Lewis Acidity of Si₆Cl₁₂ and Its Role as Convenient SiCl₂ Source

The free cyclohexasilane Si₆Cl₁₂ (<b>1</b>) was obtained in 66% yield from the corresponding Cl^– diadduct [<i>n</i>Bu₄N]₂[<b>1</b>·2Cl] and AlCl₃ in C₆H₆. The substituted cyclohexasilane 1,1-(Cl₃Si)₂Si₆Cl₁₀ (<b>2</b>), however, cannot be liberated from [<i>n</i>Bu₄N]₂[<b>2</b>·2Cl] under comparable reaction conditions. Instead, a mixture of several products was obtained, from which the oligosilane Si₁₉Cl₃₆ (<b>3</b>) crystallized in low yields. X-ray crystallography revealed <b>3</b> to consist of two Si₅ rings, bridged by one silicon atom. Compound <b>1</b> possesses Lewis acidic sites above and below the ring centroid. Competition experiments reveal that their corresponding acid strengths are comparable to that of BCl₃. The reaction of <b>1</b> with 6 equiv of 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (Idipp) leads to a complete breakdown of the cyclic scaffold and furnishes the dichlorosilylene adduct Idipp–SiCl₂

Two-Coordinate Gallium Ion [<i>t</i>Bu₃Si-Ga-Si<i>t</i>Bu₃]⁺ and the Halonium Ions [<i>t</i>Bu₃Si-X-Si<i>t</i>Bu₃]⁺ (X = Br, I): Sources of the Supersilyl Cation [<i>t</i>Bu₃Si]⁺

The ion pair [tBu3Si-Ga-SitBu3]­[Al­(OC­(CF3)3)4] was formed quantitatively by treatment of (tBu3Si)2GaCl with Ag­[Al­(OC­(CF3)3)4] in methylene chloride. Single crystals of yellow [tBu3Si-Ga-SitBu3]­[Al­(OC­(CF3)3)4] were available from the filtered reaction solution at ambient temperature (space group P21/c). The isolated [tBu3Si-Ga-SitBu3]+ cation is isostructural with isoelectronic [tBu3Si-Zn-SitBu3] and [tBu3Si-Cu-SitBu3]−, respectively. Additionally, the reactions of tBu3SiX (X = Br, I) with Ag­[Al­(OC­(CF3)3)4] are described by which the halonium ions [tBu3Si-X-SitBu3]+ were formed. We found that the two-coordinate Ga cation [tBu3Si-Ga-SitBu3]+ and the halonium ions [tBu3Si-X-SitBu3]+ (X = Br, I) are highly reactive. The salts [tBu3Si-X-SitBu3]­[Al­(OC­(CF3)3)4] (X = Ga, Br, I) decompose in CH2Cl2 at room temperature to give tBu3SiF and tBu3SiCl. It is worth mentioning that the ratio of tBu3SiF to tBu3SiCl in these decomposition reactions is the same. We concluded that the same reactive intermediate, the supersilyl cation [tBu3Si]+, was thereby formed

Two-Coordinate Gallium Ion [<i>t</i>Bu₃Si-Ga-Si<i>t</i>Bu₃]⁺ and the Halonium Ions [<i>t</i>Bu₃Si-X-Si<i>t</i>Bu₃]⁺ (X = Br, I): Sources of the Supersilyl Cation [<i>t</i>Bu₃Si]⁺

The ion pair [tBu3Si-Ga-SitBu3]­[Al­(OC­(CF3)3)4] was formed quantitatively by treatment of (tBu3Si)2GaCl with Ag­[Al­(OC­(CF3)3)4] in methylene chloride. Single crystals of yellow [tBu3Si-Ga-SitBu3]­[Al­(OC­(CF3)3)4] were available from the filtered reaction solution at ambient temperature (space group P21/c). The isolated [tBu3Si-Ga-SitBu3]+ cation is isostructural with isoelectronic [tBu3Si-Zn-SitBu3] and [tBu3Si-Cu-SitBu3]−, respectively. Additionally, the reactions of tBu3SiX (X = Br, I) with Ag­[Al­(OC­(CF3)3)4] are described by which the halonium ions [tBu3Si-X-SitBu3]+ were formed. We found that the two-coordinate Ga cation [tBu3Si-Ga-SitBu3]+ and the halonium ions [tBu3Si-X-SitBu3]+ (X = Br, I) are highly reactive. The salts [tBu3Si-X-SitBu3]­[Al­(OC­(CF3)3)4] (X = Ga, Br, I) decompose in CH2Cl2 at room temperature to give tBu3SiF and tBu3SiCl. It is worth mentioning that the ratio of tBu3SiF to tBu3SiCl in these decomposition reactions is the same. We concluded that the same reactive intermediate, the supersilyl cation [tBu3Si]+, was thereby formed

