Bis(1,3-dithiol-2-ylidene)-[3.3]paracyclophanes: orthogonal intramolecular charge transfer interaction

A novel donor-cyclophane, orthogonally incorporated 1,3-dithiol-2-ylidene units (DT) to the cyclophane benzene rings, was synthesized in order to observe the intramolecular charge transfer (ICT) between the donor units and the cyclophane benzene rings.     

Thiolated pi-extended tetrathiafulvalenes: versatile multifunctional pi-systems

Derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) have been synthesized by a new synthetic methodology, viz., direct phosphite-mediated cross-couplings of anthraquinone with 1,3-dithiole-2-thione derivatives. These ex-TTFs bear one, two, or four cyanoethyl-protected thiol groups on the dithiole rings. Deprotection (NaOMe, MeOH, DMF, 20 degrees C) and trapping of the transient thiolates with electrophiles have afforded the new ex-TTF trimer 19, dimeric cyclophanes 22 and 25, the tetrakis(hydroxyethylthio) derivative 23, and the strained cyclophane 24. Solution redox properties have been studied by cyclic voltammetry. For compounds 19, 22, and 25 each ex-TTF unit behaves as an independent 2-electron redox system giving rise to a single, quasi-reversible 6-, 4-, and 4-electron wave, respectively. The Eox value for 24 (0 --> 2+ wave) is positively shifted by 290 mV compared to that of its precursor 15 due to the short bridge in 24 obstructing the conformational change which accompanies oxidation. X-ray crystal structures of 23.2.5MeOH, 23.1.5MeCN, 24.CH2Cl2, and 24.1.5CH2Cl2 show the saddle-shape folding (typical of ex-TTF derivatives), which in 24 is enhanced by the pentamethylene chain bridging the dithiole units. Both solvates of 23 show an unprecedented crystal packing motif due to hydrogen bonding.     

Synthesis and radical coupling of pyridine-bridged pi-extended tetrathiafulvalene (TTF)-type donors and push-pull analogues

A new family of pi-extended TTF analogues (3a-c) and D-pi-A chromophores (5a-c), in which the electroactive units (1,3-dithiole rings and 2,2-dicyanovinyl groups) are connected through a pyridine bridge with a meta substitution pattern, is reported. The redox behavior of these compounds has been investigated by cyclic voltammetry and theoretical calculations performed at the B3P86/6-31G** level. Unlike many pi-extended TTF derivatives, the 1,3-dithiole rings in compounds 3a-c do not behave independently and two oxidation processes are observed with an anodic separation ranging from 50 to 150 mV. Calculations show that electrons are equally extracted from both dithiole rings. A biradical structure is predicted for the dication state due to the near-degeneracy of the HOMO and HOMO - 1 orbitals. The presence of both donor (D) and acceptor (A) fragments in conjugates results in irreversible oxidation and reduction processes associated with the 1,3-dithiole ring and with the 2,2-dicyanovinyl moiety, respectively. An electrochemical-chemical-electrochemical (ECE) process takes place for all the compounds reported. The chemical process implies the dimerization of the radical cation for compounds 5 and the oligomerization of the biradical dication for compounds 3. The ECE process therefore generates new neutral dimeric (5) or oligomeric (3) species that incorporate the TTF vinylogue core.     

Modular Synthesis and Dynamics of a Variety of Donor–Acceptor Interlocked Compounds Prepared by Click Chemistry

