Synthesis of Cycloparaphenyleneacetylene via Alkyne Metathesis: C70 Complexation and Copper-Free Triple Click Reaction

A Cycloparaphenylene Acetylene as Potential Precursor for an Armchair Carbon Nanotube

The bottom-up synthesis of carbon nanotubes (CNTs) is a long-standing goal in synthetic chemistry. Producing CNTs with defined lengths and diameters would render these materials and thus their fascinating properties accessible in a controlled way. Inspired by a recently reported synthesis of armchair graphene sheets that relied on a benzannulation and Scholl oxidation of a poly(p-phenylene ethynylene), the same strategy is applied on a cyclic substrate with a short, but well defined CNT as target structure. Herein we report the synthesis of a derivatized [12]cycloparaphenylene acetylene ([12]CPPA) that was accessible employing a Sonogashira macrocyclization. The obtained macrocycle is the largest [n]CPPA reported to date and displays bright turquoise fluorescence with a large quantum yield of 77 %. The [12]CPPA can be transformed by a 12-fold benzannulation that converts each alkyne to a naphthalene and therefore allows formation of an armchair [12,12]CNT precursor. The final 72-fold Scholl oxidation to the [12,12]CNT turned out to be challenging and its optimization requires an improved synthetic strategy to produce large quantities of the final precursor. The developed approach poses a potential break through strategy for the production of CNTs and certainly incentivizes synthetic chemists to apply the same methodology for various conjugated macrocycles.

Host-Guest Chemistry in Binary and Ternary Complexes Utilizing π-Conjugated Carbon Nanorings

The carbon nanorings, possessing a radial π system, have garnered significant attention primarily due to their size-dependent photophysical properties and the presence of a unique curved π-conjugated cavity. This is evidenced by the rapid proliferation of publications. Furthermore, the integration of building blocks into CPP skeletons can confer [n]CPPs with novel and exceptional photophysical and electronic characteristics, as well as chiral properties and host-guest interactions, thereby augmenting the diversity of [n]CPPs. Notably, the curved π surface structures and concave cavity of carbon nanorings enable them to host aromatic or non-aromatic guests with a complementarily curved surface, resulting in interesting binary or ternary complexes. This review provides a comprehensive treatment of literature reports on binary and ternary complexes, focusing on both their host-guest interactions and properties. It is important to note that the scope of this review is limited to host-guest chemistry in binary and ternary complexes based on π-conjugated carbon nanorings.

A π-extended molecular belt with selective binding capability for fullerene C70

A molecular belt incorporating naphthalene moieties, featuring an ellipsoidal cavity, was precisely engineered through bottom-up synthesis. Its pre-arranged geometry exhibits excellent complementarity to fullerene C70, resulting in remarkable selective binding ability (K = 1.3 × 106 M-1) for C70 compared to C60 (K = 176 M-1), forming a 1 : 1 complex. This superiority was unequivocally demonstrated by the single crystal structure of the complex, which revealed outstanding concave-convex shape complementarity between the two components. This highlights the potential application of molecular belts in the purification and separation of fullerenes.

Tris-Azo Triangular Paraphenylenes: Synthesis and Reversible Interconversion into Radial π-Conjugated Macrocycles

We report the synthesis of cycloparaphenylene derivatives featuring tris-azo groups. The smaller derivative, [3]cycloazobenzene, adopts a triangular all-cis form and exhibits thermally and photochemically stable characteristics due to significant ring strain as well as symmetric Kagome-patterned crystal packing. In contrast, the as-synthesized [3]cycloazobenzene with three biphenylene bridges adopts a triangular all-cis form, which undergoes photoinduced isomerization, leading to a photostationary state. Interestingly, the addition of an excess of acid selectively leads to the formation of an all-trans form. DFT calculations reveal that the interconversion from a triangular to a circular shape correlates with an increase in HOMO and a decrease in LUMO, characteristics intrinsic to radial π-conjugated systems.

