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A family of neutral bis-cyclometalated Ir(III) complexes based on phenanthridine (phent) derivates as cyclometalating ligands and picolinate as an ancillary ligand are described. The influence of extended conjugation, rigidity, and hydrophobicity as well as the electronic nature of the substituents were investigated in relation to the photoluminescence, PL, and electrochemiluminescence, ECL, properties. A significant increase of ECL in aqueous media is observed upon extension of the aromatic system or by substituting the phenyl with a dibenzofurane moiety, in compounds

The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The 1H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n‐alkyls, n‐Ω‐alkenyls or n‐Ω‐alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation., A stabilizing effect: Clear trends can be found in the seemingly chaotic distribution of dimerization constants of hierarchically assembled helicates in DMSO, revealing the stabilizing effect of solvent‐supported London dispersion effects.

The development of switchable molecular units is a challenging task of modern synthetic and supramolecular chemistry. In the present study, alkyl bridged bis(catecholketone) ligands are introduced in order to obtain helicates which cation triggered show some spring type dynamics. The preparation of the ligands as well as of the complexes and corresponding switching processes are described.

Copper complexes with the ligands bispiperidine (BP) or bisquinoline (BQ) were investigated. A dinuclear carbonato bridged copper(II) complex as well as a dinuclear copper(I) complex with BP as ligand were structurally characterized. The reaction of a copper(I) BP complex investigated by low temperature stopped-flow techniques showed the very fast formation of a bis--oxido copper intermediate leading to an intramolecular ligand hydroxylation. However, substrates such as e. g. benzyl alcohol could be oxidized as well with this complex. In contrast, no intermediates could be spectroscopically observed when BQ or derivatives of this ligand were used. Instead complex reaction behaviour was observed when copper(II) chloride was reacted with BQ as a ligand in air or under inert conditions. Several crystal structures helped to establish a mechanism for these reactions. An interesting reaction product obtained that way was a new coordination polymer.

Novel analogues of oxadiazole-substituted naphtho[2,3-b]thiophene-4,9-diones were synthesized in which the tricyclic quinone skeleton was systematically replaced with simpler moieties, such as structures with fewer rings and open-chain forms, while the oxadiazole ring was maintained. In addition, variants of the original 1,2,4-oxadiazole ring were explored. Overall, the complete three-ring quinone was essential for potent suppression of human keratinocyte hyperproliferation, whereas analogous anthraquinones were inactive. Also, the oxadiazole ring per se was not sufficient to elicit activity. However, rearrangement of the heteroatom positions in the oxadiazole ring resulted in highly potent inhibitors with compound 24b being the most potent analogue of this series showing an IC50 in the nanomolar range. Furthermore, experiments in isolated enzymatic assays as well as in the keratinocyte-based hyperproliferation assay did not support a major role of redox cycling in the mode of action of the compounds.

Diastereoselective radical coupling was achieved with chiral auxiliaries. The radicals were generated by anodic decarboxylation of five malonic acid derivatives. These were prepared from benzyl malonates and four menthol auxiliaries. Coelectrolyses with 3,3-dimethylbutanoic acid in methanol at platinum electrodes in an undivided cell afforded hetero-coupling products in 22–69% yield with a diastereoselectivity ranging from 5 to 65% de. Electrolyses without a coacid led to diastereomeric homo-coupling products in 21–50% yield with ratios of diastereomers being 1.17:2.00:0.81 to 7.03:2.00. The stereochemistry of the new stereogenic centers was confirmed by X-ray structure analysis and 13C NMR data.

Three novel N-acylamidines 1a–c with varying steric bulk and substitution patterns were synthesized and thoroughly characterized by X-ray diffraction. Compounds 1a and 1b, which contain two additional binding sites located at two pyridine substituents, were treated with equimolar amounts of cyclopentadienylzirconium(IV) trichloride at room temperature. The X-ray data of the resulting coordination compounds 7a and 7b indicate the formation of five-membered metallacycles with one of the pyridine nitrogen atoms and the carbonyl oxygen atom acting as binding sites. For the complexation of ligand 1c, a different route was chosen: 1c was first deprotonated to yield the polymeric potassium compound 8 with a very complex substitution pattern based on O , N, and aromatic interactions with the potassium ions. Transmetalation of 8 with cyclopentadienylzirconium(IV) trichloride gave amidinate complex 9, which is dimeric in the solid state but exists in solution in equilibrium with monomeric species. After addition of...

