Chalcogenatetrasilacyclopentenes: Five-Membered Rings with Endocyclic Si−Si Double Bonds

Grybat, Andreas; Boomgaarden, Sven; Saak, Wolfgang; Marsmann, H.C.; Weidenbruch, Manfred

doi:10.1002/(sici)1521-3773(19990712)38:13/14<2010::aid-anie2010>3.0.co;2-t

Cited by 41 publications

(14 citation statements)

References 4 publications

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“…It has been shown previously that at ambi-ent temperatures these compounds keep their structural integrity also in THF or arene solvents and, in particular, no diarylsilylenes or diarylgermylenes are formed under these conditions. [1,2,21,24] Table 1 summarizes both oxidation and reduction potentials of four multiply bonded derivatives of Si and Ge studied (1-4) as measured by CV in two different solvents and electrolytes. In o-dichlorobenzene (o-DCB) and in the presence of an extremely "naïve" electrolyte, [25] disilene 1 exhibited reversible redox couples in both oxidation and reduction processes.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical Properties of a Disilene, a Tetrasila‐1,3‐butadiene, and Their Germanium Analogues

Schäfer

Weidenbruch

Müller

et al. 2009

Chemistry A European J

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The redox properties of aryl-substituted disilene (1), tetrasila-1,3-butadiene (2), digermene (3), and tetragerma-1,3-butadiene (4) (in which the aryl group is 2,4,6-triisopropylphenyl) have been studied by cyclic voltammetry (CV) in two different solvents. In o-dichlorobenzene, disilene 1 exhibited reversible redox couples in both oxidation and reduction processes, whereas tetrasilabutadiene 2 showed a reversible behavior only in its oxidation and an irreversible wave in its reduction. Tetragermabutadiene 4 afforded a reversible couple in its reduction and an irreversible wave in its oxidation, whereas digermene 3 showed only an irreversible oxidation wave but no reduction one. In comparison, all observed oxidation and reduction waves in THF were irreversible. In both solvents, the same trend of decreasing ease of oxidation has been observed: 2>4>3>1. The calculated vertical ionization energies (E(i)) for the 2,6-dimethylphenyl-substituted model compounds 9-12 afforded a trend of ease of oxidation that decreases in the series tetrasilabutadiene 10>tetragermabutadiene 12>disilene 9>digermene 11. This predicted trend parallels the measured oxidation potentials in the sense that the heavy butadienes are easier to oxidize than the heavy alkenes. The trend in the reduction direction has been found to be different in the two solvents studied. The computed electron affinities (E(ea)) for compounds 9-12 indicated that the ease of reduction decreased in the sequence tetragermabutadiene 12>tetrasilabutadiene 10>digermene 11>disilene 9. However, no straightforward relation between the computed electron affinities and the experimentally measured reduction potentials has been found.

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Section: Resultsmentioning

confidence: 99%

Electrochemical Properties of a Disilene, a Tetrasila‐1,3‐butadiene, and Their Germanium Analogues

Schäfer

Weidenbruch

Müller

et al. 2009

Chemistry A European J

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“…Chlorosilanes Ph 3 SiCl, Et 3 SiCl and 2-(cyclohex-3-enyl)ethyl-dimethyl chlorosilane (ABCR) were distilled over Mg, hexaphenyldisilane Ph 3 SiSiPh 3 (ABCR) was used as received. 2,2,3,4,5,5-Hexakis(2,4,6-triisopropylphenyl)-1-thia-2,3,4,5-tetrasilacyclopent-3-ene (TSCP) 22 was provided for the study by Prof. M. Weidenbruch.…”

Section: Chemicalsmentioning

confidence: 99%

Reversed redox generation of silyl radicals in a four-electrode flow-through EPR spectroelectrochemical cell

Zeitouny

Jouikov

2009

Phys. Chem. Chem. Phys.

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A flow-through four-electrode EPR spectroelectrochemical cell was developed which allowed the observation of silyl radical formation in apparently multielectron electrochemical processes, in which these species could not be detected directly because of the high driving force of their further reduction/oxidation leading to non-paramagnetic products. Silyl radicals thus generated were characterized by spin trapping with alpha-phenyl-N-tert-butyl nitrone (PBN), intramolecular spin trapping or by direct detection. The overall multielectron process is realized in the first, generating, compartment of the cell and the ionic species formed are then transformed into the corresponding radicals in the second compartment via a one-electron redox process in the opposite direction, e.g. two-electron reductions of Ph(3)SiCl or Et(3)SiCl followed by one-electron oxidation of the resulting Ph(3)Si(-) or Et(3)Si(-) anions (+2e/-e process). These radical species were then identified as their secondary paramagnetic products or by their spin trapping with PBN. Using (2-[cyclohex-3-enyl]ethyl)dimethyl chlorosilane in this process, the formation of the silicon-centered radical and its intramolecular addition across the internal double bond were evidenced by spin trapping. The reduction of electrophilic silicon intermediates issued from the oxidation of Ph(3)SiSiPh(3) (-2e/+2e process) resulted in Ph(3)Si* radicals trapped with PBN. The reduction of the electrochemically prepared persistent dication of a stable disilene, thiatetrasilacyclopentene, allowed generation of a disilene cation radical characterized by EPR.

