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A series of macrocyclic phenthrolines and a tris(biphenyl)methyl derivative are synthesized. [2]Rotaoxanes with large ring components were synthesized by the template method, and the stability of rotaxanes was examined.

The tetravalency of carbon and its ability to form covalent bonds with itself and other elements enables large organic molecules with complex structures, functions and dynamics to be constructed. The varied electronic configurations and bonding patterns of inorganic elements, on the other hand, can impart diverse electronic, magnetic, catalytic and other useful properties to molecular-level structures. Some hybrid organic--inorganic materials that combine features of both chemistries have been developed, most notably metal--organic frameworks (1), dense and extended organic--inorganic frameworks (2) and coordination polymers (3). Metal ions have also been incorporated into molecules that contain interlocked subunits, such as rotaxanes (4-7) and catenanes (6,8), and structures in which many inorganic clusters encircle polymer chains have been described (9). Here we report the synthesis of a series of discrete rotaxane molecules in which inorganic and organic structural units are linked together mechanically at the molecular level. Structural units (dialkyammonium groups) in dumb-bell-shaped organic molecules template the assembly of essentially inorganic 'rings' about 'axles' to form rotaxanes consisting of various numbers of rings and axles. One of the rotaxanes behaves as a 'molecular shuttle' (10): the ring moves between two binding sites on the axle in a large-amplitude motion typical of some synthetic molecular machine systems (11-15). The architecture of the rotaxanes ensures that the electronic, magnetic and paramagnetic characteristics of the inorganic rings--properties that could make them suitable as qubits for quantum computers (16-18)--can influence, and potentially be influenced by, the organic portion of the molecule., The basis for the hybrid organic--inorganic rotaxane synthesis lies in the observation (19) that the formation of heterometallic rings of various shapes and sizes, containing seven or more trivalent Cr(III) [...]

In this article, we report on the efficient synthesis of well defined, homogeneous [n]rotaxanes (n up to 11) by a template-directed thermodynamic clipping approach. By employing dynamic covalent chemistry in the form of reversible imine bond formation, [n]rotaxanes with dialkylammonium ion (-C[H.sub.2]N[H.sup.+.sub.2]C[H.sub.2-]) recognition sites, encircled by [24]crown-8 rings, were prepared by a thermodynamically controlled, template-directed clipping procedure, that is, by mixing together a dumbbell compound containing a discrete number of -C[H.sub.2]N[H.sup.+.sub.2]C[H.sub.2]-ion centers with appropriate amounts of a dialdehyde and a diamine to facilitate the [n]rotaxane formation. A 21-component self-assembly process is operative during the formation of the [11]rotaxane. The oligomeric dumbbells containing -C[H.sub.2]N[H.sub.2]+C[H.sub.2]- ion recognition sites were prepared by a stepwise protocol. Several of the dynamic [n]rotaxanes were converted into their kinetically stable counterparts, first by reduction ('fixing') of imine bonds with the B[H.sub.3]*THF complex, then by protonation of the complex by addition of acid. dynamic covalent chemistry | molecular recognition | polyrotaxanes | self-assembly | template-directed synthesis

A study on the properties of rotaxanes describes a new type of phenomenon resulting from mechanical bonding where the conformation adopted by one of the mechanically interlocked components is regulated through selectively activated non-covalent interactions with another. In such tertiary amide peptido[2]rotaxanes, the macrocycle 'remembers' or 'forgets' the intercomponent amide hydrogen bonding motif originally responsible for rotaxane formation based on the nature of its environment.

