Retraction Note: Living annulative π-extension polymerization for graphene nanoribbon synthesis.

This article has been retracted. Please see the Retraction Notice for more detail: https://doi.org/10.1038/s41586-020-2950-0 .

Living annulative π-extension polymerization for graphene nanoribbon synthesis.

The properties of graphene nanoribbons (GNRs)1-5-such as conductivity or semiconductivity, charge mobility and on/off ratio-depend greatly on their width, length and edge structure. Existing bottom-up methods used to synthesize GNRs cannot achieve control over all three of these parameters simultaneously, and length control is particularly challenging because of the nature of step-growth polymerization6-18. Here we describe a living annulative π-extension (APEX)19 polymerization technique that enables rapid and modular synthesis of GNRs, as well as control over their width, edge structure and length. In the presence of palladium/silver salts, o-chloranil and an initiator (phenanthrene or diphenylacetylene), the benzonaphthosilole monomer polymerizes in an annulative manner to furnish fjord-type GNRs. The length of these GNRs can be controlled by simply changing the initiator-to-monomer ratio, achieving the synthesis of GNR block copolymers. This method represents a type of direct C-H arylation polymerization20 and ladder polymerization21, activating two C-H bonds of polycyclic aromatic hydrocarbons and constructing one fused aromatic ring per chain propagation step.

π-Extended Rubrenes via Dearomative Annulative π-Extension Reaction.

Among a large variety of organic semiconducting materials, rubrene (5,6,11,12-tetraphenyltetracene) represents one of the most prominent molecular entities mainly because of its unusually high carrier mobility. Toward finding superior rubrene-based organic semiconductors, several synthetic strategies for related molecules have been established. However, despite its outstanding properties and significant attention in the field of materials science, late-stage functionalizations of rubrene remains undeveloped, thereby limiting the accessible chemical space of rubrene-based materials. Herein, we report on a late-stage π-extension of rubrene by dearomative annulative π-extension (DAPEX), leading to the generation of rubrene derivatives having an extended acene core. The Diels-Alder reaction of rubrene with 4-methyl-1,2,4-triazoline-3,5-dione occurred to give 1:1 and 1:2 cycloadducts which further underwent iron-catalyzed annulative diarylation. The thus-formed 1:1 and 1:2 adducts were subjected to radical-mediated oxidation and thermal cycloreversion to furnish one-side and two-side π-extended rubrenes, respectively. These π-extended rubrenes displayed a marked red shift in absorption and emission spectra, clearly showing that the acene π-system of rubrene was extended not only structurally but also electronically. The X-ray crystallographic analysis uncovered interesting packing modes of these π-extended rubrenes. Particularly, two-side π-extended rubrene adopts a brick-wall packing structure with largely overlapping two-dimensional face-to-face π-π interactions. Finally, organic field-effect transistor devices using two-side π-extended rubrene were fabricated, and their carrier mobilities were measured. The observed maximum hole mobility of 1.49 × 10-3 cm2V-1 s-1, which is a comparable value to that of the thin-film transistor using rubrene, clearly shows the potential utility of two-side π-extended rubrene in organic electronics.

Expanded [2,1][n]Carbohelicenes with 15- and 17-Benzene Rings.

Expanded carbohelicenes with structures fused to 15- and 17-benzene were successfully synthesized. Establishing a new synthetic strategy is crucial to realize the development of longer expanded [2,1][n]helicenes with a kekulene-like projection drawing structure. This article describes the sequential integration of the π-elongating Wittig reaction of functionalized phenanthrene units and ring-fusing Yamamoto coupling for the synthesis of [2,1][15]helicenes and [2,1][17]helicenes. X-ray crystallographic structures, photophysical properties, and density functional theory (DFT) calculations revealed the unique characteristics of the synthesized expanded helicenes. Furthermore, because of the high enantiomerization barrier derived from a wide-range intrahelix π-π interaction, the optical resolution of [2,1][17]helicene was successfully achieved, and chiroptical properties such as circular dichroism and circularly polarized luminescence were elucidated for the first time as enantiomers of pristine [2,1][n]helicene core.

Lithium-Mediated Mechanochemical Cyclodehydrogenation.

Cyclodehydrogenation is an essential synthetic method for the preparation of polycyclic aromatic hydrocarbons, polycyclic heteroaromatic compounds, and nanographenes. Among the many examples, anionic cyclodehydrogenation using potassium(0) has attracted synthetic chemists because of its irreplaceable reactivity and utility in obtaining rylene structures from binaphthyl derivatives. However, existing methods are difficult to use in terms of practicality, pyrophoricity, and lack of scalability and applicability. Herein, we report the development of a lithium(0)-mediated mechanochemical anionic cyclodehydrogenation reaction for the first time. This reaction could be easily performed using a conventional and easy-to-handle lithium(0) wire at room temperature, even under air, and the reaction of 1,1'-binaphthyl is complete within 30 min to afford perylene in 94% yield. Using this novel and user-friendly protocol, we investigated substrate scope, reaction mechanism, and gram-scale synthesis. As a result, remarkable applicability and practicality over previous methods, as well as limitations, were comprehensively studied by computational studies and nuclear magnetic resonance analysis. Furthermore, we demonstrated two-, three-, and five-fold cyclodehydrogenations for the synthesis of novel nanographenes. In particular, quinterrylene ([5]rylene or pentarylene), the longest nonsubstituted molecular rylene, was synthesized for the first time.

