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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.

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.

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.

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.

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.

The first members of a new class of supramolecular organometallic compounds with mixed-alkali-metal cluster cores, LiK5 and Li3 K3 , sandwiched between two four-fold reduced corannulene decks are prepared and fully characterized. The triple-decker supramolecular anions, [(C20 H10 (4-) )(LiK5 )(6+) (C20 H10 (4-) )](2-) and [(C20 H10 (4-) )(Li3 K3 )(6+) (C20 H10 (4-) )](2-) , illustrate a record ability of bowl-shaped and highly charged corannulene to provide all its sites, five benzene rings fused to a central five-membered ring, for binding of six alkali-metal ions. The previously unseen engagement of the hub-site of C20 H10 (4-) in lithium binding is accompanied by unprecedented shifts up to -24 ppm in (7) Li NMR spectra. The discussion of product formation mechanism, augmented by calculations, is provided.

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...

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.

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.

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 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.

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.

The vibrational spectra of tetravalent metal halides (M = Si, Ge, Sn) and the corresponding dihalocarbene analogs MIIHal2, obtained by the authors, and the relevant published data are compared. The spectra of the MIIHal2 species exhibit inversion of the M-Hal stretching frequencies (νs(MIIHal) > ν as(MIIHal)). This can be used for analytical purposes and allows one to distinguish between the spectra of the MIV and MII halides. The IR and Raman spectra of the complexes of dihalogermylenes and -stannylenes with triphenylphosphine and 1,4-dioxane also exhibit inversion of the ν(MHal) stretching frequencies. This confirms the conclusion drawn earlier based on the analysis of the geometric parameters and reactivities of the complexes in question that the divalent state of the M atom in these species is retained.

A new class of exceptionally stable asymmetric N-heterocyclic germylenes, stannylenes, and plumbylenes has been successfully isolated and characterized by single-crystal X-ray diffraction analysis and multinuclear NMR spectroscopy. Their stability results from tetrameric supramolecular aggregation through strong intermolecular Npy →E(II) (E=Ge, Sn, Pb) interactions involving the nitrogen atom of a neighboring pyridine moiety. The electronic structures and stabilities of the prepared divalent derivatives of Ge, Sn, and Pb in monomeric and aggregated forms are discussed based on theoretical investigations.

1,3-Di-tert-butyl-2,2-dichloro-1,3-diaza-2-germa-4-cyclopentene (1) was synthesized from N,N-di-tert-butyl-1,2-diiminoethane (NN) and GeCl2. 1 undergoes slow transformation at room temperature to t...

This work overviews the coordination properties and aggregation patterns of charged π-carbon surfaces with the Group 1 metal ions. A detailed account of works on single- and multielectron reduction of planar and curved polyarenes is given based on structural considerations. First, a wealth of structurally characterized examples of alkali metal complexes with planar polyaromatic hydrocarbons having fused six-membered rings only and a mix of six- and five-membered ring systems is presented. This follows by the discussion of coordination preferences of negatively charged geodesic polyarenes that include fullerene fragments (also referred to as buckybowls or π-bowls) and fullerenes. Only recently, the first anionic products of buckybowls with alkali metal counterions have been isolated in the solid state and crystallographically characterized. This allowed to reveal the coordination preferences of mono-, di-, and tetrareduced bowl-shaped anions and to evaluate geometric perturbations of their core upon multielectron acquisition. Only a few structurally confirmed examples of fullerene anions isolated from solutions with alkali metal counterions have been so far reported. Their charges range from 1 − to 3 − only with the highly charged anions of C60 still awaiting their isolation and structural characterization. These recent findings and their implications for our understanding of alkali metal intercalation relevant to the design and advancement of novel carbon-based electrode materials are highlighted.

Benzannulated bisstannylenes, exhibiting a CH 2 C(CH 3 ) 2 CH 2 linking unit and CH 2 tBu (1) or CH 2 CH 2 CH 2 NMe 2 (2) N-substituents, and their molybdenum tetacarbonyl complexes 3 and 4 have been prepared. The complexes 3 and 4 exhibit remarkably short Mo-E bond lengths compared to the related biscarbene and bisgermylene complexes. The experimentally determined bonding parameters of the molybdenum bisstannylene complexes are discussed based on DFT calculations.

The reaction of the benzannulated bisstannylene ligand 2 with Sn═O or Pb═O generated in situ gave the pincer complexes 3 and 4. Both complexes have been characterized by X-ray diffraction and multinuclear NMR spectroscopy. A divalent state has been found by Mossbauer spectroscopy for the tin atoms in complexes 3 and 4.

The intercalation of alkali metal ions into carbon-based aromatic systems is of great interest in materials science due to the increased need for stable anode materials with high capacity of energy storage. Currently, graphite, a sp2-hybirdized carbon network, is the key anode component in rechargeable Li-ion batteries. Carbon allotropes with nonplanar π-surfaces, ranging from fullerenes to nanotubes, are now under investigation as prospective anode materials. The curved carbon networks of fullerenes and nanotubes are often modeled by open bowl-shaped polyaromatic hydrocarbons, such as the smallest curved fullerene fragment, corannulene (C20H10). One of the most fascinating properties of such bowl-shaped polyarenes and fullerenes is their ability to reversibly uptake and delocalize extra electrons upon multi-electron reduction without significant rearrangement and deformation of their carbon framework [1,2]. Notably, the anode material fabricated from corannulene shows a high reversible lithium capacity (602 mAh/g). This is almost twice as high as the theoretical capacity of the commonly used fully lithiated planar graphite material (LiC6, 372 mAh/g). In our work, we target the X-ray structural elucidation of metal intercalation patterns of carbon-rich curved polyarenes with light alkali metal ions, such as Li and Na, and compare those with extended planar polyaromatic systems. Recently, we expanded this study to the light alkaline earth metal, Mg, as its atomic radius is very close to that of Li. In addition, magnesium is cost effective and abundant, and thus presents great interest in the emerging energy storage technologies.

The cover picture shows some selected examples of benzannulated germylenes, stannylenes and plumbylenes and their aggregation behaviour. In addition, some complexes of bidentate bis(germylenes) and bis(stannylenes) are depicted, demonstrating the versatile coordination chemistry of these ligands with transition and main group metals. Details are presented in the Microreview by A. V. Zabula and F. E. Hahn on p. 5165 ff.

Reaction of stoichiometric amounts of the benzannulated bisstannylene with [Pt(nbe)(3)] in the presence of PPh(3) and OPPh(3) gave complex with an Sn(2)PtP(2) core and an O[double bond, length as m-dash]PPh(3) molecule coordinated to one of the stannylene donors according to an X-ray diffraction study. Complex was also obtained by substitution of two PPh(3) ligands in [Pt(PPh(3))(4)] by the bisstannylene in the presence of OPPh(3). The reaction of 2 equivalents of the bisstannylenes and exhibiting different spacers between the stannylene donors with one equivalent of [Pt(nbe)(3)] gave the intensely coloured homoleptic [Pt(bisstannylene)(2)] complexes and . Both complexes were characterized by X-ray diffraction studies which demonstrated the presence of four identical tin atoms for complex and two different types of tin atoms for complex . Temperature dependent (119)Sn NMR spectra for complex with the 1,3-(CH(2))(2)C(6)H(4) bridging unit between the stannylene donors indicate the presence of an equilibrium between complexes with three- and tetra-coordinated platinum atoms in solution.