Convenient synthesis of [3]catenane by olefin metathesis dimerizations

[3]Catenane 5a and 5b were synthesized conveniently by olefin metathesis dimerization of pseudorotaxanes 3a and 3b. The yields of 5a and 5b were influenced by concentrations of 3a and 3b, and a ring size of a center wheel of [3]catenane.     

Translational isomerism in a [3]catenane and a [3]rotaxane

[structure: see text] Post-assembly covalent modification using Wittig chemistry of [2]rotaxane ylides, wherein NH(2)(+) centers in the dumbbell-shaped components are recognized by dibenzo[24]crown-8 (DB24C8) rings, has afforded a [3]catenane and a [3]rotaxane with a precise and synthetically prescribed shortage of DB24C8 rings. The nondegenerate pairs of translational isomers present in both of these interlocked molecular compounds provide the fundamental platform on which to construct sensory devices and nanochemomechanical systems.     

The effects of conformation on the noncovalent bonding interactions in a bistable donor-acceptor [3]catenane

A switchable donor-acceptor bistable [3]catenane, composed of a crown ether containing a pair of alternating π-electron rich tetrathiafulvalene and 1,5-dioxynaphthalene units, encircled by two π-electron deficient cyclobis(paraquat-p-phenylene) rings, has been synthesised and the redox-activated switching it undergoes investigated.     

Anion-templated assembly of a [2]catenane

The first example of a [2]catenane structure to be synthesized using anion templation is described. The nature of the anion template is demonstrated to be crucial to the assembly process, with only chloride anion producing the [2]catenane in acceptable yield. Anion binding studies reveal a dramatic catenation effect on anion selectivity properties as compared to a noncatenated acyclic receptor.     

A [2]catenane constructed around a rhodium(III) center used as a template

Rhodium(III) has been used as a templating metal center for building a [2]catenane. In the first stage, a Rh(phen)(2) motif has been incorporated into a large ring. Subsequently, a 2,2'-bipyridine derivative has been threaded through the ring, this process being driven by coordination of the chelate to the Rh(III) center. The formation of the second ring has been performed using the ring-closing metathesis approach. Contrary to the other catenanes synthesized around transition metals, the second ring is formed at the rear of the coordination unit which it contains, by cyclizing two flexible end-functionalized fragments attached at the 4 and 4' positions of the 2,2'-bipyridine chelate.     

A high yielding template-directed synthesis of the first fluorenone-containing [2]catenane

A new crownophane containing both 2,7-dioxyfluorenone and 1,5-dioxynaphthalene moieties bridged by triethylene glycol units has been synthesized and used as a highly efficient template for the preparation of the first fluorenone-containing [2]catenane incorporating a cyclobis(paraquat-p-phenylene) tetracation as a second macrocyclic component.     

A [2]catenane constructed around a Ru(diimine)(3)(2+) complex used as a template

A [2]catenane has been constructed using an octahedral complex of the Ru(diimine)( 2+)(3) family as a scaffold. Two diimine chelates have been incorporated in a ring prior to the ruthenium(II) complexation reaction. The macrocyclic complex thus obtained has been subsequently threaded by a long linear fragment containing the third chelate. The rutheniuml(II)-complexed catenane, cyclized by ring-closing metathesis, is the first example of an interlocking ring system built around an octahedral tris-chelate complex.     

Construction of a hetero pseudo[2]rota[2]catenane

A novel ammonium template containing three ammonium sites was synthesized. Two ammoniums located on the linear component served as template for cucurbit[6]uril to form the CB-based pseudo[2]rotacane while another one located on the macrocyclic component played a role of template for clipping reaction. As a result of a ‘‘threading-followed-by-clipping' approach, a novel hetero pseudo[2]rota[2]catenane was successfully constructed.     

