Formation of a Metallomacrocycle Possessing Nitrogen Donors Assembled in the Cavity and Unique Water Clusters.

2,2'-Bipyridyl (bpy) is widely used as a chelating unit for metal complexation but is not usually considered as a hydrogen-bonding unit. This is because the metal-free bpy units are usually in a transoid conformation, and the two nitrogen lone pairs are pointed to the opposite sides. We now report a metallomacrocycle whose three metal-free bpy units are in a cisoid conformation and are fixed in the cavity. The complexation of nickel(II) only at the salen units of the triangular bpytrisalen ligand produced this rigid and planar macrocycle. Its cavity is surrounded by hydrogen-bond acceptors (N of bpy and O of salen), and it was found that unique pentagonal prism clusters of water molecules templated by the cavity were formed in the crystal. This study has not only increased the variation of the synthetic methodologies of multinuclear complexes but has also provided the structural platform on which multiple bpy units exert hydrogen-bonding functions.

Synthesis and optical properties of antimony(V) complexes of a trianionic N2O2-type tetradentate dipyrrin ligand.

LSbCl2, an air- and moisture-stable antimony(V)-dipyrrin complex at room temperature, was obtained by treating an excess amount (20 eq.) of SbCl3 with a trianionic N2O2-type tetradentate dipyrrin ligand (L) under visible-light irradiation and O2 atmosphere. The Cl ligands in LSbCl2 were replaced by OH ligands via hydrolysis, yielding LSb(OH)2. Further, the molecular structures and optical properties of the Sb(V)-dippyrin complexes were investigated. While LSbCl2 was non-fluorescent, LSb(OH)2 exhibited an intense red fluorescence with a photoluminescence quantum yield of 68%.

Rotaxane formation by an allosteric pseudomacrocyclic anion receptor utilising kinetically labile copper(I) coordination properties.

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.

Evidence of C-F···H-C Attractive Interaction: Enforced Coplanarity of a Tetrafluorophenylene-Ethynylene-Linked Porphyrin Dimer.

The formation of C-F···H-C "hydrogen bonds" has been a controversial subject because, in principle, fluorine is hardly an acceptor for less acidic protons contrasting to the C-F···H-O and C-F···H-N hydrogen bonds. Nevertheless, the interaction is emerging as a powerful implement for confining the torsional rotation in the design of fully coplanar π-conjugated polymers. Heretofore, no evidence of the C-F···H-C interaction has been observed in solutions. We herein disclose comprehensive evidence that the C-F···H-C interaction produces an attractive force. A 19F-1H heteronuclear Overhauser effect experiment elucidated the close proximity of the F and H atoms in the doubly edge-facing C-F···H-C interactions of a meso-tetrafluorophenylene-ethynylene-conjugated porphyrin dimer (1). Extensive electronic and photophysical property investigations confirmed that all the aromatic units were torsionally restricted by the C-F···H-C interactions. Moreover, the enforced coplanarity invoked a markedly high π-staking propensity. Thus, we have firmly established the formation of a C-F···H-C interaction that produces a hydrogen-bond-like attractive force in solution.

Synthesis of a chiral metallo-capsule composed of concave molecules and chirogenesis upon fullerene binding.

An enantiopure molecular capsule was synthesized quantitatively using complexation of four phosphangulenes as concave molecules with four Zn2+ ions and applied to fullerene binding and chirogenesis. The capsule encapsulated selectively fullerene and its derivatives based on the size of cavity. The fullerene C60 incorporated in the capsule exhibited induced-CD signals at the transitions of C60.

Enhancement of Alkali Metal Ion Recognition by Metalation of a Tris(saloph) Cryptand Having Benzene Rings at the Bridgeheads.

