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A cluster composed of three dilithium dibenzosilepinides and two Li2O molecules showed downfield shifted 7Li{1H} NMR signals (δ = 6.3, 4.4) due to the paratropic ring currents of the dianionic dibenzosilepins.

Herein we propose a new strategy for hyperconjugative antiaromatic compounds utilizing negative charges and design the 5,5-diphenyldibenzo[b,f]silepinyl dianion (pseudo 16π-electron system) in which negative hyperconjugation occurs between the anionic π-cloud and the σ*(Si–Ph) orbital. Essentially, reduction of the dibenzo[b,f]silepin with lithium readily generated a dilithium salt of the dibenzosilepinyl dianion, and its hyperconjugative antiaromaticity has been evidenced by the upfield shifts of 1H NMR signals and theoretical calculations, including large NICSzz values and ACID plots.

Double CH activation at a bridging methylene group in methylenediphenols to generate carbene-bridged dinuclear iridium complexes is presented. Reaction of 2,2′-methylenediphenol derivatives CH2(C6H...

The synthesis and electronic structure of a tin analogue of the cycloheptatrienyl anion are described. The reaction of 5,5-diphenyldibenzo[b,f]stannepin with lithium at low temperatures reductively...

Investigation of the vinylidene rearrangement of phosphorus- and sulfur-substituted internal alkynes at a ruthenium center unveiled selective 1,2-migration of P- and S-substituents and unexpected d...

Perfluorinated aromatic compounds, the so-called perfluoroarenes, are widely used in materials science owing to their high electron affinity and characteristic intermolecular interactions. However, methods to synthesize highly strained perfluoroarenes have remained elusive so far, which greatly limits their structural diversity. Herein, we report the synthesis and isolation of perfluorocycloparaphenylenes (PFCPPs) as a class of ring-shaped perfluoroarenes. Using macrocyclic nickel complexes, we succeeded in synthesizing PF[n]CPPs (n = 10, 12, 14, 16) in one-pot without noble metals. The molecular structures of PF[n]CPPs (n = 10, 12) were determined by X-ray crystallography to confirm their tubular alignment. Photophysical and electrochemical measurements revealed that PF[n]CPPs (n = 10, 12) exhibit wide HOMO–LUMO gaps, high electron affinity, and strong phosphorescence at low temperature. PFCPPs are not only useful as electron-accepting organic semiconductors but can also be used for accelerating the creation of topologically unique molecular nanocarbon materials.

Herein we propose a new strategy for hyperconjugative antiaromatic compounds utilizing negative charges and design the 5,5-diphenyldibenzo[

A new possibility of a Rh(I) complex is demonstrated. An inverted sandwich Rh(I) complex bearing a dianionic plumbole ligand was synthesized by the reaction a dilithioplumbole with [Rh(cod)Cl]2. The plumbole ligand functions as a π-donor stronger than the cyclopentadienyl ligand, as evidenced by quantum-chemical calculations. The Rh(I)−plumbole complex can be applied as a catalyst for an intramolecular [2+2+2] cycloaddition reaction of a triyne.

Vinylidene rearrangement of internal acylalkynes and sulfonylalkynes at a d6 molybdenum center is presented. Treatment of [(η7-C7H7)MoBr(dppe)] with various acylalkynes R–C≡C–COR′ in the presence o...

New types of diaryloxystannylenes and -plumbylenes have been synthesized and structurally characterized. Lappert's diaminostannylene and -plumbylene E[N(SiMe3)2]2 (E = Sn, Pb) react with 1,3-diethers of tetrathiacalix[4]arene bearing benzyl or SiiPr3 groups to give the corresponding diaryloxystannylenes and -plumbylenes embedded in thiacalix[4]arene, respectively. X-ray diffraction analysis revealed that these tetrylenes exist as monomers in the solid-state. The structure of the thiacalix[4]arene scaffold is highly dependent on the substituents on the phenolic oxygen atoms. The benzyl derivatives adopt apparently C2-symmetric structures with a strong intramolecular Sn⋯OBn coordination, whereas the SiiPr3 derivatives have a distorted thiacalix[4]arene skeleton with relatively weak intramolecular E⋯OSiiPr3 and E⋯S interactions. On the basis of the 119Sn{1H} and 207Pb NMR studies in solution, the tin and lead atoms in the benzyl derivatives are strongly coordinated by the ethereal oxygen atoms, whereas those in the SiiPr3 derivatives are weakly coordinated by the bridging sulfur atoms or ethereal oxygen atoms. The tetrylene complexes of thiacalix[4]arene presented here do not show any isomerization in a temperature range from 20 to 110 °C, which is in sharp contrast to the fact that related diaryloxygermylenes and -stannylenes embedded in calix[4]arene underwent isomerization under heating conditions. This difference could be attributable to the ring size of thiacalix[4]arene larger than that of calix[4]arene.

