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The marriage of heterocyclic compounds with ferrocene has proven to be an extremely fruitful field of research. In fact, in the last years, several ferrocene‐embedded heterocyclic compounds have been reported. In some cases, the synergistic combination of the properties of the heterocyclic and metallacyclic motifs provides to the fused systems interesting applications. This Review summarizes the major advances in the synthesis of ferrocene‐fused nitrogen heterocyclic compounds and their applications, particularly in asymmetric catalysis. [ABSTRACT FROM AUTHOR]

Cationic triangulenes, and related helicenes, constitute a rich class of dyes and fluorophores, usually absorbing and emitting light at low energy, in the orange to red domains. Recently, to broaden the scope of applications, regioselective late‐stage functionalizations on these core moieties have been developed. For instance, with the introduction of electron‐donating groups (EDGs), important bathochromic shifts are observed pushing absorptions towards or in the near‐infrared (NIR) spectral domain while emissive properties disappear essentially completely. Herein, to upset this drawback, acetylene derivatives of cationic diazaoxa triangulenes (DAOTA) and [4]helicenes are prepared (16 examples). Contrary to other EDG‐functionalized derivatives, C≡C− functionalized products remain broadly fluorescent, with red‐shifted absorptions (Δλabs up to 25 nm) and emissions (Δλem up to 73 nm, ΦPL up to 51 %). Quite interestingly, a general dynamic stereoisomerism phenomenon is evidenced for the compounds derived from achiral DAOTA cores. At low temperature in 1H NMR spectroscopy (218 K), N−CH2 protons become diastereotopic with chemical shifts differences (Δδ) as high as +1.64 ppm. The signal coalescence occurs around 273 K with a barrier of ∼12 kcal mol−1. This phenomenon is due to planar chiral conformations (Sp and Rp configurations), induced by the geometry of the alkyl (n‐propyl) side‐chains next to the acetylenic substituents. Ion pairing studies with Δ‐TRISPHAT anion not only confirm the occurrence of the chiral conformations but evidence a moderate but definite asymmetric induction from the chiral anion onto the cations. Finally, DFT calculations offer a valuable insight on the geometries, the corresponding stereodynamics and also on the very large difference in NMR for some of the diastereotopic protons. [ABSTRACT FROM AUTHOR]

Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]paracyclophane ([2.2]PCP) lead to optical‐active chiral macrocycles with intriguing properties. X‐ray crystal analysis revealed aesthetic necklace‐shaped structures and size‐dependent packages with long‐range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82 %, and the fluorescent color varies with ring size. In addition, size‐dependent chiroptical properties with moderately large CPL dissymmetry factor of 10−3 and CPL brightness in the range of 30–40 M−1 cm−1 were observed. [ABSTRACT FROM AUTHOR]

With the aim of finding and characterizing new simple organic molecules (SOM) generating circularly polarized luminescence (CPL), we test here nine [2]paracyclo[2](5,8)‐quinoliphane derivatives, whose circular dichroism (CD) spectra were previously measured at short wavelengths in a study encompassing also OR and VCD (CD in the IR). Completion of the CD spectra is carried out with attention paid to weaker and longer wavelength features. The observed signs of the CPL spectra are compared to the signs of the CD band at the longest wavelength and are found coincident except in two cases. The magnitudes of dissymmetry ratios g in luminescence are of the order 10−3, like the corresponding |g| values for the absorption case. TD‐DFT calculations for the two simplest cases provide details on the molecular orbitals involved in the transitions responsible for the observed signals of these molecules. The calculations allow us to provide also a first explanation of the two observed behaviors of the |glum|/|gabs| ratios. [ABSTRACT FROM AUTHOR]

[2.2]Paracyclophane (PCP) and its derivatives have attracted growing widespread interest in recent years due to their unique chemical structures, specific photophysical properties and potential chiroptical activities, especially in the study of circularly polarized luminescence (CPL). Among the CPL‐active small organic molecules, the introduction of a PCP skeleton with planar chirality is one of the most effective strategies to obtain emitters with both high photoluminescence quantum yields (PLQYs) and luminescent dissymmetry factors (glum). At present, the development of CPL emitters based on the PCP skeleton is still limited and only a few molecular design strategies have been reported. This review summarizes and discusses the corresponding reports, and the emitters are sorted according to their chemical structures. It is expected that this review can provide researchers with a practical perspective in CPL studies and can provide inspiration for future research on CPL. [ABSTRACT FROM AUTHOR]

Despite the increasing number of applications based on halogen bond (XB), asymmetric catalysis purely based on such supramolecular interactions still remains a huge challenge. The first step toward its development is the design of appropriate XB chiral donor molecules with good catalytic properties. In this context, we report the synthesis of a series of iodinated compounds based on the triazole or triazolium ring and possessing the planar chirality of ferrocene. Their XB donor property was attested by X‐ray diffraction analysis, showing short I⋅⋅⋅N and I⋅⋅⋅F interactions in the triazole‐based derivatives and in the tetrafluoroborate salt of a idodotriazolium, respectively. The potential of these compounds to act as XB‐based catalysts was demonstrated in the aza‐Diels‐Alder reaction involving an imine and a diene. Whereas triazole‐based derivatives were inactive in this reaction, the triflate salts of iodotriazoliums delivered the expected cycloadduct with high yield. [ABSTRACT FROM AUTHOR]

