyst

This study aims to develop highly efficient, recyclable solid catalysts for the epoxidation of vegetable oils. An Al₂O₃–ZrO₂–TiO₂ solid acid catalyst was prepared by a co‐precipitation/impregnation method and characterised through scanning electron microscopy, energy‐dispersive spectroscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, Fourier‐transform infrared and nitrogen adsorption–desorption analyses. The solid acid catalyst with a high surface area and typical slit pore adsorption was successfully synthesised. Al₂O₃–ZrO₂–TiO₂ also exhibits high stability and improved catalytic efficiency in the epoxidation of soybean oil. An oil conversion rate of 86.6%, which is higher than that of conventional catalysts, was obtained with a catalyst loading of 0.8 wt% and was maintained at 76.6% even after recycling the catalyst three times. The performance of the solid catalyst was slightly superior to that of H₂SO₄. Therefore, this novel catalyst may potentially be applicable in catalysing soybean oil epoxidation.     

[Co(g5‐Me5C5)(g3‐tBu2PPCH–CH3)] aus [Co(g5‐Me5C5)(g2‐C2H4)2] und tBu2P–P=P(Me)tBu2

Coordination Chemistry of P‐rich Phosphanes and Silylphosphanes. XVII [1] [Co(g⁵‐Me₅C₅)(g³‐^tBu₂PPCH–CH₃)] from [Co(g⁵‐Me₅C₅)(g²‐C₂H₄)₂] and ^tBu₂P–P=P(Me)^tBu₂ [Co(η⁵‐Me₅C₅)(η³‐^tBu₂PPCH–CH₃)] 1 is formed in the reaction of [Co(η⁵‐Me₅C₅)(η²‐C₂H₄)₂] 2 with ^tBu₂P–P 4 (generated from ^tBu₂P–P=P(Me)^tBu₂ 3 ) by elimination of one C₂H₄ ligand and coupling of the phosphinophosphinidene with the second one. The structure of 1 is proven by ³¹P, ¹³C, ¹H NMR spectra and the X‐ray structure analysis. Within the ligand ^tBu₂P¹P²C¹H–CH₃ in 1 , the angle P1–P2–C1 amounts to 90°. The Co, P1, P2, C1 atoms in 1 look like a „butterfly”︁. The reaction of 2 with a mixture of ^tBu₂P–P=P(Me)^tBu₂ 3 and ^tBu–C?P 5 yields [Co(η⁵‐Me₅C₅){η⁴‐(^tBuCP)₂}] 6 and 1 . While 6 is spontaneously formed, 1 appears only after complete consumption of 5 .     

Photophysical properties of σ–π‐conjugated alternating oligothienylene–oligosilylene polymers

UV‐visible absorption and fluorescence properties of three series of σ–π‐conjugated polymers (copolymers of alternative oligothienylene and oligosilylene units) have been studied in dioxane solution. The energies of the absorption maximum, fluorescence maximum, and the 0–0 transition are found to be linearly dependent on the reciprocal of the number of thiophene rings in the repeating unit of the polymer chain, but almost independent of the silicon atom number. The σ–π‐conjugation in the polymers results in red shift in the absorption and fluorescence maxima, higher fluorescence quantum yields, and longer fluorescence lifetimes of the polymers, with respect to their corresponding analogous α‐oligothiophenes. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1873–1880, 1999     

The Prominent Enhancing Effect of the Cation–π Interaction on the Halogen–Hydride Halogen Bond in M1⋅⋅⋅C6H5X⋅⋅⋅HM2

