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Designed site-directed dimerization of the monoanion radicals of a π-bowl in the solid state is reported. Dibenzo[a,g]corannulene (C28 H14 ) was selected based on the asymmetry of the charge/spin localization in the C28 H14.- anion. Controlled one-electron reduction of C28 H14 with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs+ (diglyme)}2 (C28 H14 -C28 H14 )2- ] (1), as revealed by single crystal X-ray diffraction study performed in a broad range of temperatures. The C-C bond length between two C28 H14.- bowls (1.560(8) A) measured at -143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ-bond character of the C-C linker is confirmed by calculations. The trans-disposition of two bowls in 1 is observed with the torsion angles around the central C-C bond of 172.3(5)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C28 H14.- radicals confirmed that the trans-isomer found in 1 is energetically favored.

The coordination of C-F moieties to electrophilic metal cations has been increasingly recognized in f-element chemistry over the last two decades. These C-F→Ln/An interactions are readily identified in the solid state and can persist in solution. The binding energies of C-F→Ln/An interactions lead to their ready displacement to expose metal centers to substrates, which is implicated in cationic polymerization catalysts. C-F→Ln/An coordination is also an elementary step in C-F bond activation, proceeding through either homolytic or heterolytic cleavage of chemically inert C-F bonds. The influence of C-F→Ln/An interactions on the geometries of coordination compounds and their electronic impact on metal cations are also examined in this Perspective article.

An important goal in corrosion research is to develop inexpensive and environmentally-benign corrosion inhibitors to replace commonly-used, toxic, chromate passivators. Herein, we report a high-throughput experimentation (HTE) method for fast and convenient measurement of corrosion protective activity of molecular inhibitors. This new screening method has enabled discovery of new corrosion inhibitors, consisting of carboxylates and lanthanides, exhibiting substantially lower corrosion rates compared to commonly used chromates at lower concentrations. These results have demonstrated a molecular basis for the corrosion inhibition and are applicable to problems in atmospheric corrosion.

ConspectusThe 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 (C20H104–) with multiple lithium ions, using X-ray crystallography coupled with NMR spectroscopy and theoretical calcula...

Molecular cerium complexes are a new class of tunable and energy-efficient visible- and UV-luminophores. Understanding and controlling the emission brightness and color are important for tailoring them for new and specialized applications. Herein, we describe the experimental and computational analyses for series of tris(guanidinate) (1–8, Ce{(R2N)C(NiPr)2}3, R = alkyl, silyl, or phenyl groups), guanidinate-amide [GA, A = N(SiMe3)2, G = (Me3Si)2NC(NiPr)2], and guanidinate-aryloxide (GOAr, OAr = 2,6-di-tert-butylphenoxide) cerium(III) complexes to understand and develop predictive capabilities for their optical properties. Structural studies performed on complexes 1–8 revealed marked differences in the steric encumbrance around the cerium center induced by various guanidinate ligand backbone substituents, a property that was correlated to photoluminescent quantum yield. Computational studies revealed that consecutive replacements of the amide and aryloxide ligands by guanidinate ligand led to less nonradia...

A detailed structural overview of a family of bowl-shaped polycyclic aromatic carbocations of the type [C20 H10 R](+) with different R functionalities tethered to the interior surface of corannulene (C20 H10 ) is provided. Changing the identity of the surface-bound groups through alkyl chains spanning from one to four carbon atoms and incorporating a different degree of halogenation has led to the fine tuning of the bowl structures and properties. The deformation of the corannulene core upon functionalization has been revealed based on X-ray crystallographic analysis and compared for the series of cations with R=CH3 , CH2 Cl, CHCl2 , CCl3 , CH2 CH3 , CH2 CH2 Cl, and CH2 CH2 Br. The resulting carbocations have been isolated with several metal-based counterions, varying in size and coordinating abilities ([AlCl4 ](-) , [AlBr4 ](-) , [(SnCl)(GaCl4 )2 ](-) , and [Al(OC(CF3 )3 )4 ](-) ). A variety of aggregation patterns in the solid state has been revealed based on different intermolecular interactions ranging from cation-anion to π-π stacking and to halogen⋅⋅⋅π interactions. For the [C20 H10 CH2 Cl](+) ion crystallized with several different counterions, the conformation of the R group attached to the central five-membered ring of corannulene moiety was found to depend on the solid-state environment defined by the identity of anions. Solution NMR and UV/Vis investigations have been used to complement the X-ray diffraction studies for this series of corannulene-based cations and to demonstrate their different association patterns with the solvent molecules.

