Oxidative N-N Bond Formation Versus the Curtius Rearrangement.

The oxidative formation of N-N bonds from primary amides has been recently reported and then retracted in the journal Nature Communications by Kathiravan, Nicholls, and coauthors, utilizing a hypervalent iodane reagent. Unfortunately, the authors failed to recognize the Curtius reaction taking place under the described reaction conditions. Thus, the claimed N-N coupling products were not formed. Instead, the Curtius rearrangement urea coupling products were obtained. We demonstrate this herein by means of NMR and x-ray analysis, as well as with the support of an alternative synthetic route.

Solvent Dependence of the Monomer-Dimer Equilibrium of Ketone-Substituted Triscatecholate Titanium(IV) Complexes.

Hierarchical helicates based on ketone-substituted titanium(IV)triscatecholates show different monomer-dimer behavior depending on different solvents. The dimerization constants of a whole series of differently alkyl-substituted complexes is analyzed to show that the solvent has a very strong influence on the dimerization. Hereby, effects like solvophobicity/philicity, sterics, electronics of the substituents and weak side-chain-side-chain interactions seem to act in concert.

Supramolecular Metallacycles and Their Binding of Fullerenes.

The synthesis of a new triaminoguanidinium-based ligand with three tris-chelating [NNO]-binding pockets and C3 symmetry is described. The reaction of tris-(2-pyridinylene-N-oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C60 can be observed by NMR spectroscopy and single-crystal X-ray diffraction and is verified using computation.

Catechol Thioesters: Ligands for Hierarchically Formed Lithium-Bridged Titanium(IV) Helicates and Helicate-Based Switches.

The thioester moiety is introduced as a lithium binding unit for the hierarchical formation of titanium(IV) catecholate-based lithium-bridged helicates. In solution, the coordination compounds show a monomer-dimer equilibrium which -in comparison to the oxo esters- is significantly shifted towards the monomers. In addition, the influence of the thioester side chain on the dimerization behavior is investigated and an expansible/compressible molecular switch is synthesized. In the latter case expansion and compression are performed reversibly in methanol, whereas in DMSO spontaneous expansion occurs.

Shedding Light on the Interactions of Hydrocarbon Ester Substituents upon Formation of Dimeric Titanium(IV) Triscatecholates in DMSO Solution.

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 1 H 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.

Stability of Hierarchically Formed Titanium(IV) Tris(catecholate ester) Helicates with Cyclohexyl Substituents in DMSO.

A cyclohexyl substituent strongly prefers the chair conformation with large substituents in equatorial positions, while other cycloalkyls are structurally more flexible. In hierarchically formed dimeric titanium(IV) tris(catecholates) equatorial versus axial connection of the cyclohexane to the ester results in either a more compact (axial) or more expanded (equatorial) structure. In DMSO solution the axial position results in a compact structure which minimizes solvophobic effects, leading to higher stability. However, computational investigations indicate that additionally intramolecular London dispersion interactions significantly contribute to the stability of the dimer. Thus, weak side-chain-side-chain interactions are responsible for the high stability of cyclohexyl ester derivatives with axial compared to equatorial ester connection.

MeSi(CH2 SnRO)3 (R=Ph, Me3 SiCH2 ): Building Blocks for Triangular-Shaped Diorganotin Oxide Macrocycles.

