Figure-of-eight Shaped Metal-free Amide-containing Schiff-base Macrocycles and Two Dicobalt(III) Amide Complexes

Abstract

Two 36-membered (2+2) Schiff-base macrocycles have been prepared and characterised without the use of template ions or high dilution techniques. Rather, intramolecular hydrogen-bonding and π-π interactions promote the isolation of these “figure-of-eight” products in good yields. Two cobalt(III) complexes of the 18-membered (1+1) Schiff-base macrocycles are formed when cobalt(II) is used as a template. The structures of one “figure-of-eight' metal-free (2+2) macrocycle and of one dicobalt(III) complex of a (1+1) macrocycle, in which the cobalt centres are octahedral, are presented. [H₄L1tBu]₂: C₇₀H₇₀N₈O₉, space group P-1, a=7.747(1), b=17.106(3), c=23.662(4) å, α=104.83(3), β=95.86(3), γ=97.80(3)°, U=2972.4(8) å³, Z=2, D_c=1.30 g cm^?3, T=100K, 554 parameters, R1=0.072 [for 4137 reflections having F>4[(F)], wR₂=0.191 and goodness of fit 0.97 (for all 8343 independent F² data). [Co₂(L1tBu)(OAc)₂(pyridine)] 1.5DMF 0.5MeCN, C_47.5H₄₉N₇O9.5Co₂, space group P2(1)/n, a=13.067(2), b=26.071(4), c=14.023(3) å, β=93.02(1)°, U=4770.6(15) å³, Z=4, D_c=1.38 g cm^?3, T=168 K, 622 parameters, R1=0.075 [for 5233 reflections having F > 4[?F?], wR2=0.133 and good ness of fit 1.08 (for all 8512 independent F² data).     

Complexation of Calix[4]arene With Alkali Metal Cations: Conformational Binding Selectivity and Cation-π Driven Inclusion

Hartree-Fock, second order Møller-Plesset perturbation theory, and density functional theory calculations were carried out to analyse the complexation of calix[4]arene with cationic species including H + and the alkali metal cations (Li + , Na + , K + , Rb + , and Cs + ). Special emphasis has been placed on conformational binding selectivity, and on the structural characterization of the complexes. Li + and Na + cations are located in the calix[4]arene lower rim. The larger cations (K + , Rb + , and Cs + ) complex preferentially with the calix[4]arene cone conformer, and their endo (inclusive) complexation is driven by cation- ~ interactions, leading in the case of K + to a structure that reflects a preferential interaction with two phenol rings. The endo complexation of Cs + with calix[4]arene is in agreement with X-ray diffraction data.     

Synthesis of cyclic compounds consisting of face-to-face p-oligophenyls

Facile synthesis of xanthene-based π-stacked compounds consisting of face-to-face p-oligophenyls has been described. Just by mixing xanthene-4,5-diboronic acid and p-oligophenyls containing a benzenetetraol unit yielded cyclic compounds selectively due to the reversibility of the boronate esterification. In the ground state, weak π–π interactions between two p-oligophenyl moieties were observed, whereas their π–π interactions were clearly shown in the excited state.     

磺化冠醚的分子键合与组装

冠醚作为第一代大环主体分子,具有柔性的空腔,因其对金属离子、有机阳离子的络合作用而被广泛用于构筑超分子组装体。磺化冠醚是一种水溶性良好的阴离子型冠醚衍生物,相比于冠醚,它具有更多的键合位点,对金属离子、有机阳离子具有更强的键合和良好的选择性。本文从磺化冠醚的合成,对碱金属离子、镧系金属的络合,对有机阳离子客体的组装等方面介绍了磺化冠醚的研究进展。然后从热力学、晶体结构学的角度综合分析了磺化冠醚键合与组装的模式及驱动力。最后讨论了磺化冠醚的分子键合与组装发展所面临的挑战,并对其应用前景进行了展望。     

