聚磷阴离子的立体构型和稳定性

聚磷阴离子的种类繁多, 存在于过渡金属盐、稀土金属盐、有机物、氢化物和以配位体形式生成的金属络合物等化合物中, 聚磷阴离子是磷烷、聚磷金属盐以及聚磷有机物的组成和结构核心。在形成聚磷化物时, 稳定的聚磷阴离子扮演着重要的中间体角色。从大量聚磷化物的实验结构和理化性质出发, 用从头算(ab initio)RHF/6-311++G(d)和MPW1PW91/G96PW-91/6 -311++G(d)方法, 就其中独立聚磷阴离子P33～P213的稳定性、笼型结构和成键特点、溶剂化形成的稳定性等进行了定量的描述, 得到符合实验事实的独立离子优化立体构型、组成聚阴离子的主要结构单元、μ2P原子对聚阴离子独立稳定性的影响等多方面的结论。由此指出聚磷阴离子是路易斯碱, 并与各种路易斯酸化合组成一大类化合物。最后, 讨论了笼型结构特征频率的振动模式, 对实验谱峰进行了归属。论文绘出了14个离子的结构图, 以及普遍存在的结构单元P33、P73 和P113的简正振动模式图。 33     

Structural Characters and Isolated Stability of Phosphorus Polyanions

The optimized geometries at the RHF/6-311 G^** level, the relatively stable energy at the MPW1PW91/6-311 G^** level and the structural characters of anions have been acquired, indicating the stability is related to the chemical bonding of μ2-P atoms and the distribution of negative charges. The configurations of cage units P8^4- and P9^5- are stable due to the less torsion, but their Es values are relatively higher than that of P7^3- with more μ2-P atoms and the isolated stability is lower than that of P7^3-. They potentially play an important role as intermediate in chemical reaction of producing complicated polyphosphides. Based on the related electronic properties, a stable polyanion must have low valence electron concentration, no (μ2-P)-(μ2-P) bond and a little dispersive charge. The earmark IR frequencies of cage units have been assigned to the vibration models in the end.     

Prototropy,Intramolecular Interactions,Electron Delocalization,and Physicochemical Properties of 1,8-dihydroxy-9-anthrone—DFT-D3 Study of Substituent Effects

1,8-dihydroxy-9-anthrone are tricyclic compounds with a ketone group in the middle ring and two hydroxyl groups substituted in the side-aromatic rings what results in formation of two intramolecular hydrogen bonds in which the oxygen atom from the ketone group is the proton acceptor. 1,8-dihydroxy-9-anthrones in which intramolecular proton transfer between C10 and CO in the middle ring occurs, can exist in a tautomeric keto-enol equilibrium. For anthralin, the most important representative of this group, this equilibrium has been studied previously, but it has not been studied for its derivatives. Substituents in the middle ring change the geometry of 1,8-dihydroxy-9-anthrones so they are also expected to affect the keto-enol equilibrium. It is also important to study the effect of intramolecular hydrogen bonds on the structure of both tautomeric forms. It was found that the nature of the substituent in the middle ring could affect the antioxidant properties of the investigated compound.     

Delocalization in Substituted Benzene Dications: A Magnetic Point of View

In this work, the induced magnetic field is analyzed for a series of substituted benzenes dications with formula C₆R₆²⁺ (R=I, At, SeH, SeCH₃, TeH, TeCH₃), presumably exhibiting concentric aromaticity. Previous studies concluded that in the carbon skeleton, just π-electrons are delocalized. However, our results support that both the σ- and π-electrons are delocalized in the carbon skeleton, combined with a σ-delocalization in the external ring. The role of the relativistic effects in these dications is discussed in detail.     

Experimental and Theoretical Study of the n‐Doped Successive Polyanions of Oligocruciform Molecular Wires: Up to Five Units of Charge

The electronic structure of polyanions of sterically encumbered triisopropylsilyl‐substituted linear and cyclic oligo(phenyleneethynylene)s ( M onomer, T rimer, P entamer, and Tr iangle) is investigated by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and UV/Vis–near‐infrared (NIR) spectroscopies, cyclic voltammetry, and theoretical calculations (DFT). Increasing anion orders are generated sequentially in vacuo at room temperature by chemical reaction with potassium metal up to the pentaanion. The relevance of these compounds acting as electron reservoirs is thus demonstrated. Even‐order anions are EPR silent, whereas the odd species exhibit different signatures, which are identified after comparison of the measured hyperfine couplings by ENDOR spectroscopy with those predicted by DFT calculations. With increasing size of the oligomers the electron spin density is first distributed over the backbone carbon atoms for the monoanions, and then further localized at the outer phenyl rings for the trianion species. Examination of the UV/Vis‐NIR spectra indicates that the monoanions ( T^.? , P^.? ) exhibit two transitions in the Vis‐NIR region, whereas a strong absorption in the IR region is solely observed for higher reduced states. Electronic transitions of the neutral monoanions and trianions are redshifted with increasing oligomer size, whereas for a given oligomer a blueshift is observed upon increasing the charge, which suggests a localization of the spin density.     

