Unexpected Ti-catalyzed formal intramolecular [4+4] cycloaddition of 1,1′-bi[(S,S)-6-(trimethylsilyl)cyclohepta-2,4-dien-1-yl]

Reductive disilylation (Li+Me₃SiCl−THF) of 1,3,5-cycloheptatriene led to 1,1′-bi[(S^∗,S^∗)-6-(trimethylsilyl)cyclohepta-2,4-dien-1-yl] (2). In the presence of TiCl₄ in dichloromethane, 2 gave rise to a spherical molecule 5 resulting from an intramolecular formal [4+4] supra-supra cycloaddition.     

Spectroscopic, thermal and structural studies of cocrystal of 2,2′-diamino-4,4′-bis(1,3-thiazole) with 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethylene and 1,3-bis(4-pyridyl)propane

Three new cocrystals based upon 2,2′-diamino-4,4′-bis(1,3-thiazole) (DABTZ) with 4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethylene (bpe) and 1,3-bis(4-pyridyl)propane (bpp): [(DABTZ) (4,4′-bipy)], [(DABTZ) (bpe)] and [(DABTZ) (bpp)] have been synthesized and characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy and studied by thermal and X-ray crystallography. Self-assembly of these compounds in the solid state is likely caused by both hydrogen bonding, and π-π stacking.     

Reductive opening of 2,7-dihydrodinaphthoxepine and thiepine: easy regioselective preparation of 2,2′-difunctionalised binaphthyls

The lithiation of 2,7-dihydrodinaphthoheteroepines (5) with 2.2 equiv of lithium naphthalenide in THF at −78 °C gives dianionic intermediates 8, which by reaction with different electrophiles [H₂O, D₂O, ^tBuCHO, Me₂CO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO] at the same temperature, followed by hydrolysis, leads to unsymmetrically 2,2′-disubstituted binaphthyls 6. When the lithiation is performed with an excess of lithium in the presence of a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 10 mol %), a double reductive cleavage takes place to give dianionic intermediate 9, which by reaction with different electrophiles [H₂O, Me₂CO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO], followed by hydrolysis with water, yields symmetrically 2,2′-disubstituted binaphthyls 7. In the case of starting from (R)-5a, the reductive opening by treatment with 2.2 equiv of lithium naphthalenide followed by reaction with H₂O or (CH₂)₅CO as electrophiles and final hydrolysis, leads to enantiomerically pure compounds (R)-6aa and (R)-6af, respectively.     

Synthesis,structure and reactivity of novel palladiumdichloride-2,2′-bipyridine with 4,4′-bis(fluorous-ponytail)

With the readily available fluorous alkanols R_fCH₂OH, a series of novel fluorous-ponytailed bpy ligands, 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy (1a–e), were prepared and treated with [PdCl₂(CH₃CN)₂] to result in the corresponding novel Pd complexes [PdCl₂(4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy)] (2a–e) where R_f = n-C₃F₇ (a), HCF₂(CF₂)₃ (b), HCF₂(CF₂)₇ (c), n-C₈F₁₇ (d), n-C₁₀F₂₁ (e). The new ligands and Pd complexes were spectroscopically characterized by multi-nuclei NMR (¹H, ¹⁹F and ¹³C), FTIR and high resolution mass (FAB). The structure for the Pd complex 2b, the first with fluorinated ponytails on bpy and not on phosphine, was also established by a single crystal X-ray diffraction study. The TGA data of both ligands and Pd complexes indicated that the Pd-complexes were resistant to higher temperatures than the corresponding ligands. The Pd catalysts derived from 2a–c showed an almost quantitative conversion and could be reused for eight runs with Heck reactions, in that the products and unspent reactants were directly removed by distillation. With the highest fluorine content in the series, Pd complex 2e was successfully applied in the Heck reaction using the fluorous biphasic catalysis strategy.     