A cryptand derivative, H6L, which has three H2saloph arms connected by two benzene ring bridgeheads, was synthesized and converted into the trinuclear metallocryptand, LNi3. The nonmetalated host, H6L, was found to bind to alkali metal ions (Na+, K+, Rb+, Cs+; logKa = 3.37-6.67) in its well-defined cavity in DMSO/chloroform (1:9). The binding affinity was enhanced by 1-2 orders of magnitude upon the conversion into the metallocryptand, LNi3, which can be explained by the more polarized phenoxo groups in the [Ni(saloph)] arms. The guest binding affinity of Na+ < K+ < Rb+ ≈ Cs+ was clearly demonstrated by the 1H NMR competition experiments. The DFT calculations suggested that the Rb+ ion most suitably fit into the benzene-benzene spacing with a cation-π interaction and that only the largest Cs+ ion can almost equally interact with all six phenoxo oxygen donor atoms. The metallocryptand, LNi3, also showed a strong binding affinity to Ag+ by taking advantage of cation-π interactions, which was confirmed by spectroscopic titrations and crystallographic analysis as well as DFT calculations. Thus, the well-defined three-dimensional cavity of LNi3 was found to be suitable for strong binding with alkali metal ions as well as Ag+.

Solvent-dependent fac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part.

Tris-chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers, facial (fac) and meridional (mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of the fac/mer isomers of the triply helical FeII complexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example of fac/mer isomerism of a labile tris(2,2'-bipyridine) FeII complex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only the fac isomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.

Exclusive formation of a meridional complex of a tripodand and perfect suppression of guest recognition.

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.

Synthesis of Single Isomeric Complexes with Dissymmetric Structures Using Macrocyclic Homooligomers.

Bottom-up chemical synthesis to construct intricate molecules has been a profound challenge. An effective approach is to utilize organic ligands and metal ions, but the formation of a single product among other possible candidates has proven difficult for dissymmetric structures. We now report the synthesis of single isomeric complexes with dissymmetric structures using the mismatch in the coordination valences of macrocyclic homooligomers and metal ions. A series of amide-cyclodextrin derivatives possessing multiple 2,2'-bipyridyl (bpy) groups forms mononuclear complexes whose specific three bpy groups are linked in the fac-Λ configuration. The intermolecular coordination of the ß-cyclodextrin metal complex produces a dissymmetric cyclodextrin trimer as a single isomer, whose initially equivalent 21 (=7×3) bipyridylamide-pyranose units are placed in different environments. Furthermore, we realize chiral recognition of amino acid anions utilizing the distinctive amide groups arranged on the unsymmetrically fixed scaffold.

Kinetic and Thermodynamic Behaviors of Pseudorotaxane Formation with C3v Macrocyclic BODIPY Trimers and the Remarkable Substituent Effect on Ring-Face Selectivity.

The thermodynamic and kinetic behaviors of the pseudorotaxane formation between the C3v macrocyclic BODIPY trimers and unsymmetrical secondary ammonium guests are investigated. We find a remarkable substituent effect of the BODIPY trimer on the ring-face selectivity during the threading. The difference in the small substituents (H or CH3) in the macrocyclic host molecules significantly modulated the thermodynamic and kinetic selectivity of the threading direction of the unsymmetrical ammonium ions.

Efficient luminescent properties and cation recognition ability of heavy group 13 element complexes of N2O2- and N2O4-type dipyrrins.

The first mononuclear 1 : 1 complexes of heavy group 13 elements (Ga and In) and N2O2/N2O4-type dipyrrins were synthesized and characterized. The N2O2-type complexes showed efficient luminescent properties even in polar solvents. The N2O4-type complexes exhibited fluorometric responses to alkaline earth metal ions.

Bpytrisalen/Bpytrisaloph: A Triangular Platform That Spatially Arranges Different Multiple Labile Coordination Sites.

Complexes that possess multiple metals in their proximity exert useful functions such as multivalent capture and catalytic activities. However, it is often challenging to arrange multiple metals with regular distances and to maintain the reactive coordination sites. We have now designed and synthesized organic macrocyclic ligands, bpytrisalen and bpytrisaloph, as platforms to spatially arrange different kinds of metals and their coordination sites. Metals coordinating to the bpy N2 units of the triangular ligands are assembled in the cavity with their labile coordination sites directed inward. Meanwhile, the metals at the salen/saloph N2O2 units have axial coordination sites that are vertically pointing out of the triangle. As a result, planar homo- and heterohexanuclear complexes with different kinds of coordination sites are obtained. Furthermore, a double-decker structure was selectively constructed upon coordinating a ditopic linker ligand to the axial coordination sites of the salen units, which shows the orthogonality of the coordination sites at the bpy and salen units. The consistency in the array of metal centers and their coordination sites irrespective of the elements is a desirable feature in the pursuit of applications for the multinuclear complexes.

