Disilanes Hexakis disilane

The distance-dependent Pauling bond orders range from 1.00 in hexamethyldisilane with a SiSi bond of 235 pm in length (Fig. 4 standard d(l)) to 0.26 for hexakis(rert.butyl)disilane with an extremely elongated spacer distance of 270 pm between its bulky Si(C(CH3)3)3 half-shells [6b]. To rationalize the sometimes considerably weakened SiSi bonds - hexakis(rm.butyl)disilane does not dissociate into two radicals -, it has been proposed [6b,7] that additional attractive van der Waals interactions within the hydrocarbon wrapping contribute to the bonding within the respective organosilicon molecules. This assumption is further supported by the structure of hexakis(trimethylsilyl)disilane (Fig. 2), in which (presumably due to the considerable polarization Si -C5e-H5 calculated [5b]) extremely short non-bonded C(H3)-- (H3)C distances of only 352 pm are found. 

Tris(trimethylsilyl)silyllithium, which is readily formed upon treatment of tetrakis(trimethylsilyl)silane with methyllithium or triphenylsilyllithium in ether-tetrahydrofuran (63), is useful as the reagent for construction of molecules of an interesting class of highly sterically hindered methyl-polysilanes. The synthesis of hexakis(trimethylsilyl)disilane gives an example (59). 

FIGURE 12. Low-energy region of the (He I)PE spectrum of hexakis(trimethylsilyl)disilane (a) Gaussian-shape band deconvolution between 7.5 and 9.5 eV and (b) topological SiSi bond interaction model with radical cation state assignment... 

In contrast, hexakis(trimethylsilyl)disilane, (Me3Si)3SiSi(SiMe3)3, is cleaved with lithium metal in THF [Eq. (35)] (73c), as well as with MeLi... 

In addition, cyclotrisilane derivatives can be subjected to photolysis to generate organylsilylenes. For instance, the photolysis of hexakis-t-butylcyclotrisilane (369) in the presence of substituted acetylenes, e.g. (370) affords 1,1,4,4-tetrakis-t-butyl-2,3,5,6-tetraorganyl-l,4-disilacyclohexa-2,5-diene (371) (equation 167)190. Alternatively, thermolysis of disilanes in the presence of alkynes is a viable route to disilacyclohexane derivatives. Thus, thermolysis of l,2-dimethoxy-l,l,2,2-tetramethyldisilane (338) in the presence of diphenylacetylene (370) in a pressure vessel—via reactive intermediates and,... 

First attempts to achieve the synthesis of a,ci>bis[tris(trimethylsilyl)silyl] alkanes by the reaction of two equivalents of tris(trimethylsilyl)silyl potassium with the respective a,(0-dibromoalkanes proved to be fruitless, leading mainly to the formation of hexakis(trimethylsilyl)disilane [3]. Since the reason for this reaction is the ease of the halogen metal exchange reaction we decided to use (X,co-ditosyl alkanes as starting materials instead. And indeed these gave rise to the formation of the desired a,(0-bis[tris(trimethylsilyl)silyl] alkanes (Scheme 2). 

Tricyclic silicon chalcogenides with a [3.3.3]propellane skeleton have been synthesized by reactions of hexakis(chlorodimethylsilyl)disilane (Fig. 4) with U2E (E = S, Se, Te) [12] according to Scheme 2. 

Fig. 4. Crystal structures of hexakis(chlorodimethylsilyl)disilane and its reaction product with li2S.

Another unique highly branched and symmetrical organopolysilane, developed with Harrell, has become available recently. This is hexakis(tri-methylsilyl)disilane. 

The solubility of these compounds in common organic solvents is generally good. An exception is hexakis[biphenylyl(4) ]disilane [477] which is soluble only in nitrobenzene. 

Hexaaryldisilanes are thermally extremely stable. Hexakis(4-methylphenyl) and hexakis[biphenylyl(4)] disilanes do not react with oxygen, iodine or other reagents, even upon heating hexaarylethanes are attacked under the same conditions. In such cases, steric considerations may be decisive. 

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