The syntheses of the novel silicon-bridged tris(tetraorganotin) compounds MeSi(CH2 SnPh2 R)3 (2, R=Ph; 5, R=Me3 SiCH2 ) and their halogen-substituted derivatives MeSi(CH2 SnPh(3-n) In )3 (3, n=1; 4, n=2) and MeSi(CH2 SnI2 R)3 (6, R=Me3 SiCH2 ) are reported. The reaction of compound 4 with di-t-butyltin oxide (t-Bu2 SnO)3 gives the oktokaideka-nuclear (18-nuclear) molecular diorganotin oxide [MeSi(CH2 SnPhO)3 ]6 (7) while the reaction of 6 with sodium hydroxide, NaOH, provides the trikonta-nuclear (30-nuclear) molecular diorganotin oxide [MeSi(CH2 SnRO)3 ]10 (8, R=Me3 SiCH2 ). Both 7 and 8 show belt-like ladder-type macrocyclic structures and are by far the biggest molecular diorganotin oxides reported to date. The compounds have been characterized by elemental analyses, electrospray mass spectrometry (ESI-MS), NMR spectroscopy, 1 H DOSY NMR spectroscopy (7), IR spectroscopy (7, 8), and single-crystal X-ray diffraction analysis (2, 7, 8).

Cation-Controlled Formation and Interconversion of the fac/fac and mer/mer Stereoisomers of a Triple-Stranded Helicate.

Two biscatecholester ligands with oligoether spacers were used to prepare dinuclear titanium(IV) triscatecholate based helicates. In the case of Li4 [(1/2)3 Ti2 ], "classical" helicates with three internally bound Li+ ions and syn-oriented ligands in the complex units (fac/fac isomer) were obtained. In the case of the sodium salt Na4 [(2)3 Ti2 ], a different homochiral dinuclear triple-stranded helicate with two internally bound Na+ ions was formed. The complex units are anti-configured, and two of the ligand spacers are connecting internal with external positions of the helicate (mer/mer isomer). Removal of the sodium ions and addition of lithium ions leads to the switching from one topology to the other with an expanded helicate [(2)3 Ti2 ]4- as an intermediate. Switching back to the "non-classical" helicate cannot be observed because severe structural rearrangements would be required.

A Helicate-Based Three-State Molecular Switch.

The control of structural transformations triggered by external signals is important for the development of novel functional devices. In the present study, it is demonstrated that helicates can be designed to structurally respond to the presence of different counterions and to adopt either a compressed or an expanded structure. Reversible switching is not only possible between those two states, furthermore, the twist of the aggregate also can be controlled. Thus, three out of four possible states of a helicate (expanded/left-handed, expanded/right-handed, compressed/left-handed) based on an enantiomerically pure ester bridged dicatecholate ligand are specifically addressed by introduction, exchange, or removal of countercations. This approach is used to reversibly switch between the different states or to successively address them.

The σ-aromatic clusters [Zn3]⁺ and [Zn2Cu]: embryonic brass.

The triangular clusters [Zn3Cp*3](+) and [Zn2CuCp*3] were obtained by addition of the in situ generated, electrophilic, and isolobal species [ZnCp*](+) and [CuCp*] to Carmona's compound, [Cp*Zn-ZnCp*], without splitting the ZnZn bond. The choice of non-coordinating fluoroaromatic solvents was crucial. The bonding situations of the all-hydrocarbon-ligand-protected clusters were investigated by quantum chemical calculations revealing a high degree of σ-aromaticity similar to the triatomic hydrogen ion [H3](+). The new species serve as molecular building units of Cu(n)Zn(m) nanobrass clusters as indicated by LIFDI mass spectrometry.

A shape-persistent quadruply interlocked giant cage catenane with two distinct pores in the solid state.

Discrete interlocked three-dimensional structures are synthetic targets that are sometimes difficult to obtain with "classical" synthetic approaches, and dynamic covalent chemistry has been shown to be a useful method to form such interlocked structures as thermodynamically stable products. Although interlocked and defined hollow structures are found in nature, for example, in some viruses, similar structures have rarely been synthesized on a molecular level. Shape-persistent interlocked organic cage compounds with dimensions in the nanometer regime are now accessible in high yields during crystallization through the formation of 96 covalent bonds. The interlocked molecules form an unprecedented porous material with intrinsic and extrinsic pores both in the micropore and mesopore regime.

A permanent mesoporous organic cage with an exceptionally high surface area.