Neutral green-emitting four-coordinate Cu(I) complexes with general formula POPCu(NN), where POP = bis[2-(diphenylphosphino)phenyl]ether and NN = substituted 2-pyridine-1,2,4-triazole ligands, were synthesized. The crystal structures of (POPCuMeCN)(+)(PF6)(-) (1), POPCuPhPtp (2a, PhPtp = 2-(5-phenyl-2H-[1,2,4]triazol-3-yl)-pyridine), and POPCu(3,5-2FPhPtp) (2d, 3,5-2FPhPtp = 2-(5-(3,5-difluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine) were determined by single-crystal X-ray diffraction analysis. The electronic and photophysical properties of the complexes were examined by UV-vis, steady-state, and time-resolved spectroscopy. At room temperature, weak emission was observed in solution, while in the solid state, all complexes exhibit intense green emission with quantum yield up to 0.54. The electronic and photophysical properties were further supported by calculation performed at the (time-dependent) density functional theory level. One of the complexes was also tested as dopant in electroluminescent devices.

Tetra­hydro-3-benzazepines with a hy­droxy group in the 1-position and a methyl group in the 2-position were designed as conformationally restricted ifenprodil analogues. The enanti­omerically pure 3-benzazepine (S,R)-4 representing a constitutional isomer of ifenprodil shows high affinity towards the ifenprodil binding site (Ki = 26 nM) and high antagonistic activity at the NMDA receptor (IC50 = 9.0 nM). The crystal structure analysis of the inter­mediate sulfonamide (S,R)-2 was performed in order to assign unequivocally the relative configuration of the methyl and hy­droxy groups., In the title compound, C25H27NO4S, which crystallized as a racemate, the relative configuration of the adjacent OH and CH3 groups on the azepine ring is trans. The seven-membered azepin ring has a chair-like conformation. The planar aromatic rings of the benzyl and tosyl­ate moiety are inclined to the planar 3-benzazepine ring by 78.39 (15) and 77.03 (14)°, respectively, and to each another by 13.82 (15)°. In the crystal, mol­ecules are linked via O—H⋯O and C—H⋯O hydrogen bonds, forming double-stranded chains along the a-axis direction. The chains are linked via C—H⋯π inter­actions, forming a three-dimensional architecture.

Introduction of the flexible amino­alcohol substructure of ifenprodil into a more rigid ring system resulted in 2-methyl-2,3,4,5-tetra­hydro-1H-3-benzazepin-1-ols, (3) and (4), showing GluN2B affinity in the low nanomolar range. The chiral pool synthesis starting with (R)-alanine led to two diastereomers. The relative configuration of the benzazepines (3) and (4), that crystallized as racemates, was determined to be (S*,R*)-3 and (R*,R*)-4., The title compounds, C22H29NO2 (3) and C22H29NO2 (4) [systematic names: (1S*,2R*)-7-meth­oxy-2-methyl-3-(4-phenyl­but­yl)-2,3,4,5-tetra­hydro-1H-3-benzazepin-1-ol and (1R*,2R*)-7-meth­oxy-2-methyl-3-(4-phenyl­but­yl)-2,3,4,5-tetra­hydro-1H-3-benzazepin-1-ol, are diastereomers with the relative configuration of the adjacent hydroxyl and methyl groups at the seven-membered azepine ring being trans in (3) and cis in (4). In the crystals the orientation of these groups is −anti-periplanar (3) and +syn-clinal (4). In both cases, the crystals studied proved to be of a racemic mixture, with relative configurations (R*,S*)-3 and (R*,R*)-4. In both compounds, the seven-membered azepine ring has a chair-like conformation, and the 4-phenyl­butyl side chain adopts a extended conformation in (R*,S*)-3, but a twisted conformation in (R*,R*)-4. In the crystal of (S*,R*)-3, mol­ecules are linked via C—H⋯O hydrogen bonds, forming slabs parallel to the ac plane. In the crystal of (R*,R*)-4, mol­ecules are linked via O—H⋯N hydrogen bonds, forming chains propagating along the c-axis direction. The chains are linked by C—H⋯O hydrogen bonds, forming slabs parallel to the ac plane.

1,3,5-Triazapentadienes usually show U- or twisted S-shaped conformations along the N-C-N-C-N skeleton due to dominating n/π* interactions. If, however, the 1,3,5-triazapentadiene unit is part of a ring, its W conformation might be restricted to the plane. Here, we describe the synthesis of 13 new 1,3,5-triazapentadienes 10-12, which are sterically restrained by incorporation into six- or seven-membered ring systems, by addition of a lithiated primary amine or hydrazine 5 to a dinitrile 7, 8, or 9 with the two cyano groups in 1,3 or 1,4 distance. These novel compounds show very strong tendency for aggregation due to hydrogen bonding, especially to form homodimers as seen from X-ray data in the solid state. Additional hydrogen bonding generates also linear chains in the crystal. Several of the new compounds show fluorescence in solution. Quantum chemical DFT calculations were used for evaluation of the dimerization energies and for interpretation of the photophysical properties.

