Bildung siliciumorganischer Verbindungen. 96. Bildung und Struktur von P-Yliden des 1,3,5-Trisilacyclohexans (Einfluß der Substituenten)

Formation of Organosilicon Compounds. 96. Preparation and Structure of P-Ylides of the 1,3,5-Trisilahexanes (Influence of the Substituents) The influence of the substituents at the silicon atoms on formation and structure of ylides of 1,3,5-trisilacyclohexanesis investigated. The reactions of 1 , 2 , 3 with Me₃Si? PMe₂ lead via cleavage of the Si? P bond and subsequent rearrangement to the ylides 4 , 5 and 6 . The x-ray structure determination reveals, that the atoms of the ylid part of 4 are in a plane with the shortened bond distances d(C? P) = 168.6 pm and d(Si? C) = 180.1 pm, whereas the other endocyclic Si? C distances remain nearly unaffected by the ylid formation. Only the endocyclic bond angles C? Si? C of the Si atoms of the ylid are enlarged (116°). In the molecule 6 d(C? P) = 164.6 pm is much shorter, but d(P? Br) = 236.6 pm is enlarged. This enlargement is coupled with a deviation of 17 pm for the ylidic C atom from the ylid plane. Distances and angles are normal in the methylated trisilnhexane. The ring in 6 has boat conformation, in 4 a flat chair conformation.     

Bildung siliciumorganischer Verbindungen. 112. Über den Einfluß der Reaktionsbedingungen auf die Umsetzung von (Cl3Si)2CCl2 mit Silicium. Die Struktur von 2,2,3,3,5,5,6,6-Octachlor-1,4-bis(trichlorsilyl)-2,3,5,6-tetrasilabicyclo[2.1.1]hexan und 1,1,3,4,6,6-Hexakis(trichlorsilyl)hexatetraen

Formation of Organosilicon Compounds. 112. The Influence of Reaction Conditions on the Reaction of (Cl₃Si)₂CCl₂ with Silicon. The Structures of 2,2,3,3,5,5,6,6-Octachloro-1,4-bis(trichlorosilyl)-2,3,5,6-tetrasilabicyclo[2.1.1]-hexane and 1,1,3,4,6,6-Hexakis(trichlorosilyl)hexatetraene While reactions of (Cl₃Si)₂CCl₂ 1 with Si(Cu) in a fluid bed at 320°C exclusively yield products by silylation of the CCl₂ group in 1 does the reaction in a stirred bed preferrably give rize to chlorosilanes containing C? C double and triple bonds. Compounds 5, 6, 7, 8 and 9 in Tab. 1 belong to the first group, whereas 3 and 4 belong to the second one. The reaction of 1 with elemental copper under dehalogenation at carbon produces 3, 4 and 11 . In the reaction of 1 with CaSi₂ no additional Si? C bonds are formed, exclusively chlorosilanes with multiple C? C bonds as 3, 4 and 10 were found besides of SiCl₄. The bicyclo[2.1.1]hexane 6 (Tab. 1) crystallizes monoclinically in the space group C2/c (no. 15) with a = 1557.8, b = 857.4, c = 1727.3 pm, β = 104.34° und Z = 4 molecules per unit cell; the hexatetraene 10 (Tab. 1) crystallizes monoclinically in the space group C2/m (no. 12) with a = 1189.6, b = 1433.8, c = 983.5 pm, β = 98.75° pm, and Z = 2 molecules per unit cell. The skeleton of 6 is a system of high bond stress with 2-C₂ symmetry. The strongly folded (138.8°) four-membered ring (sum of angles = 344.2°) and the presence of both a Si? Si bond length of 238.2 pm and a Si? Si non-bonding distance of 255.1 pm are remarkable aspects of this feature. The mean bond lengths in the bicyclic compound were found to be d(Si? C) = 190.9 pm and d(Si? C) = 185.1 pm for exo- and endocyclic bonds, respectively. The skeleton of 10 is of the symmetry 2/m-C_2h. The six-membered chain is plane. The central C? C single bond length and the mean distance of the cumulated double bonds are 148.6 pm and 130.5 pm, respectively.     