A series of donor–acceptor [2]‐, [3]‐, and [4]rotaxanes and self‐complexes ([1]rotaxanes) have been synthesized by a threading‐followed‐by‐stoppering approach, in which the precursor pseudorotaxanes are fixed by using Cu^I‐catalyzed Huisgen 1,3‐dipolar cycloaddition to attach the required stoppers. This alternative approach to forming rotaxanes of the donor–acceptor type, in which the donor is a 1,5‐dioxynaphthalene unit and the acceptor is the tetracationic cyclophane cyclobis(paraquat‐p‐phenylene), proceeds with enhanced yields relative to the tried and tested synthetic strategies, which involve the clipping of the cyclophane around a preformed dumbbell containing π‐electron‐donating recognition sites. The new synthetic approach is amenable to application to highly convergent sequences. To extend the scope of this reaction, we constructed [2]rotaxanes in which one of the phenylene rings of the tetracationic cyclophane is perfluorinated, a feature which significantly weakens its association with π‐electron‐rich guests. The activation barrier for the shuttling of the cyclophane over a spacer containing two triazole rings was determined to be (15.5±0.1) kcal mol^?1 for a degenerate two‐station [2]rotaxane, a value similar to that previously measured for analogous degenerate compounds containing aromatic or ethylene glycol spacers. The triazole rings do not seem to perturb the shuttling process significantly; this property bodes well for their future incorporation into bistable molecular switches.     

Dynamic chirality: keen selection in the face of stereochemical diversity in mechanically bonded compounds

The template-directed syntheses, employing bisparaphenylene-[34]crown-10 (BPP34C10), 1,5-dinaphthoparaphenylene-[36]crown-10 (1/5NPPP36C10), and 1,5-dinaphtho-[38]crown-10 (1/5DNP38C10) as templates, of three [2]catenanes, whereby one of the two bipyridinium units in cyclobis(paraquat-p-phenylene) is replaced by a bipicolinium unit, are described. The crude reaction mixtures comprising the [2]catenanes all contain slightly more of the homologous [3]catenanes, wherein a "dimeric" octacationic cyclophane has the crown ether macrocycles encircling the alternating bipyridinium units with the bipicolinium units completely unfettered. X-ray crystallography, performed on all three [2]catenanes and two of the three [3]catenanes reveals co-conformational and stereochemical preferences that are stark and pronounced. Both the [3]catenanes crystallize as mixtures of diastereoisomers on account of the axial chirality associated with the picolinium units in the solid state. Dynamic (1)H NMR spectroscopy is employed to probe in solution the relative energy barriers for rotations by the phenylene and pyridinium rings in the tetracationic cyclophane component of the [2]catenanes. Where there are co-conformational changes that are stereochemically "allowed", crown ether circumrotation and rocking processes are also investigated for the relative rates of their occurrence. The outcome is one whereby the three [2]catenanes containing BPP34C10, 1/5NPPP36C10, and 1/5DNP38C10 exist as one major enantiomeric pair of diastereoisomers amongst two, four, and eight diastereoisomeric pairs of enantiomers, respectively. The diastereoisomerism is a consequence of the presence of axial chirality together with helical and/or planar chirality in the same interlocked molecule. These [2]catenanes constitute a rich reserve of new stereochemical types that might be tapped for their switching and mechanical properties.     

μ1,3‐Azido‐di­azidotetrakis(1,10‐phenanthroline)dicopper(II) azide tetra­hydrate

In the title compound, [Cu₂(μ‐_1,3‐N₃)(N₃)₂(phen)₄](N₃)·4H₂O (phen is 1,10‐phenanthroline, C₁₂H₈N₂), each of the two Cu atoms is surrounded by two N atoms of two azide anions and by four N atoms of two 1,10‐phenanthroline ligands [Cu—N distances are 1.964 (3), 2.009 (3), 2.018 (3), 2.054 (3), 2.306 (3) and 2.759 (4) Å], forming an elongated CuN₆ octahedron. An ideally linear μ_1,3‐azide anion bridges two Cu atoms to form a dimeric structure with the central N atom located on a centre of inversion. Moreover, the adjacent dimeric units are connected by hydrogen‐bond interactions to produce one‐dimensional chains. A two‐dimensional supramolecular array is formed by π–π interactions between the aromatic rings of 1,10‐phenanthroline ligands of adjacent dimeric units.     