Rhenium Alkyne Catalysis: Sterics Control the Reactivity

Metathesis reactions, including alkane, alkene, and alkyne metatheses, have their origins in the fundamental understanding of chemical reactions and the development of specialized catalysts. These reactions stand as transformative pillars in organic chemistry, providing efficient rearrangement of carbon-carbon bonds and enabling synthetic access to diverse and complex compounds. Their impact spans industries such as petrochemicals, pharmaceuticals, and materials science. In this work, we present a detailed mechanistic study of the Re(V) catalyzed alkyne metathesis through density functional theory calculations. Our findings are in agreement with the experimental evidence from Jia and co-workers and unveil critical factors governing catalyst performance. Our work not only enhances our understanding of alkyne metathesis but also contributes to the broader landscape of catalytic processes, facilitating the design of more efficient and selective transformations in organic synthesis.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Recent update on the electroactive oligopyrrolic macrocyclic hosts with a Bucky-ball heart

Supramolecular chemistry is a multidisciplinary research area mostly associated with the investigation of host-guest interactions within intricate three-dimensional (3D) molecular architectures held together reversibly by various non-covalent interactions. Continuous efforts to develop such kinds of complex host-guest systems with designer oligopyrrolic macrocyclic receptors are a rapidly growing research domain, which is deeply involved in applied supramolecular chemistry research. These host-guest supramolecular complexes can be constructed by combining suitable electron-rich oligopyrrolic donors (as a host) with complementary electron-poor guests (as acceptors), held together by the ionic force of attraction triggered by intermolecular charge/electron transfer (CT/ET) transitions. Some of these resulting CT/ET ensembles are potential candidates for the construction of efficient optoelectronic materials, optical sensors, molecular switches, etc. In this Feature Article we aim to focus on these supramolecular ensembles composed by size and shape complementary electroactive oligopyrrolic molecular containers, which are suitable for spherical guest (e.g., buckminsterfullerene) complexation. We also provide a "state-of-the-art" overview on plausible applications of these particular host-guest systems. Our aim is to cover only specific electron-rich tetrathiafulvalene (TTF)-based oligopyrrolic receptors, e.g., TTF-calix[4]pyrroles, TTF-cryptands, TTF-porphyrins and exTTF-porphyrin-based molecular motifs reported to date, along with a brief outlining of their "functional behaviour" in materials chemistry research.

Ring Expansion Alkyne Metathesis Polymerization

The synthesis, characterization, and preliminary activity of an unprecedented tethered alkylidyne tungsten complex for ring expansion alkyne metathesis polymerization (REAMP) are reported. The tethered alkylidyne 7 is generated rapidly by combining alkylidyne W(CtBu)(CH2tBu)(O-2,6-i-Pr2C6H3)2 (6) with 1 equiv of an yne-ol proligand (5). Characterized by NMR studies and nuclear Overhauser effect spectroscopy, complex 7 is a dimer. Each metal center contains a tungsten-carbon triple bond tethered to the metal center via an alkoxide ligand. The polymerization of the strained cycloalkyne 3,8-didodecyloxy-5,6-dihydro-11,12-didehydrodibenzo[a,e]-[8]annulene, 8, to generate cyclic polymers was demonstrated. Size exclusion chromatography (SEC) and intrinsic viscosity (η) measurements confirm the polymer's cyclic topology.

Experimental and theoretical elucidation of SPAAC kinetics for strained alkyne-containing cycloparaphenylenes

Tuning strained alkyne reactivity via organic synthesis has evolved into a burgeoning field of study largely focused on cyclooctyne, wherein physical organic chemistry helps guide rational molecular design to produce molecules with intriguing properties. Concurrent research in the field of carbon nanomaterials has produced new types of strained alkyne macrocycles, such as cycloparaphenyleneacetylenes, that possess uniquely curved aromatic π systems but hover on the edge of stability. In 2018, we introduced a strained alkyne scaffold that marries the synthetic accessibility and stability of cyclooctyne with the curved π system of carbon nanomaterials. These molecules are strained alkyne-containing cycloparaphenylenes (or [n+1]CPPs), which have been shown to possess size-dependent reactivity as well as the classic characteristics of the unfunctionalized parent CPP, such as a tunable HOMO-LUMO gap and bright fluorescence for large sizes. Herein, we elaborate further on this scaffold, introducing two modifications to the original design and fully characterizing the kinetics of the strain-promoted azide-alkyne cycloaddition (SPAAC) for each [n+1]CPP with a model azide. Additionally, we explain how electronic (the incorporation of fluorine atoms) and strain (a meta linkage which heightens local strain at the alkyne) modulations affect SPAAC reactivity via the distortion-interaction computational model. Altogether, these results indicate that through a modular synthesis and rational chemical design, we have developed a new family of tunable and inherently fluorescent strained alkyne carbon nanomaterials.