Exhaustively Trichlorosilylated C₁ and C₂ Building Blocks: Beyond the Müller–Rochow Direct Process

The Cl–-induced heterolysis of the Si–Si bond in Si2Cl6 generates an [SiCl3]− ion as reactive intermediate. When carried out in the presence of CCl4 or Cl2CCCl2 (CH2Cl2 solutions, room temperature or below), the reaction furnishes the monocarbanion [C­(SiCl3)3]− ([A]−; 92%) or the vicinal dianion [(Cl3Si)2C–C­(SiCl3)2]2– ([B]2–; 85%) in excellent yields. Starting from [B]2–, the tetrasilylethane (Cl3Si)2(H)­C–C­(H)­(SiCl3)2 (H2B) and the tetrasilylethene (Cl3Si)2CC­(SiCl3)2 (B; 96%) are readily available through protonation (CF3SO3H) or oxidation (CuCl2), respectively. Equimolar mixtures of H2B/[B]2– or B/[B]2– quantitatively produce 2 equiv of the monoanion [HB]− or the blue radical anion [B•]−, respectively. Treatment of B with Cl– ions in the presence of CuCl2 furnishes the disilylethyne Cl3SiCCSiCl3 (C; 80%); in the presence of [HMe3N]­Cl, the trisilylethene (Cl3Si)2CC­(H)­SiCl3 (D; 72%) is obtained. Alkyne C undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH2Cl2, 50 °C, 3d) and thus provides access to 1,2-bis­(trichlorosilyl)-4,5-dimethylbenzene (E1; 80%) after oxidation with DDQ. The corresponding 1,2-bis­(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (E2; 83%) was prepared from C and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH2Cl2, 180 °C, 4 d). All closed-shell products were characterized by 1H, 13C­{1H}, and 29Si NMR spectroscopy; an EPR spectrum of [nBu4N]­[B•] was recorded. The molecular structures of [nBu4N]­[A], [nBu4N]2[B], B, E1, and E2 were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [A]−, [B]2–, C, and D are postulated

Exhaustively Trichlorosilylated C₁ and C₂ Building Blocks: Beyond the Müller–Rochow Direct Process

The Cl^–-induced heterolysis of the Si–Si bond in Si₂Cl₆ generates an [SiCl₃]⁻ ion as reactive intermediate. When carried out in the presence of CCl₄ or Cl₂CCCl₂ (CH₂Cl₂ solutions, room temperature or below), the reaction furnishes the monocarbanion [C­(SiCl₃)₃]⁻ ([<b>A</b>]⁻; 92%) or the vicinal dianion [(Cl₃Si)₂C–C­(SiCl₃)₂]^2– ([<b>B</b>]^2–; 85%) in excellent yields. Starting from [<b>B</b>]^2–, the tetrasilylethane (Cl₃Si)₂(H)­C–C­(H)­(SiCl₃)₂ (H₂<b>B</b>) and the tetrasilylethene (Cl₃Si)₂CC­(SiCl₃)₂ (<b>B</b>; 96%) are readily available through protonation (CF₃SO₃H) or oxidation (CuCl₂), respectively. Equimolar mixtures of H₂<b>B</b>/[<b>B</b>]^2– or <b>B</b>/[<b>B</b>]^2– quantitatively produce 2 equiv of the monoanion [H<b>B</b>]⁻ or the blue radical anion [<b>B</b>^<b>•</b>]⁻, respectively. Treatment of <b>B</b> with Cl^– ions in the presence of CuCl₂ furnishes the disilylethyne Cl₃SiCCSiCl₃ (<b>C</b>; 80%); in the presence of [HMe₃N]­Cl, the trisilylethene (Cl₃Si)₂CC­(H)­SiCl₃ (<b>D</b>; 72%) is obtained. Alkyne <b>C</b> undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH₂Cl₂, 50 °C, 3d) and thus provides access to 1,2-bis­(trichlorosilyl)-4,5-dimethylbenzene (<b>E1</b>; 80%) after oxidation with DDQ. The corresponding 1,2-bis­(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (<b>E2</b>; 83%) was prepared from <b>C</b> and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH₂Cl₂, 180 °C, 4 d). All closed-shell products were characterized by ¹H, ¹³C­{¹H}, and ²⁹Si NMR spectroscopy; an EPR spectrum of [<i>n</i>Bu₄N]­[<b>B</b>^<b>•</b>] was recorded. The molecular structures of [<i>n</i>Bu₄N]­[<b>A</b>], [<i>n</i>Bu₄N]₂[<b>B</b>], <b>B</b>, <b>E1</b>, and <b>E2</b> were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [<b>A</b>]⁻, [<b>B</b>]^2–, <b>C</b>, and <b>D</b> are postulated