"Chirality" governs many fundamental properties in chemistry and biochemistry. While early investigations on stereochemistry are primarily dedicated to static chirality, there is an increasing interest in the field of dynamic chirality (chiral switches). These chiral switches are essential in controlling the directionality in molecular motors. Dynamic chiralities are equally crucial in switchable stereoselectivity, switchable asymmetric catalysis and enantioselective separation. Herein, we limit our discussion to recent advances on stimuli‐induced chiroptical switching of axial, helical, and planar chirality in response to external stimuli. We also discuss a few examples of applications of the switchable chirality. [ABSTRACT FROM AUTHOR]

Optically active cyclic dimer, trimer, and tetramer, in which the p‐arylene‐ethynylenes were stacked, were prepared using enantiopure 4,7,12,15‐tetrasubstituted [2.2]paracyclophane as the chiral building block. All molecules exhibited clear Cotton effects in their absorption bands with mirror image spectra, and the signals of the longest wavelengths of the (Rp)‐ and (Sp)‐isomers were positive and negative, respectively. Their circularly polarized luminescence (CPL) signs corresponded with the those of the first Cotton effect. For all molecules, molecular orbitals were localized in one of the stacked p‐arylene‐ethynylenes in the excited states, resulting in a similar photoluminescence behavior. Although the cyclic dimer did not emit CPL, the cyclic trimer and tetramer exhibited intense CPL emissions with a relatively high dissymmetry factor in the order of 10−3. Their optical and chiroptical properties were reproduced by time‐dependent density functional theory calculations. [ABSTRACT FROM AUTHOR]

Metal-catalyzed [2+2+2] cycloaddition is a powerful tool that allows rapid construction of functionalized 6-membered carbo- and heterocycles in a single step through an atom-economical process with high functional group tolerance. The reaction is usually regio- and chemoselective although selectivity issues can still be challenging for intermolecular reactions involving the cross-[2+2+2] cycloaddition of two or three different alkynes and various strategies have been developed to attain high selectivities. Furthermore, enantioselective [2+2+2] cycloaddition is an efficient means to create central, axial, and planar chirality and a variety of chiral organometallic complexes can be used for asymmetric transition-metal-catalyzed inter- and intramolecular reactions. This review summarizes the recent advances in the field of [2+2+2] cycloaddition. 1 Introduction 2 Formation of Carbocycles 2.1 Intermolecular Reactions 2.1.1 Cyclotrimerization of Alkynes 2.1.2 [2+2+2] Cycloaddition of Two Different Alkynes 2.1.3 [2+2+2] Cycloaddition of Alkynes/Alkenes with Alkenes/Enamides 2.2 Partially Intramolecular [2+2+2] Cycloaddition Reactions 2.2.1 Rhodium-Catalyzed [2+2+2] Cycloaddition 2.2.2 Molybdenum-Catalyzed [2+2+2] Cycloaddition 2.2.3 Cobalt-Catalyzed [2+2+2] Cycloaddition 2.2.4 Ruthenium-Catalyzed [2+2+2] Cycloaddition 2.2.5 Other Metal-Catalyzed [2+2+2] Cycloaddition 2.3 Totally Intramolecular [2+2+2] Cycloaddition Reactions 3 Formation of Heterocycles 3.1 Cycloaddition of Alkynes with Nitriles 3.2 Cycloaddition of 1,6-Diynes with Cyanamides 3.3 Cycloaddition of 1,6-Diynes with Selenocyanates 3.4 Cycloaddition of Imines with Allenes or Alkenes 3.5 Cycloaddition of (Thio)Cyanates and Isocyanates 3.6 Cycloaddition of 1,3,5-Triazines with Allenes 3.7 Cycloaddition of Aldehydes with Enynes or Allenes/Alkenes 3.8 Totally Intramolecular [2+2+2] Cycloaddition Reactions 4 Conclusion [ABSTRACT FROM AUTHOR]

The synthesis and crystal structures of three new disubstituted [13]-macrodilactones, namely, trans-4,8-dimethyl-1,10-dioxacyclotridec-5-ene-2,9-dione, C13H20O4, I, cis-4-(4-bromophenyl)-13-methyl-1,10-dioxacyclotridec-5-ene-2,9-dione C18H21BrO4, II, and trans-11-methyl-4-phenyl-1,10-dioxacyclotridec-5-ene-2,9-dione, C18H22O4, III, are reported and their conformations are put in the context of other [13]-macrodilactone structures reported previously. Together, they show that the number, location, and relative disposition of groups attached at the termini of planar units of the [13]-macrodilactones subtly influence their aspect ratios.

Two optically active molecules were prepared using enantiopure planar chiral [2.2]paracyclophane as chiral building blocks, in which π‐electron systems were stacked at 120° to form a V‐shaped structure. The optical and chiroptical properties of the synthesized molecules were investigated experimentally and theoretically. The chiroptical properties depended strongly on the orientation of the stacked π‐electron systems; in other words, these properties could be regulated by changing the orientation of the stacked π‐electron systems. [ABSTRACT FROM AUTHOR]

Planar‐chiral transition metal complexes are useful chiral auxiliaries in organic and organometallic chemistry, and they have been utilized as chiral ligands, chiral catalysts, or chiral building blocks, etc. Despite the importance of such planar‐chiral species in asymmetric synthesis, their preparation in optically active forms is still a challenging problem. Indeed, reported examples of catalytic enantioselective synthesis of planar‐chiral complexes have been rare, and this has been a developing area in this field. In this personal account, recent results from our research group on the catalytic asymmetric synthesis of various planar‐chiral transition metal complexes are summarized. The asymmetric ring‐closing metathesis reactions catalyzed by the well‐defined molybdenum‐alkylidene species are powerful methods to control the planar chirality in ferrocenes, ruthenocenes, (η6‐arene)chromium complexes, and (η5‐cyclopentadienyl)manganese(I) complexes. Application of the enantiomerically enriched complexes obtained by our methods is described as well. [ABSTRACT FROM AUTHOR]