Synthesis of Heptagon-Containing Polyarenes by Catalytic C-H Activation.

Nanocarbons incorporating non-hexagonal aromatic rings - such as five-, seven-, and eight-membered rings - have various intriguing physical properties such as curved structures, unique one-dimensional packing, and promising magnetic, optical, and conductivity properties. Herein, we report an efficient synthetic approach to polycyclic aromatics containing seven-membered rings via a palladium-catalyzed intramolecular Ar-H/Ar-Br coupling. In addition to all-hydrocarbon scaffolds, heteroatom-embedded heptagon-containing polyarenes can be efficiently constructed with this method. Rhodium- and palladium-catalyzed sequential six- and seven-membered ring formations also afford complex heptagon-containing molecular nanocarbons from readily available arylacetylenes and biphenyl boronic acids. Detailed mechanistic analysis by DFT calculations showed the feasibility of seven-membered ring formation by a concerted metalation-deprotonation mechanism. This reaction can serve as a template for the synthesis of a wide range of seven-membered ring-containing molecular nanocarbons.

Noncovalent Modification of Cycloparaphenylene by Catenane Formation Using an Active Metal Template Strategy.

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π-conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π-conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2'-bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post-modification. Following the AMT strategy, the [9]CPP-bipyridine catenane was successfully synthesized through Ni-mediated aryl-aryl coupling. Catalytic C-H borylation/cross-coupling and metal complexation of the bipyridine macrocycle moiety, an effective post-functionalization method, were also demonstrated with the [9]CPP-bipyridine catenane. Single-crystal X-ray structural analysis revealed that the [9]CPP-bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions.

Infinitene: A Helically Twisted Figure-Eight [12]Circulene Topoisomer.

New forms of molecular nanocarbon particularly looped polyarenes adopting various topologies contribute to the fundamental science and practical applications. Here we report the synthesis of an infinity-shaped polyarene, infinitene (1) (cyclo[c.c.c.c.c.c.e.e.e.e.e.e]dodecakisbenzene), comprising consecutively fused 12-benzene rings forming an enclosed loop with a strain energy of 60.2 kcal·mol-1. Infinitene (1) represents a topoisomer of still-hypothetical [12]circulene, and its scaffold can be formally visualized as the outcome of the "stitching" of two homochiral [6]helicene subunits by both their ends. The synthetic strategy encompasses transformation of a rationally designed dithiacyclophane to cyclophadiene through the Stevens rearrangement and pyrolysis of the corresponding S,S'-bis(oxide) followed by the photocyclization. The structure of 1 is a unique hybrid of helicene and circulene with a molecular formula of C48H24, which can be regarded as an isomer for kekulene, [6,6]carbon nanobelt ([6,6]CNB), and [12]cyclacene. Infinitene (1) is a bench-stable yellow solid with green fluorescence and soluble to common organic solvents. Its figure-eight molecular structure was unambiguously confirmed by X-ray crystallography. The scaffold of 1 is significantly compressed as manifested by a remarkably shortened distance (3.152-3.192 Å) between the centroids of two π-π stacked central benzene rings and the closest C···C distance of 2.920 Å. Fundamental photophysical properties of 1 were thoroughly elucidated by UV-vis absorption and fluorescence spectroscopic studies and density functional theory calculations. Its configurational stability enabled separation of the corresponding enantiomers (P,P) and (M,M) by a chiral HPLC. Circular dichroism (CD) and circularly polarized luminescence (CPL) measurements revealed that 1 has moderate |gCD| and |gCPL| values.

Construction of Heptagon-Containing Molecular Nanocarbons.

Molecular nanocarbons containing heptagonal rings have attracted increasing interest due to their dynamic behavior, electronic properties, aromaticity, and solid-state packing. Heptagon incorporation can not only induce negative curvature within nanocarbon scaffolds, but also confer significantly altered properties through interaction with adjacent non-hexagonal rings. Despite the disclosure of several beautiful examples in recent years, synthetic strategies toward heptagon-embedded molecular nanocarbons remain relatively limited due to the intrinsic challenges of heptagon formation and incorporation into polyarene frameworks. In this Review, recent advances in solution-mediated and surface-assisted synthesis of heptagon-containing molecular nanocarbons, as well as the intriguing properties of these frameworks, will be discussed.