Exhaustively Trichlorosilylated C₁ and C₂ Building Blocks: Beyond the Müller–Rochow Direct Process

The Cl^–-induced heterolysis of the Si–Si bond in Si₂Cl₆ generates an [SiCl₃]⁻ ion as reactive intermediate. When carried out in the presence of CCl₄ or Cl₂CCCl₂ (CH₂Cl₂ solutions, room temperature or below), the reaction furnishes the monocarbanion [C­(SiCl₃)₃]⁻ ([<b>A</b>]⁻; 92%) or the vicinal dianion [(Cl₃Si)₂C–C­(SiCl₃)₂]^2– ([<b>B</b>]^2–; 85%) in excellent yields. Starting from [<b>B</b>]^2–, the tetrasilylethane (Cl₃Si)₂(H)­C–C­(H)­(SiCl₃)₂ (H₂<b>B</b>) and the tetrasilylethene (Cl₃Si)₂CC­(SiCl₃)₂ (<b>B</b>; 96%) are readily available through protonation (CF₃SO₃H) or oxidation (CuCl₂), respectively. Equimolar mixtures of H₂<b>B</b>/[<b>B</b>]^2– or <b>B</b>/[<b>B</b>]^2– quantitatively produce 2 equiv of the monoanion [H<b>B</b>]⁻ or the blue radical anion [<b>B</b>^<b>•</b>]⁻, respectively. Treatment of <b>B</b> with Cl^– ions in the presence of CuCl₂ furnishes the disilylethyne Cl₃SiCCSiCl₃ (<b>C</b>; 80%); in the presence of [HMe₃N]­Cl, the trisilylethene (Cl₃Si)₂CC­(H)­SiCl₃ (<b>D</b>; 72%) is obtained. Alkyne <b>C</b> undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH₂Cl₂, 50 °C, 3d) and thus provides access to 1,2-bis­(trichlorosilyl)-4,5-dimethylbenzene (<b>E1</b>; 80%) after oxidation with DDQ. The corresponding 1,2-bis­(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (<b>E2</b>; 83%) was prepared from <b>C</b> and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH₂Cl₂, 180 °C, 4 d). All closed-shell products were characterized by ¹H, ¹³C­{¹H}, and ²⁹Si NMR spectroscopy; an EPR spectrum of [<i>n</i>Bu₄N]­[<b>B</b>^<b>•</b>] was recorded. The molecular structures of [<i>n</i>Bu₄N]­[<b>A</b>], [<i>n</i>Bu₄N]₂[<b>B</b>], <b>B</b>, <b>E1</b>, and <b>E2</b> were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [<b>A</b>]⁻, [<b>B</b>]^2–, <b>C</b>, and <b>D</b> are postulated

Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl₃SiSiCl₃

The addition compound Cl₃SiSiCl₃·TMEDA was formed quantitatively by treatment of Cl₃SiSiCl₃ with tetramethylethylenediamine (TMEDA) in pentane at room temperature. The crystal structure of Cl₃SiSiCl₃·TMEDA displays one tetrahedrally and one octahedrally bonded Si atom (monoclinic, <i>P</i>2₁/<i>n</i>). ²⁹Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the <i>meridional</i> isomer of Cl₃SiSiCl₃·TMEDA is 6.3 kcal lower in energy than that of <i>facial</i> coordinate species. Dissolving of Cl₃SiSiCl₃·TMEDA in CH₂Cl₂ resulted in an immediate reaction by which oligochlorosilanes Si_<i>n</i>Cl_2<i>n</i> (<i>n</i> = 4, 6, 8, 10; precipitate) and the Cl^–-complexed dianions [Si_<i>n</i>Cl_2<i>n</i>+2]^2– (<i>n</i> = 6, 8, 10, 12; CH₂Cl₂ extract) were formed. The constitutions of these compounds were confirmed by MALDI mass spectrometry. Additionally, single crystals of [Me₃NCH₂CH₂NMe₂]₂[Si₆Cl₁₄] and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] were obtained from the CH₂Cl₂ extract. We found that Cl₃SiSiCl₃·TMEDA reacts with MeCl, forming MeSiCl₃ and the products that had been formed in the reaction of Cl₃SiSiCl₃·TMEDA with CH₂Cl₂. X-ray structure analysis indicates that the structures of [Me₃NCH₂CH₂NMe₂]₂[Si₆Cl₁₄] (monoclinic, <i>P</i>2₁/<i>n</i>) and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] (monoclinic, <i>P</i>2₁/<i>n</i>) contain dianions adopting an “inverse sandwich” structure with inverse polarity and [Me₃NCH₂CH₂NMe₂]⁺ as countercations. Single crystals of SiCl₄·TMEDA (monoclinic, <i>Cc</i>) could be isolated by thermolysis reaction of Cl₃SiSiCl₃·TMEDA (50 °C) in tetrahydrofuran (THF)

Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl₃SiSiCl₃

The addition compound Cl₃SiSiCl₃·TMEDA was formed quantitatively by treatment of Cl₃SiSiCl₃ with tetramethylethylenediamine (TMEDA) in pentane at room temperature. The crystal structure of Cl₃SiSiCl₃·TMEDA displays one tetrahedrally and one octahedrally bonded Si atom (monoclinic, <i>P</i>2₁/<i>n</i>). ²⁹Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the <i>meridional</i> isomer of Cl₃SiSiCl₃·TMEDA is 6.3 kcal lower in energy than that of <i>facial</i> coordinate species. Dissolving of Cl₃SiSiCl₃·TMEDA in CH₂Cl₂ resulted in an immediate reaction by which oligochlorosilanes Si_<i>n</i>Cl_2<i>n</i> (<i>n</i> = 4, 6, 8, 10; precipitate) and the Cl^–-complexed dianions [Si_<i>n</i>Cl_2<i>n</i>+2]^2– (<i>n</i> = 6, 8, 10, 12; CH₂Cl₂ extract) were formed. The constitutions of these compounds were confirmed by MALDI mass spectrometry. Additionally, single crystals of [Me₃NCH₂CH₂NMe₂]₂[Si₆Cl₁₄] and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] were obtained from the CH₂Cl₂ extract. We found that Cl₃SiSiCl₃·TMEDA reacts with MeCl, forming MeSiCl₃ and the products that had been formed in the reaction of Cl₃SiSiCl₃·TMEDA with CH₂Cl₂. X-ray structure analysis indicates that the structures of [Me₃NCH₂CH₂NMe₂]₂[Si₆Cl₁₄] (monoclinic, <i>P</i>2₁/<i>n</i>) and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] (monoclinic, <i>P</i>2₁/<i>n</i>) contain dianions adopting an “inverse sandwich” structure with inverse polarity and [Me₃NCH₂CH₂NMe₂]⁺ as countercations. Single crystals of SiCl₄·TMEDA (monoclinic, <i>Cc</i>) could be isolated by thermolysis reaction of Cl₃SiSiCl₃·TMEDA (50 °C) in tetrahydrofuran (THF)

Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl₃SiSiCl₃

The addition compound Cl₃SiSiCl₃·TMEDA was formed quantitatively by treatment of Cl₃SiSiCl₃ with tetramethylethylenediamine (TMEDA) in pentane at room temperature. The crystal structure of Cl₃SiSiCl₃·TMEDA displays one tetrahedrally and one octahedrally bonded Si atom (monoclinic, <i>P</i>2₁/<i>n</i>). ²⁹Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the <i>meridional</i> isomer of Cl₃SiSiCl₃·TMEDA is 6.3 kcal lower in energy than that of <i>facial</i> coordinate species. Dissolving of Cl₃SiSiCl₃·TMEDA in CH₂Cl₂ resulted in an immediate reaction by which oligochlorosilanes Si_<i>n</i>Cl_2<i>n</i> (<i>n</i> = 4, 6, 8, 10; precipitate) and the Cl^–-complexed dianions [Si_<i>n</i>Cl_2<i>n</i>+2]^2– (<i>n</i> = 6, 8, 10, 12; CH₂Cl₂ extract) were formed. The constitutions of these compounds were confirmed by MALDI mass spectrometry. Additionally, single crystals of [Me₃NCH₂CH₂NMe₂]₂[Si₆Cl₁₄] and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] were obtained from the CH₂Cl₂ extract. We found that Cl₃SiSiCl₃·TMEDA reacts with MeCl, forming MeSiCl₃ and the products that had been formed in the reaction of Cl₃SiSiCl₃·TMEDA with CH₂Cl₂. X-ray structure analysis indicates that the structures of [Me₃NCH₂CH₂NMe₂]₂[Si₆Cl₁₄] (monoclinic, <i>P</i>2₁/<i>n</i>) and [Me₃NCH₂CH₂NMe₂]₂[Si₈Cl₁₈] (monoclinic, <i>P</i>2₁/<i>n</i>) contain dianions adopting an “inverse sandwich” structure with inverse polarity and [Me₃NCH₂CH₂NMe₂]⁺ as countercations. Single crystals of SiCl₄·TMEDA (monoclinic, <i>Cc</i>) could be isolated by thermolysis reaction of Cl₃SiSiCl₃·TMEDA (50 °C) in tetrahydrofuran (THF)