The preparation of a series of planar chiral, ferrocenyl-substituted hydrosilanes as precursors of ferrocene-stabilized silicon cations is described. These molecules also feature stereogenicity at the silicon atom. The generation and (29)Si NMR spectroscopic characterization of the corresponding silicon cations is reported, and problems arising from interactions of the electron-deficient silicon atom and adjacent C(sp(3))-H bonds or aromatic π donors are discussed. These issues are overcome by tethering another substituent at the silicon atom to the ferrocene backbone. The resulting annulation also imparts conformational rigidity and steric hindrance in such a way that the central chirality at the silicon atom is set with complete diastereocontrol. These chiral Lewis acid catalysts were then tested in difficult Diels-Alder reactions, but no enantioinduction was seen.

The series of differently substituted ketenimines 1 was hydroluminated using di-iso-butyl aluminum hydride. For the sterically congested ketenimine 1a, preferred hydroalumination of the C═N-bond was proven by X-ray crystallography (compound 5a). In situ treatment of the hydroaluminated ketenimines 5 with various heterocumulenes like carbodiimides, isocycanates, isothiocyanates and ketenimines as electrophiles and subsequent hydrolytic workup resulted in novel enamine derived amide species in case of N-attack (sterically less hindered ketenimines) under formation of a new C-N-bond or in 1,3-diimines by C-C-bond-formation in case of bulky substituents at the ketenimine-nitrogen atom. Furthermore, domino reactions with more than 1 equiv of the electrophile or by subsequent addition of two different electrophiles are possible and lead to polyfunctional amide derivatives of the biuret type which are otherwise not easily accessible.

Conformationally constrained perhydroquinoxalines 4 show high κ receptor affinity, selectivity over related receptors and full agonistic activity. Since the κ affinity can be correlated with the dihedral angle of the ethylenediamine pharmacophore (4a: 55°/71°), the dihedral angles of the postulated cyclopentane derivative 5a (73°/84°) and indane derivative 6a (77°/81°) were calculated. The first step of the synthesis represents a double Henry reaction of 1,4-dialdehydes 8 and 10 with nitromethane, leading predominantly to the trans,trans-configured nitrodiols 9 and 11. X-ray crystal structure analyses of 9 and 11 led to dihedral angles O2 N−C−C−OH of 73.4 and 88.3°, respectively, which reflect the calculated dihedral angles of the hypothesized final products 5a and 6a.

A series of novel benzene centered mono-, bis- and tris-1,3,5-triazapentadiene ligands 6a–e was synthesized and investigated with respect to their reactivity towards triphenylborane. The resulting blue-fluorescent boron complexes 14a–e with a six-membered ring chelate structure show excellent thermal and chemical stability. All title compounds were completely characterized including X-ray diffraction studies for 14a–c and 14e. Whereas the absorption spectra of all three classes of compounds are similar, the fluorescence spectra show distinct differences. Thus, the emission spectra of 14a,b show Stokes shifts of 4100–6700 cm−1 with low quantum yields both in solution and in the solid state. However, the more bulky compounds 14c–e show markedly larger molar extinction coefficients and smaller bathochromic shifts compared to 14a,b. For all compounds, we observe significantly more intense red-shifted fluorescence in the solid state compared to that in dichloromethane solutions. For the interpretation of the absorption properties TD-DFT studies were performed based on DFT geometry optimizations.

The terpenols L(−)-borneol, (1S2S3S5R)-3-pinanol, (−)-menthol, and (−)-myrtenol are easily available chiral alcohols for the preparation of enantiomerically pure catechol esters 1–4-H2. Those ligands are used for the hierarchical assembly of triple lithium-bridged dinuclear titanium(IV) triscatecholate helicates Li[Li3(1–4)6Ti2]. In solution, the dimeric species are in a solvent dependent equilibrium with the monomer Li2[(1–4)3Ti]. The equilibrium is studied by 1H NMR. CD spectroscopy indicates that the configuration at the complex units of the enantiomerically pure dimeric α-chiral derivatives Li[Li3(1–3)6Ti2] is opposite to the configuration of the monomers Li2[(1–3)3Ti]. For the γ-chiral complex Li2[(4)3Ti] only a de of 25% is observed and in this case no interpretation of the mechanism of stereocontrol is possible.

