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

Stueger H, Hasken B, Gross U, Fischer R, Torvisco Gomez A - Organometallics (2013)

Bottom Line: Endocyclic bond lengths, bond angles, and dihedral angles are not influenced considerably by the substituents attached to the bridgehead silicon atoms.Due to σ(SiSi)/π(aryl) conjugation, a 20-30 nm bathochromic shift of the longest wavelength UV absorption band relative to Me3Si-Si8Me12-SiMe3 (1) is evident in the UV absorption spectra of the phenyl and ferrocenyl derivatives.Otherwise, UV absorption data do not support the assumption of aryl/aryl or aryl/C=O interaction via the σ(SiSi) bicyclooctasilane framework.

View Article: PubMed Central - PubMed

Affiliation: Institute of Inorganic Chemistry, Graz University of Technology , Stremayrgasse 9, A-8010 Graz, Austria.

ABSTRACT
A series of previously unknown bridgehead-functionalized bicyclo[2.2.2]octasilanes, Me3Si-Si8Me12-X, X-Si8Me12-X, and X-Si8Me12-Y [X, Y = -SiMe n Ph3-n (n = 1, 2) (2, 3, 10), -SiMe2Fc (Fc = ferrocenyl) (4, 11, 13, 14), -COR (R = Me, tBu) (6, 7, 12), COOMe (8), COOH (9)], have been prepared by the reaction of the silanides Me3Si-Si8Me12 (-)K(+) or K(+-)Si8Me12 (-)K(+) with proper electrophiles and fully characterized. The molecular structures of 2, 3, 4, 6, 8, 9, 10, and 13 as determined by single-crystal X-ray diffraction analysis exhibit a slightly twisted structure of the bicyclooctasilane cage. Endocyclic bond lengths, bond angles, and dihedral angles are not influenced considerably by the substituents attached to the bridgehead silicon atoms. Due to σ(SiSi)/π(aryl) conjugation, a 20-30 nm bathochromic shift of the longest wavelength UV absorption band relative to Me3Si-Si8Me12-SiMe3 (1) is evident in the UV absorption spectra of the phenyl and ferrocenyl derivatives. Otherwise, UV absorption data do not support the assumption of aryl/aryl or aryl/C=O interaction via the σ(SiSi) bicyclooctasilane framework.

No MeSH data available.


Absorption spectra of 1 andaryl-substituted bicyclo[2,2,2]octasilanes (n-hexanesolution; c = 4 × 10–5 M;inset c = 10–3 M): (···,gray) 1;15b (−··–,red) 2; (---, blue) 3; (—, green) 4; (— — —, purple) 10; (−·–, magenta) 11; (−– −, black) 13.
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fig8: Absorption spectra of 1 andaryl-substituted bicyclo[2,2,2]octasilanes (n-hexanesolution; c = 4 × 10–5 M;inset c = 10–3 M): (···,gray) 1;15b (−··–,red) 2; (---, blue) 3; (—, green) 4; (— — —, purple) 10; (−·–, magenta) 11; (−– −, black) 13.

Mentions: Figure 8 compares the absorptionspectrum of 1 with the spectra of the phenyl- and ferrocenyl-substitutedcompounds 2, 3, 4, 10, 11, and 13. The ferrocenylsilanes 4, 11, and 13 show characteristicweak absorption bands near 460 and 330 nm, which arise from localtransitions within ferrocene.26 All spectraexhibit additional bands in the near UV region. For 1 a typical shoulder appears at 240 nm, which previously has beenassigned to σ→π* type electron transitions involvingthe σ-SiSi skeleton.16 In the spectraof 2 and 4 this band is shifted considerablyto the red by 20 and 30 nm, respectively. This behavior is usuallyobserved when aromatic side groups are attached to permethylated oligosilaneframeworks and is easily rationalized if one assumes σ–πtype hyperconjugative interactions between the aromatic π- andthe SiSi σ-electrons.27,28 In the case of open-chainedpermethyloligosilanes the most striking red shift was found upon introductionof the first phenyl group, while a second phenyl substituent is muchless effective. Thus, Me3SiSiMe2SiMe3 exhibits a first absorption maximum at 216 nm,29 which is shifted to 240 nm in PhMe2SiSiMe2SiMe330 and to 243 nmin PhMe2SiSiMe2SiMe2Ph.31 In line with this observation the absorptionspectrum of 3 displays a 5 nm red shift of the firstabsorption maximum relative to 2, while 10 and 11 show identical λmax valuesas compared to 2 and 4, respectively. Apparentlythe σ–π conjugated bond system within 2 and 4 is not extended further by the presence of thesecond aryl group, which makes any electronic coupling of the aromaticsubstituents via the bicyclooctasilane cage rather unlikely.