The monoanion of dihydrogenated corannulene isolated in the form of its potassium salt, namely tris(diglyme-κ3O,O′,O′′)potassium hexacyclo[11.5.2.04,17.07,16.010,15.014,18]icosa-1,3,5,7(16),8,10(15),11,13,17-nonaenide, [K(C6H14O3)3](C20H12), has been structurally characterized for the first time. The X-ray study confirms the previous NMR spectroscopic prediction that the two H atoms are attached to the same six-membered ring to form 1,2-dihydrocorannulene, thus destroying the aromaticity of only one arene ring of the corannulene core. The direct comparison of (C20H12)−with the parent corannulene anion, (C20H10)−, is provided to illustrate the geometry perturbations caused by rim hydrogenation.

Cesium salts of mono- and doubly-reduced bowl-shaped corannulene have been prepared in the presence of different O-donors and isolated as bulk crystalline solids. Crystallization of corannulene monoanions with cesium ions from diglyme afforded green blocks of [Cs(diglyme)+(C20H10−)] (1). Its X-ray structural investigation revealed the formation of a 1D polymer built on simultaneous binding of large cesium ion to the convex and concave faces of the adjacent C20H10•− anions, with each bowl functioning in the rare η5-endo:η6-exo bridging mode. The coordination environment of the Cs+ ion is completed by a side-bound diglyme molecule. The cesium salt of corannulene dianion, C20H102−, was crystallized in the presence of dicyclohexano-18-crown-6 ether as [Cs2(dc-18-crown-6)1.52+(C20H102−)] (2). This product has a discrete linear tetranuclear structure built by aggregation of two terminal exo-hub-bound {Cs(dc-18-crown-6)(C20H102−)}− anionic moieties with the central {Cs2(dc-18-crown-6)}2+ cationic gluing block. The cesium ions of the latter, sharing one crown ether molecule, occupy the concave cavities of the doubly-charged corannulene bowls. As a result, each bowl functions in the symmetric η5-endo:η5-exo bridging mode which has not been previously seen. The bowl depths of the resulting carbanions in 1 and 2 are 0.915(15) A and 0.852(13) A, respectively, vs. that of 0.875(2) A in neutral corannulene.

The degree of π-electron delocalization in a series of unsaturated N-heterocyclic compounds containing divalent group-14 atoms, (HCRN)2EII (E = C, Si, Ge, Sn), has been estimated by applying different experimental and theoretical criteria (vibrational and UV–vis spectroscopy, nucleus-independent chemical shifts, and isomerization stabilization energies). All of the methods used confirmed the aromaticity of these heterocyclic molecules involving six π electrons, and most of the methods indicated that the aromaticity increases in going from the silylene to the stannylene.

The products of 1,2-cycloaddition of dihalocarbene to the bowl-shaped corannulene (C20H10, 1) have been isolated in the solid state and fully characterized. The first X-ray diffraction analysis of mono- and bis-adducts, C20H10CCl2 (2) and C20H10(CCl2)2 (3), has been accomplished to reveal structural changes of the corannulene framework upon addition of dichlorocarbene groups as well as to show variations in the solid state packing of the functionalized polar bowls. For the monoadduct 2, the Cs symmetric molecular structure with the hub attachment of the CCl2 group to a bowl was confirmed. In the solid state, the polar C20H10CCl2 molecules form one-dimensional (1D) columns based on strong concave–convex π···π interactions (ca. 3.36–3.37 A). The resulting polar 1D stacks in 2 are all oriented in the same direction to form polar crystals. The addition of the second dichlorocarbene group in C20H10(CCl2)2 caused the drastic reduction of the dipole moment from 3.7 D in 2 to 2.0 D in 3, which was also accompanie...

Self-assembly processes of the highly reduced bowl-shaped corannulene generated by the chemical reduction with a binary combination of alkali metals, namely Li-Rb, have been investigated by variable-temperature 1H and 7Li NMR spectroscopy. The formation of several unique mixed metal sandwich products based on tetrareduced corannulene, C20H104- (14-), has been revealed followed by investigation of their dynamic transformations in solutions. Analysis of NMR data allowed to propose the mechanism of stepwise alkali metal substitution as well as to identify experimental conditions for the isolation of intermediate and final supramolecular products. As a result, two new triple-decker aggregates with a mixed Li-Rb core, [{Rb(THF)2}2]//[Li3Rb2(C20H10)2{Li+(THF)}] (2) and [{Rb(diglyme)}2]//[Li3Rb3(C20H10)2(diglyme)2]·0.5THF (3·0.5THF), have been crystallized and structurally characterized. The Li3Rb2-product has an open coordination site at the sandwich periphery and thus is considered transient on the way to the Li3Rb3-sandwich having the maximized intercalated alkali metal content. Next, the formation of the LiRb5 self-assembly with 14- has been identified by 7Li NMR as the final step in a series of dynamic transformations in this system. This product was also isolated and crystallographically characterized to confirm the LiRb5 core. Notably, all sandwiches have their central cavities, located in between the hub-sites of two C20H104- decks, occupied by an internal Li+ ion which exhibits the record high negative shift (ranging from -21 to -25 ppm) in 7Li NMR spectra. The isolation of three novel aggregates having different Li-Rb core compositions allowed us to look into the origin of the unusual 7Li NMR shifts at the molecular level. The discussion of formation mechanisms, dynamic transformations as well as unique electronic structures of these remarkable mixed alkali metal organometallic self-assemblies is provided and supported by DFT calculations.

