Guest-dependent complexation of triptycene-based macrotricyclic host with paraquat derivatives and secondary ammonium salts: a chemically controlled complexation process

The triptycene-based macrotricyclic host containing two dibenzo-[24]-crown-8 moieties has been found to form stable 1:1 or 1:2 complexes in different complexation modes with different functional paraquat derivatives and secondary ammonium salts in solution and in the solid state. Consequently, the alkyl-substituted paraquat derivatives thread the lateral crown cavities of the host to form 1:1 complexes. It was interestingly found that the paraquat derivatives containing two beta-hydroxyethyl or gamma-hydroxypropyl groups form 1:2 complexes, in which two guests thread the central cavity of the host. Other paraquat derivatives containing terminal hydroxy, methoxy, 9-anthracylmethyl, and amide groups were included in the cavity of the host to form 1:1 complexes. Moreover, the host also forms a 1:2 complex with two 9-anthracylmethylbenzylammonium salts, in which the 9-anthracyl groups were selectively positioned outside the lateral crown cavities. The competition complexation process between the host and two different guests (the propyl-substituted paraquat derivative and a dibenzylammonium salt) could be chemically controlled.     

A triptycene-based bis(crown ether) host: complexation with both paraquat derivatives and dibenzylammonium salts

[reaction: see text] A novel triptycene-based bis(crown ether) host (1) incorporating two dibenzo-24-crown-8 ether moieties has been synthesized. It can form not only a new bis[2]pseudorotaxane with dibenzylammonium salts but also stable clip-shaped complexes with paraquat derivatives. Moreover, the complexation process between 1 and the two classes of guests can be chemically controlled.     

Formation of 1:2 host-guest complexes based on triptycene-derived macrotricycle and paraquat derivatives: anion-π interactions between PF6(-) and bipyridinium rings in the solid state

A triptycene-derived macrotricyclic host containing two dibenzo-[30]-crown-10 moieties forms stable 1:2 host-guest complexes with paraquat derivatives in both solution and the solid state, in which anion-π interactions between PF(6)(-) and the bipyridinium rings play an important role. Moreover, it was found that binding and release of the guest molecules in the complexes could be easily controlled by the addition and removal of potassium ions.     

Ion pairing in fast-exchange host-guest systems: concentration dependence of apparent association constants for complexes of neutral hosts and divalent guest salts with monovalent counterions

An equilibrium treatment of complexation of neutral hosts with dicationic guests having univalent counterions includes two possible modes: (1) dissociation of the ion pair prior to interaction of the free dication with the host to produce a complex that is not ion paired and (2) direct complexation of the ion pair to produce an ion paired complex. This treatment is easily modified for complexation of neutral guests by dianionic hosts, or divalent hosts by neutral guests. The treatment was tested by a study of fast-exchange host-guest systems based on paraquats or viologens (G(2+)2X(-)) and crown ethers (H). The bis(hexafluorophosphate) salts of viologens are predominantly ion paired in acetone; the value of the dissociation constant of paraquat bis(hexafluorophosphate) was determined to be 4.64 (+/- 1.86) x 10(-4) M(2). The complex based on dibenzo-24-crown-8 and paraquat bis(hexafluorophosphate) is not ion paired in solution, resulting in concentration dependence of the apparent association constant K(a,exp), (= [complex]/[H][G(2+)2X(-)]) which is well fit by the treatment, according to mode (1), yielding K(ap) = 106 (+/-42) M(-1). However, the four complexes of two different bis(m-phenylene)-32-crown-10 derivatives and bis(p-phenylene)-34-crown-10 with paraquat derivatives are all ion paired in solution and therefore K(a,exp) is not concentration dependent for these systems, mode (2). X-ray crystal structures support these solution-based assessments in that there is clearly ion pairing of the cationic guest with its PF(6)(-) counterions in the solid states of the latter four examples in which access of the counterions to the guests is granted by the relatively large cavities of the hosts and dispositions of the guest species within them.     

Li+-templated complexation of cylindrical macrotricyclic host with naphthalene diimide: Cation-controlled switchable complexation processes

Anthracene-based cylindrical macrotricyclic polyether (1) containing two dibenzo-30-crown-10 cavities has been proved to be an efficient host for the templated complexation with N,N’-dipropyl-1,4,5,8-naphthalenetetracarboxylic diimide in the presence of lithium ions in both solution and solid state. Host 1 could also form 1:1 complex with the bispyridinium salt with two β-hydroxyethyl groups in solution and in the solid state. Moreover, it was also found that the switchable complexation processes between the macrotricyclic host and two different kinds of guests could be chemically controlled by the addition and removal of lithium ions.     

