Adducts of Lewis acidic stibanes with phosphane chalcogenides.

Starting from ClSbR (R = CF, 3,5-(CF)CH) and H(E)P(Bu) (E = O, S), we prepared the oxy- and sulphanediyl-bridged adducts RSb(Cl)-E-(H)P(Bu), which are stable against the elimination of HCl. The different electron-withdrawing substituents and chalcogen bridging units influence the size of the Sb-E-P angle. ClSb(CF) and BuSnH react to give HSb(CF), which seems to interact weakly with H(O)P(Bu) in solution as observed NMR.

Host-guest chemistry of tridentate Lewis acids based on tribenzotriquinacene.

Flexible poly-Lewis acids (PLA) based on the tribenzotriquinacene (TBTQ) scaffold have been synthesised. Hydrosilylation of 4b,8b,12b-triallyltribenzotriquinacene and subsequent exchange of the chlorine substituents with weaker coordinating triflate groups afforded a novel triple silyl-functionalised PLA. By regioselective hydroboration of triallyl-TBTQ with various organoboranes, PLAs with different Lewis acidities were obtained.

Tridentate Lewis Acids Based on Tribenzotriquinacene Chalices.

Chalice-shaped tridentate poly-Lewis acids (PLA) based on the tribenzotriquinacene (TBTQ) scaffold have been synthesised. Stannylation of the alkyne units, attached via phenyl-spacers to the benzhydrylic positions to the TBTQ scaffold, with MeNSnMe afforded the trimethyltin substituted TBTQ derivative. Replacement of these tin functions with other elements resulted in rigid boron- and aluminium-functionalised PLAs.

Photoresponsive Dissipative Macrocycles Using Visible-Light-Switchable Azobenzenes.

Visible light can be used to shift dynamic covalent imine assemblies out of equilibrium. We studied a fluorinated azobenzene building block that reliably undergoes geometric isomerism upon irradiation. The building block was used in combination with two different amines, ethylenediamine and R,R-1,2-diaminocyclohexane, to create a library of imine macrocycles.

Carbon dioxide reduction by an Al-O-P frustrated Lewis pair.

The reaction of BuP(O)H with BisAlH (Bis = CH(SiMe)) afforded the adduct BuP(H)-O-Al(H)Bis (3). It slowly releases H to form the first oxygen-bridged geminal Al/P frustrated Lewis pair BuP-O-AlBis. It is capable of reversibly binding molecular hydrogen to afford 3, shown by NMR and H/D scrambling experiments, and forms a 1,2-adduct with CO.

Noncovalent Synergy: Aurophilicity and Aryl Stacking in Bis(gold(I)aryl)-dmpm Complexes.

Bis(dimethylphosphino)methane (dmpm) was used as a ligand to synthesize four semi-supported dinuclear gold(I) complexes, dmpm(AuR) (R = Cl, CH, CCl, and CF), which were studied concerning the synergistic effects of two weak noncovalent interactions: aurophilic and aryl-aryl stacking interactions. The chloro-substituted complex was synthesized by the ligand substitution of (tht)AuCl with dmpm and further functionalized by the reaction with PhMgBr or generated CClLi to afford the phenyl- and pentachlorophenyl-substituted compounds, respectively. The pentafluorophenyl-substituted gold complex was generated by the ligand substitution of (tht)Au(CF) with dmpm.

Host-guest chemistry of a bidentate silyl-triflate bis-Lewis acid - complex complexation behaviour unravelled by diffusion NMR spectroscopy.

The bidentate silicon-based Lewis acid, bis(dimethyl-(trifluoromethylsulfonyl)silylethyl)dimethylsilane, MeSi[(CH)SiMeOTf], was prepared in a two-step synthesis starting from dimethyldivinylsilane by hydrosilylation with dimethylchlorosilane and subsequent Lewis acidity enhancement of the terminal silicon atoms by substituting the chlorine with triflate groups using silver triflate. The potential of the resulting MeSi[(CH)SiMeOTf] for binding of Lewis basic guests was explored in reactions with mono- and bifunctional aromatic nitrogen bases. A 1 : 2-adduct with pyridine and a 2 : 2-adduct with 4,4'-bipyridine was structurally characterised in the solid state.

Evaluation of the binding mode of a cytotoxic dinuclear nickel complex to two neighboring phosphates of the DNA backbone.

A family of dinuclear complexes based on 2,7-disubstituted 1,8-naphthalenediol-ligands has been designed to bind covalently to two neighboring phosphate diester groups in the backbone of DNA. The dinuclear Cu and Ni complexes bind to DNA resulting in the inhibition of DNA synthesis in PCR experiments and in a cytotoxicity that is stronger for human cancer cells than for human stem cells of the same proliferation rate. These experiments support but cannot prove that the dinuclear complexes bind as intended to two neighboring phosphate ester groups of the DNA backbone.

Monitoring dynamic pre-crystallization aggregation processes in solution by VT-DOSY-NMR spectroscopy.