A series of dinuclear platinum(II) complexes, [(dien)Pt(N[H.sub.2] [(C[H.sub.2]).sub.n]N[H.sub.2])Pt(dien)]C[l.sub.4](dien = diethylenetriamine, n = 8, 9, 10, and 12) and their corresponding [2]rotaxanes with (α-cyclodextrin ((α-CD), [(dien)Pt{N[H.sub.2] [(C[H.sub.2]).sub.n]N[H.sub.2]-(αCD}Pt(dien)]C[l.sub.4], have been synthesized and characterized by ¹H, [sup.13]C, and [sup.195]Pt NMR spectroscopy and electrospray mass spectrometry. The rotaxanes were prepared by reacting the {N[H.sub.2][(C[H.sub.2]).sub.n]N[H.sub.2]-(α-CD} pseudorotaxanes with [Pt(dien)]Cl, to stopper the included linear (α,ω-diaminoalkane chains with the inert Pt(II) end groups. The kinetics of the self-assembly and dissociation of the β-CD rotaxane, [(dien)Pt{N[H.sub.2][(C[H.sub.2]).sub.10]N [H.sub.2]-β-CD}Pt [(dien)].sup.4+], were investigated by using ¹H NMR and are indicative of a slippage mechanism, owing to the comparable sizes of the β-CD cavity and the [[Pt(dien)].sup.+] end group. A relatively weak inclusion of the end group in the β-CD cavity precedes a thermally promoted passage of the β-CD over the [[Pt(dien)].sup.+] end group onto the hydrophobic polymethylene chain of the bridging ligand of the thread. Key words: rotaxanes, pseudorotaxanes, cyclodextrin, platinum complexes, slippage mechanism. On a synthetise une serie de complexes binucleaires du platine(II), de formule generale |(dien)Pt(N[H.sub.2]- [(C[H.sub.2]).sub.n]N[H.sub.2])Pt(dien)]C[l.sub.4] (dien = diethylbnetriamine; n = 8, 9, 10 et 12), ainsi que les [2]rotaxanes correspondants avec la (α-cyclodextrine ((α-CD), de formule generale [(dien)Pt{N[H.sub.2][(C[H.sub.2]).sub.n]N[H.sub.2]-(α-CD}Pt(dien)]C [l.sub.4] et on les a caracterises par spectroscopie RMN du ¹H, du [sup.13]C et du [sup.195]Pt et par spectrometrie de masse avec electronebulisation. On a prepare les rotaxanes en faisant reagir les pseudorotaxanes {N[H.sub.2][(C[H.sub.2]).sub.n]H[N.sub.2]+β-CD} avec du [Pt(dien)]C1 pour bloquer les chaines lineaires α,ωinoalcanes incluses avec des groupes terminaux Pt(II) inactifs. Faisant appel a la RMN du ¹H, on a etudie la cinetique de l'autoassemblage et de la dissociation du β-CD rotaxane, [(dien)Pt{N[H.sub.2][(C[H.sub.2]).sub.10]N[H.sub.2]+ β-CD}[Pt(dien)].sup.4+] et les resultats suggerent l'existence d'un mecanisme de glissement en raison des tailles comparables de la cavite de la β-CD et du groupe terminal [[Pt(dien)].sup.+]. Une faible inclusion du groupe terminal dans la cavite de la βCD precede un passage favorise par la chaleur de la β-CD par-dessus le groupe terminal [[Pt(dien)].sup.+] et sur la chaine polymethylene hydrophobe du ligand qui assure le pont du filament. Mots cles : rotaxanes, pseudorotaxanes, cyclodextrine, complexes du platine, mecanisme de glissement. [Traduit par la Redaction], Introduction Cyclodextrins (CD) (1) are a homologous family of cyclic oligosaccharides that are constructed of α-(1 →4)-linked glucopyranose units (1-5). The three most common cyclodextrins consist of six ((α-CD), seven [...]

Equilibrating dynamic [2]rotaxanes are formed by dialkylammonium ion templates being present, as the incipient dumbbell-shaped components, in a dynamic combinatorial library (DCL) of equilibrating cyclic and acyclic oligoimines. The crystallization of the mixture has furnished only the [24]crown-8-like macrocycle on its own-evidence of a kinetic selection process occurring between phase transitions.