Synthetic methods for the coordination of the monoanionic bis[2-(diisopropylphosphino)-4-methylphenyl]amido (PNP) ligand framework to the cerium(III) cation have been developed and applied for the isolation of a series of {(PNP)Ce} and {(PNP)2Ce} type complexes. The structures of the complexes were studied by X-ray diffraction and multinuclear NMR spectroscopy. We found that the cerium(III) ion can induce the elimination of one of the iPr groups at phosphorus to yield a new dianionic PNP tridentate framework (PNP-iPr) featuring a phosphido-donor functionality, which is bound to the cerium ion with the shortest known Ce−P bond of 2.7884(14) A for molecular compounds. The reaction of the complex [(PNP)Ce{N(SiMe3)2}2] (1) with Ph2CO gave the Ce-bound product of C−C coupling, -N(SiMe3)SiMe2CH2-CPh2O−, through the C−H bond activation of a SiMe3 group. 31P NMR spectroscopy was used to estimate the presence of a vacant coordination position at the cerium ion in the CeIII–PNP complexes by the examination of the δ(31P) shift recorded both in non-polar (C6D6) and polar ([D8]THF) solvents. Moreover, 31P NMR spectroscopy was also found to be a useful tool for the estimation of the Ce−P bond distances in {(PNP)CeIII} and {(PNP)2CeIII} systems. Electrochemical and computational studies for 1 and its lanthanum analogue containing a redox-innocent metal center revealed the stabilization of the CeIII oxidation state by the PNP ligand.

A series of benzannulated N-heterocyclic compounds containing divalent 14 group atoms, C

A series of alkali metal capped cerium(IV) imido complexes, [M(solv)x][Ce═N(3,5-(CF3)2C6H3)(TriNOx)] (M = Li, K, Rb, Cs; solv = TMEDA, THF, Et2O, or DME), was isolated and fully characterized. An X-ray structural investigation of the cerium imido complexes demonstrated the impact of the alkali metal counterions on the geometry of the [Ce═N(3,5-(CF3)2C6H3)(TriNOx)]- moiety. Substantial shortening of the Ce═N bond was observed with increasing size of the alkali metal cation. The first complex featuring an unsupported, terminal multiple bond between a Ce(IV) ion and a ligand fragment was also isolated by encapsulation of a Cs+ counterion with 2.2.2-cryptand. This complex shows the shortest recorded Ce═N bond length of 2.077(3) A. Computational investigation of the cerium imido complexes using DFT methods showed a relatively larger contribution of the cerium 5d orbital than the 4f orbital to the Ce═N bonds. The [K(DME)2][Ce═N(3,5-(CF3)2C6H3)(TriNOx)] complex cleaves the Si-O bond in (Me3Si)2O, yielding the [(Me3SiO)CeIV(TriNOx)] adduct. The reaction of the rubidium capped imido complex with benzophenone resulted in the formation of a rare Ce(IV)-oxo complex, that was stabilized by a supramolecular, tetrameric oligomerization of the Ce═O units with rubidium cations.

The first X-ray structural characterization of bicorannulenyl dianion has been accomplished for two alkali metal salts, [Li+(THF)4]2[C40H182–] (1) and [Cs+(18-crown-6)]2[C40H182–] (2). This crystallographic study revealed the biaryl stereochemistry, geometry transformation upon acquiring two electrons, and different binding preferences of Li+ vs Cs+ ions in the solid-state products.

X-ray crystal structure study of cocrystallites of buckycatcher (2, C60H28) demonstrates a remarkable versatility of the molecular clip to accommodate guest molecules of various sizes and shapes. As demonstrated by the B97-D calculations, concave–concave conformation of the clip seems to be preferred for the gas-phase 1:1 inclusion complexes of 2 with a series of potential guests. However, the unprecedented concave–convex conformations were found in two of the reported solvates [i.e., 2·0.75(p-xylene) and 2·2PhNO2]. Three of the studied inclusion complexes with the highest calculated gas-phase binding energies (1,3,5-trinitrobenzene@2, and the previously reported C60@2 and C70@2) exhibit the analogous 1:1 supramolecular arrangements in the crystal state. On the other hand, p-xylene and PhNO2 solvates as well as DDQ/MeCN cocrystallite exhibit quite different stoichiometries and supramolecular arrangements, presumably enforced by the crystal packing forces. Dramatic variations of the intercentroid distances...