Practical generation of 3,5‐dimethoxybenzyllithium: application to the synthesis of 5‐substituted‐resorcinols

Reductive lithiation of 3,5‐dimethoxybenzyl methyl ether was successfully performed with lithium wire and a catalytic amount of naphthalene in dry tetrahydrofuran at ?15°C, leading to the quantitative generation of 3,5‐dimethoxybenzyllithium. This organometallic compound, which can be stored for at least 24 h, was trapped with a variety of different electrophiles, including, besides aldehydes, non‐functionalized and functionalized alkyl halides and an epoxide. Accordingly, it is a useful intermediate in the synthesis of 5‐substituted natural and non‐natural resorcinols. Copyright © 2003 John Wiley & Sons, Ltd.     

Octulene: A Hyperbolic Molecular Belt that Binds Chloride Anions

Octulene, the higher homologue of kekulene and septulene, was synthesized using the fold‐in method. This new hydrocarbon macrocycle contains a large 24‐membered inner circuit, which is peripherally fused to 24 benzene rings. Such an arrangement produces considerable hyperbolic distortion of the π‐conjugated surface. The consequences of distortion in octulene were explored using photophysical methods, which revealed a reduced electronic band gap and greater flexibility of the π system. Octulene contains a functional cavity with a diameter larger than 5.5 Å that is capable of efficiently binding the chloride anion in a nonpolar solvent (K_a= 2.2(4)×10⁴ m ^?1, 1 % dichloromethane (DCM) in benzene). The octulene–chloride interaction is stabilized by eight weak C(sp²)H???Cl bonds, providing the first example of a hydrocarbon‐based anion receptor.     

Bicyclo[6.3.0]undecapentaenyl Anion: The Next Higher Homolog of the Indenyl Anion with Exceptionally Large Ion‐Pairing Effects on its Tropicity

The title anion 1 was generated as a fairly thermally stable species in tetrahydrofuran (THF) and dimethylsulfoxide (DMSO) by the action of several bases (sodium hydride, potassium hydride, lithium diisopropylamide, and lithium hexamethyldisilazide) with appropriate bicyclo[6.3.0]undecapentaenes. Variable‐temperature ¹H NMR spectra of 1? Li⁺ in [D₈]THF reveal that the anion exhibits exceptionally large ion‐pairing effects; proton chemical shifts vary by more than 1 ppm as a function of ion‐pairing conditions. Thus, anion 1 , in a contact ion pair (Li⁺ at ambient temperature in THF), behaves as an aromatic cyclopentadienyl anion that is perturbed only slightly by the electronic effects of a paramagnetic cyclooctatetraene (COT), whereas 1 in a separated ion pair (Li⁺ at low temperatures in THF or at ambient temperature in DMSO) behaves as an overall paratropic species with a 12 π‐electron periphery. ¹³C NMR spectroscopy indicates no major skeletal rearrangement and only small variations of the electron density. The variable tropicity of 1 can be ascribed to small conformational changes of the molecule. In addition to its unusual, tunable tropicity, anion 1 can also serve as a versatile building block for the synthesis of cyclopentanoid conjugated systems fused to a fully unsaturated eight‐membered ring. A theoretical calculation predicts that the 10‐position of 1 should have the highest electron density. In agreement with this prediction, the reactions of 1 with electrophiles occur predominantly at the 10‐position. The corresponding ferrocene, two fulvenes, two diazo derivatives, and a COT‐fused azulene were obtained by the reactions of 1 with appropriate electrophiles.     

Facile Conversion of Red Phosphorus into Soluble Polyphosphide Anions by Reaction with Potassium Ethoxide

Soluble polyphosphide anions were successfully generated in a number of organic solvents by the reaction between shelf‐stable red phosphorus and potassium ethoxide. The species were identified by ³¹P NMR spectroscopy in solution and by X‐ray crystal‐structure determination of (Bu₄N)₂P₁₆ in the solid state. The reaction was scaled up to gram quantities by using a flow‐chemistry process.     