Two classes of alongside charge-transfer interactions defined in one [2]catenane

A [2]catenane, which incorporates hydroquinone (HQ) and a sterically bulky tetrathiafulvalene (TTF) into a bismacrocycle, has been designed to probe the alongside charge-transfer (CT) interactions taking place between a TTF unit and one of the bipyridinium moieties in the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+). A template-directed strategy employs the HQ unit as the primary template for formation of the tetracationic cyclophane CBPQT4+, affording the desired [2]catenane structure but as an uncharacteristic green solid. The X-ray crystal structure and detailed 13C NMR assignments have identified a stereoselective preference for catenation about the cis isomer. The 1H NMR spectroscopy, electrochemistry, and X-ray crystallography all confirm that the CBPQT4+ cyclophane encircles the HQ unit, thereby defining a structure which would normally determine a red color. The visible-NIR region of the absorption spectrum displays a band at approximately 740 nm that is unambiguously assigned to a TTF --> CBPQT4+ CT transition on the basis of resonance Raman spectroscopy using 785 nm excitation. The profile of the CT band changes depending on the ratio of the cis- to trans-TTF isomers in the [2]catenane for which the molar absorptivity of each isomer is estimated to be significantly different at epsilon max = 380 and 3690 M-1 cm-1, respectively. Molecular modeling studies confirmed that the observed difference in the absorption spectroscopic profile can be accounted for by both a better overlap of the HOMO(TTF) and LUMO+1(CBPQT4+) as well as a more stable face-to-face (pi...pi) conformation in the trans isomer compared to the edge-to-face cis isomer of the [2]catenane. The latter is arranged for pi-orbital overlap through the sulfur atoms of the TTF unit, thereby defining an [Spi...pi] interaction.     

Sulfate anion-templated assembly of a [2]catenane

The sulfate anion's templating role in catenane formation is demonstrated for the first time; a novel bis-pyridinium nicotinamide [2]catenane is prepared in a remarkable high yield and is shown to exhibit selectivity for sulfate, the templating anion.     

M3L2 metallo-cryptophanes: [2]catenane and simple cages

Crystalline M(3)L(2) complexes with either single cage or triply interlocking [2]catenane chiral structures are formed the self-assembly of host-like ligands with transition metals.     

The microscopic switching mechanism of a [2]catenane

We apply numerical simulations at an all-atom level to investigate the switching mechanism of a [2]catenane, a prototype of a molecular machine. This system is able to switch reversibly between two different stable states, upon external stimuli, with a time scale ranging from microseconds up to milliseconds, well over the typical domain of molecular dynamics (MD) computer simulations. However, combining a strategy recently developed for investigating rare events with ordinary MD, we are able to unravel the microscopic mechanism of the conformational rearrangements involved in the switching process, including dynamical effects. Along the path that connects the product and reactant state, we find several intermediate states characterized by pi-pi stacking interactions and hydrogen bonds. Moreover, counterions interact strongly with the system in a correlated way, in agreement with recent static calculations performed on [2]rotaxanes.     

Anion induced and inhibited circumrotation of a [2]catenane

The first example of a catenane capable of performing circumrotation via an anion switching methodology is described; of particular interest is a conformational locking mechanism which results from chloride coordination in the catenane binding cavity.     

Host-guest interactions in aqueous media withp-tert.-butylcalix[4]arene bearing polyoxyethylene chains

The interactions ofp-tert.-butylcalix[4]arene bearing polyoxyethylene chains (C3) with pyrene (Py), 1-anilino-8-naphthalenesulfonate (ANS) andN-phenyl-naphthylamine (NPN) in aqueous solution were studied by absorption and fluorescence measurements. Absorption spectral changes and fluorescence enhancements reveal that C3, which has a hydrophobic cavity, can include organic molecules and ions in aqueous solution and form 11 host-guest complexes with ANS and NPN. C3 forms inclusion complexes with Py at different stoichiometries depending on the host: guest molar ratio. Binding constants of 2.2×10⁴, 2.0×10⁴ and 3.6×10⁵ dm³ mol^–1 were calculated for the C3Py, C3ANS and C3NPN complexes (11), respectively, based on the Benesi-Hildebrand equation.Author for correspondence.     

An electrochemical color-switchable RGB dye: tristable [2]catenane

We propose a design for an electrochemically driven RGB dye based on a tristable [2]catenane, in which the color of the molecule can be switched between Red, Green, and Blue by merely changing voltage. Based on DFT calculations, we conclude that the tristable [2]catenane should consist of a CBPQT4+ ring interlocked with a polyether macrocyle containing DNP (red), TTF (green), and FBZD (blue) units as the tunable RGB color-generating donors. Thus, at controllable voltages 0, V1, and V2, the [2]catenane is expected to display green, blue, and red colors, respectively. The advent of these RGB tristable molecules may have potential applications in low cost paperlike electronic displays.