The first examples of κ3-O,C,O tridentate calix[4]arene transition-metal complexes [Cp*M(p-tBucalix[4]arene(2−)-κ3-O,C,O)] (M = Ir, Rh) that are stable both in the solid state and in solution were synthesized. The reaction of the Ir complex with 2 equiv of xylyl isocyanide afforded the (η1-Cp*)Ir(CNXy)2 complex in which the Cp* ligand is slipped from an η5 to an η1 fashion, although ring slippage of an η5-Cp* ligand is very uncommon in comparison with that of Cp. The reaction of the (η1-Cp*)Ir complex with additional 1 equiv of isocyanide resulted in the liberation of the Cp* ligand as Cp*H, which was confirmed by 1H NMR. This study provides the first observation of stepwise dissociation of a Cp* ligand from group 4–10 transition-metals via η1 coordination. This unique phenomenon seems to be facilitated by flexible coordination of an OH group in the C-metalated calix[4]arene ligand.

Reactions of [Cp*Ir(PPh3)Cl2] with various internal acyl­alkynes in the presence of NaBArF 4 resulted in the selective formation of iridacycles via vinylidene rearrangement. 13C-labeling experiments revealed that the acyl group selectively migrates to the other acetylenic carbon atom. This trend is the same as that in the vinylidene rearrangement of internal alkynes at a group 8 metal center.

Rare examples of P–C reductive elimination in ruthenium complexes to generate phosphonium salts are presented. Triarylphosphines are converted into benzophospholium or phosphaphenalenium ligands via cyclometalation and 1,2-insertion of an alkyne followed by P–C reductive elimination. The intermediate in each step was successfully characterized using NMR and X-ray diffraction studies.

A palladium-free, short-step synthesis of [10]cycloparaphenylene ([10]CPP) has been developed. The key macrocyclization step was performed by a nickel-mediated homocoupling of a newly designed U-shaped unit 2. Surprisingly, the rectangular macrocycle 3 was obtained in high yield compared with previous macrocyclization reactions in CPP syntheses. X-ray crystallography as well as DFT calculation revealed unstrained structure of the macrocycle 3.

Reactions of an anionic heavy ruthenocene with CCl4, MeI, EtBr and Me3SiCl afforded the first stannole monoanion complexes. Surprisingly, coordination modes of the stannole rings are highly dependent on the substituents on the tin atom. The chloro derivative exhibits a η(4)-fashion-like coordination mode with a bent stannole ring, whereas the trimethylsilyl derivative adopts the conventional η(5)-coordination mode. Coordination modes of the alkyl derivatives are in between the two types. Cyclic voltammograms for these complexes reveal that the electron-donating character of the stannole ligand becomes stronger as the stannole ring becomes planar. Theoretical calculations elucidate that the different coordination modes originate from both electronegativity of an adjacent atom to the tin atom and bulkiness of a substituent on the tin atom.

To explore the coordination chemistry of dibenzopentalene dianion, reactions of two dilithium dibenzopentalenides having different silyl substituents with Cr(CO)

Dilithiostannoles, which are aromatic tin-containing ring compounds, were proposed to have stannylene character, as judged from their NMR analysis. We herein report on the synthesis of silyl-substituted dilithiostannoles, which were characterized by NMR spectroscopy and X-ray diffraction analysis. The silyl-substituted derivatives also exhibit features characteristic of aromatic dilithiostannoles such as 7Li NMR signals at high-field area and no C–C bond alternation in the stannole rings. Theoretical calculations and the 119Sn NMR chemical shifts revealed that the stannylene character in the silyl-substituted dilithiostannoles is enhanced due to greater interaction between 5p (Sn) and LUMO (butadiene) in comparison to those in alkyl and aryl derivatives. The 119Sn Mossbauer spectra of dilithiostannoles were measured for the first time, indicating that each of the tin atoms in dilithiostannoles can be characterized as having Sn(II) character.

An anionic ruthenocene with an η5-coordinating plumbole ligand was prepared and reacted with electrophiles to afford plumbole complexes., An anionic ruthenocene derived from a dilithioplumbole complex was prepared. In the complex, the plumbole ligand coordinates a ruthenium atom in an η5-fashion, similar to the cyclopentadienyl ligand in ferrocene. The ruthenocene that has the aromatic π-ligand with the heaviest group 14 element reacted with electrophiles to afford the plumbole complexes wherein the plumbole ligands show deviation from planarity, in contrast to the planar plumbole ring in the anionic ruthenocene. The bent angles of the plumbole ligands are dependent on the substituents on the lead atoms. Cyclic voltammetry measurements revealed that the plumbole complexes are oxidized more easily than the corresponding stannole complexes.

In contrast to olefin complexes, their congeners of heavier elements display various coordination modes, and their complexes may be present as bis(metallylene) complexes, with side-on coordination, as metallacyclopropanes, or as π complexes. In the course of our studies on the reactivity of dilithiostannoles towards transition-metal reagents, three-membered TiSn2 and six-membered Ti2 Sn4 ring complexes were obtained. According to its geometric parameters, NMR analysis, and theoretical calculations, the TiSn2 complex cannot be categorized into any of these previously described bonding modes. Therefore, a novel resonance structure has been proposed for a complex that has a delocalized σ-orbital over the TiSn2 ring to understand its electronic structure. The mechanism for the formation of the Ti2 Sn4 ring complex and its EPR spectrum are also discussed.