Bildung siliciumorganischer Verbindungen. 94. Die Kristallstruktur des Hexaphenyltrisilacyclohexans Si3C39H36

Formation of Organosilicon Compounds. 94. Crystal Structure of Hexaphenyltrisilacyclohexane Si₃C₃₉H₃₆ 1.1.3.3.5.5-Hexaphenyl-1.3.5-trisilacyclohexane crystallizes monoclinically in the space group P2₁/n (No. 14) with a = 1718.3 pm, b = 1769.2 pm, c = 1091.4 pm, β = 90.72° and Z = 4 molecules per unit cell. The trisilacyclohexane sceleton is present in a flattened twist boat conformation with mean bond angles of 110.0° at the Si atoms and 117.9° at the C atoms, respectively. The mean bond lengths are d(Si? C) = 187.1 pm in the six membered ring and 187.9 pm to the substituents.     

Bildung und Struktur des iso-Tetraphosphans P[P(SiMe3)Me]3

Formation and Structure of iso-Tetraphosphane P[P(SiMe₃)Me]₃ The reaction of MeP(SiMe₃)₂ with PCl₃ (molar ratio 3:1, ?78°C, n-pentane) yields by cleaving of the P? Si bond P[P(SiMe₃)Me]₃ 1 with Cl₂P? P(SiMe₃)Me and ClP[P(SiMe₃)Me]₂ as intermediates. The reaction rate decreases by the increase of phosphorylation. The last reaction step (formation of 1 ) occurs while warming up to room temperature. 1 forms colorless hexagonal crystals, melting point 65 ± 1°C. Tris(trimethylsilyl-methyl-phosphino)phosphane 1 crystallizes monoclinically in the space group Cc (No. 8) with Z = 8 formula units per unit cell. The molecules possess approximated C₃ symmetry and have (RRR) and (SSS) configurations, respectively. The bond distances d?(P? P) = 220.1 pm, d?(P? C) = 186.5 pm, and d?(P? Si) = 225.2 pm are normal and within the expected range of known distances. According to repulsive interactions between the non bonded electron pairs of the terminal P atoms and the protons of the methyl groups the angles at the central and terminal P atoms are enlarged to ? P P P = 105.1° and ? P P C = 106.9°, respectively.     

Bildung siliciumorganischer Verbindungen. 83. Bildung,Reaktionen und Struktur von Yliden aus perchlorierten Carbosilanen

Formation of Organosilicon Compounds. 83. Formation, Reactions, and Structure of Ylides Generated from Perchlorinated Carbosilanes The CCl-moiety in perchlorinated carbosilanes as (Cl₃Si)₂ a, Cl₃Si? CH₂? SiCl₂? CCl₂? SiCl₃ b, (Cl₃Si? CCl₂)₂SiCl₂ c or (Cl₂Si? CCl₂)₃ d, e.g., cleaves the Si? P bond of me₃Si? Pme₂ e (me = CH₃); and by subsequent rearrangement ylides are formed. Such, treating e with a yields (Cl₃Si)₂CPme₂Cl 1, which also results from the reaction of me₂P? Pme₂ with a. The ylides also can be obtained by means of treating the carbosilanes a, b, c or d with LiPme₂. Thus, c with one mole of LiPme₂ yields Cl₃Si? CCl₂? SiCl₂? C(Pme₂Cl)? SiCl₃ or Cl₃Si? C(Pme₂Cl)? SiCl₂? C(Pme₂Cl)? SiCl₃, resp., with two moles of LiPme₂. The corresponding Si-methylated derivates do not form ylides; (me₃Si)₂CCl₂, e.g., with e in benzene yields me₃Si? CH(Pme₂)? Sime₃. One mole of Lime methylates 1 to yield (Cl₃Si)₂CPme₃ 11. With either LiPme₂, me₃Si? Pme₂ or Me₂P? Pme₂ 1 forms (Cl₃Si)₂CPme₂-Pme₂. Reacting 1 with CH₃OH/(C₂H₅)₂NH, (Cl₃Si)[SiCl₂(OCH₃)]CPme₂(OCH₃) is formed. Ylides also result from the reactions of partially C-chlorinated 1,1,3,3,5,5-hexachloro-1,3,5-trisilacyclohexanes with me₃Si? Pme₂, (Cl₂Si? CCl₂)₃ with three moles of me₃Si? Pme₂ or LiPme₂, resp., yields (Cl₂Si? CPme₂Cl)₃ 16, the 1,1,3,3,5,5-Hexachlor-2,4,6-tris(chlordimethylphosphoranyliden)-1,3,5-trisilacyclohexan, which crystallizes with one mole of monoglyme. X-ray structure determinations revealed that 1, 11 and 16 are planar. As well the (P? C) as the (Si? C) bond lengths are remarkably shortened; in 1 (P? C) to 173.3 pm, (Si? C) to 173.3 pm, (Si? C) to 179.5 pm, in 16 (P? C) to 168.7 pm, (Si? C) to 180 pm. The (Si? C) and (P? C) bond orders amount to about 1.33, and are relatively equally distributed. Therefore, the charge of the formal carbanion is equally distributed, which shall be expressed by means of the following kind of writing for 1 and 16 see “Inhaltsübersicht”.     

