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We synthesized a planar macrocyclic dinuclear nickel(II) metallohost from the corresponding macrocyclic imine ligand containing two N2O2 chelate coordination sites and an O6 cation binding site like 18‐crown‐6 as well as peripheral hexyl groups. Due to the lipophilic nature of the hexyl groups, the metallohost was soluble in less polar media where its interaction with alkali metal ions was enhanced. The binding studies by NMR spectroscopy clearly showed its strong tendency to form multi‐layered structures. The metallohost formed 2 : 1 and 1 : 1 (host/guest) complexes with Na+ with the two‐step binding constants of logK1=6.6 and logK2=3.0. In contrast, its complexation with larger alkali metal ions (K+, Rb+, Cs+) preferentially gave 3 : 2 (host/guest) complexes when 2/3 equiv. of the guest was present. The three‐layered structures of these 3 : 2 complexes were well characterized by mass spectrometry and 2D COSY/ROESY experiments as well as DFT calculations, elucidating their unique structural feature with three chemically different environments due to the oppositely curved two [Ni(saloph)] moieties of the metallohost. Therefore, the three‐layered structures were preferentially formed when larger alkali metal ions (K+, Rb+, Cs+) were complexed with the metallohost. [ABSTRACT FROM AUTHOR]

We report the reversible transformation between a singly stapled dynamic α‐helical peptide and a doubly stapled quasi‐static one through redox‐triggered dithiol/disulfide conversions of a stapling moiety. This process allows the rate of interconversion between the right‐handed (P) and left‐handed (M) α‐helices to be altered by a factor of approximately 103 before and after the transformation. An as‐obtained doubly stapled α‐helical peptide, which is composed of an achiral peptide having an l‐valine carboxylic acid residue at the C‐terminus, a disulfide‐based reversible staple, and a biphenyl‐based fixed staple, adopts an (M)‐rich form as a kinetically trapped state. The (M)‐rich helix was subsequently transformed into the thermodynamically stable (P)‐rich form in 1,1,2,2‐tetrachloroethane with the half‐life time (t1/2) of approximately 44 days at 25 °C. Reduction of the doubly stapled peptide with tri‐n‐butylphosphine in tetrahydrofuran/water (10/1, v/v) produced the corresponding singly stapled dynamic α‐helical peptide bearing two thiol groups at the side chains, which underwent solvent‐induced reversible helicity inversion. The resulting dithiol of the singly stapled peptide could be reoxidized to form the original doubly stapled form using 4,4'‐dithiodipyridine. Furthermore, the P/M interconversion of a doubly stapled peptide with two flexible hydrocarbon‐based staples is considerably more rapid than that with more rigid staples. [ABSTRACT FROM AUTHOR]

Self‐inclusion complexes consisting of host‐guest conjugates are one of the unique supramolecular structures because they form in‐state and out‐state depending on the external stimuli. Despite many reports of the stimuli‐responsive self‐inclusion complex formation, study of the structural relaxation from out‐state to in‐state by photoexcitation has been unexplored. Herein, we report that an electron‐donating host and an electron‐accepting guest conjugate exhibits the structural relaxation from out‐state to in‐state by photoexcitation. Formation of the in‐state in the excited state resulted in exciplex emission along with the locally excited emission from the out‐state. Moreover, this structural relaxation by photoexcitation was suppressed not only by temperature, but also by the presence of guest molecules, resulting in changes in the ratio of the dual emission intensities. [ABSTRACT FROM AUTHOR]

Dynamic M/P invertible helicity was successfully induced at a SiO2 surface immobilized with a dynamic helical trinuclear cobalt complex, [LCo3(NHMe2)6](OTf)3, using chiral ((R) or (S))-1-phenylethylamine. Solid-state CD spectra and theoretical calculations suggested that the fixation of the M/P helical complex on the surface via coordination interactions was the key factor of the induced chirality at the surface. [ABSTRACT FROM AUTHOR]