Reaction of a dilithiostannole with Cp2HfCl2 (Cp = cyclopentadienyl anion, C5H5–) afforded a dinuclear hafnium complex bridged by a stannole dianion ligand, (Cp2ClHf)2[μ-η1;η1-{SnC4(SitBuMe2)2Ph2}]. The product was fully characterized by NMR, elemental analysis, and X-ray diffraction analysis. The product adopts a new coordination pattern in the coordination chemistry of metallole dianion ligands, μ-η1;η1-fashion. Unlike aromatic μ-η5;η5-stannole dianion ligands in triple-decker-type sandwich complexes we previously reported, the stannole ring of the product has 1,3-diene character, revealing its nonaromatic nature. Electronic structures of stannole dianion ligands are therefore strongly affected by their coordination modes.

Research on zero-valent p-block elements is a recent hot topic in synthetic and theoretical chemistry because of their novel electronic states having two lone pairs in both the s- and p-orbitals. It is considered that σ-donating ligands bearing large substituents are essential to stabilize these species. Herein, we propose a new approach using butadiene as a 4π-electron donor to stabilize zero-valent group 14 elements. During our study to explore the coordination chemistry of stannacyclopentadienyl ligands, unexpected products, in which the tin atom is coordinated by a butadiene in a η(4)-fashion, were obtained. Because butadiene is a neutral 4π-electron donating ligand, the formal oxidation number of the tin atoms of the products should be zero, which is supported by X-ray diffraction analysis and theoretical calculations. A mechanism for the formation of the products is also described.

Many optoelectronic organic materials are based on donor-acceptor (D-A) systems with heteroatom-containing electron donors. Herein, we introduce a new molecular design for all-carbon curved oligoparaphenylenes as donors, which results in the generation of unique shape-persistent D-A macrocycles. Two types of acceptor-inserted cycloparaphenylenes were synthesized. These macrocycles display positive solvatofluorochromic properties owing to their D-A characteristics, which were confirmed by theoretical and electrochemical studies.

Reduction of THF-stabilized plumbacyclopentadienylidene with lithium afforded dilithioplumbole. On the other hand, oxidation of the dilithioplumbole provided the starting plumbacyclopentadienylidene. This is the unprecedented example of a reversible interconversion between group 14 M(II) and its dianionic species bearing organic substituents.

The neutral triple-decker ruthenocenes and anionic ruthenocene bearing a stannole dianion were successfully synthesized by the reactions of dilithiostannoles with [Cp*RuCl]4. This is the first example of a transition-metal complex bearing a group 14 metallole dianion with μ-η(5):η(5) coordination mode. These complexes were fully characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. In the complexes, each of the ruthenium atoms is coordinated by the stannole ring in an η(5)-fashion. The aromaticity of the stannole dianion moieties is retained judging from no C-C bond alternation in the stannole rings. CH/π interaction was found in the packing structure of the SiMe3 derivative, which leads to a well-ordered column-like structure. The oxidation wave of the triple-decker complex was observed at -0.43 V (vs ferrocene), which reveals that the triple-decker type heavy ruthenocene is oxidized more easily than the ferrocene. Comparison of the oxidation potential between the triple-decker complex and decamethylruthenocene (Cp*2Ru, Cp* = η(5)-C5Me5) reveals that a stannole ligand functions as an electron-donating ligand much stronger than the conventional electron-rich Cp* ligand.

Reduction of phenyl(silyl)ethynes with potassium followed by quenching with iodine gave dibenzopentalenes in moderate yields. The intermediates of the reactions, dipotassium dibenzopentalenides, were isolated. The first dibenzopentalene-transition-metal complex was successfully synthesized. The ruthenium atoms are located above the six-membered rings. However, X-ray diffraction analysis and theoretical calculations revealed that the aromatic nature of the five-membered rings was retained. The cyclic voltammetry of the Ru complex revealed two oxidation waves with relatively large separation.

1-Lithio-1-phenyl- and 1-lithio-1-trimethylsilylstannoles were synthesized and the corresponding lithium salts of stannole anions were characterized by X-ray diffraction analysis. The five-membered...

Reactions of tetraethyldilithiostannole 1 with [Cp*RuCl]4 afforded not η(5)-stannole dianion complexes but two novel bis(stannylene)-bridged dinuclear ruthenium complexes, which have butterfly and inverse-sandwich structures, respectively, depending on the stoichiometry of [Cp*RuCl]4 toward dilithiostannole. The redox behavior between the two complexes is found to be reversible. The molecular structures were determined by X-ray diffraction analysis. The Ru-Ru bond of the butterfly complex is 2.3428(6) Å, which is the shortest among those of dinuclear ruthenium complexes having Cp or Cp*Ru units. Theoretical calculations revealed that the very short Ru-Ru bond is due to the presence of one σ bond between the ruthenium atoms and two three-centered bonds delocalized over the two Ru2Sn rings.

Reduction of tetraethyldiphenylstannole 3 with lithium afforded tetraethyldilithiostannole 2, and its considerable aromatic character was evaluated by X-ray diffraction analysis and theoretical cal...