Sur la synthèse du pollinastanol à partir du cycloartanol

The partial synthesis of pollinastanol (14) from cycloartanol (3) is reported. The transformation proceeds through the methylenic intermediate 12; the ring enlargement with cyanogen azide affords pollinastanone (13) further reduced to 14, The 4-keto isomer of pollinastanone (17) as well as a series of 5-β isomeric compounds are also described.     

Oligomérisation anionique de l'ethylène. III. Application à la synthèse d'alcools à longue chaine

Living oligomers of ethylene obtained by n-BuLi complexed with TMEDA have been deactivated by ethylene oxide. The nuclear magnetic resonance study of the product obtained allowed us to follow the influence of TMEDA toward the functionalization. Three products have been characterized: By increasing the ratio [TMEDA]/[n-BuLi] one obtains a decrease of the functionalization reaction.     

A Self‐Assembled Calix[4]arene Dimer Linked through Hydrogen‐Bonded 2‐Ureidopyrimidin‐4(1H)‐one Groups

Tightly linked! A linear array of complementary hydrogen bonds forms between two 2‐ureidopyrimidin‐4(1H)‐one rings attached to the upper rims of facing 1,3‐alternate calix[4]arenes (shown schematically). The strength of the binding (K_ass>10⁶ M ⁻¹ in chloroform) and the efficiency of the self‐assembly open up interesting perspectives in the design of highly ordered multicomponent cages.     

Dynamic covalent gels assembled from small molecules: from discrete gelators to dynamic covalent polymers

Dynamic covalent chemistry has emerged recently to be a powerful tool to construct functional materials. This article reviews the progress in the research and development of dynamic covalent chemistry in gels assembled from small molecules. First dynamic covalent reactions used in gels are reviewed to understand the dynamic covalent bonding. Afterwards the catalogues of dynamic covalent gels are reviewed according to the nature of gelators and the interactions between gelators. Dynamic covalent bonding can be involved to form low molecular weight gelators. Low molecular weight molecules with multiple functional groups react to form dynamic covalent cross-linked polymers and act as gelators. Two catalogues of gels show different properties arising from their different structures. This review aims to illustrate the structure-property relationships of these dynamic covalent gels.     

Towards the construction of mesoscopic species with emergent and functional properties via the derivatisation of molybdenum-oxide ‘Giant-Wheel’ clusters

Polyoxometalate chemistry has proved to be an extraordinary source of a large variety of compounds, clusters and solid–state structures—these are built using very simple metal oxygen fragments linked together in an enormous variety of modes. Herein we focus on the ‘Giant-Wheel’ clusters which contain 154 and 176 Mo atoms and examine the variety of structural modifications that has been achieved to date with these systems. The generation of structural vacancies (here referred to as defects), substitution of ligands, and incorporation of hetero-metallic centres offers many fascinating possibilities with respect to the targeted functionalisation of these species for a pre-determined function and application. Furthermore, evidence is presented which suggests the identity of the most labile and, therefore, most easily derivatised units present in these systems. The consequences of this assignment are then discussed in the context of inter- (formation of layers and chains) and intra- (assembly inside the cavity) molecular growth.     

Desulfuration and Cyclization of (Z)‐2‐[Amino(pyridine‐2‐yl)methylene]‐ hydrazonecarbothioamide in the Presence of Manganese(II)

The reaction of (Z)‐2‐[amino(pyridine‐2‐yl)methylene]hydrazonecarbothioamide (HAm4DH) with Mn(ClO₄)₂·6H₂O afforded different mononuclear or polynuclear manganese(II) complexes, the nature of which apparently depended on the solvent used. For example, in ethanol a compound of formula [Mn(HAm4DH)₂](ClO₄)₂ ( 1 ) was obtained, where HAm4DH coordinates as a common tridentate NNS donor, but the [Mn(bpy)₂(NCS)₂] complex ( 2 ) (bpy = 2,2'‐bipyridine) has also been obtained – probably due to C–N bond cleavage of the thiosemicarbazone. Nevertheless, in a basic aqueous medium [Mn(bpy)₃](ClO₄)₂·0.5bpy ( 3 ) is formed and there is structural evidence for chemical transformations of the thiosemicarbazone promoted by Mn^II. Thus, the sulfate in {[Mn(py)₄Mn(py)₂(H₂O)₂(μ‐SO₄)₂]·4H₂O}_n ( 4 ) or sulfate and cyclooctasulfur in [Mn(pta)₂(pdo)]₄(SO₄)₂·4H₂O·S₈] ( 5 ), where pta is 3‐(pyridin‐2‐yl)‐1,2,4‐triazol‐5‐amine and pdo is (2R,4R/2S,4S)‐pentane‐2,4‐diolato, arise from the desulfuration and oxidation of the thiosemicarbazone ligand. The structures of complexes 2 to 5 were established by single‐crystal X‐ray diffraction. The formation of pta is the result of the oxidative cyclization of HAm4DH. In the polynuclear complex 4 , the sulfate acts as an (O,O') bridge between alternating Mn(py)₂(H₂O)₂ and Mn(py)₄ centers. In the tetranuclear complex 5 , pta acts as a bischelating ligand through the N‐pyridine and N‐triazole, and pdo act as a bridge between two manganese atoms. It is also noteworthy that in complexes 4 and 5 hydrogen bonds give rise to different self‐assembly behaviour that leads to complicated supramolecular structures.     