Bildung Siliciumorganischer Verbindungen. 103. Bildung und Struktur von cis- und trans-2,4-Dichloro-2,4-bis(trimethyl-silyl)-1,1,3,3-tetramethyl-1,3-disilacyclobutan

Formation of Organosilicon Compounds. 103. Formation and Structure of cis and trans 2,4-Dichloro-2,4-bis(trimethylsilyl)-1,1,3,3-tetramethyl-1,3-disilacyclobutane The reaction of Me₃Si? CCl₂? SiMe₂Cl with LiBu in THF yields 1,1,3,3-Tetramethyl-2,4-bis(trimethylsilyl) 1,3-disilabicyclo[1.1.0]butane. The product of the first reaction stage is Me₃Si? CCl(Li)-SiMe₂Cl. The 1,3-Disilacyclobutane 2 and 3 were isolated, when Me₃Si? CCl₂? SiMe₂Cl was treated with LiBu in Et₂O. This way the proof is given that 2 and 3 are intermediates of the formation of product 1 . The further products are 4 and 5 (CCl in 2 and 3 substituted by CH) and Me₃Si? CH₂? C(SiMeCl)₂SiMe₃. 2 crystallizes orthorhombically in the space group Fdd 2 (no. 43) with a = 2149.1 pm, b = 2229.2 pm, c = 1763.6 pm and Z = 16 molecules per cell. The central ring of disilacyclobutane is slightly folded (17.9°). The configuration of the C-Atoms in this four membered ring gets closer to a sp² configuration built up by three Si? C bonds. The Cl-atoms approximately have orthogonal positions to these CSi₃ arrangements. The extension of the C? Cl bonds (184.6 pm) and the mutual approximations of the Cl-atoms in the cis-position indicate a high reactivity of the molecule.     

Bildung siliciumorganischer Verbindungen. 86. Si-phenylierte und butylierte 1,3,5-Trisilacyclohexane

Formation of Organosilicon Compounds. 86. Si-phenyl and Si-butyl Substituted 1,3,5-Trisilacyclohexanes By treating (BrHSi? CH₂)₃ with phMgBr or t-buLi, resp., and subsequent separation of the isomers, the pure cis-cis substituted 1,3,5-trisilacyclohexanes I are accessible which yield II (Formula see Inhaltsübersicht) by reaction with Br₂. (F₂Si? CH₂)₃ 8 can be transferred into (ph₂Si? CH₂)₃ 7 with phLi. With HCl/AlCl₃ 7 forms (Cl₂Si? CH₂)₃, whereas even with an excess of Br₂ it only yields (phBrSi? CH₂)₃. Cleavage of 7 with one equivalent of Br₂ yields (H₂C? Si)₃ph₅Br 14, which with LiAlH₄ forms (H₂C? Si)₃ph₅H 10. 10 is not so easy to obtain via (H₂C? Si)₃ph₅F 9 from the reaction of 8 with 5 equivalents of phLi. All of the SiH and SiBr groups in I and II, resp., occupy axial positions as well as the Br atom in 14 the H atom at Si in 10 and the F atom in 9.     

