Nouvelles syntheses de Me2SiCl2 et Me3SiCl

Partial reduction of MeSiCl₃ and Me₂SiCl₂ using CaH₂ or (TiH₂)_n at high temperature (300°C) leads to MeSiHCl₂ and Me₂SiHCl, respectively, in good yields but in low proportion. In the presence of AlCl₃ as catalyst the reaction affords Me₂SiCl₂ and Me₃SiCl, in yields higher than those previously observed in the absence of a reducing agent. These redistribution reactions involve MeSiHCl₂ and Me₂SiHCl as intermediates. Consequently Me₂SiHCl with or without Me₂SiCl₂ and Alcl₃ deposited on carbon black as catalyst can undergo disproportionation to give Me₃SiCl.     

Functionalization and further crosslinking of the nicalon polycarbosilane based on its metalation with the n-butyllithium—postassium t-butoxide reagent

Reaction of the Nicalon polycarbosilane with the n-BuLi/Me₃COK reagent resulted in metalation of approximately one CH₂ group in four. Reaction of the metalated polymer with Me₂ (CH₂ = CH)SiCl gave a Me₂(CH₂ = CH)Si-substitued Nicalon polycarbosilane. The polymer was heated with different amounts of the [(MeSiH)_～0.8(MeSi)_～0.2]_n polysilane in the presence of azobisisobutyronitrile in refluxing benezene. Hydrosilylation by the Si? H-containing polysilane of the CH₂?CH groups of the Me₂(CH₂?CH) Si-substituted Nicalon polycarbosilane gave a new hybrid polymer (when appropriate quantities of reactant polymers were used) whose pyrolyis in a stream of argon to 1000°C left a ceramic residue in 77% yield whose elemental analysis indicated a nominal composition of 91% by weight SiC and 9% C.     

Kinetics of dichlorosilylene trapping by methane and mechanism and kinetics of the methyldichlorosilane decomposition

Data relative to methane trapping of SiCl₂ and a rate constant for the SiCl₂ into C(SINGLEBOND)H bond insertion process of k₋₁=13.4 M⁻¹s⁻¹ at 921 K are reported. Results on the decomposition of the trapping product, methyldichlorosilane, are also reported. This decomposition follows first-order kinetics with a rate constant of k=1.5±0.2×10⁻³ s⁻¹ at 905 K and produces methane, trichlorosilane, methyltrichlorosilane, and tetrachlorosilane. It is argued that the decomposition involves silylene intermediates, is nonchain, and is initiated primarily by the molecular methane elimination process MeSiHCl₂(SINGLEBOND)1→ CH⁴+SiCl₂. Free radicals and Si(SINGLEBOND)C bond fission may also contribute to the decomposition but are not dominant. The kinetics of MeSiHCl₂ decomposition are shown to be consistent with the kinetics of the reverse SiCl₂/CH₄ trapping reaction and with the overall reaction thermochemistry. Reaction modeling gives product yields, reactant conversions, and rates in reasonable agreement with the data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 89–97, 1998.     

Escaping the Tyranny of Carbothermal Reduction: Fumed Silica from Sustainable,Green Sources without First Having to Make SiCl4

Fumed silica is produced in 1000 tons per year quantities by combusting SiCl₄ in H₂/O₂ flames. Given that both SiCl₄ and combustion byproduct HCl are corrosive, toxic and polluting, this route to fumed silica requires extensive safeguards that may be obviated if an alternate route were found. Silica, including rice hull ash (RHA) can be directly depolymerized using hindered diols to generate distillable spirocyclic alkoxysilanes or Si(OEt)₄. We report here the use of liquid‐feed flame spray pyrolysis (LF‐FSP) to combust the aforementioned precursors to produce fumed silica very similar to SiCl₄‐derived products. The resulting powders are amorphous, necked, <50 nm average particle sizes, with specific surface areas (SSAs) of 140–230 m² g^?1. The LF‐FSP approach does not require the containment constraints of the SiCl₄ process and given that the RHA silica source is produced in million ton per year quantities worldwide, the reported approach represents a sustainable, green and potentially lower‐cost alternative.     

