Ferrocene-Containing Pseudorotaxanes in Crystals: Aromatic Interactions with Hammett Correlation.

Single crystals of pseudorotaxanes, [(FcCH2NH2CH2Ar)(DB24C8)][PF6] (DB24C8 = dibenzo[24]crown-8, Fc = Fe(C5H4)(C5H5), Ar = -C6H3-3,4-Cl2, -C6H3-3,4-F2, -C6H4-4-F, -C6H4-4-Cl, -C6H4-4-Br, -C6H3-3-F-4-Me, -C6H4-4-I) and [(FcCH2NH2CH2C6H4-4-Me)(DB24C8)][Ni(dmit)2] (dmit = 1,3-dithiole-2,4,5-dithiolate), were obtained from solutions containing DB24C8 and ferrocenylmethyl(arylmethyl)ammonium. X-ray crystallographic analyses of the pseudorotaxanes revealed that the aryl ring of the axle moiety and the catechol ring of the macrocyclic component were at close centroid distances and parallel or tilted orientation. The structures with parallel aromatic rings showed correlation of the distances between the centroids to Hammett substituent constants of the aryl groups.

Convenient synthesis of copper(I) halide quasi-one-dimensional coordination polymers: their structures and solid-state luminescent properties.

The heterogeneous reaction between copper(i) halide and pyridine derivative ligand in a suspension conveniently afforded luminescent copper(i) complexes. The progress of the reaction was confirmed by powder X-ray diffraction (PXRD) and thermogravimetric (TG) measurements. The structure of the obtained complexes was clarified by comparison with the X-ray analysis of a single crystal obtained by the homogeneous reaction in a solution. The reaction was affected by the type of solvent and substituents on the pyridine ligand. The reaction proceeded quantitatively, not depending on copper(i) halide, when ethyl acetate and 3-bromopyridine were used as the solvent and ligand, respectively. X-ray analysis of the single-crystals obtained by the corresponding reaction in solution revealed that the reaction in suspension afforded the same stair-shaped quasi-one-dimensional structure. The obtained copper(i) complex powders displayed luminescence, which was attributed to the halide/metal-to-ligand charge transfer (XMLCT), as elucidated by crystal orbital distribution and principal component of excitation based on density functional theory (DFT) calculations.

Cyclodextrin Rotaxanes of Pt Complexes and Their Conversion to Pt Nanoparticles.

The cationic Pt complex (Pt(NC6H4-C6H4N-(CH2)10-O(C6H3-3,5-(OMe)2)(MeN-(CH2CH2NMe2)2))+ was prepared by the reaction of alkylbipyridinium ligand with a nitrateplatinum(II) complex. Mixing the complex and α- and ß-cyclodextrins in aqueous media produced the corresponding [2]rotaxanes with 1:1 stoichiometry. γ-Cyclodextrin and the Pt complex formed a rotaxane having components in a 1:1 or 2:1 molar ratio. The results of mass and nuclear magnetic resonance (NMR) measurements confirmed the rotaxane structures of the Pt complexes. Transmission electron microscopy (TEM) and atomic force microscope (AFM) analyses revealed the formation of micelles or vesicles. The addition of NaBH4 to the rotaxanes in aqueous media formed Pt nanoparticles with diameters of 1.3-2.8 nm, as characterized by TEM. The aggregated size of the nanoparticles formed from the rotaxane did not change even at 70 °C, and they showed higher thermal stability than those obtained from the reduction of the cyclodextrin-free Pt complex.

Photoinduced Mechanical Motions of Pseudorotaxane Crystals Composed of Azobenzene and Ferrocenyl Groups on an Axle and a Crown Ether Ring.

