Showing papers on "Carbon group published in 2007"

Synthesis, structure, reactions, and photoelectron spectra of new mixed sulfur‐, selenium‐ or tellurium and silicon‐ or tin‐containing heterocycles

Abstract: More than 40 new 4- to 12-membered ring heterocycles containing various combinations of Group 14 elements (Si and Sn) and Group 16 elements (S, Se, and Te) have been synthesized and fully characterized. Synthesis of these small-ring as well as medium-ring (mesocyclic) heterocycles from α, ω-dihalides was facilitated by the presence of gem-dialkylsilyl and gem-dialkylstannyl groups in the precursors. Solid-state conformations of the new ring systems have been determined by X-ray crystallography. Oxidation of mixed S(Se, Te)/Si eight-membered ring mesocycles as well as 1,5-dithia-, 1,5-diselena-, and 1,5-ditelluracyclooctane with NOPF6 gave dications, which can be characterized by NMR. On treatment with nucleophiles, mesocyclic dications or the corresponding radical cations underwent ring contraction to give five- or six-membered ring heterocycles. The ionization energies of the above conformationally constrained β-disilanyl sulfides and selenides were determined by photoelectron spectroscopy. These ionization energies reflect substantial (0.53--0.75 eV) orbital destabilizations. The basis for these destabilizations was investigated by theoretical calculations, which reveal geometry-dependent interaction between sulfur or selenium lone pair orbitals and σ-orbitals, especially Si–Si σ-orbitals. These results suggest facile redox chemistry for these compounds and significantly extend the concept of σ-stabilization of electron-deficient centers. © 2007 Wiley Periodicals, Inc. 18:509–515, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20333

Metallocanes of group 14 elements 2.* Derivatives of tin (Review)

Abstract: Results on the synthesis of stannocanes-eight-membered heterocycles with the general formula D(CH2CH2Z)2SnXY-are reviewed and analyzed. The chemical behavior of the compounds is examined, and the nature of the transannular bond is studied.

Carbon-Carbon Bond-Forming Reactions of Compounds of Boron, Silicon, and Tin

Abstract: In this chapter, we will discuss the use of boron, silicon, and tin compounds to form carbon-carbon bonds. These elements are at the boundary of the metals and nonmetals, with boron being the most and tin the least electronegative of the three. The neutral alkyl derivatives of boron have the formula R3B, whereas for silicon and tin they are R4Si and R4Sn, respectively. These compounds are relatively volatile, nonpolar substances that exist as discrete molecules and in which the carbon-metal bonds are largely covalent. The boranes are Lewis acids, whereas the silanes and stannanes are not, unless substituted by a leaving group. The synthetically important reactions of these compounds involve transfer of a carbon substituent with one (radical equivalent) or two (carbanion equivalent) electrons to a reactive carbon center. This chapter will emphasize the nonradical reactions. In contrast to the transition metals, which often undergo a change in oxidation level at the metal during the reaction, there is usually no oxidation level change for boron, silicon, and tin compounds. We have already discussed one important aspect of boron and tin chemistry in the transmetalation reactions involved in Pd-catalyzed cross-coupling reactions discussed in Section 8.2.3.

Recent Developments in the Field of Organic Heterobimetallic Compounds of the Alkaline‐Earth Metals

Abstract: Heterobimetallic compounds of the alkaline-earth metals show a wide structural variety with strongly differing reactivity patterns. The combination of magnesium and alkali metal amides yields cyclic molecules with an extreme high reactivity which often are considered as “inverse crowns” with the metal atoms as coordination sites for Lewis bases. In other metallates of the alkaline-earth metals an activation of alkyl groups succeeds. In alkaline-earth metal zincates an inverse coordination of the type M2[(μ-R)2ZnR]2 is observed and the alkyl groups are in bridging positions between zinc and the s-block metals thus forming a very reactive M–C–Zn three-center–two-electron bond. Furthermore, the metals of the carbon group form alkaline-earth metal–silicon, –germanium and –tin bonds or, in the presence of very strong Lewis bases, even solvent-separated ion pairs. For electronegative substituents at tin an inverse coordination mode such as M[(µ-R)2SnR]2 is observed.

Synthesis, Structure, Reactions, and Photoelectron Spectra of New Mixed Sulfur-, Selenium- or Tellurium and Silicon- or Tin-Containing Heterocycles

Abstract: More than 40 new 4- to 12-membered ring heterocycles containing various combinations of Group 14 elements (Si and Sn) and Group 16 elements (S, Se, and Te) have been synthesized and fully characterized. Synthesis of these small-ring as well as medium-ring (mesocyclic) heterocycles from α, ω-dihalides was facilitated by the presence of gem-dialkylsilyl and gem-dialkylstannyl groups in the precursors. Solid-state conformations of the new ring systems have been determined by X-ray crystallography. Oxidation of mixed S(Se, Te)/Si eight-membered ring mesocycles as well as 1,5-dithia-, 1,5-diselena-, and 1,5-ditelluracyclooctane with NOPF6 gave dications, which can be characterized by NMR. On treatment with nucleophiles, mesocyclic dications or the corresponding radical cations underwent ring contraction to give five- or six-membered ring heterocycles. The ionization energies of the above conformationally constrained β-disilanyl sulfides and selenides were determined by photoelectron spectroscopy. These ionization energies reflect substantial (0.53--0.75 eV) orbital destabilizations. The basis for these destabilizations was investigated by theoretical calculations, which reveal geometry-dependent interaction between sulfur or selenium lone pair orbitals and σ-orbitals, especially Si–Si σ-orbitals. These results suggest facile redox chemistry for these compounds and significantly extend the concept of σ-stabilization of electron-deficient centers. © 2007 Wiley Periodicals, Inc. 18:509–515, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20333