Recently, porous organic cage crystals have become a real alternative to extended framework materials with high specific surface areas in the desolvated state. Although major progress in this area has been made, the resulting porous compounds are restricted to the microporous regime, owing to the relatively small molecular sizes of the cages, or the collapse of larger structures upon desolvation. Herein, we present the synthesis of a shape-persistent cage compound by the reversible formation of 24 boronic ester units of 12 triptycene tetraol molecules and 8 triboronic acid molecules. The cage compound bears a cavity of a minimum inner diameter of 2.6 nm and a maximum inner diameter of 3.1 nm, as determined by single-crystal X-ray analysis. The porous molecular crystals could be activated for gas sorption by removing enclathrated solvent molecules, resulting in a mesoporous material with a very high specific surface area of 3758 m(2) g(-1) and a pore diameter of 2.3 nm, as measured by nitrogen gas sorption.

(Hexafluorosilicato-κ(2)F,F')bis(1,10-phenanthroline-κ(2)N,N')zinc(II) methanol monosolvate.

The title compound, [Zn(SiF6)(C12H8N2)2]·CH3OH, contains a neutral heteroleptic tris-chelate Zn(II) complex, viz. [Zn(SiF6)(phen)2] (phen is 1,10-phenanthroline), exhibiting approximate molecular C2 point-group symmetry. The Zn(II) cation adopts a severely distorted octahedral coordination. As far as can be ascertained, the title complex represents the first structurally characterized example of a Zn(II) complex bearing a bidentate-bound hexafluorosilicate ligand. A density functional theory study of the isolated [Zn(SiF6)(phen)2] complex was undertaken to reveal the influence of crystal packing on the molecular structure of the complex. In the crystal structure, the methanol solvent molecule forms a hydrogen bond to one F atom of the hexafluorosilicate ligand. The hydrogen-bonded assemblies so formed are tightly packed in the crystal, as indicated by a high packing coefficient (74.1%).

Container molecules based on imine type ligands.

This chapter will give a short overview about container molecules, their synthesis and possible applications. The main focus is on those which are based on imine type ligands. These containers can be used for example for guest exchange, gas separation, as chemical sensors or for the stabilisation of white phosphorus under water. The described cages have wide openings or tightly closed ones. For one cage the reversible opening and closing is also described.

Periphery-substituted [4+6] salicylbisimine cage compounds with exceptionally high surface areas: influence of the molecular structure on nitrogen sorption properties.

The synthesis of various periphery-substituted shape-persistent cage compounds by twelve-fold condensation reactions of four triptycene triamines and six salicyldialdehydes is described, where the substituents systematically vary in bulkiness. The resulting cage compounds were studied as permanent porous material by nitrogen sorption measurements. When the material is amorphous, the steric demand of the cages exterior does not strongly influence the gas uptake, resulting in BET surface areas of approximately 700 m(2) g(-1) for all cage compounds 3 c-e, independently of the substituents bulkiness. In the crystalline state, materials of the same compounds show a strong interconnection between steric demand of the peripheral substituent and the resulting BET surface area. With increasing bulkiness, the overall BET surface area decreases, for example 1291 m(2) g(-1) (for cage compound 3 c with methyl substituents), 309 m(2) g(-1) (for cage compound 3 d with 2-(2-ethyl-pentyl) substituents) and 22 m(2) g(-1) (for cage compound 3 e with trityl substituents). Furthermore, we found that two different crystalline polymorphs of the cage compound 3 a (with tert-butyl substituents) differ also in nitrogen sorption, resulting in a BET surface area of 1377 m(2) g(-1), when synthesized from THF and 2071 m(2) g(-1), when recrystallized from DMSO.

Thermal generation of pentacenes from soluble 6,13-dihydro-6,13-ethenopentacene precursors by a Diels-Alder-retro-Diels-Alder sequence with 3,6-disubstituted tetrazines.