This work describes the design and characterization of photoresponsive dynamic pseudorotaxane crystals composed of azobenzene and ferrocenyl groups in an ammonium cation axle component threaded through dibenzo[24]crown-8 ether rings. Pseudorotaxanes provide flexibility for cis and trans isomerization of azobenzene groups in a crystal state, enabling reversible bending motions under alternating 360 and 445 nm laser irradiation. For such bending motions, strained azobenzene structures were essential; these motifs were obtained by increasing the bulkiness of the substituents on the axle and ring molecules. In addition, the crystals showed photosalient effects, such as jumping motions, under 445 nm laser irradiation. These motions were assisted by the photoabsorption of the ferrocenyl group, which converted 445 nm laser light into heat. The maximum lifting weight accompanied by the photoinduced mechanical motion of a particular crystal was estimated to be 9600 times the crystal weight. These pseudorotaxane crystals exhibit promising features for applications in micro-nanometer-sized miniature mechanical devices.

Reversible Laser-Induced Bending of Pseudorotaxane Crystals.

This study investigated the dynamic photoresponse of pseudorotaxane crystals with azobenzene and ferrocenyl groups in the axle component. X-ray crystallography showed pseudorotaxanes with a methylazobenzene group and a dibromophenylene ring in the cyclic component to exhibit twisting of the trans-azobenzene groups at torsion angles of 17° and 38°, respectively. Repeated alternating laser irradiation of the crystals at 360 and 445 nm produced bending of 20-30° in opposite directions, with no evidence of decay. Under 445 nm irradiation, bending took place within 0.3 s. A crystal of nonsubstituted pseudorotaxane showed bending of only 2° under 360 nm irradiation due to multiple π-π interactions between the planar trans-azobenzene groups. The pseudorotaxane crystals have two chromophores, bent rapidly and reversibly on irradiation at rates depending on the molecular structure.

Cationic and Neutral Rotaxanes Having Different Functional Groups in the Axle Molecule and Their Coordination to PtII.

Dibenzo[24]crown-8 (DB24C8) forms rotaxanes with a linear molecule having a dialkylammonium group and a triazole group as well as with the acetylation product of a cationic axle molecule. The former cationic rotaxane is stabilized by multiple intermolecular hydrogen bonds between the NH2+ and oxyethylene groups. The neutral rotaxane contains the macrocycle in the vicinity of the terminal aryl group. The co-conformation of both the cationic and neutral rotaxanes can be fixed by coordination of the triazole group of the axle molecule to PtCl2 (dmso)2 . A 1 H NMR spectroscopic study on the thermodynamics of the Pt coordination revealed a larger association constant for the rotaxanes than for the corresponding axle molecules and a larger value for the neutral rotaxane than for the cationic rotaxane.

Rapid and reversible photoinduced switching of a rotaxane crystal.

Crystalline phase transitions caused by external stimuli have been used to detect physical changes in the solid-state properties. This study presents the mechanical switching of crystals of ferrocene-containing rotaxane controlled by focused laser light. The expansion and contraction of the crystals can be driven by turning on and off laser light at 445 nm. The irradiation-induced expansion of the crystal involves elongation along the a, b and c axes at 30 °C, whereas heating of the crystal at 105 °C causes the shortening of c axis. The expansions reversibly occur and have the advantage of a rapid relaxation (reverse) process. Single-crystal X-ray crystallography reveals the detailed structural changes of the molecules, corresponding to a change in the size of the crystals on laser irradiation. This molecular crystal behaviour induced by laser irradiation, is demonstrated for the remote control of objects, namely, microparticle transport and microswitching in an electric circuit.

Dynamic properties of molecular tweezers with a bis(2-hydroxyphenyl)pyrimidine backbone.