Two kinds of optically active V‐shaped molecules were synthesized from enantiopure disubstituted and tetrasubstituted [2.2]paracyclophane as chiral building blocks. The p‐arylene‐ethynylene‐type π‐electron systems in these species were stacked at an angle of 60°, and although the two molecules consisted of the same π‐electron system, the orientations of these systems were different. In addition, their optical properties were almost identical, while in contrast, significant differences were observed between their chiroptical properties. It was therefore suggested that circularly polarized luminescence behavior could be controlled by adjusting the orientation of the stacked π‐electron systems. [ABSTRACT FROM AUTHOR]

Multinuclear metal complexes have seen tremendous progress in synthetic advances, their versatile structural features, and emerging applications. Here, we conceptualize Metal‐to‐Metal distance modulation in cyclophanyl metal complexes by bridging ligand design employing the co‐facially stacked cyclophanyl‐derived pseudo‐geminal, ‐ortho, ‐meta, and ‐para constitutional isomers grafted with N‐, O‐, and P‐ containing chelates that allow the installation of diverse (hetero)metallic moieties in a distance‐defined and spatially‐oriented relation to one another. Metal‐to‐Metal distance modulation and innate transannular "through‐space" π–π electronic interactions via the co‐facially stacked benzene rings in cyclophanyl‐derived complexes as well as their specific stereochemical structural features (element of planar chirality) are crucial factors that contribute to the tuning of structure‐property relationships, which stand at the very center from the perspective of cooperative effects in catalysis as well as emerging material applications. [ABSTRACT FROM AUTHOR]

The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured for the enantiomers of [1]rotaxane 1. These experimental spectra have been analyzed using predicted VCD and ECD spectra for (S, Rmp) or (S, Smp) diastereomers using density functional theory. This comparison allowed for a definitive assignment of the absolute configuration of 1. [ABSTRACT FROM AUTHOR]

Mechanically Interlocked Molecules (MIMs), such as catenanes, knots, and rotaxanes, are a class of molecules that possess mechanical bonds. These bonds constitute an entanglement in space between components of the MIMs that cannot be separated without breaking a participating covalent bond. Although it is possible to synthesize chiral MIMs with covalent stereogenic centers, this new bond opens up the possibilities of axial, planar and helical chirality, as well as topologically chiral compounds. A growing number of chiral MIMs have been investigated and employed in numerous applications, ranging from sensing to catalysis. While the investigation of the properties of MIMs is highly developed, it is also essential to study their chiroptical properties. In this review, we focus on the chiroptical properties of chiral MIMs. We discuss their electronic circular dichroism (ECD) since these properties have been analyzed in some detail in relation to their structures and stereochemistry. Although only a few examples have been described to date, we discuss the encouraging circularly polarized luminescence (CPL) properties of MIMs. The review also includes a recent study of vibrational circular dichroism (VCD) in mechanically planar chiral rotaxanes suggesting that this technique is a promising tool for analyzing the structures of MIMs. The study of the chiroptical properties of MIMs can have a large impact on their use in materials science or as catalysts. One of the key advantage of chiral MIMs is that they provide a means of generating efficient chiroptical switches that have a bright future in the context of multiple applications. [ABSTRACT FROM AUTHOR]

The stability of magnetism in reduced dimensions has become a major scientific agenda in the pursuit of implementing magnetic nanostructures as functional components in spintronic devices. Methods to probe and control magnetization states of such structures in a deterministic manner include use of spin polarized currents, photon absorption, and relatively recently, electric fields that tailor magnetoelectric coupling in multiferroic based structures. In theory, a short electric pulse is able to generate localized magnetic fields that can couple to the local magnetic dipoles electrodynamically. Here, using the Landau–Lifshitz–Gilbert formalism of magnetism dynamics combined with continuum Maxwell relations, the response of a ferromagnetic permalloy nanodisc to nanosecond electric field pulses is studied. The dynamics of the magnetic order of the nanodiscs during this process are examined and discussed. Ferromagnet nanodiscs, when below a critical size and in the absence of any external field, relax to a vortex phase as the ground state due to the demagnetizing field. Simulations demonstrate that the planar chirality of such a ferromagnet nanodisc can be switched via a time‐wise asymmetric electric field pulse on the order of a few ns duration that generates radially varying tangential magnetic fields. These fields couple to the vortex state of the nanodisc ferromagnet electrodynamically, revealing an effective and robust method to control chirality. [ABSTRACT FROM AUTHOR]

We investigate the properties and characteristics of planar Ti/TiOx/Ti junctions, which consist of transverse TiOx lines drawn on Ti test patterns. Junctions are elaborated by means of local anodic oxidation using atomic force microscopy. An irreversible morphological transformation occurring in a reproducible manner is observed when these planar junctions are electrically stressed under ambient atmosphere. Structural and chemical analyses based on transmission electron microscopy techniques reveal the extension of the initial amorphous TiOx into a crystalline rutile phase. This irreversible transformation is proven to vanish completely if the electrical stress occurs under vacuum atmosphere. Finally, we carry out temperature dependent electrical measurements in order to elucidate their conduction mechanism: Schottky emission above an ultra-low potential barrier is assumed to dominate under vacuum atmosphere whereas ionic conduction seems to prevail in air. [ABSTRACT FROM AUTHOR]