[2]Pseudorotaxanes have been prepared by threading N, N'-bis(4-pyridinylmethylene)-1,2-ethanediimine (L2), -1,4-butanediimine (L4), and -1,6-hexanediimine (L6) ligands through [alpha]-cyclodextrin ([alpha]-CD) and [beta]-cyclodextrin ([beta]-CD), and have subsequently been converted to the corresponding [2]rotaxane species by coordinating bulky [[Fe[(CN).sub.5]].sup.3-] end groups. The stability constants for the [2]pseudorotaxanes were determined by [sup.1]H NMR chemical shift titrations and increase with the polymethylene chain length n. The rate constants for both the formation of the [[Fe[(CN).sub.5](Ln)].sup.3-] complexes from the [[Fe[(CN).sub.5O[H.sub.2]].sup.3-] ion and Ln, and the rate constants for the dissociation of Ln from the metal complexes, exhibit significant diminutions in the presence of [alpha]- and [alpha]-CD, owing to inclusions of the free and coordinated ligands, respectively. The lability of the iron(II)-pyridine bonds also permits the spontaneous serf-assembly of the [2]rotaxane upon the addition of cyclodextrin to the iron dimer complexes. The mechanism for this process involves the rate-determining dissociation of a [[Fe(CN).sub.5].sup.3-] unit from [[[(NC).sub.5] Fe(Ln)Fe[(CN).sub.5]].sup.6-], followed by CD inclusion of the Ln ligand to form a semirotaxane, and subsequent recomplexation by the [[Fe[(CN).sub.5]O[H.sub.2]].sup.3-] ion. Key words: cyclodextrins, rotaxanes, pentacyanoferrate(II), ligand substitution, kinetics.

Research has been conducted on the hetero[3]rotaxanes. The use of the intermolecular hydrogen bonding and donor-acceptor interactions in assembling these hetero[3]rotaxanes is described, and the results indicate that [3]rotaxanes with different ring components have kinetic feature not available in [3]rotaxanes with identical ring components.

The template effects exerted by guests in the ring closure reaction of the precursor are analyzed. The results have indicated that the formation of tetracationic aromatic cycles templated by aromatic donors are benefited from the use of extended [pi]-surfaces, both in the acceptor and in the donor components.

Two new host-[2]rotaxanes were assembled through the key step of combining a DCC-[2]rotaxane with a cyclophane or aromatic cleft. The hosts are tighter complexes with amino acids, dipeptides, and fluorophores than a more traditional cyclophane in water, DMSO, and 72/25 (v/v) water to DMSO solution.

An impressive research effort aimed at the preparation, characterization, and the study of the properties of rotaxanes and catenanes is witnessed. The results illustrate the potential of zeolites in the field of molecular machines as a medium to stabilize short-lived transients.

The hydrogen-bond-directed synthesis X-ray crystal structures and optical properties of the first chiral peptide rotaxanes are reported. A combination of semiempirical calculations and geometrical modeling using the continuous chirality measure show that chirality is transmitted from the amino acid asymmetric center on the thread via the macro cycle to the C-terminal stopper of the rotaxane.

A new study shows that structural rigidity and preorganized guest binding sites have a strong influence on template efficiency when synthesizing hydrogen bond-assembled rotaxanes.

One-station and two-station (2)rotaxanes contain one and two dialkoxybenzene subunits respectively while the cyclophane consists of two 4,4'-bipyridinium groups attached by 1,4-xylyl groups. Closed conformations are formed by anthracene or ferrocene terminal stoppers by pi-stacking with the cyclophane. Reversible and fast electron transfer occurs from the excited anthracene stoppers to the cyclophane. A second electron transfer occurs from the donor dialkoxybenzene to the cyclophane, on direct excitation in the charge-transfer absorption band. Conformational exchange affects the electron transfer rate.

Studies involving the mechanically-interlocked compounds of rotaxanes and catenanes which utilize cyclodextrins as one of their ring components are reviewed. The three mechanisms for the formation of rotaxanes are cyclodextrin-based pseudorotaxanes, rotaxanes with stoppers connected by coordinative or ionic bonds and cyclodextrin-containing (2)rotaxanes with covalently bound stoppers. Cyclodextrin-containing polyrotaxanes are either inclusion complexes of polymers with cyclodextrins, linear-chain cyclodextrin-based polyrotaxanes or side-chain cyclodextrin-based polyrotaxanes.

The series of [2]rotaxanes was generated based on a template-directed synthetic process involving the reaction of an excess resorcinol with benzyl bromide. The synthetic process for the self-assembly of the novel [2]rotaxanes with hydroquinone and resorcinol rings was characterized by the LiBr-mediated formation of a phenol intermediate. The reaction of the intermediate product with tosylate also led to the formation of the benzyl-protected compound which formed the symmetrical dumbell compounds.

