Calix[4]arene-based bis[2]catenanes: synthesis and chiral resolution

The exclusive formation of hydrogen-bonded dimers between tetraaryl and tetratosylurea calix[4]arenes has been used to prepare a series of ten "bisloop" tetraurea calix[4]arenes 3, in which adjacent phenylurea groups are covalently linked through alpha,omega-dioxyalkane chains. This dimerization with tetratosylurea 2 as template preorganizes the alkenyl residues of tetra(m-alkenyloxyphenyl) ureas 1 and enables their selective connection in high yield (up to 95 %) by olefin metathesis followed by hydrogenation. The "bisloop" calixarenes 3 also exclusively form heterodimers with 1. Thus, in a separated metathesis/hydrogenation sequence, a series of 14 cyclic bis[2]catenanes 4, in which two calix[4]arenes are connected through their wide rims by two pairs of interlocked rings (total size 29 to 41 atoms), were prepared in yields of up to 97 %. Optical resolution of these chiral bis[2]catenanes was studied by HPLC on chiral stationary phases. The single-crystal X-ray structure of one example (4(P,10)) confirmed the interlocking rings and revealed that the hydrogen-bonded dimeric capsule of the calix[4]arene can be "completely" opened.     

Bispyrrolotetrathiafulvalene-containing [2]catenanes

Two [2]catenanes incorporating bispyrrolotetrathiafulvalene (BPTTF) and weaker aryl donors, hydroquinone (HQ) and 1,5-dioxynaphthalene (DNP), respectively, have been prepared and characterized. These [2]catenanes show a predominant amount (>95:5) of the co-conformation in which either the HQ or the DNP unit is encircled by a tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT4+), contrary to what is observed in systems based on the parent tetrathiafulvalene (TTF). These new [2]catenanes act effectively as molecular switches which are always configured in the "on" state.     

Macrocyclic gold(I) complexes and [2]catenanes containing carbonyl functionalized diacetylide ligands

The carbonyl derivatized bis(alkyne) O=C(4-C₆H₄OCH₂CCH)₂ was converted into the imine derivatives RN=C(4-C₆H₄OCH₂CCH)₂ [R=OH, NHC(O)NH₂, NHC₆H₃-2,4-(NO₂)₂] and into the 4-bromomethyl-1,3-dioxolane derivative BrCH₂C₂H₃O₂C(4-C₆H₄OCH₂CCH)₂. The alkyne units in these compounds react with [AuCl(SMe₂)] in the presence of base to form the corresponding digold(I) diacetylide complexes, that exist as insoluble oligomers or polymers. They reacted with the diphosphines Ph₂PZPPh₂ [Z=CC, trans-HC=CH and (CH₂)_n, n=3–5] to give macrocyclic gold(I) complexes of the type [Au₂(μ-LL)(μ-PP)], where LL is the diacetylide and PP the diphosphine ligand. The ability of these macrocyclic complexes to self-assemble to [2]catenanes has been studied. The ketone and imine derivatives do not form [2]catenanes because the orientation of the aryl groups is unfavorable, but the 1,3-dioxolane derivatives may catenate if the ring size is optimum.     

Self-assembly of gold(I) rings and reversible formation of organometallic [2]catenanes

The reaction of the digold(I) diacetylide [(AuCCCH2OC6H4)2CMe2] with diphosphane ligands can lead to formation of either macrocyclic ring complexes or [2]catenanes by self-assembly. This gives an easy route to rare organometallic [2]catenanes, and the effect of the diphosphane ligand on the selectivity of self-assembly is studied. With diphosphane ligands Ph2P(CH2)xPPh2, the simple ring complex [Au2[(CCCH2OC6H4)2CMe2](Ph2P(CH2)xPPh2)] is formed selectively when x = 2, but the [2]catenanes [Au2[(CCCH2OC6H4)2CMe2](Ph2P(CH2)xPPh2)]2 are formed when x = 4 or 5. When x = 3, a mixture of the simple ring and [2]catenane is formed, along with the "double-ring" complex, [Au4[(CCCH2OC6H4)2CMe2]2(Ph2P(CH2)3PPh2)2] and a "hexamer" Au2[(CCCH2OC6H4)2CMe2](Ph2P(CH2)3PPh2)]6] whose structure is not determined. A study of the equilibria between these complexes by solution NMR techniques gives insight into the energetics and mechanism of [2]catenane formation. When the oligomer [(AuCCCH2OC6H4)2CMe2] was treated with a mixture of two diphosphane ligands, or when two [2]catenane complexes [[Au2[(CCCH2OC6H4)2CMe2](diphosphane)]2] were allowed to equilibrate, only the symmetrical [2]catenanes were formed. The diphosphanes Ph2PCCPPh2, trans-[Ph2PCH=CHPPh2] and (Ph2PC5H4)2Fe give the corresponding ring complexes [Au2[(CCCH2OC6H4)2CMe2](diphosphane)], and the chiral, unsymmetrical diacetylide [Au2[(CCCH2OC6H4C(Me)(CH2CMe2)C6H3OCH2CC)] gives macrocyclic ring complexes with all diphosphane ligands Ph2P(CH2)xPPh2 (x = 2-5).     

Synthesis and topology of [2+2] calix[4]resorcarene-based chiral cavitand-salen macrocycles

Chiral diastereomeric cavitand-salen macrocycles have been synthesized by the high-dilution condensation of a tris-(quinoxaline-bridged)-diformyl-calix[4]resorcarene with (1R,2R)-diphenylethylenediamine. The reaction produced a couple of diastereoisomers, consisting of two cavitand cavities bis-bridged by two chiral diimino moieties, which differ in a convergent (C-shaped) or divergent (S-shaped) orientation of the two cavities.     

