Synthesis of ortho‐Phenylenebis(guanidine) Derivatives with Potential Chirality

We report the synthesis and potential chirality of ortho‐phenylenebisguanidines (BGs) with substituents at C(3) and C(6). Guanidinylation of 3,6‐disubstituted benzene‐1,2‐diamines with 2‐chloro‐4,5‐dihydro‐1,3‐dimethyl‐1H‐imidazolium chloride gave the corresponding BGs. X‐Ray crystallography showed that the two guanidine moieties occupy different faces of the benzene ring, creating potential chirality, although optical resolution of ^tBu‐substituted BG by chiral HPLC failed. However, a methylated acyclic bisguanidinium salt (BGms) was obtained as a chiral crystal with a space group of P2₁2₁2₁.     

Dynamic Stereochemistry of M8Pd6 Supramolecular Cages Based on Metal-Center Lability for Differential Chiral Induction,Resolution, and Recognition

A series of isostructural supramolecular cages with a rhombic dodecahedron shape have been assembled with distinct metal-coordination lability (M₈Pd₆-MOC-16, M=Ru²⁺, Fe²⁺, Ni²⁺, Zn²⁺). The chirality transfer between metal centers generally imposes homochirality on individual cages to enable solvent-dependent spontaneous resolution of Δ₈/Λ₈−M₈Pd₆ enantiomers; however, their distinguishable stereochemical dynamics manifests differential chiral phenomena governed by the cage stability following the order Ru₈Pd₆ > Ni₈Pd₆ > Fe₈Pd₆ > Zn₈Pd₆. The highly labile Zn centers endow the Zn₈Pd₆ cage with conformational flexibility and deformation, enabling intrigue chiral-Δ₈/Λ₈−Zn₈Pd₆ to meso-Δ₄Λ₄−Zn₈Pd₆ transition induced by anions. The cage stabilization effect differs from inert Ru²⁺, metastable Fe²⁺/Ni²⁺, and labile Zn²⁺, resulting in different chiral-guest induction. Strikingly, solvent-mediated host–guest interactions have been revealed for Δ₈/Λ₈−(Ru/Ni/Fe)₈Pd₆ cages to discriminate the chiral recognition of the guests with opposite chirality. These results demonstrate a versatile procedure to control the stereochemistry of metal-organic cages based on the dynamic metal centers, thus providing guidance to maneuver cage chirality at a supramolecular level by virtue of the solvent, anion, and guest to benefit practical applications.     

Translation of helical chirality from polymer into monomer: supramolecular polymerization of a chirality-memory molecule with an asymmetric Pd(II) complex

A chirality-memorizing saddle-shaped porphyrin (1_2H) with 3,5-dipyridylphenyl side arms at the opposite meso positions underwent supramolecular polymerization in CH₂Cl₂ with a chiral Pd(II) complex of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (Pd^II(BINAP)), forming a ladder-shaped polymer (3_2H) with a prevailing one-handed helical chirality. When this polymer was poured into AcOH containing 1,3-bis(diphenylphosphino)propane (DPPP) as a decomplexing agent, 3_2H was depolymerized in a stereochemically retentive way to give optically active 1_2H, hydrogen-bonded with AcOH. Although a cyclodimeric reference of 3_2H, formed from 2_2H having two 3-pyridylphenyl meso substituents in conjunction with Pd^II(BINAP), behaved similar to 3_2H, the translation efficiency of helical chirality was lower than that in the case with 3_2H.     

P[(S,S,S)-CH3NCH(CH2Ph)CH2]3N: a new C3-symmetric enantiomerically pure proazaphosphatrane

A new approach for the synthesis of C₃-symmetric proazaphosphatranes with chirality at the bridging methylene positions is reported.     

