Molekül‐ und Kristallstruktur des 1,4‐Bis[tris(tetrahydrofuran)lithium]‐octaphenyltetrasilans

Becker, Gerd; Hartmann, Hans-Martin; Hengge, E.; Schrank, Franz

doi:10.1002/zaac.19895720108

Cited by 40 publications

(6 citation statements)

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“…A THF-solvate of 1,4-dilithiooctaphenyltetrasilane 3THF • [Li(Ph 2 Si) 4 Li] • 3THF (Section 3.2.6, Scheme 3.14, B) is monomeric, existing in a planar zigzag-shaped conformation with a Si-Li bond length of 2.714(10)Å. 72 Unsolvated pentamethyldisilanyllithium (Me 3 SiMe 2 SiLi) 4 has a tetrameric structure with the four lithium atoms at the vertices of the tetrahedron and an average Li-Li distance of 2.780Å (Figure 3.4). 62a,73 Each Me 3 SiMe 2 Si unit is located above one of the faces of the Li 4 tetrahedron with the three nearly equal Si-Li distances of 2.683Å (av.)…”

Section: X-ray Crystallography (Crystal Structure)mentioning

confidence: 99%

Heavy Analogs of Carbanions: Si‐, Ge‐, Sn‐ and Pb‐Centered Anions

2010

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

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Standard organic chemistry textbooks typically define a carbanion as a highly reactive species with a trivalent carbon that has a lone electron pair and bears a negative charge. In contrast to electron-deficient carbenium ions (see Chapter 1), carbanions, featuring eight valence electrons around the central carbon, are electron rich being strong nucleophiles and Lewis bases, typically more powerful than amines. The best-known examples of carbanionic species are definitely the Grignard reagents RMgX and organolithium reagents RLi, readily accessible and extremely useful organometallic derivatives extensively applied in synthetic organic chemistry. Known for more than a hundred years, metal salts of carbanions have been thoroughly studied from the viewpoint of their fundamental properties, such as basicity, stability, ion-pairing behavior and aggregation states.Carbanions contain an sp 3 -hybridized anionic carbon adopting a trigonal-pyramidal geometry with one of its tetrahedral valencies occupied by a lone electron pair. Such geometry is highly reminiscent of that of amines, for example NH 3 , which is isoelectronic with the simplest methyl anion CH 3 − . This was indeed confirmed by PES measurements suggesting a barrier to inversion and pyramidal structure for CH 3 − , 1 that agreed well with the computational data, revealing an H-C-H bond angle for the methyl anion of 109.4 • . 2 The preference for the pyramidal geometry of carbanions can be readily understood from simple orbital considerations. Thus, in a planar carbanion the lone pair would occupy a pure p-orbital, whereas in a pyramidalized carbanion the lone pair orbital has a substantial s-character (close to sp 3 ) gaining an additional stabilization through the

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Section: X-ray Crystallography (Crystal Structure)mentioning

confidence: 99%

Heavy Analogs of Carbanions: Si‐, Ge‐, Sn‐ and Pb‐Centered Anions

2010

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

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“…A potent strategy for the construction of structurally more challenging silicon frameworks is the use of di- or multifunctionalized starting materials such as α,ω-dianions. Gilman , and Hengge , were pioneers in this area and developed the cleavage of strained cyclosilanes to obtain dianions. Sekiguchi, Tokitoh, Kira, and Apeloig also contributed with their groups to this research field and prepared some previously unknown 1,1-, 1,2-, and 1,4-dilithiooligosilanes.…”

Section: Introductionmentioning

confidence: 99%

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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“…The prepared compounds Li(SiPh 2 ) 5 Li and Li(SiPh 2 ) 4 Li probably contain coordinated THF. [89] However, the stoichiometry of the following reactions with these reagents were calculated referring to the starting material Si 5 Ph 10 (that means 2.74 mmol Si 5 Ph 10 correspond to 2.74 mmol Li(SiPh 2 ) 5 Li, which reacts with 5.49 mmol ClPR 2 or ClSiR 3 ). So the amount of coordinated THF is insignificant to the outcome of the reaction.…”

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confidence: 99%

Linear Phenylsilanes with PSi₄P, PSi₅P, and Si₇ Backbones

2022

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Linear α,ω‐diphosphaoligosilanes were prepared starting from 1,5‐dilithiodecaphenyl‐n‐pentasilane, Li(SiPh2)5Li, and chlorodiorganophosphanes. The compounds 1,5‐bis(diphenylphosphanyl)decaphenyl‐n‐pentasilane, (Ph2P)Si5Ph10(PPh2), 1,5‐bis(di‐iso‐propylphosphanyl)decaphenyl‐n‐pentasilane, (iPr2P)Si5Ph10(PiPr2), and 1,4‐bis(di‐iso‐propylphosphanyl)octaphenyl‐n‐tetrasilane, (iPr2P)Si4Ph8(PiPr2), were obtained in moderate to good yields and characterized with IR‐, Raman‐, UV‐, 31P‐, 29Si‐, and 1H‐NMR spectroscopy. Single crystal structure analyses of these three silanes show all‐transoid conformations of the atoms along the phosphorus‐silicon backbone of the molecules in the solid state. The silicon‐silicon and the silicon‐phosphorus‐bonds are elongated. This is caused by the complete substitution of these molecules by sterically demanding phenyl‐ and i‐propyl‐substituents and effective σ‐conjugation along the main chains. Hexadecaphenyl‐n‐heptasilane, Si7Ph16, was prepared for comparison with the other three compounds. The latter one shows a long wavelength UV‐absorption in the same region as 1,5‐bis(diphenylphosphanyl)decaphenyl‐n‐pentasilane.

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Molekül‐ und Kristallstruktur des 1,4‐Bis[tris(tetrahydrofuran)lithium]‐octaphenyltetrasilans

Cited by 40 publications

References 28 publications

Heavy Analogs of Carbanions: Si‐, Ge‐, Sn‐ and Pb‐Centered Anions

Heavy Analogs of Carbanions: Si‐, Ge‐, Sn‐ and Pb‐Centered Anions

Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates

Linear Phenylsilanes with PSi₄P, PSi₅P, and Si₇ Backbones

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Molekül‐ und Kristallstruktur des 1,4‐Bis[tris(tetrahydrofuran)lithium]‐octaphenyltetrasilans

Cited by 40 publications

References 28 publications

Heavy Analogs of Carbanions: Si‐, Ge‐, Sn‐ and Pb‐Centered Anions

Heavy Analogs of Carbanions: Si‐, Ge‐, Sn‐ and Pb‐Centered Anions

Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates

Linear Phenylsilanes with PSi4P, PSi5P, and Si7 Backbones

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Linear Phenylsilanes with PSi₄P, PSi₅P, and Si₇ Backbones