A Metallofullertube of Ce2 @C100 with a Carbon Nanotube Segment: Synthesis, Single-Molecule Conductance and Supramolecular Assembly

Tubular fullerenes can be considered as end-capped carbon nanotubes with accurate structure, which are promising nanocarbon materials for advanced single-molecule electronic devices. Herein, we report the synthesis and characterization of a metallofullertube Ce₂ @D₅ (450)-C₁₀₀ , which has a tubular C₁₀₀ cage with a carbon nanotube segment and two fullerene end-caps. As there are structure correlations between tubular Ce₂ @D₅ (450)-C₁₀₀ and spherical Ce₂ @I_h -C₈₀ , their structure-property relationship has been compared by means of experimental and theoretical methods. Notably, single-molecule conductance measurement determined that the conductivity of Ce₂ @D₅ (450)-C₁₀₀ was up to eight times larger than that of Ce₂ @I_h -C₈₀ . Furthermore, supramolecular assembly of Ce₂ @D₅ (450)-C₁₀₀ and a [12]CPP nanohoop was investigated, and theoretical calculations revealed that metallofullertube Ce₂ @D₅ (450)-C₁₀₀ adopted a "standing" configuration in the cavity of [12]CPP. These results demonstrate the special nature of this kind of metallofullertube.

Alkyne Metathesis with d2 Re(V) Alkylidyne Complexes Supported by Phosphino-Phenolates: Ligand Effect on Catalytic Activity and Applications in Ring-Closing Alkyne Metathesis

A family of d² Re(V) alkylidyne complexes bearing two decorated phosphino-phenolates (POs) and a labile pyridine ligand were prepared that can efficiently promote alkyne metathesis reactions in toluene. The relative activity of these complexes varies with the PO ligands. Complexes with an electron-rich metal center have a higher activity. Ligand exchange experiments suggest that the pyridine ligands of the Re(V) alkylidynes with more electron-donating PO ligands are more labile and are more easily released to generate catalytically active species. However, complexes with electron-withdrawing PO ligands are more air-stable than those with electron-donating PO ligands. These Re(V) alkylidyne catalysts can promote the homometathesis of functionalized internal alkyl- and aryl-alkynes, as well as ring-closing alkyne metathesis (RCAM) of methyl-capped diynes, forming macrocycles with a ring size ≥12 efficiently for concentrations ≤5 mM. These reactions represent the first examples of RCAM mediated by non-d⁰ alkylidyne complexes. The Re(V) alkylidyne catalysts tolerate a wide range of functional groups including ethers, esters, ketones, aldehydes, alcohols, phenols, amines, amides, and heterocycles. Moreover, the catalytic RCAM reactions promoted by robust Re(V) alkylidyne catalysts could also proceed normally in wet toluene.

Molecular tetrominoes: selective masking of the donor π-face to control the configuration of donor-acceptor complexes

Understanding the doping mechanism in organic semiconductors and generating molecular design rules to control the doping process are crucial for improving the performance of organic electronics. Even though controlling the location and orientation of the dopant along the semiconductor backbone is an important step in the doping mechanism, studies in this direction are scarce as it is a challenging task. To address this, herein, we incorporated π-face masked (strapped) units in 1,4-bis(phenylethynylene)benzene (donor) to control the acceptor (dopant) location along the trimer, donor-acceptor binding strength, and acceptor ionization. Two strapped trimers, PCP and CPC, are synthesized with control over the location of the strapped repeat unit in the trimer. The trimers are complexed with the 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) acceptor in solution. DFT calculations show that DDQ residing on the non-strapped repeat unit (the percentage of this configuration is at least ca. 73%) has the highest binding energy for both PCP and CPC. The percentage of dopant ionization is higher in the case of strapped trimers (PCP and CPC) compared to that of linear control trimers (PLP and LPL) and the completely non-strapped (PPP) trimer. The percentage of dopant ionization increased by 15 and 59% in the case of PCP and CPC respectively compared to that of PPP.