Assemblies of 1D and 2D Copper(II) Chiral Coordination Polymers by Salicylaldehyde Schiff Bases: Synthesis,Crystal Structures,and Magnetic Properties

Reaction of CuCl₂ · 2H₂O with chiral Schiff bases and sodium dicyanamide led to the formation of two chiral copper(II) coordination polymers, namely [Cu₄(L¹)₂(dca)₄]_n ( 1 ) and [Cu₂(L²)(μ‐Cl)(dca)(H₂O)]_n · nH₂O ( 2 ) {H₂L¹ = (1R, 3S)‐N′,N′′‐bis[salicylidene]‐1,3‐diamino‐ 1,2,2‐trimethylcyclopentane, H₂L² = (1R, 3S)‐N′,N′′‐bis[3‐ethoxysalicylidene]‐1,3‐diamino‐ 1,2,2‐trimethylcyclopentane, dca = dicyanamide}. Both complexes were structurally characterized by elemental analyses, IR spectroscopy and single‐crystal X‐ray diffraction. Complex 1 exhibits a two‐dimensional polymeric structure formed by single dca bridging tetranuclear Cu₄ units. Complex 2 displays a left‐handed helical chain structure constructed from Cu₂ dimers with single dca bridges. The chirality of 1 and 2 was confirmed by circular dichroism (CD) measurements in solution. Both complexes exhibit strong antiferromagnetic couplings with J = –308(4) cm^–1 for 1 and J = –123(1) cm^–1 for 2 in 2–300 K.     

Yellow Circularly Polarized Luminescence from C1-Symmetrical Copper(I) Complexes

The synthesis of chiral C₁-symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |g_lum|=1.2×10⁻³. These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL-emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.     

Yellow Circularly Polarized Luminescence from C1‐Symmetrical Copper(I) Complexes

The synthesis of chiral C₁‐symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |g_lum|=1.2×10^?3. These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL‐emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.     

Lyotropic Supramolecular Helical Columnar Phases Formed by C3‐Symmetric and Unsymmetric Rigid Molecules

Unlike thermotropic liquid‐crystalline C₃‐symmetric molecules with flexible chains, the herein‐designed fully rigid three‐armed molecules (C₃‐symmetric and unsymmetric) create a fancy architecture for the formation of lyotropic liquid crystals in water. First, hollow columns with triple‐stranded helices, analogous to helical rosette nanotubes, are spontaneously constructed by self‐organization of the rigid three‐armed molecules. Then, the helical nanotubes arrange into hexagonal liquid‐crystalline phases, which show macroscopic chirality as a result of supramolecular chiral symmetry breaking. Interestingly, the helical nanotubes constructed by the fully rigid molecules are robust and stable over a wide concentration range in water. They are hardly affected by ionic defects at the molecular periphery, that is, further decoration of functional groups on the molecular arms can presumably be realized without changing the helical conformation. In addition, the formed columnar phases can be aligned macroscopically by simple shear and show anisotropic ionic conductivity, which suggests promising applications for low‐dimensional ion‐conductive materials.     

Selective Encapsulation and Chiral Induction of C60 and C70 Fullerenes by Axially Chiral Porous Aromatic Cages

Chiral induction has been an important topic in chemistry, not only for its relevance in understanding the mysterious phenomenon of spontaneous symmetry breaking in nature but also due to its critical implications in medicine and the chiral industry. The induced chirality of fullerenes by host–guest interactions has been rarely reported, mainly attributed to their chiral resistance from high symmetry and challenges in their accessibility. Herein, we report two new pairs of chiral porous aromatic cages (PAC), R- PAC-2 , S- PAC-2 (with Br substituents) and R- PAC-3 , S- PAC-3 (with CH₃ substituents) enantiomers. PAC-2 , rather than PAC-3 , achieves fullerene encapsulation and selective binding of C₇₀ over C₆₀ in fullerene carbon soot. More significantly, the occurrence of chiral induction between R- PAC-2 , S- PAC-2 and fullerenes is confirmed by single-crystal X-ray diffraction and the intense CD signal within the absorption region of fullerenes. DFT calculations reveal the contribution of electrostatic effects originating from face-to-face arene-fullerene interactions dominate C₇₀ selectivity and elucidate the substituent effect on fullerene encapsulation. The disturbance from the differential interactions between fullerene and surrounding chiral cages on the intrinsic highly symmetric electronic structure of fullerene could be the primary reason accounting for the induced chirality of fullerene.     

