Tetraarylethylenes from Diarylmethanones and Hexachlorodisilane: The “Sila‐McMurry” Reaction

Hexachlorodisilane reacts with diarylmethanones (aryl=C₆H₅, 4‐MeC₆H₄, 4‐tBuC₆H₄, 4‐ClC₆H₄, 4‐BrC₆H₄) to furnish the corresponding tetraarylethylenes in good yields. The reductive conversion requires temperatures of about 160 °C and reaction times of 60–72 h. In the initial step, the Lewis‐basic carbonyl groups likely generate low‐valent [SiCl₂] as an analogue of [TiCl₂] in the classical McMurry reaction. The coupling sequence further proceeds via benzopinacolones, which have been isolated as key intermediates.     

Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl(3)SiSiCl(3)

The addition compound Cl(3)SiSiCl(3)·TMEDA was formed quantitatively by treatment of Cl(3)SiSiCl(3) with tetramethylethylenediamine (TMEDA) in pentane at room temperature. The crystal structure of Cl(3)SiSiCl(3)·TMEDA displays one tetrahedrally and one octahedrally bonded Si atom (monoclinic, P2(1)/n). (29)Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the meridional isomer of Cl(3)SiSiCl(3)·TMEDA is 6.3 kcal lower in energy than that of facial coordinate species. Dissolving of Cl(3)SiSiCl(3)·TMEDA in CH(2)Cl(2) resulted in an immediate reaction by which oligochlorosilanes Si(n)Cl(2n) (n = 4, 6, 8, 10; precipitate) and the Cl(-)-complexed dianions [Si(n)Cl(2n+2)](2-) (n = 6, 8, 10, 12; CH(2)Cl(2) extract) were formed. The constitutions of these compounds were confirmed by MALDI mass spectrometry. Additionally, single crystals of [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(6)Cl(14)] and [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(8)Cl(18)] were obtained from the CH(2)Cl(2) extract. We found that Cl(3)SiSiCl(3)·TMEDA reacts with MeCl, forming MeSiCl(3) and the products that had been formed in the reaction of Cl(3)SiSiCl(3)·TMEDA with CH(2)Cl(2). X-ray structure analysis indicates that the structures of [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(6)Cl(14)] (monoclinic, P2(1)/n) and [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(8)Cl(18)] (monoclinic, P2(1)/n) contain dianions adopting an "inverse sandwich" structure with inverse polarity and [Me(3)NCH(2)CH(2)NMe(2)](+) as countercations. Single crystals of SiCl(4)·TMEDA (monoclinic, Cc) could be isolated by thermolysis reaction of Cl(3)SiSiCl(3)·TMEDA (50 °C) in tetrahydrofuran (THF).     

A structural study of Si6‐ring‐containing [Si6Cl14]2− chlorosilicates

The crystal structures of four substituted‐ammonium dichloride dodecachlorohexasilanes are presented. Each is crystallized with a different cation and one of the structures contains a benzene solvent molecule: bis(tetraethylammonium) dichloride dodecachlorohexasilane, 2C₈H₂₀N⁺·2Cl⁻·Cl₁₂Si₆, (I), tetrabutylammonium tributylmethylammonium dichloride dodecachlorohexasilane, C₁₆H₃₆N⁺·C₁₃H₃₀N⁺·2Cl⁻·Cl₁₂Si₆, (II), bis(tetrabutylammonium) dichloride dodecachlorohexasilane benzene disolvate, 2C₁₆H₃₆N⁺·2Cl⁻·Cl₁₂Si₆·2C₆H₆, (III), and bis(benzyltriphenylphosphonium) dichloride dodecachlorohexasilane, 2C₂₅H₂₂P⁺·2Cl⁻·Cl₁₂Si₆, (IV). In all four structures, the dodecachlorohexasilane ring is located on a crystallographic centre of inversion. The geometry of the dichloride dodecachlorohexasilanes in the different structures is almost the same, irrespective of the cocrystallized cation and solvent. However, the crystal structure of the parent dodecachlorohexasilane molecule shows that this molecule adopts a chair conformation. In (IV), the P atom and the benzyl group of the cation are disordered over two sites, with a site‐occupation factor of 0.560 (5) for the major‐occupied site.     

