Si—H Functional Polysilanes via a Homogeneous Reductive Coupling Reaction

A polysilane copolymer with reactive Si—H side groups was obtained through a homogeneous coupling reaction of dichlorodiphenylsilane with dichloromethylsilane. The reaction was carried out in a tetrahydrofuran (THF) solution of a sodium‐potassium alloy complex with 18‐crown‐6 with a well defined composition of alkali metal ion pairs (Mt⁺/crown ether, Mt^–) at –75°C. The product was characterized using ¹H NMR, ¹³C NMR, FT‐IR and UV/Visible spectroscopies and gel permeation chromatography. The results were compared with those obtained by the heterogeneous coupling reaction of the same monomers.     

Metal Ions Drive Thermodynamics and Photochemistry of the Bis(styryl) Macrocyclic Tweezer

UV/Vis and NMR spectroscopy were used for the structural elucidation and thermodynamic and photochemical studies of the metal‐coordinated crown‐containing macrocyclic tweezer (E,E)‐ 1 . The bis(styryl) tweezer (E,E)‐ 1 formed two types of complexes with magnesium(II): a 1:1 intramolecular asymmetric sandwich complex [(E,E)‐ 1 ]?Mg²⁺ and a 1:2 complex [(E,E)‐ 1 ]?(Mg²⁺)₂. In the former case, there is direct cation intramolecular exchange (0.299 s^?1, ΔG^≠=69.4 kJ mol^?1) between two parts of the bis(styryl) tweezer (E,E)‐ 1 . Addition of barium(II) to the bis(styryl) tweezer (E,E)‐ 1 led to an intramolecular centrosymmetric sandwich 1:1 complex [(E,E)‐ 1 ]?Ba²⁺. Irradiation of [(E,E)‐ 1 ]?Ba²⁺ afforded reversible intramolecular [2π+2π] photocyclization with excellent stereoselectivity and quantitative yield. In contrast, irradiation of [(E,E)‐ 1 ]?(Mg²⁺)₂ resulted in reversible stepwise E,Z‐isomerization.     

Metal Ion Modulated Torsion Angle in a Ditopic Oligothiophene Ligand: Toward Supramolecular Control of π Conjugation

A π‐conjugated oligomer bearing two 15‐crown‐5‐containing styryl moieties connected at the inner β positions of the terminal thiophene nuclei can adopt either a U or a Z shape depending on the structures of its complexes with magnesium and barium ions. We show that barium cations lead to the formation of a mononuclear complex in solution, which causes the system to fold into the U shape. Magnesium ions lead to the same effect at low concentration, but force the ligand to adopt the Z‐shaped geometry at high concentrations favoring formation of a binuclear complex. These geometrical reorganizations in solution are accompanied by profound changes in spectroscopic properties, which can be rationalized in terms of variations in the extent of electron delocalization along the oligothiophene backbone. The effects are analyzed by mass spectrometry and ¹H NMR, UV/Vis absorption, and fluorescence spectroscopy in the steady‐state and time‐resolved regimes. The experimental results are compared to data calculated by using MOPAC2007 with the PM6 Hamiltonian including the COSMO solvation model.     

Synthesis of Novel (p‐Substituted Styryl) Spirobenzopyrans

A series of (p‐substituted styryl) spirobenzopyrans were synthesized by the Wittig reaction of Fisher's bases with 5‐(p‐substituted styryl) salicylaldehyde derivatives. The final spirobenzopyrans were characterized by the ¹H NMR, IR, UV, and GC‐MS analyses.     

Complexes of Diquat with Dibenzo-24-Crown-8

The complexation between dibenzo‐24‐crown‐8 ( 1 ) and diquat ( 2 ) was investigated in detail by NMR, MS and X‐ray analysis. It was found that dibenzo‐24‐crown‐8 and diquat formed a 1:1 complex 1 · 2 in acetone with K_a=2.0×10² L·mol^?1, but, as shown by X‐ray analysis, a crystalline 2:1 host:guest inclusion complex 1 ₂· 2 was isolated, in which a single molecule of diquat is enclosed in the concave cavity provided by two dibenzo‐24‐crown‐8 host molecules. Both results are different from the previously assumed stoichiometry of the complexation between dibenzo‐24‐crown‐8 and diquat. This result enriches the range of host‐guest complexes based on dibenzo‐24‐ crown‐8 and provides new opportunities for developing more complicated structures and chemosensors for diquat.     