The stable silylene Si[(NCH2Bu)2C6H4-1,2]: Reactions with Group 14 element halides

Reaction of the thermally stable silylene Si[(NCH₂Bu^t)₂C₆H₄-1,2] (1) [abbrev. as Si(NN)] with SiX₄ (X = Cl or Br) afforded the disilanes (NN)SiX(SiX₃) and [(NN)SiX]₂ (X = Br only), the trisilane (NN)SiX-[(SiX₃)Si(NN)] and the monosilane (NN)SiX₂ (X = Br only), whereas treatment of 1 with MCl₄ (M = Ge or Sn) yielded (NN)SiCl₂ and MCl₂. [(NN)SiBr]₂ and (NN)SiBr₂ were also obtained by reaction of 1 with Br₂. Reaction of 1 with PhSiCl₃ yielded the disilane (NN)SiCl(SiCl₂Ph) and trisilane [(NN)SiCl]₂SiClPh, whereas the disilane (NN)SiCl(SiCl₂Me) was obtained with MeSiCl₃. The trisilane (NN)SiCl-[(SiCl₃)Si(NN)] was thermally labile and converted to [(NN)SiCl]₂SiCl₂.     

Poly(dimethylsilylene-co-diphenylsilylene)

In this work several polyorganosilylenes were synthesized including homo-and copolymers containing SiMe₂ and SiPh₂ units. A Wurtz-type coupling reaction of the respective dichlorodiorganosilanes with sodium metal, varying the Ph₂SiCl₂/Me₂SiCl₂ ratio was the chosen synthesis method. Products with different characteristics for solubility, structure (cyclic or linear), composition, and molecular weight distribution could be obtained depending on the comonomer ratios employed. The polysilane derivatives were characterized by infrared spectroscopy (IR), proton nuclear magnetic resonance (¹H-NMR), and gel permeation chromatography (GPC). Valuable information related to the comonomers' reactivities was obtained, such as molecular weight distribution, composition, and relationships between yields of soluble, insoluble, and cyclic materials of each polycondensation reaction. © 1992 John Wiley & Sons, Inc.     

The Weakly Coordinating Tris(trichlorosilyl)silyl Anion

Closely following the procedure for the preparation of the base‐stabilized dichlorosilylene complex NHC^Dipp⋅SiCl₂ reported by Roesky, Stalke, and co‐workers (Angew. Chem. Int. Ed . 2009 , 48 , 5683–5686), a few crystals of the salt [NHC^Dipp−H⋅⋅⋅Cl⋅⋅⋅H−NHC^Dipp]Si(SiCl₃)₃ were isolated, aside from the reported byproduct [NHC^Dipp−H⁺⋅⋅⋅Cl⁻], and characterized by X‐ray crystallography (NHC^Dipp=N,N‐di(2,6‐diisopropylphenyl)imidazo‐2‐ylidene). They contain the weakly coordinating anion Si(SiCl₃)₃⁻, which was also obtained in high yields upon deprotonation of the conjugate Brønsted acid HSi(SiCl₃)₃ with NHC^Dipp or PMP (PMP=1,2,2,6,6‐pentamethylpiperidine). The acidity of HSi(SiCl₃)₃ was estimated by DFT calculations to be substantially higher than those of other H‐silanes. Further DFT studies on the electronic structure of Si(SiCl₃)₃⁻, including the electrostatic potential and the electron localizability, confirmed its low basicity and nucleophilicity compared with other silyl anions.     

