1,1,3,3-Tetramethyl-1,3-disilacyclobutane

Generation of ChIoro(lithiomethyl)dimethylsilane. Treatment of (bromomethyl)chlorodimethylsilane in THF/ether with 1 equiv of n-butyllithium in hexanes at — 120°C produces chloro (lithiomethyl)dimethylsilane. This lithiated derivative spontaneously eliminates LiCl to give an intermediate silaethylene species, which undergoes dimerization to afford 1,1,3,3-tetramethyl-1,3-disilacyclobutane (45%), together with a small amount of l,l,3,3,5,5-hexamethyl-l,3,5-trisilacyclohexane (15%) (eq9). ... 

The ROP of all known saturated SCHs proceeds via the rupture of endocyclic Si-C bonds. In the US patent issued in 1958, the first attempt was made to use a 4-membered SCH for the synthesis of heterochain PCSs [2]. From the late 1950s to the early 1980s, Vdovin and co-workers intensively investigated a new class of polymers - high-molecular-weight heterochain PCSs, prepared by the ROP of 4-membered SCHs - dimethyl-silacyclobutane (MSCB), tetramethyl-disilacyclobutane (DSCB) and their derivatives (see Sects. 1.1 and 1.2). The energy and structural characteristics of silacyclobutanes were analyzed in [3-10]. Though these publications are rather old, their results remain valid up to the present time. 

Ring-Opening Polymerization of Tetramethyl-Disilacyclobutanes Under the Action of Metal (Ag, Cu, Bi, etc.) Halides... 

This section deals with the most important control experiments to be considered when molecular complexes or NPs want to be proved as true catalysts. But in some cases both types of catalysts can be present in the same reaction. For example, in the ring opening polymerisation of l,l,3,3-tetramethyl-l,3-disilacyclobutane catalysed photo-chemically by Pt(acac)2, the co-existence of both homogeneous and colloidal catalytic species has been proved, giving each of them different type of polymers [10]. 

Tetramethyl-l,3-disilacyclobutane had been prepared earlier by Knoth and Lindsey [10], but a multistep synthesis was involved which was not generalizable to the synthesis of Si-functional 1,3-disilacyclobutanes. The reaction shown in eq. 4, provided it is carried out in the right way, represents a good, general route to 1,3-disilacyclobutanes. This reaction was reported first by Muller and his coworkers [11]. In this work, diethyl ether was used as reaction solvent and the product yield was only around 4%. Somewhat better yields were obtained" by Russian workers [12], but it was the detailed studies of the (chloromethyl)chlorosilane/ magnesium reaction by Kriner [13] which provided a good synthesis of... 

A more useful thermolytic polymerization which produces linear polysilmethylenes is that of 1,3-disilacyclobutanes carried out in the liquid phase. Such polymerization of l,l,3,3,-tetramethyl-l,3-disilacyclobutane was reported first by Knoth [17] (eq. 7). This process was studied in some detail by Russian workers [18]. l,l,3,3-Tetramethyl-l,3-disila-cyclobutane is more thermally stable than 1,1-dimethyl-l-silacyclobutane. 

Although the preparative cathodic reduction of halomethylsilanes has not been investigated extensively, Dunogues and coworkers revealed that the electrochemical reduction of (chloromethyl)dimethylchlorosilane with an aluminum cathode afforded polycarbosilanes [92]. l,1.3,3-Tetramethyl-l,3-disilacyclobutane is also formed under these condition (Scheme 43). 

Irradiation of l,l,3,3-tetramethyl-l,3-disilacyclobutane or 1,1-dimethylsilacyclobutane in the presence of Pt(acac)2 induces the same type of polymerization (acac = acetylacetonate Scheme 16) <1999MM6003, 1999CM3687>. 

An electron diffraction study of the molecular structure and a study of the inversion potential for 1,1,3,3-tetramethyl-l,3-disilacyclobutane have been published <1999JST135, 2000ZSK217>. 