We present a theoretical and experimental study of electrodynamics of a planar spiral superconducting resonator of a finite length. The resonator is made in the form of a monofilar Archimedean spiral. By making use of a general model of inhomogeneous alternating current flowing along the resonator and specific boundary conditions on the surface of the strip, we obtain analytically the frequencies fn of resonances which can be excited in such system. We also calculate corresponding inhomogeneous RF current distributions ψn(r) , where r is the coordinate across a spiral. We show that the resonant frequencies and current distributions are well described by simple relationships fn = f1n and ψn(r) ≃ ?sin[πn(r/Re)2] , where n = 1, 2... and Re is the external radius of the spiral. Our analysis of electrodynamic properties of spiral resonators' is in good agreement with direct numerical simulations and measurements made using specifically designed magnetic probe and laser scanning microscope. [ABSTRACT FROM AUTHOR]

In this report, we describe a series of cyclophanyl‐derived mono‐ and binuclear N,C‐palladacycles by regioselective ortho‐palladation of amine‐functionalized [2.2]paracyclophanes. Employing Pd(OAc)2 followed by LiCl and with the subsequent modular treatment of Ph3P, Cy3P, and (Ph2PCH2)2, this strategy allows to prepare stable cyclophanyl‐derived planar and central chiral N,C‐palladacycles in a highly selective manner. The regioselective ortho‐palladation mono‐ and bimetallic product formation was analyzed by detailed spectroscopic techniques, mass spectrometry and unambiguously confirmed by single‐crystal X‐ray analysis. [ABSTRACT FROM AUTHOR]

The last step of on-surface synthesis of graphene nanoribbons (GNR) includes also cyclodehydrogenation.[22-24] Starting with polyanthrylene polymers, annealing to 600 K causes partial cyclodehydrogenation, and annealing at 670 K causes formation of planar ribbons. As the distal ends of both enantiomers spiral up away from the center, C-C coupling and dehydrogenation leads to planar coronocoronene ( B 2 b ) enantiomers, which aggregate upon cooling into homochiral domains, that is, into a 2D conglomerate. Keywords: chirality; helicenes; polyaromatic hydrocarbons; scanning tunneling microscopy; surface chemistry EN chirality helicenes polyaromatic hydrocarbons scanning tunneling microscopy surface chemistry 13523 13526 4 09/28/21 20210924 NES 210924 B Flattening helices while keeping the handedness b : On-surface cyclodehydrogenation of bishelicene enantiomers leads stereospecifically to ( I M i , I M i ) and ( I P i , I P i ) chiral planar polyaromatic hydrocarbons. Once the dehydrogenation starts on one side of the molecule, the chirality of the product is fixed, thus explaining the stereospecificity. [Extracted from the article]

Optically active conjugated molecules bearing one-handed helical structures, in which two [4]helicenes or two phenanthrenes are stacked at terminal benzene moieties, were prepared using enantiopure [2.2]paracyclophane as a chiral scaffold. The obtained molecules exhibited excellent chiroptical properties such as circularly polarized luminescence with high disymmetry factors. Planar chiral pseudo-meta-disubstituted [2.2]paracyclophane was also optically resolved on the sub-gram-scale. [ABSTRACT FROM AUTHOR]

Chiral macrocycles possess significant value in chiral science and supramolecular chemistry. Pillararenes, as a class of relatively young supramolecular macrocyclic hosts, have been widely used for host–guest recognition and self-assembly. Since the position of substituents on the benzene rings breaks the molecular symmetry (symmetric plane and symmetric center), pillararenes possess planar chirality. However, it is a great challenge to synthesize stable and resolvable enantiomers because of the easy rotation of the phenylene group. In this review, we summarize the construction methods of resolvable chiral pillararenes. We also focus on their applications in enantioselective recognition, chiral switches, chirality sensing, asymmetric catalysis, circularly polarized luminescence, metal–organic frameworks, and highly permeable membranes. Finally, we discuss the future research perspectives in this field of pillararene-based planar chiral materials. We hope that this review will encourage more researchers to work in this exciting field. [ABSTRACT FROM AUTHOR]

A practical synthetic method for preparing bis‐(para)‐pseudo‐ortho and bis‐(para)‐pseudo‐meta type 4,7,12,15‐tetrasubstituted [2.2]paracyclophanes is reported. Regioselective double Rieche formylation was successfully applied to the corresponding dibromo[2.2]paracyclophanes under slightly modified conditions. Aldehydes reacted in an unknown direction with Rieche formylation agents, dichloromethyl methyl ether and titanium(IV) tetrachloride, leading to the formation of benzal chlorides. Formylated products were obtained after hydrolysis of these benzal chloride derivatives. Optical resolution was performed with the diastereomer method and (RP)‐4,12‐dibromo‐7,15‐diformyl[2.2]paracyclophane was successfully obtained in an enantiomerically pure form (99 % ee). Their synthetic utility is demonstrated with some exploratory transformations to access corresponding differently functionalized tetrasubstituted [2.2]paracyclophane derivatives. [ABSTRACT FROM AUTHOR]