Cobalt（Ⅱ） Salen Complex with Two Aza-crown Pendants and Its Analogues as Synthetic Oxygen Carriers

Salen with two aza‐crown ether pendants H₂L¹ and its analogues H₂L^2‐H₂L⁴ were successfully synthesized starting from benzo‐10‐aza‐15crown‐5 (BN15C5) or morpholine. Their structures were characterized by IR, MS, ¹H NMR and elemental analysis, and were confirmed by X‐ray diffraction analysis of H₂L¹. Moreover, the saturated oxygen uptake of their cobalt(II) complexes CoL^1‐CoL⁴ in diethyleneglycol dimethyl ether was determined at different temperature. The oxygenation contants (K_O2 ) and thermodynamic parameters (ΔH° and ΔS°) were calculated. The modulation of O₂‐binding capabilities by pendant substituents were investigated as compared with the parent Schiff base complex CoL⁵ (CoSalen). The results indicate that the dioxygen affinities of CoL have been much more enhanced by aza‐crown pendants than that by morpholino pendants, and the O₂‐binding capabilities of CoL¹ and CoL² with aza‐crown pendants would also be enhanced by adding alkali metal cations.     

7Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

⁷Li NMR titration was used to determine stepwise complexation constants for the second‐order complexation of lithium cation with 12‐crown‐4 in acetonitrile, propylene carbonate and a binary mixture of propylene carbonate and dimethyl carbonate. The anions used were perchlorate, hexaflurophosphate and trifluromethanesulfonate. A second ligand 1‐aza‐12‐crown‐4 was similarly investigated. The exchange between the free and complexed cation in these reactions is fast on an NMR timescale resulting in a single lithium peak which is a concentration‐weighted average of the free and bound species. Solvent effects show that the 1:1 complex is much more stable in acetonitrile than in propylene carbonate or in the propylene carbonate dimethyl carbonate mixture. Anion effects for a given solvent were small. Optimized geometries of the free ligands and the 1:1 and 1:2 (sandwich) metal–ligand complexes were predicted by hybrid‐density functional theory using the Gaussian 03 software package. Results were compared to literature values for 1:1 stability constants found by microcalorimetry for several of these systems and are found to be in good agreement. Although microcalorimetry only considered the formation of 1:1 complexes, ⁷Li NMR shows evidence that both 1:1 and 1:2 complexes should be considered. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,Photophysical Properties,and Antimicrobial Activity of Novel Styryl Colorants Derived from 7‐Methoxy‐1,4‐diphenethyl‐1,2,3,4‐tetrahydroquinoxaline‐6‐carbaldehyde

The novel 1,4‐diphenethyl‐1,2,3,4‐tetrahydro‐7‐methoxyquinoxalin‐6‐carbaldehyde was synthesized by reductive alkylation of 6‐methoxy quinoxaline with phenyl acetic acid and was further subjected to Knoevenagel condensation with various active methylene compounds to synthesize novel styryl colorants. Photophysical properties of styryl colorants were studied using UV–visible and fluorescence spectroscopy. These colorants displayed orange to violet hue and showed fluorescence emission maxima in the region of 560–640 nm, and displayed a large Stokes shift (85–104 nm). Compounds were subjected to thermogravimetric analysis which showed excellent stability up to 310°C. These styryl compounds were evaluated for their antimicrobial study as antifungal against Candida albicans C. albicans and Aspergillus niger and antibacterial against Escherichia coli and Staphylococcus aureus. The results revealed good antimicrobial activity against tested organisms. The synthesized chromophores were characterized using elemental analysis, FTIR, ¹³C‐NMR and ¹H‐NMR spectroscopy and mass spectrometry.     

