Borohydrides from Organic Hydrides: Reactions of Hantzsch’s Esters with B(C6F5)3

We report herein that the reaction between a series of Hantzsch’s ester analogues 1 a – d with the Lewis acidic species B(C₆F₅)₃ results in facile transfer of hydride to boron. The main products of this reaction are pyridinium borohydride salts 2 a – d , which are obtained in high to moderate yields. The N‐substituted substrates (N‐Me, N‐Ph) reacted in high yield 90–98 % and the connectivity of the products were confirmed by an X‐ray crystallographic analysis of the N‐Me borohydride salt 2 a . Unsubstituted Hanztsch’s ester 1 a reacted less effectively generating only 60 % of the corresponding borohydride salt, with the balance of the material sequestered as the ester‐bound Lewis acid–base adduct 3 a . Formation of the Lewis acid–base adduct could be minimized by increasing the steric bulk about the ester groups as in 1 d . The connectivity of the carbonyl‐bound adduct was confirmed by an X‐ray crystallographic analysis of 3 e the product of the reaction of methyl ketone 1 e with B(C₆F₅)₃. We also explored the generation of these pyridinium salts by employing frustrated Lewis pair methodology. However, the reaction of mixtures of the corresponding pyridine and B(C₆F₅)₃ with hydrogen gas only resulted in formation of trace amounts of the pyridinium borohydride, along with the Lewis acid–base adduct of the starting material and B(C₆F₅)₃. The 1,2‐dihydropyridine adduct was the final product of this reaction. This was ascribed to the low basicity of the pyridine nitrogen and the complicating formation of an ester bound Lewis acid–base adduct.     

Structure and dynamic features of an intramolecular frustrated Lewis pair

Di(mesityl)cyclohexenylphosphine undergoes hydroboration with Piers' borane [HB(C₆F₅)₂] to yield the cyclohexylene‐anellated frustrated Lewis pair 5 . This P/B pair splits H₂ with the formation of the product 4 and adds to the C?O double bond of phenyl isocyanate to yield 6 . In the crystal, compound 5 features a puckered four‐membered heterocyclic core structure with a long P? B bond (av. 2.197(5) Å). The activation energy of the P? B cleavage of the frustrated Lewis pair 5 was determined by dynamic ¹⁹F NMR spectroscopy at ΔG^≠(298 K)=12.1±0.3 kcal mol^?1.     

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

The twisted lateral tetraalkyloxy ortho‐terphenyl units in dibenzo[18]crown‐6 ethers 1 a – f were readily converted into the flat tetraalkyloxytriphenylene systems 2 a – f by oxidative cyclization with FeCl₃ in nitromethane. Reactions of the latter with potassium salts gave complexes KX ?2 , which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene‐substituted crown ethers KX ?2 , only those with the soft anions I^? and SCN^? displayed mesophases with expanded phase temperature ranges of 93 °C and 132 °C (for KX ?2 e ), respectively, as compared to the corresponding o‐terphenyl‐substituted crown ether complexes KI ?1 e (ΔT=51 °C) and KSCN ?1 e (plastic crystal phase). Anions such as Br^?, Cl^?, and F^? decreased the mesophase stability, and PF₆^? led to complete loss of the mesomorphic properties of KPF₆ ?2 although not for KPF₆ ?1 . For crown ether complexes KX ?2 (X=F, Cl, Br, I, BF₄, and SCN), columnar rectangular mesophases of different symmetries (c2 mm, p2 mg, and p2 gg) were detected. In contrast to findings for the twisted o‐terphenyl crown ether complexes KX ?1 , the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI ?2 e in CH₂Cl₂ revealed a network of fibers.     

Anion‐Dependent Tendency of Di‐Long‐Chain Quaternary Ammonium Salts to Form Ion Quadruples and Higher Aggregates in Benzene

The self‐aggregation tendency of [N(CH₃)₂(C₁₈H₃₇)₂]X [ 1 X; X^?=BF₄^?, PF₆^?, OTf^?, NTf₂^?, BPh₄^?, BTol₄^?, BAr^F?, and B(C₆F₅)₄^?] salts to form ion quadruples (IQs) and higher aggregates (HAggs) in [D₆]benzene is investigated by means of diffusion NMR spectroscopy. The experimental results indicate that salts containing small anions ( 1 BF₄, 1 PF₆, and 1 OTf) are present in solution as IQs even at the lowest investigated concentration of C=5×10^?5 M and show a limited tendency to further self‐aggregate, reaching a maximum average aggregation number (N=V_H/${V_{\rm{H}}^{{\rm{0IP}}} }$ , where V_H=measured hydrodynamic volume and ${V_{\rm{H}}^{{\rm{0IP}}} }$ =hydrodynamic volume of the ion pair) of about 6–8 (C=0.050–0.100 M ). Salts with larger counterions [ 1 BPh₄, 1 BTol₄, 1 BAr^F, and 1 B(C₆F₅)₄] form instead ion pairs at low concentration but steadily self‐aggregate (especially the non‐fluorinated ones) on increasing their concentration up to N values exceeding 50 (C=0.030–0.050 M ). 1 NTf₂ behaves in an intermediate fashion. The self‐aggregation tendency of salts is quantified by formulating the dependence of V_H on C by means of the equations of indefinitive aggregation models. The following rankings for the formation of IQs and HAggs are obtained: IQs: 1 BF₄≈ 1 PF₆≈ 1 OTf> 1 NTf₂> 1 B(C₆F₅)₄≥ 1 BPh₄≥ 1 BTol₄≥ 1 BAr^F; HAggs: 1 BTol₄> 1 BPh₄> 1 NTf₂> 1 B(C₆F₅)₄> 1 BAr^F> 1 BF₄≈ 1 PF₆≈ 1 OTf. Interionic NOE NMR studies and DFT calculations were conducted in order to determine the relative anion–cation orientation in the self‐aggregating units.     

