Cucurbit[7]uril⋅Guest Pair with an Attomolar Dissociation Constant

Host?guest complexes between cucurbit[7] (CB[7]) or CB[8] and diamantane diammonium ion guests 3 or 6 were studied by ¹H NMR spectroscopy and X‐ray crystallography. ¹H NMR competition experiments revealed that CB[7]? 6 is among the tightest monovalent non‐covalent complexes ever reported in water with K_a=7.2×10¹⁷ M ^?1 in pure D₂O and 1.9×10¹⁵ M ^?1 in D₂O buffered with NaO₂CCD₃ (50 mM ). The crystal structure of CB[7]? 6 allowed us to identify some of the structural features responsible for the ultratight binding, including the distance between the NMe₃⁺ groups of 6 (7.78 Å), which allows it to establish 14 optimal ion‐dipole interactions with CB[7], the complementarity of the convex van der Waals surface contours of 6 with the corresponding concave surfaces of CB[7], desolvation of the C?O portals within the CB[7]? 6 complex, and the co‐linearity of the C₇ axis of CB[7] with the N⁺???N⁺ line in 6 . This work further blurs the lines of distinction between natural and synthetic receptors.     

Naphthocrown‐Strapped Calix[4]pyrroles: Formation of Self‐Assembled Structures by Ion‐Pair Recognition

A new approach to the construction of self‐assembled structures is reported that is based on ion‐pair recognition. Towards this end, the calix[4]pyrrole naphthocrown‐4 hybrid structures 2 and 3 were prepared. These multitopic receptors contain recognition sites for both anions and cations. On the basis of solution‐phase ¹H NMR spectroscopic analysis and solid‐state single‐crystal X‐ray diffraction structural studies, it was established that receptors 2 and 3 are able to bind specific ion pairs with high selectivity via different binding modes. In the case of CsF and CsCl, the ion‐pair complexes formed from receptors 2 and 3 were found to self‐assemble to produce either linear supramolecular polymeric crystalline solids or nanotube‐like cyclic hexamers depending on the specific choice of ion pairs and crystallization solvents. Proton NMR studies provided evidence for solution‐phase self‐association in organic media.     

High‐Yield Formation of Substituted Tetracyanobutadienes from Reaction of Ynamides with Tetracyanoethylene

A high‐yielding sequence of [2+2] cycloaddition–retroelectrocyclization of ynamides with tetracyanoethylene (TCNE) is described. The reaction provided tetracyanobutadiene (TCBD) species, which were characterized by various techniques. DFT and TD‐DFT calculations were also performed to complement experimental findings.     

Comparative Studies of Thermally Induced Homolytic CarbonCarbon Bond Cleavage Reactions of Strained Dicarba[2]ferrocenophanes and Their Ring‐Opened Oligomers and Polymers

Reactivity studies of dicarba[2]ferrocenophanes and also their corresponding ring‐opened oligomers and polymers have been conducted in order to provide mechanistic insight into the processes that occur under the conditions of their thermal ring‐opening polymerisation (ROP) (300 °C). Thermolysis of dicarba[2]ferrocenophane rac‐[Fe(η⁵‐C₅H₄)₂(CHPh)₂] (rac‐ 14 ; 300 °C, 1 h) does not lead to thermal ROP. To investigate this system further, rac‐ 14 was heated in the presence of an excess of cyclopentadienyl anion, to mimic the postulated propagating sites for thermally polymerisable analogues. This afforded acyclic [(η⁵‐C₅H₅)Fe(η⁵‐C₅H₄)‐CH₂Ph] ( 17 ) through cleavage of both a Fe?Cp bond and also the C?C bond derived from the dicarba bridge. Evidence supporting a potential homolytic C?C bond cleavage pathway that occurs in the absence of ring‐strain was provided through thermolysis of an acyclic analogue of rac‐ 14 , namely [(η⁵‐C₅H₅)Fe(η⁵‐C₅H₄)(CHPh)₂‐C₅H₅] ( 15 ; 300 °C, 1 h), which also afforded ferrocene derivative 17 . This reactivity pathway appears general for post‐ROP species bearing phenyl substituents on adjacent carbons, and consequently was also observed during the thermolysis of linear polyferrocenylethylene [Fe(η⁵‐C₅H₄)₂(CHPh)₂]_n ( 16 ; 300 °C, 1 h), which was prepared by photocontrolled ROP of rac‐ 14 at 5 °C. This afforded ferrocene derivative [Fe(η⁵‐C₅H₄CH₂Ph)₂] ( 23 ) through selective cleavage of the ?H(Ph)C?C(Ph)H? bonds in the dicarba linkers. These processes appear to be facilitated by the presence of bulky, radical‐stabilising phenyl substituents on each carbon of the linker, as demonstrated through the contrasting thermal properties of unsubstituted linear trimer [(η⁵‐C₅H₅)Fe(η⁵‐C₅H₄)(CH₂)₂(η⁵‐C₅H₄)Fe(η⁵‐C₅H₄)(CH₂)₂(η⁵‐C₅H₄)Fe(η⁵‐C₅H₅)] ( 29 ) with a ?H₂C?CH₂? spacer, which proved significantly more stable under analogous conditions. Evidence for the radical intermediates formed through C?C bond cleavage was detected through high‐resolution mass spectrometric analysis of co‐thermolysis reactions involving rac‐ 14 and 15 (300 °C, 1 h), which indicated the presence of higher molecular weight species, postulated to be formed through cross‐coupling of these intermediates.     