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

Stueger H, Hasken B, Gross U, Fischer R, Torvisco Gomez A - Organometallics (2013)

Absorption spectra of 1 andaryl-substituted bicyclo[2,2,2]octasilanes (n-hexanesolution; c = 4 × 10–5 M;inset c = 10–3 M): (···,gray) 1;15b (−··–,red) 2; (---, blue) 3; (—, green) 4; (— — —, purple) 10; (−·–, magenta) 11; (−– −, black) 13.
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fig8: Absorption spectra of 1 andaryl-substituted bicyclo[2,2,2]octasilanes (n-hexanesolution; c = 4 × 10–5 M;inset c = 10–3 M): (···,gray) 1;15b (−··–,red) 2; (---, blue) 3; (—, green) 4; (— — —, purple) 10; (−·–, magenta) 11; (−– −, black) 13.
Mentions: Figure 8 compares the absorptionspectrum of 1 with the spectra of the phenyl- and ferrocenyl-substitutedcompounds 2, 3, 4, 10, 11, and 13. The ferrocenylsilanes 4, 11, and 13 show characteristicweak absorption bands near 460 and 330 nm, which arise from localtransitions within ferrocene.26 All spectraexhibit additional bands in the near UV region. For 1 a typical shoulder appears at 240 nm, which previously has beenassigned to σ→π* type electron transitions involvingthe σ-SiSi skeleton.16 In the spectraof 2 and 4 this band is shifted considerablyto the red by 20 and 30 nm, respectively. This behavior is usuallyobserved when aromatic side groups are attached to permethylated oligosilaneframeworks and is easily rationalized if one assumes σ–πtype hyperconjugative interactions between the aromatic π- andthe SiSi σ-electrons.27,28 In the case of open-chainedpermethyloligosilanes the most striking red shift was found upon introductionof the first phenyl group, while a second phenyl substituent is muchless effective. Thus, Me3SiSiMe2SiMe3 exhibits a first absorption maximum at 216 nm,29 which is shifted to 240 nm in PhMe2SiSiMe2SiMe330 and to 243 nmin PhMe2SiSiMe2SiMe2Ph.31 In line with this observation the absorptionspectrum of 3 displays a 5 nm red shift of the firstabsorption maximum relative to 2, while 10 and 11 show identical λmax valuesas compared to 2 and 4, respectively. Apparentlythe σ–π conjugated bond system within 2 and 4 is not extended further by the presence of thesecond aryl group, which makes any electronic coupling of the aromaticsubstituents via the bicyclooctasilane cage rather unlikely.

Bottom Line: Endocyclic bond lengths, bond angles, and dihedral angles are not influenced considerably by the substituents attached to the bridgehead silicon atoms.Due to σ(SiSi)/π(aryl) conjugation, a 20-30 nm bathochromic shift of the longest wavelength UV absorption band relative to Me3Si-Si8Me12-SiMe3 (1) is evident in the UV absorption spectra of the phenyl and ferrocenyl derivatives.Otherwise, UV absorption data do not support the assumption of aryl/aryl or aryl/C=O interaction via the σ(SiSi) bicyclooctasilane framework.

View Article: PubMed Central - PubMed

Affiliation: Institute of Inorganic Chemistry, Graz University of Technology , Stremayrgasse 9, A-8010 Graz, Austria.

ABSTRACT
A series of previously unknown bridgehead-functionalized bicyclo[2.2.2]octasilanes, Me3Si-Si8Me12-X, X-Si8Me12-X, and X-Si8Me12-Y [X, Y = -SiMe n Ph3-n (n = 1, 2) (2, 3, 10), -SiMe2Fc (Fc = ferrocenyl) (4, 11, 13, 14), -COR (R = Me, tBu) (6, 7, 12), COOMe (8), COOH (9)], have been prepared by the reaction of the silanides Me3Si-Si8Me12 (-)K(+) or K(+-)Si8Me12 (-)K(+) with proper electrophiles and fully characterized. The molecular structures of 2, 3, 4, 6, 8, 9, 10, and 13 as determined by single-crystal X-ray diffraction analysis exhibit a slightly twisted structure of the bicyclooctasilane cage. Endocyclic bond lengths, bond angles, and dihedral angles are not influenced considerably by the substituents attached to the bridgehead silicon atoms. Due to σ(SiSi)/π(aryl) conjugation, a 20-30 nm bathochromic shift of the longest wavelength UV absorption band relative to Me3Si-Si8Me12-SiMe3 (1) is evident in the UV absorption spectra of the phenyl and ferrocenyl derivatives. Otherwise, UV absorption data do not support the assumption of aryl/aryl or aryl/C=O interaction via the σ(SiSi) bicyclooctasilane framework.

No MeSH data available.