Disilene, tetramesityl

With even larger substituent groups, the disilene becomes the thermodynamically preferred form, and can then be isolated.24 The best-known example is tetramesityl-disilene (5.5), ordinarily synthesized as shown in equation (13). The stable, isolable disilenes have an elaborate and beautiful chemistry, but they cannot be polymerized.25... 

The first isolable disilene compound, a yellow tetramesityl disilene, was made by R. West via the reaction... 

An unusual cyclotriarsane" was recently prepared by reaction of AS4 with tetramesityl-disilene in toluene at 25 °C (equation 13). The ring system was characterized by X-ray diffractometry and other methods. In the triarsirane ring the As—As distances vary from 245.0 pm to 246.3 pm the As angles are very close to 60°. 

The disilenes [Mes(R)Si]2 (R = Mes or t-Bu) will both add sulphur stereospecifically in solution to give colourless crystalline adducts. The structure of the tetramesityl derivative shows the product to have a three-membered isosceles ring which shows no tendency to dimerise to the 1,4-dithia six-membered one reported for less hindered substituents (equation 51 )46. A double-bond addition is also reported for silylenes to thioketones. 

Tetramesityldisilene is an air- and moisture-sensitive material and must be handled under an inert atmosphere. It reacts with oxygen and decolorizes, forming 2,2,4,4-tetramesityl-l,3-dioxetane, a colorless crystalline solid, mp 215°. The chemical properties of tetramesityldisilene are described in reviews. The disilene is characterized by -NMR (CsDs) d 2.03 (s, 12H), 2.49 (s, 24H), 6.70 (s, 8HX and SiNMR (CgDe) 5 63.7. 

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