Synthesis and electrochemical behavior of linear oligo(ferrocenylsilane) and hyperbranched poly(ferrocenylsilane)

Linear oligo(ferrocenylsilane) and hyperbranched poly(ferrocenylsilane) (LOFS and HPFS) were synthesized by polycondensation of 1,1′‐dilithioferrocene (FcLi₂) with dimethyldichlorosilane (Me₂SiCl₂) and FcLi₂ with methyltrichlorosilane (MeSiCl₃) in THF under different conditions, respectively. The electrochemical behaviors of LOFS and HPFS in different solvents, such as THF, CH₂Cl₂, and CHCl₃, were investigated systematically by means of cyclic voltammetry (CV). The influences of the solvent, structure of polymer, and scan rate on electrochemical behavior of poly(ferrocenylsilane) solutions are discussed. It is found that ΔE_1/2 decreases with the fall of solvent polarity apart from the solvent donor effect and increases with the increase of the acceptor number (AN) of the solvent. More interestingly, the structure of polymer imposes greatly on the interaction between ferrocene units. According to the result, the mechanism of stepwise oxidation of the ferrocene units was proposed, that is, the different conformations of polymers, attaching to electrode surface, before and after oxidized resulted in the stepwise oxidation of ferrocene groups along a chain. Kinetic parameters from CVs indicate that the electrode processes are controlled by both the electrode reaction and mass diffusion and the electrochemical irreversibility of poly(ferrocenylsilane) solutions may be ascribed to the lower electron exchange efficiency on the electrode surface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2880–2889, 2007     

Synthese der Silatetraphospholane (tBuP)4SiMe2, (tBuP)4SiCl2 und (tBuP)4Si(Cl)SiCl3 Molekül- und Kristallstruktur von (tBuP)4SiCl2

Synthesis of the Silatetraphospholanes (tBuP)₄SiMe₂, (tBuP)₄SiCl₂, and (tBuP)₄Si(Cl)SiCl₃ Molecular and Crystal Structure of (tBuP)₄SiCl₂ The reaction of the diphosphide K₂[(tBuP)₄] 7 with the halogenosilanes Me₂SiCl₂, SiCl₄ or Si₂Cl₆ in a molar ratio of 1:1 leads via a [4 + 1]-cyclocondensation reaction to the silatetraphospholanes (tBuP)₄SiMe₂ 1,1-dimethyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 1 , (tBuP)₄SiCl₂, 1,1-dichloro-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 2 , and (tBuP)₄Si(Cl)SiCl₃, 1-chloro-1-trichlorsilyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 3 , respectively, with the 5-membered P₄Si ring system. The reaction leading to 1 is accompanied with the formation of the by-product Me₂(Cl)-Si–(tBuP)₄–Si(Cl)Me₂ 1a (5:1), which has a chain structure. On warming to 100°C 1a decomposes to 1 and Me₂SiCl₂. The compounds 2 and 3 do not react further with an excess of 7 due to strong steric shielding of the ring Si atoms by the t-butyl groups. 1, 2 and 3 could be obtained in a pure form and characterized NMR spectroscopically; 2 was also characterized by a single crystal structure analysis. 1a was identified by NMR spectroscopy only.     

Etude de la metallation de l'oxyde de diferrocenyl phenyl phosphine

The reaction of n-BuLi with phenyldiferrocenylphosphine oxide yields a mixture of two isomeric dianions. This mixture reacts with Me₃SiCl, Br₂, CO₂, PhCHO and PhCHNPh to give bifunctional products. With CoCl₂, Me₂SiCl₂, Ph₂SiCl₂, Bu₂SnCl₂ and PhCOOEt, the same mixture gives cyclic products. In almost every case each of these compounds is a mixture of two isomers corresponding to the original compound. The characteristic patterns of the PMR spectra are in full agreement with the structures proposed for the isomeric dianions.     

The hydrosilylation of propylene

The reactions of separate and competitive hydrosilylation of propylene with HSiCl₃, MeSiHCl₂, Me₂SiHCl, and MePh₂SiH in the presence of the Speier catalyst (SC) with different additives and a catalyst obtained from SC and propylene were studied. A mutual influence of the hydrosilanes in the competitive reactions was found. The influence of various additives to SC on the process was considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2048–2051, October, 1998.     

