Branched chains silanes

Si-Si coupling and Si-X functionalization had to be modified and extended. The preparation of CH3Si[Si(CH3)3]3 is based on the procedure reported by Marsmann et al.6 The functionalization of the branched-chain silane occurs by the method introduced by Ishikawa et al.7,8 and leads to the desired trichloro-derivative,9 which can easily be converted to a tripodal amine by aminolysis with a primary amine.5... 

Silanes Si IF , 2 re now known as unbran-ched and branched chains (up to n = 8) and as cyclic compounds Si H2/i (n = 5,6). Silanes are colourless gases or volatile liquids they... 

Since the pioneering work of Gilman and co-workers in the 1960s,1-3 several standard preparative methods have been developed for the synthesis of chain and branched-chain organopolysilanes. More recently, the latter have been used in the design of new dendrimeres4 or cage structures. However, only a few donor-functionalized silanes have found an application in coordination chemistry. 

Further complications with silanes arise from lack of convenient syntheses and difficulties in separation. Nevertheless, compounds from n = I to n = 8 have been isolated, including both straight-chain and branched-chain compounds We should nol judge silicon s tendency to catenate by looking at these hydrides, however, since a much dilfereni result is obtained when substituents other than hydrogen are present.7 Flutters other than inherent Si—Si bond strength must be involved because it is possible to isolate a large number of polysilane polymers 8... 

A highly branched-chain permethylated polysilane, tetrakis(trimethyl-silyl)silane, can be prepared in 70% yield by a mixed lithium coupling of trimethylchlorosilane (20% molar excess) and silicon tetrachloride in tetrahydrofuran (63). 

Interestingly, when large excesses of both trimethyl(trifluoromethyl)silane and potassium fluoride are reacted with oxalyl fluoride (3 or 4 1). a new oligomer (CF3)3C0[C(CF3)20] -C(0)Cp3 (n = 2-4) is obtained these symmetrical branched-chain polyethers are difficult to... 

Silanes Si H2 + 2 with straight or branched chains are known for 1 < n < 10, and Figure 13.10 compares the boiling points of the first five straight-chain silanes with their hydrocarbon analogues. Silanes are explosively inflammable in air (equation 13.21). 

Another highly effect chain extender is trimellitic anhydride (TMA) which gives rise to branching of the PET structure. Note that the multifunctional epoxies (see Table 14.2) react quickly with the terminal carboxylic acid groups of PET but can also react with the film former and the silane coupling agent on glass fibre reinforcements. 

It should also be noted that the viscometric technique can detect the presence of star-shaped aggregates, having the ionic active centers. The addition of ethylene oxide to hydrocarbon solutions of poly(isoprenyl)lithium leads to a nearly two-fold increase in viscosity144). Conversely, this results in an approximately twenty-fold decrease in solution viscosity, after termination by the addition of trimethylchloro-silane. This change in solution viscosity is reflected in the gelation which occurs when difunctional chains are converted to the ionic alkoxy active centers 140,145,146). Branched structures have also been detected 147> by viscometry for the thiolate-lithium active center of polypropylene sulfide) in tetrahydrofuran. 

Many kinds of longer chain and branched silanes with organic substituents are known. The principal reactions of the Si-Si bonding in these substances correspond with those which have been discussed for disilanes. 

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