Ring-closing olefin metathesis reactions (RCM) using Grubbs II or Hoveyda's catalysts have been applied to a series of N-alkenyl-N-benzyl-α-fluoroacrylamides. α-Fluoro-α,β-unsaturated γ- or δ-lactams incorporating a fluorinated double bond were obtained in moderate to good yields, depending on the nature of substituents on the benzyl ring. The corresponding seven- and eight-membered lactams were not formed under similar conditions. When the N-benzyl group was replaced by an N-tosyl group, the corresponding ϵ-lactam was also formed in 38 % yield. When N-(2-fluoroallyl) derivatives were used instead of fluoroacryloyl derivatives, six-, seven-, and eight-membered N-heterocycles were obtained in low yields. This method was also used to synthesize fluorinated α,β-unsaturated analogues of pyrrolizidine and indolizidine alkaloids from prolinol, and also to synthesize N-benzyl-3-fluoroquinolone in three steps from commercially available 2-vinylaniline in 44 % overall yield. Also 3-fluorocoumarin and 3-fluorochromene were prepared from o-vinylphenol, and 3-fluoro-benzoxepine was available from o-allylphenol.

From a series of bis(alkynyl)mesityl phosphanes 5, we prepared phosphirenium borate compounds 6 in high yields by reaction with B(C6F5)3 at room temperature. The zwitterionic compounds 6 are conveniently accessible and can be obtained with unique substitution patterns by this route. For two examples, we show the conversion of 6 to the respective 3-borylated phosphole derivatives 7 through multiple 1,1-carboboration reactions. In a useful one-pot methodology, the phosphirenium borates 6 are converted to air-stable 3-arylated phospholes 8 by a sequential 1,1-carboboration/ Suzuki-Miyaura type cross-coupling reaction.

A study on the key parameters involved in the anion-binding process and catalytic activity of the new family of CH-bond-based, anion-binding bis-triazole catalysts BisTri was carried out. The effects of substitution at the side arms and the central backbone structure of the catalyst were investigated. Electron-deficient 3,5-bis(trifluoromethyl)phenyl groups at the side arms led to the most strongly bound structures. The evaluation of differently shaped anions showed remarkable binding selectivity of the BisTri derivatives for the chloride anion. Examination of various nucleophiles in a model catalytic alkylation reaction suggested a more complex mechanism than the expected SN 1, in which the nucleophiles also participate partially in activation of the electrophile. DFT calculations were performed to investigate the relationship between the catalyst conformation and the binding affinity. Finally, in silico design and identification of a new, more efficient BisTri catalyst was accomplished.

Compounds 1 a-f-H2 form "monomeric" triscatecholate titanium(IV) complexes [Ti(1 a-f)3](2-), which in the presence of Li cations are in equilibrium with the triple lithium-bridged "dimers" [Li3(Ti(1 a-f)3)2](-). The equilibrium strongly depends on the donor ability of the solvent. Usually, in solvents with high donor ability, the stereochemically labile monomer is preferred, whereas in nondonor solvents, the dimer is the major species. In the latter, the stereochemistry at the complex units is "locked". The configuration at the titanium(IV) triscatecholates is influenced by addition of chiral ammonium countercations. In this case, the induced stereochemical information at the monomer is transferred to the dimer. Alternatively, the configuration at the metal complexes can be controlled by enantiomerically pure ester side chains. Due to the different orientation of the ester groups in the monomer or dimer, opposite configurations of the triscatecholates were observed by circular dichroism (CD) spectroscopy for [Ti(1 c-e)3](2-) or [Li3(Ti(1 c-e)3)2](-). A surprising exception was found for the dimer [Li3(Ti(1 f)3)2](-). Herein, the dimer is the dominating species in weak donor (methanol), as well as strong donor (DMSO), solvents. This is due to the bulkiness of the ester substituent destabilizing the monomer. Due to the size of the substituent in [Li3(Ti(1 f)3)2](-) the esters have to adopt an unusual conformation in the dimer resulting in a stereocontrol of the small methyl group. Following this, opposite stereocontrol mechanisms were observed for the central metal-complex units of [Li3(Ti(1 c-e)3)2](-) or [Li3(Ti(1 f)3)2](-).

The t-Bu3P/B(C6F5)3 frustrated Lewis pair (6a) undergoes competing acetylene deprotonation (to give the phosphonium–alkenylborate salt 8) and 1,4-P/B FLP addition to the conjugated enyne 2-methylbutenyne to yield the zwitterionic allene derivative 9a. The less basic (o-tolyl)3P/B(C6F5)3 system (6b) avoids the acetylene deprotonation pathway. The zwitterionic allene derivative 9b formed by 1,4-P/B FLP addition to the enyne is again a prominent reaction product; here competing 1,2-addition is observed to give the olefinic product 10. The allene derivatives 9a and 9b and their competing products 8 and 10 were characterized by X-ray diffraction.

Diarylphosphino-substituted alkynes undergo a 1, 1-carboboration reaction with tris(pentafluorophenyl)borane to yield 2-diarylphosphino-substituted alkenylboranes. These unsaturated systems show a P/B interaction. Nevertheless, they feature a limited frustrated Lewis pair (FLP) reactivity. Four such unsaturated vicinal FLPs were shown to react with benzaldehyde to give the respective six-membered heterocyclic P/B FLP 1, 2-addition products, which were characterized by X-ray diffraction.