4,6-Bis(2-hydroxyphenyl)-2-alkylpyrimidines with two anthryl or 9-ethylnylanthryl substituents at the positions para to the OH groups prefer a U-shaped conformation supported by two intramolecular OH⋅⋅⋅N hydrogen bonds in the solid state and in CDCl3 solution. The compound with a hexyl substituent on the pyrimidine group and two 9-ethynylanthryl arms at the hydroxyphenyl groups forms a 1:1 complex with 2,4,7-trinitrofluorenone. Its association constant K(a) was estimated to be 2100 M(-1) at 298 K, which is larger than those of other molecular tweezers (K(a) < 1000 M(-1)). DFT calculations suggested that the complex adopts a stable conformation supported by intramolecular hydrogen bonds among the OH groups and the pyrimidine ring as well as by intermolecular π-π interaction between the anthryl groups and 2,4,7-trinitrofluorenone. Addition of nBu4NF to a solution of the molecular tweezers or their complexes causes the cleavage of one or two OH⋅⋅⋅N hydrogen bonds, formation of new O⋅⋅⋅HF hydrogen bonds, and changes in the molecular conformation. The resulting structure of the molecular tweezers contains nonparallel anthryl groups, which do not bind the guest molecule. Photochemical measurements on 4,6-bis(2-hydroxyphenyl)-2-methylpyrimidine with two anthryl substituents showed negligible luminescence (quantum yield ϕ<0.01), owing to photoinduced electron transfer of the molecule with a U-shaped structure. However, the O-hexylated compound exhibits emission from the anthryl groups with ϕ=0.39.

A rhomboid-shaped organic host molecule with small binding space. Unsymmetrical and symmetrical inclusion of halonium ions.

A shape persistent rhomboid-shaped organic host molecule having two pyridyl units was synthesized which induces size selective halonium inclusion. Cl(+) and Br(+) are included to form unsymmetric and symmetric complexes, while I(+) does not form a stable complex. The difference among the haloniums was ascribed to the matching (or mismatching) of the shape of the cavity and the guest ions. The complexation of the host molecule with other cations, such as Ag(+), Pd(2+), Zn(2+) and H(+), is also mentioned.

Amphiphilic ferrocenylated alkylpyridinium: the formation of micelles and hydrogels and their disaggregation induced by an external stimulus.

Ferrocene-containing amphiphiles [py-N-(CH2)nOCH2Fc]Cl (n = 6 (1a), 8 (1b), 10 (1c); py = C5H5N, Fc = Fe(C5H4)(C5H5)) were synthesized. The absorption spectra of 1a-1c in the presence of a small amount of dye (Nile red and pyrene) in aqueous media suggested the formation of micelles which encapsulated the dye molecules. Two critical micelle concentrations were observed at 1.1 mM and 2.3 mM at 20 °C. Compounds 1a and 1c showed a single CMC for each, while the formation of two kinds of micelles, the spherical and rod-like ones, depended on the concentrations. The addition of an oxidant, NaOCl, to the aqueous solution of the micelles of 1b turned ferrocene to ferrocenium and caused the disaggregation of the micelles. The addition of α-cyclodextrin (α-CD) to 2b caused the disaggregation of the micelle and the formation of water-soluble [2]- and [3]pseudorotaxane [{py-N-(CH2)8OCH2Fc}(α-CD)m]Cl (1b(α-CD)m) (m = 1, 2), while mixing 1c and α-CD in water formed the rotaxane gel. The addition of NaOCl to the hydrogel of 1c and α-CD changed the gel to sol.

Introduction of ferrocene-containing [2]rotaxanes onto siloxane, silsesquioxane and polysiloxanes via click chemistry.

The reaction of N(3)(CH(2))(3)Si(OTMS)(3) (TMS = SiMe(3)) with a dialkylammonium having hexynyl group 1, [FcCH(2)NH(2)CH(2)C(6)H(4)-4-O(CH(2))(4)C≡CH]PF(6) (Fc = Fe(C(5)H(4))(C(5)H(5))), in the presence of dibenzo[24]crown-8-ether (DB24C8) and [Cu{Fe(CN)(4)}]PF(6) catalyst yielded the [2]rotaxane containing the dialkylammonium unit terminated by a bulky silyl group. Azides with a silsesquioxane group react similarly to form the corresponding [2]rotaxanes having a bulky silsesquioxane end group. The azide-functionalized polysiloxane, [-O-SiMe{(CH(2))(3)N(3)}-](n)[-O-SiMe(2)-](m) also undergoes a click reaction with 1 to produce the side chain polyrotaxane. Cyclic voltammograms of these rotaxanes and 1 [(DB24C8)1] show the Fe(II)/Fe(III) redox at the same potential, but with different current depending on their molecular weights. Addition of PdCl(2)(MeCN)(2) to a solution of the side-chain polyrotaxane forms gel which regenerates the sol upon addition of PPh(3).

