Novel Macrocycles. Part 6. Synthesis, Structures and Cation Binding from Optical Spectroscopy of 9,10-Anthraquinone-crown Ethers

The 9,10-anthraquinone-[12]crown-4, [15]crown-5 and [18]crown-6 derivatives were synthesized from 1,2-dihydroxy-9,10-anthraquinone and 1,8-dihydroxy-9,10-anthraquinone which were condensed with dihalides or ditosylates of polyethylene glycols in alkali carbonate/DMSO. The 9,10-anthraquinone derived polyoxacyclo-alkanes were characterized with IR, mass spectrometry, ¹H, ¹³C spectroscopy and elemental analysis. The cation binding properties were studied with UV-vis spectroscopy. The association constants found in acetonitrile were selectively dependent on the cation radius and macrocycle size as well as the molecular structures. The observed results from UV-vis studies, however, showed the stronger complexing role of 1,2-derived macrocycles compared to those of 1,8-derivatives. The theoretical conformational analysis and the energy optimisations of the 9,10-anthraquinone-macrocycles carried out with MM+ method explained the binding results.     

四烃硫基四硫富瓦烯的电化学性质及三维定量结构性能关系研究

以四烃硫基四硫富瓦烯(TTF)为研究对象,合成了6个新的π电子给体化合物,并用循环伏安法考察了其电化学性质,同时用比较分子力场(CoMFA)研究了TTF衍生物的结构与其电化学性质的三维定量结构性能关系,提出了对TTF结构改造的方法,对新型TTF类化合物的合成有重要的指导意义.     

Steric effects in the electroreduction of 9-anthryl styryl ketone and 9,10-anthryl bis(styryl ketone)

The electrochemical behavior of 9-anthryl styryl ketone (ASK) and 9,10-anthryl bis(styryl ketone) (ABSK) in acetonitrile and N,N-dimethylformamide at a Pt electrode was investigated by cyclic and rotating ring disk electrode (RRDE) voltammetry and controlled potential coulometry. ASK is reduced in a reversible one-electron step to form the radical anion which rapidly couples (k₂=10⁵M^?1 s^?1) to form the dimeric dianion. The dimer can be reoxidized to form ASK. ABSK is reversibly reduced to the stable dianion which shows no tendency to couple. The cyclic voltammogram wave shape suggests that the styryl-keto groups in the 9-and 10-positions are non-interacting so that the reduction occurs in two steps whose standard potentials differ by the statistically predicted 36 mV.     

Synthesis and Redox Behavior of Novel 9,10‐Diphenylphenanthrenes

The synthesis and electrochemical investigations of 9,10‐diphenylphenanthrene 2a and its derivatives 2b – 2e are reported. The cyclic voltammetry of derivatives 2a – 2c and 2e in different solvent/Bu₄NPF₆ electrolyte systems reveals that the redox properties are dependent on solvent, temperature, and sweep rate. The oxidation of 9,10‐diphenylphenanthrene 2a occurred as an irreversible process, while two fully reversible oxidation waves were observed for dimethoxy derivative 2c . The room‐temperature oxidation of brominated compound 2b is reversible, whereas AcO‐substituted phenanthrene 2e displayed a reversible oxidation peak only at low temperature. Furthermore, the electronic nature of the substituent affects the oxidation potentials. In the CH₂Cl₂‐based electrolyte system, the first oxidation potentials increase in the order 2c < 2e < 2b .     

Mechanistic study on the electrochemical reduction of 9,10-anthraquinone in the presence of hydrogen-bond and proton donating additives