螺桨烷型分子BX[(CH_2)_n]_3和BX(CH_2)[CH(CH_2)_nCH](X=N,P)的结构和性质

采用密度泛函理论(DFT)研究了螺桨烷型分子BX[(CH2)n]3和BX(CH2)[CH(CH2)n CH](X=N,P;n=1-6)的结构、稳定性、化学键和电子光谱性质.计算结果表明这些分子都是稳定的.BX[(CH2)n]3(X=N,P;n=1-6)的最高占据分子轨道(HOMO)和最低空分子轨道(LUMO)之间的能隙均大于5.20 eV,其中BN[CH2]3和BP[CH2]3的能隙超过7.0 eV,与C5H6的能隙(7.27 eV)很接近,BX(CH2)[CH(CH2)n CH](X=N,P;n=1-6)的能隙在6.80 eV左右.所研究分子能量的二阶差分表明BN[(CH2)3]3、BP[(CH2)4]3及BX(CH2)[CH(CH2)2CH](X=N,P)是最稳定的.BX[(CH2)n]3的Wiberg键级表明除了BN[(CH2)n]3(n=2和6)中不存在B―N键,其它化合物中B和N均形成了化学键,BP[(CH2)n]3中除了BP[(CH2)2]3不存在B―P键,其它的均存在.电子密度的拓扑分析表明N―B键属于离子键,而P―B键具有共价键特征.BX[(CH2)n]3(X=N,P)的第一垂直激发能分别在191.1-284.8 nm和191.8-270.1 nm之间,BX(CH2)[CH(CH2)n CH](X=N,P)的第一垂直激发能分别在190.5-199.7 nm和209.0-221.3 nm之间.     

A Facile Approach for Synthesis of Benzofuro[2,3‐c]pyridines via Intramolecular Cascade Annulations

A facile synthesis of benzofuro[2,3‐c]pyridines has been achieved under mild conditions by using ammonium acetate as the nitrogen source through intramolecular cascade annulation. This reaction could efficiently construct pyridine ring and furan ring in one step. Moreover, the key annulation step was demonstrated through dihydrobenzofuran intermediates.     

Synthesis of benzo[g]indeno[2,1-b]quinoline derivatives via four-component and one-pot synthesis in presence of 3-methyl-1-sulfonic acid imidazolium hydrogen sulfate

A simple and facile synthesis of 12-arylbenzo[g]indeno[2,1-b]quinoline-6,11,13-trione deriv-atives was accomplished by the one-pot condensation of 2-hydroxynaphthalene-1,4-dione, aryl aldehydes, 2H-ind...     

A New Cadmium（II） Coordination Polymer Constructed by 2-（2-Chloro-6-fluorophenyl）-lH-imidazo[4,5-f] [1, 10]phenanthroline and 1,2,3-Benzenecarboxylate： Synthesis,Structure and Luminescence

A new Cd（II） coordination polymer, namely, [Cd3（1,2,3-BTC）2（L）2]·2.25H2O （1, L = 2-（2-chloro-6-fluorophenyl）-1H-imidazo[4,5-A][1,10]phenanthroline and 1,2,3-BTC = 1,2,3-ben- zenetricarboxylate）, has been synthesized under hydrothermal conditions. The compound was characterized by single-crystal X-ray diffraction. It crystallizes in triclinic, space group Pī with α = 11.650（2）, b = 12.240（2）, c = 19.760（4） A, α = 72.01（3）, β = 77.11（3）, γ = 83.48（3）°, V = 2609.4（9） A3, Z = 2, C56H31Cd3Cl2F2N8O14.25, Mr = 1489.99, Dc = 1.896 g/cm3, F（000） = 1466, μ（MoKa） = 1.401 mm^-1, R = 0.0401 and wR = 0.1104. Compound 1 shows a 1D chain structure, and the neigh- boring 1D chains of 1 are joined together by π···π interactions to result in a 2D supramolecular layer. In addition, the luminescent property of 1 has been studied in the solid state at room temperature.     

Rhodium-Catalyzed Highly Diastereo- and Enantioselective Synthesis of a Configurationally Stable S-Shaped Double Helicene-Like Molecule

An S-shaped double helicene-like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex-catalyzed highly diastereo- and enantioselective intramolecular double [2+2+2] cycloaddition of a 2-naphthol- and benzene-linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S-shaped double helicene-like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S-shaped double helicene-like molecule forms a trimer through the multiple C−H⋅⋅⋅π and C−H⋅⋅⋅O interactions in the solid-state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S-shaped double helicene-like molecule enhanced the chiroptical properties.