Gas Chromatographic Separation of Enantiomers on Optically Active Metal-Complex-Free Stationary Phases. New Analytical Methods (24)

If a stationary phase A employed in gas chromatography possesses a chemical affinity for substance B, which is to be separated, then the retention behavior is not only determined by the normal physical equilibrium between the gas and liquid phases but also by the chemical equilibrium A + B ? AB. If A and B are chiral and A is present in optically active form while B is a racemic mixture, then it is possible to achieve a gas chromatographic enantiomer resolution without the isolation of diastereomers: the energetically different diastereomeric associates A_R B_R and A_R B_S are formed rapidly and reversibly. This enantiospecific resolution principle was first demonstrated in 1966 by the quantitative resolution of racemic amino acid derivatives on optically active peptide phases in analogy to the well-known stereospecificity of enzymes. The anchoring of the chiral resolving agent to thermally stable polysiloxanes together with the employment of high resolution capillary columns and the use of appropriate derivatization strategies has led to the development of enantiomer resolution into a routine modern method for many classes of substances. The demonstration of enantiospecificity in the gas chromatographic separation process is of fundamental interest, and its systematic study can result in a significant contribution to the understanding of the molecular mechanism of “chiral recognition”. The gas chromatographic separation of enantiomers has also proven to be an accurate and sensitive method for the determination of the enantiomeric composition of natural products and products of enantioselective transformations (asymmetric syntheses, “chiral pool” transformations, kinetic resolutions, biomimetic reactions) and for the quantification of racemization, e.g. in the synthesis and hydrolysis of peptides. In any research program devoted to the phenomenon of chirality, the gas chromatographic separation of the enantiomers of volatile compounds constitutes an indispensable modern instrumental technique.     

Novel 1D Copper(II) Helical Chain Formed by Weak Coordination‐driven Self‐assembly: Synthesis,Structure, and Magnetic Property

A novel 1D copper(II) helical chain is constructed through the connection of tetranuclear copper(II) units [Cu₄(L)(Py)₄] (H₈L=N,N′‐(BINOL‐3,3′‐dicarboxyl)‐disalicylhydrazide, where BINOL is 1,1′‐binaphthalenyl‐2,2′‐diol, py=pyridine) by weak coordination‐driven self‐assembly, and characterized by IR, single crystal X‐ray diffraction, thermogravimetric analysis, and X‐ray power diffraction analysis. Interestingly, the helical chains are packed in an alternating left‐(M) and right‐handed (P) chirality, the orientation of the helices was determined by the axial chirality of the ligand. The complex shows antiferromagnetic interactions between the copper centers.     

Integrating Achiral and Chiral Organic Ligands in Zero-Dimensional Hybrid Metal Halides to Boost Circularly Polarized Luminescence

Chiral zero-dimensional hybrid metal halides (0D HMHs) could combine excellent optical properties and chirality, making them promising for circularly polarized luminescence (CPL). However, chiral 0D HMHs with efficient CPL have been rarely reported. Here, we propose an efficient strategy to achieve simultaneously high photoluminescence quantum yield (PLQY) and large dissymmetry factor (g_lum), by integrating achiral and chiral ligands into 0D HMHs. Specifically, three pairs of chiral 0D hybrid indium-antimony chlorides are synthesized by combing achiral guanidine with three types of chiral methylbenzylammonium-based derivatives as the organic cations. These chiral 0D HMHs exhibit near-unity PLQY and large g_lum values up to around ±1×10⁻². The achiral guanidine ligand is not only essential to crystallize these hybrid indium-antimony chlorides to achieve near-unity PLQYs, but also greatly enhances the chirality induction from organic ligands to inorganic units in these 0D HMHs. Furthermore, the choice of different chiral ligands can modify the strength of hydrogen bonding interactions in these 0D HMHs, to maximize their g_lum values. Overall, this study provides a robust way to realize efficient CPL in chiral HMHs, expanding their applications in chiroptical fields.     

Remote Control of the Planar Chirality in Peptide‐Bound Metallomacrocycles and Dynamic‐to‐Static Planar Chirality Control Triggered by Solvent‐Induced 310‐to‐α‐Helix Transitions

The dynamic planar chirality in a peptide‐bound Ni^II‐salphen‐based macrocycle can be remotely controlled. First, a right‐handed (P)‐3₁₀‐helix is induced in the dynamic helical oligopeptides by a chiral amino acid residue far from the macrocyclic framework. The induced planar chirality remains dynamic in chloroform and acetonitrile, but is almost completely locked in fluoroalcohols as a result of the solvent‐induced transition of the peptide chains from a 3₁₀‐helix to a wider α‐helix, which freezes the rotation of the pendant peptide units around the macrocycle.     