Equimolar mixtures of pyridine (Py) with -halotetrafluoropyridine (BrTFP and ITFP) were investigated by VT-diffusion NMR experiments. The formation of a halogen-bond-stabilized ITFPPy complex was detected upon cooling a solution in methylcyclohexane- to 260 K; this allows monitoring a halogen-bond-driven aggregation process preceding crystallization in solution.

The Structure of Bis(catecholato)silanes: Phase Adaptation by Dynamic Covalent Chemistry of the Si-O Bond.

Catechols occupy a unique role in the structural, bio-, and geochemistry of silicon. Although a wealth of knowledge exists on their hypercoordinate complexes, the structure of tetracoordinate bis(catecholato)silane, Si(cat) , has been enigmatic since its first report in 1951. Indeed, the claim of a planar-tetracoordinated silicon in triggered a prominent debate, which is unsettled to this day.

Novel glucosinolate metabolism in larvae of the leaf beetle Phaedon cochleariae.

Plants of the Brassicales are defended by a binary system, in which glucosinolates are degraded by myrosinases, forming toxic breakdown products such as isothiocyanates and nitriles. Various detoxification pathways and avoidance strategies have been found that allow different herbivorous insect taxa to deal with the glucosinolate-myrosinase system of their host plants. Here, we investigated how larvae of the leaf beetle species Phaedon cochleariae (Coleoptera: Chrysomelidae), a feeding specialist on Brassicaceae, cope with this binary defence.

A Rational Approach to Tetra-Functional Photo-Switches.

α,ω-Bis(1,8-dichloroanthracen-10-yl)alkanes with (CH) -linker units (=1-4) were synthesized starting from 1,8-dichloroanthracen-10(9)-one. This was transformed into anthracenes with allyl, bromomethyl and propargyl substituents in position 10; these were converted in various C-C-bond formation reactions (plus hydrogenation), leading to two anthracene units flexibly linked by α,ω-alkandiyl groups. 1,2-Ethandiyl- and 1,3-propandiyl-linked derivatives were functionalized with ethynyl groups in positions 1, 8, 1' and 8', and these terminally functionalized by MeSn groups using MeNSnMe.

A Neutral Geminal Tin/Phosphorus Frustrated Lewis Pair.

The geminal frustrated Lewis pair (FLP) (F C ) SnCH P(tBu) (2) was prepared by reacting (F C ) SnCl with LiCH P(tBu) . It is neutral and contains an extremely electronegatively substituted, but relatively soft (hard-soft acid-base, HSAB) acidic tin function. Its FLP-type reactivity was proven by reaction with a variety of small molecules (CO , SO , CS , PhNCO, HCl, (Ph P)AuCl).

Shear-Induced Transformation of Polymer-Rich Lamellar Phases to Micron-Sized Vesicles.

In the present work, we study the shear-induced transformation of polymer-rich lamellar phases into vesicles. The evolution of vesicle size is studied by different scattering techniques, rheology, and microscopy methods. The lamellar phase found in the system DO/ o-xylene/ Pluronic PE9400/CTAB can be fully transformed to multilamellar vesicles (MLVs) by applying shear.

The Viability of C5-Protonated- and C4,C5-Ditopic Carbanionic Abnormal NHCs: A New Dimension in NHC Chemistry.

The first C5-protonated abnormal N-heterocyclic carbene (aNHC), PhC{N(2,6-iPr C H )} CHC: (4) is readily accessible by C4-deprotonation of [ArC{N(2,6-iPr C H )} CHCH]X (3 a-X) (Ar=Ph, X=Br or I) with a base. The aNHC 4 is stable at 298 K in [D ]THF solution and has been spectroscopically characterized. The facile availability of 4 enables the synthesis of a series of main-group compounds as well as transition-metal complexes featuring a new phosphorus-aNHC hybrid ligand.

From Bidentate Gallium Lewis Acids to Supramolecular Complexes.

Bidentate gallium Lewis acids were prepared by the reaction of diethynyldiphenylsilane with neat trimethyl- or triethylgallium. Bis[(dimethylgallyl)ethynyl]diphenylsilane (1) and diethylgallyl derivative 2 were characterized as Et O or pyridine adducts by NMR spectroscopy; 2⋅2Py was isolated. Lewis acids 1 and 2 form host-guest adducts with bidentate nitrogen bases, but defined cyclic 1:1 adducts are only formed between 1 and bases with matching N⋅⋅⋅N distances: 4,4'-dimethyl-3,3'-bipyridinylacetylene (3), bis[(pyridin-3-yl)ethynyl]diphenylsilane (4), and bis[(2-methylpyridin-5-yl)ethynyl]diphenylsilane (5).

Fluoride complexation by bidentate silicon Lewis acids.

Diethynyldiphenylsilane (1) and divinyldiphenylsilane (2) were functionalized by hydrosilylation reactions with HSiMeCl, HSiMeCl and HSiCl. Fluorination of the resulting compounds generates bidentate open-chain Lewis acids of increasing acidity. All semi-flexible [PhSi(CH[double bond, length as m-dash]CHSiFMe) (n = 1, 2, 3)] and flexible [PhSi(CH-CHSiFMe) (n = 1, 2, 3)] bidentate Lewis acids were obtained in good to excellent yields.