This short review focuses on enantiopure planar chiral [2.2]paracyclophanes (pCps), a fascinating class of molecules that possess an unusual three‐dimensional core and intriguing physicochemical properties. In the first part of the review, different synthetic strategies for preparing optically active pCps are described. Although classical resolution methods based on the synthesis and separation of diastereoisomeric products still dominate the field, recent advances involving the kinetic resolution of racemic compounds and the desymmetrization of meso derivatives open up new possibilities to access enantiopure key intermediates on synthetically useful scales. Due to their advantageous properties including high configurational and chemical stability, [2.2]paracyclophanes are increasingly employed in various research fields, ranging from stereoselective synthesis to material sciences. The applications of [2.2]paracyclophanes in asymmetric organocatalysis are described in the second part of the review. While historically enantiopure pCps have been mainly employed by organic chemists as chiral ligands in transition‐metal catalysis, these compounds can also be used as efficient catalysts in metal‐free reactions and may inspire the development of new transformations in the near future. [ABSTRACT FROM AUTHOR]

Chirality at different levels is widely observed in nature, but the clue to connect it all together, and the way chirality transfers among different levels are still obscure. Herein, a l‐/d‐lysine‐based self‐assembly system was constructed, in which two‐step chirality transfer among three different levels was observed in aqueous solution. The chirality originated from the point chirality of amino acid derivatives l‐/d‐PyLys hydrochloride, and was transferred to the planar conformational chirality of water‐soluble pillar[5]arene pR‐/pS‐WP5. Then, with the aid of pR‐/pS‐WP5, nanoparticles were formed that exhibited L‐/R‐handed circularly polarized luminescence with a dissymmetry factor of up to ±0.001, arising from pyrene chiral excimers. This multilevel chirality transfer not only provides a perspective to trace potential clues, and to pursue certain ways by which the chirality transfers, but also offers a strategy to create controllable CPL emission in aqueous media. [ABSTRACT FROM AUTHOR]

Herein, we report a simple and convenient procedure to prepare para‐disubstituted [2.2]paracyclophanes in a straightforward manner. Our approach relies on a regioselective formylation of N‐substituted 4‐amino[2.2]paracyclophanes, which allows an easy access to a series of products incorporating a reactive aldehyde function para to the electron‐donating group. These compounds can be engaged in a variety of orthogonal late‐stage derivatization processes involving either the carbonyl group or the amine function, and can serve as precursors to rapidly access more complex paracyclophane derivatives. Control of planar chirality is also possible by performing a kinetic resolution of key racemic intermediates through asymmetric transfer hydrogenation. The formylation can be run on a synthetically useful scale, thus confirming the practical applicability of our method. [ABSTRACT FROM AUTHOR]

The simultaneous construction of two different chiralities via a simple operation poses considerable challenge. Herein a cationic gold-catalyzed asymmetric hydroarylation of ortho-alkynylaryl ferrocenes derivatives is developed, which enable the simultaneous construction of axial and planar chirality. The here identified TY-Phos derived gold complex is responsible for the high yield, good diastereoselectivity (>20:1 dr), high enantioselectivities (up to 99% ee) and mild conditions. The catalyst system also shows potential application in the synthesis of chiral biaryl compounds. The cause of high enantioselectivity of this hydroarylation is investigated with density functional theory caculation. The simultaneous construction of two different types of chiralities is challenging. Here, the authors report a cationic gold-catalyzed asymmetric hydroarylation of ortho-alkynylaryl ferrocene derivatives, which enabled the simultaneous construction of axial and planar chirality. [ABSTRACT FROM AUTHOR]

Auxetic metamaterials are architected structures that possess a unique property known as a negative Poisson's ratio. This remarkable characteristic enables them to expand or contract in a direction perpendicular to stretch or compression. Due to their exceptional attributes such as energy absorption and fracture resistance, these auxetic metamaterials hold great promise for various applications across multiple domains. However, the widespread development of these materials has been hindered by the absence of an efficient design method. Addressing this limitation, our work introduces a minimal 2D auxetic structure and a corresponding design approach that comprises two geometric transformations. This design method not only allows for the replication of existing auxetic structures but also facilitates the creation of novel structures. Additionally, it enables the classification of these structures into six distinct categories. To enhance the understanding and standardization of these structures, we propose a naming protocol and define their associated unit cell. Furthermore, we explore the possibilities of tessellations within this framework. Finally, we examine the auxetic structures from the perspective of surface strain, which is closely linked to the Poisson's ratio, the Bulk modulus and compressibility. • A chiral auxetic element is proposed as a base for all planar auxetic metamaterials. • Two geometrical transformations can create all existing and novel auxetic structures. • Auxetic structures are classified in six groups, with increasing order. • A naming protocol encodes the geometry and chirality of planar auxetic metamaterials. • High and low order auxetics can be tiled in the plane. [ABSTRACT FROM AUTHOR]

(2-Acetylferrocen-1-yl)boronic acid, [Fe(C5H5)(C7H8BO3)] or 2-C(O)CH3-1-B(OH)2–Fc [Fc = Fe(η5-C5H3)(η5-C5H5)], crystallizes in the centrosymmetric space group P21/n. The boronic acid functionality interacts via intramolecular hydrogen bonds with the acetyl group and with the –B(OH)2 functionality of an adjacent molecule. The resulting centrosymmetric dimer exhibits an anti-positioning of the ferrocenyl moieties towards the central B2O4 plane. Consequently, an (Rp,Sp)-, i.e. a meso configuration is present for this dimer. In the crystal, weak C—H...O hydrogen bonds consolidate the molecular packing.