On the interaction of ascorbic acid and the tetrachlorocuprate ion [CuCl4]2- in CuCl nanoplatelet formation from an ionic liquid precursor (ILP)

The formation of CuCl nanoplatelets from the ionic liquid precursor (ILP) butylpyridinium tetrachlorocuprate [C(4)Py](2)[CuCl(4)] using ascorbic acid as a reducing agent was investigated. In particular, electron paramagnetic resonance (EPR) spectroscopy was used to evaluate the interaction between ascorbic acid and the Cu(II) ion before reduction to Cu(I). EPR spectroscopy suggests that the [CuCl(4)](2-) ion in the neat IL is a distorted tetrahedron, consistent with DFT calculations. Addition of ascorbic acid leads to the removal of one chloride from the [CuCl(4)](2-) anion, as shown by DFT and the loss of symmetry by EPR. DFT furthermore suggests that the most stable adduct is formed when only one hydroxyl group of the ascorbic acid coordinates to the Cu(II) ion.     

Elucidation of the extraordinary 4-membered pyrrole ring-contracted azeteoporphyrinoid as an intermediate in chlorin oxidation

Reaction of 2,3-dioxochlorins with benzeneselenic anhydride (BSA) results in the formation of unusual ring-contracted azetine derivatives that further react with BSA to afford porpholactones.     

On the electronic structure of neutral and ionic azobenzenes and their possible role as surface mounted molecular switches

We report quantum chemical calculations, mostly based on density functional theory, on azobenzene and substituted azobenzenes as neutral molecules or ions, in ground and excited states. Both the cis and trans configurations are computed as well as the activation energies to transform one isomer into the other and the possible reaction paths and reaction surfaces along the torsion and inversion modes. All calculations are done for the isolated species, but results are discussed in light of recent experiments aiming at the switching of surface mounted azobenzenes by scanning tunneling microscopes.     

Exploiting Sparsity for Semi-Algebraic Set Volume Computation

Foundations of Computational Mathematics - We provide a systematic deterministic numerical scheme to approximate the volume (i.e., the Lebesgue measure) of a basic semi-algebraic set whose...     

Analysis of geometric parameters and packing considerations for triphenylboroxine derivatives,with tris(pentafluorophenyl)boroxine as an example

Molecules of the title compound [systematic name: 2,4,6‐(pentafluorophenyl)‐1,3,5,2,4,6‐trioxatriborinane], C₁₈B₃F₁₅O₃, are located on crystallographic twofold rotation axes which run through the boroxine and one of the pentafluorophenyl rings. The boroxine ring (r.m.s. deviation = 0.027 Å) and the pentafluorophenyl rings (r.m.s. deviations = 0.004 and 0.001 Å) are essentially planar. The dihedral angles between the boroxine and the two symmetry‐independent benzene rings are 8.64 (10) and 8.74 (12)°. The two benzene rings are mutually coparallel [dihedral angle = 0.80 (11)°]. The packing shows planes of molecules parallel to (01), with an interplanar spacing of 2.99 Å. Within these planes, all the molecules are oriented in the same direction, whereas in neighbouring planes the direction is inverted. Short B...F contacts of 3.040 (2) and 3.1624 (12) Å occur between planes. The geometric parameters of the boroxine ring in the title compound agree well with those of comparable boroxine structures, while the packing reveals some striking similarities and differences.     

Molecular response properties from explicitly time-dependent configuration interaction methods

In this paper we report the calculation of molecular electric response properties with the help of explicitly time-dependent configuration interaction (TD-CI) methods. These methods have the advantage of being applicable (within the limitations of the time-dependent Schrodinger equation) to time-dependent perturbations of arbitrary shape and strength. Three variants are used to solve the time-dependent electronic Schrodinger equation, namely, the TD-CIS (inclusion of single excitations only), TD-CISD (inclusion of single and double excitations), and TD-CIS(D) (single excitations and perturbative treatment of double excitations) methods and applied for illustration to small molecules, H(2) and H(2)O. In the calculation, slowly varying off-resonant electric fields are applied to the molecules and linear (polarizabilities) and nonlinear (hyperpolarizabilities, harmonic generation) response properties are determined from the time-dependent dipole moments.