Radical Anions of Polyalkylazulenes: An ESR and ENDOR Study

Proton-hyperfine data are reported for the radical anions generated from azulene ( 1 ) and its alkyl derivatives 2 – 11 in 1,2-dimethoxyethane both ‘chemically’ with K and electrolytically. The alkyl derivatives are 1,3-dimethyl- ( 2 ), 5,7-dimethyl- ( 3 ), 1,3,5,7-tetramethyl- ( 4 ), 2-methyl- ( 5 ), 4,6,8-trimethyl- ( 6 ), 2,4,6,8-tetramethyl-( 7 ), 1,3,4,6,8-pentamethyl- ( 8 ), 1,3,4,8-tetramethyl-6-propyl- ( 9 ), 6-(tert-butyl)-1,3,4,8-tetramethyl- ( 10 ), and 1,2,3,4,6,8-hexamethylazulene ( 11 ). Alkyl substituents at the odd-numbered centers μ = 1, 3, 5, and 7 partly shift the π-spin population from the seven- to the five-membered ring, whereas those at the even-numbered centers μ = 4, 6, and 8 exert an opposite effect on the π-spin distribution.     

Fusion of Aza- and Oxadiborepins with Furans in a Reversible Ring-Opening Process Furnishes Versatile Building Blocks for Extended π-Conjugated Materials

A modular synthesis of both difurooxa- and difuroazadiborepins from a common precursor is demonstrated. Starting from 2,2′-bifuran, after protection of the positions 5 and 5’ with bulky silyl groups, formation of the novel polycycles proceeds through opening of the furan rings to a dialkyne and subsequent re-cyclization in the borylation step. The resulting bifuran-fused diborepins show pronounced stability, highly planar tricyclic structures, and intense blue light emission. Deprotection and transformation into dibrominated building blocks that can be incorporated into π-extended materials can be performed in one step. Detailed DFT calculations provide information about the aromaticity of the constituent rings of this polycycle.     

Measurement of the CP-violating phase ϕ(s) in the decay B(s)(0) → J/ψϕ

We present a measurement of the time-dependent CP-violating asymmetry in B(s)(0) → J/ψ? decays, using data collected with the LHCb detector at the LHC. The decay time distribution of B(s)(0) → J/ψ? is characterized by the decay widths Γ(H) and Γ(L) of the heavy and light mass eigenstates, respectively, of the B(s)(0) - B(s)(0) system and by a CP-violating phase ?(s). In a sample of about 8500 B(s)(0) → J/ψ? events isolated from 0.37 fb(-1) of pp collisions at sqrt[s] = 7 TeV, we measure ?(s) = 0.15 ± 0.18(stat) ± 0.06(syst) rad. We also find an average B(s)(0) decay width Γ(s) ≡ (Γ(L) + Γ(H))/2 = 0.657 ± 0.009(stat) ± 0.008(syst) ps(-1) and a decay width difference ΔΓ(s) ≡ Γ(L) - Γ(H) = 0.123 ± 0.029(stat) ± 0.011(syst) ps(-1). Our measurement is insensitive to the transformation (?(s),ΔΓ(s)) ? (π - ?(s), -ΔΓ(s)).     

Synthesis of aminosaccharide‐derived polymers with urea,urethane, and amide linkages

The synthesis of novel polyurethanes and polyureas based on modified glycosylamines and glucosamines has been successfully accomplished by catalytic polymerizations. Several modified glucosamine monomers were synthesized to study their reactivities during these polymerization reactions. It was found that the anomeric hydroxyl groups are more reactive than the amino groups. The resulting polymers were characterized by NMR and IR spectroscopy, elementary analysis, viscosimetry, and gel permeation chromatography. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2332–2341, 2001     

Strong Electronic Effects in the cis‐Selective Asymmetric Cyclopropanation of Olefins Catalyzed by [RuCl(PNNP)]+

The cationic [RuCl(PNNP)]⁺ catalysts containing tetradentate ligands with a P₂N₂ donor set (PNNP) show strong electronic effects in the cyclopropanation of para‐substituted styrenes. The reactivity trend confirms that the carbene transfer to the olefin has electrophilic character. Linear free‐energy relationships are observed for the relative reactivity, the cis/trans selectivity, and for the enantioselectivity (of the cis‐cyclopropane). The linear correlation between log (k_X/k_H) and σ shows a large value of ρ (−2.4), which is indicative of significant charge buildup in the transition state of the carbene transfer to the olefin. All the relevant parameters (reactivity, diastereoselectivity, and enantioselectivity) increase with the increasing electron density at the C=C bond. To define the scope of the [RuCl(PNNP)]⁺ catalysts, 1‐ and 2‐substituted styrenes, and oct‐1‐ene were also investigated.     

Preparation of a new C18 stationary phase containing embedded urea groups for use in high-performance liquid chromatography

A new C18 urea stationary phase was prepared by a single-step modification process through the reaction of ProntoSil spherical silica (3 microm, Bischoff) with the trifunctional alkoxysilane (CH3CH2O)3-Si-(CH2)3-NH-C(O)-NH-(CH2)17-CH3, prepared in our laboratory. The phase was characterized by elemental analysis and solid-state 29Si and 13C nuclear mangnetic resonance spectrometry. Chromatographic evaluations of the new phase in 150 x 3.9 mm HPLC columns involving the separation of different test mixtures, indicate good performance for both polar and basic mixtures and also show promising results for further applications.     

Einkristalluntersuchungen an AgF2

Single Crystal Investigation on AgF₂ For the first time single crystals of AgF₂ (black, metalic bright) have been obtained by heating AgF₂ powder under a mixture of HF and F₂ in autoclaves at 400°C. It crystallizes orthorhombic in the space group Pbca – D (Nr. 61) – with a = 556.8(1), b = 583.1(1) and c = 510.1(1) pm; Z = 4. The Madelung Part of Lattice Energy, MAPLE, and the Effective Coordination Number, ECoN, via the Mean Fictive Ionic Radii, MEFIR, are calculated and discussed.     

Multielectron chemistry of zinc porphyrinogen: a ligand-based platform for two-electron mixed valency

The synthesis, electronic structure, and oxidation-reduction chemistry of a homologous series of Zn(II) porphyrinogens are presented. The fully reduced member of the series, [LZn](2-), was prepared in two steps from pyrrole and acetone. The compound undergoes consecutive two-electron, ligand-based, oxidations at +0.21 and +0.63 V vs NHE to yield [L(Delta)Zn] and [L(Delta Delta)Zn](2+), which also have been independently prepared by chemical means. X-ray diffraction analysis of the redox intermediary, [L(Delta)Zn], shows that the partly oxidized macrocycle is composed of a methylene-bridged dipyrrole that is doubly strapped to a two-electron oxidized dipyrrole bridged by a cyclopropane ring (L(Delta)). The localization of two hole equivalents on the oxidized side of the porphyrinogen framework is consistent with a two-electron mixed valency formulation for the [L(Delta)Zn] species. Electronic structure calculations and electronic spectroscopy support this formalism. Density functional theory computations identify the HOMO to be localized on the reduced half of the macrocycle and the LUMO to be localized on its oxidized half. As implicated by the energy level diagram, the lowest energy transition in the absorption spectrum of [L(Delta)Zn] exhibits charge-transfer character. Taken together, these results establish the viability of using a ligand framework as a two- and four-electron/hole reservoir in the design of multielectron redox schemes.