Yamamoto Coupling Research Articles

A Poly(2,7‐anthrylene) with peri‐Fused Porphyrin Edges

AbstractAnthracene has served as an important building block of conjugated polymers with the connecting positions playing a crucial role for the electronic structures. Herein, anthracene units have been coupled through their 2,7‐carbons to develop an unprecedented, conjugated polymer, namely, poly(2,7‐anthrylene) featuring additional peri‐fused porphyrin edges. The synthesis starts from a 2,7‐dibromo‐9‐nickel(II) porphyrinyl‐anthracene as the pivotal precursor. Polymerization is achieved by an AA‐type Yamamoto coupling, followed by a polymer‐analogous oxidative cyclodehydrogenation to obtain a peri‐fusion between porphyrin and anthracene moieties. Although further cyclodehydrogenation between the repeating units cannot be achieved in solution, the thermal treatment of the precursor polymer derived from 2,7‐dibromo‐9‐porphyrinyl‐anthracene on a metal surface realizes the full cyclodehydrogenation. The difference between solution and on‐surface reactivity can be rationalized by the larger dihedral angle between repeat units in solution, which is reduced under the pronounced interaction with the metal surface. The peri‐fusion in the title polymer gives rise to a narrow electronic band gap optical absorptions extending far into the near‐infrared region. Oligomeric models are synthesized as well to support the analyses of the electronic and photophysical properties.

High Charge Carrier Mobility in Porphyrin Nanoribbons

Polydisperse edge‐fused nickel(II) porphyrin nanoribbons have been synthesized by Yamamoto coupling followed by gold(III)‐mediated fusion, with average degrees of polymerization of up to 37 repeat units (length 31 nm). Time‐resolved optical‐pump terahertz spectroscopy measurements indicate that photo‐generated charge carriers have dc mobilities of up to 205 cm2 V–1 s–1 in these nanoribbons, exceeding the values previously reported for most other types of nanoribbon or π‐conjugated polymer.

High Charge Carrier Mobility in Porphyrin Nanoribbons.

Polydisperse edge-fused nickel(II) porphyrin nanoribbons have been synthesized by Yamamoto coupling followed by gold(III)-mediated fusion, with average degrees of polymerization of up to 37 repeat units (length 31 nm). Time-resolved optical-pump terahertz spectroscopy measurements indicate that photo-generated charge carriers have dc mobilities of up to 205 cm2 V-1 s-1 in these nanoribbons, exceeding the values previously reported for most other types of nanoribbon or π-conjugated polymer.

Highly Strained, Fully π‐Conjugated Porphyrin Cyclophanes: Template‐free Synthesis and Global Aromaticity

Porphyrin‐based nanohoops, nanorings, and cages with fully π‐conjugated structures are highly sought after, but their synthesis remains challenging. Herein, we report the template‐free synthesis of a highly strained, bithiophene‐bridged porphyrin cyclophane (1) from a porphyrin quinone via a stereoselective nucleophilic addition followed by intermolecular Yamamoto coupling strategy. X‐ray crystallographic analyses of 1 and its dication 12+ reveal significantly distorted cyclophane‐like geometries, with calculated strain energies of 51.2 and 80.7 kcal/mol, respectively. While the neutral compound 1 exhibits localized aromaticity, the dication 12+ is globally aromatic, with the porphyrin unit displaying weak antiaromaticity. Additionally, the dication 12+ undergoes nucleophilic addition with chloride, relieving strain. This work presents a novel synthetic strategy for highly strained, fully π‐conjugated systems with intriguing electronic properties and chemical reactivity.

Highly Strained, Fully π-Conjugated Porphyrin Cyclophanes: Template-free Synthesis and Global Aromaticity.