Spirogermabifluorene (C24H16Ge, 1) and the anionic products of its reduction with alkali metals were prepared and investigated by single-crystal X-ray diffraction. A monoanionic intermediate product of the reduction, formed upon the cleavage of a Ge–C bond and proton abstraction from the solvent, was isolated in the form of the cesium salt, [Cs+(diglyme)(C12H8GeC12H9−)] (2). Structural investigation of 2 revealed the presence of a tricoordinated germanium center and complexation of the cesium cation by two aromatic moieties. The reduction of 1 with an excess of alkali metals leads to the cleavage of the second Ge–C bond with subsequent elimination of biphenyl to give the C12H8Ge2− dianion which was crystallized as the sodium adduct, [{Na+(THF)}2(C12H8Ge2−)] (3). The structural elucidation for complex 3 shows η3- and η5-coordinations of the sodium ions to the π-system of dianions. The resulting Na⋯C and Na⋯Ge contacts along with the Na⋯OTHF interactions lead to the formation of the zigzag polymeric chains in the crystal lattice of 3.

Downsizing of alkali metal belts sandwiched between triply-reduced corannulene decks allows for the fine-tune separation and magnetic coupling of C20H10˙3– radicals., The first heterobimetallic sandwich-type aggregate formed by bowl-shaped corannulene trianion-radicals, C20H10˙3–, has been synthesized using mixed-metal reduction of C20H10. The product was crystallographically characterized to reveal the self-assembly of [Cs+//(C20H10 3–)/4K+/(C20H10 3–)//Cs+], in which two triply-charged corannulene decks encapsulate a rectangle of four potassium ions (the K···K separations are 4.212(4) and 5.185(4) Å), with the exterior concave bowl cavities being selectively filled by one cesium ion each. In order to provide insights into the geometrical features and electronic structure of this novel mixed-metal organometallic self-assembly, an in-depth theoretical investigation has been carried out. Specifically, the influence of internal metal binding on the geometry and magnetic coupling of C20H10˙3– radicals is investigated for Group 1 metals. This study reveals that replacement of the sandwiched potassium ions with larger (Cs) and smaller (Li) ions allows variation of the size of the encapsulated metal belts, and thus enables tuning of the coupling of C20H10˙3– radicals.

Mono- and dianions of a polycyclic compound with a central sp3-hybridized silicon atom, spirosilabifluorene (C24H16Si, 1), were prepared by reduction with alkali metals. The salts containing 1•– and 12– anions were isolated and studied by single-crystal X-ray diffraction. The lithium salt of the C24H16Si•– radical monoanion ([Li(THF)4+][1•–], 2) exists as a solvent-separated ion pair in the solid state. Substantially different geometrical parameters were found for each of the fluorene groups within the C24H16Si•– anion of 2 due to asymmetric charge distribution. The C24H16Si2– dianion was isolated in the form of its sodium ([{Na(THF)3+}{Na(THF)+(12–)], 3) or potassium ([{K(THF)+}2(12–)], 4) salt. The environment at the central silicon atom in the dianion is flattened in comparison to the monoanion and neutral compound, with the angle between the two fluorene planes measured at 55° in 12– vs 89° in 1•– and 83° in 10. The aggregation of dianions and alkali-metal counterions leads to the formation of dimeric...

Two new rubidium salts of the bowl-shaped corannulene monoanion radical C20H10•– (1•–), [Rb(15-crown-5)2+][C20H10–] (2) and [Rb(dicyclohexano-18-crown-6)+][C20H10–] (3), have been synthesized and structurally characterized in this work. An excess of 15-crown-5 ether provided full encapsulation of the rubidium ion in [Rb(15-crown-5)2]+, which precluded metal-directed π interactions with the anionic surface of C20H10•– in the solid-state structure of 2. The use of more sterically demanding dicyclohexano-18-crown-6 ether prevented the formation of polymeric chains previously seen with 18-crown-6 ether and favored the isolation of the discrete contact ion pair 3. Complex 3 is built on a convex η6 coordination of Rb+ to C20H10•–, reaffirming the exo-binding preference of rubidium ions toward the singly charged corannulene bowl. A rubidium salt of the planar coronene monoanion radical C24H12•– (4•–), [Rb(18-crown-6)+][C24H12–] (5), has also been prepared and structurally characterized to reveal a new binding mo...