Double-Circularly Connected Saloph-Belt Macrocycles Generated from a Bis-Armed Bifunctional Monomer.

Belt-shaped macrocycles possessing saloph units as their walls have been generated by the double-circular connection of a bis-armed bifunctional monomer bearing both o-phenylenediamine and salicylaldehyde functionalities. The saloph-belt macrocycles showed unique properties, such as the selective inclusion of fullerenes ( Ka(C70)/ Ka(C60) > 100), utilizing their rigid scaffolds.

Synthesis of per(5-N-carboxamide-5-dehydroxylmethyl)-ß-cyclodextrins and their selective recognition ability utilizing multiple hydrogen bonds.

Per(5-N-carboxamide-5-dehydroxylmethyl)-ß-cyclodextrin derivatives with seven equivalent amide groups directly attached to each pyranose ring were synthesized. The amide cyclodextrins show unique recognition properties toward hydrogen phosphonate anions. An X-ray crystallographic analysis revealed its recognition mode in which unsymmetrically arranged amide groups play distinctive roles both as a hydrogen bond donor and acceptor.

A twisted macrocyclic hexanuclear palladium complex with internal bulky coordinating ligands.

A macrocyclic hexanuclear palladium complex, which accumulates coordination sites on metals inside the cavity, was synthesized. The macrocycle was found to take a uniquely-twisted C2-symmetric conformation when six molecules of a bulky pyridine derivative coordinated to the palladium.

Ligand Exchange Strategy for Tuning of Helicity Inversion Speeds of Dynamic Helical Tri(saloph) Metallocryptands.

We developed a new strategy, ligand exchange strategy, for tuning the response speeds of helicity inversion of a metal-containing helical structure. This is based on the exchange of the two axial amine ligands of the octahedral Co3+ centers in the metallocryptands [LCo3 X6 ] (X=axial amine ligand). The response speeds of the helicity induction were controlled by using different combinations of achiral and chiral amines as the starting and entering ligands, respectively. The response speeds of the helicity inversion from P to M were also tuned by using different combinations of chiral amines.

A Closed Metallomolecular Cage that can Open its Aperture by Disulfide Exchange.

A closed metallomolecular cage based on the tris(saloph) framework, in which its aperture can be opened by disulfide exchange, was designed. At the apertures of the molecular cage, bridging diamine ligands having a disulfide bond were introduced to close the cage structure. These bridging ligands efficiently blocked the uptake of a guest, Cs+ , but the presence of a thiolate anion significantly accelerated the guest uptake. This clearly means that this cage complex became open by the addition of the thiolate anion, because the cage closure becomes more dynamic due to the disulfide exchange reaction.

A Conformationally Flexible Macrocyclic Dipyrrin Tetramer and Its Unsymmetrically Twisted Luminescent Zinc(II) Complex.

A macrocyclic dipyrrin tetramer containing flexible m-phenylene linkages and its tetranuclear zinc(II) complex were synthesized. The obtained complex has an unsymmetrical figure-of-eight structure because of the conformational flexibility of the macrocyclic framework. The first µ-hydroxo- and µ-acetato-bridged dinuclear zinc(II) dipyrrin complex structure is realized in the twisted macrocyclic complex. Furthermore, the complex exhibited an efficient emission in toluene and chloroform.

Correction: Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties.

Correction for 'Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties' by Makoto Saikawa et al., Chem. Commun., 2016, 52, 10727-10730.

Functional Supramolecular Architectures of Dipyrrin Complexes.

Dynamic formation of self-assemblies from molecular components is a useful and efficient way to produce molecular and supramolecular architectures with sophisticated functions. The labile coordination bond and dynamic covalent bond as a reversible bond have often been used to create a well-organized supramolecular self-assembly. In order to realize sophisticated novel functions of the supramolecular self-assemblies, dipyrrin complexes have recently been employed as a functional unit and incorporated into the supramolecular architectures because of their outstanding properties and functions such as a high photostability and strong light absorption/emission. This review article summarizes recent development in functional supramolecular architectures of the dipyrrin complexes produced by coordination to a metal ion and dynamic covalent bond formation. We first describe the synthesis and unique functions of a series of discrete supramolecular architectures: helicates, macrocycles, and cages. The polymeric supramolecular self-assemblies with 1D, 2D, and 3D structures are then introduced as a functional infinite supramolecular architecture.