Bildung siliciumorganischer Verbindungen. 109. Reaktionen vollhydrierter Carbosilane mit Lithiumalkylen

Formation of Organosilicon Compounds. 109. Reactions of Perhydrogenated Carbosilanes with Alkyl-Lithium Compounds Si-hydrogenated linear carbosilanes react with MeLi or nBuLi to give the Si-alkylated derivatives. In contrast to the Si-methylated derivatives of (H₃Si? CH₂)₂SiH₂ 1 and (H₃Si)₂CH₂ 2 and to (Me₂Si? CH₂)₃ no lithiation of CH₂ groups is observed. Such, 1 with nBuLi yields nBuH₂Si? CH₂? SiH₂? CH₂? SiH₃ 5 and (nBuH₂Si? CH₂)₂SiH₂ 6 . 2 reacts with nBuLi to give nBuH₂Si? CH₂SiH₃ 7 and (nBuH₂Si)₂CH₂ 8 besides of 1, 5 und 6 . The latter results from a cleavage of a Si? C bond in 2 Producing nBuSiH₃ and LiCH₂? SiH₃ which combines with 2 to 1 . Subsequently 1 forms 5 and 6 . No higher alkylated derivatives of 1 or 2 could be detected.     

Bildung siliciumorganischer Verbindungen, 47. Die Kristall- und MolekülStruktur von 1,3,5,7- Tetramethyl-tetrasila-adamantan

Formation of organosilicon compounds. 47. The crystal land molecular structure of 1,3,5,7-tetramethyl-tetrasila-adamantan 1,3,5,7- Tetramethyl-tetrasila-adamantan, Si₄C₁₀H₂₄, is a pyrolysis product of Si(CH₃)₄. It crystallizes in the monoclinic space group P2₁/c with a = 8.859 Å, b = 9.844 Å, c = 18.316 Å, β = 91.04°, Z = 4. The molecule exhibits T_d-symmetry within the experimental error. The mean bond lengths Si? C are 1.889 Å and 1.866 Å for the Si? CH₃ and Si? CH₂ bonds respectively.     

Die Strukturen der Heptahetero-Nortricyclene P7(Sime3)3 und P4(Sime2)3

The Structures of the Heptahetero-Nortricyclenes P₇(Sime₃)₃ and P₄(Sime₂)₃ Tris(trimethylsilyl)heptaphospha-nortricyclene P₇(Sime₃)₃ 1 and Hexamethyl-trisila-tetraphospha-nortricyclene P₄Si₃me₆ 2 are structural analogons to the hetero-nortricyclenes P and P₄S₃. 1 crystallizes in the space group P2₁ with a = 965.7 pm, b = 1746.5 pm, c = 693.3 pm, β = 99.61° and Z = 2 formula units. In the P₇ system tge P? P bond lengths differ functionally, namely 221.4 pm in the three-membered ring, 219.2 pm at the ring atoms and 217.9 pm at the bridgehead atom. The P? Si and Si? C bond lengths are 228.8 pm and 187.8 pm respectively. 2 crystallizes in the space group R3 with a_R = 1129.3 pm, α_R = 50.01° (hexagonal axes: a = 954.7 pm, c = 2956.9 pm) and Z = 2 formula units. In the P₄Si₃ systems the bond lengths are P? P = 220.2 pm, P? Si = 228.3 pm and 224.7 pm (to the bridgehead atom). The Si? C bond lengths are 187.3 pm. The structures are discussed with related compounds.     

Bildung siliciumorganischer Verbindungen. 93 [1]. Untersuchungen zum Bildungsmechanismus cyclischer Carbosilane durch Einwirkung von AlBr3

Formation of Organosilicon Compounds. 93. Investigations of the Mechanism of the AlBr₃ Initiated Formation of Cyclic Carbosilanes. The mechanism of the formation of ringsystems in carbosilanes with AlBr₃ is investigated using the deuterium compounds 1a and 3a . The number of deuterium atoms in the methyl groups of the reaction products shows at which points of the molecules the regrouping occurs under formation of the ringsystem. In the first initially the reaction of 1a yields D₃C? Si(CH₃)₃ and 2a under separation of a CD₃ group. The rearrangement forming 2a occurs at the marked Si? C-bonds (formula 1a ). No Al-organic intermediate compound is observed under cleavage of Si? C bond. Therefore the formation of ring-systems is based on the polarisation by the Lewis-acid AlBr₃. Compound 3a reacts in an analogous way, what is shown by the isolation of Sime₄ and 4a . The cleavage of the bonds is marked in formula 3a . The reaction of 8 forming 9 and (Sime₃)₂CH₂ follows the same mechanism; it is investigated by ¹H and ²⁷Al-NMR spectroscopy.     