3,6-Substituted tetrazines 2 (a: R(2) = 2-pyridyl or b: CO(2)Me) react with 2,3,9,10-(R(1))(4)-dihydro-6,13-ethenopentacene 3 in solution at elevated temperature to the corresponding pentacene 1 (a: R(1) = H, b: OBn, c: F).

Two-step synthesis of hexaammonium triptycene: an air-stable building block for condensation reactions to extended triptycene derivatives.

A simple two-step synthesis of an air-stable hexaammoniumtriptycene is introduced, which can be used for a variety of transformations by condensation reactions, e.g., to benzimidazole, benzotriazole, and quinoxaline derivatives in high yields.

µ-2,2',6,6'-Tetramethyl-4,4'-bipyridine-κ2N1:N1'-bis[(diethylenetriamine-κ3N,N',N'')palladium(II)] tetranitrate.

The title compound, [Pd(2)(C(4)H(13)N(3))(2)(C(14)H(16)N(2))](NO(3))(4), comprises discrete tetracationic dumbbell-type dinuclear complex molecules and noncoordinating nitrate anions. Two Pd(dien)(2+) moieties (dien is diethylenetriamine) are joined by the rigid linear exo-bidentate bridging 2,2',6,6'-tetramethyl-4,4'-bipyridine ligand to form the dinuclear complex, which lies across a centre of inversion in the space group P2(1)/n, so that the rings in the 2,2',6,6'-tetramethyl-4,4'-bipyridine bridging ligand are parallel. In the crystal, the primary and secondary amino groups of the dien ligand act as hydrogen-bond donors towards the nitrate anions to form a three-dimensional hydrogen-bond network.

Redetermination of cyclo-tetra-kis-(µ-5,10,15,20-tetra-4-pyridyl-porphyrinato)tetra-zinc(II) dimethyl-formamide octa-solvate trihydrate at 100†K.

The structure of the title compound, [Zn(4)(C(40)H(24)N(8))(4)]·8C(3)H(7)NO·3H(2)O, has been redetermined at 100 K. The redetermination is of significantly higher precision and gives further insight into the disorder of pyridyl groups and solvent mol-ecules. The mol-ecules of (5,10,15,20-tetra-4-pyridyl-porphyrinato)zinc(II) (ZnTPyP) form homomolecular cyclic tetra-mers by coordination of a peripheral pyridyl group to the central Zn atom of an adjacent symmetry-related mol-ecule. The tetra-mer so formed exhibits mol-ecular S(4) symmetry and is located about a crystallographic fourfold rotoinversion axis. Severely disordered dimethyl-formamide and water mol-ecules are present in the crystal, the contributions of which were omitted from refinement. Inter-molecular C-H⋯N hydrogen bonding is observed.

Synthesis and structural characterization of 9-azido-9-borafluorene: monomer and cyclotrimer of a borole azide.

The reaction of 2,2'-dilithiobiphenyl, generated from 2,2'-dibromobiphenyl and n-BuLi, with BCl(3) using n-hexane as solvent provides a high-yielding, simple preparative route to 9-chloro-9-borafluorene 1a. This in turn can be reacted with trimethylsilyl azide to yield 9-azido-9-borafluorene 2. Compound 2 exists as a cyclic trimer in the solid state, but in dichloromethane solution the monomer can coexist with the trimer. Azide 2 is rather unstable both in the solid state and in solution, and it transforms with trace amounts of water and oxygen to the 1,3,5-tris(2-biphenylyl)cyclotriboroxane that was characterized by X-ray diffraction analysis. Addition of pyridine and t-butyl pyridine to azide 2 afford the corresponding pyridine adducts. Compound 1a as well as the Lewis base adducts of 2 have been characterized by multinuclear NMR spectroscopy, and the structures were confirmed by X-ray diffraction analysis. The structural features of azide 2 and the strong Lewis acidity of its boron center have also been investigated by computational chemistry techniques at the MP2 level of theory.