Poly(alkylene oxide) ionomers. XIII. Copolymers of trioxane with the epoxide and 1,3-dioxolane of methyl 10-undecenoate

Cationic copolymerization of 1,3,5-trioxane with methyl 10,11-epoxyundecanoate or methyl 7,8-epoxyoctanoate and terpolymerization with 1,3-dioxolane was successfully carried out. Co-and terpolymerization of 1,3,5-trioxane with 4-(1-carbomethoxynonyl)-1,3-dioxolane was also achieved. Feed compositions of the functional comonomers were varied from 5 to 40 mol %; in all cases the isolated copolymers contained less than 5% of the functional mer units. The composition of the copolymers showed that the methyl ω-epoxyalkanoates were much less reactive than 1,3,5-trioxane. A similar trend was observed with the functional dioxolane monomer, although significantly shorter induction periods were observed in comparison with the epoxy/trioxane copolymerizations. The oxymethylene copolymers and terpolymers were characterized primarily by their infrared spectra; however, the thermal and base stabilities of selected copolymers were also determined.     

Catenation of 1,3‐Diphosphacyclobutane‐2,4‐diyl Units Having 2,4,6‐Tri‐tert‐butylphenyl Protecting Groups and a P‐sec‐Butyl Group in the Ring

Two and three stable 1‐sec‐butyl‐2,4‐bis(2,4,6‐tri‐tert‐butylphenyl)‐1,3‐diphosphacyclobutane‐2,4‐diyl units were catenated to construct multi‐biradical derivatives by utilizing 1,3‐di‐, 1,4‐di‐, and 1,3,5‐trimethylenebenzenes as bridging groups, respectively. UV/Vis spectroscopic and cyclovoltammetric (CV) properties of the multi‐biradicals indicate a non‐conjugative interaction between the concatenated biradical units.     

A cyclic oligophenylene containing two 1,8-naphthalene units bridged by two face-to-face biphenyl linkages exhibiting unusual strain and pi-pi interaction

1,8-[1,8-Naphthalenediylbis(4',4-biphenyldiyl)]naphthalene, a very stable strained cyclophane, has been synthesized in moderate yield using the copper-catalyzed coupling of 1, 8-bis(4-(tributylstannyl)phenyl)naphthalene. The X-ray analysis of the titled compound discloses bent p,p'-biphenylylene chains with splayed naphthalene rings, and the p,p'-biphenylylene chains located face-to-face indicate a fairly strong pi-pi interaction.     

Synthesis and conformational analysis of a small meta‐cyclophane,bis(5‐carbomethoxy‐1,3‐phenylene)‐14‐crown‐4

A small cyclophane, bis(5‐carbometh‐oxy‐1,3‐phenylene)‐14‐crown‐4 (BCMP14C4, 3 ) and its diacid, bis(5‐carboxy‐1,3‐phenylene)‐14‐crown‐4 ( 4 ), were synthesized and characterized. The solid‐state molecular structures of 3 and 4 were determined by X‐ray crystallography as ladder or stepped conformations in which the two aromatic rings are antiparallel to each other without overlap and the ethylene tethers both take trans‐conformations. Diester 3 is formed in the lowest cyclization yield (under the same reaction conditions) and exhibits the highest melting point compared to its larger ring (20‐, 26‐ and 32‐membered) analogs. In CD₂Cl₂ solution, diester 3 exists predominantly as a nonplanar gauche–gauche structure as deduced by H NMR studies. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:48–54, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20393     

