From Stilbenes to carbo-Stilbenes: an Encouraging Prospect.

Beyond previously described carbo-naphthalene and carbo-biphenyl, a novel type of bis-carbo-benzenic molecules is envisaged from the stilbene parent. The synthesis, structure, spectroscopic and electrochemical properties of two such carbo-stilbenes are described at complementary experimental and computational DFT levels. In the selected targets, the bare skeletal carbo-mer of carbo-stilbene is decorated by 8 or 10 phenyl groups, 0 or 2 tert-butyl groups, and 2 n-octyl chains, the later substituents being introduced to compensate anticipated solubility issues. As in the parent stilbene series, isomers of the phenylated carbo-stilbenes are characterized. The cis- and trans-isomers are, however, formed in almost equal amounts and could not be separated by either chromatography or crystallization. Nevertheless, due to a slow interconversion at the NMR time scale (up to 55 °C) the 1H NMR signals of both isomers of the two carbo-stilbenes could be tentatively assigned. The calculated structure of the cis-isomer exhibits a helical shape, consistent with the observed magnetic shielding of phenyl p-CH nuclei residing inside the shielding cone of the facing C18 ring. The presence of the two isomers in solution also gives rise to quite broad UV-vis absorption spectra with main bands at ca 460, 560 and 710 nm, and a significant bathochromic shift for the decaphenylated carbo-stilbene vs the di-tert-butyl-octaphenylated counterpart. Square wave voltammograms do not show any resolution of the two isomers, giving a reversible reduction wave at -0.65 or -0.58 V/SCE, and an irreversible oxidation peak at 1.11 V/SCE, those values being classical for most carbo-benzene derivatives. Calculated NICS values (NICS(1)=-12.5±0.2 ppm) also indicate that the aromatic nature of the C18 rings is not markedly affected by the dialkynylbutatriene (DAB) connector between them.

π-Extended benzo[1,2:4,5]di[7]annulene bis(dicarboximide)s - a new class of non-alternant polycyclic aromatic dicarboximides.

Aromatic dicarboximides are a class of molecules represented by the well-known rylene bis(dicarboximide)s, in particular perylene or naphthalene bis(dicarboximide)s, which show pronounced optoelectronic properties and are applied as color pigments, fluorescent dyes and organic semiconductors. Herein we extend the family of aromatic bis(dicarboximide)s and report the synthesis of the first series of non-alternant aromatic dicarboximides by twofold Pd-catalyzed [5 + 2] annulation. Characterization by UV/vis spectroscopy and cyclic voltammetry (CV) measurements give insight into the optoelectronic characteristics of the hitherto unexplored substance class of heptagon-containing imides. Theoretical studies by nucleus independent chemical shift (NICS) XY-scans and anisotropy of the induced current density (ACID) plots demonstrate the influence of both the non-alternant carbon framework and the imide moieties on aromaticity of the synthesized bisimides.

Effects of Post-Weld Heat Treatment on Microstructure and Mechanical Properties of the Brazed Joint of a Novel Fourth-Generation Nickel-Based Single Crystal Superalloy.

A novel fourth-generation nickel-based single crystal superalloy was brazed with Co-based filler alloy. The effects of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of brazed joints were investigated. The experimental and CALPHAD simulation results show that the non-isothermal solidification zone was composed of M3B2, MB-type boride and MC carbide, and the isothermal solidification zone was composed of γ and γ' phases. After the PWHT, the distribution of borides and the morphology of the γ' phase were changed. The change of the γ' phase was mainly attributed to the effect of borides on the diffusion behavior of Al and Ta atoms. In the process of PWHT, stress concentration leads to the nucleation and growth of grains during recrystallization, thus forming high angle grain boundaries in the joint. The microhardness was slightly increased compared to the joint before PWHT. The relationship between microstructure and microhardness during the PWHT of the joint was discussed. In addition, the tensile strength and stress fracture life of the joints were significantly increased after the PWHT. The reasons for the improved mechanical properties of the joints were analyzed and the fracture mechanism of the joints was elucidated. These research results can provide important guidance for the brazing work of fourth-generation nickel-based single crystal superalloy.

Effect of Ru on Deformation Mechanism and Microstructure Evolution of Single-Crystal Superalloys under Medium-Temperature and High-Stress Creep.

In this work, the effect of the Ru element on the γ'-phase evolution and deformation mechanism in the fourth-generation Ni-based single-crystal superalloy was investigated. Results show that the Ru element alters the distribution coefficient of other elements in the alloy to produce reverse partitioning behavior, which leads to a difference in microstructure between 0Ru and 3Ru. The addition of Ru triggered the incubation period before the beginning of the primary creep stage, which depends on the creep temperature and stress during creep deformation. TEM results revealed that Ru addition inhibits the slip system {111}<112> at medium-temperature (760-1050 °C) and high-stress (270-810 MPa) creep, which brings a considerably low creep rate and high creep life to the Ru-containing alloy.