Bildung siliciumorganischer Verbindungen. LX. Die Kristall- und MolekülStruktur des Heptamethyl-tetrasila-[2,2,2]-barrelans Si4C11H28

Formation of Organosilicon Compounds. LX. Crystal and Molecular Structure of Heptamethyl-tetrasila-[2,2,2]-barrelan Si₄C₁₁H₂₈ 1,1,3,5,5,7,7-Heptamethyl-1,3,5,7-tetrasila-[2,2,2]-barrelan Si₄C₁₁H₂₈ crystallizes in the orthorhombic space group Pn2₁a with a = 12.293, b = 9.903, c = 14.018 Å and Z = 4 formula units. The six-membered rings have the skew-boat conformation with a torsion angle of 23.5° with respect to the molecular axis. The skew-boat conformation results from the interaction of CH₃- and CH₂- groups. The mean value for the bond length is Si? C = 1.881 Å. The distances Si? CH₂ = 1.873 Å are somewhat smaller than the others (1.887 Å).     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. XXX. Die Struktur des Tetra-t-butoxy-1,3,2,4-dithiadisiletans

Contributions to the Chemistry of Silicon-Sulfur Compounds. XXX. Structure of Tetra-t-butoxy-1,3,2,4-dithiadisiletane Alcoholysis of silicon disulfide by t-butanol yielded the title compound. [(t-BuO)₂SiS]₂ crystallizes orthorhombically in the space group Pbca (no. 61) with a = 1708.4(5), b = 1560.8(3), c = 907.1(3) pm and Z = 4 molecules per unit cell. The molecule has the crystallographic 1 –C_i point symmetry and consequently the Si₂S₂ four-membered ring is rigid plane. The bond distances of this ring are Si? S = 214.2 and 213.1 pm and the bond angles S? Si? S = 97.8° and Si? S? Si = 82.2°. Related details of the structure are discussed.     

Bildung siliciumorganischer Verbindungen. LVI. Reaktionen Si- und C-chlorierter 1,3,5-Trisilapentane mit CH3MgCl

Formation of Organosilicon Compounds. LVI. Reactions of Si- and C-Chlorinated 1,3,5-Trisilapentanes with CH₃MgCl (Cl₃Si? CCl₂)₂SiCl₂ (1) reacts with an excess of meMgCl (me = CH₃) forming me₃Si? C?C? Sime₃ (2), Sime₄, H₂C?C(Sime₃)[CH(Sime₃)₂] (3) as main products and (me₃Si)₂C? CH(Sime₃) and as by-products. The cleavage reaction of (1) to (2) and (3) does not occur when the meMgCl-concentration is lowered. The reaction is started by the formation of a GRIGNARD reagent at a CCl-group in compound (1). Cl₃Si? CCl₂? SiCl₂? CH₂? SiCl₃ forms with ; me₃Si? CCl₂? SiCl₂? CHCl? SiCl₃ forms (me₃Si)₂C?CH(Sime₃). A reaction sequence is given.     

Bildung siliciumorganischer Verbindungen. 95. Die Kristallstruktur eines Hexadecamethyl-octasila-dispiro-[5.1.5.1]-tetradecans,Si8C22H65

Formation of Organosilicon Compounds. 95. Crystal Structure of a Hexadecamethyloctasila-dispiro [5.1.5.1]tetradecane, Si₈C₂₂H₅₆ 1,1,3,3,5,5,7,7,9,9,11,11,13,13,14,14-Hexadecamethyl-1,3,5,7,9,11,13,14-octasila-dispiro[5.1.5.1]tetradecane crystallizes monoclinically in the space group P2₁/n (No. 14) with a = 1352.4 pm, b = 1215.5 pm, c = 1001.2 pm, β = 92.11° and Z = 2 molecules per unit cell. The dispiro system is formed by a central disilacyclobutane and two C-spiro connected trisilacyclohexane rings. The symmetry of the molecule is 2/m, with flattened six membered rings in chair conformation. The Si? C bonds are enlarged (192 pm) at the strained spiro region whereas the Si? C bonds are distinctly shortened (186 pm) at the opposite Si atoms in the six membered rings.     

