Reversed Cation Selectivity of G8‐Octamer and G16‐Hexadecamer towards Monovalent and Divalent Cations

A reverse‐binding‐selectivity between monovalent and divalent cations was observed for two different self‐assembly G₁₆‐hexadecamer and G₈‐octamer systems. The dissociation constant between G₄‐quadruplex and monomer was calculated via VT‐¹H NMR experiments. Quantitative energy profiles revealed entropy as the key factor for the weaker binding toward Ba²⁺ compared with K⁺ in the G₈‐octamer system despite stronger ion‐dipole interactions. This study is the first direct comparison of the G₄‐quartet binding affinity between mono and divalent cations and will benefit future applications of G‐quadruplex‐related research. Further competition experiments between the G₈‐octamer and 18‐crown‐6 with K⁺ demonstrated the potential of this G₈ system as a new potassium receptor.     

Crystal Engineering of an nbo Topology Metal–Organic Framework for Chemical Fixation of CO2 under Ambient Conditions

Crystal engineering of the nbo metal–organic framework (MOF) platform MOF‐505 with a custom‐designed azamacrocycle ligand (1,4,7,10‐tetrazazcyclododecane‐N,N′,N′′,N′′′‐tetra‐p‐methylbenzoic acid) leads to a high density of well‐oriented Lewis active sites within the cuboctahedral cage in MMCF‐2, [Cu₂(Cu‐tactmb)(H₂O)₃(NO₃)₂]. This MOF demonstrates high catalytic activity for the chemical fixation of CO₂ into cyclic carbonates at room temperature under 1 atm pressure.     

Cobalt-catalyzed asymmetric cyclopropanation with diazosulfones: rigidification and polarization of ligand chiral environment via hydrogen bonding and cyclization

A new D2-symmetric chiral porphyrin P6 (2,6-DiMeO-ZhuPhyrin) with enhanced chiral rigidity and polarity was designed and synthesized through incorporation of hydrogen bonding and cyclic structure. Its cobalt(II) complex [Co(P6)] is a highly active and selective catalyst for asymmetric cyclopropanation of alkenes with diazosulfones. The [Co(P6)]-based catalytic system is suitable for various aromatic olefins as well as electron-deficient olefins, including alpha,beta-unsaturated esters, ketones, and nitriles, forming the corresponding cyclopropyl sulfones under mild conditions in high yields and high selectivities. In most cases, both excellent diastereo- and enantioselectivities were achieved.     

Quest for zeolite-like metal-organic frameworks: on pyrimidinecarboxylate bis-chelating bridging ligands

Two novel porous zeolitelike metal-organic frameworks (ZMOFs) were constructed via the single metal ion-based molecular building block approach from rigid and directional tetrahedral building units and pyrimidinecarboxylate bridging ligands; their ion exchange and hydrogen sorption properties were evaluated.     

Interplay between acetate ions, peripheral groups, and reactivity of the core nitrogens in transmetalation of tetrapyrroles

The mechanism of acetate-assisted transmetalation of tetrapyrroles was investigated in a model system consisting of chlorophyll a and copper(II) acetate in organic solvents by using a spectroscopic and kinetic approach. Surprisingly, acetate ions bind to the central Mg in chlorophyll much more strongly than do acetonitrile, methanol and even pyridine, one of the best ligands in chlorophyllic systems. This exceptionally strong non-symmetrical axial ligation of the central Mg by acetate causes its out-of-plane displacement and deformation of the tetrapyrrole ring, thus facilitating the interaction with an incoming CuII complex. This mechanism is controlled by a keto-enol tautomerism of the chlorophyll isocyclic ring. Additionally, depending on solvent, acetate activates the incoming metal ions. These new insights allow to suggest a mechanism for the acetate method of metal exchange in tetrapyrrolic macrocycles, which resembles biological insertion of metal ions into porphyrins. It also provides a guideline for the design of more efficient methods for the metalation of porphyrins and related macrocycles.     

Soluble Flavanthrone Derivatives: Synthesis,Characterization, and Application to Organic Light‐Emitting Diodes

Simple modification of benzo[h]benz[5,6]acridino[2,1,9,8‐klmna]acridine‐8,16‐dione, an old and almost‐forgotten vat dye, by reduction of its carbonyl groups and subsequent O‐alkylation, yields solution‐processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and ?3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16‐dioctyloxybenzo[h]benz[5,6]acridino[2,1,9,8‐klmna]acridine ( FC‐8 ), the most promising compound, was solved. It crystallizes in space group P and forms π‐stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC‐8 have a strong tendency to self‐organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16‐Dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8‐klmna]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80 %. They show efficient electroluminescence, and can be used as guest molecules with a 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl host in guest/host‐type organic light‐emitting diodes. The best fabricated diodes showed a luminance of about 1900 cd m^?12, a luminance efficiency of about 3 cd A^?1, and external quantum efficiencies exceeding 0.9 %.     

Highly recoverable pyridinium-tagged Hoveyda-Grubbs pre-catalyst for olefin metathesis. Design of the boomerang ligand toward the optimal compromise between activity and reusability

Whereas the boomerang ligand of Hoveyda-Grubbs pre-catalysts can be modified by attachment of a pyridinium tag to its benzylidene moiety, a precise adjustment of the length of the spacer allows the optimum balance to be reached between the activity of the catalyst and its recoverability, exceeding 98% after 6 catalytic runs in the best case.     

Boryl (Hetero)aryne Precursors as Versatile Arylation Reagents: Synthesis through C?H Activation and Orthogonal Reactivity

(Pinacolato)boryl ortho‐silyl(hetero)aryl triflates are presented as a new class of building blocks for arylation. They demonstrate unique versatility by delivering boronate or (hetero)aryne reactivity chemoselectively in a broad range of transformations. This approach enables the unprecedented postfunctionalization of fluoride‐activated (hetero)aryne precursors, for example, as substrates in transition‐metal catalysis, and offers valuable new possibilities for aryl boronate postfunctionalization without the use of specialized protecting groups.     

Precise Molecular Fission and Fusion: Quantitative Self‐Assembly and Chemistry of a Metallo‐Cuboctahedron

Inspiration for molecular design and construction can be derived from mathematically based structures. In the quest for new materials, the adaptation of new building blocks can lead to unexpected results. Towards these ends, the quantitative single‐step self‐assembly of a shape‐persistent, Archimedean‐based building block, which generates the largest molecular sphere (a cuboctahedron) that has been unequivocally characterized by synchrotron X‐ray analysis, is described. The unique properties of this new construct give rise to a dilution‐based transformation into two identical spheres (octahedra) each possessing one half of the molecular weight of the parent structure; concentration of this octahedron reconstitutes the original cuboctahedron. These chemical phenomena are reminiscent of biological fission and fusion processes. The large 6 nm cage structure was further analyzed by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross‐section analysis. New routes to molecular encapsulation can be envisioned.