Porphyrin-based nanohoops, nanorings, and cages with fully π-conjugated structures are highly sought after, but their synthesis remains challenging. Herein, we report the template-free synthesis of a highly strained, bithiophene-bridged porphyrin cyclophane (1) from a porphyrin quinone via a stereoselective nucleophilic addition followed by intermolecular Yamamoto coupling strategy. X-ray crystallographic analyses of 1 and its dication 12+ reveal significantly distorted cyclophane-like geometries, with calculated strain energies of 51.2 and 80.7 kcal/mol, respectively. While the neutral compound 1 exhibits localized aromaticity, the dication 12+ is globally aromatic, with the porphyrin unit displaying weak antiaromaticity. Additionally, the dication 12+ undergoes nucleophilic addition with chloride, relieving strain. This work presents a novel synthetic strategy for highly strained, fully π-conjugated systems with intriguing electronic properties and chemical reactivity.

A Poly(2,7-anthrylene) with peri-Fused Porphyrin Edges.

Anthracene has served as an important building block of conjugated polymers with the connecting positions playing a crucial role for the electronic structures. Herein, anthracene units have been coupled through their 2,7-carbons to develop an unprecedented, conjugated polymer, namely, poly(2,7-anthrylene) featuring additional peri-fused porphyrin edges. The synthesis starts from a 2,7-dibromo-9-nickel(II) porphyrinyl-anthracene as the pivotal precursor. Polymerization is achieved by an AA-type Yamamoto coupling, followed by a polymer-analogous oxidative cyclodehydrogenation to obtain a peri-fusion between porphyrin and anthracene moieties. Although further cyclodehydrogenation between the repeating units cannot be achieved in solution, the thermal treatment of the precursor polymer derived from 2,7-dibromo-9-porphyrinyl-anthracene on a metal surface realizes the full cyclodehydrogenation. The difference between solution and on-surface reactivity can be rationalized by the larger dihedral angle between repeat units in solution, which is reduced under the pronounced interaction with the metal surface. The peri-fusion in the title polymer gives rise to a narrow electronic band gap optical absorptions extending far into the near-infrared region. Oligomeric models are synthesized as well to support the analyses of the electronic and photophysical properties.

Size-Increased All-Phenylene Molecular Spoked Wheels - A Combined Theoretical and Experimental Approach.

A lateral expansion of molecular spoked wheels (MSWs) based on an all-phenylene backbone is described. The MSWs contain a central hub, six spokes, and a rim that is formed by a sixfold Yamamoto coupling of the respective non-cyclized dodecabromo precursor yielding MSWs with up to 30 phenylene rings in the perimeter. Attempts to prepare compounds of such size without flexible side groups at the spokes were unsuccessful, most probably due to an aggregation and accompanying oligomerization of the precursors during the cyclization. To overcome these problems, fluorene units are inserted into the spokes. These contain additional alkyl chains and lead to a curvature of the wheels. Quantum chemical calculations on the mechanism of the Yamamoto coupling lead to geometry and strain-related criteria for the successful rim closure to the respective MSW. Subsequently, MSWs are prepared with four and even six phenylene units at each edge of the hexagonal wheels. The resulting MSWs are characterized by spectroscopic methods, and additionally some of them are visualized via scanning tunneling microscopy (STM).

Unusually Short H⋅⋅⋅H Contacts in Intramolecularly Cyclized Helically Fused Anthracenes.

The intramolecular coupling of dichloro-substituted helically fused anthracenes using the Yamamoto coupling yielded cyclized products with sterically congested molecular structures. The X-ray analysis and DFT calculations showed that the aromatic framework adopted a nonplanar structure with a twisted conformation about the newly formed single bond, which acts as a chiral axis. Interestingly, the X-ray structure obtained through the Hirshfeld atom refinement revealed short interatomic distances between the inner hydrogen atoms (1.648-1.692 Å), much shorter than the sum of their van der Waals radii. Owing to these unusually short contacts, the 1H NMR spectrum exhibited a significant deshielding (12.5 ppm) and a large nuclear Overhauser effect (44 %). Additionally, the IR spectrum displayed a high-frequency shift of the C-H stretching vibration. These observations, along with the noncovalent interaction plot indicative of a characteristic steric environment, strongly support the presence of steric hindrance. Moreover, dynamic NMR measurement of the mesityl-substituted derivative yielded a barrier to helical inversion of 84 kJ mol-1. The optical properties and crystal packing of the cyclized products are also reported.