Bildung siliciumorganischer Verbindungen. 84 [1]. Synthese und thermische Umlagerung von verschieden substituierten linearen und cyclischen Silanen

Formation of organosilicon compounds. 84. Synthesis and thermal rearrangement of some substituted linear and cyclic silanes In part IR we report on the synthesis of substituted silanes, and in part II on their thermal rearrangement. I: me₃i--Sime₃(me = CH₃) is formed by dropwise addition of THF to a suspension of Li powder in me₃SiCl; yield ～ 80%. The mixture me₃Si--Sime₂Cl, me₃SiCl, Li powder and THF reacts analogously to form me₂Si(Sime₃)₂; yield 80%. By the same type of reaction the following compounds are obtained: compound 1 from Brme₂Si? CH₂? Sime₂Br, 1 from Brme₂Si? CH₂? Sime₂Br, 2 from Brme₂Si? Sime₂? CH₂? Sime₂Br 16 and 3 from Bret₂Si? CH₂? CH₂? Siet₂Br (et = C₂H₅). 2 decomposes during its isolation from THF. 16 is formed from phme₂Si? Sime₂? CH₂? Sime₂ph 17 (ph = C₆H₅) by reaction with HBr, 17 either from phme₂SiLi and Clme₂SiCH₂Cl or from phme₂Si? Sime₂Br and LiCH₂? Sime₂ph. II: me₂Si(Sime₃)₂ rearranges at 440 °C (56 h) with insertion of the CH₂ group (Si? H formation) into the Si? Si bond and the formation of me₃Si? Sime₂? CH₂? Sime₂H, me₂HSi? CH₂? Sime₂? CH₂? SiHme₂, and me₃Si? CH₂? Sime? CH₂? Sime₂H. 1 reacts analogously. Methylated halogenated disilanes like Brme₂Si? Sime₂Br react with separation of: Sime₂ and its insertion into the Si-halogen bond to form trisilanes. Different from both are the phenylated derivatives, though phme₂Si? Sime₂ph still forms phme₂Si? Sime₂? Sime₂ph. 3 reacts with separation of C₂H₄, formation of the Si? H group and insertion of C₂H₄ into the Si? Si bond.     

Bildung siliciumorganischer Verbindungen. 108. Thermisch induzierte Reaktionen aminosubstituierter Disilane

Formation of Organosilicon Compounds. 108 [1]. Thermally Induced Reactions of Amino-Substituted Disilanes Thermally induced reactions of amino-substituted disilanes yield Si rich silanes. At 300°C, Me₃Si? SiMe₂? NMeH 1 yields Me₃Si? NMeH 2 and Me₃Si? (SiMe₂)₂-NMeH 3 in a ratio 1 : 2 : 3 = 1,6 : 1 : 1, whereas Me₃Si? SiMe₂? N(iPr)H 4 at 350°C yields Me₃Si? N(iPr)H 5 , Me₃Si? (SiMe₂)₂-N(iPr)H 6 and Me₃Si? (SiMe₂)₃? N(iPr)H 7 in a ratio of 4 : 6 : 7 = 0.8 : 1.0 : 0.6. Me₃Si? SiMe₂? NMe₂ 8 at 300°C (72 h) yields Me₃Si? NMe₂ 9 and Me₃Si-(SiMe₂)₂-NMe₂ 10 in a ratio of 9 : 8 : 10 = 1 : 0.22 : 0.44 The thermal stability of these disilanes is determined by the sterical requirements of the amino substituents NMeH < NMe₂ < N(iPr)H. The introduction of a second NMe₂ group decreases the stability and favours the formation of Si rich silanes. Such, Me₂N? (SiMe₂)₂? NMe₂ 11 already at 250°C (2 h) yields Me₂N? SiMe₂? NMe₂ 12 , Me₂N? (SiMe₂)₂? NMe₂ 13 and Me₂N? (SiMe₂)₄? NMe₂ 14 in a ratio of 11 : 13 : 14 = 0.3 : 0.9 : 1.0. The reactions can be understood as insertions of thermally produced dimethylsilylene into the Si? N bond of the disilanes. This process is strongly favoured as compared to the trapping reactions with Ph? C?C? Ph or Et₃SiH. The mentioned reactions correspond closely to those of the methoxy-disilanes[2]. However (MeN? SiMe₂? SiMe₂)₂ 15 , obtained from HMeN? (SiMe₂)₂? NMeH by condensation [3], at 400°C suffers a ring contraction to octymethyl-1,3-diaza-2,4,5-trisilacyclopentane (69 weight %), and yields also some solid residue, the composition of which corresponds to Si₃C₇NH₂₁.     