Controlled reduction of corannulene (C20H10, 1) with lithium metal has been investigated in several O-donor solvent media (THF, DME, and diglyme). In contrast to the prior reduction studies performed in situ, the isolation of solid products of singly and doubly charged corannulene in the form of crystalline lithium salts has been accomplished. The single-crystal X-ray diffraction studies of two products containing monoreduced corannulene, [Li(DME)3+][1–] (2) and [{Li(15-crown-5)+}2][1–]2 (3), revealed the presence of naked bowl-shaped monoanions. The corannulene dianions have been crystallized from two different media as corresponding salts, [{Li(DME)+}{Li(DME)1.5+}]2[12–]2 (4) and [Li(diglyme)2+]2[12–] (5), illustrating the effect of solvents on the alkali metal coordination environment and binding to the curved π-carbon surfaces. The adduct 4 has Li+ ions bound to the five- and six-membered rings of the doubly reduced corannulene convex face. In contrast to the above contact ion pair obtained from the D...

N-Heterocyclic carbenes (NHC's) are known to serve as efficient substrates for the stabilization of various transient species possessing low-valent Group 14 elements and for the generation of double E=C bonds. Herein, we report that the thermal tri- and tetramerizations of pyridoannulated silylene 1 lead to the formation of remarkably stable silenes 2 and 3 featuring zwitterionic distribution of electron density. Co-oligomerization of 1 and its germanium analogue gives a related tetrameric product 4 containing low-valent germanium atom stabilized by binding with the partial carbene-character C atom. Bonding situations in 2–4 are best described as silene or germene with the significant zwitterionic distribution of electron density. The singlet diradical electronic state of 2 is 10 kcal mol−1 higher than the ground state configuration.

The coordination of C-F moieties to electrophilic metal cations has been increasingly recognized in f-element chemistry over the last two decades. These C-F→Ln/An interactions are readily identified in the solid state and can persist in solution. The binding energies of C-F→Ln/An interactions lead to their ready displacement to expose metal centers to substrates, which is implicated in cationic polymerization catalysts. C-F→Ln/An coordination is also an elementary step in C-F bond activation, proceeding through either homolytic or heterolytic cleavage of chemically inert C-F bonds. The influence of C-F→Ln/An interactions on the geometries of coordination compounds and their electronic impact on metal cations are also examined in this Perspective article.

Structurally authenticated, terminal lanthanide-ligand multiple bonds are rare and expected to be highly reactive. Even capped with an alkali metal cation, poor orbital energy matching and overlap of metal and ligand valence orbitals should result in strong charge polarization within such bonds. We expand on a new strategy for isolating terminal lanthanide-ligand multiple bonds using cerium(IV) complexes. In the current case, our tailored tris(hydroxylaminato) ligand framework, TriNOx(3-), provides steric protection against ligand scrambling and metal complex oligomerization and electronic protection against reduction. This strategy culminates in isolation of the first formal Ce═N bonded moiety in the complex [K(DME)2][Ce═N(3,5-(CF3)2C6H3)(TriNOx)], whose Ce═N bond is the shortest known at 2.119(3) Å.

X-ray data obtained for germylene 1 evidence its monomeric structure, unlike that of stannylene 2, which had been shown previously to form a coordination dimer. Raman spectra of solid and liquid 1 are identical, whereas the Raman spectra of solid 2 and its solution 2a differ significantly. The spectrum of 2 is complicated and contains the lines corresponding to N → Sn coordination bonds forming a dimer. The spectrum of 2a is simpler and close to that of monomeric 1, thus pointing to the rupture of the dimer in solution. The UV–vis spectrum of solid 2 exhibits a band corresponding to a transition involving the N → Sn coordination bonds. Quantum theory of atoms in molecules data estimate the energy of this bond as ∼19 kcal/mol. The aromaticity of 1 and 2 with their 10 π-electron systems including divalent Ge or Sn atoms is confirmed by negative nucleus-independent chemical shift values.

The reduction of corannulene (C20H10) with excess lithium metal in a strong chelating O-donor solvent, diglyme, leads to the formation of the highly reduced C20H104– anion. However, in contrast to the formation of the sandwich-type supramolecular aggregate [Li5(C20H104–)2]3– observed in THF, corannulene tetraanions and lithium counterions in diglyme form only contact ion pairs according to 7Li NMR spectroscopy. Furthermore, the slow dissociation of the premade sandwich [Li5(C20H104–)2]3– in neat diglyme has been demonstrated by multinuclear NMR spectroscopy. In contrast, the [Li5(C20H104–)2]3– sandwich can be crystallized from the THF/diglyme mixture as the new crystalline product [Li(THF)2(diglyme)]+[Li2(THF)(diglyme)//Li5(C20H104–)2]−, showing a complex 1D hybrid architecture according to the single-crystal X-ray diffraction study.