Cyclooctatetraene‐Embedded Carbon Nanorings

AbstractWith the prosperity of the development of carbon nanorings, certain topologically or functionally unique units‐embedded carbon nanorings have sprung up in the past decade. Herein, we report the facile and efficient synthesis of three cyclooctatetraene‐embedded carbon nanorings (COTCNRs) that contain three (COTCNR1 and COTCNR2) and four (COTCNR3) COT units in a one‐pot Yamamoto coupling. These nanorings feature hoop‐shaped segments of Gyroid (G‐), Diamond (D‐), and Primitive (P‐) type carbon schwarzites. The conformations of the trimeric nanorings COTCNR1 and COTCNR2 are shape‐persistent, whereas the tetrameric COTCNR3 possesses a flexible carbon skeleton which undergoes conformational changes upon forming host–guest complexes with fullerenes (C60 and C70), whose co‐crystals may potentially serve as fullerene‐based semiconducting supramolecular wires with electrical conductivities on the order of 10−7 S cm−1 (for C60⊂COTCNR3) and 10−8 S cm−1 (for C70⊂COTCNR3) under ambient conditions. This research not only describes highly efficient one‐step syntheses of three cyclooctatetraene‐embedded carbon nanorings which feature hoop‐shaped segments of distinctive topological carbon schwarzites, but also demonstrates the potential application in electronics of the one‐dimensional fullerene arrays secured by COTCNR3.

Cyclooctatetraene-Embedded Carbon Nanorings.

With the prosperity of the development of carbon nanorings, certain topologically or functionally unique units-embedded carbon nanorings have sprung up in the past decade. Herein, we report the facile and efficient synthesis of three cyclooctatetraene-embedded carbon nanorings (COTCNRs) that contain three (COTCNR1 and COTCNR2) and four (COTCNR3) COT units in a one-pot Yamamoto coupling. These nanorings feature hoop-shaped segments of Gyroid (G-), Diamond (D-), and Primitive (P-) type carbon schwarzites. The conformations of the trimeric nanorings COTCNR1 and COTCNR2 are shape-persistent, whereas the tetrameric COTCNR3 possesses a flexible carbon skeleton which undergoes conformational changes upon forming host-guest complexes with fullerenes (C60 and C70), whose co-crystals may potentially serve as fullerene-based semiconducting supramolecular wires with electrical conductivities on the order of 10-7 S cm-1 (for C60⊂COTCNR3) and 10-8 S cm-1 (for C70⊂COTCNR3) under ambient conditions. This research not only describes highly efficient one-step syntheses of three cyclooctatetraene-embedded carbon nanorings which feature hoop-shaped segments of distinctive topological carbon schwarzites, but also demonstrates the potential application in electronics of the one-dimensional fullerene arrays secured by COTCNR3.

Solid-state nickel(0)-mediated Yamamoto coupling enabled by mechanochemistry

Abstract Herein, we report the first solid-state protocol for nickel(0)-mediated Yamamoto-coupling reactions using ball milling. A variety of aryl halides reacted efficiently in the presence of bis(cyclooctadiene)nickel(0) [Ni(cod)2] and 4,4'-di-tert-butyl-2,2'-bipyridyl under solid-state mechanochemical conditions, affording the corresponding biaryls in high yields. Considering that potentially harmful and high-boiling organic solvents are not required, the present study provides a more convenient, environmentally friendly, and sustainable alternative to conventional solution-based Yamamoto coupling. Solid-state Yamamoto-coupling polymerization and the development of a catalytic variant are also described.

Stabilization of Acenes: "Geländer"-Pentacenes.

We report soluble tetrakis-biphenylyl substituted pentacenes comprised of sp2 carbons and synthesized from pentacene-5,7,12,14-tetraone. Intramolecular Yamamoto coupling of two tetrakis(chlorobiphenylyl)pentacenes yields helical, doubly wrapped pentacenes, in which the quaterphenylene units solubilize the pentacenes and shield their central anthracene units to an unprecedented degree. The criss-cross-bridged pentacenes resist (photo)oxidation, Diels-Alder reactions and are much less reactive than TIPS-ethynylated pentacene. Extension of this concept might provide access to the larger acenes.