New fluorinated aromatic poly(ether-amide)s derived from 2,2′-bis(3,4,5-trifluorophenyl)-4,4′-diaminodiphenyl ether and various dicarboxylic acids

A new class of highly fluorinated aromatic poly(ether-amide)s was prepared through triphenyl phosphite-activated polycondensation of 2,2′-bis(3,4,5-trifluorophenyl)-4,4′-diaminodiphenyl ether (FPAPE) and four dicarboxylic acid comonomers. All the resulting polymers were thoroughly characterized by FT-IR, UV, and NMR spectroscopic methods. The effects of the fluorine atoms directly linked to the lateral phenyl rings as well as fluoro-containing phenyl groups attached to the macromolecular chains on some properties of the polymers were investigated by comparing with poly(ether-amide)s prepared from 4,4′-oxydianiline (4,4′-ODA) and 2,2′-diphenyl-4,4′-diaminodiphenyl ether (PAPE). The FPAPE-derived polymers exhibited excellent solubility in a variety of organic solvents. Results obtained from X-ray studies showed that the presence of the bulky fluoro-containing phenyl groups attached to the chains disrupts their structural order in a great amount, and leads to a decrease in crystallinity extent of the macromolecules. Furthermore, the highly fluorinated polymeric chains showed a significant enhancement in organo-solubility, heat-stability and T_g values when compared to their non-fluorinated counterparts.     

Synthesis and characterizations of 3,3′-bis(diphenylphosphinoamine)-2,2′-bipyridine and 3,3′-bis(diphenylphosphinite)-2,2′-bipyridine and their chalcogenides

New bis(phosphinoamine) and bis(phosphinite) derivatives of 2,2′-bipyridine were prepared through a single step reaction of 3,3′-diamino-2,2′-bipyridine or 3,3′-dihydroxy-2,2′-bipyridine with diphenylchlorophosphine, respectively. Their P = E chalcogenides (E = O, S, Se) were also prepared. All the new compounds were characterized by elemental analysis, IR and NMR spectroscopies. The molecular structure of 3,3′-bis(diphenylthiophosphinite)-2,2′-bipyridine was elucidated by single-crystal X-ray crystallography.     

1,1′-Methylene-bis(1,1′,2,2′,3,3′,4,4′-octahydroisoquinoline): synthesis, reaction, resolution, and application in catalytic enantioselective transformations

The preparation of new chiral 1,3-diamine ligand systems based on the 1,1′-methylene-bis(1,1′,2,2′,3,3′,4,4′-octahydroisoquinoline) framework is described. Synthesis of various mono-, di-, and bridged N-alkyl derivatives are presented. Resolution of one compound, its Cu(I)Br X-ray crystallographic structure and the preliminary results on its application in the enantioselective Henry and Aldol reactions are disclosed.     

Ordered porous films based on fluorinated polyimide derived from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 3,3′-dimethyl-4,4′-diaminodiphenylmethane

One of fluorinated polyimides was synthesized from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′-dimethyl-4,4′-diaminodiphenylmethane (DMMDA) by two-steps method, which had good solubility and hydrophilicity. 6FDA-DMMDA polyimide was dissolved in chloroform (CHCl₃) and cast on a glass substrate in a humid atmosphere. It was found that 6FDA-DMMDA/CHCl₃ solution was easy to form ordered porous structure at high concentration, and the reason was discussed in detail. In addition, the influences of solution concentration, the atmosphere humidity, were also tested.     

Reactions of methyl(pentafluorophenyl)- and methyl(pentafluorophenyl)phenylsilanes with electrophiles. A convenient preparative route to halogeno(methyl)pentafluorophenylsilanes C6F5SiMe2X and C6F5SiMeX2 (X=F, Cl and Br)

Halogeno(methyl)pentafluorophenylsilanes C₆F₅SiMe_nX_3−n (n=1, 2) (X=F, Cl, Br) were prepared in good yields from the corresponding phenylsilanes C₆F₅SiMe_nPh_3−n by reactions with the electrophiles aHF, HCl–AlCl₃, Br₂–AlBr₃ or AlX₃ (X=Cl, Br) halogenated hydrocarbons. Additionally, reactions of C₆F₅SiMe₃ and (C₆F₅)₂SiMe₂ with selected electrophiles were studied.     

Exchange reactions of 1,3-bis(nitroarylthio)propanes with propane-1,3-dithiols

Base-catalyzed reactions of propane-1,3-dithiols with 2-chloronitrobenzene, 3,4-dichloronitrobenzene, and 2-chloro-3-nitropyridine afforded 1,3-bis(nitroarylthio)propanes, whose thiolate-thiolate exchange with propane-1,3-dithiols gave dihydrobenzodithiepines. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 163–166, January, 2006.     