Mono-, di- and tetraanions of rubrene, (C42H28, Rub0), were generated by the controlled reduction of neutral polyarene with various alkali metals in the appropriate solvent. The X-ray diffraction studies of the resulting adducts of Rub1–, Rub2– and Rub4– with alkali-metal ions revealed the distortion of the rubrene core upon the stepwise acquisition of electrons. Coordination of the Cs+ ion and a noticeable deformation of Rub1– are observed at the first reduction step. Two types of rubrene dianions showing an essentially different conformation and coordination environment for the central tetracene core have been seen in the cesium adduct of Rub2–. Various types of supramolecular assembly between the tetrareduced rubrene anion, Rub4–, and lithium or rubidium cations have been found in the corresponding products in the solid state. The structures of rubrene anions and their aggregation with alkali-metal ions in solution have been studied by ESR and multinuclear NMR (1H, 13C, 7Li and 133Cs) spectroscopy.

Bowl-shaped mono- and dianions are prepared by reduction of corannulene (C(20)H(10), 1) with sodium and potassium metals in the presence of [18]crown-6 ether. Single-crystal X-ray diffraction studies of two sodium salts, [Na(THF)(2)([18]crown-6)](+)[1(-)] (2a) and [Na([18]crown-6)](+)[1(-)] (2b), reveal the presence of naked corannulene monoanions 1(-) in both cases. In contrast, the potassium adduct, [K([18]crown-6)](+)[1(-)] (3), shows an η(2)-binding of the K(+) ion to the convex face of 1(-). For the first time, corannulene dianions have been isolated as salts with sodium, [Na(2)([18]crown-6)](2+)[1(2-)] (4a) and [Na(THF)(2)([18]crown-6)](+)[Na([18]crown-6)](+)[1(2-)] (4b), and potassium counterions, [K([18]crown-6)](2)(+)[1(2-)] (5). Their structural characterization reveals geometry perturbations upon addition of two electrons to a bowl-shaped polyarene. It also demonstrates η(5)- or η(6)-binding of metals to the curved carbon surface of 1(2-), depending on the crystallization conditions. Both mono- and doubly-charged corannulene bowls show the preferential exo binding of Na(+) and K(+) ions in all investigated compounds. Various types of C-H···π interactions are found in the crystals of 2-5. The UV/Vis, ESR, and (1)H NMR spectroscopic studies of 2-5 indicate different coordination environment of corannulene anions in solution, depending on the metal ion.

Stable nonplanar polyaromatic carbocation, [C20H10CH2Cl]+ (1) having the chloromethyl group covalently bound to the hub site of corannulene was prepared by reaction of C20H10 with CH2Cl2 and GaCl3 in the presence of SnCl2. The X-ray diffraction study of the resulting salt, [1]∙[(SnCl)(GaCl4)2], revealed the presence of two rotational isomers for 1 in the crystal lattice. In the solid state, a complex polymeric inorganic anion of the overall composition [(Sn2Cl2)∙(GaCl4)4]∞ is formed with the cationic π-bowls being attached to its backbone. Both X-ray and nuclear magnetic resonance spectroscopic data of 1 indicate the sp3 hybridization of the C-atom of corannulene at the attachment point. An electrochemical investigation of 1 and the series of related corannulene cations, [C20H10R]+ (R = CHxCl3–x (x = 0–3) and CH2CH2Cl), was carried out to elucidate the electronic consequences triggered by the above changes. This study revealed that the surface decoration of corannulene core makes the reduction of the resulting [C20H10R]+ species significantly more difficult (by about 0.3 V) with respect to the parent bowl. To evaluate the consequences of the observed one-electron reduction and conceivable but not seen second-electron reduction on the corannulene core, theoretical calculations at the density functional theory level have been carried out. Copyright © 2012 John Wiley & Sons, Ltd.

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.

The ion size matters: the structures of corannulene monoanions crystallized with Cs(+) and Rb(+) ions in the presence of [18]crown-6 reveal the intrinsic binding preferences of alkali metals and allow evaluation of the bowl deformation caused by negative charge distribution and metal binding. The large cesium cation coordinates exclusively to the concave face of C(20) H(10)(-), whereas the smaller rubidium cation exhibits convex binding.

In addition toits own unique properties, corannulene serves as a primarymodel for both theoretical and experimental studies for avariety of curved carbon networks ranging from fullerenes tonanotubes.Todate,theorganicreactionsofcorannulenehavebeen mainly limited tothe derivatization of its exteriorand tosynthetic transformations of rim-bound functional groups.

The X-ray crystallographic study of C60H28 consisting of two tethered corannulene bowls revealed a unique solid-state packing based on tight convex-concave π-π interactions. The controlled reduction of C60H28 resulted in the isolation and structural characterization of its dianion in the form of the rubidium salt that shows an entrapment of counterions by an anionic pincer.

