Showing papers on "Carbon group published in 2011"

Oxidation of Intramolecularly Coordinated Distannyne by S8: From Tin(I) to Tin(IV) Polysulfide Via Tin(II) Sulfide

Abstract: The investigation of heavier Group 14 element analogues of alkynes of the type (RE)2 (where E=Si, Ge, Sn, or Pb) is of current interest. These studies showed that the presence of rather bulky substituents such as a variety of substituted aryl and silyl groups allowed the synthesis of RE ER, which possess multiple bonds. The studies dealing with the reactivity of the RE ER multiple bonds showed scission of the Si Si or Ge Ge triple bond by the addition of an olefin, and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene. Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. The reactivity studies of [ArSnSnAr] towards N2O also showed the reducing character of the Sn species, yielding the organotin(II) oxide [ArSnOSnAr] as the final product. Recently, the single-bonded dimeric species [{SiACHTUNGTRENNUNG(NtBu)2CPh}2] and [({2,6-(Me2NCH2)2C6H3}Sn)2] (1), as the first example of an Sn N intramolecularly coordinated distannyne containing a built-in N,C,N-pincer-type ligand, were reported as well. The redox reaction of [{Si ACHTUNGTRENNUNG(NtBu)2CPh}2] with N2O showed the reducing character of the Si I species, and led to the production of the well-defined [R4Si4O6] compound (R= (NtBu)2CPh) with a double-decker structure. [8]

Intramolecularly coordinated tin(II) selenide and triseleneoxostannonic acid anhydride.

Abstract: Understanding the nature of chemical bonding remains a central focus of fundamental research, and one of the valuable methods for the increasing of the understanding of intramolecular binding forces is the investigation of compounds containing multiple bonds between heavier Group 14 elements of the type RE ER (where E= group elements Si, Ge, Sn, and Pb). Recent studies of these heavier Group 14 element analogues of alkynes revealed essential structural differences between alkynes, RC CR, and their heavier Group 14 analogues, RE ER (E=Si, Ge, Sn, Pb) and opened debate as to whether the Group 14 analogue compounds exhibit a true triple bond (A), a double bond (B), or a single bond whose geometry is strongly trans-bent (C) (see Scheme 1). The presence of rather bulky substituents such as a variety of substituted aryl and silyl groups afforded the synthesis of RE ER that possess multiple bonds. The presence of a multiple bond was proposed by the UV/Vis absorptions, molecular orbital (MO) calculations, and also by the reactivity studies on these molecules. All these experiments afforded insights into the nature of the E E triple bonds. Scission of the Si Si or Ge Ge triple bond was observed by the addition of an olefin 9, 22–27] and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene or by cyclic polyolefinic molecules. 29] Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. Recently, we have shown that the use of intramolecularly coordinating built-in N,C,N-coordinating pincer-type ligands is an alternative concept for the synthesis and stabilization of the reactive distannyne [({2,6-(Me2NCH2)2C6H3}Sn)2] (1). This compound showed, however, Sn Sn single bond character with a central tin atom in the oxidation state + I. We have, therefore, concentrated on the redox-type reaction of compound 1 instead of cycloadditions of the olefins. In the course of a systematic studies on the metal-type redox reactivity of 1 we present here the reaction of 1 with Se as the oxidizing agent and show that the reaction results in the two-step oxidation of the tin(I) atom along with complete cleavage of the Sn Sn bond to give a new organotin(II) selenide [({2,6-(Me2NCH2)2C6H3}Sn)2Se] (2) in the first step of the oxidation (Scheme 2). This compound is unprecedented and there is no report on well-defined selenides of low-valent Group 14 elements. Preparation of organotin(IV) selenide [({2,6-(Me2NCH2)2C6H3}Sn(Se))2Se] (3), the first example of an intramolecularly coordinated triseleneoxostannonic acid anhydride, as the final product of the oxidation of 1 by Se is reported as well (Scheme 2). Compound 3 contains two terminal Sn Se bonds and represents a new [a] M. Bouška, Dr. L. Dost l, Dr. A. Růžička, Dr. R. Jambor Department of General and Inorganic Chemistry Faculty of Chemical Technology University of Pardubice Čs legi 565, 53210, Pardubice (Czech Republic) E-mail : roman.jambor@upce.cz [b] Dr. F. de Proft Eenheid Algemene Chemie (ALGC) Vrije Universiteit Brussel (VUB) Pleinlaan 2, 1050 Brussels, (Belgium) [c] Prof. A. Lyčka Research Institute for Organic Chemistry VUOS a.s. 532 10, Pardubice, (Czech Republic) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002641. Scheme 1. Canonical formulas for compounds of the type REER.