Donor-acceptor ring-in-ring complexes

The self-assembly of three donor-acceptor ring-in-ring complexes, prepared from the π-electron-deficient tetracationic cyclophane, cyclobis(paraquat-4,4'-biphenylene), and three large π-electron-rich crown ethers (each 50-membered rings) containing dioxynaphthalene (DNP) and tetrathiafulvalene (TTF) units in pairs (DNP/DNP, DNP/TTF and TTF/TTF), is reported. (1)H NMR spectroscopic analyses are indicative of the formation of 1:1 complexes in CD(3)CN, whilst the charge-transfer interactions between the DNP and TTF units of the crown ethers and the tetracationic cyclophane have permitted the measurement of binding constants of up to 4×10(3) M(-1) in CH(3)CN to be made using UV/Vis spectroscopy. Ring-in-ring complexes are proposed as intermediates in the stepwise synthesis of molecular Borromean rings (BRs) comprised of three different rings. With the particular choice of crown ethers, the 1:1 complexes have polyether loops that protrude from the donor-acceptor recognition point above and below the mean plane of the tetracationic cyclophane, which, ideally, could conceivably bind dialkylammonium centers present in a third ring. X-ray crystallographic analyses of the solid-state superstructures of two of the three 1:1 complexes reveal, however, the presence of prodigious CH···O interactions between the polyether loops of the crown ethers and the rims of the cyclophane, no doubt stabilizing the complexes, but, at the same time, masking their potential recognition sites from further interactions that are essential to the subsequent emergence of the third ring. The solid-state superstructure of one of the crown ethers binding two dibenzylammonium ions provides some insight into the design requirements for the next generation of these systems; longer polyether loops may be required to allow optimal interactions between all components. It has become clear during a pursuit of the stepwise synthesis of the molecular BRs that, when designing complex mechanically interlocked molecules utilizing multiple recognition sites, the unsullied orthogonality of the recognition motifs is of the utmost importance.     

Synthesis and reactivity of [(η-[32](1,3)Cyclophane)Mn(CO)3][BF4]

The manganese cyclophane complex, [(η⁶-[3₂](1,3)cyclophane)Mn(CO)₃][BF₄] 2, was prepared by the reaction of [[3₂](1,3)cyclophane] 1 with Mn(CO)₅FBF₃. Reaction of 2 with NaBH₃CN yielded the cyclohexadienyl manganese complex [(η⁵-6H-[3₂](1,3)cyclophane)Mn(CO)₃] 3. Interestingly, treatment of 3 with Mn(CO)₅FBF₃ gave the bis-manganese complex (η⁶,η⁵-6H-[3₂](1,3)cyclophane)[Mn(CO)₃]₂[BF₄] 4. When NaBH₃CN was treated with 4, [(η⁵,η⁵-6H,6^′H-[3₂](1,3)cyclophane)Mn(CO)₃] 5 was isolated as yellow crystals. The structure of compounds 2 and 3 were determined by single-crystal X-ray crystallography.     

Synthesis and structural characterization of a silver complex of a mixed-donor N-heterocyclic carbene linked cyclophane

The synthesis of a dicationic imidazolium-linked cyclophane and a dimeric silver-N-heterocyclic carbene complex, that is the first silver complex with a N-heterocyclic carbene ligand involved in a pi-bonding interaction, is reported.     

Structural and co-conformational effects of alkyne-derived subunits in charged donor-acceptor [2]catenanes

Four donor-acceptor [2]catenanes with cyclobis(paraquat-p-phenylene) (CBPQT4+) as the pi-electron-accepting cyclophane and 1,5-dioxynaphthalene (DNP)-containing macrocyclic polyethers as pi-electron donor rings have been synthesized under mild conditions, employing Cu+-catalyzed Huisgen 1,3-dipolar cycloaddition and Cu2+-mediated Eglinton coupling in the final steps of their syntheses. Oligoether chains carrying terminal alkynes or azides were used as the key structural features in template-directed cyclizations of [2]pseudorotaxanes to give the [2]catenanes. Both reactions proceed well with precursors of appropriate oligoether chain lengths but fail when there are only three oxygen atoms in the oligoether chains between the DNP units and the reactive functional groups. The solid-state structures of the donor-acceptor [2]catenanes confirm their mechanically interlocked nature, stabilized by [pi...pi], [C-H...pi], and [C-H...Omicron] interactions, and point to secondary noncovalent contacts between 1,3-butadiyne and 1,2,3-triazole subunits and one of the bipyridinum units of the CBPQT4+ ring. These contacts are characterized by the roughly parallel orientation of the inner bipyridinium ring system and the 1,2,3-triazole and 1,3-butadiyne units, as well as by the short [pi...pi] distances of 3.50 and 3.60 A, respectively. Variable-temperature 1H NMR spectroscopy has been used to identify and quantify the barriers to the conformationally and co-conformationally dynamic processes. The former include the rotations of the phenylene and the bipyridinium ring systems around their substituent axes, whereas the latter are confined to the circumrotation of the CBPQT4+ ring around the DNP binding site. The barriers for the three processes were found to be successively 14.4, 14.5-17.5, and 13.1-15.8 kcal mol-1. Within the limitations of the small dataset investigated, emergent trends in the barrier heights can be recognized: the values decrease with the increasing size of the pi-electron-donating macrocycle and tend to be lower in the sterically less encumbered series of [2]catenanes containing the 1,3-butadiyne moiety.     