The tetranuclear mixed-valent oxo-cluster [SnIISnIVO(O2CCF3)4]2 (1) has been prepared by reacting SnCl2 with AgO2CCF3 in a sealed ampoule at 90 °C. Alternatively, 1 was obtained by acidolysis of Ph3SnSnPh3 with trifluoroacetic acid in solution. The X-ray diffraction study of 1 revealed the presence of a SnIIOSn 2 IV OSnII core comprised of the penta-coordinated divalent and six-coordinated tetravalent tin atoms. The 119Sn NMR studies confirmed the stability of the cluster in solution and the presence of two different oxidation states of tin. An acidolysis of Ph3SnSnPh3 in the presence of [Cu 2 II (O2CCF3)4] followed by sublimation of the resulting product at 90 °C afforded the first trinuclear mixed metal Sn–Cu cluster [(C6H5)2Sn 2 IV CuIIO(O2CCF3)6] (2). The X-ray diffraction analysis of 2 revealed the presence of two phenyl groups attached to the six-coordinated tin(IV) atoms and the tetragonal pyramidal environment of the copper(II) atom. Both complexes have been obtained free of exogenous ligands.

The Raman and IR spectra of the complexes (CO)5CrSnCl2·THF (1), (CO)5WSnCl2·THF (2), (CO)5CrGeCl2·THF (3), (CO)5WGeCl2·THF (4), (CO)5CrSnCl2·2THF (5), and (CO)5WSnCl2·2THF (6) were measured and interpreted using quantum chemical calculations. Complexes 3 and 5 were characterized by X-ray analysis. The stretching vibrations of the CO groups in the spectra of solutions of complexes 1–6 obey the selection rules for C 4ν local symmetry. For the complexes containing 0 (type A), 1 (type B), and 2 (type C) THF molecules, a comparison was made of the calculated and experimental M $$ \underline \cdots $$ EII bond lengths and energies, as well as the ν(CO) vibrational frequencies. The contribution of the π-component to the M $$ \underline \cdots $$ EII bond decreases in the order A→B→C and leads to enhancement of the donor ability of the carbene-like ligand and to a slight elongation and weakening of this bond. An attempt to grow crystals of complex 6 in air unexpectedly resulted in a polynuclear complex [(CO)5WSn(Cl)(μ-OH)2SnCl2(μ-OH)]2·6THF, which was characterized by X-ray analysis and Raman spectroscopy.

The cyclic tetraamine 2, prepared by the hydrogenation of tetraimine 1, was used for the preparation of the macrocyclic bisgermylene 3 with two lutidine bridging groups. The molecular structure determination of tetraamine 2 exhibits a Ci-symmetric molecule in the solid state. The macrocyclic bisgermylene 3 shows weak intramolecular Ge···Ge and Ge···N interactions in the solid state.

The reaction of 2 equiv of Sn[N(SiMe3)2]2 with 1,2-benzodithiol gave the unstable N,S-substituted bis-stannylene 1, which decomposes in solution to yield Sn[N(SiMe3)2]2 and the S-heterocyclic stannylene 2. An X-ray diffraction analysis with crystals of 1 revealed the presence of two three-coordinated tin atoms with an S,S,N donor set and strong intramolecular Sn−S interactions. The related reaction of 3 equiv of Sn[N(SiMe3)2]2 with 2 equiv of 1,2-benzodiol gave the tris-stannylene 3 with two different types of SnII atoms. An X-ray diffraction analysis with crystals of 3 shows the central tin(II) atom to be coordinated by four oxygen donors while two additional peripheral tin(II) atoms are three-coordinated by a mixed O,O,N donor set. The central O4Sn core in 3 is strongly pyramidalized. In contrast to bis-stannylene 1 tris-stannylene 3 is stable both in the solid state and in solution.

The current state of the chemistry of mono- and bidentate N-heterocyclic germylenes, stannylenes, plumbylenes, and related compounds is reviewed with special emphasis placed on benzannulated derivatives. The preparation, electronic structure, aggregation behaviour, and the coordination chemistry of the free benzannulated carbene analogues and their adducts with Lewis bases and complexes with transition metals are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The N-heterocyclic benzannulated bisgermylene 3 with a 1,3-(CH2)2C6H4 linker between the germylene moieties and steri- cally non-demanding N-CH2CH3 groups has been prepared. An X- ray diffraction study shows intermolecular Ge···N interactions in the solid state. This interaction leads to a polymeric arrangement of the bisgermylene molecules in the crystal lattice. The bisgermy- lene 4 with a long and flexible (CH2)5 linking unit between the germylene moieties reacts with (Mo(ndb)(CO)4) to yield complex

The benzannulated bisstannylenes linked by a CH2C(CH3)2CH2 (3) or 1,3-(CH2)2C6H4 bridging unit (4) react with [Ni(cod)2] to give the intensely colored homoleptic Ni0 complexes 5 and 6. X-ray diffraction and 119Sn NMR studies for the complex of the bisstannylene with the CH2C(CH3)2CH2 linker 5 reveal the presence of four identical tin atoms. For the nickel complex 6 of the bisstannylene ligand, which contains a 1,3-(CH2)2C6H4 bridging unit, two types of tin atoms with different coordination environments were found both in solution and in the solid state.