Thermally-induced phase transition of pseudorotaxane crystals: changes in conformation and interaction of the molecules and optical properties of the crystals.

This paper presents a pseudorotaxane that acts as a thermally driven molecular switch in the single-crystal state. Crystals of the cationic pseudorotaxane consisting of dibenzo[24]crown-8 (DB24C8) and N-(xylylammonium)-methylferrocene as the cyclic and axle component molecules, respectively, undergo crystalline-phase transition at 128 °C with heating and 116 °C with cooling, according to differential-scanning-calorimetry measurements. X-ray crystallographic analyses revealed that the phase transition was accompanied by rotation of the 4-methylphenyl group of the axle component molecule and a simultaneous shift in the position of the PF(6)(-) counteranion. Crystalline phase transition changes the conformation and position of the DB24C8 molecule relative to the ammonium cation partially; the interaction between the cyclic component and the PF(6)(-) anion in the crystal changes to a greater extent. Moreover, there are changes in the vibration angle (θ) and birefringence (Δn) on the (001) face of the crystal transitionally; θ is rotated by +12°, and Δn is decreased from 0.070 to 0.059 upon heating across the phase transition temperature. The phase transition and accompanying change in the optical properties of the crystal occur reversibly and repeatedly upon heating and cooling processes. The switching rotation of the aromatic plane of the molecule induces a change in the optical anisotropy of the crystal, which is regarded as a demonstration of a new type of optical crystal. Partial replacement of the PF(6)(-) anion with the bulkier AsF(6)(-) anion forms crystals with similar crystallographic parameters. An increase in the AsF(6)(-) content decreases the reversible-phase-transition temperature gradually down to 99 °C (T(end)) and 68 °C (T(exo)) ([AsF(6)(-)]:[PF(6)(-)] = 0.4:0.6).

Organometallic rotaxanes with a triazole group in the axle component and their behavior as ligands of PtII complexes.

Two ferrocenylmethyl ammonium salts were used as axle components of pseudorotaxanes with dibenzo[24]crown-8. The pseudorotaxane with an alkyne terminal group in the axle component underwent a Cu-catalyzed Huisgen coupling reaction (click reaction) with an alkyl azide to afford cationic [2]rotaxanes with a triazole group in the axle molecule. The rotaxane reacted with Ac(2) O to produce neutral rotaxanes with an amide group in the axle component. Both cationic and neutral rotaxanes were treated with K[PtCl(3)(CH(2)=CH(2))] to form the Pt(II)-containing rotaxanes.

[3]Rotaxane-based dinuclear palladium catalysts for ring-closure Mizoroki-Heck reaction.

[3]Rotaxane containing two Pd centers in the cyclic compounds catalyzes a Mizoroki-Heck reaction of substrates with two iodophenyl groups with bisacrylate. Formation of the cyclic products is enhanced by the rotaxane catalyst more smoothly than Pd(OAc)(2).

Hydrogels composed of organic amphiphiles and alpha-cyclodextrin: supramolecular networks of their pseudorotaxanes in aqueous media.