Guest-dependent complexation of triptycene-derived macrotricyclic host containing one anthracene moiety with paraquat derivatives: construction of [2]rotaxanes

Complexation between the triptycene-derived macrotricyclic polyether containing an anthracene unit and paraquat derivatives in both solution and solid state was investigated. It was found that the macrotricyclic host with multi-cavity structure could form a series of [2]pseudorotaxanes with different terminal functionalised paraquat derivatives in different threading modes, which subsequently resulted in the construction of two novel [2]rotaxanes.     

Two protocols for the preparation of [2]rotaxanes based on the dibenzo-24-crown-8-based cryptand/paraquat recognition motif

Host–guest complexation between a dibenzo-24-crown-8-based cryptand and a paraquat derivative was studied. Subsequently, two novel [2]rotaxanes based on the dibenzo-24-crown-8-based cryptand/paraquat recognition motif were prepared by threading-followed-by-stoppering method and single-pot method, respectively. The obtained mechanically interlocked structures were confirmed by ¹H NMR, ¹³C NMR, 2D NMR, and ESI-MS.     

Competitive interactions of two ion-paired salts with a neutral host to form two non-ion-paired complexes

It is demonstrated that our reported equilibrium treatments that take into account ion-paired guest and non-ion-paired complexes can be applied to competitive complexations. Satisfactory results were obtained for a system with two cationic guests [N,N'-dimethyl-4,4'-biyridinium bis(hexafluorophosphate) (1) and dibenzylammonium hexafluorophosphate (2)] having a common counterion and a single neutral host dibenzo-24-crown-8 (3), even though for this system one exchange process is slow and the other fast on the 1H NMR time scale. The competitive complexation protocol presented here provides a convenient method for the determination of KapKipd (the product of the ion-pair dissociation constant of the guest salt and the association constant for the host with the resultant free cation) for new systems from ion-paired guests that form complexes that are not ion paired.     

Bis(m-phenylene)-32-crown-10-based cryptands, powerful hosts for paraquat derivatives

Four new bis(m-phenylene)-32-crown-10-based cryptands with different third bridges were prepared. Their complexes with paraquat derivatives were studied by proton NMR spectroscopy, mass spectrometry, and X-ray analysis. It was found that these cryptands bind paraquat derivatives very strongly. Specifically, a diester cryptand with a pyridyl nitrogen atom located at a site occupied by either water or a PF(6) anion in analogous complexes exhibited the highest association constant K(a) = 5.0 x 10(6) M(-1) in acetone with paraquat, 9000 times greater than the crown ether system. X-ray structures of this and analogous complexes demonstrate that improved complexation with this host is a consequence of preorganization, adequate ring size for occupation by the guest, and the proper location of the pyridyl N-atom for binding to the beta-pyridinium hydrogens of the paraquat guests. This readily accessible cryptand is one of the most powerful hosts reported for paraquats.     

Synthesis of a novel triptycene-based molecular tweezer and its complexation with paraquat derivatives

[reaction: see text] A novel triptycene-based molecular tweezer has been synthesized, and its complexation with paraquat derivatives in solution and in the solid state has been studied. Due to its electron-rich cavity, the molecular tweezer could form stable complexes with paraquat derivatives with different functional groups. Moreover, it was also found that formation of the complexes was caused by a charge transfer interaction and the complexes dissociated upon two one-electron reduction of the bipyridinium ring.     

Benzo-21-crown-7/secondary dialkylammonium salt [2]pseudorotaxane- and [2]rotaxane-type threaded structures

We demonstrate that secondary dialkylammonium salts can thread through the cavity of benzo-21-crown-7 to form [2]pseudorotaxanes with binding constants (527-1062 M-1 in acetone) higher than the corresponding values (135-261 M-1 in acetone) of the analogous complexes with their traditionally used host, dibenzo-24-crown-8. Based on this new benzo-21-crown-7/secondary dialkylammonium salt recognition motif, a [2]rotaxane was successfully prepared. The formation of these threaded structures was confirmed by proton NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray single crystal analysis.     