The electrochemical reduction of 9,10-anthraquinone (AQ) was investigated in CH(3)CN in both the absence and presence of the hydrogen-bond and proton donating additives, CH(3)OH, CH(CF(3))(2)OH, phenol, 4-methoxyphenol, 4-cyanophenol, 2,4,6-trichlorophenol, and benzoic acid (BA). Three clearly different types of electrochemical behavior were observed with increasing concentrations of the additives, and were simulated to analyze the reaction mechanisms. Type I was observed for weakly interacting additives, such as CH(3)OH, characterized by positive shifts of the two well-separated reduction waves, corresponding to the formation of AQ(?-) and AQ(2-), with no loss of reversibility. The second wave shifted more strongly, and finally merged with the first. These behaviors are explained by the association of AQ(2-) with the additives via strong hydrogen-bonding. Type II is attributed to a reduction mechanism involving quantitative formation of strong hydrogen-bonded complexes of AQ(2-) with additives, such as CH(CF(3))(2)OH, phenol and 4-methoxyphenol, showing a reversible or quasireversible two-electron reduction wave with increasing concentrations of the additives. The behavior of Type III, observed in the presence of strongly interacting additives, such as 2,4,6-trichlorophenol and BA, is characterized by a voltammogram composed of the 2-electorn cathodic and the broad anodic waves without keeping reversibility, facilitated by proton transfer in the hydrogen-bonded complexes, AQ(?-)-BA and AQ(2-)-BA. The effects of hydrogen-bonding and protonation on the electrochemistry of AQ have been systematically demonstrated in terms of the potentials and reaction pathways of the various species, which appear in quinone-hydroquinone systems.     

Study of electrochemical properties of pyrrolidinofullerenes by microelectrode voltammetry

The electrochemical behavior of nine pyrrolidinofullerenes has been investigated by cyclic voltammetry on a gold microdisk electrode. Four reversible reduction peaks and two irreversible reduction peaks are observed for each fullerene derivative. The half-wave potentials of all pyrrolidinofullerenes are more negative than those of C₆₀ itself. The diffusion coefficient of these compounds is measured by their steady-state voltammograms.     

Electrochemical characterization of mono- and bisfullerene compounds involving 2,5-dimethoxycarbonylpyrrolidinofullerene using microelectrode voltammetry

The electroreduction behavior of nine 2,5-dimethoxycarbonylpyrrolidinofullerenes and three 2,5-dimethoxycarbonylpyrrolidinofullerene dimers has been investigated by cyclic voltammetry (CV) on a gold microdisk electrode. Four reversible reduction peaks and two irreversible reduction peaks are observed for each fullerene derivatives. The half-wave potentials of all the derivatives are more negative than that of C₆₀ itself. The diffusion coefficient of each monofullerene derivatives is measured according to their steady-state voltammograms.     

Esr and polarography of nitroazoles. 4. Polarographic study of nitrobenzimidazoles

The electrochemical reduction of 2-substituted 5(6)-benzimidazoles has been studied with the aid of classical polarography and cyclic voltammetry in acetonitrile. The influence of the substituents in position 2 on the magnitudes of the half-wave potentials of the first stage is exerted by induction and resonance mechanisms with approximately the same contributions, and that on the magnitudes of the half-wave potentials of the second stage predominantly by the resonance mechanism. The possibilities of taking the radical-stabilizing factor into account in the correlations are discussed. In order to study the 2-substituted 5(6)-nitrobenzimidazole series, their pK _a values in acetonitrile have been determined by potentiometric titration.For communication 3, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1246–1251, September, 1984.     

Para-phenylenediamine oxidation at a platinum electrode in acetonitrile solutions

p-Phenylenediamine oxidation at platinum electrodes in acetonitrile solutions has been studied under a very wide range of experimental conditions. Chronopotentiometry, rotating disc electrode and cyclic voltammetry were used as electrochemical techniques. Coulometry at constant potential and product analysis were also performed.The electrochemical reaction appears as a fast and reversible one electron exchange per molecule of PPD. The electrode reaction is further complicated by follow-up chemical reactions giving unknown products in the bulk of the solution.The whole polarization curve under steady state conditions shows two waves, while under non-steady state conditions a small wave at intermediate potentials is also apparent.The reaction pathway for the first wave was interpreted as a non-conventional e.c.e. mechanism where the parent molecule acts as a base in the chemical step.These assumptions were confirmed through experiments performed with pyridine or water addition.     

2—氨基—9,10—蒽醌及其衍生物的光谱电化学研究

用循环伏安法研究了２－氨基－９，１０－蒽醌及其衍生物在ＤＭＦ－０．１ｍｏｌ／ＬＴＢＡＰ溶液中的电化学行为，结果表明它们在铂电极上均发生两步连续的单电子还原过程，取代基Ｒ及水和苯甲酸等质子性试剂的加对伏安曲线有很大的影响。     

Extreme conformational constraints in pi-extended tetrathiafulvalenes: unusual topologies and redox behavior of doubly and triply bridged cyclophanes