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“…64 The doubly bonded silicons were observed as expected in a low-field region (86.0 ppm for 72, 90.3 ppm for 73 and 97.8 ppm for 74), although the extent of deshielding in heavy cyclopentenes was less important than that in the heavy cyclopropenes and cyclobutenes (Table 5.2). 64 The doubly bonded silicons were observed as expected in a low-field region (86.0 ppm for 72, 90.3 ppm for 73 and 97.8 ppm for 74), although the extent of deshielding in heavy cyclopentenes was less important than that in the heavy cyclopropenes and cyclobutenes (Table 5.2).…”

Section: Five-membered Ring Compounds (Heavy Cyclopentenes)mentioning

confidence: 51%

Heavy Analogs of Alkenes, 1,3‐Dienes, Allenes and Alkynes: Multiply Bonded Derivatives of Si, Ge, Sn and Pb

Lee

Sekiguchi

2010

Organometallic Compounds of Low‐Coordinate Si, Ge, Sn and Pb

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Unsaturated hydrocarbons, alkenes, alkynes and dienes are among the most fundamental classes of organic compounds. The great variety and richness of organic chemistry are to a large extent caused by the disposition of carbon to form highly reactive carbon-carbon and carbon-heteroatom multiple bonds. Standard textbooks on organic chemistry describe the C=C double bond as one made of a σ -bond, formed by the linear end-on overlap of sp 2 -hybrid orbitals of each carbon partner (sp 2 -sp 2 interaction), and a π -bond, formed by the side-on overlap of unhybridized 2p-orbitals (2p π -2p π interaction). Analogously, the carbon-carbon triple bond consists of a σ -bond, formed by the linear end-on overlap of the two sp-hybrids (sp-sp interaction), and two mutually orthogonal π -bonds, each formed by the side-on overlap of unhybridized 2p-orbitals (2p π -2p π interaction). Because the s-character of the hybrid orbitals used for the formation of carbon-carbon bonds progressively increases from the single (sp 3 -sp 3 ) to the double (sp 2 -sp 2 ) and triple (sp-sp) bonds, C=C double bonds are shorter (and stronger) than C-C single bonds, and C≡C triple bonds are shorter (and stronger) than C=C double bonds. In accord with their hybridization types, the geometry of the carbon-carbon double bond in alkenes R 2 C=CR 2 is planar with an idealized R-C=C bond angle of 120 • , and the geometry of the carbon-carbon triple bond in alkynes R-C≡C-R is linear with an idealized R-C≡C bond angle of 180 • .The structures and bonding of the alkene analogs of heavy group 14 elements, both in the crystalline form and in solution, are sharply distinctive from those of their organic counterparts (alkenes); therefore, before proceeding to the discussion on each class of heavy alkenes we will briefly comment on the specific structural features of the title compounds. Structure and bondingIn contrast to organic alkenes, which are typically planar and feature diagnostically short double bonds (av. 1.34Å for >C=C< vs av. 1.54Å for >C-C<), their analogs of the heavy group 14 elements >E=E< (E = Si-Pb) revealed diverse types of structural modes sharply distinctive from those of their organic counterparts. Thus, apart from the stretching of the E=E bond descending group 14, there are two fundamental structural deformations characteristic of heavy alkenes >E=E< and leading to their departure from planarity: trans-bending at E centers and twisting about the E=E bond. The peculiar trans-bending geometry, resulting in the overall pyramidalization at the heavy group 14 elements, was rationalized in the framework of two different MO models providing alternative explanations for this phenomenon. 5 The first qualitative model considered formation of the double bond as a result of the interaction of two monomeric carbene units, taking into account the different groundstate multiplicities of carbenes and their heavy analogs. Thus, interaction of the two monomeric carbenes, which typically have triplet ground states (or alternatively, singlet ground states with ...

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Chalcogenatetrasilacyclopentenes: Five-Membered Rings with Endocyclic Si−Si Double Bonds

Cited by 41 publications

References 4 publications

Electrochemical Properties of a Disilene, a Tetrasila‐1,3‐butadiene, and Their Germanium Analogues

Electrochemical Properties of a Disilene, a Tetrasila‐1,3‐butadiene, and Their Germanium Analogues

Reversed redox generation of silyl radicals in a four-electrode flow-through EPR spectroelectrochemical cell

Heavy Analogs of Alkenes, 1,3‐Dienes, Allenes and Alkynes: Multiply Bonded Derivatives of Si, Ge, Sn and Pb

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