Design and Synthesis of Calixarene‐Based Bis‐alkynyl‐Bridged Dinuclear AuI Isonitrile Complexes as Luminescent Ion Probes by the Modulation of Au⋅⋅⋅Au Interactions

Two calixarene‐based bis‐alkynyl‐bridged Au^I isonitrile complexes with two different crown ether pendants, [{calix[4]arene‐(OCH₂CONH‐C₆H₄C≡C)₂}{Au(CNR)}₂] (R=benzo[15]crown‐5 ( 1 ); R=benzo[18]crown‐6 ( 2 )), together with their related crown‐free analogue 3 (R=C₆H₃(OMe)₂‐3,4) and a mononuclear gold(I) complex 4 with benzo[15]crown‐5 pendant, have been designed and synthesized, and their photophysical properties have been studied. The X‐ray structure of the ligand, calix[4]arene‐(OCH₂CONH‐C₆H₄C?CH)₂ has been determined. The cation‐binding properties of these complexes with various metal ions have been studied using UV/Vis, emission, ¹H NMR, and ESI‐MS techniques, and DFT calculations. A new low‐energy emission band associated with Au???Au interaction could be switched on upon formation of the metal ion‐bound adduct in a sandwich fashion.     

Synthesis,Structure, Spectroscopic Studies,and Complexation of Novel Crown Ether Butadienyl Dyes

Butadienyl dyes of the benzothiazole series with various fragments of benzocrown ethers 1a – c were synthesized for the first time. The structures and spectral properties of crown‐containing butadienyl dyes and their complexes with alkali and alkaline‐earth metal cations were studied by X‐ray diffraction analysis and ¹H‐NMR, UV/VIS, and resonance Raman spectroscopy. To interpret the experimental results, quantum‐chemical calculations were performed. In the case of Sr²⁺ and Ba²⁺ ions, the formation of strong sandwich complexes [M( 1b )₂]²⁺ of an unusual structure involving stacking interactions was established; the dye molecules are arranged one above another in the complex according to the ‘head‐to‐head' pattern.     

“Two‐Point” Self‐Assembly and Photoinduced Electron Transfer in meso‐Donor‐Carrying Bis(styryl crown ether)‐BODIPY–Bis(alkylammonium)fullerene Donor–Acceptor Conjugates

BF₂‐chelated dipyrromethene, BODIPY, was functionalized to carry two styryl crown ether tails and a secondary electron donor at the meso position. By using a “two‐point” self‐assembly strategy, a bis‐alkylammonium‐functionalized fullerene (C₆₀) was allowed to self‐assemble the crown ether voids of BODIPY to obtain multimodular donor–acceptor conjugates. As a consequence of the two‐point binding, the 1:1 stoichiometric complexes formed yielded complexes of higher stability in which fluorescence of BODIPY was found to be quenched; this suggested the occurrence of excited‐state processes. The geometry and electronic structure of the self‐assembled complexes were derived from B3LYP/3‐21G(*) methods in which no steric constraints between the entities was observed. An energy‐level diagram was established by using spectral, electrochemical, and computational results to help understand the mechanistic details of excited‐state processes originating from ¹bis‐styryl‐BODIPY*. Femtosecond transient absorbance studies were indicative of the formation of an exciplex state prior to the charge‐separation process to yield a bis‐styryl‐BODIPY ^{. +}–C₆₀ ^{. −} radical ion pair. The time constants for charge separation were generally lower than charge‐recombination processes. The present studies bring out the importance of multimode binding strategies to obtain stable self‐assembled donor–acceptor conjugates capable of undergoing photoinduced charge separation needed in artificial photosynthetic applications.     

Synthetic, structural, and theoretical investigations of alkali metal germanium hydrides--contact molecules and separated ions

The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether)_nGeH₃ through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH₃^? ion. Germyl derivatives displaying M? Ge bonds in the solid state are of the general formula [M([18]crown‐6)(thf)GeH₃] with M=K ( 1 ) and M=Rb ( 4 ). The compounds display an unexpected geometry with two of the GeH₃ hydrogen atoms closely approaching the metal center, resulting in a partially inverted structure. Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display M? H interactions. Separated ions display alkali metal cations bound to two crown ethers in a sandwich‐type arrangement and non‐coordinated GeH₃^? ions to afford complexes of the type [M(crown ether)₂][GeH₃] with M=K, crown ether=[15]crown‐5 ( 2 ); M=K, crown ether=[12]crown‐4 ( 3 ); and M=Cs, crown ether=[18]crown‐6 ( 5 ). The highly reactive germyl derivatives were characterized by using X‐ray crystallography, ¹H and ¹³C NMR, and IR spectroscopy. Density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2) calculations were performed to analyze the geometry of the GeH₃^? ion in the contact molecules 1 and 4 .     