Tridentate Lewis-acids based on triphenylsilane.

Several derivatives of the propeller-shaped ortho-substituted triphenylsilanes, carrying metal- or silicon-based acceptor groups, are reported. They were synthesized starting from tris(2-bromophenyl)fluorosilane, tris(2-vinylphenyl)fluorosilane and tris(2-ethynylphenyl)fluorosilane to generate a scope of Lewis-acidic molecules with different cavities. An improved synthetic protocol for donor-free tris(2-lithiophenyl)silanes is described.

Recombinant expression and characterization of a L-amino acid oxidase from the fungus Rhizoctonia solani.

L-Amino acid oxidases (L-AAOs) catalyze the oxidative deamination of L-amino acids to the corresponding α-keto acids, ammonia, and hydrogen peroxide. L-AAOs are homodimeric enzymes with FAD as a non-covalently bound cofactor. They are of potential interest for biotechnological applications.

Intramolecular Lewis pairs with two acid sites - reactivity differences between P- and N-based systems.

The doubly acid-functionalised aniline PhN[(CH)B(CF)] shows rapidly exchanging boron acid groups at the central base function and is an active frustrated Lewis pair due to cooperative hydride binding by both Lewis acids. Here we report investigations on the effect of different substituents at the central nitrogen atom and on the effect of exchanging nitrogen by phosphorus. Treatment of diallyl-tert-butylaniline with one equivalent of HB(CF) led to formation of a seven-membered iminium hydridoborate ring; after mono-hydroboration the intermediately formed frustrated Lewis pair reacts with the second allylamine function under ring closure.

Intramolecular cooperativity in frustrated Lewis pairs.

The doubly Lewis-acid functionalised aniline PhN[(CH2)3B(C6F5)2]2 features two competing boron functions in fast exchange for binding to the central Lewis base. It shows catalytic activity typical for FLPs in H/D-scrambling and catalytic hydrogenation experiments. By contrast, the singly acid-functionalised PhMeN(CH2)3B(C6F5)2 reveals a dramatically smaller catalytic activity in analogous experiments.

A Neutral Silicon/Phosphorus Frustrated Lewis Pair.

Frustrated Lewis pairs (FLPs) have a great potential for activation of small molecules. Most known FLP systems are based on boron or aluminum atoms as acid functions, few on zinc, and only two on boron-isoelectronic silicenium cation systems. The first FLP system based on a neutral silane, (C2F5)3SiCH2P(tBu)2 (1), was prepared from (C2F5)3SiCl with C2F5 groups of very high electronegativity and LiCH2P(tBu)2.

Tridentate Lewis Acids Based on 1,3,5-Trisilacyclohexane Backbones and an Example of Their Host-Guest Chemistry.

Directed tridentate Lewis acids based on the 1,3,5-trisilacyclohexane skeleton with three ethynyl groups [CH2Si(Me)(C2H)]3 were synthesised and functionalised by hydroboration with HB(C6F5)2, yielding the ethenylborane {CH2Si(Me)[C2H2B(C6F5)2]}3, and by metalation with gallium and indium organyls affording {CH2Si(Me)[C2M(R)2]}3 (M = Ga, In, R = Me, Et). In the synthesis of the backbone the influence of substituents (MeO, EtO and iPrO groups at Si) on the orientation of the methyl group was studied with the aim to increase the abundance of the all-cis isomer. New compounds were identified by elemental analyses, multi-nuclear NMR spectroscopy and in some cases by IR spectroscopy.

Solid-state structure of a Li/F carbenoid: pentafluoroethyllithium.

Lithium carbenoids are versatile compounds for synthesis owing to their intriguing ambiphilic behavior. Although this class of compounds has been known for several years, few solid-state structures exist because of their high reactivity and often low thermal stability. Using cryo X-ray techniques, we were now able to elucidate the first solid-state structure of a Li/F alkyl carbenoid, pentafluoroethyllithium (LiC2F5), finally yielding a prototype for investigating structure-reactivity relationships for this class of molecules.

Polyalkynylanthracenes--syntheses, structures and their behaviour towards UV irradiation.

A series of bis- and tris[(trimethylsilyl)ethynyl]anthracenes (1,5-, 1,8-, 9,10- and 1,8,10-) has been synthesised by multistep (cross coupling) reactions and the behaviour of the SiMe3-functionalised alkynylanthracene derivatives towards UV irradiation was qualitatively studied by NMR spectroscopy. In the case of 9,10-bis[(trimethylsilyl)ethynyl]anthracene we observed a photodimerisation upon UV irradiation; the third example was reported for a symmetrically 9,10-difunctionalised anthracene derivative, besides those with small fluorine- and methyl-substituents. The anthracene dimerisation is completely thermally reversible and the temperature dependence of the cycloelimination reaction was studied by (1)H VT-NMR experiments.