Mixtures of N-alkyl pyridinium compounds [py-N-(CH(2))(n)OC(6)H(3)-3,5-(OMe)(2)](+)(X(-)) (1bCl: n = 10, X = Cl; 1cBr: n = 12, X = Br) and alpha-cyclodextrin (alpha-CD) form supramolecular hydrogels in aqueous media. The concentrations of the two components influences the sol-gel transition temperature, which ranges from 7 to 67 degrees C. Washing the hydrogel with acetone or evaporation of water left the xerogel, and (13)C CP/MAS NMR measurements, powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) revealed that the xerogel of 1bCl (or 1cBr) and alpha-CD was composed of pseudorotaxanes with high crystallinity. (13)C{(1)H} and (1)H NMR spectra of the gel revealed the detailed composition of the components. The gel from 1bCl and alpha-CD contains the corresponding [2]- and [3]pseudorotaxanes, [1b x (alpha-CD)]Br and [1b x (alpha-CD)(2)]Br, while that from 1cBr and alpha-CD consists mainly of [3]pseudorotaxane [1c x (alpha-CD)(2)]Br. 2D ROESY (1)H NMR measurements suggested intermolecular contact of 3,5-dimethoxyphenyl and pyridyl end groups of the axle component. The presence of the [3]pseudorotaxane is indispensable for gel formation. Thus, intermolecular interaction between the end groups of the axle component and that between alpha-CDs of the [3]pseudorotaxane contribute to formation of the network. The supramolecular gels were transformed into sols by adding denaturing agents such as urea, C(6)H(3)-1,3,5-(OH)(3), and [py-N-nBu](+)(Cl(-)).

Thermosensitive hydrogels composed of cyclodextrin pseudorotaxanes. Role of [3]pseudorotaxane in the gel formation.

Pseudorotaxanes composed of an alkylpyridinium and alpha-cyclodextrin (alpha-CD) form supramolecular hydrogels which show sol-gel transitions at 7-67 degrees C depending on the type and amount of the guest compound.

Rotaxanes of a macrocyclic ferrocenophane with dialkylammonium axle components.

Octaoxa[22]ferrocenophane, 1, was synthesized and employed as the macrocyclic component of [2]rotaxanes. [2]Pseudorotaxanes composed of macrocyclic molecule 1 and dialkylammonium derivatives with a terminal vinyl group undergo end-capping via cross-metathesis of the terminal group with bulky acrylates. The [2]rotaxanes of 1 with axle components having bulky terminal groups, such as 3,5-dimethylphenyl, 9-anthryl, and ferrocenyl groups, maintain an interlocked structure in CDCl(3) solution, but they are gradually converted into a mixture of the individual components via dethreading of the end groups in polar solvents such as CD(3)CN and dmso-d(6). The reaction rate varies depending on the end group and solvent. The cationic rotaxane with an anthryl end group of the axle component, [(){AnCH(2)NH(2)CH(2)C(6)H(4)-4-OCH(2)CH(2)CH[double bond, length as m-dash]CHCOOC(6)H(4)-4-C(C(6)H(4)-4-tBu)(3)}](BAr(F)) (An = 9-anthryl, BAr(F) = B{C(6)H(3)-3,5-(CF(3))(2)}(4)) shows weak emission upon excitation of the anthryl group (12b, lambda(em) = 419 nm, quantum yield, phi = 0.012). The quantum yield is lower than that of the neutral rotaxane 13b(phi = 0.030) formed by N-acetylation of 12b and a physical mixture of the corresponding free axle molecule, AnCH(2)N(Ac)CH(2)C(6)H(4)-4-OCH(2)CH(2)CH=CHCOOC(6)H(4)-4-C(C(6)H(4)-4-tBu)(3) (8), and 1 (phi = 0.34). The efficiency of the quenching caused by the ferrocenylene group caused by energy transfer is affected significantly by the relative positions of the anthryl and ferrocenylene groups in the rotaxane. The rotaxane with axles having a secondary ammonium moiety has a redox potential E(1/2) = -0.03-0.02 V (vs. Ag(+)/Ag), which is lower those of than compound 1 (E(1/2) = -0.10 V) and the neutral [2]rotaxanes with the N-acetylated axle components (E(1/2) = -0.11 and -0.22 V).

Rotaxanes and pseudorotaxanes with Fe-, Pd- and Pt-containing axles. Molecular motion in the solid state and aggregation in solution.