Ultrafast Photoinduced Charge Separation in Wide‐Band‐Capturing Self‐Assembled Supramolecular Bis(donor styryl)BODIPY–Fullerene Conjugates

A new series of self‐assembled supramolecular donor–acceptor conjugates capable of wide‐band capture, and exhibiting photoinduced charge separation have been designed, synthesized and characterized using various techniques as artificial photosynthetic mimics. The donor host systems comprise of a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) containing a crown ether entity at the meso‐position and two styryl entities on the pyrrole rings. The styryl end groups also carried additional donor (triphenylamine or phenothiazine) entities. The acceptor host system was a fulleropyrrolidine comprised of an ethylammonium cation. Owing to the presence of extended conjugation and multiple chromophore entities, the BODIPY host revealed absorbance and emission well into the near‐IR region covering the 300–850 nm spectral range. The donor–acceptor conjugates formed by crown ether–alkyl ammonium cation binding of the host–guest system was characterized by optical absorbance and emission, computational, and electrochemical techniques. Experimentally determined binding constants were in the range of 1–2×10⁵ M ^?1. An energy‐level diagram to visualize different photochemical events was established using redox, computational, absorbance, and emission data. Spectral evidence for the occurrence of photoinduced charge separation in these conjugates was established from femtosecond transient absorption studies. The measured rates indicated ultrafast charge separation and relatively slow charge recombination revealing their usefulness in light‐energy harvesting and optoelectronic device applications. The bis(donor styryl)BODIPY‐derived conjugates populated their triplet excited states during charge recombination.     

Synthesis and Complexation Behavior Studies of Novel Bis-crown Ethers

The novel unique structures of bis-crown ethers were successfully synthesized from tri (propylene glycol) di-acrylate with amino- and aza-crown ethers through Michael addition. The crown ethers contained the primary and the secondary amine group such as 2-aminomethyl crown ethers, 4-aminobenzo crown ethers and 1-aza crown ethers. The newly synthesized bis-crown ethers were characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR, mass spectrum, respectively. The newly synthesized host compounds of bis-crown ethers showed complex ability with various sizes of alkali metal cations such as Na⁺, K⁺, Rb⁺ and Cs⁺. The complexation behavior was examined by ¹H NMR spectroscopy and UV spectrometry.     

Synthesis of a calix[4]crown modified with germanium‐containing side chains

A germacalix‐crown, 25,27‐bis[1‐(3‐trimethylgermylpropyl)oxy]calix[4]arene‐crown‐6, 1,3‐alternate ( 1a ), and its carbon analog, 25,27‐bis‐[1‐(4,4‐dimethylpentyl)oxy]calix[4]arene‐crown‐6, 1,3‐alternate ( 1b ), were prepared and their structures were confirmed by elemental analysis and ¹H and ¹³C NMR spectroscopy. A cation transport test indicated that both compounds exhibited much the same cation transport ability, so that the role of the germanium moiety in capturing and transporting counteranions is not yet clear. Copyright © 2005 John Wiley & Sons, Ltd.     

Hyperbranched polymers generated from oxyanionic vinyl polymerization of commercially available methacrylate inimers

Hyperbranched polymethacrylates were prepared by means of oxyanionic vinyl polymerization of commercially available monomers, including hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEG‐MA). Hyperbranched polymethacrylates with high molecular weight were obtained with the complex of potassium hydride and 18‐crown‐6 as the initiator. The effect of 18‐crown‐6 is very important, and only oligomer can be obtained in the polymerization without 18‐crown‐6. The molecular structure of the hyperbranched polymers was confirmed with ¹H NMR and ¹³C NMR spectra. The ratio of initiator to monomer significantly affects the architecture of the resultant polymers. When the ratio of initiator to monomer equals 1 in the oxyanionic vinyl polymerization of HEMA, the degree of branching of the resulting polymer was calculated to be around 0.49. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3502–3509, 2005     