Dichlorosilylene and dichlorogermylene transfer to alkylidenephosphanes

The detection of Me₃GeSiCl₃, a product from the Si₂Cl₆ cleavage of trimethylgermylphosphanes, as a useful new source of SiCl₂ moieties, as well as new trapping reactions of SiCl₂ and GeCl₂ with functional alkylidenephosphanes (Me₃Si)₂CPX (X = halide or dialkylphosphanyl [PRR^′; R = i-propyl, R^′ = t-butyl]) are reviewed. In the primary step of the reactions, insertion into the P-X bond is competing with addition to the PC bond. SiCl₂ and GeCl₂ insertions are followed by dimerisation reactions leading to new highly functional P-phosphanylalkylidenephosphanes, that may rearrange to diphosphenes like (XCl₂Si)(Me₃Si)₂C-PP-C(SiMe₃)₂SiCl₂X (X = F, Cl, P-i-Pr₂) or (Cl₃Ge)(Me₃Si)₂C-PP-C(SiMe₃)₂GeCl₂PRR^′ or/and react further with SiCl₂ or GeCl₂. Reaction of (Me₃Si)₂CP-PRR^′ (R = i-propyl, R^′ = t-butyl) with Me₃GeSiCl₃ leads in a very selective fashion to a complete PC double bond cleavage by unique double SiCl₂ addition with formation of a stable P-phosphanylphosphadisiletane.     

New Cyclic and Polycyclic Ring Systems Containing Group 14 (Si,Ge, Sn) and 16 (S,Se, Te) Elements

The reactions of Me₂MCl₂ (M = Si, Ge, Sn), Si₂Me₄Cl₂, Si₂Me₂Cl₃, Si₂Me₂Cl₄ and CH₂(SiCl₂Me)₂, and suitable mixtures thereof, with H₂S / NEt₃ and Li₂E (E = Se, Te) have been investigated and lead to a variety of new group 14 chalcogenide systems.     

Chemical Vapor Deposition of Silicon Carbide and Silicon Nitride—Chemistry's Contribution to Modern Silicon Ceramics

Pure silicon carbide and silicon nitride have valuable properties in bulk pore-free form; however, their industrial exploitation has hardly been possible so far. Neither compound can be melted or sintered in pure form; hot pressing or sintering at normal pressure requires the presence of additives; and the reaction-sintering process in which only Si and C or Si and N are employed as additives affords porous materials.–The novel process of chemical vapor deposition has partly overcome the drawbacks of the previous methods. In the new process SiC is produced, e.g., by pyrolysis of CH₃SiCl₃, and Si₃N₄ by reaction of SiCl₄ with NH₃. This technique can also be used for pore filling in objects made of SiC and Si₃N₄ (gas phase impregnation) and for producing extremely fine SiC and Si₃N₄ (gas phase impregnation) and for producing extremely fine SiC and Si₃N₄ powder and SiC monofilaments suitable as components for SiC composites. Moreover, gas phase impregnation can also give fiber composites.     

Effect of chlorosilanes on the radical polymerization of styrene and methyl methacrylate

Styrene (St) and methyl methacrylate (MMA) were polymerized by azobisisobutyronitrile at 50°C. in the presence of silanes such as tetramethylsilane, trimethylcholorosilane, dimethyldichlorosilane, methyltrichlorosilane, and tetrachlorosilane. The polymerization rates of both St and MMA in the presence of silanes were nearly equal to those in the absence of silanes. On the other hand, the molecular weights decreased gradually as the concentration of chlorosilane increased. The chain transfer constants of all the silanes in the polymerization of St and MMA at 50°C. were calculated by Mayo's equation. The chain transfer constants of Me₄Si, Me₃SiCl, Me₂SiCl, MeSiCl₃, and SiCl₄ were 0.31 × 10^?3, 1.25 × 10^?3, 1.78 × 10^?3, 1.92 × 10^?3, and 2.0 × 10^?3, for St and 0.13 × 10^?3, 0.22 × 10^?3, 0.245 × 10^?3, 0.27 × 10^?3, and 0.30 × 10^?3, for MMA, respectively. From these results, it was found that the Si? Cl bond was radically cleaved. The Q_tr values of the silanes, in the same order as above, were found to be 1.03 × 10^?4, 2.33 × 10^?4, 2.83 × 10^?4, 3.10 × 10^?4, and 3.35 × 10^?4, respectively and the e_tr values were +0.58, +1.30, +1.50, +1.48, and +1.43, respectively.     