Ion mobility spectrometric investigation of aromatic cations in the gas phase

In this work, ion mobility (IM) spectra of more than 50 aromatic compounds were recorded with a laser-based IM spectrometer at atmospheric pressure. IM spectra of PAH in the laser desorption experiment show a high complexity resulting from the occurrence of monomeric, dimeric, and oligomeric cluster ions. The mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Omega(calc)) on the basis of the exact hard sphere scattering model and their comparison with the experimentally determined diffusion cross sections (Omega(exp)). Extended Omega(exp)/Omega(calc) and Omega(exp)/mass correlations were performed in order to gain insight into conformational properties of cationic alkyl benzenes and internal rotation of phenyl rings in aromatic ions. This is demonstrated with some examples, such as the evaluation of the dihedral angle of the ions of 9,10-diphenylanthracene, o- and m-terphenyl, and 1,2,3- and 1,3,5-triphenylbenzene. Furthermore, sandwich and T-structures of dimeric PAH cations are discussed. The analysis was extended to oligomeric ions with up to nine monomer units. Experimental evidence is presented suggesting the formation of pi-stacks with a transition toward modified pi-stacks with increasing cluster size. The distance between monomeric units in dimeric and oligomeric ions was obtained.     

Persistance of the Cyclopnane Radical Anions and its Relation to Structure

Reactions of [2_N]cyclophanes (N = 2, ?6) with solvated electrons in 1,2-di-methoxyethane at 193 K have been studied by ESR. and ENDOR. spectroscopy. All but the two most highly bridged cyclophanes (N = 5 and 6) are reduced to paramagnetic species under these conditions. Whereas the radical anions of [2.2]-paracyclophane and [2₃](1,2,4)- and [2₄](l,2,4,5)cyclophanes are sufficiently persistent to be characterized by their hyperfine data, those of the remaining five cyclophanes undergo a rapid cyclization to the radical anions of 4,5,9,10-tetrahydropyrenes. These have been identified as the unsubstituted tetrahydropyrene (from [2.2]-metacyclophane and [2₃](l,2,3)cyclophane), the 2,7-dimethyl-derivative (from [2₃](1,3,5)- and [2₄](l,2,3,5)cyclophanes) and the 1,8-dimethyl-derivative (from (2₄l,2,3,4)cyclophane). The persistence of the cyclophane radical anions seems to depend on the numbers, n_meta and n_para, of the meta-and para-positions of the bridging ethano groups in the two benzene rings. The prerequisite for the radical anion to be persistent is n_meta?n_para.     

Magnetic face-to-face interaction and electrocommunication in chromium sandwich compounds