The enamine piperidinocyclopentene reacts with HB(C6F5)2 by formation of the C-Lewis base/B-Lewis acid adduct 10. It shows a zwitterionic iminium ion/hydridoborate structure. However, this adduct f...

2-Isocyanoacetophenone (3a) was found to be an easily accessible starting material for the unexpected formation of various heterocyclic systems. Thus, a hitherto unknown rather unstable 4-methylene-4H-benzoxazine derivative 4, which could be characterized by NMR spectroscopy, was formed in situ by the reaction of 3a in the presence of weak acids. In the presence of benzylamines, a new class of 3,4-dihydroquinazoline derivatives 6 and their oxidation products, quinazolin-4-ones 9, were obtained. The starting materials and products were completely characterized by spectroscopic and X-ray analysis. The scope and limitations of these cyclization reactions were investigated under various reaction conditions. High-level quantum chemical calculations were carried out to elucidate the mechanisms leading to scaffolds 4 and 6. The calculations suggest that the formation of 4 and 6 involves the generation of an unusual six-membered N-heterocyclic carbene or its C-protonated form as a reaction intermediate, followed by tautomerisation. This mechanism might also be applicable to other isocyanide cyclization reactions.

Bis(dimesitylphosphanyl)butadiyne (14) reacts with B(C6F5)3 by a 1,1-carboboration sequence. The selective attack at a single phosphanyl-alkyne moiety is observed. First a phosphirenium-borate zwitterion 15 is formed at r. t. Thermolysis (80 °C) results in the E-selective formation of the 1,1- carboboration product, the frustrated Lewis pair (FLP) E-16, which upon heating to 160 °C eventually undergoes isomerization followed by an internal nucleophilic aromatic substitution reaction to give the product 17 featuring a -B(F)(C6F5)2 substituent at the five-membered P-heterocycle. Finally, the FLP E-16 was reacted with n-butylisocyanide to yield the five-membered heterocyclic product 18, formed by P,B addition to the isonitrile carbon atom. Compounds 14, 15, 17, and 18 were characterized by X-ray crystal structure analyses

'Lene' and mean: The strong Lewis acid B(C6F5)3 efficiently converts some bis(arylethynyl)benzenes into dibenzopentalenes through a series of Lewis acid induced cyclization reactions at room temperature. Thus the reaction has the potential to be useful in the synthesis of substituted dibenzopentalene derivatives which are difficult to make by conventional means.

Hydroalumination of cyanamides 1 with di(isobutyl)aluminium hydride affords intermediate compounds 3, which have dimeric structures in the solid state with four-membered Al2N2 heterocycles and exocyclic N=C double bonds. The reactions of 3 with acyl chlorides yield N′,N′-disubstituted N-acylformamidines 5, whereas reaction with sulfonyl chlorides give the corresponding N-sulfonylformamidines 7. In contrast, carbodiimides 8 react with dialkylaluminium hydrides R2AlH (R = tBu, iBu) to give compounds 9 in which one C=N bond of the carbodiimide is reduced to form an amidinate ligand and a second molecule of the hydride is coordinated through an Al–N and an Al–H–Al bond. Treatment of 9 with acyl chlorides yields N,N′-disubstituted N-acylformamidines 10, whereas reaction with sulfonyl chlorides gives the corresponding N-sulfonylformamidines 11.

We have synthesized a series of new fluorescent boron systems 1a-c and 2a-d based on nitrogen (NNN) or nitrogen and oxygen (ONO)-containing tridentate ligands. These novel dyes are characterized by high thermal and chemical stability. They show large Stokes shifts (mostly above 3200 cm(-1)) and quantum yields in solution and in the solid state up to 40%. The easy, modular synthesis facilitates the convenient variation of the axial substituent on the central boron atom, allowing the functionalization of this dye for biochemical use. Introducing a long alkyl chain with a phenyl spacer at this axial position enables the self-assembly of the boron compound 2d to form a fluorescent vesicle, which is able to encapsulate small molecules such as sulforhodamine. Additionally, boron compound 2d was found to serve as a dye for cell imaging since it has the capability of binding to the nuclear membranes of HeLa cells. With phospholipids such as DOPC, giant unilamelar vesicles (GUV) are formed. These results demonstrate the wide applicability of this new boron system in supramolecular and medicinal chemistry.

The binding behaviour of (thio)urea- and amide-functionalized quinoline-based anion receptors towards halide anions was investigated in detail in CDCl3 and [D6]DMSO solutions by using 1H and 19F NMR spectroscopic methods. The electronic, solvent, and fluoro-substitution effects were studied. The (thio)urea- and amide-functionalized quinoline-based anion receptors showed medium to strong anion affinity and good selectivity in solution. Single crystals of key compounds were obtained and studied by X-ray diffraction spectroscopy.