Stabilisierung von Acenen: Geländerpentacene

AbstractWir berichten über aus Pentacen‐5,7,12,14‐tetraon synthetisierte, lösliche, tetrakisbiphenylylsubstituierte Pentacene bestehend aus sp2‐Kohlenstoffen. Intramolekulare Yamamoto‐Kupplung zweier Tetrakis(chlorbiphenylyl)pentacenen führt zu helikalen, zweifach überbrückten Pentacenen, bei denen die Quaterphenyleneinheiten die Pentacene solubilisieren und ihre zentrale Anthraceneinheit in einem noch nie dagewesenen Maße abschirmen. Die kreuzweise verbrückten Pentacene trotzen (Photo‐)Oxidation und Diels–Alder‐Reaktionen, sie sind weniger reaktiv als TIPS‐ethinyliertes Pentacen. Eine Erweiterung dieses Konzeptes könnte den Zugang zu den größeren Acenen ermöglichen.

A novel porous aromatic framework with mesopores for removal of antibiotics from water

Porous aromatic frameworks (PAFs) display high potential for wastewater treatment, due to their high surface area and extreme stability. PAF-134 was synthesized based on a 3-connected non-planar building unit, tris(4-bromophenyl)(phenyl)silane (PBTSi-3-Br), via Yamamoto coupling reaction. PAF-134 exhibited high BET surface area of 865.7 m2/g, large mesopore ratio of 69 % pore volume and excellent stability. Three tetracycline pollutants, tetracycline (TC), oxytetracycline (OTC) and chlortetracycline hydrochloride (CTC), were chosen to study the antibiotics adsorption performance for PAF-134. The adsorption isotherms, kinetics, and thermodynamics were measured and analyzed. Moreover, PAF-134 in removing antibiotics from actual water exhibited high efficiency and possessed outstanding recyclability and stability, thus showing that it is a promising adsorbent for wastewater treatment.

Stereogenic π-Conjugated Macrocycles: Synthesis, Structure, and Chiroptical Properties Including Circularly Polarized Luminescence

AbstractHighly symmetrical and aesthetically pleasing molecules have attracted the attention of organic chemists. We synthesized new highly symmetric stereogenic π-conjugated macrocycles with planar or axial chirality. Macrocyclic oligomers synthesized by Yamamoto coupling or Suzuki–Miyaura cross-coupling from the π-unit containing chirality. These cyclization reactions gave multiple oligomers in relatively high yields. We then elucidated their structures and investigated their chiroptical properties, including circular dichroism (CD) and circularly polarized luminescence (CPL). Because of the selection rule for rigid and symmetric structures, these macrocycles exhibit a high dissymmetry factor (g abs or g lum) for circularly polarized light in CD or CPL. Several rigid cyclic compounds retain a highly symmetric structure in the excited state and exhibit higher g lum values than common chiral organic compounds. This Account provides a brief background regarding chiroptical properties, followed by a summary of the various macrocycles synthesized in this study. We are glad if this Account will be a source of ideas not only for chemists working with π-conjugated compounds, but also for synthetic chemists working with chiral compounds, especially those engaged in asymmetric synthesis.1 Introduction2 Brief Description of Chiroptical Properties3 Stereogenic Macrocycle Based on [2.2]Paracyclophane3.1 Stereogenic Double-decker Oligothiophene3.2 Stereogenic Biselenophene Macrocycle3.3 Helical Oligophenylene Linked with [2.2]Paracyclophane4 Stereogenic Macrocycle Based on Binaphthyl4.1 Cyclic Oligomer of Chiral Binaphthyl4.2 Doubly Twisted Binaphthyl Dimer4.3 Cyclic Oligomer of Binaphthyl Extended with Paraphenylene4.4 Curved Helical Paraphenylene Anchoring Chiral Binaphthyl4.5 Binaphthyl-Hinged [5]-Helicene5 Summary

Microwave-Assisted Synthesis of Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) with Well-Defined End Groups and Narrow Dispersity

