Silicon-Containing Dienes

Silylative Coupling Condensation of Silicon-Containing Dienes.225... 

Ring-Closing Metathesis of Silicon-Containing Dienes.227... 

CF3)2MeCO)]2(ArN)-M=CH( -Bu), where M = Mo and W [3] and Grubbs ruthenium catalyst - RuCl2(=CHPh)(PCy3)2 [4]. ADMET of silicon-containing dienes such as dialkenylsilanes and siloxanes (except vinyl derivatives), furnishes a variety of unsaturated homopolymers including carbosilanes [5] and carbosiloxanes [6] units (equation 1). 

A STUDY ON THE REACTIVITY OF WCU-e -Al-CHzCh WITH THE SILICON-CONTAINING DIENES... 

Diels-Alder Reactions.—The synthesis and use in organic chemistry of a variety of oxygen, sulphur and silicon containing dienes is summarized in Table 12. This area continues to be one of intense interest. 

Silole (silacyclopentadiene) is a silicon-containing five-membered cyclic diene, that is, a silicon analog of cyclopentadiene. Since the first synthesis of a silole, 1,1,2,3,4, 5-hexaphenylsilole, by Braye and Hubei in 19591, the chemistry of siloles has been... 

The ADMET step condensation polymerization of carbosila- and carbosiloxa-dienes has generated a new class of unsaturated silicon-containing polymers when monomer structure/reactivity relationships, as described earher for the polar functionalities, are obeyed (equation 22). 

Although the silylative coupling cyclization is accompanied by linear oligomeric products and the process required a longer reaction time (3-4 weeks), this particular method opens up a new route to synthesize silicon-containing e ro-methylenes, which cannot be prepared via ring-closing diene metathesis. 

The photochemistry of silicon-containing compounds has attracted increased attention with the publication of some interesting results. In particular, studies of the effect of the inclusion of silicon in organic molecules which undergo well-known photochemical reactions have been initiated. The photochemical isomerization of 1-silacyclohexa-2,4-dienes should be of interest because the proposed intermediates and products are the elusive silahexatrienes and sila-cyclopropanes. In fact, irradiation through Pyrex of the diphenyl derivative (283) affords the bicyclic product (284) via the silahexatriene (285) 817 convincing... 

The use of highly reactive carbanions in polymer synthesis has proven to be an interesting subject. The work which has been described here indicates some of the potential for novel polymeric materials. Examination of the polymers prepared in this work hints at some of the endless possibilities for the preparation of similar materials. There are many other dicarbanions which can be used in analogous syntheses. One molecule which would be interesting to examine is the dicarbanion of 2,3-dimethyl-1,3-butadiene which would result in a silicon containing polymer that contains a backbone diene unit. Another area of interest which has emerged from this work is the preparation of polymers which contain other inorganic atoms in the polymer backbone such as tin. We believe materials such as these would have some very unique properties. 

Ball milling of stoichiometric amounts of two solid reagents, Diels-Alder partners led to synthesis of silicon-containing heterocyclic product. Cyclic diene 1,1-dimethyl-2,3,4,5-tetraphenylsilole 1 reacts with iV-methyl maleimide in solid-state milling to afford the enrfo-Diels-Alder cycloadduct 3 stereospeciflcally (Scheme 5.1) [1]. Notably, transfer of reaction conditions from solution chemistry to solvent-free procedure does not have any effect on stereochemical outcome [2]. 

For the cross-metathesis reactions we used two different homogeneous ruthenium catalysts one multicomponent catalyst prepared in situ, and the other catalyst consisting of one single component. Both are based on ruthenium(II) and the latter can be isolated in pure form. Figure 1 shows the ruthenium catalysts that were used in cross-metathesis reactions to synthesize silicon-containing ot,(o-dienes. 

The results of the investigated cross-metathesis reactions of silicon containing norbomene derivatives with ethylene showed a poor reactivity for some substituents. Reactive chlorosilanes act as catalyst poisons and silazanes diminish the catalyst s activity by coordination of nitrogen to the metal center. Starting from norbomene derivatives with alkoxy-substituted silicon moieties, a selective synthesis of new silicon-containing a,(0-dienes could be accomplished (Scheme 2). 

Metathesis of 1,9-decadiene and cyclooctene with trialkoxy- and trisiloxy-substituted vinylsilanes in the presence of Grubbs catalyst, carried out in appropriate conditions, leads to the formation of bis(silyl)diene with a high yield. Similar processes performed with divinyl-substituted siloxane lead to the formation of silicon-containing polymers (via ADMET copolymerization and tandem ROM/CD polymerization), thus opening a new convenient route to synthesis of unsaturated organosilicon copolymers. 

Acyclic Diene Metathesis (ADMET) Polymerization of dialkenylsubstituted silicon compounds (except of divinylderivatives) can provide a universal route toward synthesis of well-defined linear organosilicon polymers. Under some conditions the ring closure of the substrate occurs in the presence of metallacarbene (Ru, Mo, W, Re) to yield silicon-containing cyclic olefins efficiently. 

Matloka, P.P.and Wagener, K.B. (2006) The acyclic diene metathesis (ADMET) polymerization approach to silicon containing materials. Journal of Molecular Catalysis A Chemical, 257,89-98. 

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