Dynamical Cooperativity in Electron Delocalization of Mixed-Valence Biferrocenium Complexes

Abstract

Intramolecular electron transfer in the mixed-valence biferrocenium complexes in crystals shows qualitatively different behavior from that in the complexes in solutions. The ‘extra’ electron in a mixed-valence complex in the crystal may be localized at low temperature and delocalized at higher temperature. The electron localization-delocalization transition induced thermally corresponds to a kind of order-disorder phase transition. In order to clarify the mechanism of the transition, a statistical mechanical model has been proposed (T. Kambara, D.N. Hendrickson, T.-Y. Dong, and M. J. Cohn, J. Chem. Phys., 86, 2362 (1987)). The temperature dependences of the physical quantities relevant to the cooperative electron localization-delocalization transition are calculated base on the model. In the calculation a more elaborate treatment is adopted for the intermolecular interactions. Those calculated values are compared with the observed ones for various kinds of mixed-valence biferrocenium trihalide crystals and reasonable agreements are obtained.     

The Nucleophilicity of Persistent α‐Monofluoromethide Anions

α‐Fluorocarbanions are key intermediates in nucleophilic fluoroalkylation reactions. Although frequently discussed, the origin of the fluorine effect on the reactivity of α‐fluorinated CH acids has remained largely unexplored. We have now investigated the kinetics of a series of reactions of α‐substituted carbanions with reference electrophiles to elucidate the effects of α‐F, α‐Cl, and α‐OMe substituents on the nucleophilic reactivities of carbanions.     

C68 Fullerene Isomers,Anions, and their Metallofullerenes: Charge‐Stabilizing Different Isomers

The complete set of 6332 classical isomers of the fullerene C₆₈ as well as several non‐classical isomers is investigated by PM3, and the data for some of the more stable isomers are refined by the DFT‐based methods HCTH and B3LYP. C₂:0112 possesses the lowest energy of all the neutral isomers and it prevails in a wide range of temperatures. Among the fullerene ions modeled, C₆₈^2?, C₆₈^4? and C₆₈^6?, the isomers C₆₈^2?(C_s:0064), C₆₈^4?(C_2v:0008), and C₆₈^6?(D₃:0009) respectively, are predicted to be the most stable. This reveals that the pentagon adjacency penalty rule (PAPR) does not necessarily apply to the charged fullerene cages. The vertical electron affinities of the neutral C_s:0064, C_2v:0008, and D₃:0009 isomers are 3.41, 3.29, and 3.10 eV, respectively, suggesting that they are good electron acceptors. The predicted complexation energy, that is, the adiabatic binding energy between the cage and encapsulated cluster, of Sc₂C₂@C₆₈(C_2v:0008) is ?6.95 eV, thus greatly releasing the strain of its parent fullerene (C_2v:0008). Essentially, C₆₈ fullerene isomers are charge‐stabilized. Thus, inducing charge facilitates the isolation of the different isomers. Further investigations show that the steric effect of the encaged cluster should also be an important factor to stabilize the C₆₈ fullerenes effectively.     

Ambient Water-Stable Dianionic Electron Donors: Intramolecular Noncovalent Conduits Assist Charge Delocalization

Electron-rich π-conjugated dianions are known to be ambient unstable and their stabilization in ambient water is yet to be realized. We report the first example of an exceptionally stable naphthalenediimide-based dianion in ambient and hot water, forming one of the most stable redox-active dianion. The half-life (t_1/2) of dianion ( 1 a²⁻ ) is more than four months in ambient water. The dianionic state was confirmed by X-ray crystallography and by various spectroscopic methods. The noncovalent electronic conduits introduced for the first time in dianions, embrace n_O→π*_C≡N interactions and aid in delocalizing the dianionic charge as validated from theoretical studies. The dianions harness strong NIR absorption and electron donor ability to organic acceptors and metal ions, which make them suitable for potential green energy applications.     

Electron Localization versus Delocalization and Ferromagnetic Coupling in Mixed Valence Polyoxometalates

We show that the ferromagnetism, recently found in the doubly-reduced hexanuclear polyoxometalate [V₆O₁₂ (μ₂−OCH₃)₄(L)₄] does not contradict to the proposed earlier delocalization mechanism of the stabilization of a spin- singlet state. The ground state triplet state yields from the internal and/or external complex asymmetry leading to the spin density localization.     

Radical Cations of Dithia- and Tetraselenaradialenes with Restricted Delocalization of the Unpaired Electron

The radical cations of the permethylated dithia[6]radialene 1 and the tetraselena[8]radialene 2 have been investigated by ESR- and ENDOR-spectroscopy. It is shown that in the radical cation of 1 the unpaired electron is delocalized only in one half of the molecule. The magnitude of the (33)S coupling constant suggests a restricted localization within the 2,3-dithiatetramethyl-butadiene unit. We ascribe the slow electron transfer from one part of the molecule to the other to steric effects. The analysis of the ESR spectrum of 2(*)()(+)() shows that only two of the four selenium atoms are involved. The delocalization of the unpaired electron is restricted to only one of the divinyl diselenide moieties with a slow electron transfer rate to the other one.