The kinetics of the slipping approach to rotaxanes is investigated, The size of the macrocyclic component and the stoppers at the end of the dumbbell-shaped component of the rotaxanes are changed systematically. Absorption ultraviolet-visible and 1H-nuclear magnetic resonance spectroscopies were analyzed. Rate constants for the processes were found to be affected by the size complementarity between the stoppers and macrocyclic components.

A synthetic process for the self-assembly of (2)-, (3)-, and (4)rotaxanes, integrating bis-p-phenylene-34-crown-10 as the ring component(s) surrounding bipyridinium-based dumbbell-shaped components with dendritic stoppers at both ends is presented. Due to the hydrophobic dendritic framework, these (n)rotaxanes are soluble in a wide variety of organic solvents, despite the polycationic natures of their bipyridinium-based backbones. There is a significant dependence of the rate of molecular shuttling action of the (2)rotaxane, upon the polarity of the media.

Self-assembling of pi-electron rich hydroquinone-based macrocyclic polyether, BPP34C10, and pi-electron deficient bipyridium-based dumbbell shaped components gives rise to rotaxanes under appropriate thermal energy. Absorption and luminescence spectroscopies reveal the energy and charge transfer processes between the chromophores. Electroactive components undergo redox processes. The 1-H-NMR shows the shuttling process of BPP34C10 unit between the bipyridinium. X-ray crystallography, 13C-NMR , mass spectroscopies characterize the rotaxanes.

Research has been conducted on the electron transfer reactions. The hypothesis coordination of the metal cations can enhance electron transfer rates and the role of the space jumps versus metal-ligand bonds in the electron transfer pathway have been investigated and the details are reported.

Research has been conducted on the crown ether-containing macrobicycles. The molecular structure of these macrobicycles has been characterized via NMR spectroscopy and X-ray crystallography and the results demonstrate that the macrobicycle's chloride-binding ability is weak.

The translational isomerism which is experimentally seen in some [2]rotaxanes was investigated and modelled through molecular mechanics and molecular dynamics computations applying Allinger's MM3 force field and MM3*, the implemented version of MM3 for MacroModel. Results showed accetable agreements between the calculated and experimental values for translational barriers. Translational barriers were caused by nonbonded interactions and can be tuned by introducing alkyl groups in the polyether chain.

The mechanism and the size complementarity requirements behind the slippage process involving linear rotaxanes were described. A computational investigation was performed using the pi-electron rich macrocycle bis-p-phenylene-34-crown-10 (BPP34C10) macrocyle and the tetraarylmethane-based model stoppers R-S. Two major energy barriers were identified and a substituent effect was observed between the bulky i-Pr group and one of the polyether chains of the BPP34C10 macrocycle.

NMR spectroscopic studies of the stability constants of pentacyano(N-heterocycle)ferrate(II) rotaxanes of alpha-cyclodextrin (alpha-CD) reveal that increase in chain length increases the stability constants, and substitution of 4,4'-bipyridinium for pyrazinium head groups slightly increase the stability. Mechanistic and kinetic studies of the spontaneous self-assembly of the rotaxanes reveal that rate constants are decreased by the alpha-CD inclusion of the free and coordinated ligands.

A novel technique for the preparation of metal-containing catenanes and rotaxanes in which the principle of pure coordination chemistry is applied, was developed. The method is carried out via a stepwise reaction of organic fragments, terpyridine ligands and diphenylphenanthroline moiety, with two transition metals, copper and ruthenium. The metals served as the assembling and templating species which utilize different coordinating fragments of the organic backbone precursors. This strategy would serve as a new way of preparing multicomponent chemical species with promising photochemical properties.

1H nuclear magnetic resonance spectroscopy, supplemented with kinetic studies employing stopped-flow spectrophotometric techniques were done to study the assembly of alpha-cyclodextrin rotaxanes of the type ((NC)5Fe(CNpyr(CH2)nCNpyr.alpha-CD)Fe(CN)5)4- from dimeric iron complexes. It was found that such complex formation involves the dissociation of a (Fe(CN)5)3- unit.