Pillar[n]arenes can be constructed using a Friedel–Crafts alkylation process. However, due to the reversible nature of the alkylation, mixture of large pillar[n]arenes (n≥7) are obtained as minor products, and thus laborious purification are necessary to isolate the larger pillar[n]arenes. Moreover, inert methylene bridges are introduced during the alkylation process, and the multi‐functionalization of the bridges has never been investigated. Herein, an irreversible Friedel–Crafts acylation is used to prepare pillar[n]arenes. Due to the irreversible nature of the acylation, the reaction of precursors bearing carboxylic acids and electron‐rich arene rings results in a size‐exclusive formation of pillar[n]arenes, in which the ring‐size is determined by the precursor length. Because of this size‐selective formation, laborious separation of undesired macrocycles is not necessary. Moreover, the bridges of pillar[n]arenes are selectively installed with reactive carbonyl groups using the acylation method, whose positions are determined by the precursor used. The carbonyl bridges can be easily converted into versatile functional groups, leading to various laterally modified pillar[n]arenes, which cannot be accessed by the alkylation strategy. [ABSTRACT FROM AUTHOR]

Controlling dynamic chirality and memorizing the controlled chirality are important. Chirality memory has mainly been achieved using noncovalent interactions. However, in many cases, the memorized chirality arising from noncovalent interactions is erased by changing the conditions such as the solvent and temperature. In this study, the dynamic planar chirality of pillar[5]arenes was successfully converted into static planar chirality by introducing bulky groups through covalent bonds. Before introducing the bulky groups, pillar[5]arene with stereogenic carbon atoms at both rims existed as a pair of diastereomers, and thus showed planar chiral inversion that was dependent on the chain length of the guest solvent. The pS and pR forms, regulated by guest solvents, were both diastereomerically memorized by introducing bulky groups. Furthermore, the diastereomeric excess was amplified by crystallization of the pillar[5]arene. The subsequent introduction of bulky groups yielded pillar[5]arene with an excellent diastereomeric excess (95 % de). [ABSTRACT FROM AUTHOR]

Dynamic helical molecules, which can undergo a reversible chirality inversion between the P and M forms, are useful as a platform for switchable chiral functional molecules. The chirality inversion of these molecules has been extensively studied. However, it has mostly been discussed from the viewpoint of the equilibrated P/M ratios before and after the inversion; control of the response speeds or kinetic profiles has rarely been explored. In order to construct helical structures with controllable kinetic profiles, triple-helical metallocryptands, LM3, have been designed and synthesized. These molecules can undergo a relatively slow dynamic P/M chirality inversion (helicity inversion) to produce an equilibrated mixture. The P/M equilibration was accelerated or decelerated based on the following two strategies. One is based on the guest binding in the cryptand cavity. The P/M racemization kinetics of LNi3 was significantly decelerated by recognition of guanidinium ion in the cavity. The other strategy is based on the ligand exchange reactions at the octahedral cobalt(III) centers in LCo3(amine)6. The P/M chirality inversion speeds were controlled by changing the initial and entering amine ligands. In addition, a unique transient chirality inversion behavior was observed when chiral amine ligands were removed from the metallocryptand by the ligand exchange reaction with piperidine. [ABSTRACT FROM AUTHOR]

Switching between the formation/dissociation of rotaxanes is important to control the function of various types of rotaxane‐based materials. We have developed a convenient and simple strategy, the so‐called "accelerator addition", to make a static rotaxane dynamic without apparently affecting the chemical structure. As an interlocked molecule that enables tuning of the formation/dissociation speed, a metallorotaxane was quantitatively generated by the complexation of a triptycene‐based dumbbell‐shaped mononuclear complex, [PdL2]2+ (L=2,3‐diaminotriptycene), with 27C9. As a result of the inertness of the Pd2+‐based coordination structure, the metallorotaxane was slowly formed (the static state). This rotaxane formation was accelerated 27 times simply by adding Br− as an accelerator (the dynamic state). A similar drastic acceleration was also demonstrated during the dissociation process when Cs+ was added to the metallorotaxane to form the free axle [PdL2]2+ and the 27C9‐Cs+ complex. [ABSTRACT FROM AUTHOR]

The article in Chemistry - A European Journal discusses the preferential formation of three-layered host-guest complexes by complexing a macrocyclic dinickel metallohost with larger alkali metal ions (K+, Rb+, Cs+). Spectroscopic and theoretical investigations confirm the unique structure of these complexes, where three metallohost molecules are stacked in a parallel manner with oppositely curved nickel complex moieties. The research was conducted by S. Akine and co-workers, providing further details in the Research Article (DOI: 10.1002/chem.202403071). [Extracted from the article]