Zur Bildung und Struktur der Phosphinophosphiniden-phosphorane tBu2P?PP(Me)tBu2 1, tBu(Me3Si)P?PP(Me)tBu2 2 und tBu2P?PP(Br)tBu2 3

Synthesis and Structure of Phosphinophosphinidene-phosphoranes tBu₂P? P?P(Me)tBu₂ 1, tBu(Me₃Si)P? P?P(Me)tBu₂ 2, and tBu₂P? P?P(Br)tBu₂ 3 A new method for the synthesis of 1 and 2 (Formulae see ?Inhaltsübersicht”?) is reported based on the reaction of 5 with substitution reagents (Me₂SO₄ or CH₃Cl). The results of the X-ray structure determination of 1 and 2 are given and compared with those of 3 . While in 3 one P? P distance corresponds to a double bond and the other P? P distance to a single bond (difference 12.5 pm) the differences of the P? P distances in 1 and 2 are much smaller: 5.28 pm in 1 , 4.68 pm in 2 . Both 1 and 2 crystallize monoclinic in the space group P2₁/n (Z = 4). 2 additionally contains two disordered molecules of the solvent pentane in the unit cell. Parameters of 1 : a = 884.32(8) pm, b = 1 924.67(25) pm, c = 1 277.07(13) pm, β = 100.816(8)°, and of 2 : a = 1 101.93(12) pm, b = 1 712.46(18) pm, c = 1 395.81(12) pm, β = 111.159(7)°, all data collected at 143 K. The skeleton of the three P atoms is bent (PPP angle 100.95° for 1 , 100.29° for 2 and 105.77° for 3 ). Ab initio SCF calculations are used to discuss the bonding situation in the molecular skeleton of the three P atoms of 1 and 3 . The results show a significant contribution of the ionic structure R₂P? P(^?)? P(⁺)(X)R₂. The structure with (partially) charged P atoms is stabilized by bulky polarizable groups R (as tBu) as compared to the fully covalent structure R₂P? P(X)? PR₂.     

Bildung siliciumorganischer Verbindungen. LIX. Die Kristall- und MolekülStruktur des Dodecamethyl-heptasila-[4,4,4]-propellans Si7C19H48

Formation of Organosilicon Compounds. LIX. Crystal and Molecular Structure of Dodecamethyl-heptasila-[4,4,4]-propellan Si₇C₁₉H₄₈ 1,1,3,3,7,7,9,9,11,11,13,13-Dodecamethyl-1,3,5,7,9,11,13-heptasila-[4,4,4]-propellan Si₇C₁₉H₄₈ crystallizes in the monoclinic space group P2₁/c with a = 11.499, b = 11.411, c = 22.171 Å, β = 96.95° and Z = 4 formula units. The three independent six-membered rings of the molecule have the same skew-boat-conformation. Along the central Si? C? bond the mean value of the torsion angle within the six-membered rings is 19°. The mean value for the bond length is Si-C = 1.893 Å, but the bond length diminishes within the polycyclic system from the axial C-atom to the outer members of the rings (1.916; 1.880; 1.864 Å). The interatomic distances between CH₃- groups and from CH₃- groups to CH₂- groups shows the twisted conformation to be a result of the contacts between these groups.     

Bildung siliciumorganischer Verbindungen. LXI. Die Kristall- und MolekülStruktur des 1,1,3,3,5,5,7,7-Octamethyl-1,3,5,7-tetrasila-cyclooctans Si4C12H32

Formation of Organosilicon Compounds. LXI. Crystal and Molecular Structure of 1.1.3.3.5.5.7.7-Octamethyl-1.3.5.7-tetrasila-cyclooctane Si₄C₁₂H₃₂ Octamethyl-tetrasila-cyclooctan Si₄C₁₂H₃₂ crystallizes in the monoclinic space group C2 with a = 17.807, b = 6.121, c = 10.856 Å, β = 126.09° und 2 molecules in the unit cell. The molecule has a C₂-conformation which deviates slightly from C_2v symmetry. The mean Si? C bond length is 1.879 ± 0.011 Å. The mean Si? CH₂ bond length is greater than the Si? CH₃ bond length (1.897(15) Å and 1.861(10) Å respectively).