This article reviews our recent studies on structure and properties of rotaxanes and pseudorotaxanes with Fe-, Pd- and Pt-containing complexes as the axle component. Electrochemical oxidation of ferrocenylmethylamine in the presence of a hydrogen radical precursor induces formal protonation of the amino group and produces a pseudorotaxane of the resulting ammonium species with a crown ether. Single crystals of the ferrocene-containing pseudorotaxane undergo a thermal crystalline phase transition accompanied by changes in the optical properties of the crystals. X-Ray crystallographic studies of the low- and high-temperature phases revealed different intermolecular interactions and orientations of the aromatic rings in the crystalline state depending on the temperature. End-capping of the ferrocene-containing [2]pseudorotaxane using a cross-metathesis reaction yields [2]rotaxane under mild conditions. A rotaxane having a platinum-carboxylate complex as its axle is converted into related organic and inorganic rotaxanes by partial dissociation of the Pt-O bond. An N-alkylbipyridinium forms [3]pseudorotaxane with alpha-cyclodextrin (alpha-CD), and it reacts with platinum and palladium complexes to form the corresponding [5]rotaxanes containing four alpha-cyclodextrin moieties. Complexes without alpha-CD components form micelles in aqueous solution, while the addition of alpha-CD causes degradation of the micelles and the formation of rotaxanes.

Pd(II) and Pt(II) complexes with amphiphilic ligands: formation of micelles and [5]rotaxanes with alpha-cyclodextrin in aqueous solution.

[3]Pseudorotaxanes [1(alpha-CD)(2)][X] (X=Cl, NO(3)), prepared from reaction of an N-alkylbipyridinium [4,4'-bpy-N-(CH(2))(10)OC(6)H(3)-3,5-(OMe)(2)][X] ([1][X]) and alpha-CD, react with M(NO(3))(2)(en) (M=Pd, Pt; en=1,2-ethylenediamine) in a 2:1 molar ratio to afford [5]rotaxanes [M{(4,4'-bpy-N-(CH(2))(10)OC(6)H(3)-3,5-(OMe)(2))(alpha-CD)(2)}(2) (en)][NO(3)](4) ([2(alpha-CD)(4)][NO(3)](4), M=Pd; [3(alpha-CD)(4)][NO(3)](4), M=Pt). A similar reaction of [1][Cl] with [M(NO(3))(2)(en)] (M=Pd, Pt) produces amphiphilic Pd and Pt complexes, [2][NO(3)](4) and [3][NO(3)](4). Complexes [2][NO(3)](4) and [3][NO(3)](4) form micelles in the presence of small amounts of dyes (Nile red and pyrene) in water. The critical micelle concentration (CMC) was determined by the absorption peak of the dye, which is encapsulated in the micelles in solution. Micelle formation is confirmed by dynamic light scattering measurement of the solution and TEM (transmission electron microscopy) images of the micelles deposited from the solution. Addition of alpha-CD to the aqueous solution containing these amphiphilic complexes results in degradation of the micelle structure and the formation of [5]rotaxanes, [2(alpha-CD)(4)][NO(3)](4) and [3(alpha-CD)(4)][NO(3)](4).

Ferrocene-containing [2]- and [3]rotaxanes. Preparation via an end-capping cross-metathesis reaction and electrochemical properties.

Cross-metathesis reactions of terminal olefins with acrylic esters catalyzed by a Ru-carbene complex ((H2IMes)(PCy3)Cl2Ru = CHPh, H2IMes = N,N-bis(mesityl)-4,5-dihydroimidazol-2-ylidene) were applied to the end-capping of [2]pseudorotaxanes composed of dibenzo[24]crown-8 (DB24C8) and ferrocenylmethylammonium derivatives as the macrocyclic and axle components. A [3]rotaxane consisting of two DB24C8s and an axle molecule having ferrocenyl groups at both ends was obtained from the cross-metathesis reaction of two [2]pseudorotaxanes with Fe(C5H4CH2OCOCH = CH2)2. Cyclic voltammograms of the ferrocene-containing rotaxanes show reversible redox reactions whose potentials vary depending on the presence or absence of cationic dialkylammonium groups in the vicinity of the ferrocene units.