Complexation between pentiptycene derived bis(crown ether)s and CBPQT4+ salt: ion-controlled switchable processes and changeable role of the CBPQT4+ in host-guest systems

The pentiptycene derived bis(crown ether)s with two 24-crown-8 moieties in the cis position could include the CBPQT(4+) ring inside their cavities to form 1:1 complexes, and the naphthalene groups connected in the crown ether moieties showed less effective complexation ability toward the CBPQT(4+) ring than the host containing two terminal benzene rings. This result was probably due to the stereohindrance effect of the naphthalene groups, and it was obviously different from that of the pentiptycene derived mono(crown ether)s. For the pentiptycene derived bis(crown ether) with two 24-crown-8 moieties in the trans position, it formed a 1:2 stable complex with the CBPQT(4+) salt in solution and in the solid state, in which the pentiptycene moiety played an important role in stabilizing the complex. Moreover, binding and release of the CBPQT(4+) ring in the complexes based on the pentiptycene-derived crown ethers could be chemically controlled by adding and removing potassium ions, in which the complexation modes played the key role. Interestingly, it was further found that switching the role of the CBPQT(4+) ring in host and guest systems based on the pentiptycene derived bis(crown ether)s was easily achieved, which represents a new kind of supramolecular system.     

Complexation of ferrocene derivatives by the cucurbit[7]uril host: a comparative study of the cucurbituril and cyclodextrin host families

The formation of inclusion complexes between cucurbit[7]uril (CB[7]) and ferrocene and its derivatives has been investigated. The X-ray crystal structure of the 1:1 inclusion complex between ferrocene and CB[7] revealed that the guest molecule resides in the host cavity with two different orientations. Inclusion of a set of five water-soluble ferrocene derivatives in CB[7] was investigated by 1H NMR spectroscopy and calorimetric and voltammetric techniques. Our data indicate that all neutral and cationic guests form highly stable inclusion complexes with CB[7], with binding constants in the 10(9)-10(10) M(-)(1) and 10(12)-10(13) M(-1) ranges, respectively. However, the anionic ferrocenecarboxylate, the only negatively charged guest among those surveyed, was not bound by CB[7] at all. These results are in sharp contrast to the known binding behavior of the same guests to beta-cyclodextrin (beta-CD), since all the guests form stable inclusion complexes with beta-CD, with binding constants in the range 10(3)-10(4) M(-1). The electrostatic surface potentials of CB[6], CB[7], and CB[8] and their size-equivalent CDs were calculated and compared. The CD portals and cavities exhibit low surface potential values, whereas the regions around the carbonyl oxygens in CBs are significantly negative, which explains the strong affinity of CBs for positively charged guests and also provides a rationalization for the rejection of anionic guests. Taken together, our data suggest that cucurbiturils may form very stable complexes. However, the host-guest interactions are very sensitive to some structural features, such as a negatively charged carboxylate group attached to the ferrocene residue, which may completely disrupt the stability of the complexes.     

Selective templated complexation of a cylindrical macrotricyclic host with neutral guests: three cation-controlled switchable processes

A novel triptycene-based cylindrical macrotricyclic host 1 containing an anthracene unit and two dibenzo [24]crown-8 moieties was synthesized, and its cation binding properties were studied. It was found that the host could not only form complex with the paraquat derivative 4, but also show selective templated complexation with pyromellitic diimide 2 and anthraquinone 3 in the presence of lithium and potassium ions, respectively. Consequently, two novel cascade complexes with neutral molecules as bridging species were formed in solution and in the solid state, which were structurally studied by NMR, MS spectra, and X-ray methods. Moreover, we also found that the association and dissociation of the complexes could be easily achieved by the addition and removal of lithium or potassium ions, which resulted in three cation-controlled switchable processes.     

Unraveling the molecular recognition of "three methylene spacer" bis(benzimidazolium) moiety by dibenzo-24-crown-8: pseudorotaxanes under study

"Three methylene spacer" bis(benzimidazolium) derivatives act as a new template for threading dibenzo-24-crown-8 into [2]pseudorotaxanes. In this Article we sought to unveil the difference in the extent of threading of various "three methylene spacer" bis-benzimidazolium moieties based on differences in aromatic methyl substituent positions and anions through the macrocycle dibenzo-24-crown-8. The temperature of the systems were also varied (low temperatures of 240 K and 253 K), when such interwinding of the thread and crown were not detected at room temperature of 308 K. The presence of such threaded complexes was determined based on (1)H-NMR initially and finally corroborated by high resolution mass spectrometry and DFT calculations. 2D-NMR experiments ((1)H-(1)H-NOESY) proved to be a very important tool in elucidating the interaction present between the components of the pseudorotaxanes. The dethreading/rethreading process was studied. DFT optimized structures suggest lower energy H-bonding orientations and compare the effect of methyl substituents on the axle.     