The reaction of [{(C5Me5)CrCl2}2] with [2.2](1,4)cyclophane gave [(C5Me5)Cr{[2.2](1,4)cyclophane}] (1) and [(C5Me5)Cr{[2.2](1,4)cyclophane}Cr(C5Me5)] (2), depending on the reaction conditions. X-ray structure analysis showed 2 to be a ministack which in turn is stacked in the lattice. The chromium atoms are 6.035 A apart, and the distortion of the benzene rings to boat-shaped moieties is less pronounced than in parent [2.2](1,4)cyclophane. The NMR and EPR spectra were consistent with a S=1/2 ground state for 1 and with two interacting S=1/2 centers in 2. Spin density was found in the ligand pi systems, where its sign was negative when the pi system was adjacent to chromium, while on the nonbonded benzene moiety of 1 it was positive. Cyclic voltammograms showed reductions to 1- and 2(2-), as well as oxidations to 1+, 2+, and 2(2+) which were quasireversible, whereas oxidations to 1(2+) and 2(3+) were irreversible. Interaction between the metal ions was revealed by a 260 mV separation of the redox waves belonging to 2+, and 2(2+). Both cations were isolated as [B(C6H5)4]- salts, which in solution decomposed to [2.2](1,4)cyclophane and [(C5Me5)Cr{(eta6-C6H5)B(C6H5)3}] (3). The 1H and 13C NMR spectra of 3 were in accordance with an S=1 ground state. Solid-state magnetic measurements of the dimetallic compounds showed antiferromagnetic interaction with J=-122 cm-1 for 2, J=-31 cm-1 for 2+ (ground state S=1/2), and J=-23.5 cm-1 for 2(2+) (with H=-JS1S2). The decrease of J in the series 2, 2+, and 2(2+) was traced to the number of unpaired electrons and, for the mixed-valent cation 2+, to additional double exchange.     

Enantioselective synthesis of the dimeric pyranonaphthoquinone core of the cardinalins using a late-stage homocoupling strategy

The enantioselective synthesis of a dimeric pyranonaphthoquinone closely related to the cardinalins is described. Whilst attempts to effect a double Hauser-Kraus annulation of enone 5 were unsuccessful using both bis-phthalide 4 and bis-sulfone 21, a single annulation of cyanophthalide 28 with enone 5 furnished functionalised naphthalene 31. Suzuki-Miyaura homocoupling of the aryl triflate 29 derived from 31 effected a late-stage construction of the biaryl bond and facilitated access to the biaryl 3. Double stereoselective lactol reduction installed the 1,3-cis stereochemistry of the pyran rings and a final double oxidative demethylation step furnished model dimer 1, completing the enantioselective synthesis of a dimeric pyranonaphthoquinone bearing the core structure of cardinalin 3.     

An enaminone-directed benzannulation/macrocyclization approach to cyclophane ring systems

A straightforward and modular preparative approach to 1,3,5-triaroylbenzene-based functionalized cyclophane ring systems has been developed. The key cyclophane-forming macrocyclization reaction was accomplished during the course of a regioselective cross-benzannulation between bis(aryl ethynyl) ketone and enaminone reactants. Macrocyclic products with ring sizes ranging from 18- to 22-membered were successfully constructed. The composition of the tether connecting the two aryl ethynyl ketone fragments can be easily varied; consequently, this method is suitable for construction of a diverse range of structurally distinct cyclophane products. To illustrate this feature, cyclophanes possessing xylyl, alkyl, di(ethylene triamine), and di(ethylene oxy) bridging units were synthesized in isolated yields of 11-46%. Three new cyclophanes (calixarene-like macrocyles 8 and 9, as well as crownophane 18) were structurally characterized by X-ray diffractometry.     

First X-ray structural characterisation of host-guest interactions in tetra-tetrazole macrocycles

The syntheses of tetra-tetrazole macrocycles, containing two 1,3-bis(tetrazole)benzene units linked by a variety of n-alkyl (n=3, 5, 7 or 9 carbon atoms) chain lengths, are described. The crystal structures of two 1,3-bis(tetrazole)benzenes containing pendant bromoalkyl chains (n=3 or 5) are reported. A tetra-tetrazole macrocycle has also been structurally characterised and contains an unexpected ‘host-guest’ interaction through binding of a chloroform solvent molecule. The resulting deviation of the macrocycle from planarity results from a combination of the ‘host-guest’ interaction and strong intermolecular interactions between adjacent tetrazole and phenylene rings.