Pyrolytic conversion of an Al?Si?N?C precursor prepared via hydrosilylation between [Me(H)SiNH]4 and [HAlN(allyl)]m[HAlN(ethyl)]n

An iminoalane‐silazane polymer (ISP), an Al? Si? N? C precursor, has been synthesized via Pt‐catalyzed hydrosilylation between poly(allyl iminoalane‐co‐ethyl iminoalane) {[HAlN(allyl)]_m[HAlN (ethyl)]_n, AE‐alane} and 1,3,5,7‐tetrahydro‐1,3,5,7‐tetramethylcyclotetrasilazane {[Me(H)SiNH]₄, TCS}. The IR and ¹H NMR spectra of ISP indicate that the relative amounts of the allyl groups decrease slightly in comparison with those of AE‐alane, suggesting that hydrosilylation occurs partially. TG analysis up to 900 °C reveals that the ceramic yield of ISP is 83.1 mass%. It is suggested that the high ceramic yield can be ascribed to cross‐linking reactions occurring during pyrolysis. Possible reactions during pyrolysis are hydrosilylation, polymerization of the C?C bonds in the allyl groups and dehydrocoupling among the SiH groups, NH groups and AlH groups in ISP. The pyrolyzed residue at 1700 °C contains crystalline AlN, 2H‐SiC, β‐SiC and β‐Si₃N₄ and amorphous carbon, as revealed by solid‐state nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy and X‐ray diffraction (XRD) analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

The Diels—Alder reaction in organometallic chemistry VI. Diels—Alder reactions of α-pyrone with group IV element-substituted acetylenes

The Diels—Alder reactions of α-pyrone with Me₃SiCCSiMe₃, Me₃SiCCSiMe₂H, Me₂HSiCCSiMe₂H, Me₃GeCCGeMe₃, Me₃SiCCGeMe₃, Me₃SiCCSnMe₃ and EtCCEt were examined. All except the first two acetylenes gave the expected 1,2-disubstituted benzene product, in line with results obtained previously with Me₃SnCCSnMe₃. The first two acetylenes, Me₃SiCCSiMe₃ and Me₃SiCCSiMe₂H, also yielded benzene products containing substantial amounts of the 1,3-disubstituted benzenes, as well as minor amounts of the 1,4-isomers. This formation of unexpected isomers during these reactions was shown to result from acid-catalyzed rearrangement of the initially formed 1,2-disubstituted products, 1,2-(Me₃Si)₂C₆H₄ and 1-Me₃Si-2-Me₂HSiC₆H₄. The acidic impurities arose from pyrolysis of the bromobenzene solvent used or were introduced as contaminants of the α-pyrone. Such isomerizations were inhibited by addition of small amounts of triethylamine. The fact that no rearrangement took place with the other acetylenes is due to the scavenging of acidic impurities which might cause isomerization by the starting acetylene and the benzene product via metal—carbon bond cleavage processes.     

Diselenastanna‐, ‐sila‐ and ‐carbacycles with an annelated dicarba‐closo‐dodecaborane(12) unit

The reactions of the 1,2‐diselenolato‐1,2‐dicarba‐closo‐dodecaborane(12) dianion 1 with diorganoelement(IV) dichlorides (Ph₂CCl₂, Me₂SiCl₂, Ph₂SiCl₂, Me₂SnCl₂, Ph₂SnCl₂) gave novel five‐member heterocycles along with other products. The molecular structures of the five‐member rings containing CPh₂ ( 2 ) and SnPh₂ ( 9 ) moieties between the selenium atoms were determined by X‐ray analyses. In the case of the chlorosilanes, the analogous five‐member ring containing the SiPh₂ unit ( 4 ) could be identified in mixtures. The expected reaction was accompanied by rearrangement leading to formation of another five‐member ring 6 containing the Ph₂Si? Se? Se moiety. Oxidative addition of the five‐member heterocycles containing tin ( 7, 9 ) to ethene‐bis(triphenylphosphane)platinum(0) gave at low temperature the bis(triphenylphosphane)platinum(II) complexes 12 and 13 , where the Pt(PPh₃)₂ fragment had been inserted into one of the Sn? Se bonds. Extensive decomposition of these complexes was observed above ? 20 °C. The proposed solution‐state structures of the new compounds are supported by multinuclear magnetic resonance data (¹H, ¹¹B, ¹³C, ²⁹Si, ³¹P, ⁷⁷Se, ¹¹⁹Sn and ¹⁹⁵Pt NMR). Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and Reactions of P-Rich Silylphosphanes

