Cobalt-catalyzed Cyclotrimerization Research Articles

Covalent Template-Directed Synthesis of a Spoked 18-Porphyrin Nanoring.

Rings of porphyrins mimic natural light-harvesting chlorophyll arrays and offer insights into electronic delocalization, providing a motivation for creating larger nanorings with closely spaced porphyrin units. Here, we demonstrate the first synthesis of a macrocycle consisting entirely of 5,15-linked porphyrins. This porphyrin octadecamer was constructed using a covalent six-armed template, made by cobalt-catalyzed cyclotrimerization of an H-shaped tolan with porphyrin trimer ends. The porphyrins around the circumference of the nanoring were linked together by intramolecular oxidative meso-meso coupling and partial β-β fusion, to give a nanoring consisting of six edge-fused zinc(II) porphyrin dimer units and six un-fused nickel(II) porphyrins. STM imaging on a gold surface confirms the size and shape of the spoked 18-porphyrin nanoring (calculated diameter: 4.7 nm).

Electrochemical Cobalt-catalyzed Cyclotrimerization of Alkynes to 1,2,4-Substituted Arenes

The transition-metal-catalyzed [2 + 2 + 2] cyclotrimerization of alkynes is one of the most straightforward routes for constructing six-membered ring motifs. Although this strategy possesses high a...

Perovskite Solar Cells Based on Oligotriarylamine Hexaarylbenzene as Hole-Transporting Materials.

A cobalt-catalyzed cyclotrimerization of bis(aryl)alkyne is used as an innovative tool to obtain hole-transport materials (HTMs). The novel HTM containing six units of oligotriarylamine (HAB1), characterized by UV-vis, cyclic voltammetry,DFT, and thermogravimetric analysis, confirms its suitability as an efficient HTM in PSCs. A PCE of 17.5% was obtained in HAB1-containing PSCs, a performance comparable to that obtained with spiro-OMeTAD and with slightly better thermal stability.

Novel naphthylpyridines from cobalt-catalyzed cyclotrimerization of a chiral diyne

The concise synthesis of a novel chiral diyne substrate for the assembly of chiral naphthylpyridines was described and different conditions for the cobalt-catalyzed co-cyclotrimerization with nitriles investigated. The products are novel naphthylpyridines possessing configurationally stable biaryl axes.Graphical abstract

Synthesis and coordination of star-shaped electron-deficient hexaheteroarylbenzene derivatives containing three pyrimidylbenzene derivatives

The synthesis of novel electron-deficient hexaheteroarylbenzene derivatives containing three pyrimidylbenzene derivatives 1 and 2 with carboxylic acidic arms is described. They are prepared through hydrolyzing pyrimidine-substituted carboxylated hexaheteroarylbenzene derivatives 8 and 9 by KOH, respectively. Compound 8 and 9 are synthesized via cobalt-catalyzed cyclotrimerization of methyl 4′-((2-dodecylpyrimidin-5-yl)ethynyl)-[1,1′-biphenyl]-4-carboxylate 7. The isomeric C3-symmetric compound 1 and unsymmetric 2 are successfully isolated by thin-layer chromatography in 1:2 ratios. The coordination of symmetric 1 titrated by Ag+, compared with unsymmetric 2, is investigated by UV–vis, fluorescence spectroscopy and TEM. The coordination of 1 and 2 with In3+ by solvothermal method is studied by SEM and TEM, respectively. These results indicate that the molecular configuration is an important factor, which influences the coordination behavior of these two hexaheteroarylbenzene derivatives.

Charge‐Transfer Interactions in Tris‐Donor–Tris‐Acceptor Hexaarylbenzene Redox Chromophores

Symmetric- and asymmetric hexaarylbenzenes (HABs), each substituted with three electron-donor triarylamine redox centers and three electron-acceptor triarylborane redox centers, were synthesized by cobalt-catalyzed cyclotrimerization, thereby forming compounds with six- and four donor-acceptor interactions, respectively. The electrochemical- and photophysical properties of these systems were investigated by cyclovoltammetry (CV), as well as by absorption- and fluorescence spectroscopy, and compared to a HAB that only contained one neighboring donor-acceptor pair. CV measurements of the asymmetric HAB show three oxidation peaks and three reduction peaks, whose peak-separation is greatly influenced by the conducting salt, owing to ion-pairing and shielding effects. Consequently, the peak-separations cannot be interpreted in terms of the electronic couplings in the generated mixed-valence species. Transient-absorption spectra, fluorescence-solvatochromism, and absorption spectra show that charge-transfer states from the amine- to the boron centers are generated after optical excitation. The electronic donor-acceptor interactions are weak because the charge transfer has to occur predominantly through space. Moreover, the excitation energy of the localized excited charge-transfer states can be redistributed between the aryl substituents of these multidimensional chromophores within the fluorescence lifetime (about 60 ns). This result was confirmed by steady-state fluorescence-anisotropy measurements, which further indicated symmetry-breaking in the superficially symmetric HAB. Adding fluoride ions causes the boron centers to lose their accepting ability owing to complexation. Consequently, the charge-transfer character in the donor-acceptor chromophores vanishes, as observed in both the absorption- and fluorescence spectra. However, the ability of the boron center as a fluoride sensor is strongly influenced by the moisture content of the solvent, possibly owing to the formation of hydrogen-bonding interactions between water molecules and the fluoride anions.