Peripheral thiophen-2-yl substituents extend the macrocyclic conjugation of zinc(II)azaphthalocyanines, (ZnAzaPc), due to coplanarity between the two ring systems, and red-shifted UV–Vis Q-bands are observed. This lowering in energy is favourable for various applications. Pyrazine-2,3-dicarbonitriles substituted in the 5-position with alkyl-thiophen-2-yl groups or bithienyl groups, were synthesized as precursors for the parent tetrasubstituted ZnAzaPcs, expected to show further red-shifted Q-bands. The reagent Zn(quinoline)2Cl2 was used for one-step cyclotetramerizations. None of the bithienyl substituted precursors gave clean reactions, and mainly polymeric material resulted. Two ZnAzaPcs tetrasubstituted with respectively 5-ethyl-thiophen-2-yl and 3,4-dimethyl-thiophen-2-yl groups, were obtained in fair yields, 40–50%. UV–Vis Q-bands at 660 nm and molar extinction coefficients 111 000 and 89 000 M−1 cm−1 were observed for the blue-green DMF solutions of the two tetramers. 2D NMR methods were applied in analyses of DMF-d7 solutions. Broad and partly overlapping 1H NMR signals for both compounds indicate aggregation. In addition, the extensive number and distribution of sharp peaks in the spectrum reflect structural isomerism. Molecular ions were determined by mass spectrometry (MALDI-TOF). Four pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles, substituted with phenyl or alkylated thiophen-2-yl groups, were synthesized from 5,6-diamino-pyrazine-2,3-dicarbonitrile and aryl glyoxylaldehydes. These precursors were not sufficiently stable for cyclotetramerization. Structure analyses of 5-(5-ethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile, and 5-(5′-ethyl-2,2′-bithiophen-5-yl)pyrazine-2,3-dicarbonitrile, reveal extended π-electron systems in both structures. The high degree of electron delocalization in the three-ring system of the latter compound presumably makes self-association through π-π interactions the greatly preferred mechanism for condensation.

In order to synthesize enantiomerically pure tetrahydro-3-benzazepines with diverse substitution patterns, the lactams 3 were converted into thiolactams 4 upon treatment with Lawesson’s reagent. Instead of an Eschenmoser sulfide contraction a thiophene annulation reaction occurred, when the thiolactams 4 were reacted with ethyl bromoacetate. Altogether, enantiomerically pure thiopheneannulated 3-benzazepines 7 were prepared in a very short reaction sequence (five reaction steps) starting from commercially available o-phenylenediacetic acid

The nitrate complexes of cerium, praseodymium and neodymium with 2,2’-bipyridine of general formulae, [Ln(bipy) 2 (NO 3 ) 3 ], have been prepared and characterized by X-ray crystallography. Thermal studies were undertaken using thermogravimetry (TG), TG (DTA) differential thermal analysis and ignition delay measurements. The kinetics of thermal decomposition of these complexes was investigated using isothermal TG data by applying model-fitting and iso-conversional methods. The cerium complex decomposes in single step whereas praseodymium and neodymium complexes decompose in three steps.

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)3 in THF to form neutral complexes, [CrCl3{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV–Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH2 (complex 3) and from the fac configuration when the spacer is CO (complex 4).

The vicinal frustrated P/B Lewis pair (FLP) Mes(2)PCH(2)CH(2)B(C(6)F(5))(2) reacts with 9-borabicyclo[3.3.1]nonane (9-BBN) by C(6)F(5)vs. H exchange at boron to give the new [B]-H functionalized FLP Mes(2)PCH(2)CH(2)B(H)(C(6)F(5)) (4) and 9-C(6)F(5)-BBN. The latter was characterized as an isonitrile adduct by X-ray diffraction. The new FLP 4 forms an adduct with pyridine and it undergoes clean hydroboration reactions with 1-pentyne or added styrene or dimesitylvinylphosphane. The products formed stable adducts with pyridine; two such examples were also characterized by X-ray crystal structure analysis. A similar alkyl vs. hydrogen exchange was observed upon treatment of an Al/N based Lewis pair, iBu(2)Al-(Me(3)Si)C=C(H)-N(CH(2)CH(2))(2)NMe (14), with 9-BBN.

Two copper(II) complexes, [Cu(bipy)(5-Br-2-hap)(ClO4)]2 (1) and [Cu(bipy)(2-hap)(ClO4)] (2) (where bipy = 2,2′-bipyridine, 5-Br-2-hap = 5-bromo-2-hydroxyacetophenone, 2-hap = 2-hydroxyacetophenone), were synthesized and characterized. The crystal structure of 1 was determined by single crystal X-ray diffraction while 2 was reported earlier. Structural characterization reveals that the presence of bromine in 5-Br-2-hap plays a structure-determining role in dimeric 1 in comparison with the mononuclear 2 where 2-hap was used. Studies of the catalytic potential toward styrene epoxidation in homogeneous system using H2O2 as oxidant reveal that 1 is more efficient than 2 with respect to epoxide selectivity.