Third-order nonlinear optical property contrast as self-assembly recognition for nanorings⊃C60

High third-order NLO contrasts tuned by self-assembly can be applied for the recognition of host–guest nanorings⊃C60.

Macrocyclic host molecules with aromatic building blocks: the state of the art and progress

Macrocyclic host molecules play the central role in host-guest chemistry and supramolecular chemistry. The highly structural symmetry of macrocyclic host molecules can meet people's pursuit of aesthetics in molecular design, and generally means a balance of design, synthesis, properties and applications. For macrocyclic host molecules with highly symmetrical structures, building blocks, which could be described as repeat units as well, are the most fundamental elements for molecular design. The structural features and recognition ability of macrocyclic host molecules are determined by the building blocks and their connection patterns. Using different building blocks, different macrocyclic host molecules could be designed and synthesized. With decades of developments of host-guest chemistry and supramolecular chemistry, diverse macrocyclic host molecules with different building blocks have been designed and synthesized. Aromatic building blocks are a big family among the various building blocks used in constructing macrocyclic host molecules. In this feature article, the recent developments of macrocyclic host molecules with aromatic building blocks were summarized and discussed.

Scalable synthesis of [8]cycloparaphenyleneacetylene carbon nanohoop using alkyne metathesis

Large scale synthesis of cycloparaphenyleneacetylenes has been challenging due to low macrocyclization yields and harsh aromatization methods that often decompose strained alkynes. Herein, a cis-stilbene-based building block is subjected to alkyne metathesis macrocylization. The following sequence of alkene-selective bromination and dehydrobromination afforded a [8]cycloparaphenyleneacetylene derivative in high yield with good scalability. X-Ray crystal structure and computational analysis revealed a unique same-rim conformation for the eight methyl groups on the nanohoop.

Monocyclic and Dicyclic Dehydro[20]annulenes Integrated with Perylene Diimide

A novel kind of monocyclic and dicyclic dehydro[20]annulenes exhibiting specific sizes and topologies from regioselective unilateral ortho-diethynyl PDI, is developed by Cu-catalyzed Glaser-Hay homo-coupling and cross-coupling. Through the integration of electron-deficient PDI chromophores into the dehydroannulene scaffolding, these macrocycles exhibit intense and characteristic absorption properties and the degenerated LUMO levels. The single-crystal X-ray diffraction analysis unambiguously revealed unique porous supramolecular structures, which display micropore characteristics with surface area of 120.74 m²  g^-1 . A moderate electron mobility of 0.05 cm²  V^-1  s^-1 for chlorine-free dehydro[20]annulene based on micrometer-sized single-crystalline transistors was witnessed. The porous and yet semiconducting features signify the prospects of PDI-integrated dehydroannulenes in organic optoelectronics.

Impact of Ligands and Metals on the Formation of Metallacyclic Intermediates and a Nontraditional Mechanism for Group VI Alkyne Metathesis Catalysts

The intermediacy of metallacyclobutadienes as part of a [2 + 2]/retro-[2 + 2] cycloaddition-based mechanism is a well-established paradigm in alkyne metathesis with alternative species viewed as off-cycle decomposition products that interfere with efficient product formation. Recent work has shown that the exclusive intermediate isolated from a siloxide podand-supported molybdenum-based catalyst was not the expected metallacyclobutadiene but instead a dynamic metallatetrahedrane. Despite their paucity in the chemical literature, theoretical work has shown these species to be thermodynamically more stable as well as having modest barriers for cycloaddition. Consequentially, we report the synthesis of a library of group VI alkylidynes as well as the roles metal identity, ligand flexibility, secondary coordination sphere, and substrate identity all have on isolable intermediates. Furthermore, we report the disparities in catalyst competency as a function of ligand sterics and metal choice. Dispersion-corrected DFT calculations are used to shed light on the mechanism and role of ligand and metal on the intermediacy of metallacyclobutadiene and metallatetrahedrane as well as their implications to alkyne metathesis.