We designed M¹???C₆H₅X???HM² (M¹=Li⁺, Na⁺; X=Cl, Br; M²=Li, Na, BeH, MgH) complexes to enhance halogen–hydride halogen bonding with a cation–π interaction. The interaction strength has been estimated mainly in terms of the binding distance and the interaction energy. The results show that halogen–hydride halogen bonding is strengthened greatly by a cation–π interaction. The interaction energy in the triads is two to six times as much as that in the dyads. The largest interaction energy is ?8.31 kcal mol^?1 for the halogen bond in the Li⁺???C₆H₅Br???HNa complex. The nature of the cation, the halogen donor, and the metal hydride influence the nature of the halogen bond. The enhancement effect of Li⁺ on the halogen bond is larger than that of Na⁺. The halogen bond in the Cl donor has a greater enhancement than that in the Br one. The metal hydride imposes its effect in the order HBeH<HMgH<HNa<HLi for the Cl complex and HBeH<HMgH<HLi<HNa for the Br complex. The large cooperative energy indicates that there is a strong interplay between the halogen–hydride halogen bonding and the cation–π interaction. Natural bond orbital and energy decomposition analyses indicate that the electrostatic interaction plays a dominate role in enhancing halogen bonding by a cation–π interaction.     

Dual Organocatalysis: Asymmetric Allylic–Allylic Alkylation of α,α‐Dicyanoalkenes and Morita–Baylis–Hillman Carbonates

The first highly enantioselective allylic–allylic alkylation of α,α‐dicyanoalkenes and Morita–Baylis–Hillman carbonates by dual catalysis of (DHQD)₂AQN and (S)‐BINOL has been investigated. Excellent stereoselectivities have been achieved for a broad spectrum of substrates (d.r. > 99:1, up to 99 % ee). The multifunctional allylic products could be efficiently converted to a range of complex chiral cyclic frameworks. EWG=electron‐withdrawing group, (DHQD)₂AQN=hydroquinidine (anthraquinone‐1,4‐diyl) diether, (S)‐BINOL =(S)‐(?)‐1,1′‐bi‐2‐naphthol.

     

Concise Approach to (ent)‐14 β‐Hydroxysteroids through Highly Diastereo‐/Enantioselective Diels–Alder Reactions

14β‐Hydroxysteroids, especially 14β‐hydroxyandrostane derivatives are closely related to the cardenolide skeletons. The latter were readily available through highly diastero/enantioselective Diels–Alder (DA) reactions requiring high pressure or Lewis acid activation. Moreover, in the presence of (R)‐ or (S)‐carvone as a chiral dienophile, the DA‐reaction takes place under chemodivergent parallel kinetic resolution control affording highly enantiomerically enriched 14β‐hydroxysteroid derivatives or the corresponding (ent)‐14β‐hydroxysteroid derivatives.     

Yb6Ir5Ga7 – A MgZn2 Superstructure

The gallide Yb₆Ir₅Ga₇ was synthesized by high‐frequency melting of the elements in a sealed niobium ampoule. The structure was refined from single‐crystal X‐ray diffractometer data: Nb_6.4Ir₄Al_7.6 type, P6₃/mcm, a = 930.4(1), c = 843.0(1) pm, wR₂ = 0.0597, 379 F² values and 22 variables. Yb₆Ir₅Ga₇ adopts a superstructure of the MgZn₂ Laves phase by a complete ordering of the iridium and gallium atoms on the zinc substructure, i.e. the network consists of ordered and condensed Ir₃Ga and IrGa₃ tetrahedra with Ir–Ga distances ranging from 260 to 265 pm. The crystal chemical details and the underlying group‐subgroup scheme are discussed.     

σ–π Continuum in Indole–Palladium(II) Complexes

The intrinsic features of (hetero‐arene)–metal interactions have been elusive mainly because the systematic structure analysis of non‐anchored hetero‐arene–metal complexes has been hampered by their labile nature. We report successful isolation and systematic structure analysis of a series of non‐anchored indole–palladium(II) complexes. It was revealed that there is a σ–π continuum for the indole–metal interaction, while it has been thought that the dominant coordination mode of indole to a metal center is the Wheland‐intermediate‐type σ‐mode in light of the seemingly strong electron‐donating ability of indole. Several factors which affect the σ‐ or π‐character of indole–metal interactions are discussed.