The 1,2-bis[(diarylphosphino)ethynyl]benzene derivatives 1a (R=Ph) and 1b (R=o-tolyl) undergo 1,1-carboboration at one of their acetylene units upon treatment with (C6F5)3B at elevated temperature to give the products 5a and 5b, respectively. At room temperature, we observed the formation of the corresponding phosphireniumborate zwitterions, 7a and 7b, respectively, which may be intermediates of the 1,1-carboboration reactions. The reaction of the more bulky 1,2-bis[(dimesitylphosphino)ethynyl]benzene 1c with (C6F5)3B takes a different course. At 110°, we observed the complete conversion to the benzopentafulvene derivative 8 which is probably formed in a typical carbocation rearrangement sequence after the initial (C6F5)3B Lewis acid-addition step. The compounds 5a, 5b, 7b, and 8 were characterized by X-ray crystal-structure analyses.

Phenanthroline-based hexadentate ligands L(1) and L(2) bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as La(III), Eu(III), Tb(III), Lu(III), and Y(III) metal ions, were synthesized, and the crystal structures of [ML(1)Cl(3)] (M=La(III), Eu(III), Tb(III), Lu(III), or Y(III)) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big Ln(III) ion exhibits a coordination number (CN) of 10, whereas the corresponding Eu(III), Tb(III), Lu(III), and Y(III) centers with smaller ionic radii show CN=9. Complexes of L(2), namely [ML(2)Cl(3)] (M=Eu(III), Tb(III), Lu(III), or Y(III)) ions could also be prepared. Only the complex of Eu(III) showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5'-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5'-diphosphate (ADP) and adenosine-5'-monophosphate (AMP) was found. (31)P NMR spectroscopic studies revealed the formation of a [EuL(2)(ATP)] coordination species.

In a chiral-pool synthesis starting from D-mannono-1,4-lactone 1a, the four diastereomeric C-aryl furanosides (1S,4R)-4a, (1S,4S)-4b, (1R,4R)-4c, and (1R,4S)-4d were obtained in a stereocontrolled manner. The key steps of the synthetic pathway comprise a stereoselective reduction of the diastereomeric hemiketals (4R)-2a and (4S)-2b as well as a stereospecific cycloetherification of the resulting diols (1R,4R)-5a, (1S,4R)-5c, and (1S,4S)-5d. This ring closure which led to the desired C-glycosides was achieved by a Mitsunobu reaction or by preparing the 1-O-benzoyl-4-O-methylsulfonyl derivative 7 which was then treated with sodium methoxide. Final hydrolysis of the 5,6-O-isopropylidene protecting group led to the diastereomeric diols (1S,4R)-4a, (1S,4S)-4b, (1R,4R)-4c, and (1R,4S)-4d, representing versatile building blocks for further synthetic transformations.

A diamine-bridged bis-N-heterocyclic carbene ligand was synthesized as imidazolium salts with chloride or triflate counteranions. Deprotonation of the chloride salt by an iron bis-amide complex or addition of the free diamine-bis-carbene ligand to FeCl2 led to the formation of an Fe(II) dichloride complex having a diamine-bis-carbene ligand, in which the iron atom is in a highly distorted octahedral geometry with weak Fe-N interactions. This iron complex was found to catalyze the hydrosilylation of acetophenone.

D-(+)-Camphor forms the enamine 2 with piperidine. Compound 2 adds HB(C(6)F(5))(2) at the enamine carbon atom C3 to form a Lewis acid/Lewis base adduct (exo-/endo-isomers of 3). Exposure of 3 to dihydrogen (2.5 bar, room temperature) leads to heterolytic splitting of H(2) to form the H(+)/H(-) addition products (4, two diastereoisomers) of the "invisible" frustrated Lewis pairs (5, two diastereoisomers) that were apparently generated in situ by enamine hydroboration under equilibrium conditions.

The intramolecular frustrated P/B Lewis pair Mes2PCH2CH2B(C6F5)2 (7) reacts readily with phenylsilane by heterolytic cleavage of the Si-H bond to give the zwitterion [Mes2(PhH2Si)P+CH2CH2B-H(C6F5)2] (8a), which has been fully characterized and its structure confirmed by X-ray crystal structure analysis. Variable-temperature NMR studies revealed that the reaction is reversible. Adduct 8a is the predominant species (ca. 98%) in CD2Cl2 solution at low temperature (193 K), whereas at ambient temperature (299 K) it exists in a ca. 7 : 3 equilibrium with unreacted 7 and PhSiH3. Diphenylsilane reacted similarly with the frustrated Lewis pair 7, however, the equilibrium was found to favor the starting materials in the investigated temperature range.