By-design molecular architectures via alkyne metathesis

Shape-persistent purely organic molecular architectures have attracted tremendous research interest in the past few decades. Dynamic Covalent Chemistry (DCvC), which deals with reversible covalent bond formation reactions, has emerged as an efficient synthetic approach for constructing these well-defined molecular architectures. Among various dynamic linkages, the formation of ethynylene linkages through dynamic alkyne metathesis is of particular interest due to their high chemical stability, linearity, and rigidity. In this review, we focus on the synthetic strategies of discrete molecular architectures (e.g., macrocycles, molecular cages) containing ethynylene linkages using alkyne metathesis as the key step, and their applications. We will introduce the history and challenges in the synthesis of those architectures via alkyne metathesis, the development of alkyne metathesis catalysts, the reported novel macrocycle structures, molecular cage structures, and their applications. In the end, we offer an outlook of this field and remaining challenges.

The recent synthesis of novel shape-persistent 2D and 3D molecular architectures via alkyne metathesis is reviewed and the critical role of catalysts is also highlighted.

Highly active alkyne metathesis catalysts operating under open air condition

Alkyne metathesis represents a rapidly emerging synthetic method that has shown great potential in small molecule and polymer synthesis. However, its practical use has been impeded by the limited availability of user-friendly catalysts and their generally high moisture/air sensitivity. Herein, we report an alkyne metathesis catalyst system that can operate under open-air conditions with a broad substrate scope and excellent yields. These catalysts are composed of simple multidentate tris(2-hydroxyphenyl)methane ligands, which can be easily prepared in multi-gram scale. The catalyst substituted with electron withdrawing cyano groups exhibits the highest activity at room temperature with excellent functional group tolerance (-OH, -CHO, -NO₂, pyridyl). More importantly, the catalyst provides excellent yields (typically >90%) in open air, comparable to those operating under argon. When dispersed in paraffin wax, the active catalyst can be stored on a benchtop under ambient conditions without any decrease in activity for one day (retain 88% after 3 days). This work opens many possibilities for developing highly active user-friendly alkyne metathesis catalysts that can function in open air.

Alkyne metathesis catalysts usually suffer from high moisture/air sensitivity, which limit their wide applicability. Here, the authors report efficient alkyne metathesis catalysts that can operate under open-air conditions with a broad functional group tolerance.

The shape selectivity of corannulene dimers based on concave-convex and convex-convex shape complementarity as hosts for C60 and C70

In the formation of noncovalent complexes, the stacking arrangements of corannulene and fullerene are diverse, most of which are combinations of multiple corannulenes and fullerene. Here, a composition ratio of 2 : 1 was selected for the complex between corannulene and fullerene (C60 and C70) to investigate the effects of different superposition modes, including concave-convex and convex-convex interactions, on the stability and third-order nonlinear optical (NLO) properties of the composite materials. It was found that the concave-convex interaction was stronger and it was reported to stabilize the charge-transfer (CT) complex more effectively than the convex-convex interaction. The dispersion range of the concave-convex interaction was larger than that of the convex-convex interaction, which is consistent with the interaction energy results. The packing design with the double convex-convex interactions exhibited the largest linear optical response and third-order NLO response, which showed that the convex-convex interaction was more likely to be excited and cause intermolecular CT as compared to the concave-convex interaction. This work confirmed that the packing arrangement significantly affected the NLO response and will advance the development of NLO crystals.

183 W NMR Spectroscopy Guides the Search for Tungsten Alkylidyne Catalysts for Alkyne Metathesis

Triarylsilanolates are privileged ancillary ligands for molybdenum alkylidyne catalysts for alkyne metathesis but lead to disappointing results and poor stability in the tungsten series. 1 H,183 W heteronuclear multiple bond correlation spectroscopy, exploiting a favorable 5 J-coupling between the 183 W center and the peripheral protons on the alkylidyne cap, revealed that these ligands upregulate the Lewis acidity to an extent that the tungstenacyclobutadiene formed in the initial [2+2] cycloaddition step is over-stabilized and the catalytic turnover brought to a halt. Guided by the 183 W NMR shifts as a proxy for the Lewis acidity of the central atom and by an accompanying chemical shift tensor analysis of the alkylidyne unit, the ligand design was revisited and a more strongly π-donating all-alkoxide ligand prepared. The new expanded chelate complex has a tempered Lewis acidity and outperforms the classical Schrock catalyst, carrying monodentate tert-butoxy ligands, in terms of rate and functional-group compatibility.