Pristine Graphene as a Racemization Catalyst for Axially Chiral BINOL

Despite versatile applications of functionalized graphene in catalysis, applications of pure, unfunctionalized graphene in catalysis are in their infancy. This work uses both computational and experimental approaches to show that single-layer graphene can efficiently catalyze the racemization of axially chiral BINOL in solution. Using double-hybrid density functional theory (DHDFT) we calculate the uncatalyzed and catalyzed Gibbs free reaction barrier heights in a number of representative solvents of varying polarity: benzene, diphenyl ether, dimethylformamide (DMF), and water. These calculations show that (i) graphene can achieve significant catalytic efficiencies (▵▵G^≠_cat) varying between 47.2 (in diphenyl ether) and 60.7 (in DMF) kJ mol⁻¹. An energy decomposition analysis reveals that this catalytic activity is driven by electrostatic and dispersion interactions. Based on these computational results, we explore the graphene-catalyzed racemization of axially chiral BINOL experimentally and show that single-layer graphene can efficiently catalyze this process. Whilst the uncatalyzed racemization requires high temperatures of over 200 °C, a pristine single-layer graphene catalyst makes it accessible at 60 °C.     

NMR investigation of substituent effects on strength of π-π stacking and hydrogen bonding interactions to supports the formation of [2 + 2] photodimerization in (para-X-ba):::(bpe)||(bpe):::(para-X-ba) complexes

We have investigated the ability of para-X-phenylboronic acid (para-X-ba) to enable reactivity of trans-1,2-bis(4-pyridyl)ethylene (bpe) to direct intermolecular [2 + 2] photodimerization via computational chemistry. Para-X-ba would support the formation of discrete four component hydrogen bonded molecular assemblies wherein π-π stacking of a pyridyl-functionalized alkene would conform to undergo [2 + 2] photodimerization.We have demonstrated by computational ¹H NMR data the effect of electron-withdrawing and donating substituents in (para-X-ba):::(bpe)||(bpe):::(para-X-ba) complexes to assemble bpe into π-π stacking via –(B)O − H···N– hydrogen bonds to react to afford (para-X-ba):::tpcb:::(para-X-ba) complexes (X = NO2, CN, F, Cl, Br, C(O)CH₃, OCH₃, OH, NH₂ and H where || and ∙∙∙ denote π-π stacking and hydrogen bonds).Also, these interactions have been investigated at M05-2X/6-311++G** level of theory in detail in terms of the energetic, geometrical parameters and electron density properties to characterize and to examine the strengthening of the interactions. There are good relationships between the NMR, AIM, energy data and Hammett constants.     

A tryptophan-analog host whose interactions with ammonium ions in water are dominated by the hydrophobic effect

The binding of quaternary ammonium guests to a flexible, indole-based host has been studied in both aqueous and organic solvents. Binding was shown to depend strongly on the hydrophobic effect and less on the cation-π interaction.     

Synthesis and Structure of a Zinc(II) Complex:[Zn(Pybta)·Cl_2]_n

The title compound, [Zn(Pybta)Cl2]n (Pybta = 1-(2-pyridylmethyl)benzontriazole), has a zigzag chain structure. It crystallizes in the monoclinic system, space group P21/c with a = 9.0103(11), b = 17.0276(18), c = 9.2288(11) , β = 101.309(6)o, Mr = 346.51, V = 1388.4(3) 3, Z = 4, Dc = 1.658 g/cm3, F(000) = 696, μ = 2.143 mm1, the final R = 0.0492 and wR = 0.1236 for 2545 observed reflections with I > 2σ(I). The Zn atom is four-coordinated by two N and two Cl atoms, forming a slightly distorted tetrahedral geometry. Each zigzag chain links its adjacent symmetry- related equivalents via multiple π-π interactions, which are not frequently observed in the previously reported architectures.     

Chloride Binding Modulated by Anion Receptors Bearing Tetrazine and Urea

Modulation and fine-tuning of the strength of weak interactions to bind anions are described in a series of synthetic receptors. The general design of the receptors includes both a urea motif and a tetrazine motif. The synthetic sequence towards three receptors is detailed. Impacts of H-bond strength and linker length between urea and tetrazine on chloride complexation are studied. Binding properties of the chloride anion are examined in both the ground and excited states using a panel of analytical methods (NMR spectroscopy, mass spectrometry, UV/Visible spectroscopies, and fluorescence). A ranking of the receptors by complexation strength has been determined, allowing a better understanding of the structure-properties relationship on these compounds.