The reaction between 2,5-bis(diphenylphosphinomethyl)pyrrole and Me3SiN3 gave the new pyrrole-based bis(phosphinimine) L1H in an excellent yield. L1H reacts with [CuCl(COD)]2, AgBF4, or AgOTf to give the corresponding two-coordinate mononuclear ionic complex formulated as [M{(L1H)-κ2N,N}]+[X]− where M = Cu and Ag; X = [CuCl2], BF4 or OTf. Their single crystal X-ray diffraction studies confirmed the two-coordinate geometry formed by the chelate bonding mode of L1H. These 10-membered metalacycles exhibit planar chirality and were also characterized by spectroscopic methods. In addition, in all three structures, there exists a hitherto unknown π-interaction between the pyrrole ring atoms and metal, represented as η2-(Cα–N) in the copper(I) complex, and η3-(Cα–N–Cα′) in the silver(I) complexes. These weak interactions were supported by DFT calculations in terms of their electron densities, non-covalent interaction plots and the decrease in the aromaticity of the pyrrole ring. [ABSTRACT FROM AUTHOR]

In recent years, transition-metal-catalyzed enantioselective C–H bond functionalization using chiral transient directing groups (cTDGs) or native directing groups (NDGs) has emerged as a powerful and attractive- synthetic approach to streamline the synthesis of chiral molecules-. This short review focuses on recent advances on imine-based cTDGs strategies and native amine and carboxylic acid directed strategies for the asymmetric functionalization of various C–H bonds. We have endeavored to highlight the great potential of this methodology and hope that this review will inspire further research in this area. 1 Introduction 2 Transient-Directing-Group-Enabled Enantioselective C–H Functionalization 2.1 Generation of Central Chirality 2.2 Generation of Axial Chirality 2.3 Generation of Planar Chirality 3 Native-Directing-Group-Enabled Enantioselective C–H Functionalization 3.1 Native Amines as Directing Groups 3.2 Native Carboxylic Acids as Directing Groups 4 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

[2.2]Paracyclophane (PCP) derivatives have been promising platforms to study the element of planar chirality and through‐space electronic communications in π‐stacked molecular systems. To access enantiomerically pure derivatives thereof, a kinetic resolution of 4‐acetyl[2.2]‐PCP employing a ruthenium‐catalyzed enantioselective hydrogenation process was developed. This method can be performed on a multigram‐scale and gives access to enantiomerically pure derivatives with planar and central chirality of (Rp)‐4‐acetyl‐PCP (≥97% ee, 43%) and (Sp,S)‐PCP derivatives (≥97% ee, 46%), which are useful intermediates for the synthesis of sterically demanding PCP‐based ligand/catalyst systems and chiral synthons for engineering cyclophane‐based chiroptical materials. [ABSTRACT FROM AUTHOR]

Stimuli-responsive intelligent molecular machines/devices are of current research interest due to their potential application in minimized devices. Constructing molecular machines/devices capable of accomplishing complex missions is challenging, demanding coalescence of various functions into one molecule. Here we report the construction of intelligent molecular chiroptical photoswitches based on azobenzene-fused bicyclic pillar[n]arene derivatives, which we defined as molecular universal joints (MUJs). The Z/E photoisomerization of the azobenzene moiety of MUJs induces rolling in/out conformational switching of the azobenzene-bearing side-ring and consequently leads to planar chirality switching of MUJs. Meanwhile, temperature variation was demonstrated to also cause conformational/chiroptical inversion due to the significant entropy change during the ring-flipping. As a result, photo-induced chiroptical switching could be prohibited when the temperature exceeded an upper limit, demonstrating an intelligent molecular photoswitch having over-temperature protection function, which is in stark contrast to the low-temperature-gating effect commonly encountered. Realizing overtemperature protection with a molecular device is challenging. Here, the authors demonstrate an overtemperature protection function by integrating thermo- and photoresponsive functions into a pillar[6]arene based pseudocatanene. [ABSTRACT FROM AUTHOR]

In the course of an ongoing synthetic project on cyclic diferrocenylphosphines, we obtained a group of planar–chiral diferrocenyl compounds useful as precursors for subsequent cyclization. Here we report the crystal structures of two symmetric compounds [(FcA)2(Ph)P], one of which contains four stereogenic centres (two C chiral and two planar chiral centres), i.e. 1,1′‐(phenylphosphanediyl)bis{(2Sp)‐2‐[(1R)‐1‐(acetyloxy)ethyl]ferrocene}, [Fe2(C5H5)2(C24H25O4P)], and the other phosphine sulfide is a purely planar–chiral compound (two planar chiral centres), i.e. bis[(2Sp)‐‐2‐ethenylferrocen‐1‐yl]phenylphosphane sulfide, [Fe2(C5H5)2(C20H17PS)]. Owing to the stereocentres present, reactions performed on [(FcA)2(Ph)P]‐type compounds strongly favour one ferrocene unit over the other due to diastereoselectivity. Furthermore, we present four related structures where the ferrocene units are not identical [(FcA)(FcB)(Ph)P]. These are {(2Sp)‐2‐[(1R)‐1‐(acetyloxy)ethyl]ferrocen‐1‐yl}[(2Sp)‐2‐ethenylferrocen‐1‐yl]phenyl‐(S)‐phosphine sulfide, [Fe2(C5H5)2(C22H21O2PS)], [(2Sp)‐2‐ethenylferrocen‐1‐yl]{(2Sp)‐2‐[(1R)‐1‐hydroxyethyl]ferrocen‐1‐yl}phenyl‐(S)‐phosphine sulfide, [Fe2(C5H5)2(C20H19OPS)], {(2Sp)‐2‐[(1R)‐1‐(acetyloxy)ethyl]ferrocen‐1‐yl}{(2Sp)‐2‐[(1R)‐1‐hydroxyethyl]ferrocen‐1‐yl}phenyl‐(R)‐phosphine sulfide, [Fe2(C5H5)2(C22H23O3PS)], and {(2Sp)‐2‐[(1R)‐1‐benzylamino)ethyl]ferrocen‐1‐yl}[(2Sp)‐2‐ethenylferrocen‐1‐yl]phenyl‐(S)‐phosphine sulfide, [Fe2(C5H5)2(C27H26NPS)]. All of the structures are accessible in one step from known precursors. [ABSTRACT FROM AUTHOR]