Chiral Macrocycles Having C3 Symmetry Resulting from Orientation of Thiophene Rings

An chiral Rh^II -catalyzed cyclooligomerization reaction of thiophenes having triazolyl and vinyl substituents at the 2- and 4-positions was studied. Structurally interesting cyclic trimers, having chirality that is ascribed only to the orientation of the 2,4-disubstituted thiophene rings, are obtained. The 2,4-disubstitution of the starting thiophene monomer allows production of each of the enantiomers. The observed electronic circular-dichroism spectra are in accord with those simulated by density-functional theory calculations.

Synthesis, Structures, and Properties of Highly Strained Cyclophenylene-Ethynylenes with Axial and Helical Chirality

Single and double cyclophenylene-ethynylenes (CPEs) with axial and helical chirality have been synthesized by the Sonogashira cross-coupling of di- and tetraethynyl biphenyls with a U-shaped prearomatic diiodoparaphenylene followed by reductive aromatization. X-ray crystallographic analyses and DFT calculations revealed that the CPEs possess highly twisted bent structures. Bend angles on the edge of the paraphenylene units were close to the value of [5]cycloparaphenylene (CPP)-the smallest CPP to date. The double and single CPEs possessed stable chirality despite flexible biphenyl structures because of the high strain in the diethynyl-paraphenylene moiety. In both the single and double CPEs, orbital interactions along the biphenyl axis were observed by DFT calculations in LUMO and LUMO+2 of the single CPE and LUMO+1 of the double CPE, which likely cause lowering of these orbital energies. Concerning chiroptical properties: boosting of the g_abs value was observed in the biphenyl-based double CPE, as well as the binaphthyl-based single CPE, compared to the biphenyl-based single CPE.

Synthesis, Structure, and Photophysical Properties of m-Phenylene-Embedded Cycloparaphenylene Nanorings

Five m-phenylene-embedded cycloparaphenylenes m₃[9]CPP 1-5 were synthesized by the platinum-mediated cyclooligomerization strategy with high overall yields. The structures of m₃[9]CPP 1-3 were determined by X-ray diffraction analysis. Compared to [9]CPP, m₃[9]CPP 1 caused a significant blueshift in the UV-vis absorption and fluorescence spectra. This result shows that the radial π-conjugation is distorted and partially interrupted. The photophysical properties of m₃[9]CPP 1 were further tuned by the introduction of various substituents for m₃[9]CPP 2-5. Methoxy group substitution at m-phenylene did not change the photophysical properties significantly. Replacement of m-phenylene by tetrafluoro-m-phenylene achieved a significant blueshift. When the carboxyl group was embedded at m-phenylene or the methoxy group was embedded at p-phenylene, significant redshifts were observed with blue color emission. Theoretical calculations revealed that the decrease in the HOMO-LUMO gap in m₃[9]CPP 4 and 5 is favorable for the redshift of the fluorescence spectrum.

Exploring Approaches for the Synthesis of Few-Layered Graphdiyne

Graphdiyne (GDY) is an emerging carbon allotrope in the graphyne (GY) family, demonstrating extensive potential applications in the fields of electronic devices, catalysis, electrochemical energy storage, and nonlinear optics. Synthesis of few-layered GDY is especially important for both electronic applications and structural characterization. This work critically summarizes the state-of-art of GDY and focuses on exploring approaches for few-layered GDY synthesis. The obstacles and challenges of GDY synthesis are also analyzed in detail. Recently developed synthetic methods are discussed such as i) the copper substrate-based method, ii) the chemical vapor deposition (CVD) method, iii) the interfacial construction method, and iv) the graphene-templated method. Throughout the discussion, the superiorities and limitations of different methods are analyzed comprehensively. These synthetic methods have provided considerable inspiration approaching synthesis of few-layered or single-layered GDY film. The work concludes with a perspective on promising research directions and remaining barriers for layer-controlled and morphology-controlled synthesis of GDY with higher crystalline quality.

