Disilene

Disilene

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Identifiers
CAS Number	15435-77-5 Y
ChemSpider	123409 Y
PubChem	139934
Properties
Chemical formula	Si 2H 4
Molar mass	60.2028 g mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Disilene /daɪsaɪliːn/ (systematically named disilicon tetrahydride) is an inorganic compound with the chemical formula Si
₂H
₄. The name disilene, referring to the structure of a particular prototropic tautomer of the molecule. It is the simplest silene.

Properties and bonding

Disilene is a molecule with one Si=Si bond, and four equivalent Si-H bonds.

Unlike ethylene, disilene is kinetically unstable with respect to tautomerisation. Disilene has two other tautomers, that are very close in energy: (μ²-H)disilene, and disilanylidene.

Organodisilenes

File:WestsDisilene.png

Structure of tetramesityl disilene.

Disilenes bearing sterically bulky substituents are isolable and have been well characterized although they remain mainly of academic interest. The first stabilised disilene was tetramesityldisilene, (C₆Me₃H₂)₄Si₂. The Si=Si distance in this molecule is 2.15 Å, about 10% shorter than a typical Si–Si single bond. The Si₂C₄ core is roughly planar. Such species are typically prepared by reduction of organosilicon halides:

R₂SiCl₂ + 2 Na → R₂Si=SiR₂ + 4 NaCl

An alternative synthesis involves photolysis of trisilacyclopropanes. When the R group is not bulky, cyclic or polymeric polysilanes are the products.

In one study a disilene is prepared by an intramolecular coupling of a 1,1-dibromosilane with potassium graphite. The silicon double bond in the resulting compound has a bond length of 227 picometer (second largest ever found) with trans-bent angles 33° and 31° (by X-ray diffraction).

Tricyclic Disilenes with Highly Strained Si-Si Double Bonds

In addition to this the substituents around the Si-Si bond are twisted by 43°. The disilene isomerizes to a tetracyclic compound by heating at 110°C in xylene thereby releasing its strain energy.