π-Extended Pleiadienes by [5+2] Annulation of 1-Boraphenalenes and ortho-Dihaloarenes.

Palladium-catalyzed [5+2] annulation of 1-boraphenalenes with ortho-dihaloarenes afforded negatively curved π-extended pleiadienes. Two benzo[1,2-i:4,5-i']dipleiadienes (BDPs) featuring a seven-six-seven-membered ring arrangement were synthesized and investigated. Their crystal structure revealed a unique packing arrangement and theoretical calculations were employed to shed light onto the dynamic behavior of the BDP moiety and its aromaticity. Further, a naphthalene-fused pleiadiene was stitched together by oxidative cyclodehydrogenation to yield an additional five-membered ring. This formal azulene moiety led to distinct changes in optical and redox properties and increased perturbation of the aromatic system.

Supramolecular Substructure of C60-Embedded Schwarzite.

Herein we present a new concept of carbon allotrope, namely, fullerene-embedded schwarzite. We isolated crystals of fullerene embedded in 4 equiv of a negatively curved polycyclic aromatic hydrocarbon (PAH), 1, which could be viewed as a substructure of the hypothetical fullerene-schwarzite complex. On the basis of crystal structure, the stability of the complex (C60⊂(1)4) was studied by theoretical methods (ALMO-EDA), showing that the noncovalent interactions driven by dispersion forces is key for stabilizing the complex, which was further supported by noncovalent interactions (NCI) plots and Hirshfeld-surface analyses. Our findings of C60⊂(1)4 provide a perspective toward the development of novel sp2-carbon allotropes comprising multiple components.

Carbo-mer of Barrelene: A Rigid 3D-Carbon-Expanded Molecular Barrel.

After extensive studies of 1D and 2D skeletal carbo-mers based on C8 π-conjugating dialkynylbutatriene units (DABs: ∼C≡C-(R)C=C=C=C(R)-C≡C∼) bridging sp or sp2 centers in carbo-butene, carbo-xylylene or carbo-benzene derivatives, 3D versions are envisaged through carbo-barrelenes and partially reduced derivatives thereof where two or three DAB blades span a bridge between sp3 carbinol vertices or ether thereof. For R=Ph, stable representatives were synthesized through a pivotal [6]pericyclynedione, and extensively characterized by spectroscopic, electrochemical and crystallographic methods. Density functional theory calculations allow detailed analysis of structural and electronic features of the 7 Šhigh C26 barrel-shaped molecules, and show that they can behave as cages for ionic species. Beyond aesthetical concerns, the results could open prospects of applications in host-guest supramolecular chemistry and single molecule charge transport.

Conformation and Aromaticity Switching in a Curved Non-Alternant sp2 Carbon Scaffold.

A curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd-catalyzed [5+2] annulation from a 3,9-diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly-like motion. Stepwise oxidation produced radical cation 1.+ and dication 12+ . In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π-overlap between the enantiomers. For the radical cation 1.+ , a less curved cisoid conformation is observed with a π-dimer-type arrangement. 12+ adopts a more planar structure with transoid conformation and slip-stacked π-overlap with closest neighbors. We also observed an intermolecular mixed-valence complex of 1⋅(1.+ )3 that has a huge trigonal unit cell [(1)72 (SbF6 )54 ⋅(hexane)101 ] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.

Carbo-biphenyls and Carbo-terphenyls: Oligo(phenylene ethynylene) Ring Carbo-mers.

Ring carbo-mers of oligo(phenylene ethynylene)s (OPEn, n=0-2), made of C2 -catenated C18 carbo-benzene rings, have been synthesized and characterized by NMR and UV-vis spectroscopy, crystallography and voltammetry. Analyses of crystal and DFT-optimized structures show that the C18 rings preserve their individual aromatic character according to structural and magnetic criteria (NICS indices). Carbo-terphenyls (n=2) are reversibly reduced at ca. -0.42 V/SCE, i.e. 0.41 V more readily than the corresponding carbo-benzene (-0.83 V/SCE), thus revealing efficient inter-ring π-conjugation. An accurate linear fit of E1/2red1 vs. the DFT LUMO energy suggests a notably higher value (-0.30 V/SCE) for a carbo-quaterphenyl congener (n=3). Increase with n of the effective π-conjugation is also evidenced by a red shift of two of the three main visible light absorption bands, all being assigned to TDDFT-calculated excited states, one of them restricting to a HOMO→LUMO main one-electron transition.

The Forgotten Nitroaromatic Phosphines as Weakly Donating P-ligands: An N-Aryl-benzimidazolyl Series in RhCl(CO) Complexes.