Doubly and triply bridged 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) derivatives have been synthesized. Key steps are the generation and macrocyclization reactions of ex-TTF-dithiolate reagents. The X-ray crystal structures of the doubly bridged cyclophanes 15 and 16 and the triply bridged system 23 show that the saddle-like conformation of the ex-TTF framework is enhanced by the short bridges between the dithiole rings. Unlike all previous ex-TTF derivatives (which display a single quasi-reversible two-electron oxidation wave, D0 --> D2+), cyclic voltammetry of the cyclophanes reveals two reversible, one-electron oxidation steps (D0 --> D*+ --> D2+), with differences between the half-wave potentials (E2(1/2) - E1(1/2)) of 0.22-0.26 V. The conformational changes and gain in aromaticity which drive the second oxidation process in unrestricted ex-TTF systems (including singly bridged cyclophanes) have been prevented by multiple bridging. The radical cation species gives rise to a very broad, low-energy band (lambdamax = 2175 and 2040 nm for 15 and 21, respectively), assigned to an intramolecular interaction. The steric constraints imposed by multiple bridging have become so extreme that the pi-framework of 15, 16, 21, and 23 exhibits remarkable optical and redox behavior which is not characteristic of ex-TTF systems.     

Polarographic Properties and Electrochemical Reduction of 1,2-Dimethyl-3-indolyl Heteroaryl Ketones

The reduction of a series of 1,2-dimethyl-3-indolyl heteroaryl ketones, where the heteroaryl components are 2-benzoxazolyl, 2-behzpthiuzolyl. 1-methyl-2-benz-imidazolyl, 4- and 2-pyridyl, in aprotic and prone solution are described by means of DC. and AC. polarography, cyclic voltammetry and coulometry. In acetonitrile a two-step reduction mechanism with a reversible first and an irreversible second one-electron transfer has been observed, confirmed by AC.-polarographic and cyclovoltammetric measurements. The reduction potentials, between ?1.377 and ?1.787 V for the first step, and between ?1.937 and ?2.250 V (vs. Ag/AgCl) for the second, could not be correlated with the LUMO energies from HMO calculations which was explained as being due to a distorted configuration of the π systems. In protic media (ethanol/water) reduction occurs in an irreversible one-step mechanism. Measurements of the pH dependence of the half-wave potential in the pH* range 0–12 and the evaluated transfer coefficients show that the reduction step represents the transfer of two electrons and two protons yielding secondary alcohols and no dimerization products under any condition. These findings are supported by coulometric and macroscale electrolysis of the ketones; the products isolated were characterized by IR. and ¹H-NMR. data.     

Valence-state analysis through spectroelectrochemistry in a series of quinonoid-bridged diruthenium complexes [(acac)(2)Ru(mu-L)Ru(acac)(2)](n) (n=+2, +1, 0, -1, -2)

The quinonoid ligand-bridged diruthenium compounds [(acac)(2)Ru(mu-L(2-))Ru(acac)(2)] (acac(-)=acetylacetonato=2,4-pentanedionato; L(2-)=2,5-dioxido-1,4-benzoquinone, 1; 3,6-dichloro-2,5-dioxido-1,4-benzoquinone, 2; 5,8-dioxido-1,4-naphthoquinone, 3; 2,3-dichloro-5,8-dioxido-1,4-naphthoquinone, 4; 1,5-dioxido-9,10-anthraquinone, 5; and 1,5-diimido-9,10-anthraquinone, 6) were prepared and characterized analytically. The crystal structure analysis of 5 in the rac configuration reveals two tris(2,4-pentanedionato)ruthenium moieties with an extended anthracenedione-derived bis(ketoenolate) pi-conjugated bridging ligand. The weakly antiferromagnetically coupled {Ru(III)(mu-L(2-))Ru(III)} configuration in 1-6 exhibits complicated overall magnetic and EPR responses. The simultaneous presence of highly redox-active quinonoid-bridging ligands and of two ruthenium centers capable of adopting the oxidation states +2, +3, and +4 creates a large variety of possible oxidation state combinations. Accordingly, the complexes 1-6 exhibit two reversible one-electron oxidation steps and at least two reversible reduction processes. Shifts to positive potentials were observed on introduction of Cl substituents (1-->2, 3-->4) or through replacement of NH by O (6-->5). The ligand-to-metal charge transfer (LMCT) absorptions in the visible region of the neutral molecules become more intense and shifted to lower energies on stepwise reduction with two electrons. On oxidation, the para-substituted systems 1-4 exhibit monocation intermediates with intervalence charge transfer (IVCT) transitions of Ru(III)Ru(IV) mixed-valent species. In contrast, the differently substituted systems 5 and 6 show no such near infrared (NIR) absorption. While the first reduction steps are thus assigned to largely ligand-centered processes, the oxidation appears to involve metal-ligand delocalized molecular orbitals with variable degrees of mixing.     