TMSCl Promoted Direct sp3 C‐H Alkenylation to Construct (E)‐2‐Styryl‐tetrahydrobenzo[d]thiazoles

A high‐efficient and stereo‐specific approach for the preparation of biologically important (E)‐2‐styryl‐tetrahydrobenzo[d]thiazoles has been developed via TMSCl promoted direct sp³ C‐H alkenylation of 2‐methyl‐5,6‐dihydrobenzo[d]thiazol‐7(4H)‐one under metal‐free conditions. Seventeen target compounds were synthesized in excellent yields of 82% –98% under the optimal conditions of 300 mol% TMSCl at 110°C for 2 h, and their chemical structures were elucidated by IR, NMR, ESI‐MS, elemental analyses and X‐ray crystallography analysis. A plausible mechanism was also proposed, and this method provided a good functional group conversion for the sp³ C‐H substrates.     

Crowned dendron: ion-responsive flexibility of macromolecules induced by integrated crown ether moieties

Polybenzyl ether type dendrons bearing the crown ether moieties at the periphery, namely, crowned dendrons were synthesized, and the effect of complex formation on their flexibility with metal-ion binding properties was examined. Upon addition of Na⁺, ¹H NMR spectra of the crowned dendrons in CD₃CN were significantly broadened, reflecting the flexibility restriction of the crowned dendrons by the complex formation with Na⁺. Such a significant flexibility restriction was observed only with Na⁺, although ESI-MS studies revealed that the crowned dendrons formed 1:2 complexes (a metal ion:the crown ether moiety) regardless of the kind of metal ions. The flexibility restriction became significant with increasing dendron generation on the basis of ¹H NMR spectra and spin-lattice relaxation time (T₁) measurements. Binding constants of the crowned dendrons with metal ions in CD₃CN decreased with the increase of the dendron generation, reflecting an influence of the charge repulsion as well as a dendrimer effect to cause the steric hindrance. The examination of UV-vis absorption spectra for complexes of the crowned dendron with metal picrates in THF displayed the formation of a loose ion-pair complex with Na⁺, namely, a typical sandwich type complex. However, in CH₃CN, all metal picrates were solvated to be in a loose ion-pair even without complex formation. These results suggested that the control of macromolecular flexibility with metal ions is feasible by the integration of crown ether moieties with a dendritic structure.     

A Terminal Iron Nitrilimine Complex: Accessing the Terminal Nitride through Diazo N−N Bond Cleavage

A novel method for the N?N bond cleavage of trimethylsilyl diazomethane is reported for the synthesis of terminal nitride complexes. The lithium salt of trimethylsilyl diazomethane was used to generate a rare terminal nitrilimine transition metal complex with partially occupied d‐orbitals. This iron complex 2 was characterized by CHN combustion analysis, ¹H and ¹³C NMR spectroscopic analysis, single‐crystal X‐ray crystallography, SQUID magnetometry, ⁵⁷Fe Mössbauer spectroscopy, and computational analysis. The combined results suggest a high‐spin d ⁶ (S=2) electronic configuration and an allenic structure of the nitrilimine ligand. Reduction of 2 results in release of the nitrilimine ligand and formation of the iron(I) complex 3 , which was characterized by CHN combustion analysis, ¹H NMR spectroscopic analysis, and single‐crystal X‐ray crystallography. Treatment of 2 with fluoride salts quantitatively yields the diamagnetic Fe^IV nitride complex 4 , with concomitant formation of cyanide and trimethylsilyl fluoride through N?N bond cleavage.     

Synthesis and Fluorescence Properties of a Novel Supramolecular Complex Containing [60]Fullerene Moiety

Abstract

A new crown ether styryl dye containing [60]Fullerene moiety has been synthesized, and characterized by FT-IR, NMR and Mass spectra. Fluorescence spectra of the compound have also been studied. The results indicate a strong hypsochromic shift from 548 nm to 526 nm is observed on cation complexation, and the intensity of peaks at 504 nm, 548 nm and 590 nm decrease as the metal cation concentration is increased at 77K.