Nickel and copper nitrate complexes with 2,2′-bipyridine (bipy) as a N donor and nitrate and water as oxygen donor ligands of the general formula [M(NO 3 )(C 10 H 8 N 2 )(H 2 O) 3 ](NO 3 ), where M = Ni and Cu, have been obtained from the corresponding metal nitrate salts. These complexes were characterized by X-ray crystallography, FT-IR, and CHN analysis. Both the complexes have been found to be six coordinated. Their thermal decomposition behaviour was investigated by TG, DTA, and ignition delay measurements. TG–DTA examinations of these complexes revealed multistep thermal decomposition. The corresponding metal oxide residues obtained after thermolysis were identified from their X-ray diffraction patterns (XRD). Kinetics of isothermal decomposition of the complexes was established from both the model-fitting as well as isoconversional methods.

We prepared the 2-hydroxy-5-trimethylsilylferrocenecarbaldimine systems 13 enantioselectively by a short synthetic route starting from the chiral ferrocene carbaldehyde acetal 5. The imines 13a–c were used to synthesize the zwitterionic (“ferrocene-salaldiminato”)2ZrCl4 complexes 14a–c. Activation with MAO gave homogeneous Ziegler–Natta catalysts, which showed only a moderate ethylene polymerization activity, similar to the unsubstituted parent “ferrocene-salaldiminato” zirconium systems. Consequently, a synthetic route was devised and carried out to make the corresponding 2-hydroxy-3,5-bis(trimethylsilyl)ferrocenecarbaldimines (21) available. The enantiomerically highly enriched ligands (pS)-21a and -d derived from the aldehyde and aniline or cyclohexylamine, respectively, were used to synthesize the corresponding (“ferrocene-salaldiminato”)2ZrCl4 complexes 22a,d. Both gave highly active homogeneous Ziegler–Natta catalysts upon activation with MAO for the formation of linear low molecular weight polyethy...

A new strategy for the synthesis of tetrahydro-3-benzazepinones 6 by reductive amination of keto acid 3 and subsequent carbonyl diimidazole (CDI) mediated cyclization was developed. Use of enantiomerically pure (R)-1-phenylethylamine led to the formation of diastereomeric lactams (Rα-R)-6d and (Rα-S)-6e in a 80:20 ratio. Diastereoselective alkylation of (Rα-R)-6d, BH3-mediated reduction and exchange of the N-phenylethyl substituent provided enantiomerically pure tetrahydro-3-benzazepines with various substituents in the 1-, 3-, and 4-positions. High σ1 affinity was achieved with a benzyl, cyclohexylmethyl, or 1-phenylethyl moiety at the N-atom. Whereas (R)-configuration of the N-substituent is crucial for high σ1 affinity, the configuration of the 3-benzazepine ring system does not influence the σ1 affinity considerably. Introduction of additional substituents in the 1-position led to almost complete loss of σ1 affinity. Potent σ1 ligands show high selectivity against the σ2 subtype and the NMDA receptor.

A flexible synthesis of bifunctional thiourea derivatives based on the TADDOL framework is described. Hydroxy as well as primary, secondary, and tertiary amino-substituted bifunctional hydrogen­-bond donors were synthesized.

Herein we provide an overview on the unique properties of the sterically demanding IBiox-[(−)-menthyl]∙HOTf ligand (such as flexibility and sterics) and an application of this ligand in Pd-catalyzed asymmetric intra- and intermolecular α-arylation reactions. Furthermore we demonstrate the synthesis of novel NHC–metal complexes and a new bifunctional NHC ligand whilst insight into the mechanistic mode of action of IBiox-[(−)-menthyl]∙HOTf in catalysis is provided.

The reactive intramolecular frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 reacts rapidly with thionyl chloride to yield the zwitterionic chlorination product [Mes2PCl+]CH2–CH2[BCl(C6F5)2–]. Analogous zwitterionic products were obtained by the reaction of the FLP with chlorine or bromine. Compounds [Mes2PX+]CH2CH2[BX(C6F5)2–] (X = Cl, Br) were characterized by X-ray crystal structure analyses.

Give and take: The introduction of NHC-borane moieties to thiophene-based π skeletons endows a zwitterionic character, which makes the π system electron-donating, while the NHC ring acts as an electron-accepting moiety. The NHC-borane-substituted thiophene underwent a clean photoisomerization with a drastic color change, however, the expanded bithiophene derivatives were inert to this photoreaction, showed low oxidation potentials, and formed a slipped π-stacked array in the crystal.