The deboronation of enantiomers of planar-chiral benzyl (3-formamido-1,2-dicarba-closo-dodecaboran-1-yl)acetate gave the individual (RP)- and (SP)-enantiomers (ee > 98%) of a new amino acid containing a nido-carborane fragment, (3-ammonio-7,8-dicarba-nido-undecaboran-7-yl)acetic acid. Chiral HPLC methods for the analysis of enantiomeric purity of this compound was developed. [ABSTRACT FROM AUTHOR]

After earlier unsuccessful attempts, this work reports the application of covalent templating for the synthesis of mechanically interlocked molecules (MiMs) bearing no supramolecular recognition sites. Two linear strands were covalently connected in a perpendicular fashion by a central ketal linkage. After subsequent attachment of the first strand to a template via temporary benzylic linkages, the second was linked to the template in a backfolding macrocyclization. The resulting pseudo[1]rotaxane structure was successfully converted to a [2]catenane via a second macrocyclization and cleavage of the ketal and temporary linkages. [ABSTRACT FROM AUTHOR]

Chiral zirconium(IV) double cage sandwich complex Zr(1)2 has been synthesized in one step from porphyrin cage H21. Zr(1)2 was obtained as a racemate, which was resolved by HPLC and the enantiomers were isolated in >99.5% ee. Their absolute configurations were assigned on the basis of X-ray crystallography and circular dichroism spectroscopy. Vibrational circular dichroism (VCD) experiments on the enantiomers of Zr(1)2 revealed that the chirality around the zirconium center is propagated throughout the whole cage structure. The axial conformational chirality of the double cage complex displayed a VCD fingerprint similar to the one observed previously for a related chiral cage compound with planar and point chirality. Zr(1)2 shows fluorescence, which is quenched when viologen guests bind in its cavities. The binding of viologen and dihydroxybenzene derivatives in the two cavities of Zr(1)2 occurs with negative allostery, the cooperativity factors α (= 4 K2/K') being as low as 0.0076 for the binding of N,N'-dimethylviologen. These allosteric effects are attributed to a pinching of the second cavity as a result of guest binding in the first cavity. [ABSTRACT FROM AUTHOR]

Significant recent contributions to the advancement of asymmetric organic synthesis featuring transformations of stoichiometric transition metal complexes are described. Studies that led to the development of powerful synthetic methodologies, as well as projects aimed at elucidation of relevant fundamental concepts, are included. A particular emphasis is placed on applications of complexes with planar chirality. [ABSTRACT FROM AUTHOR]

An unprecedented study of the application of planar chiral compounds in antiviral pesticide development is reported. A class of multifunctional planar chiral ferrocene derivatives bearing α-amino phosphonate moieties was synthesized. These compounds, exhibiting superior optical purities, were subsequently subjected to antiviral evaluations against the notable plant pathogen potato virus Y (PVY). The influence of the absolute configurations of the planar chiral compounds on their antiviral bioactivities was significant. A number of these enantiomerically enriched planar chiral molecules demonstrated superior anti-PVY activities. Specifically, compound ( S p , R )- 9n displayed extraordinary curative activities against PVY, with a 50% maximal effective concentration (EC 50 ) of 216.11 μg/mL, surpassing the efficacy of ningnanmycin (NNM, 272.74 μg/mL). The protective activities of compound ( S p , R )- 9n had an EC 50 value of 152.78 μg/mL, which was better than that of NNM (413.22 μg/mL). The molecular docking and defense enzyme activity tests were carried out using the planar chiral molecules bearing different absolute configurations to investigate the mechanism of their antiviral activities against PVY. ( S p , R )- 9n . Investigations into the mechanisms revealed that the planar chiral configurations of the compounds played pivotal roles in the interactions between the PVY-CP molecules and could augment the activities of the defense enzymes. This study contributes substantial insights into the role of planar chirality in defending plants against viral infections.S p , R )- 9o , and NMM all showed stronger affinities to the PVY-CP than the ( R p , S )- 9n . Investigations into the mechanisms revealed that the planar chiral configurations of the compounds played pivotal roles in the interactions between the PVY-CP molecules and could augment the activities of the defense enzymes. This study contributes substantial insights into the role of planar chirality in defending plants against viral infections.