A series of amphiphilic salen complexes, [L1a,bM] and [L2a,bM], were designed and synthesized. These complexes consist of two or four hydrophilic triethylene glycol (TEG) chains and a hydrophobic π-extended metallosalen core based on naphthalene or phenanthrene. The obtained amphiphilic complexes, [L1bM] (M = Ni, Cu, Zn), formed a monolayer at the air–water interface, while the monocationic [L1bCo(MeNH2)2](OTf) did not form a well-defined monolayer. The number of hydrophilic TEG chains also had an influence on the monolayerformation behavior; the tetra-TEG derivatives, [L1bNi] and [L2bNi], showed a pressure rise at a less compressed region than the bis-TEG derivatives, [L1aNi] and [L2aNi]. In addition, the investigation of their compressibility and compression modulus suggested that the tetra-TEG derivatives, [L1bNi] and [L2bNi], are more flexible than the corresponding bis-TEG analogues, [L1aNi] and [L2aNi], and that the phenanthrene derivatives [L1a,bNi] were more rigid than the corresponding naphthalene analogues, [L2a,bNi]. The Langmuir–Blodgett (LB) films of one of the complexes, [L1bNi], showed CD spectra slightly different from that in solution, which may originate from the unique anisotropic environment of the air–water interface. Thus, we demonstrated the possibility of controlling the chiroptical properties of metal complexes by mechanical compression. [ABSTRACT FROM AUTHOR]

A C4h symmetrically substituted phthalocyanine, 1,8,15,22‐tertrakis(2,4‐dimethylpent‐3‐oxy)phthalocyanine (H2TdMPPc), was used to synthesize Tb3+‐phthalocyanine double‐decker complexes ([Tb(TdMPPc)2]s). Because H2TdMPPc has C4h symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc)2] were obtained depending on the difference in the direction of the coordination plane of two C4h‐type phthalocyanines with respect to a central Tb3+ ion. We investigated the physical properties of these [Tb(TdMPPc)2] isomers, including their single‐ion magnetic properties, and found that the spin‐reversal energy barrier (Ueff) of the meso isomer was apparently higher than that of the enantiomers. Detailed crystal structural analyses indicated that the meso isomer has a more symmetrical structure than do the enantiomers, thereby suggesting that the higher Ueff of the meso isomer originated from the more highly symmetrical structure. [ABSTRACT FROM AUTHOR]

Rotaxanes, which are composed of ring and axle components, are important interlocked molecules with wide applications such as molecular machines and switchable catalysts. The construction of interlocked structures targeting anions is an important issue, as evidenced by the fact that anionic groups are usually abundant in many biomacromolecules. We now report an allosteric pseudomacrocyclic anion receptor as a ring that spontaneously generates a rotaxane in an auto-clipping way, which does not require the successive ring forming reaction like usual clipping, in the presence of an axle with an anionic station. We designed a linear ligand 1 bearing three anion recognition moieties, i.e., one thiourea group at the centre and two urea groups near the 2,2′-bipyridine ends of 1. The complexation of 1 with Cu+ proceeded in an intramolecular manner that quantitatively led to a macrocyclic structure [1·Cu]+. Compared to 1, the anion binding ability of [1·Cu]+ was significantly larger (positive allosteric effect) due to the macrocyclization arrangement of the three anion recognition moieties in a cyclic fashion and electrostatic interaction. In addition, the kinetically labile but thermodynamically stable coordination properties of the pseudomacrocyclic ring unit promoted the spontaneous rotaxane formation with a phosphate axle at room temperature. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structure of octanuclear zinc(II) and cobalt(II) clusters that could be obtained by the cooperative tetrameric assembling of the 3-hydroxy-salamo ligand is reported. The structural analysis of the zinc(II) complex in solution has displayed the significant stability of the octanuclear core, suggesting that the tetrameric self-assembly took place highly cooperatively.