The Supramolecular Chemistry of Strained Carbon Nanohoops

Since 1996, a growing number of strained macrocycles, comprising only sp² - or sp-hybridized carbon atoms within the ring, have become synthetically accessible, with the [n]cycloparaphenyleneacetylenes (CPPAs) and the [n]cycloparaphenylenes (CPPs) being the most prominent examples. Now that robust and relatively general synthetic routes toward a diverse range of nanohoop structures have become available, the research focus is beginning to shift towards the exploration of their properties and applications. From a supramolecular chemistry perspective, these macrocycles offer unique opportunities as a result of their near-perfect circular shape, the unusually high degree of shape-persistence, and the presence of both convex and concave π-faces. In this Minireview, we give an overview on the use of strained carbon-rich nanohoops in host-guest chemistry, the preparation of mechanically interlocked architectures, and crystal engineering.

Synthesis of a Macrocycle Bearing a Carbon Framework of [16]Cyclophenacene as a Carbon Nanobelt

A synthetic pathway to a functionalized tetrahydro[5]phenacene was developed, which served as a precursor, leading to a dehydrobenzo[32]annulene macrocycle containing four carbon-carbon triple bonds. The high efficiency of the macrocyclization step can be attributed to the structural rigidity of its immediate precursor. Hydrogenation of the four carbon-carbon triple bonds produced a macrocycle bearing a carbon framework of [16]cyclophenacene as the shortest macrocyclic belt-like structure of an (8,8)armchair carbon nanotube.

A tetrahedral molecular cage with a responsive vertex

Dynamic covalent chemistry (DCC) is a widely used method for the self-assembly of three-dimensional molecular architectures. The orthogonality of dynamic reactions is emerging as a versatile strategy for controlling product distributions in DCC, yet the application of this approach to the synthesis of 3D organic molecular cages is limited. We report the first system which employs the orthogonality of alkyne metathesis and dynamic imine exchange to prepare a molecular cage with a reversibly removable vertex. This study demonstrates the rational and controlled application of chemical orthogonality in DCC to prepare organic cages of expanded functionality which respond to chemical stimuli.

Size-Selective Synthesis of Large Cycloparaphenyleneacetylene Carbon Nanohoops Using Alkyne Metathesis

Size selective synthesis of large cycloparaphenyleneacetylene carbon nanohoops was achieved using alkyne metathesis. The large nanohoops were stable in ambient conditions due to their reduced strain. The nanohoops exhibited blue fluorescence with high quantum yields.

Thermally activated isomeric all-hydrocarbon molecular receptors for fullerene separation

A new all-hydrocarbon macrocycle, cyclo[8](1,3-(4,6-dimethyl)benzene) (CDMB-8) has been reported. As prepared, it exists in Cs symmetry and shows no interaction with fullerenes (e.g., C60 or C70). High temperature (573 K) treatment induces thermal conversion of the material to an isomeric conformer with D4d symmetry as a receptor for fullerene separation.

Unbiased Rotational Motions of an Ellipsoidal Guest in a Tight Yet Pliable Host

In the design of machinery such as steel bearings, a fundamental understanding of material characteristics provides an indispensable basis for the design. Although hydrocarbon cycloarylenes have started to be used for providing unique supramolecular bearings with anomalous dynamic behaviors, their fundamental understanding is immature. A unique property of the cycloarylene host is now reported: the cyclic host is so pliable that it tracks the orientational changes of the ellipsoidal guest, that is, C₇₀ fullerene. Unique structures of the complex were revealed by spectroscopic and crystallographic analyses, and additional theoretical investigations deepened our understanding by revealing the structural changes associated with unbiased rotational motions.

Well-Defined Alkyne Metathesis Catalysts: Developments and Recent Applications

Although alkyne metathesis has been known for 50 years, rapid progress in this field has mostly occurred during the last two decades. In this article, the development of several highly efficient and thoroughly studied alkyne metathesis catalysts is reviewed, which includes novel well-defined, in situ formed and heterogeneous systems. Various alkyne metathesis methodologies, including alkyne cross-metathesis (ACM), ring-closing alkyne metathesis (RCAM), cyclooligomerization, acyclic diyne metathesis polymerization (ADIMET), and ring-opening alkyne metathesis polymerization (ROAMP), are presented, and their application in natural product synthesis, materials science as well as supramolecular and polymer chemistry is discussed. Recent progress in the metathesis of diynes is also summarized, which gave rise to new methods such as ring-closing diyne metathesis (RCDM) and diyne cross-metathesis (DYCM).