Observation of a Short-Lived Triplet Precursor in CpCo(CO)-Catalyzed Alkyne Cyclotrimerization

The picosecond dynamics of CpCo(CO), a catalytic intermediate in the cyclotrimerization of alkynes, have been studied using time-resolved infrared spectroscopy and density functional theory calculations. In neat 1-hexyne or 1-hexene solution, the first intermediate to form is a triplet η2-coordinated species, which then converts to a singlet η2 species in ca. 30–40 ps. The η2 triplet is the only solvent-coordinated species observed at early times, suggesting that this is the dominant mechanistic pathway for coordination of alkynes and alkenes to the CpCo(CO) catalyst. These new results complement the recent discovery that CpCo(CO) can coordinate to certain solvent molecules in both singlet and triplet spin states and further support previous studies implicating triplet intermediates in cobalt-catalyzed cyclotrimerization and cyclo-oligomerization reaction mechanisms.

Symmetric Six-Fold Arrays of Photo- and Electrochromic Dithienylethene Switches

The direct synthesis of six-fold symmetric hexaphenylbenzenes with multiple photochromic dithienylethene units via a cobalt-catalyzed cyclotrimerization is reported. This approach allows for six photochromic units to be held in proximity with a well-defined spatial separation without affecting the photochromic properties of each unit.

Regioselective Cobalt-Catalyzed Diels-Alder Reaction towards 1,3-Disubstituted and 1,2,3-Trisubstituted Benzene Derivatives

A straightforward reaction sequence consisting of the Wittig olefination of aldehydes utilizing allyltriphenylphosphonium bromide for the generation of 1-substituted 1,3-dienes, cobalt-catalyzed neutral Diels-Alder reaction with terminal and internal alkynes, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation of the dihydroaromatic intermediates leads to regiochemically enriched biphenyl, terphenyl, and silyl-functionalized benzene derivatives in good to excellent yields. Starting from a 1,3-diyne and a 1,3-diene, the reaction sequence consisting of cobalt-catalyzed Diels-Alder reaction, DDQ oxidation, and cobalt-catalyzed cyclotrimerization with acetylene gave an axially chiral biphenyl-terphenyl product.

Hexakis(4-(N-butylpyridylium))benzene: A Six-Electron Organic Redox System

The cobalt-catalyzed cyclotrimerization of bis(4-pyridyl)acetylene affords hexakis(4-pyridyl)benzene in moderate yield. Alkylation with n-butyltriflate gives hexakis(4-(N-butylpyridylium))benzene triflate (1 6+), which can be reduced with Na/Hg in DMF to neutral 10. A single-crystal X-ray diffraction structure reveals that 1 0 has a chair-cyclohexane-like core and a [6]radialene structure. Cyclic voltammetry shows that 1 6+ is reversibly reduced to 1 2+ in one four-electron step and 1 2+ is reversibly reduced to 1 0 in one two-electron step. A reduction by four electrons at one potential is unprecedented for a molecule in which the electrochemically active centers are in electronic communication. The large structural transformation from 1 6+ to 1 0 is responsible for the "potential inversion" in the cyclic voltammetry, and DFT calculations suggest a possible structure for the stable intermediate 1 2+. A comparison is made to the electrochemistry and structural transformations in a previously prepared [4]radialene analogue of 1 0.

Cobalt-Catalyzed Cyclotrimerization of Alkynes: The Answer to the Puzzle of Parallel Reaction Pathways

To understand some experimental data at odds with the computed mechanism of the CpCo(L2)-catalyzed [2 + 2 + 2] cyclotrimerization of ethyne, DFT computations were carried out following the fate of methyl- and hydroxycarbonyl-substituted alkynes to give the corresponding arenes. The key intermediate in all cases is a triplet cobaltacyclopentadiene obtained by oxidative coupling of the corresponding CpCo(bisalkyne) complex and subsequent spin change via a minimum energy crossing point (MECP). From that species, two different catalytic cycles lead to an arene product, depending on the nature of the alkyne and other ligands present: either alkyne ligation to furnish a cobaltacyclopentadiene(alkyne) intermediate or trapping by a sigma-donor ligand to generate a coordinatively saturated cobaltacyclopentadiene(PR3) complex. The former leads to the CpCo-complexed arene product via intramolecular cobalt-assisted [4 + 2] cycloaddition, whereas the latter may, in the case of a reactive dienophile (butynedioic acid), undergo direct intermolecular [4 + 2] cycloaddition to generate a cobaltanorbornene. The bridgehead cobalt atom is then reductively eliminated after another change in spin state from singlet to triplet. The necessary conditions for one or the other mechanistic pathway are elaborated.