A series of PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) polymers were synthesized using a Ni(0)-mediated Yamamoto coupling. Polymers with different molecular weights and only one series of well-defined end groups were obtained with various amounts of a tailormade endcapper. This level of structural uniformity has not yet been described for PTAA. By using microwave heating, it was possible to shorten the reaction time from at least 1 day to 30 min. The synthetic strategy allows the separation of single PTAA oligomers with up to 6 repeating units and polymer fractions with low dispersities from 1.06 to 1.17 by using preparative size exclusion chromatography. The carrier mobilities of the PTAA oligomers and polymers were derived from organic field-effect transistors. Mobilities increase with increasing molecular weight of the PTAAs and are higher compared to commercially available PTAA samples.

Aromaticity in Fully π-Conjugated Multicyclic Macrocycles.

The research on aromaticity has mainly focused on monocyclic [n]annulene-like systems or polycyclic aromatic hydrocarbons. For fully π-conjugated multicyclic macrocycles (MMCs), the electronic coupling between the individual constitutional macrocycles would lead to unique electronic structures and aromaticity. The studies on MMCs, however, are quite limited, presumably due to the great challenges to design and synthesize a fully π-conjugated MMC molecule. Herein, we report the facile synthesis of two MMCs (2TMC and 3TMC) in which two and three thiophene-based macrocycles are fused together by employing both intramolecular and intermolecular Yamamoto coupling reactions of a properly designed precursor (7). The monocyclic macrocycle (1TMC) was also synthesized as a model compound. The geometry, aromaticity, and electronic properties of these macrocycles at different oxidation states were investigated by X-ray crystallographic analysis, NMR, and theoretical calculations, which disclosed how the constitutional macrocycles interplay with each other and lead to unique aromatic/antiaromatic character. This study provides new insights into the complex aromaticity in MMC systems.

β,β-Directly Linked Porphyrin Rings: Synthesis, Photophysical Properties, and Fullerene Binding.

Cyclic porphyrin oligomers have been studied as models for photosynthetic light-harvesting antenna complexes and as potential receptors for supramolecular chemistry. Here, we report the synthesis of unprecedented β,β-directly linked cyclic zinc porphyrin oligomers, the trimer (CP3) and tetramer (CP4), by Yamamoto coupling of a 2,3-dibromoporphyrin precursor. Their three-dimensional structures were confirmed by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analyses. The minimum-energy geometries of CP3 and CP4 have propeller and saddle shapes, respectively, as calculated using density functional theory. Their different geometries result in distinct photophysical and electrochemical properties. The smaller dihedral angles between the porphyrin units in CP3, compared with CP4, result in stronger π-conjugation, splitting the ultraviolet-vis absorption bands and shifting them to longer wavelengths. Analysis of the crystallographic bond lengths indicates that the central benzene ring of the CP3 is partially aromatic [harmonic oscillator model of aromaticity (HOMA) 0.52], whereas the central cyclooctatetraene ring of the CP4 is non-aromatic (HOMA -0.02). The saddle-shaped structure of CP4 makes it a ditopic receptor for fullerenes, with affinity constants of (1.1 ± 0.4) × 105 M-1 for C70 and (2.2 ± 0.1) × 104 M-1 for C60, respectively, in toluene solution at 298 K. The formation of a 1:2 complex with C60 is confirmed by NMR titration and single-crystal X-ray diffraction.

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.

Merging a Negatively Curved Nanographene and a Carbon Nanoring

Two molecular nanocarbons result from merging a negatively curved nanographene and a carbon nanoring in two constitutional isomers of D2 and C2v symmetry, respectively. They were synthesized by attachment of C-shaped paraphenylene precursors to 2,11,18,27-tetrabromooctabenzo[8]circulene and the subsequent intramolecular Yamamoto coupling and reductive aromatization reactions. The flexible nature of octabenzo[8]circulene enabled two different ways of connection in the Yamamoto coupling reactions, leading to the two constitutional isomers. The D2 isomer is shaped like a figure eight, as revealed by X-ray crystallography, and is resolved into two enantiomers by chiral HPLC. The synthesis of the C2v isomer is regarded as a further step toward precision synthesis of carbon schwarzites through a bottom-up approach.