Symmetrically and unsymmetrically N,N'-substituted benzimidazolin-2-stannylenes with sterically nondemanding alkyl (Me and Et) and Lewis base functional groups (-(CH2)nOMe, -(CH2)nNMe2; n=2, 3) have been synthesized by the transamination reaction between suitably substituted o-phenylenediamines and Sn[N(SiMe3)2]2. The N,N'-dimethyl-substituted stannylene 3 exists in the solid state as a bimolecular aggregate which is held together by strong intermolecular Sn...N interactions leading to three-coordinated tin atoms. The benzimidazolin-2-stannylenes with N,N'-(CH2)nOMe substituents (5, n=2; 6, n=3) exhibit weak intramolecular Sn...O interactions in solution. Benzannulated stannylenes with N,N'-(CH2)nNMe2 substituents (7, n=2; 8, n=3) are again dimers which exhibit both intramolecular Sn...NMe2 and intermolecular Sn...N interactions, which leads to tri- or tetracoordinated tin atoms. Some unsymmetrically N,N'-substituted benzimidazolin-2-stannylenes have also been synthesized. The molecular structures of 3, 5, and 8 and the relation between the chemical shift recorded for the tin atoms and the solvent (C6D6 or THF-d8) used for recording 119Sn NMR spectra will be discussed.

Benzannulated N-heterocyclic bis(germylenes) with pincer ligand topology have been prepared by the reaction of N,N′,N″,N″′-tetralithiated tetraamines with GeCl2·1,4-dioxane or by the transamination reaction between a tetraamine and Ge[N(SiMe3)2]2. X-ray diffraction studies have shown, that the bis(germylenes) exist as monomers in the solid state. Significant intramolecular Ge···Ge and Ge···N interactions have been observed for the lutidine-bridged bis(germylene). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Bridged bis(benzimidazoline-2-germylene)s have been prepared in good yield by the reaction of N,N‘,N,‘ ‘N‘ ‘‘-tetralithiated tetraamines with GeCl2·1,4-dioxane or by the direct transamination reaction between tetraamines and Ge[N(SiMe3)2]2. Four bis(benzimidazoline-2-germylene)s with different bridging groups between the benzimidazoline-2-germylene groups have been shown by X-ray diffraction analysis to exhibit different types of weak intermolecular interactions, but no significant Ge···Ge interaction was observed in the solid state. One of the bisgermylenes disproportionates in solution at ambient temperature to yield a Ge(IV) spiro compound and elemental germanium. The bisgermylenes can act as chelate ligands replacing norbornadiene in [Mo(nbd)(CO)4] with formation of complexes of the type [Mo(η2-bisgermylene)(CO)4], which have been investigated by 1H NMR and vibrational spectroscopy and X-ray diffraction analysis.

The first X-ray structural characterization of the triply-reduced corannulene (C20H10) reveals its ability to form a novel type of supramolecular assembly with large cesium ions, [Cs+//(C20H103–)/4Cs+/(C20H103–)//Cs+]., The first structural characterization of the transient triply-reduced state of corannulene (C20H10) is accomplished. The X-ray crystallographic study reveals that the C20H10˙3– trianions, generated by corannulene reduction with metallic cesium, form a novel type of supramolecular sandwich-type assembly, [Cs+//(C20H103–)/4Cs+/(C20H103–)//Cs+]. In the product, two triply-charged corannulene decks encapsulate a rectangle of four cesium ions with the external concave bowl cavities being filled by one cesium ion each. The structural investigation is augmented by in-depth theoretical calculations to provide insights into the geometrical features and electronic structure of this unique organometallic self-assembly.

Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh 3 have been reported, the structures of the complexes Cl 2 Ge·C 4 H 8 O 2 and Cl 2 Ge·PPh 3 updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X 2 M with 1,4-dioxane, intermolecular coordination X⋯M plays a prominent role, whereas the corresponding complexes with PPh 3 are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X 2 M II particles, still persists, suggesting that the X 2 M moieties preserve their specifity as carbene analogues also in the complexes.