Hydrosilylation and double silylation of carbonyl compounds with 1,1′-bis(dimethylsilyl)ferrocene using nickel- and platinum-catalysts

A series of ferrocene-based organosilicon compounds have been prepared via hydrosilylation or double silylation of carbonyl compounds with 1,1′-bis(dimethylsilyl)ferrocene using (C₂H₄)Pt(PPh₃)₂ or Ni(PEt₃)₄ catalysts. In general, while the platinum catalyst (C₂H₄)Pt(PPh₃)₂ preferentially produced cyclic double-silylated products, the Ni(PEt₃)₄ catalyst led to the hydrosilylated ferrocene products from aldehydes or ketones.     

Scandium triflate-catalyzed 6,6′-diiodination of 2,2′-dimethoxy-1,1′-binaphthyl with 1,3-diiodo-5,5-dimethylhydantoin

Scandium triflate-catalyzed iodination of 2,2′-dimethoxy-1,1′-binaphthyl with 2 equiv of 1,3-diiodo-5,5-dimethylhydantoin (DIH) proceeded to give 6,6′-diiodo-2,2′-dimethoxy-1,1′-binaphtyl in 98% yield and subsequent deprotection of methyl groups provided 6,6′-diiodo-1,1′-binaphthol, which is a useful ligand or reagent for many enantioselective transformations. Use of 2 equiv of NIS in place of DIH in the presence of scandium triflate, however, did not successfully yield 6,6′-diiodo-2,2′-dimethoxy-1,1′-binaphtyl, indicating that one of two types of iodine atoms in DIH is more reactive toward the iodination than iodine in NIS.     

Study of electrochemical stability of conducting polymers by bidimensional spectroelectrochemistry: p- and n-doping of poly(4,4′-bis(butylthio)-2,2′-bithiophene) films

UV-vis bidimensional spectroelectrochemistry has been applied to the study of the electrochemical stability of conducting polymer films during p- and n-doping processes. Specifically, poly(4,4′-bis(butylthio)-2,2′-bithiophene) has been chosen as example to prove the usefulness and suitability of this multi-response technique to characterize polymer stability during p- and n-doping. It was found that oxidative doping and corresponding de-doping alone did not result in noticeable polymer film degradation. However, in experiments involving both p- and n-doping of this conducting polymer, soluble species arising from the polymer film were detected in solution for the first time, indicating a lower electrochemical stability of the film under these experimental conditions. Moreover, bidimensional spectroelectrochemistry has enabled us not only to detect the soluble degradation products, but also the potential range in which the degradation takes place.     

A new synthetic route of 4,4′-hexafluoroisopropylidene-2,2-bis-(phthalic acid anhydride) and characterization of 4,4′-hexafluoroisopropylidene-2,2-bis-(phthalic acid anhydride)-containing polyimides

The title product 4,4′-hexafluoroisopropylidene-2,2-bis-(phthalic acid anhydride) was prepared from hexafluoroacetone and o-xylene as the starting materials by condensation, oxidation and dehydration three-step reaction sequence. It reacted with diamines in DMF or xylene to give polyimides by condensation polymerization. Thermal and viscosity analyses show that these polyimides have lower molecular weight but excellent thermal stability.     

Syntheses and properties of complexes with bis(2,2′-bipyridyl)ruthenium(II) moieties coordinated to 4,4′:2′,2′′:4′′,4′′′-quaterpyridinium ligands

Eleven new complexes of the form cis-[Ru^II(bpy)₂(L^A)]⁴⁺ (bpy = 2,2′-bipyridyl; L^A = a pyridinium-substituted bpy derivative) have been prepared and isolated as their PF₆⁻ salts. Characterisation involved various techniques including ¹H NMR spectroscopy and MALDI mass spectrometry. The UV-Vis spectra show intense intraligand π → π^∗ absorptions and metal-to-ligand charge-transfer (MLCT) bands with two distinct maxima in the visible region. Small shifts in the MLCT bands correlate with the electron-withdrawing strength of the ligand L^A. Cyclic voltammograms show quasi-reversible or reversible Ru^III/II oxidation waves, and two or more ligand-based reductions with varying degrees of reversibility. The variations in the redox potentials correlate with changes in the structure of L^A, and also with the MLCT energies. Differential pulse voltammetry allows the first reduction process for two of the complex salts to be resolved into two peaks. Single-crystal X-ray structures have been solved for three of the new complex salts and also for a pro-ligand salt. Two carboxylate-functionalised compounds have been tested as photosensitizers on TiO₂-coated electrodes, but show only negligible efficiencies, in accord with expectations.     