Dynamic Chirality Control of tropos DPCB‐digold Skeleton by Chiral Binaphthyldicarboxylate

The planar 3,4‐diphosphinidenecyclobutene (DPCB) can be remarkably twisted into a C₂‐type helical structure by dual coordination of a AuCl moiety. A prompt chirality control of the twisted DPCB skeleton ligated by the digold units affords the enantiopure structure by exchanging the chloride ligands for chiral [1,1′‐binaphthalene]‐2,2′‐dicarboxylate. The chirality of the diaurated 2,2′‐bis(diphenylphosphanyl)‐1,1′‐biphenyl (BIPHEP) system can be controlled prior to that of DPCB. Mixing of a DPCB‐bis(chlorogold) complex with the chiral silver salt dynamically leads to a single diastereomer, which was characterized by the ³¹P NMR spectrum and the CD couplet patterns in the visible (DPCB) area. The absolute configuration of the singly induced helical structure was assigned by the theoretical CD spectra determined by TD‐DFT calculations. Intramolecular alkoxycyclization of hexa‐4,5‐dien‐1‐ol catalyzed by the asymmetric DPCB‐digold structure were also attempted.     

Synthesis,structural, and retrostructural analysis of helical dendronized poly(1‐naphthylacetylene)s

Structural and retrostructural analysis of chiral, nonracemic ( poly [(3,4,5)dm8G1‐1EN] ), and achiral ( poly[(3,4,5)12G1‐1EN] ) poly(1‐naphthylacetylene)s demonstrates new design principles for helical dendronized polyarylacetylenes. The oblate cylindrical dendronized polymers self‐organize in a c2mm centered rectangular columnar (Φ_r‐c) lattice. An all cis‐polyene backbone microstructure with very high cisoid character is introduced to rationalize features from small‐ and wide‐angle X‐ray diffraction experiments. More compact helical conformations are ideal for efficient communication or amplification of chirality over long distances. Peripheral chiral tails select a preferred helical screw sense of the polyene backbone. In solution, the preferred helical conformation persists over a wide temperature range. In bulk, the naphthyl moiety facilitates a longer correlation length for helical order compared to an analogous minidendritic poly(phenylacetylene). These attributes suggest that the naphthyl moiety may be better suited for expressing helical chirality in monolayer domains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4974–4987, 2007     

Controllable Macroscopic Chirality of Coordination Polymers through pH and Anion-Mediated Weak Interactions

Helical architectures with controllable helical sense bias have recently attracted considerable interest for mimicking biological helices and developing novel chiral materials. Coordination polymers (CPs), composed of metal ion nodes and organic linkers, are intriguing systems showing tunable structures and functions. However, CPs with helical morphologies have rarely been explored so far. Particularly, chirality inversion through external stimulus has not been achieved in helical CPs. In this work, we carried out an in-depth investigation on the self-assembly of 1D gadolinium(III) phosphonate CPs using GdX₃ (X=Cl, Br, I) and Gd(RSO₃) (R=CH₃, C₆H₅, CF₃) as metal sources and R-(1-phenylethylamino)methyl phosphonic acid (R-pempH₂) as ligand. Superhelices were formed by precise control of the interchain interactions through different intercalated anions. Furthermore, the twisting direction of superhelices could be controlled by synergistic effect of anions and pH. This study may provide a new route to fabricate helical nanostructures of CPs with a desirable chiral sense and help understand the inner mechanism of the self-assembly process of macroscopic helical structures of molecular systems.     