Ion Pairing and Salt Structure in Organic Salts through Diffusion,Overhauser, DFT and X‐ray Methods

Pulsed gradient spin‐echo (PGSE) diffusion characteristics for a) the new [brucinium][X] salts 6 a – f [ a : X=BF₄^?; b : X=PF₆^?; c : X=MeSO₃^?, d : X=CF₃SO₃^?; e : X=BArF^?; f : X=PtCl₃(C₂H₄)^?], b) 4‐tert‐butyl‐N‐benzyl analogue, 7 and c) the aryl carbocations (p‐R‐C₆H₄)₂CH 9 a (R=CH₃O) and 9 b (R=(CH₃)₂N), (p‐CH₃O‐C₆H₄)_xCPh_3?x⁺ 10 a – c (x=1–3, respectively) and (p‐R‐C₆H₄)₃C⁺ 11 (R=(CH₃)₂N) and 12 (R=H) all in several different solvents, are reported. The solvent dependence suggests strong ion pairing in CDCl₃, intermediate ion pairing in CD₂Cl₂ and little ion pairing in [D₆]acetone. ¹H, ¹⁹F HOESY NMR spectra (HOESY: heteronuclear Overhauser effect spectroscopy) for 6 and 7 reveal a specific approach of the anion with respect to the brucinium cation plus subtle changes, which are related to the anion itself. Further, for carbocations 9 – 12 , (all as BF₄^? salts) based on the NOE results, one finds marked changes in the relative positions of the BF₄^? anion. In these aryl cationic species the anion can be located either a) very close to the carbonium ion carbon b) in an intermediate position or c) proximate to the N or O atom of the p‐substituent and remote from the formally positive C atom. This represents the first example of such a positional dependence of an anion on the structure of the carbocation. DFT calculations support the experimental HOESY results. The solid‐state structures for 6 c and the novel Zeise's salt derivative, [brucinium][PtCl₃(C₂H₄)], 6 f , are reported. Analysis of ¹⁹⁵Pt NMR and other NMR measurements suggest that the η²‐C₂H₄ bonding to the platinum centre in 6 f is very similar to that found in K[PtCl₃(C₂H₄)]. Field dependent T₁ measurements on [brucinium][PtCl₃(C₂H₄)] and K[PtCl₃(C₂H₄)], are reported and suggested to be useful in recognizing aggregation effects.     

A model on the financial panic

The mechanism of the financial panic is clarified by the two band model in a simplified capitalist society from statistical mechanics. A financial panic occurs on an occasion of the supercooling process to avoid completing the financial (buy-sell) cycles under the circumstances: extremely high consumption causes enormous bubbles of buy-sell pairs of securities in financial markets, which form the configuration entropy (the Kauzmann entropy) and trigger a chain recession. As society cools down, the dynamical processes of financial panic are governed by universal features such as the Kauzmann entropy crisis and the drastic drop of the dynamical motions (the VTF law), which also cause further recession so that a chain recession occurs. And the financial markets eventually freeze.     

含分压电阻的非相干耦合光折变屏蔽光伏空间孤子对

建立了含分压电阻的非相干耦合光折变屏蔽光伏空间孤子对理论.当分压电阻、晶体外加电场和晶体的光伏场取不同值时,可分别得到有无分压电阻的非相干耦合屏蔽孤子对、开路的非相干耦合光伏孤子对、有无分压电阻的闭路的非相干耦合光伏孤子对和有无分压电阻的非相干耦合屏蔽光伏孤子对.先前已报道的非相干耦合孤子对理论都可在不同的条件下从本文理论得出.     

碱基对组分、电极位能及界面耦合对DNA分子I-V特性的影响

在紧束缚近似下,利用传输矩阵方法,计算研究了碱基对组分、金属电极位能及DNA分子与电极耦合强度对DNA分子I-V特征的影响.计算结果表明:由单一碱基对构成的DNA分子的饱和电流强度远大于由两种碱基对按一定组分随机分布的DNA分子的饱和电流强度,且当DNA分子中两种碱基对的含量相等时,其饱和电流强度最小.同时,富含C-G碱基对的DNA分子比富含A-T碱基对的DNA分子的电子输运能力大.金属电极位能对DNA分子电子输运的影响体现在两方面,当偏压较小时,电极位能具有阻碍电荷注入的效果,当偏压较大时     

One-dimensional optical bright screening photovoltaic photorefractive solitons, soliton pairs and incoherent interaction between them in BaTiO3 crystal

By the use of theory of optical solitons, nonlinear equations governed by screening photorefractive photovoltaic solitons are introduced. By means of numerical methods, intensity profile, refractive index change of the media and also stability under propagation are investigated. Self-bending of solitons under first-order diffusion is also studied. Besides, incoherent coupled bright-bright soliton pairs and incoherent interaction are studied.