Carbon bowls having two distinctly different faces, convex and concave, represent a unique class of non-planar π-ligands with defined molecular compositions and structures. The smallest π-bowl called ...corannulene is known to exhibit the record alkali metal ion binding abilities upon multi-electron acquisition. In contrast, the potential of larger carbon bowls with extended π-surfaces in self-assembly with multiple metal ions is yet to be revealed. This Frontier article opens a discussion of the effect of size, charge and symmetry of the bowl-shaped π-ligands on their supramolecular assembly and metal ion intercalation trends.
Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno1,2‐afluorene scaffold have so far remained elusive. This work reports the preparation and characterization of ...7,12‐dimesitylindeno1,2‐afluorene as a highly reactive species. Experimental and computational data support the notion of a molecule with pronounced diradical character that exists in a triplet ground state. As such, both NICS and ACID calculations suggest that the indeno1,2‐afluorene scaffold is weakly Baird aromatic. Reduction of the unstable red solid with Cs metal produces the dianion of the title compound, from which single crystals could be obtained and X‐ray data acquired, thus fully corroborating the proposed indeno1,2‐afluorene hydrocarbon core.
Not a matter of IF but when: Described is the preparation of the last elusive indenofluorene (IF) regioisomer. While the body of circumstantial spectroscopic data support formation of the highly reactive triplet diradicaloid, definitive structural proof is provided by X‐ray diffraction analysis of crystals of the dianion, obtained by reduction of the indeno1,2‐afluorene with Cs metal.
Stepwise Reduction of Azapentabenzocorannulene Zhou, Zheng; Wei, Zheng; Tokimaru, Yuki ...
Angewandte Chemie International Edition,
August 26, 2019, Letnik:
58, Številka:
35
Journal Article
Recenzirano
Mono‐ and dianions of 2‐tert‐butyl‐3a2‐azapentabenzobc,ef,hi,kl,nocorannulene (1 a) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts ...in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, {Na+(18‐crown‐6)(THF)2}3{Na+(18‐crown‐6)(THF)}(1 a2−)2, revealed the presence of a naked dianion. In contrast, controlled reaction of 1 a with Cs allowed the isolation of singly and doubly reduced forms of 1 a, both forming π‐complexes with cesium ions in the solid state. In {Cs+(18‐crown‐6)}(1 a−)⋅THF, asymmetric binding of the Cs+ ion to the concave surface of 1 a− is observed, whereas in {Cs+(18‐crown‐6)}2(1 a2−), two Cs+ ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules.
N‐doped bowl adds extra electrons: The addition of one and two electrons to an N‐containing corannulene bowl (1 a) was accomplished through controlled chemical reduction with two Group 1 metals of different ionic sizes and binding abilities. The singly and doubly reduced heteroatom‐containing bowl‐shaped anions were characterized by X‐ray crystallography and DFT calculations.
Chemical reduction of sym-dibenzoa,ecyclooctatetraene (DBCOT, 1) has been investigated using group 1 metals ranging from Li to Cs as the reducing agents. With all alkali metals, DBCOT readily ...undergoes a 2-fold reduction to afford the doubly reduced DBCOT2– (1 2–) anion. Seven products of 1 2– with different alkali-metal counterions have been isolated and fully characterized. Their X-ray diffraction structural analyses reveal the ligand core planarization upon addition of two electrons as well as the versatility of 1 2– in alkali-metal coordination. The negative charge localization at the central eight-membered ring of 1 2– identified by theoretical calculations is fully consistent with the X-ray crystallographic and NMR spectroscopic results. A broad range of solid-state structural arrangements of the resulting products stems from different metal binding patterns and secondary interactions involving coordinating agents used for crystallization (THF vs 18-crown-6 and 2.2.2cryptand). This family of alkali-metal salts of 1 2– provides useful reagents for ligand metathesis reactions that can be used in the preparation of various transition-metal or lanthanide-based organometallic complexes.
Conspectus The need for advanced energy storage technologies demands the development of new functional materials. Novel carbon-rich and carbon-based materials of different structural topologies ...attract significant attention in this regard. Attractive systems include a unique class of bowl-shaped polycyclic aromatic hydrocarbons that map onto fullerene surfaces and are thus often referred to as fullerene fragments, buckybowls, or π-bowls. Importantly, carbon bowls are able to acquire multiple electrons in stepwise reduction reactions producing sets of successively reduced carbanions. The resulting negatively charged π-bowls exhibit unique supramolecular assembly and metal intercalation patterns that only recently have begun to be uncovered. First, we have resolved the long-standing mystery behind the supramolecular structure formed by a highly reduced fullerene fragment called corannulene (C20H10 4–) with multiple lithium ions, using X-ray crystallography coupled with NMR spectroscopy and theoretical calculations. This work provided a new paradigm for lithium ion intercalation between the curved carbon π-surfaces and facilitated understanding of the lithium ion storage mechanism in carbonaceous matrices. Next, we have initiated a new research direction, an investigation of the mixed alkali metal reduction reactions using bowl-shaped corannulene as a remarkable multielectron reservoir and unique ligand with open convex and concave π-surfaces. As a result, we have revealed the cooperative effect of lithium with heavier Group 1 metals in reduction and self-assembly processes of corannulene. Moreover, we have discovered a new class of organometallic supramolecules having heterometallic cores with high nuclearity and charge such as Li3M3 6+ and LiM5 6+ (M = K, Rb, and Cs) sandwiched between two tetrareduced corannulene decks. The resulting triple-decker supramolecular assemblies, fully characterized by X-ray diffraction and spectroscopic methods, were found to exhibit a record ability of the highly charged corannulene π-surfaces to be fully engaged in intercalation of multiple metal ions. Based on this unique ability, curved π-ligands with extended carbon frameworks are expected to show remarkable potential for alkali metal storage compared to flat polycyclic arenes. Notably, a previously unseen mode of internal lithium binding revealed in the heterobimetallic sandwiches is accompanied by unprecedented negative shifts (up to −25 ppm) in 7Li NMR spectra. Based on in-depth analysis of NMR data, augmented by DFT calculations, we have rationalized the observed experimental trends and proposed the mechanism of stepwise alkali metal substitution reactions. Furthermore, we have correlated the origin of the record 7Li NMR shifts with unique electronic structures of these novel supramolecular aggregates. Herein we present comprehensive analysis of unusual structural and electronic features of remarkable heterometallic self-assemblies formed by tetrareduced corannulene, using a wealth of our recent experimental and computational results. This work uncovers unique potential of highly negatively charged bowl-shaped π-ligands for new supramolecular chemistry and materials chemistry applications.