The coordination chemistry of a priori weakly σ-donating nitroaromatic phosphines is addressed through a series of nitro-substituted (N-phenyl-benzimidazol-1-yl)diphenylphosphines in RhI complexes. From a set of seven such phosphines L=Lxyz(') (x, y, z=0 or 1=number of NO2 substituents at the 5, 6 and N-Ph para positions, respectively), including the non-nitrated parent L000 and its dicationic N-methyl counterpart L000 ', three LRhCl(COD) and seven L2 RhCl(CO) complexes have been obtained in 72-95 % yield. Despite of a cis orientation of the L and CO ligands, the C=O IR stretching frequency νCO varies in the expected sense, from 1967±1 cm-1 for Lxy0 to 1978±1 cm-1 for Lxy1 , and 2005 cm-1 for L000 '. The 103 Rh NMR chemical shift δRh varies from -288 ppm for L000 to -316±1 ppm for L10z or L01z , and -436 ppm for L000 '. The νCO and δRh probes thus reveal moderate but systematic variations, and act as "orthogonal" spectroscopic indicators of the presence of nitro groups on the N-Ph group and the benzimidazole core, respectively. For the dicationic ligand L000 ', a tight electrostatic sandwiching of the Rh-Cl bond by the benzimidazole moities is evidenced by X-ray crystallography (RhClδ- ⋅⋅⋅CN2+ ≈3.01 Å). Along with the LRhCl(CO) complexes, dinuclear side-products (µ-CO)(RhClL)2 were also obtained in low spectroscopic yield: for the dinitro ligand L=L011 , a unique 1:6.7 clathrate structure, with dichloromethane as solvate, is also revealed by X-ray crystallography.

3D and 2D supramolecular assemblies and thermotropic behaviour of a carbo-benzenic mesogen.

Hexaalkoxy-di(phenylethynyl)-tetraphenyl-carbo-benzenes bearing six CnH2n+1 aliphatic chains (n = 12, 18) have been synthesized and characterized, including by single crystal XRD analysis. For n = 12, a liquid crystal behaviour was observed in the range of 109-130 °C. DSC, POM and PXRD analyses evidenced a rectangular columnar mesophase at 115 °C. The determined 3D lattice constants are consistent with 2D STM images of the so-called "carbo-mesogen" deposited on an HOPG surface.

Lipidic Carbo-benzenes: Molecular Probes of Magnetic Anisotropy and Stacking Properties of α-Graphyne.

Solubilization of the C18 fundamental circuit of α-graphyne has been envisaged by decoration with aliphatic chains R = n-CnH2n+1. The synthesis and characterization of p-dialkyl-tetraphenyl-carbo-benzenes (n = 2, 8, 14, 20) are thus presented and compared to the monoalkyl series produced concomitantly. In both series, a dramatic enhancement of solubility in organic solvents (CH2Cl2, CHCl3) is observed for n ≥ 8, and in the dialkyl series, the melting-decomposition temperature of the solid products is shown to decrease linearly from 208 °C for n = 2 to 149 °C for n = 20. Fluoroalkyl analogues with R = n-C8H4F13 are also described. The products display classical UV-vis electronic spectra of carbo-benzenes in solution (λmax = 445.5 ± 1 nm, ε ≈ 200 000 L·mol-1·cm-1). They are also characterized by UV-vis absorption in the solid state, which is found to be correlated with the color and crystal packing. The methylene groups of R provide an experimental probe of the magnetic anisotropy and aromaticity of the C18 ring through the progressive NMR shielding of the 1H nuclei from ca. 4.70 to 1.25 ppm going away from the border of the ring (as far as 8 Å away). All alkyl-carbo-benzenes were also found to be highly crystalline. Seven of them have been characterized by X-ray diffraction analysis and the C18 columnar packing compared in a systematic manner. Crystals of the diethyl and bistetradecyl derivatives, containing no solvent molecule, provided the first examples of direct π-stacking of carbo-benzene rings, with inter-ring distances very close to calculated interlayer distances in AB and ABC α-graphityne (3.255 and 3.206 Å vs 3.266 and 3.201 Å, respectively).

Copper-catalyzed direct amination of quinoline N-oxides via C-H bond activation under mild conditions.

A highly efficient and concise one-pot strategy for the direct amination of quinoline N-oxides via copper-catalyzed dehydrogenative C-N coupling has been developed. The desired products were obtained in good to excellent yields for 22 examples starting from the parent aliphatic amines. This methodology provides a practical pathway to 2-aminoquinolines and features a simple system, high efficiency, environmental friendliness, low reaction temperature, and ligand, additives, base, and external oxidant free conditions.

Direct 2-acetoxylation of quinoline N-oxides via copper catalyzed C-H bond activation.

An efficient and direct 2-acetoxylation of quinoline N-oxides via copper(I) catalyzed C-H bond activation has been developed. This transformation was achieved using TBHP as an oxidant in the cross-dehydrogenative coupling (CDC) reaction of quinoline N-oxides with aldehydes, and provided a practical pathway to 2-acyloxyl quinolines.