Synthesis and Properties of Bridgehead-Functionalized Permethylbicyclo[2.2.2]octasilanes

Stueger, Harald; Hasken, Bernd; Groß, Uwe; Fischer, Roland; Torvisco, Ana

doi:10.1021/om400184y

Cited by 9 publications

(10 citation statements)

References 48 publications

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“…The measured chemical shift value compares reasonably well with those observed for structurally related bicyclo[2.2.2]octasilanes. 12 Furthermore, the incorporation of the oxygen atom into the cyclopolysilane framework breaks the symmetry of the ring. Therefore, 5 displays three SiMe 2 signals in the typical range between −47 and −53 ppm as well as two resonance lines for the SiMe 3 groups at −12.2 and −17.3 ppm.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Reactivity of Cyclic Silenolates Revisited

et al. 2017

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The stable exocyclic silenolates 2a–c (2a, R = Mes; 2b, R = o-Tol; 2c, R = 1-Ad) were fully characterized by NMR and UV–vis spectroscopy. According to spectroscopic and structural features, 2a–c are best described as acyl silyl anions (tautomeric structure I) in solution. This behavior is also reflected by the reaction of 2a,c with MeI. Both alkylation reactions take place at the corresponding silicon atom and lead to the formation of the methylated structures 4a,b in nearly quantitative yields. Furthermore, the thermal stability of exocyclic silenolates 2a,c was investigated. In the case of 2a, a thermally induced intramolecular sila-Peterson alkenation was observed at 60 °C. This transformation allowed straightforward access to 2-oxahexasilabicyclo[3.2.1]octan-8-ide 5 as a structurally complex, bicyclic silicon framework. In contrast to that, heating of 2c, as an example of an alkyl-substituted silenolate, led to an unexpected degradation to uncharacterized polymers. However, we were able to isolate the 1-adamantyl-substituted, bicyclic compound 8, which is structurally closely related to 5, by the treatment of 1,4-dipotassium-1,4-bis(trimethylsilyl)cyclohexasilane with 1 equiv of 1-adamantoyl chloride. Again an intramolecular sila-Peterson alkenation is responsible for the formation of 8. The mechanism for this highly selective reaction sequence is outlined and supported by density functional theory (DFT) calculations, which highlight the thermodynamic driving force and the low activation barriers of this multistep transformation.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Reactivity of Cyclic Silenolates Revisited

et al. 2017

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“…The two δ 29 Si values for the bridgehead Si atoms were measured near −131 ppm (characteristic for tetrasilyl-substituted silanes) and −77 ppm (characteristic for acyl-substituted quaternary silanes). The same tendencies were found earlier by Stueger et al during the synthesis of a series of substituted bicyclo[2.2.2]octasilanes . The aryl-substituted compound 2a exclusively afforded the O -silylated silene 5 under the same conditions (compare Scheme ).…”

Section: Resultsmentioning

confidence: 63%

“…The same tendencies were found earlier by Stueger et al during the synthesis of a series of substituted bicyclo[2.2.2]octasilanes. 30 The aryl-substituted compound 2a exclusively afforded the O -silylated silene 5 under the same conditions (compare Scheme 3 ). NMR spectral data of 5 (see the Experimental Section ) are also typical for a Brook-type silene.…”

Section: Resultsmentioning

confidence: 97%

Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates

et al. 2020

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In this contribution a convenient synthetic method to obtain the previously unknown dianionic cyclic silenolates and germenolates is described. These dianions 2a , b and 4a , b are easily accessible via a one-pot synthetic protocol in high yields. Their structural properties were analyzed by a combination of NMR, single-crystal X-ray crystallography, and DFT quantum mechanical calculations. Moreover, the reactivity of 2a , b and 4a , b with selected examples of electrophiles was investigated. 2a and 4a were reacted with ClSi i Pr 3 to give new examples of polysilanes and polygermanes with exocyclic double bonds. The reaction of 2b with ClSiMe 2 SiMe 2 Cl led to the formation of the acyl bicyclo[2.2.2]octasilane 6 . Moreover, the reaction of 2a , b and 4a , b with MeI, as an example of a carbon-centered electrophile, led to selective alkylation reactions at the negatively charged silicon and germanium atoms. The corresponding methylated structures 9a , b and 10a , b were formed in nearly quantitative yields. The competitive reactivity of the silyl and silenolate anion toward 1 equiv of ClSiMe 3 showed that the outcome of the reaction was strongly influenced by the substituent at the carbonyl moiety. 2a reacted with 1 equiv of ClSiMe 3 to give the corresponding cyclic silenolate S 1 a , which demonstrated that the silyl anion is more nucleophilic than the silenolate with attached aromatic groups. 2b , on the other hand, reacted with 1 equiv of ClSiMe 3 to give the bicyclic compound 11 via an intramolecular sila-Peterson alkenation reaction. These findings clearly showed that the alkyl-substituted silenolate is more nucleophilic than the silyl anion. This paper demonstrates that 2a , b and 4a , b have the potential to be used as unique building blocks for complex polysilane and polygermane frameworks.

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“…Although alkyl and phenyl substituents are quite benign from a chemical point of view, they are particularly promising because they are realistic synthetical targets for silicon and germanium based molecular cores. [49][50][51][52][53][54][55][56][57] We hope these results will motivate studies of the properties of substituted cyclic and bicyclic silanes and germanes. The transmission suppression is less clear in the C222 systems than for the silanes and germanes.…”

Section: Manuscriptmentioning

confidence: 99%

Substituent Control of σ-interference Effects in the Transmission of Saturated Molecules

Garner

Koerstz

Jensen

et al. 2021

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The single-molecule conductance of saturated molecules can potentially be fully suppressed by destructive quantum interference in their σ-system. However, only few molecules with σ-interference have been identified and the structure-property relationship remains to be elucidated. Here, we explore the role of substituents in modulating the electronic transmission of saturated molecules. In functionalized bicyclo[2.2.2]octanes, the transmission is suppressed by σ- interference when fluorine substituents are applied. For bicyclo[2.2.2]octasilane and - octagermanes the transmission is suppressed when carbon-based substituents are used, and such molecules are likely to be highly insulating. For the carbon-based substituents we find a strong correlation between the appropriate Hammett constants and the transmission. The substituent effect enables systematic optimization of the insulating properties of saturated molecular cores.

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Synthesis and Properties of Bridgehead-Functionalized Permethylbicyclo[2.2.2]octasilanes

Cited by 9 publications

References 48 publications

Reactivity of Cyclic Silenolates Revisited

Reactivity of Cyclic Silenolates Revisited

Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates

Substituent Control of σ-interference Effects in the Transmission of Saturated Molecules

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