The reaction of calix[4]arene derivatives 1a and 1b bearing four salicylaldehyde moieties with 1,3-propanediamine gave macrocyclic trimers 5a and 5b, respectively, which have intramolecular bridges formed via the flattened cone conformation. In contrast, a capsular-shaped dimeric cage [7a·2Na]2+ was selectively formed when the conformation of the calix[4]arene moiety of 1a was fixed in the spread cone conformation by complexation with Na+ at the lower-rim amide groups. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of a monocationic μ-nitrido-bridged iron porphycene dimer, a structural analogue of a monocationic μ-nitrido-bridged iron phthalocyanine dimer, which is known to be one of the most potent molecule-based catalysts for methane oxidation. 1H-NMR and single-crystal X-ray structural analyses showed that the porphycene complex includes two Fe(IV) ions, and the structure around the Fe–N＝Fe core is quite similar to that of the monocationic μ-nitrido-bridged iron phthalocyanine dimer. Although methane was oxidized into MeOH, HCHO, and HCOOH in the presence of a silica-supported catalyst of this monocationic μ-nitrido-bridged iron porphycene dimer in an acidic aqueous solution containing excess H2O2, its reactive intermediate was not a high-valence iron-oxo species, as in the case of a monocationic μ-nitrido-bridged iron phthalocyanine dimer, but ˙OH. It is suggested that the high-valent iron-oxo species of the μ-nitrido-bridged iron porphycene dimer was gradually decomposed under these reaction conditions, and the decomposed compound catalyzed a Fenton-type reaction. This result indicates that the stability of the oxo-species is indispensable for achieving high catalytic methane oxidation activity using a μ-nitrido-bridged iron porphyrinoid dimer with an Fe–N＝Fe core as a catalyst. [ABSTRACT FROM AUTHOR]

The growth of multimetallic clusters and complexes can proceed in the presence of suitable ligands, but often leads to polydisperse structures with poor solubility. As an alternative approach, macrocyclic molecules can anchor the multimetallic complex, directing its formation and stabilizing the resulting product. This approach can provide excellent control over the growth of clusters, and offers a handle to control solubility and other properties of the resulting complexes. In this Tutorial Review, we discuss recent activity (primarily the last two decades) directed at the controlled and reproducible synthesis of multimetallic complexes using macrocyclic ligands. Throughout the review, we focus on the unusual structures that are only accessible by using macrocycles as ligands, and their unique properties. [ABSTRACT FROM AUTHOR]

Unique bench‐stable rhodium(I) complexes bearing an aryl‐substituted 1,3,5‐hexatriene chain have been synthesized by reactions of (bicyclo[2.2.1]hepta‐2,5‐diene)rhodium(I) chloride dimer ([Rh(nbd)Cl]2) with aryl boronic acids and diphenylacetylenes in the presence of a 50 % aqueous solution of KOH. X‐ray crystallographic analysis of the isolated complexes indicated a square‐planar structure stabilized by a strong interaction with one of the aryl groups on the 1,3,5‐hexatriene chain, which has a helical structure. The helical chirality of the isolated rhodium complexes was confirmed to be sufficiently stable to be resolved into enantiomers by HPLC on a chiral stationary phase at room temperature. It was confirmed that the isolated rhodium complexes functioned as initiators for living polymerization of phenylacetylene to give cis‐stereoregular poly(phenylacetylene) with a well‐controlled molecular weight. [ABSTRACT FROM AUTHOR]

The synthesis of novel zinc(II) complexes [Zn3L2(OAc)2] and their structures were determined by x-ray crystallography. The complexes between the salamo ligands and zinc (II) in methanol formed exclusively and very cooperatively.

This review describes the control of guest binding behavior of metal-containing host molecules that is driven by ligand exchange reactions at the metal centers. Recently, a vast number of metal-containing host molecules including metal-assisted self-assembled structures have been developed, and the structural transformation after construction of the host framework has now been of interest from the viewpoint of functional switching and tuning. Among the various kinds of chemical transformations, ligand exchange has a great advantage in the structural conversions of metal-containing hosts, because ligand exchange usually proceeds under mild conditions that do not affect the host framework. In this review, the structural transformations are classified into three types: (1) weak-link approach, (2) subcomponent substitution, and (3) post-metalation modification, according to the type of coordination motif. The control of their guest binding behavior by the structural transformations is discussed in detail. [ABSTRACT FROM AUTHOR]

We have designed a new chiral receptor based on two salen zinc(II) complex units connected with a spirobifluorene framework. The chiral receptor is proven to enantioselectively bind chiral carboxylate guests and the differences between the binding constants of enantiomeric guests were up to more than one order of magnitude. [ABSTRACT FROM AUTHOR]