Planar 2,2′-bithiophenes with 3,3′- and 3,3′,4,4′-substituents. A computational study

Ab initio calculations have shown that when carbonyl groups are incorporated into the 3- and 3′-positions of bithiophenes, as part of five-membered rings, the bithiophene system is planar. This is due to electrostatic attraction between the carbonyl oxygen and the sulfur atom in the adjacent ring. In the analogous systems containing a CH₂ group in place of the carbonyl, or containing six-membered rather than five-membered rings, the bithiophenes are twisted. This has implications for preparing planar polythiophenes.     

Hydrogen bonded NHO chains formed by chloranilic acid (CLA) with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP) in the solid state

In crystalline state 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) forms with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP) the hydrogen bonded chains along the b-axis. From one side of the CLA molecule the proton transfer takes place and the hydrogen bond length is very short (2.615 Å). A continuous infrared absorption is observed for dtBBP·CLA in the wavenumber range between 3100 and 800 cm⁻¹ also indicating the strong hydrogen bonds. The DSC measurements show a weak, close to continuous, phase transition at 414 K. The complex dielectric permittivity for a single crystal sample was measured in the temperature range 100-440 K and at frequencies between 200 Hz and 2 MHz. The dielectric response is a combination of semiconducting properties and a relaxation process most probably connected with the proton dynamics in the hydrogen bonds. The mechanism of the structural phase transition is discussed.     

Synthesis and structure of the chiral palladium-fullerene C60 and C70 complexes with enantiomeric ligand 2,2′,5,5′-tetramethyl-4,4′-bis(diphenylphosphino)-3,3′-bithiophene [(−)tetraMe-BITIOP]

η²-Fullerene (C₆₀ and C₇₀) palladium optically active complexes with the axially chiral enantiomeric ligand of bithienyl series, [(−)tetraMe-BITIOP], have been synthesized and investigated by ³¹P-{¹H} NMR, electronic spectroscopy, CD spectroscopy, cyclic voltammetry and by single crystal X-ray diffraction.     

Facile acid-catalyzed condensation of 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone with phenols, methoxyaromatic systems and enols

Various phenols, methoxy aromatic compounds, 3- and 4-hydroxycoumarins and enols smoothly condense with 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone 1 in an acid medium producing 2-aryl/alkyl-2,2′-biindan-1,1′,3,3′-tetrones in high yields. The adducts of resorcinol, 1,3,5-trihydroxybenzene and α- and β-naphthols of 1 preferably remain in the intramolecular hemi-ketal form, confirmed by X-ray diffraction studies. On the other hand para and meta substituted phenols condense with 1 in an acid medium to produce 6 or 7 substituted 2′,4-spiro(1′,3′-indanedion)-indeno[3,2-b]chromenes in good yields.     

Acid-catalyzed reactions of (3-(naphthalen-2-yl)-2,2-bis(trimethylsilyl)oxiran. A new synthesis of functional-group-substituted vinylsilanes

The magnesium bromide-diethyl etherate-catalyzed ring-opening of (3-(naphthalen-2-yl)-2,2-bis(trimethylsilyl)oxiran 2 with thiophenols affords (1-trimethylsilylvinyl)sulfides 3 and the (1-bromovinyl)silane 4. Nucleophilic attack occurs regioselectively at the position α- to silicon. The compound 2 has been converted into the (1-trimethylsilylvinyl)amide 5 with an excess of acetonitrile and into the (1-trimethylsilylvinyl)acetate 6 with acetic acid/acetic anhydride. These reactions proceed with catalytic amounts of boron trifluoride-diethylether. Treatment of 2 with acetic acid alone gives naphthaldehyde. The epoxide 2 reacts also with MgBr₂·OEt₂, MeLi/CuI, HX (XBr or Cl) and LiAlH₄ with nucleophilic attack at the bis(trimethylsilyl)-substituted carbon.