An X-ray diffraction study of 6cycloparaphenylene (1), crystallized under solvent-free conditions, revealed a unique solid state structure with tight packing of individual molecules that minimizes ...empty internal space. The controlled chemical reduction of this highly strained nanohoop with Group 1 metals resulted in the first isolation and structural characterization of its mono- and dianions, allowing for the evaluation of core transformations for the series ranging from 10 to 11- and 12-.
Lithium-coordinated polyaromatic anions such as tetrareduced corannulene, C 20 H 10 4- (1 4- ), are useful substrates to model and ultimately improve the graphitic electrodes in lithium-ion (Li + ) ...batteries. Previous studies suggested that 1 4- forms dimers encasing four Li + ions in solution. Here, we report a single-crystal x-ray diffraction analysis confirming the formation of a sandwich-type supramolecular aggregate with a high degree of alkali metal intercalation. In contrast to the prior model, our data reveal that five Li + ions are sandwiched between the two tetrareduced corannulene decks, and 7 Li nuclear magnetic resonance spectroscopy delineates a conserved structure in tetrahydrofuran solution. Remarkably, the sandwich is robust in both solution and solid states even in the presence of crown ethers that compete for Li + coordination. These results should help elucidate Li + intercalation motifs between curved carbon surfaces more broadly.
Perylene (PER) is a prototype of polycyclic aromatic hydrocarbons (PAHs), which play a pivotal role in various functional and electronic materials due to favorable molecule-to-molecule overlaps, ...which enhance electronic transport. This study provides guidelines regarding the impact of molecular charge on pancake bonding, a form of strong π-stacking interaction. Pancake bonding significantly boosts interaction energies within the monopositive dimer ((C20H12)2•+ or PER2 +), crucial for stabilizing aggregation and crystal formation. We discovered energetically feasible sliding and rotation pathways within the (C20H12)2•+ dimer, connecting different configurations found in the Cambridge Structural Database (CSD). The dimer’s charge profoundly influences the pancake bond order (PBO) and the strength and structural preferences of pancake bonding. The most stable configuration is found in the monocationic state (PER2 +), featuring a pancake bond order of 1/2 with one-electron multicenter bonding (1e/mc) with similar characteristics for charge −1. Increasing the total charge of the dimer to +2 or −2 leads to an unstable local minimum. Diverse distribution of pancake bonding types present in crystal structures is interpreted with modeling based on dimer computations with varying charges.
Chemical reduction of a naphthylene macrocycle, 6cyclo‐2,7‐naphthylene (6CNAP, 1), with alkali metals, Li and K, revealed the accessibility of the doubly‐reduced state of 1. The macrocyclic 12− anion ...was isolated in different coordination environments and crystallographically characterized. The single‐crystal X‐ray diffraction confirmed the formation of contact‐ion complexes with one Li+ and two K+ ions in THF, and a “naked” dianion in the solvent‐separated ion product with K+ ions in the presence of 18‐crown‐6 ether. The detailed structural analysis of 12− showed that the π‐conjugation over the biaryl linkages between naphthylene panels were enhanced upon two‐fold reduction, which was rationally explained by theoretical calculations.
Macrocycle π‐conjugation: The two‐fold reduction of 6cyclo‐2,7‐naphthylene (6CNAP) with Li and K metals affords the doubly reduced macrocycle with a large 62π conjugated system, enhanced aromaticity, and variable metal complexation patterns.
Incorporation of a five‐membered ring into a helicene framework disrupts aromatic conjugation and provides a site for selective deprotonation. The deprotonation creates an anionic cyclopentadienyl ...unit, switches on conjugation, leads to a >200 nm red‐shift in the absorbance spectrum and injects a charge into a helical conjugated π‐system without injecting a spin. Structural consequences of deprotonation were revealed via analysis of a monoanionic helicene co‐crystallized with {K+(18‐crown‐6)(THF)} and {Cs+2(18‐crown‐6)3}. UV/Vis‐monitoring of these systems shows a time‐dependent formation of mono‐ and dianionic species, and the latter was isolated and crystallographically characterized. The ability of the twisted helicene frame to delocalize the negative charge was probed as a perturbation of aromaticity using NICS scans. Relief of strain, avoidance of antiaromaticity, and increase in charge delocalization assist in the additional dehydrogenative ring closures that yield a new planarized decacyclic dianion.
Flat as a pancake: Relief of helicene strain, avoidance of antiaromaticity, and increase in charge delocalization assist in dehydrogenative ring closures that convert an anionic fused bis‐5helicene into a planarized decacyclic dianion where nine hexagonal units are fused to a single pentagon.
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