Indicator–displacement assays

Indicator displacement assays (IDAs) are now a popular method for converting most any synthetic receptor into an optical sensor. In this review many such assays are highlighted, along with biological counterparts. The focus is upon colorimetric, fluorescent, and metal containing IDAs. The power of the method can be readily appreciated by the large diversity of analytes that have been targeted with this technique. It is clear that the method is now well accepted and will continue to be one of many methods used to create optical detection methods from synthetic receptors.     

Hydrogen Bond and π–π Interactions in a 3D Supramolecular Structure Containing 1D Helical Chains

The reaction of 2, 2′‐bipyridine‐6, 6′‐dicarboxylic acid (H₂bpdc) with zinc nitrate and different rare earth chlorides generates two novel three‐dimensional supramolecules Zn(6‐bpc)₂ · 2H₂O ( 1 ) and Ce(bpdc)₂ · H₂O ( 2 ) (6‐Hbpc = 2, 2′‐bipyridine‐6‐carboxylic acid). The left‐and right‐handed helical chains give rise to a 3D supramolecular framework through hydrogen‐bond and weak π–π interactions in complex 1 . Interestingly, the decarboxylation occurred and the bpdc ligand was transformed into 6‐bpc species under the hydrothermal reaction in the presence of Nd^III ions, while the decarboxylation did not occur when Ce^III ions were used. In the structure of 2 , one central Ce(IV) atom coordinates to two bpdc ligands, resulting in a discrete molecule. These discrete units are further extended into a 3D supramolecular structure through intermolecular hydrogen bonds and π–π interactions.     

Platin(0)‐Komplexe mit amino‐substituierten Alkinen: Neue Metallorganische Bausteine für supramolekulare Architekturen und „Kristall‐Engineering”︁

Platinum(0) Complexes with Amino‐Substituted Alkynes: Novel Organometallic Building Blocks for Supramolecular Architectures and “Crystal Engineering” Homoleptic Bis(alkyne)platinum(0) compounds containing either NH₂‐ or NH₂‐/OH‐substituents are formed by reaction of Pt(cod)₂ with alkynes as stable compounds. They can be used as variable building blocks for supramolecular networks. The crystal structure analyses of Bis(2‐amino‐2,5dimethyl‐5‐hydroxy‐hex‐3‐yne)platinum(0) ( 1 ) and of Bis(1(3‐amino‐3‐methyl‐but‐1‐inyl)‐cyclohexane‐1‐ol)platinum(0) ( 2 ) exhibit that the low‐valent Pt atom is tetrahedrally surrounded by the four sp‐hybridizated carbonatoms of the alkynes. Despite the fact that the bond lengths and ‐angles of the PtC₄ units are equal, the supramolecular structures are different. While in 1 polymer strands are formed in which the bis(alkyne)‐Pt⁰ units are connected by (OH)₂(NH₂)₂‐ tetrahedrons, 2 yields only a dimer containing a network of four OH‐ and two NH₂‐groups. Platinum(0) complexes with cationic alkynes bearing ammonium substituents can be isolated as thermal stable compounds. The X‐ray structures of [Cl( FH ⁺)Pt(cod)]₄ ( 8 ) reveals that four molecular units form a cube with both four NH₃⁺ groups and Cl^– at the corners connected by hydrogen bridges. In the bis(alkyne)Pt⁰ complex [Cl_1.5( FH ⁺)_1.5( F )_0.5Pt] ( 9 ) only 1,33 of two NH₂ groups are protonated and a hydrogen bridged network connects four bis(alkyne)Pt⁰ units (cod: cycloocta‐1.5‐diene, F : 1‐(trimethylsilylethinyl)‐1‐amino‐cyclohexane).     