A dicopper(I)-complexed (3)-rotaxane was produced in 34% yield by a transition-metal-templated technique involving a bis-chelating molecular thread, macrocycles incorporating the complementary chelating unit, and porphyrin stoppers are primary components. A tetracopper(I)-complexed (5)-rotaxane was obtained as a byproduct in 8% yield. Coordination chemistry was conducted either at the 2,9-diphenyl-1,10-phenanthroline chelates or at the porphyrin stoppers.

Step growth polymerization involving diacid chloride-diol and transesterification reactions help synthesize a series of polyester rotaxanes containing polysebacate backbones, and ethylene-oxide based crown ethers. Various experiments support the physical linkage of the crown ether to the polymeric backbone. This method enables the incorporation of up to 55 wt % of the macrocycle. Rotaxane formation significantly influences Mark-Houwink K and a values, and thermal behavior. The efficiency of the macrocycles to move along the polyester backbone facilitates crystallization and aggregation without dethreading.

The electron-transfer method between zinc(II) and gold(III) porphyrinic subunits reveals the involvement of the spacer moiety as an intermediate. The speed of electron transfer is influenced by the structure of the molecule, and varies in rotaxanes. The spacer group is likely to turn when the temperature is high. The speed of electron transfer and the energy gap are inversely connected in the electron-transfer reactions. The actual intermediate in the reactions is not the spacer moiety but the reduced central zinc(II) complex.

Five triarylcarbinols were synthesized in good yields through Grignard reactions. Two methods were used to link functionalized spacers to the triarylmethyl moiety. Triarylcarbinols were reduced to triarylmethanes, which were converted to omega,omega,omega-triarylalkanols and then to chloro and iodo derivatives. p-(triarylmethyl)phenols and aniline were synthesized using carbocation chemistry. Alkylation of the former produced alcohol, benzylic bromide and carboxy functionalized derivatives. The resulting functionalized triarylmethyl chlorides could be used as end blocking groups in rotaxanes and polyrotaxanes whose macrocycle contained as much as 42 ring atoms.

An alternative synthetic approach to donor-acceptor rotaxanes-including previously inaccessible [3]- and [4]rotaxanes is described. Their synthesis relies upon the efficient stoppering of their pseudorotaxane precursors.

A new technique of assembling supramolecular species involves noncovalent interactions. The methoduses templates to direct in precise order the synthesis of 1:1 complexes as well as their products (2)rotaxanes and the (2)catenane molecular strings. Crystallographic, spectroscopic, luminescence and electrochemical studies show the highly structured way the molecules interlock and assemble in both solid and solution. The template method opens up a new technology of imprinting the assembly code within the products themselves. This may lead to highly programmable synthesis of supermolecular systems that may find application in data processing at the molecular level.

The major step in the generation of a (2)rotoxane involves inclusion complexation of 1,4-phenylenediamine or benzidine, which serve as pi-donors. The guest molecule 1,4-phenylenediamine cause variations in monoelectric oxidation potentials, due to the formation of extra positive charges. The electron transfer kinetics also vary due to the oxidation of these guests. These studies indicate the ability of the 1,4-phenylenediamine to serve as a subunit due to its repulsive nature during oxidation.

A general precursor to rotaxane-type structures results from the transition metal-directed threading of a molecular fragment having a central chelate and an end-attached gold(III) porphyrin into a presynthesized coordinating ring. A copper(I)-complexed (2)-rotaxane and a new compartmental (3)-rotaxane result from the design of the second porphyrin's functioning as a good stopper, following threading.

The 1,4-di-p-tolyl ether of p-tert-butylcalix(6)arene can be transformed to transannularly linked esters by treating them with diacid chlorides ranging from succionyl to suberoyl. Methylation of the resulting calix(6)arenes which have 1,4-CH2ArCH2 linking moieties creates the respective tetramethyl ethers. When Ar is anthrylene, the conformation of the starting material is retained. But when Ar is phenylene, the confirmation varies, and when it is duryl, a mixture of conformers is produced. When Ar is phenyl or durylene, the system can undergo a conformational change in which the linking moiety becomes spliced through the annules of the macrocyclic ring to give rise to a self-anchored rotaxane.