Synthesis and Electrochemical Properties of Fullerene-Rich Nanoclusters Synthesized by Cobalt-Catalyzed Cyclotrimerization of Bis(aryl)alkyne Fullerodendrimers

Synthesis and Electrochemical Properties of Fullerene-Rich Nanoclusters Synthesized by Cobalt-Catalyzed Cyclotrimerization of Bis(aryl)alkyne Fullerodendrimers

Synthesis and Electrochemical Properties of Fullerene‐Rich Nanoclusters Synthesized by Cobalt‐Catalyzed Cyclotrimerization of Bis(aryl)alkyne Fullerodendrimers

A lot of balls: Up to 24 C60 units were assembled around a hexaphenylbenzene core by cobalt-catalyzed cyclotrimerization of bis(aryl)alkyne fullerodendrimers (see scheme). Electrochemical investigations reveal that interactions between C60 units within a single dendrimer molecule are extremely efficient.

Cyclotrimerization Strategy toward Analogues of Amaryllidaceae Constituents. Synthesis of Deoxygenated Pancratistatin Core

[chemical reaction: see text]. A derivative of pancratistatin having no oxygenation in the aromatic ring was synthesized by a new strategy based on the cobalt-catalyzed cyclotrimerization of acetylenes as a prelude to diversity-oriented synthesis of further analogues.

Synthesis of an extended hexagonal molecule as a highly symmetrical ligand

An extended hexagonal molecule that has high symmetry and rigidity was designed and synthesized by a cobalt-catalyzed cyclotrimerization reaction. The ligand possesses six benzoic acids at its periphery, which were connected to a central hexakis(2,5-dodesyloxyphenyl)hexaphenylbenzene core with a maximum intramolecular carboxyl group distance of approximately 3.5 nm.

Syntheses of Hexakis(4-functionalized-phenyl)benzenes and Hexakis[4-(4‘-functionalized- phenylethynyl)phenyl]benzenes Directed to Host Molecules for Guest-Inclusion Networks

The syntheses of various types of hexakis(4-functionalized-phenyl)benzenes 1 and hexakis[4-(4'-functionalized-phenylethynyl)phenyl]benzenes 2 by the cobalt-catalyzed cyclotrimerization of diarylacetylenes and by the Sonogashira coupling reaction of 1e with arylacetylenes, respectively, are described. X-ray crystallographic analysis showed that host 1e or 2f forms a 2-D network by unique I...I or CH...O=C interactions, respectively.

Cobalt-catalyzed cyclotrimerization of diynes with norbornenes in one efficient step

An efficient cobalt-catalyzed [2+2+2] cyclotrimerization of diynes and norbornene is described. Treatment of diyne with norbornene in the presence of CoI 2(PPh 3) 2 and zinc powder in 1,2-dichloroethane at 80 °C for 12 h afforded [2+2+2] cyclotrimerization adduct exclusively in good yields. These cobalt-catalyzed results are in contrast to the ruthenium-catalyzed reaction of diyne with norbornene reported previously.

Synthesis of Novel Organic–Inorganic Hybrid Cages via Cobalt-catalyzed Cyclotrimerization of Dimethylethynylsilyl Groups on a Silsesquioxane

Abstract Novel organic–inorganic hybrid cages composed of a half-caged silsesquioxane skeleton and a benzene ring have been synthesized by cobalt-catalyzed intramolecular cyclotrimerization of a silsesquioxane bearing three dimethylethynylsilyl groups.

A Versatile Approach to the Solution-Phase Combinatorial Synthesis of Substituted Pyridines: The Cobalt-Catalyzed Cyclotrimerization of Alkynes with a Nitrile.

The cobalt-catalyzed trimerization of two alkynes and one nitrile was exploited to produce solution-phase libraries of pyridines. Upon addition of 2 equiv of a CO scavenger (i.e., an amine-N-oxide), the commercially available [CpCo(CO)(2)] proved to be an attractive catalyst, as the required reaction temperatures, side product formation (i.e., carbocycles), and oxygen sensitivity are moderate. Purification of the reaction mixture was performed with an acidic cation-exchange resin.

An Alternative Synthetic Approach toward Dendritic Macromolecules: Novel Benzene-Core Dendrimers via Alkyne Cyclotrimerization

An Alternative Synthetic Approach toward Dendritic Macromolecules: Novel Benzene-Core Dendrimers via Alkyne Cyclotrimerization