Supramolecular Chemistry—Scope and Perspectives Molecules,Supermolecules, and Molecular Devices (Nobel Lecture)

Supramolecular chemistry is the chemistry of the intermolecular bond, covering the structures and functions of the entities formed by association of two or more chemical species. Molecular recognition in the supermolecules formed by receptor-substrate binding rests on the principles of molecular complementarity, as found in spherical and tetrahedral recognition, linear recognition by coreceptors, metalloreceptors, amphiphilic receptors, and anion coordination. Supramolecular catalysis by receptors bearing reactive groups effects bond cleavage reactions as well as synthetic bond formation via cocatalysis. Lipophilic receptor molecules act as selective carriers for various substrates and make it possible to set up coupled transport processes linked to electron and proton gradients or to light. Whereas endoreceptors bind substrates in molecular cavities by convergent interactions, exoreceptors rely on interactions between the surfaces of the receptor and the substrate; thus new types of receptors, such as the metallonucleates, may be designed. In combination with polymolecular assemblies, receptors, carriers, and catalysts may lead to molecular and supramolecular devices, defined as structurally organized and functionally integrated chemical systems built on supramolecular architectures. Their recognition, transfer, and transformation features are analyzed specifically from the point of view of molecular devices that would operate via photons, electrons, or ions, thus defining fields of molecular photonics, electronics, and ionics. Introduction of photosensitive groups yields photoactive receptors for the design of light-conversion and charge-separation centers. Redox-active polyolefinic chains represent molecular wires for electron transfer through membranes. Tubular mesophases formed by stacking of suitable macrocyclic receptors may lead to ion channels. Molecular self-assembling occurs with acyclic ligands that form complexes of double-helical structure. Such developments in molecular and supramolecular design and engineering open perspectives towards the realization of molecular photonic, electronic, and ionic devices that would perform highly selective recognition, reaction, and transfer operations for signal and information processing at the molecular level.     

Carbohydrate Recognition through Noncovalent Interactions: A Challenge for Biomimetic and Supramolecular Chemistry

Carbohydrates are not always as “sticky” as one might expect . Even in organic solvents they are difficult targets for the supramolecular chemist, due to their complex, three-dimensional structures. In their natural environment (water) they are especially elusive, presenting challenges which will occupy synthetic and theoretical chemists for some time to come. The complex of an octaamide supramolecular receptor with β-D -glucopyranose, which binds through apolar and polar contacts, is shown.     

Perspectives in Supramolecular Chemistry—From Molecular Recognition towards Molecular Information Processing and Self-Organization

The selective binding of a substrate by a molecular receptor to form a supramolecular species involves molecular recognition which rests on the molecular information stored in the interacting species. The functions of supermolecules cover recognition, as well as catalysis and transport. In combination with polymolecular organization, they open ways towards molecular and supramolecular devices for information processing and signal generation. The development of such devices requires the design of molecular components performing a given function (e.g., photoactive, electroactive, ionoactive, thermoactive, or chemoactive) and suitable for assembly into an organized array. Light-conversion devices and charge-separation centers have been realized with photoactive cryptates formed by receptors containing photosensitive groups. Eleclroactive and ionoactive devices are required for carrying information via electronic and ionic signals. Redox-active polyolefinic chains, like the “caroviologens”, represent molecular wires for electron transfer through membranes. Push-pull polyolefins possess marked nonlinear optical properties. Tubular mesophases, formed by organized stacking of suitable macro-cyclic components, as well as “chundle”-type structures, based on bundles of chains grafted onto a macrocyclic support, represent approaches to ion channels. Lipophilic macrocyclic units form Langmuir-Blodgett films that may display molecular recognition at the air-water interface. Supramolecular chemistry has relied on more or less preorganized molecular receptors for effecting molecular recognition, catalysis, and transport processes. A step beyond preorganization consists in the design of systems undergoing self-organization, that is, systems capable of spontaneously generating a well-defined supramolecular architecture by self-assembling from their components under a given set of conditions. Several approaches to self-assembling systems have been pursued: the formation of helical metal complexes, the double-stranded helicates, which result from the spontaneous organization of two linear polybipyridine ligands into a double helix by binding of specific metal ions; the generation of mesophases and liquid crystalline polymers of supramolecular nature from complementary components, amounting to macroscopic expression of molecular recognition; the molecular-recognition-directed formation of ordered solid-state structures. Endowing photo-, electro-, and ionoactive components with recognition elements opens perspectives towards the design of programmed molecular and supramolecular systems capable of self-assembly into organized and functional supramolecular devices. Such systems may be able to perform highly selective operations of recognition, reaction, transfer, and structure generation for signal and information processing at the molecular and supramolecular levels.     

Regulated Single‐Axis Rotations of a Carbonaceous Guest in a van der Waals Complex with an Entropy Cost

In a tight host–guest complex assembled solely by nondirectional van der Waals forces, unique motions of the guest, such as solid‐state inertial rotations, emerge. The regulation of dynamic motions is an important element to be explored for novel functions of such complexes, which may be seemingly difficult to achieve because of the nondirectionality of the assembling forces. A regulated, single‐axis rotation was made possible by choosing an appropriate shape of the guest in the tubular host. Specifically, an ellipsoidal guest was made to stand along a cylinder axis of the host, which consequently resulted in single‐axis rotations of the guest in the solid. The rotational frequency was considerably high for solid‐state rotations but was suppressed to 10 GHz, which was 1/20 of the isotropic rotation of a spherical guest. In‐depth kinetic analyses quantitatively revealed that the entropy cost was a determining factor that regulated the dynamics.     