Electrochemical properties of modified carbon paste electrodes containing some amino derivatives of 9,10-anthraquinone

The preparation and aqueous electrochemistry of carbon paste electrodes modified by some amino-substituted 9,10-anthraquinones are reported. In all cases, the reduction processes studied by cyclic voltammetry reveal a quasi-reversible behavior. The half-wave potentials were calculated as a function of the solution pH and from the resulting potential-pH plots the formal potentials and pK _a ^′ values of different redox and acid-base couples involved at various pH ranges were evaluated. The diffusion coefficients of different anthraquinone derivatives used in paraffin oil were calculated by chronoamperometry. Received: 3 May 1999 / Accepted: 15 November 1999     

Electrochemical reduction of substituted cobalticinium cations in aqueous media

Summary In aqueous base, polarography, coulometry and cyclic voltammetry show that the cobalticinium skeleton is reduced in two monoelectronic and reversible steps, leading successively to cobaltocenes and cobaltocene anions. In acid solutions, the second reduction step is only observed for derivatives having electron withdrawing substituents. The height of the second reduction wave is pH dependent. Two different schemes are discussed for the reduction in acid solution.     

Photoreactions of p-quinones with dimethyl sulfide and dimethyl sulfoxide in aqueous acetonitrile. goerner@mpi-muelheim.mpg.de

The effects of dimethyl sulfide (DMS) and dimethyl sulfoxide (DMSO) on the photoreactions of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives in acetonitrile/water were studied. The observed triplet state of the quinones is quenched and the rate constant is close to the diffusion-controlled limit for reactions of most quinones with DMS and lower with DMSO. Semiquinone radical anions (Q*-) produced by electron transfer from sulfur to the triplet quinone were detected. For both DMS and DMSO the yield of Q*- is similar, being generally low for BQ and NQ, substantial for AQ and largest for chloranil. The specific quencher concentrations and the effects of quinone structure and redox potentials on the time-resolved photochemical properties are discussed.     

Solvent effect on the redox potential of quinone-semiquinone systems

Polarographic reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone and 9,10-anthraquinone was studied in pyridine, acetone, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide and propylene carbonate. The variation of the E_1/2-values proper for the first electron transfer step (measured against oxidation potential of ferrocene) with the properties of solvent is analyzed in terms of the donor-acceptor concept. Linear correlations of E_1/2 vs. acceptor number are observed; the slopes of corresponding lines correlate with the spin densities at oxygen atoms of semiquinones.     

Iridoids and anthraquinones from the Malaysian medicinal plant,Saprosma scortechinii (Rubiaceae)

A further investigation of the leaves and stems of Saprosma scortechinii afforded 13 compounds, of which 10 are new compounds. These were elucidated as the bis-iridoid glucosides, saprosmosides G (1) and H (2), the iridoid glucoside, 6-O-epi-acetylscandoside (3), and the anthraquinones, 1-methoxy-3-hydroxy-2-carbomethoxy-9,10-anthraquinone (4), 1-methoxy-3-hydroxy-2-carbomethoxy-9,10-anthraquinone 3-O-beta-primeveroside (5), 1,3-dihydroxy-2-carbomethoxy-9,10-anthraquinone 3-O-beta-primeveroside (6), 1,3,6-trihydroxy-2-methoxymethyl-9,10-anthraquinone (7), 1-methoxy-3,6-dihydroxy-2-hydroxymethyl-9,10-anthraquinone (8), 1,3,6-trihydroxy-2-hydroxymethyl-9,10-anthraquinone 3-O-beta-primeveroside (9), and 3,6-dihydroxy-2-hydroxymethyl-9,10-anthraquinone (10). Structure assignments for all compounds were established by means of mass and NMR spectroscopies, chemical methods, and comparison with published data. The new anthraquinones were derivatives of munjistin and lucidin.