Synthesis of Isomeric Dinitro and Diamino Derivatives of Polycyclic Crown Ethers: Dibenzo-18-crown-6 and Dibenzo-24-crown-8

Specific features of the synthesis of polycyclic crown ethers dibenzo-18-crown-6 and dibenzo-24-crown-8 and their dinitro and diamino derivatives have been studied. A mixture of isomers of dibenzocrown ether derivatives was obtained and separated. The spectral and thermal characteristics of the synthesized compounds and the kinetics of synthesis of dibenzo-24-crown-8 by the two-component condensation of pyrocatechol with 1-chloro-2-[2-(2-chloroethoxy)ethoxy]ethane in an alcoholic medium in the presence of a KOH template agent were studied.     

Structure of Dibenzocrown Ethers and their H-Bonded Adducts.1. [1.5]Dibenzo-18-Crown-6 and Biphenyl-20-Crown-6: Complexes with Amidosulfuric Acid

The interaction of the amidosulfuric acid NH ₃ SO ₃ with 15 distal and proximal dibenzocrown ethers, including diphenyloxide, diphenylsulfide and biphenyl ones leads to the stable (1:1) complexes only in the case of [2.4]- and [1.5]dibenzo-18-crown-6 and biphenyl-20-crown-6. According to the data of the X-ray analysis, in the two last adducts the amidosulfuric acid coordinates to hexadentate crown ethers in a zwitterion form through a near-ideal ‘tripod’ arrangement to alternate crown oxygen atoms. The conformations of crown molecules are different in complexes and in initial macrocyclic ligands.This revised version was published online in July 2005 with a corrected issue number.     

Fluorescence study of inclusion complexes between star-shaped cholic acid derivatives and polycyclic aromatic fluorescent probes and the size effects of host and guest molecules

Star-shaped host molecules containing two, three, and four cholic acid moieties have been used to form inclusion complexes with polycyclic aromatic hydrocarbon probes (guests) varying in size from four (pyrene) to five (benzo(e)pyrene) and seven aromatic rings (coronene) and investigated by steady-state fluorescence measurements and fluorescence lifetime techniques. The results indicated that these hydrophobic guest probes prefer to locate in the hydrophobic cavities formed by the host molecules in an aqueous solution. Further studies showed that the stoichiometric ratios of the complexes depended on the relative size of both the host and the guest. The complexes of 1:1 ratio (guest:host) were formed between pyrene and the host molecules of different sizes, while the complexes of 1:2 ratio (guest:host) were found for coronene in all cases. For benzo(e)pyrene with an intermediate size, the complexes with 1:1 and 1:2 ratios (guest:host) were formed depending on the relative sizes of the host molecules. The stability of the inclusion complexes was observed to change with the solvent polarity, indicative of an adaptation of the hydrophobicity of the host pockets to the polarity of the solvent. The formation of the complexes was driven by the solvophobic interactions.     

Inclusion [2]complexes based on the cryptand/diquat recognition motif

Seven diquat-based inclusion [2]complexes were studied by proton NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray analysis. The hosts used in these inclusion [2]complexes are bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10, a bis(m-phenylene)-26-crown-8-based cryptand, and five bis(m-phenylene)-32-crown-10-based cryptands. Bis(m-phenylene)-32-crown-10-based cryptands have been proved to be able to complex diquat much more strongly than bis(m-phenylene)-32-crown-10 itself and one containing a pyridyl moiety has one of the highest K_a values reported to date. These hosts form 1:1 complexes with diquat in solution and in the solid state. It was found that the improved binding from bis(m-phenylene)-32-crown-10 to bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10 was due to a supramolecular cryptand structure formed by chelation of the two terminal OH moieties of bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10 with a water molecule as a hydrogen-bonding bridge.     

Efficient syntheses of bis(m-phenylene)-26-crown-8-based cryptand/paraquat derivative [2]rotaxanes by immediate solvent evaporation method

A novel bis(m-phenylene)-26-crown-8-based cryptand has been synthesized. It has been used to prepare two 1:1 complexes with two paraquat derivatives with high association constants (6.5×10⁵ and 4.0×10⁵ M⁻¹) in acetone. In the solid state the cryptand forms a 2:1 threaded structure with paraquat and an interesting supramolecular poly[2]pseudorotaxane threaded structure with a dihydroxyethyl-substituted paraquat derivative, respectively. It has been further used to prepare cryptand/paraquat derivative [2]rotaxanes efficiently by the immediate solvent evaporation method using easily available 3,5-dimethylphenyl groups as the stoppers.