1.2- Disilacyclobutanes, synthesis

Disilacyclobutane, 1,1,3,3-tetrachloro-physical properties, 1, 590 Disilacyclobutanes synthesis, 1, 587, 598... 

Sheridan JB, Gomez-Elipe P, Manners I (1996) Transition metal-catalysed ting-opening copolymerization of silicon-bridged [l]ferrocenophanes and sUa- or disilacyclobutanes synthesis of poly(ferrocenylsilane)-poly(carbosrlane) random copolymers. Macromol Rapid Commun 17 319-324... 

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... 

Another procedure for the synthesis of 1,3-disilacyclobutanes is the pyrolysis of monosilacyclobutanes (eq. 5), [9, 14, 16], but this method has difficulties and disadvantages [14]. One of these is that polysilmethylene formation is a side-reaction when it is carried out in the gas-phase. 

Interrante and coworkers developed two polysilaethylene precursor systems, which upon pyrolysis gave nearly phase-pure SiC (95-99% SiC) in high ceramic yield (75-90%) (Scheme ll)116. The first procedure begins with a multistep synthesis of 1,1,3,3-tetrachloro-l,3-disilacyclobutane (monomer), 5. Alternately, gas phase pyrolysis will convert 6 to 5. 

ROP of cyclic carbosilanes is one of the most promising techniques for the synthesis of well-defined polycarbosilanes. ROP of four-membered ring compounds, 1,3-disilacyclobutanes, and monosilacyclobutanes, as well as copolymerizations of mixtures of monomers, have been widely investigated in the last decades <1996JOMl, B-1996MI7621, B-2000MI247>. 

Previously known methods <1984CHEC(1)573, 1996CHEC-II(1B)1175> have been modified and used for the effective synthesis of a variety of new disilacyclobutanes. 

Magnesium is a typical coupling agent for the synthesis of 1,3-disilacyclobutanes. Several new compounds have been obtained in this way (Equation (20) Table 1). 

The substituted disilacyclobutanes have been used as monomers in the ROP process employed for the synthesis of linear poly(silylenemethylene)s (see Sections 2.21.6.2 and 2.21.12). 

A new method of the synthesis of 1,3-disilacyclobutanes by a coupling of l,3-dilithio-2-silapropanes with dichloro-silanes has been described <2007ARK29>. 

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... 

Previously it was shown that ROP of 1,3-disilacyclobutane is an efhcient method for the synthesis of polycarbosilanes (Scheme 18.9). Likewise, ROP of 1,3-disiladiazetanes, cyclo-(SiR2-NR )2, delivers linear high-molecular weight polysilazanes. Synthesis of 1,3-disiladiazetanes from bis(amido)silanes [R2Si(NRLi)2] and dichlorosilanes [R2SiCl2] was reviewed in detail by Fink in 1966.9 ... 

The di-Grignard reagent 79, synthesized in a 60% yield from l,2-di(bromomethyl) tetramethyldisilane and magnesium in diethyl ether, was successfully used in the synthesis of the platinadisilacyclopentane 80, which was obtained in a 46% yield [Eq. (32) 67]. Similarly, a nickeladisilacyclopentane derivative was synthesized in 20% yield, but it was not isolated from the solution. In the formation of the di-Grignard reagent 79, the novel 1,3-disilacyclobutane 81 was also isolated in 20% yield. 

This report by Conlin raised a lot of questions in my mind, but these questions remained dormant until in a futile attempt to prepare a,a-silylenevinylene polymers we accidentally synthesized 1,3-di-methylene-l,3-disilacyclobutane 5. This serindipitious synthesis allowed us to establish a two-case generality for the isomerization of methylenesilacyclobutanes since gas-phase pyrolysis of 5 cleanly and solely produced methylenedisilacyclopentene 7 (Eq. 9). This isomerization was kinetically followed in a stirred-flow reactor to afford Arrhenius parameters that clearly revealed this to be a concerted reaction. (Well, maybe not that clearly since you wouldn t bet your life on a log A of 12.5, but there certainly aren t any 54 kcal/mol sigma bonds in 5.)... 

Synthesis of 1,3-Disilacyclobutanes, 1,3-Digermacyclo-butanes, and l-Germa-3-silacyclobutanes with New 1,3-Dimetallated Organoelement Building Blocks... 

There is no synthetic route available for selective synthesis of unsymmetrically substituted 1,3-disilacyclobutanes, l-germa-3-silacyclobutanes, or 1,3-digermacyclobutanes. 

The 1,3-disilacyclobutanes 4a-4f were formed by the addition of the appropriate dichlorosilane at -50 °C to a freshly prepared solution of bis(lithiomethyl)diphenylsilane (3a) (Scheme 2) or (lithiomethyl)[lithio(trimethylsilyl)methyl]diphenylsilane (8) (Scheme 3). After aqueous work-up, the 1,3-disilacyclobutanes 4a-4f were isolated by Kugelrohr distillation or cystallization in 34-62% yield. Polymeric materials or higher ring systems were formed as byproducts, reducing the yield. The synthesis of 4a, 4d, and 4f by another synthetic route has been described previously [4]. 

C. Strohmann, E. Wack, "Synthesis of 1,3-Disilacyclobutanes, 1,3-Digermacyclobutanes and I-Germa-3-silacyclobutanes with New 1,3-Dimetallated Organoelement Building Blocks" in Organosilicon Chemistry III From Molecules to Materials (Eds. N. Auner, J. Weis), Wiley-VCH, Weinheim, 1997, this volume p. 217. 

Abstract The presented paper is a summary of our results on synthesis and polymerization of silyl-containing norbomenes and norbomadienes via ring-opening metathesis polymerization (ROMP) and addition processes as well as ring-opening polymerization (ROP) of silacyclobutanes and disilacyclobutanes. The synthesis of heterochain and carbochain polymer families with regularly varied substituents at Si atom and various number and location Si(CH3)3-substituents has been realized. Systematic study of gas transport parameters of polycarbosilanes series of different classes allowed us to find out real eorrelations between features of chemical polymer structure and its gas separation eharacteristics. 

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