Step-Growth Annulative π-Extension Polymerization for Synthesis of Cove-Type Graphene Nanoribbons.

Graphene nanoribbons (GNRs), nanometer-wide strips of graphene, are attracting significant attention in materials science as candidates for next-generation carbon materials. As their physical properties mainly depend on their structures, the precise synthesis of structurally well-defined GNRs is highly desirable to control their properties. Herein, we report a step-growth annulative π-extension polymerization that allows for the rapid and modular synthesis of cove-type GNRs with pyrene and/or coronene diimide repeating units. The structures and photophysical properties of the separated GNRs were confirmed by various spectroscopic analyses. In addition, gas-blow-assisted uniform on-surface self-assembly of the GNRs was accomplished.

A Quest for Structurally Uniform Graphene Nanoribbons: Synthesis, Properties, and Applications.

Graphene nanoribbons are the class of next-generation carbon materials that are attracting many researchers in various research fields. Their unique properties, such as band gap, conductivity, carrier mobility, thermal conductivity, spin polarization, and on-off behavior, heavily depend on structural factors such as edge structure, width, and length. Therefore, the synthesis of graphene nanoribbons with control over these structural factors with atomic precision is crucially important. Among various synthetic approaches, bottom-up synthetic methods such as on-surface polymerizations and solution-phase polymerizations represent promising ways to control the width, length, and edge structure of graphene nanoribbons. In this Perspective, we introduce the recently reported bottom-up synthetic methods for graphene nanoribbons and the theoretical and experimental research on those physical properties and applications. Reviewing these researches along with highlighting advantages and limitations, we emphasize how structurally controlled synthesis is important and provides future outlooks in graphene nanoribbon science.

Synthesis of Nitrogen-Containing Polyaromatics by Aza-Annulative π-Extension of Unfunctionalized Aromatics.

Nitrogen-containing polycyclic aromatic compounds (N-PACs) are an important class of compounds in materials science. Reported here is a new aza-annulative π-extension (aza-APEX) reaction that allows rapid access to a range of N-PACs in 11-84 % yields from readily available unfunctionalized aromatics and imidoyl chlorides. In the presence of silver hexafluorophosphate, arenes and imidoyl chlorides couple in a regioselective fashion. The follow-up oxidative treatment with p-chloranil affords structurally diverse N-PACs, which are very difficult to synthesize. DFT calculations reveal that the aza-APEX reaction proceeds through the formal [4+2] cycloaddition of an arene and an in situ generated diarylnitrilium salt, with sequential aromatizations having relatively low activation energies. Transformation of N-PACs into nitrogen-doped nanographenes and their photophysical properties are also described.

Polycyclic Arene Synthesis by Annulative π-Extension.

Annulative π-extension (APEX) has emerged as a powerful and efficient synthetic method for the construction of polycyclic aromatic hydrocarbons, nanographenes, and π-extended fused heteroarenes. In contrast to classical multistep syntheses requiring substrate prefunctionalization, APEX reactions minimize the number of preparative steps by direct C-H activation of small aromatic templates. In this Perspective, we review recently reported APEX reactions to shed light on the utility, scope, and promise of this approach for next-generation syntheses of polycyclic arenes.

C-H Arylation of Phenanthrene with Trimethylphenylsilane by Pd/o-Chloranil Catalysis: Computational Studies on the Mechanism, Regioselectivity, and Role of o-Chloranil.

The transition-metal-catalyzed C-H arylation of aromatic hydrocarbons represents a useful and ideal method for the production of biaryls and multiarylated aromatic compounds. We have previously reported the palladium-catalyzed direct C-H arylation of polycyclic aromatic hydrocarbons, such as phenanthrene, pyrene, and corannulene with various organosilicon, -borane, and -germanium compounds. In these reactions, o-chloranil proved to be an essential and unique promoter (stoichiometrically as an oxidant) and arylation occurred exclusively at the K-region. Herein, we report our mechanistic investigation of Pd/o-chloranil catalysis in C-H arylation of phenanthrene with trimethylphenylsilane by computational calculations. The results revealed that C-H arylation occurs through a sequence of transmetalation, carbometalation, and trans-ß-hydrogen elimination steps. In addition, the triple role of o-chloranil as a ligand, oxidant, and base is also elucidated.

Associations between antithrombotic therapy and the risk of perioperative complications among patients undergoing laparoscopic gastrectomy.