We describe the synthesis of planar-chiral diferrocene compounds 4, 7 and 12, intended as key precursors for a new family of asymmetric catalyst ligands with less complex structures than their popular equivalents. In contrast to conventional 1,2-disubstituted ferrocenes containing center-chiral and planar-chiral elements, these compounds are purely planar-chiral due to the absence of α-substiuted ethyl groups. The title compounds 4, 7 and 12 were obtained from known precursors in 87%, 59% and 60% yields, respectively.

We present a synthesis of the title compound, a homochiral diferroceno cycle intended for use in asymmetric catalysis. We present a hydrovinylation protocol, which allows the production of the title compound in two steps from a known diferrocenyl precursor. We obtained one of two possible diastereomers selectively and propose a plausible regio- and stereoselective reaction mechanism.

Optically active X‐shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH–π interactions, thereby leading to the expression of the axial chirality, i.e. propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X‐shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate ΦPL and a large glum value in the order of 10−3 at 25 °C, in solution. In contrast, at −120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality. [ABSTRACT FROM AUTHOR]

Chirality transfer is widely observed in life processes, and many artificial chiral transfer systems have been developed. In these systems, chiral information is transferred from chiral inducers to chiral acceptors by a direct chiral induction process and a direct chiral memorization process. We have developed ternary nondirect chiral transfer systems based on pillar[5]arenes, in which a third factor was introduced as a regulator. The planar chirality of an acceptor was induced and memorized by a chiral inducer with precise control by a regulator. In the chiral induction period, the feed sequence of the chiral inducer and regulator affected the chiral induction behavior of the chiral acceptor. The chiral memory ability of the acceptor was substantially improved by the combined action of the chiral inducer and regulator. [ABSTRACT FROM AUTHOR]

Molecular motors and switches change conformation under the influence of an external stimulus, e.g. light. They can be incorporated into functional systems, allowing the construction of adaptive materials and switchable catalysts. Here, we present two molecular motor-functionalized porphyrin macrocycles for future photo-switchable catalysis. They display helical, planar and point chirality, and are diastereomers, which differ in the relative orientation of the motor and macrocyclic components. Fluorescence, UV-vis, and 1H NMR experiments reveal that the motor-functionalized macrocycles can bind and thread different variants of viologen guests, including a one-side blocked polymeric one of 30 repeat units. The latter feature indicates that the motor systems can find the open end of a polymer chain, thread on it, and move along the chain to eventually bind at the viologen trap, opening possibilities for catalytic writing on single polymer chains via chemical routes. Molecular motors and switches change conformation under the influence of an external stimulus and can be incorporated into functional systems, allowing the construction of adaptive materials and switchable catalysts. Here, the authors present two molecular motor-functionalized porphyrin macrocycles for future photo-switchable catalysis. [ABSTRACT FROM AUTHOR]

The development of novel methodologies for catalytic enantioselective functionalization reactions enabled by chiral transient directing groups is accompanying in a paradigm shift in the field of asymmetric synthesis. In particular, these highly atom‐ and step‐economic enantioinduction processes commonly proceed either via enantioselective C−H functionalization, or via enantioselective hydroarylation of the pro‐chiral substrates generating point, axial or planar chirality. The use of the transient directing group strategy in C−H functionalizations precludes the stoichiometric installations and removal of directing groups and enables efficient, more compatible and economical chemical routes. This minireview highlights asymmetric transition‐metal‐catalyzed methodologies involving chiral transient directing groups together with the scope, utility and future perspective of the field. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structures of three new disubstituted [13]-macrodilactones, namely, trans-4,8-dimethyl-1,10-dioxacyclotridec-5-ene-2,9-dione, C13H20O4, I, cis-4-(4-bromophenyl)-13-methyl-1,10-dioxacyclotridec-5-ene-2,9- dione C18H21BrO4, II, and trans-11-methyl-4-phenyl-1,10-dioxacyclotridec-5- ene-2,9-dione, C18H22O4, III, are reported and their conformations are put in the context of other [13]-macrodilactone structures reported previously. Together, they show that the number, location, and relative disposition of groups attached at the termini of planar units of the [13]-macrodilactones subtly influence their aspect ratios. [ABSTRACT FROM AUTHOR]

Cycloruthenation is a well known process in organometallic ruthenium chemistry. In this work, we report unprecedented cycloruthenated rhenium bis-arene compounds with planar chirality. In a two-step process, the reaction of acetyl-pyridine with [Re(η6-C6H6)2]+ introduced a pyridinyl-methanol ligand at one of the arene rings. Coordination of [Ru(CO)2Cl2] led to cycloruthenation, and the products were obtained as two diastereomeric pairs of enantiomers. Under basic pH conditions, the two pairs of enantiomers undergo spontaneous and reversible dimerization. The cycloruthenated monomers were fully characterized, and the dimerization process was studied by NMR, IR spectroscopy, and DFT calculations. [ABSTRACT FROM AUTHOR]

Cycloruthenation is a well known process in organometallic ruthenium chemistry. In this work, we report unprecedented cycloruthenated rhenium bis-arene compounds with planar chirality. In a two-step process, the reaction of acetyl-pyridine with [Re(η6-C6H6)2]+ introduced a pyridinyl-methanol ligand at one of the arene rings. Coordination of [Ru(CO)2Cl2] led to cycloruthenation, and the products were obtained as two diastereomeric pairs of enantiomers. Under basic pH conditions, the two pairs of enantiomers undergo spontaneous and reversible dimerization. The cycloruthenated monomers were fully characterized, and the dimerization process was studied by NMR, IR spectroscopy, and DFT calculations. [ABSTRACT FROM AUTHOR]