Chirality and Order in Binary Molecular Crystals of Inert Cobalt(III) Complexes

Starting from the enantiomerically pure and racemic chiral Lewis bases 1‐phenylethylamine and 1‐(1‐naphthyl)ethylamine inert cobalt(III) complexes of the general composition Co(Hdmg)₂(lig)X (Hdmg = dimethylglyoximate; lig = Lewis base; X = CN, NCO, NO₂) were synthesized and characterized by single crystal X‐ray diffraction. The enantiopure complexes were used as building blocks for the synthesis of binary crystals. Solid solutions resulted from cocrystallizing isomorphous compounds of equal chirality whereas complexes of opposite chirality formed well‐ordered heterochiral solids with efficient packing. Two binary crystals of the latter type could be studied by X‐ray diffraction: Cocrystallization of two isomorphous phenylethylamine derivatives gave a quasiracemic solid. Starting from two non‐isomorphous naphthylethylamine complexes of opposite chirality cocrystals with an unexpected composition were obtained: Their asymmetric unit comprises four independent complex molecules in a 3:1 ratio between the constituents.     

A Carbon Dioxide Bubble-Induced Vortex Triggers Co-Assembly of Nanotubes with Controlled Chirality

It is challenging to prepare co-organized nanotube systems with controlled nanoscale chirality in an aqueous liquid flow field. Such systems are responsive to a bubbled external gas. A liquid vortex induced by bubbling carbon dioxide (CO₂) gas was used to stimulate the formation of nanotubes with controlled chirality; two kinds of achiral cationic building blocks were co-assembled in aqueous solution. CO₂-triggered nanotube formation occurs by formation of metastable intermediate structures (short helical ribbons and short tubules) and by transition from short tubules to long tubules in response to chirality matching self-assembly. Interestingly, the chirality sign of these assemblies can be selected for by the circulation direction of the CO₂ bubble-induced vortex during the co-assembly process.     

Isostructural Three‐Dimensional Covalent Organic Frameworks

Herein, we reported the designed synthesis of three isostructural three‐dimensional covalent organic frameworks (3D COFs) with ‐H, ‐Me, or ‐F substituents, which have similar crystallinity and topology. Their crystal structures were determined by continuous rotation electron diffraction (cRED), and all three 3D COFs were found to adopt a fivefold interpenetrated pts topology. More importantly, the resolution of these cRED datasets reached up to 0.9–1.0 Å, enabling the localization of all non‐hydrogen atomic positions in a COF framework directly by 3D ED techniques for the first time. In addition, the precise control of the pore environments through the use of different functional groups led to different selectivities for CO₂ over N₂. We have thus confirmed that polycrystalline COFs can be definitely studied to the atomic level as other materials, and this study should also inspire the design and synthesis of 3D COFs with tailored pore environments for interesting applications.     

Tuning the Chirality of Block Copolymers: From Twisted Morphologies to Nanospheres by Self‐Assembly

New advances into the chirality effect in the self‐assembly of block copolymers (BCPs) have been achieved by tuning the helicity of the chiral‐core‐forming blocks. The chiral BCPs {[N?P(R)‐O₂C₂₀H₁₂]_200?x[N?P(OC₅H₄N)₂]_x}‐b‐ [N?PMePh]₅₀ ((R)‐O₂C₂₀H₁₂=(R)‐1,1′‐binaphthyl‐2,2′‐dioxy, OC₅H₄N=4‐pyridinoxy (OPy); x=10, 30, 60, 100 for 3 a – d , respectively), in which the [N?P(OPy)₂] units are randomly distributed within the chiral block, have been synthesised. The chiroptical properties of the BCPs ([α]_D vs. T and CD) demonstrated that the helicity of the BCP chains may be simply controlled by the relative proportion of the chiral and achiral (i.e., [N?P(R)‐O₂C₂₀H₁₂] and [N?P(OPy)₂], respectively) units. Thus, although 3 a only contained only 5 % [N?P(OPy)₂] units and exhibited a preferential helical sense, 3 d with 50 % of this unit adopted non‐preferred helical conformations. This gradual variation of the helicity allowed us to examine the chirality effect on the self‐assembly of chiral and helical BCPs (i.e., 3 a – c ) and chiral but non‐helical BCPs (i.e., 3 d ). The very significant influence of the helicity on the self‐assembly of these materials resulted in a variety of morphologies that extend from helical nanostructures to pearl‐necklace aggregates and nanospheres (i.e., 3 b and 3 d , respectively). We also demonstrate that the presence of pyridine moieties in BCPs 3 a – d allows specific decoration with gold nanoparticles.