Tripodal ligands have been utilized for complexation-induced structural change, but all the tripodal complexes reported so far are facial isomers, which do not completely reduce the recognition ability by closing the binding pocket. We now report the first example of the selective synthesis of a meridional tripodal complex. The tripodal ligand with a 1,3,5-triethyl-2,4,6-tris(methylene)benzene pivot possessing 2,2′-bipyridine on each arm exclusively formed a mononuclear complex with the mer-[Fe(bpy)]2+ unit. The meridional tripodal complex has a unique structure in which one bipyridine unit is self-penetrated. As a result of cavity blockage, the ion recognition property of the tripodand has been successfully suppressed. [ABSTRACT FROM AUTHOR]

Host–guest binding behavior of macrocyclic hosts is significantly influenced by the shapes and sizes of the hosts. In particular, closing/opening the apertures of the hosts controls the guest uptake/release. A post‐metalation modification method was used to achieve the open/close conversions. The starting open complex, [LCo2(pip)4](OTf)2, was efficiently converted to the closed complex, [LCo2(hda)2](OTf)2, which has a doubly bridged structure. The conversion of this closed complex to the open complex [LCo2(hda)2(OAc)]+ was too slow to be completed, but this gate‐opening was dramatically accelerated by the addition of Na+. The Na+ binding was also significantly enhanced by the gate‐opening, that is, conversion of [LCo2(hda)2]2+ to [LCo2(hda)2(OAc)]+. [ABSTRACT FROM AUTHOR]

A novel cooperative [3]pseudorotaxane system consisting of dibenzo-24-crown-8 (DB24C8) and diphenylviologen axle has been developed. The two-step formation of the [3]pseudorotaxane occurred in a positive-cooperative manner. The corresponding [3]rotaxane was successfully obtained from just a stoichiometric mixture of each component by end-capping without dissociation. [ABSTRACT FROM AUTHOR]

We propose post‐metalation modification as a useful strategy to control the guest recognition behavior of a metal‐containing macrocyclic host. This is based on the ligand exchange of the axial ligands of a cobalt(III) dinuclear macrocyclic host, [LCo2X4]2+ (X=axial amine ligand). Four piperidine ligands in [LCo2(pip)4]2+ (pip=piperidine) were site‐selectively replaced with primary amines. The competitive experiments revealed that the order of the affinity toward the cobalt centers in [LCo2X4]2+ is primary amine > secondary amine > tertiary amine and that the piperidine‐coordinating complex, [LCo2(pip)4]2+, was reasonably reactive among the isolable complexes. Indeed, two piperidine ligands at the diagonal positions in [LCo2(pip)4]2+ were site‐selectively replaced with pyridine or acetate ion. The replacement of piperidine with acetate ion significantly enhanced the recognition ability towards Na+. [ABSTRACT FROM AUTHOR]

Supramolecular chemistry in confined spaces constructed from macrocyclic molecules has attracted much attention because it can utilize the specific binding properties of macrocyclic cavities. Herein we report the preparation of length‐controlled discrete tubular structures by homo‐/co‐assembly of rim‐differentiated and peralkylamino‐substituted pillar[5]arenes via hydrogen bonds and salt bridges. By dimerization and trimerization, the expanded tubes show a fivefold helical structure and stepwise binding, respectively. We found that the exchange speed of guest molecules in the tubes could be controlled by varying the tube length. [ABSTRACT FROM AUTHOR]

A new type of acyclic bis([N.sub.2][O.sub.2] chelate) ligand has afforded a C-shaped [O.sub.6] site by the metalation of the [N.sub.2][O.sub.2] salamo sites. The different nature of the [N.sub.2][O.sub.2] and [O.sub.6] sites of the ligand [H.sub.4]L has led to the site-selective introduction of two different d-block transition metals.

The new salen-type [N.sub.2][S.sub.2] tetradentate ligands having a donor set comprising oxime and thiol groups and the unsymmetrical [N.sub.2]SO ligands are synthesized. Mononuclear complexes are obtained by complexation of the ligands with palladium(II) acetate without N-O bond cleavage.

The article explains the highly cis- and trans-selective synthesis of a 32-membered macrocyclic tetraoxime. The synthesis is shown to be a ring-closing olefin metathesis reaction exhibiting the oligometallic template strategy.