Palladium(II)-directed self-assembly of dynamic donor-acceptor [2]catenanes

Highly efficient syntheses of donor-acceptor [2]catenanes were developed using a combination of templation and reversible metal-ligand coordination. The desired [2]catenanes were obtained within minutes through a five-component assembly, involving a donor-containing crown ether, an acceptor-containing ligand, two Pd(II) metal centers, and a dipyridyl ligand. The [2]catenane formation was characterized by 1H NMR and UV-vis spectroscopies and cold-spray ionization mass spectrometry. In particular, great translational selectivity was observed when a crown ether with two different donor units was employed.     

Neutral pi-associated porphyrin [2]catenanes

A series of neutral porphyrin-containing catenanes has been synthesised, consisting of a zinc porphyrin strapped by a polyethylene glycol chain containing four or six ethylenoxy-units and incorporating a central naphthoquinol unit, interlinked with a naphthalene diimide macrocycle. The napthalene diimide precursor units exhibit only weak binding with the strapped porphyrins (Ka between 8 and 0.02 M(-1)), but good yields of the catenanes were obtained by Glaser coupling of the alkynyl napthalene diimide precursors in the presence of the porphyrins. Structures and solution conformations were determined by mass spectral and detailed 1H NMR studies. For the longer strapped porphyrins, the diimide macrocycle rotates around the central naphthoquinol unit at 420-450 times per second, while rotation is virtually prevented in the tighter strapped derivatives. A second dynamic process occurring in both sets of catenanes and described as 'yawing' leads to inequivalence in the naphthalene moieties. UV-Visible spectra indicate charge transfer interactions and electronic communication between the two components of the catenane.     

Synthesis and characterization of chiral catenanes based on rigid calix[4]arene

A new class of chiral calix[4]arene-based [2]catenanes was synthesized in excellent yields of 51-80%. They exhibit unique dynamic properties according to variable temperature NMR experiments. The enantiomeric pure (+)-catenane was prepared in 66% yield starting from (−)-calix[4]arene.     

Rational synthesis of multicyclic bis[2]catenanes

Bis-loop tetraurea calix[4]arene 6 has been prepared by acylation of the wide-rim calix[4]arene tetraamine 1 with the activated bis(urethane) 8 under dilution conditions. Similarly the bis(Boc-protected) tetraamine 2 is converted into the mono-loop derivative 3 which after deprotection and acylation gives the bisalkenyl derivative 5. In apolar solvents this tetraurea calix[4]arene 5 forms regioselectively a single hydrogen-bonded homodimer, from which the bis[2]catenane 10a is formed in 49% by a metathesis reaction followed by hydrogenation. Bis-loop derivative 6 forms no homodimers for steric reasons, but a stoichiometric mixture with the open-chain tetraalkenyl derivative 7a contains exclusively the heterodimer. Metathesis and subsequent hydrogenation now yields 65 % of the pure bis[2]catenane 10a which could not be isolated from the complex reaction mixture obtained from the homodimer 7a.7a. The chirality of 10a (D(2) symmetry) has been verified by optical resolution using HPLC on a chiral stationary phase.     

Heteropolymetallic copper(II)-gold(III) dithiocarbamate [2]catenanes via magic ring synthesis

A rare class of mixed-metal [2]catenane has been assembled via magic ring synthesis of dinuclear copper(II) and gold(III) dithiocarbamate macrocycles.     

Cyclobis(paraquat-p-phenylene)-based [2]catenanes prepared by kinetically controlled reactions involving alkynes

[reaction: see text] Charged donor-acceptor [2]catenanes, in which the pi-accepting cyclobis(paraquat-p-phenylene) acts as a tetracationic template for the threading-followed-by-clipping of acyclic oligoethers, incorporating centrally a pi-donating 1,5-dioxynaphthalene ring system and terminated either by acetylene units or by acetylene and azide functions, are the products of copper-mediated Eglinton coupling and Huisgen 1,3-dipolar cycloaddition, respectively.     

Polypseudorotaxanes via ring-opening metathesis polymerizations of [2]catenanes

A bis-phenanthroline [2]catenane copper complex, consisting of one olefinic macrocycle and one nonolefinic macrocycle, underwent an entropy-driven ring-opening olefin metathesis polymerization (ROMP) to provide a polypseudorotaxane. The polymerization featured an average degree of polymerization of ca. 63 wherein the polymer was effectively saturated with threaded macrocycles. Removal of the copper led to near complete release of the macrocycles from the polymer backbone.     

Path selection for conformational interconversions in [2]catenanes

[strucure: see text]The conformational interconversions of several [2]catenanes containing a dibenzo-34-crown-10 ether (BPP34C10) interlocked with rings containing two 4,4'-dipyridyls tethered by different aryl spacers have been studied. Blocking groups on the tethers enabled the two pathways for circumrotation of the BPP34C10 to be open or blocked. The activation barrier for migration along the open tethers varied from 11 to 13 kcal/mol. This study demonstrates an ability to select the pathway for conformational interconversions in [2]catenanes.     

Synthesis of [2]catenanes by template-directed clipping approach

A series of [2]catenanes were efficiently synthesized in high yields by a template-directed clipping approach with the formation of one macrocycle around another macrocycle containing a dialkylammonium recognition site. Their structures were identified by the NMR spectra and ESI mass spectrometry, and their geometries were investigated by the theoretical calculation.