Mechanical Properties and Low Elastic Anisotropy of Semiconducting Group 14 Clathrate Frameworks

Abstract: We have investigated the mechanical properties of semiconducting clathrate frameworks composed of group 14 elements carbon, silicon, germanium, and tin. The bulk moduli, Young’s moduli, and elastic anisotropies of 13 structurally different clathrate frameworks were determined using quantum chemical methods. The predicted elastic properties were compared to the properties of diamondlike, dense α-phases and experimentally known semiconducting group 14 clathrate structures. The predicted bulk and Young’s moduli of the studied carbon, silicon, germanium and tin frameworks suggest them to possess low compressibility and high stiffness, which are almost comparable to the diamondlike, dense α-phases of the elements. In particular, the studied microporous clathrate frameworks exhibit remarkably low elastic anisotropy, being clearly more isotropic than the denser α-phases.

Group 14 Multiple Bonding

Abstract: Multiply bonded compounds between heavier group 14 elements cannot exist as monomers under normal conditions owing to their inherent high reactivity, that is, they readily undergo oligomerization, oxidation, hydrolysis, and so on. The bulkiness of substituents on the reactive sites shows a great effect on the stabilization of such highly reactive compounds. Since the synthesis and isolation of the first stable disilene, Mes2SiSiMes2 (Mes = mesityl), by R. West et al. in 1981, the idea of kinetic stabilization using bulky substituents have led to the successful isolation of several types of unsaturated compounds of group 14 elements, such as heavy alkenes (double bonds between heavier group 14 elements), heavy ketones (heavier group 14–16 double bonds), heavy imines (heavier group 14–15 double bonds), heavy aromatics (aromatic systems containing heavier group 14 elements), heavy butadienes, and triply bonded systems containing heavier group 14 elements, and so on. Now, unsaturated compounds containing heavier group 14 elements are no more imaginary species but are those of real existence even in the case of lead, the heaviest group 14 element, when they are appropriately protected by bulky substituents. The synthesis and properties of the kinetically stabilized unsaturated compounds containing heavier group 14 elements will be described in this section. Although a number of multiple bondings between heavier group 14 elements and transition metal elements have been reported so far, only unsaturated compounds containing main group elements should be considered here from the viewpoint of comparisons with carbon chemistry. Keywords: multiple bond; kinetic stabilization; bulky substituent; silicon; germanium; tin; lead; heavy aromatics; heavy ketone; low-coordinated compound

Preparation and Reactions of Compounds with Heavier Group 14 Elements in Low Oxidation States

Abstract: Facile synthesis of chlorosilylene (PhC(NtBu)2SiCl) in 90% yield was reported using LiN(TMS)2 as a dehydrochlorinating agent and its versatile reactivity with various organic substrates was examined. Furthermore, the bis(silylene) [PhC(NtBu)2]2Si2 was isolated in low yield (5.2%) from the reduction of amidinato trichlorosilane with 3 equiv of potassium graphite. Theoretical calculation shows that the compound has two Si(I) centers which are connected by means of a σ-bond. Reactivities of this compound towards ketone, diketone, N2O were probed and several siloxane derivatives were obtained. Also, the addition of 2 equiv of diphenylacetylene to [PhC(NtBu)2]2Si2 has been reported. Both diphenylacetylene equivalents add across the Si-Si, with concomitant Si-Si bond rupture, to give the 1,4-disilabenzene derivative. This disilabenzene species is nearly planar in the solid state despite the tetrahedral silicon centers, and calculations show that there is some aromatic character to the system [NICS(1) = -3.6]. We also studied the reactions of elemental phosphorus with [PhC(NtBu)2]2Si2, which afforded a of the first complex with a Si-P-Si-P core through activation of the P4 molecule. X-ray structural analysis revealed most apparent feature of the compound is the planar Si-P-Si-P four membered ring, which consists of four equivalent Si P bonds. The preparation of bis-silylene was followed by the synthesis of its germanium version [PhC(NtBu)2]2Ge2. A theoretical study indicates clearly that it can be best viewed as digermylenes although they can formally be drawn as donor-stabilized digermynes. The reactivity reflects the digermylene nature of the species. For example, reaction of [PhC(NtBu)2]2Ge2 with 2 equiv of Fe2(CO)9 gives the diiron complex where each germanium center is coordinated by one Fe(CO)4 moiety to give the complex [LGe(Fe(CO)4-Ge(Fe(CO)4L, L= PhC(NtBu)2]. The only other reactivity of this species is the addition of azobenzene across the Ge-Ge bond with concomitant bond rupture to give the new 1,2-digermylene hydrazine species [LGeN(Ph)N(Ph)GeL]. All the compounds were characterized by multinuclear NMR spectroscopy, EI-MS spectrometry, elemental analysis, and single crystal X-ray diffraction studies.