Abstract

The formation of P-rich compounds like (Me₃Si)₃P₇ 1 and P₄(SiMe₂)₃ 2 generated from Na/K-alloy, white phosphorus, Me₃SiCl and Me₂SiCl₂, resp., or the formation of 1 from P₄, lithiumalkyles and Me₃SiCl on the other hand occurs in several reaction steps₁.     

Bildung siliciumorganischer Verbindungen. 110. Reaktionen von (Cl3Si)2CCl2, seiner Si-methylierten Derivate,von (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me und Me2CCl2 mit Silicium (Cu-Kat.)

Formation of Organosilicon Compounds. 110. Reactions of (Cl₃Si)₂CCl₂ and its Si-methylated Derivatives as well as of (Cl₃Si)₂CHCl, (Cl₃Si)₂C(Cl)Me and Me₂CCl₂ with Silicon (Cu cat.) The reactions of (Cl₃Si)₂CCl₂ 1 , its Si-methylated derivatives (Me₃Si)₂CCl₂ 8 , Me₃Si? CCl₂? SiMe₂Cl 9 , (ClMe₂Si)₂CCl₂ 10 , Me₃Si? CCl₂? SiMeCl₂ 11 , Cl₂MeSi? CCl₂? SiCl₃ 12 as well as of (Cl₃Si)₂CHCl 38 , (Cl₃Si)₂CClMe 39 and of Me₂CCl₂ with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl₃Si)₂CCl₂ 1 yields C(SiCl₃)₄ 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si₆C₂Cl₁₆ 3 and the related C-spiro linked disilacyclobutanes Si₈C₃Cl₂₀ 4 , Si₁₀C₄Cl₂₄ 5 , Si₁₂C₅Cl₂₈ 6 , Si₁₄C₆Cl₃₂ 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl₂MeSi? CCl₂? SiCl₃ 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si₆C₂Cl₁₅Me 34 and cis- and trans Si₆C₂Cl₁₄Me₂ 35 as well as the spiro-linked disilacyclobutanes Si₈C₃Cl₁₉Me 36 , Si₈C₃Cl₁₈Me₂ 37 . (Cl₃Si)₂CHCl 38 mainly yields HC(SiCl₃)₃ 31 and also the disilacyclobutanes cis- and trans-(Cl₃Si)HC(SiCl₂)₂CH(SiCl₃) 41 and (Cl₃Si)₂C(SiCl₂)₂CH(SiCl₃) 45 the 1,3,5-trisilacyclohexane [Cl₃Si(H)C? SiCl₂]₃ 44 as well as [(Cl₃Si)₂CH]₂SiCl₂, and (Cl₃Si)₂CClMe 39 mainly yields (Cl₃Si)₂C?CH₂and (Cl₃Si)₂besides of HC(SiCl₃)₃, MeC(SiCl₃)₃and (Cl₃Si)₃C? SiCl₂Me.,. Me₂CCl₂ 59 mainly yields Me(Cl)C?CH₂, Me₂CHCl and HCl₂Si? CMe₂? SiCl₃, besides of Me₂C(SiCl₃)₂ and Me₂C(SiCl₂H)₂ Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: α_Si = 94,2°> 85,8° = α_C.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: α_Si = 93,9°> 84,4° = α_C are comparable to those of compound 3.