Silver-Catalyzed Asymmetric Dearomatization of Electron-Deficient Heteroarenes via Interrupted Barton-Zard Reaction.

Herein we report a catalytic asymmetric dearomatization reaction of electron-deficient heteroarenes with α-substituted isocyanoacetates through an interrupted Barton-Zard reaction. A range of optically active pyrrolo[3,4-b]indole derivatives was obtained in good yields (up to 97 %) with high stereoselectivities (up to >20:1 dr and 97 % ee), using a catalytic system consisting of a cinchona-derived amino-phosphine and silver oxide. This reaction features wide substrate scope and mild conditions, and provides a new strategy for developing asymmetric dearomatization reactions.

Ferrocene-Alkynyl Conjugated Molecular Wires: Synthesis, Characterization, and Conductance Properties.

A novel series of 1,2,3-substituted ferrocene-based wires a1-a2 and b4-b5 have been synthesized by using an iterative Pd-mediated Sonogashira cross-coupling methodology. The molecular structures of a2 and b3 were determined by single-crystal X-ray analysis. Electrochemical data showed that there was a strong electronic communication among the ferrocenyl moieties in b1-b5. The UV absorption spectra indicated that replacing the 1,1'-substituted ferrocene unit with a 1,2,3-substituted ferrocene moiety causes delocalization of electrons in the extended π orbitals. The self-assembled monolayers of wire a1 and a2 on Au surfaces have been comprehensively characterized by electrochemistry and scanning tunneling microscopy break junction. The data demonstrated that 1,2,3-substituted ferrocene-based wires reduced the intermolecular π-π stacking, and furthermore solved the rotation problem in the 1,1'-substituted ferrocene-based wires.

Conductance of o-carborane-based wires with different substitution patterns.

Here, we report the synthesis, structure, and single-molecule conductance of three o-carborane-based molecular wires (ortho-, meta- and para-CN) with multiple conduction channels. The effect of connectivity in target wires compared with the corresponding phenyl-centered wires was studied using the scanning tunneling microscope break junction (STM-BJ) technique and theoretical calculations. Interestingly, the three-dimensional structure in o-carborane-based wires can effectively promote the through-space transmission paths or the formation of stable molecular junctions compared to the corresponding phenyl-centered wires. Moreover, the significant conductance difference of o-carborane-based wires was due to the combination of multiple conduction channels and quantum interference. Understanding the effects of different bridging groups and anchor group substitution patterns provides guidelines for designing o-carborane-based multichannel molecular wires.

Ag2O/squaramide cocatalyzed asymmetric interrupted Barton-Zard reaction of 8-nitroimidazo[1,2-a]pyridines.

Imidazo[1,2-a]pyridines are present in numerous biologically active compounds as the core structural motif. Herein, we report an asymmetric interrupted Barton-Zard reaction of electron-deficient imidazo[1,2-a]pyridines with α-substituted isocyanoacetates. The reaction enables the dearomatization of 8-nitroimidazo[1,2-a]pyridines and hence offers straightforward access to an array of optically active highly functionalized imidazo[1,2-a]pyridine derivatives that possess three contiguous stereogenic centers in good yields (up to 98%) with high stereoselectivities (>19:1 dr, >99% ee). It is worth noting that the catalytic system consisting of a chiral squaramide and silver oxide displays remarkable reactivity and stereoselectivity, and a gram-scale reaction is compatible with the catalyst loading of 0.5 mol%. In addition, the synthetic potential of this method was showcased by versatile transformations of the product.

A simple and highly selective 2,2-diferrocenylpropane-based multi-channel ion pair receptor for Pb(2+) and HSO4(-).

A structurally simple, 2,2-diferrocenylpropane-based ion pair receptor 1 was synthesized and characterized by (1)H NMR, (13)C NMR, HRMS, elemental analyses, and single-crystal X-ray diffraction. The ion pair receptor 1 showed excellent selectivity and sensitivity towards Pb(2+) with multi-channel responses: a fluorescence enhancement (more than 42-fold), a notable color change from yellow to red, redox anodic shift (ΔE1/2 = 151 mV), while HSO4(-) promoted fluorescence enhancement when Pb(2+) or Zn(2+) was bonded to the cation binding-site. (1)H NMR titration and density functional theory were performed to reveal the sensing mechanism based on photo-induced electron transfer (PET).

Ferrocenylethynyl-terminated azobenzenes: synthesis, electrochemical, and photoisomerization studies.

