1, 4-Additions of HCl and HBr to a Tetrasilabutadiene: Formation of Unsymmetrically Substituted Disilenes [1]Dedicated to Professor Dieter Naumann on the Occasion of his 60th Birthday
Abstract:The reactions of hexakis(2,4,6-triisopropylphenyl)tetrasilabuta-1,3-diene R 2 SiϭSiRϪSiRϭSiR 2 (1) with HCl and HBr, slowly generated from HSiCl 3 or LiBr and CF 3 COOH, respectively, furnish the unsymmetrically substituted disilenes R 2 XSiϪSiRϭ SiRϪSiHR 2 , X ϭ Cl (2), Br (3), by formal 1,4-addition of the hydrogen halides to 1. However, passing gaseous hydrogen halides
1,4-Addition von HCl und HBr an ein Tetrasilabutadien: Bildung unsymmetrisch substituierter DisileneInhaltsübersicht. Die Reaktionen von Hex… Show more
“…Because 5a could not be isolated in sufficiently pure form, meaningful UV−vis spectroscopic data could only be obtained for 5b . Its longest wavelength absorption is observed at λ max = 427 nm (ε = 24800 L mol -1 cm -1 ), which is considerably red shifted compared to λ max values of symmetrical (aryl)(silyl)disilenes (( E )- 10 : 394 nm; ( Z )- 10 : 398 nm) but similar to that of bis(chlorosilyl)-substituted disilene 11 (Table and Chart ). 1 Molecular structure of 5b in the solid state at the 50% probability level.…”
The rearrangements of (chlorosilyl)disilenes R2(Cl)Si-(Tip)Si=SiTip2 (5a,b: Tip = 2,4,6-iPr3C6H2, a: R = Me, b: R = Ph) quantitatively yield the isomeric chlorocyclotrisilanes (6a,b). The disilene precursors 5a,b are, in turn, accessible from the reactions of the disilenide Tip2Si=Si(Tip)Li (1), that is, a disila analogue to vinyl anions, with dichlorosilanes R2SiCl2. This novel approach to cyclotrisilanes potentially allows for the facile variation of the substitution pattern and grants access to the first anionic derivatives; while the rearrangement of 5a,b to 6a,b is slow at room temperature and additionally requires the presence of THF or other n-donors, reduction of 5b with lithium instantly yields the corresponding cyclotrisilanide (7b) without detection of any open-chained isomer. Heating of a neat sample of 5b to 150 degrees C provides a completely characterized 1,2,3-trisilaindane derivative (13), strongly supporting the intermediacy of a disilanyl silylene species that inserts into an ortho-CH bond of the phenyl substituents. The X-ray diffraction studies on single crystals of 6a,b and 7b reveal that the Si-Si bond distance in cyclotrisilanes depends significantly on the electronegativity of the opposing silicon atom's substituents, which is rationalized by density functional theory (DFT) calculations on model systems.
“…Because 5a could not be isolated in sufficiently pure form, meaningful UV−vis spectroscopic data could only be obtained for 5b . Its longest wavelength absorption is observed at λ max = 427 nm (ε = 24800 L mol -1 cm -1 ), which is considerably red shifted compared to λ max values of symmetrical (aryl)(silyl)disilenes (( E )- 10 : 394 nm; ( Z )- 10 : 398 nm) but similar to that of bis(chlorosilyl)-substituted disilene 11 (Table and Chart ). 1 Molecular structure of 5b in the solid state at the 50% probability level.…”
The rearrangements of (chlorosilyl)disilenes R2(Cl)Si-(Tip)Si=SiTip2 (5a,b: Tip = 2,4,6-iPr3C6H2, a: R = Me, b: R = Ph) quantitatively yield the isomeric chlorocyclotrisilanes (6a,b). The disilene precursors 5a,b are, in turn, accessible from the reactions of the disilenide Tip2Si=Si(Tip)Li (1), that is, a disila analogue to vinyl anions, with dichlorosilanes R2SiCl2. This novel approach to cyclotrisilanes potentially allows for the facile variation of the substitution pattern and grants access to the first anionic derivatives; while the rearrangement of 5a,b to 6a,b is slow at room temperature and additionally requires the presence of THF or other n-donors, reduction of 5b with lithium instantly yields the corresponding cyclotrisilanide (7b) without detection of any open-chained isomer. Heating of a neat sample of 5b to 150 degrees C provides a completely characterized 1,2,3-trisilaindane derivative (13), strongly supporting the intermediacy of a disilanyl silylene species that inserts into an ortho-CH bond of the phenyl substituents. The X-ray diffraction studies on single crystals of 6a,b and 7b reveal that the Si-Si bond distance in cyclotrisilanes depends significantly on the electronegativity of the opposing silicon atom's substituents, which is rationalized by density functional theory (DFT) calculations on model systems.
“…Highly crowded 3 adopts a puckered 1,2-disilacyclobutene ring, to which the cyclohexane ring was found to fuse with a chair conformation. The Si−Si bond distance is 2.213(3) Å, which is consistent with those reported for hindered disilenes . The most prominent structural feature of 3 is the geometry around the SiSi moiety, which has a twisted, trans-bent structure with a bend angle of 26.4° and a Bbt−SiSi−Bbt dihedral angle of 103.3(8)° .…”
The reactivity of a bulky, diaryl-substituted disilyne, Ar-Si identical withSi-Ar, was examined for the first time. Reaction of the disilyne with ethylene yielded an ethylene-bridged bis(silacyclopropane), which is interpreted as a further reaction product of the initially formed 1,2-disilacyclobutene species with ethylene. A cyclohexane fused with a 1,2-disilacyclobutene was obtained in the reaction with cyclohexene. In the reaction with 2,3-dimethyl-1,3-butadiene, a tricyclo derivative was isolated from the complex product mixture.
“…Addition of trichlorosilane to a solution of 61 resulted in the formation of bright orange crystals of the unsymmetrically substituted disilene 71 . Also, the action of hydrogen bromide, generated slowly by the reaction of trifluoroacetic acid with lithium bromide, on 61 furnishes intensely orange crystals of the disilene 72 (Scheme ) 17 …”
Section: Molecules With Conjugated Gec Sisi and
Gege Double Bondsmentioning
In less than three decades the chemistry of low-coordinated compounds of the heavier
elements of group 14 has made unforeseen and unprecedented advances. In the meantime
not only have homonuclear double bonds been realized between all elements of this group
but also the first examples of compounds analogous to the alkynes have been isolated.
Similarly, syntheses of molecules containing heteronuclear bonds have been achieved.
Analogues of the allenes as well as the first example of a spiropentasiladiene are of particular
interest. The present short review covers mainly work done in the author's laboratories
together with other relevant reports from the literature. It begins with the synthesis of hexa-tert-butylcyclotrisilane, which is cleaved photochemically into a short-lived silylene and a
marginally stable disilene; in subsequent reactions both of these species can undergo
cycloadditions to furnish a broad palette of mostly novel ring systems. Furthermore, the
first molecules with conjugated SiSi, GeC, and GeGe double bonds have been obtained
and their reactivities examined. The isolation of the first diplumbenes and a cyclotriplumbane
exhibiting an unusual bonding situation as the first homocyclic compound of lead constitute
a provisional end of these developments.
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