Historically it was the gas-phase process which first unequivocally proved the existence of species with a 7rbond to silicon [Eq. (37)] (198). In the absence of nucleophiles, the dimethylsilene gives a head-to-tail dimerization product, l,l,3,3-tetramethyl-l,3-disilacyclobutane. On the other hand, addition products across the double bond of the intermediate silene are formed in the presence of various trapping agents. 

In sharp contrast to the silicon-carbon double-bonded intermediates of type A, which never afford any volatile products in the absence of a suitable substrate, intermediates of type E may undergo dimerization to give a head-to-tail dimer. Thus, when a solution of l-phenyl-2-vinyltetrameth-yldisilane in dry hexane is photolyzed, cis- and trans-1,1,3,3-tetramethyl-2,4-bis(dimethylphenylsilylmethyl)-l,3-disilacyclobutane can be obtained in 21 and 22% yield, respectively. 

Bromination of tris(dimethylsilyl)methane yielded HC(SiMe2Br)3 (core A). [12] Hydride precursors of carbosilane cores B and C tris[1,1,1-tri(dimethylsilyl)hexy 1-dimethylsilyl]methane HC[SiMe2(CH2)3C(SiMe2H)3]3 and 1,1,3,3-tetramethyl-2,2,4,4-tetrakis-(dimethylsilyl)-l,3-disilacyclobutane [SiMe2C(SiMe2H)j2 were also prepared utilizing HC(SiMe2H)3. 

Hawrelak EJ, Ladipo FT, Sata D, Braddock-Wilking J (1999) Synthesis, Characterization, and Reactivity of [LiC(SiMejH)3] 2THF Formation of 1,1,3,3-Tetramethyl-2,2,4,4-tetrakis(dimethylsilyl)-l,3-disilacyclobutane, [MejSiC(SiMejH)Jj. Organometallics 18 1804-1807... 

Again, the application of isoprene as the quenching substrate is less effective and only low yields of the expected silacyclohexenes were obtained. Slight variations of reaction conditions lead to the formation of additional products. For example, a small amount of the 1,3,5-trisilacyclohexane 3 can be detected within 12 h in addition to tetramethyl-l,3-disilacyclobutane as the main product if the reaction of Me2SiCl2 is carried out in THF at -78 C using lithium powder with a higher content of sodium (Eq.4). 

Direct photolysis of l,l,3,3-tetramethyl-l,3-disilacyclopentene (23) at 185 nm and 254 nm in deoxygenated pentane produces a ring contraction product l,l,3,3-tetramethyl-2-methylene-l,3-disilacyclobutane (24) and a cleavage product, 2,4,4-trimethyl-2,4-disilahex-5-yne (25) in absolute... 

Upon photoexcitation, either in the gas phase or as liquid, SiMe4 undergoes mainly two primary photoprocesses (6) and (7) ([Pg.212]

Several workers have studied the photochemistry of silacyclobutanes. In the gas phase, u.v. (185 nm < X < 210 nm) excitation of 1,1-dimethylsilacyclo-butane causes elimination of ethylene and the formation of Me2Si = CH2. This silaolefin, when formed, has an internal energy which is probably in excess of the Si—C 71-bond energy, and it may be that its reactivity is different from that of Me2Si=CH2 generated thermally or in solution. In particular it is possible that its isomerization to Me2HSiCH occurs and this might be an explanation for the substantial amounts of polymer that accompany the ethylene and 1,1,3,3-tetramethyl-l,3-disilacyclobutane as products. Mass spectrometric measurements show that the products from octamethyl-l,2-disilacyclobutane are mainly 2,3-dimethylbut-2-ene and hexamethylsilacyclopropane. The primary photoprocess is probably that shown in equation (8). 

The products of photolysis of substituted silacyclobutanes in methanol solution are either those derived from initial formation of the silaolefin [e.g. equation (9)] or by cleavage of the Si—C bond [e.g. equation (10)]. A similar sensitivity to the nature of the substituent is observed with 1,3-disilacyclobutanes, where it is observed that l,l,3,3-tetramethyl-2,4-diphenyl-l,3-disilacyclobutane undergoes photocleavage of a Si—C bond, whereas l,l,3,3-tetraphenyl-l,3-disilacyclobutane is stable. 

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