Ferrocenylethynyl-terminated derivatives 8-12 have been synthesized and characterized by electrochemistry and UV/Vis spectroscopy. The electrochemical and photophysical studies indicate that the electronic communication in ferrocenylethynyl-substituted derivatives is strongly influenced by the substituted position of the ferrocenylethynyl moiety. In situ electrochemical oxidation or chemical oxidation caused a characteristically weak ligand-to-metal charge-transfer (LMCT) band to appear at 700-1000 nm. Subsequent electrochemical reduction or chemical reduction recovered the most of the original curve and the color of the solution as well. Among the derivatives, compound 8 exhibits the highest cis/trans molar ratio (64:36) in the photostationary state (PSS) upon light irradiation at 365 nm. Compound 8 exhibits excellent fatigue resistance and reversibility under several repeated reversible isomerization cycles.

Observation and analysis of abnormal absorption signals in laser flash photolysis measurement.

In order to investigate a noise-like signal appearing in dynamic mode measurement during laser flash photolysis experiments, five compounds were chosen which show this abnormal phenomenon. The reproducibility of this phenomenon was done repeatedly, indicating that it originates from each molecular structural property. Also their two regulation pattern or features were found by our analysis. One is a U-shaped curve of main frequency intensity with time and it seems to be directly related to the concentration of the T(1) excited state. The other is a high damping oscillation curve of the frequency shift with time and this curve seems to be indicating an energy transportation process from light into chemical energy. Finally, a possible origin of hydrogen nuclear optical resonance was proposed for the abnormal signal.

Ruthenium(II) bis(terpyridine) electron transfer complexes with alkynyl-ferrocenyl bridges: synthesis, structures, and electrochemical and spectroscopic studies.

Two novel alkynyl-bridged symmetric bis-tridentate ligands 1,2-bis(1'-[4'-(2,2':6',2''-terpyridinyl)]ferrocenyl)ethyne (3a; tpy-Fc-C[triple bond]C-Fc-tpy; Fc = ferrocenyl; tpy = terpyridyl) and 1,4-bis(1'-[4'-(2,2':6',2''-terpyridinyl)]ferrocenyl)-1,3-butadiyne (3b; tpy-Fc-C[triple bond]C-C[triple bond]C-Fc-tpy) and their Ru(2+) complexes 6a and 6b have been synthesized and characterized by cyclic voltammetry, UV-vis and luminescence spectroscopy, and in the case of 3b by single-crystal X-ray diffraction. Cyclic voltammograms of both compounds, 3a and 3b, display two severely overlapping ferrocene-based oxidative peaks with only one reductive peak. The redox behavior of 6a and 6b is dominated by the Ru(2+)/Ru(3+) redox couple (E(1/2) from 1.33 to 1.34 V), the Fe(2+)/Fe(3+) redox couples (E(1/2) from 0.46 to 0.80 V), and the tpy/tpy(-)/tpy(2-) redox couples (E(1/2) from -1.19 to -1.48 V). The UV-vis spectra of 6a and 6b show absorption bands assigned to the (1)[(d(π)(Fe))(6)] → (1)[(d(π)(Fe))(5)(π*(tpy)(Ru))(1)] MMLCT transition at ~555 nm. Complexes and are luminescent in H(2)O-CH(3)CN (4 : 1, v/v) solution at room temperature, and 6b exhibits the strongest luminescence intensity (λ(max)(em): 710 nm, Φ(em): 2.28 × 10(-4), τ: 358 ns) relative to analogous ferrocene-based bis(terpyridine) Ru(II) complexes reported so far.

Rare-Earth complexes of ferrocene-containing ligands: visible-light excitable luminescent materials.

The ferrocene-derivatives bis(ferrocenyl-ethynyl)-1,10-phenanthroline (Fc(2)phen) and ferrocenoyltrifluoroacetone (Hfta) have been used to synthesize ferrocene-containing rare-earth beta-diketonate complexes. The complexes [Ln(tta)(3)(Fc(2)phen)] and [Ln(fta)(3)(phen)] (where Ln = La, Nd, Eu, Yb) show structural similarities to the tris(2-thenoyltrifluoroacetonate)(1,10-phenanthroline)lanthanide(III) complexes, [Ln(tta)(3)(phen)]. The coordination number of the lanthanide ion is 8, and the coordination sphere can be described as a distorted dodecahedron. However, the presence of the ferrocene moieties shifts the ligand absorption bands of the rare-earth complexes to longer wavelengths so that the complexes can be excited not only by ultraviolet radiation but also by visible light of wavelengths up to 420 nm. Red photoluminescence is observed for the europium(III) complexes and near-infrared photoluminescence for the neodymium(III) and ytterbium(III) complexes. The presence of the ferrocene groups makes the rare-earth complexes hydrophobic and well-soluble in apolar organic solvents.