BACKGROUND: The aim of this study was to identify factors associated with perioperative morbidity among patients who underwent laparoscopic gastrectomy while receiving antithrombotic therapy (ATT). PATIENTS AND METHOD: This retrospective cohort study included 46 patients (14 females and 32 males) who underwent laparoscopic gastrectomy, including 12 (26.1 %) who received perioperative ATT, between January 2012 and November 2015 in our institution. Among patients receiving only aspirin as antiplatelet therapy, none were on anticoagulation therapy. All patients took aspirin as antiplatelet therapy for cardiac indications. The clinical findings and surgical outcomes of patients who did (ATT group) and did not (control group) receive ATT were compared. RESULTS: The intraoperative mortality was 0 % for both groups. There was no significant difference in the incidence of postoperative morbidity by univariate analysis between the control and ATT groups (8.8 vs. 8.3 %, p = 0.39). CONCLUSION: The risk of postoperative morbidity of laparoscopic gastrectomy can be equivalent between the ATT and non-ATT (control) groups.

Does antithrombotic therapy improve survival with colorectal cancer?

BACKGROUND: The study aimed to evaluate the prognosis for patients with colorectal cancer who underwent surgery while receiving antithrombotic therapy (ATT) across all disease stages and for patients at disease stages 0-III. METHODS: This retrospective cohort study included 710 Japanese patients who underwent surgery for colorectal cancer between January 2009 and November 2015 at our institution. Approximately 35% of these patients received ATT. Of these, 199 (28.0%) received antiplatelet therapy, and 76 (10.7%) received anticoagulant therapy. We investigated the prognosis among patients with colorectal cancer receiving ATT, antiplatelet therapy, or anticoagulant therapy in all-stage and stage 0-III cancers. RESULTS: For all disease stages combined, no benefit was observed for ATT, antiplatelet therapy, and anticoagulant therapy groups in the overall survival rates (ATT: 87.8 vs. 78.4%, P = 0.23; antiplatelet therapy: 87.8 vs. 78.6%, P = 0.25; and anticoagulant therapy: 92.2 vs. 80.2%, P = 0.26). However, overall survival rates of patients with stage 0-III colorectal cancer undergoing ATT, antiplatelet therapy, and anticoagulant therapy significantly improved. (ATT: 98.5 vs. 92.7%, P = 0.01; antiplatelet therapy: 98.3 vs. 91.1%, P = 0.02; and anticoagulant therapy: 100 vs. 92.1%, P = 0.00). CONCLUSION: Receiving ATT significantly improves overall survival rates in patients with stage 0-III colorectal cancer.

Rapid Access to Nanographenes and Fused Heteroaromatics by Palladium-Catalyzed Annulative π-Extension Reaction of Unfunctionalized Aromatics with Diiodobiaryls.

Efficient and rapid access to nanographenes and π-extended fused heteroaromatics is important in materials science. Herein, we report a palladium-catalyzed efficient one-step annulative π-extension (APEX) reaction of polycyclic aromatic hydrocarbons (PAHs) and heteroaromatics, producing various π-extended aromatics. In the presence of a cationic Pd complex, triflic acid, silver pivalate, and diiodobiaryls, diverse unfunctionalized PAHs and heteroaromatics were directly transformed into larger PAHs, nanographenes, and π-extended fused heteroaromatics in a single step. In the reactions that afford [5]helicene substructures, simultaneous dehydrogenative ring closures occur at the fjord regions to form unprecedented larger nanographenes. This successive APEX reaction is notable as it stiches five aryl-aryl bonds by C-H functionalization in a single operation. Moreover, the unique molecular structures, crystal-packing structures, photophysical properties, and frontier molecular orbitals of the thus-formed nanographenes were elucidated.

Annulative π-Extension (APEX): Rapid Access to Fused Arenes, Heteroarenes, and Nanographenes.

The annulative π-extension (APEX) reaction has the potential to have a tremendous impact on the fields of materials science and bioimaging, as well as on the pharmaceutical/agrochemical industries, since it allows access to fused aromatic systems from relatively simple aromatic compounds in a single step. Typically, an APEX reaction facilitates a one-pot π-extension without the need to prefunctionalize the aromatic compounds. This advantageous feature is extremely useful for tuning and modifying molecular properties in the last step of a synthesis. In this Review, the progress and applications of APEX reactions of unfunctionalized arenes and heteroarenes are described.

One-Step Annulative π-Extension of Alkynes with Dibenzosiloles or Dibenzogermoles by Palladium/o-chloranil Catalysis.

Reliable and short synthetic routes to polycyclic aromatic hydrocarbons and nanographenes are important in materials science. Herein, we report an efficient one-step annulative π-extension reaction of alkynes that provides access to diarylphenanthrenes and related nanographene precursors. In the presence of a cationic palladium/o-chloranil catalyst system and dibenzosiloles or dibenzogermoles as π-extending agents, a variety of diarylacetylenes are transformed successfully into 9,10-diarylphenanthrenes in a single step with good functional-group tolerance. Furthermore, double π-extension reactions of 1,4-bis(phenylethynyl)benzene and diphenyl-1,3-butadiyne are demonstrated, affording oligoarylene products, which show potential for application in the synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.