Tetrasilabutadienes reactions

The reaction of tetrasilabutadiene 64 with Cl2 gives 1,2,3,4-tetrachlorotetrasilane 182 [Eq. (86)].125 As chlorine gas is added, the solution of 64 turns from dark red to blue-black to orange, and finally to colorless. On this basis, the addition is proposed to proceed stepwise via the initial formation of a charge-transfer complex between 64 and Cl2 to give 183, which is converted to disilene 184 and then to 182 by the addition of a second molecule of Cl2. 

The treatment of hexakis(2,4,6-triisopropylphenyl)tetrasilabutadiene with maleic anhydride furnished the 2,9-dioxa-5,6,7,8-tetrasilatetracyclodecan-3-one derivative 29 (Scheme 19). The reaction pathway involves a [2+2] cycloaddition of one of the Si=Si bonds of tetrasilabutadiene to the highly reactive C=0 group, followed by a second cycloaddition of the remaining Si=Si bond across the C=C double bond to complete the formation of the final product 29 <20010M2451>. 

Compound 828 and two other disilenes 36 and 37, formed by the reaction of the tetrasilabutadiene (see later) with quinones in the presence of water43,47, also belong to this group. 

The situation is different for the molecules containing endocyclic Si=Si double bonds which just recently became accessible and for the as yet sole known tetrasilabutadiene, the chemistry of which still remains mostly unknown. Not only are further representatives of these classes of compounds to be expected but also novel modes of reactions that have as yet not been observed for the acyclic disilenes. Another interesting question is whether it will be possible to prepare molecules with an extended system of conjugated double bonds. 

Reactions. Experimental results of reactions of (Tip)2 Si= Si(Tip) Si(Tip)=Si(Tip)2 are summarized in Scheme 40. Treatment of the tetrasilabutadiene with a small amount of water gave an analog of tetrahydrolhran, an oxatetrasilolane derivative, probably via the 1,2-addition and the following rearrangement. Addition of an excess amount of water resulted in the formation of the tetrasila-l,4-diol derivative, which showed no tendency to ehminate water with the formation of the oxatetrasilolane derivative. 

In the following text, results concerning the syntheses and reactions of disilenes of types 1-4 are presented. In addition, dehalogenations of the disilenes 2 and 4, and dehydrobromination of the disilane R HBrSi-SiBrHR, which possibly lead to disilynes of types 5-7, will be described (in some cases, these reactions obviously proceed via cyclotrisilenes as well as cyclotetrasilenes and even tetrasilabutadienes). The disilenes 1 (R = Ph), 3, and 4 and, (obviously) the disilyne 7, could be obtained under normal conditions due to an adequate steric shielding of the reactive >Si=Si< and -Si Si- entities with bulky silicon-bound groups. 

Recently, we obtained the first and, as yet, only tetrasilabuta-1,3-diene 6 from the tetraaryldisilene as follows. The disilene was treated with excess lithium to give the putative disilenyllithium compound 4. In the second step of the reaction sequence, mesityl bromide was added in the expectation that the bulk of this aryl group and the poor solubility of mesityllithium would favor halogenation over the competing transarylation. In fact, the bromodisilene 5 does appear to be formed smoothly but, like 4, has not yet been unambiguously identified. Intermolecular cleavage of lithium bromide from the two intermediates 4 and 5 then furnished the tetrasilabutadiene 6 in up to 60% yield. 

Addition Reactions. While cycloadditions to 6 are still exceedingly rare, reactions of 6 with small molecules, as summarized in Scheme 8.1, were more successful. Treatment of the tetrasilabutadiene with small amounts of water led, via the 1,2-addition product 16 to the rearranged oxatetrasilacyclopentane 17, an analogue of tetrahydrofuran. With an excess of water the tetrasilane-l,4-diol 18 was obtained, which showed no tendency to eliminate water with the formation of 17. ... 

Kira and coworkers observed the slow transformation of tetrasilabicyclo[1.1.0]butane 11 into the silacyclobutane 2 at room temperature [2]. Two possible reaction mechanism might be envisaged (i) a multistep isomerization via the intermediacy of tetrasilabutadiene 10, or, (ii) the 1,2 shift of the substituent with reorganization of the Si4-skeleton (see Scheme 1). 

Keywords Disilenes / Tetrasilabutadiene / Oxidation Reactions / Hydrolysis Reactions... 

Keywords silylenes, disilenes, tetrasilabutadiene, multiple bonds, addition reactions, cycloadditions, germanium compounds... 

We recendy obtained the first, and as yet only, tetrasilabutadiene 24 from the tetraaryldisilene 23 by a sequence of metallation, halogenation, and coupling reactions (Scheme 5). 

Crystals of the tetrasilabutadiene (18 mg, 0.02 mmol) and tBuLi powder (5 mg, 0.08 mmol) were placed in a reaction tube. Dry... 

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