The Photooxidation of Bis(8‐dimethylaminonaphthyl) Ditelluride

The photooxidation of (8‐Me₂NC₁₀H₆Te)₂ provided a complex reaction mixture from which the novel tetranuclear telluroxane cluster (8‐MeNC₁₀H₅TeO)₄ ( 1 ) was isolated in 17 % yield. Compound 1 contains two 5,5′‐binaphthyl moieties that presumably formed by oxidation of C5–H bonds of the naphthyl ring. Upon formation of 1 , one of the two methyl groups of the 8‐dimethylamino group was cleaved and the remaining coordinative Te···N bond turned into a covalent Te–N bond. In the solid‐state, individual molecules of 1 are associated through secondary Te···O interactions giving rise to a 1D coordination polymer.     

Two 2D Metal‐organic Networks Based on a Rigid Imidazolate/Sulfonate Functionalized Ligand – Effect of the Coordination Modes of the Ligand on Crystal Structures

A rigid imidazolate/sulfonate functionalized ligand, 6‐(4‐sulfonatopheny)imidazo[4, 5‐f]isoindole‐5, 7‐dione (SPID) was designed and used for assembling reactions with Mn²⁺ and Cu²⁺ ions. Two 2D frameworks compounds, [Mn(H_‐1SPID)₂(DMAC)₂] ( 1 ) and [Cu(H_‐2SPID)(H₂O)₂] · 0.7DMAC · 0.3H₂O ( 2 ) (DMAC = N,N‐dimethylacetamide) were obtained. Single crystal X‐ray analyses show that 1 has a 2D (4, 4)‐net based on 4‐connected Mn²⁺ nodes and μ₂‐coordinated H_‐1SPID spacers, whereas compound 2 has a 2D (6, 3)‐net built of 3‐connected Cu²⁺ nodes and μ₃‐coordinated H_‐2SPID spacers. Additionally, the thermal behavior of 1 and 2 is presented.     

A Molecular Chameleon: Chromophoric Sensing by a Self-Complexing Molecular Assembly

A color change from purple to green takes place on addition of tetrathiafulvalene (TTF) to the macrobicyclic receptor 1 ⁴⁺, which is composed of a cyclobis(paraquat-p-phenylene) tetracation that shares one of its paraphenylene rings with a 1,5-naphthoparaphenylene-[36]crown-10 macrocycle. The TTF molecule forces the macrobicycle to turn inside out (see schematic drawing below) and displaces the self-complexed 1,5-dioxynaphthalene ring system from the center of the tetracationic cyclophane.     

Nouveaux polyéthers et polyesters à base d'isosorbide: synthèse et caractérisation

A new family of multifunctional polyethers was synthesized with acceptable yields by condensation of isosorbide with aliphatic and aromatic dihalides in solid-liquid heterogeneous medium (solid KOH in DMSO). Molecular weights evaluated by GPC are rather low (polydispersed oligomers with n = 2–9). On the other hand, polycondensation with aliphatic or aromatic acid dichlorides in mass or in solution allowed the elaboration of polyethers with appreciable weights (4000–8000) in good yields.     

Synthesis and host–guest properties of a calix[6]arene based receptor closed by an internal ion-paired cap

The straightforward synthesis of a C_s symmetrical calix[6]arene possessing carboxylic acid groups as well as an ammonium arm is described. This calixarene can encapsulate ammonium ions through a highly selective recognition process thanks to the presence of an internal ion-paired cap that preorganizes the cavity and constitutes an efficient binding site.     

Amino acid binding in water by a new guanidiniocarbonyl pyrrole dication: the effect of the experimental conditions on complex stability and stoichiometry

The synthesis and binding properties of a new guanidiniocarbonyl pyrrole dication 2 are reported, which efficiently binds alanine carboxylate with log K_ass = 3.9 in buffered water. Due to the increased charge density in this dication, the binding constant is five times larger than for the parent guanidiniocarbonyl pyrrole monocation 1 (log K = 3.2). However, the experimental conditions for determining the binding constant significantly influence both complex stability and stoichiometry. With increasing amount of substrate added during the titration, the overall complex stability decreases due to the increasing ionic strength of the solution. Furthermore, the formation of 1:2 complexes between 2 and 7 becomes increasingly important. Therefore, for the comparison of binding data it has to be assured that exactly the same experimental conditions are used for their determination.