Silylene

Silylene is a chemical compound with the formula SiR₂. It is the silicon analog of carbene. Silylene rapidly when condensed.

generic silylene

Simplest silylene has R=Hydrogen
Names
IUPAC name Silylene
Systematic IUPAC name Silylidene[1]
Other names Hydrogen silicide(−II) Silicene
Identifiers
CAS Number	13825-90-6
3D model (JSmol)	Interactive image
ChemSpider	4885758 Y
PubChem CID	6327230
CompTox Dashboard (EPA)	DTXSID70884652
InChI InChI=1S/H2Si/h1H2 Y Key: XMIJDTGORVPYLW-UHFFFAOYSA-N Y
SMILES [SiH2]
Properties
Chemical formula	H2Si
Molar mass	30.101 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Silylenes are formal derivatives of silylene with its hydrogens replaced by other substituents.^[2] Most examples feature amido (NR₂) or alkyl/aryl groups.^[3][4]

Silylenes have been proposed as reactive intermediates. They are carbene analogs.^[5]

Synthesis and properties

Silylenes have been generated by thermolysis or photolysis of polysilanes, by silicon atom reactions (insertion, addition or abstraction), by pyrolysis of silanes, or by reduction of 1,1-dihalosilane. It has long been assumed that the conversion of metallic Si to tetravalent silicon compounds proceeds via silylene intermediates:

Si + Cl₂ → SiCl₂

SiCl₂ + Cl₂ → SiCl₄

Similar considerations apply to the direct process, the reaction of methyl chloride and bulk silicon.

Early observations of silylenes involved generation of dimethylsilylene by dechlorination of dimethyldichlorosilane:^[6]

SiCl₂(CH₃)₂ + 2 K → Si(CH₃)₂ + 2 KCl

The formation of dimethylsilylene was demonstrated by conducting the dechlorination in the presence of trimethylsilane: the trapped product being pentamethyldisilane:

Si(CH₃)₂ + HSi(CH₃)₃ → (CH₃)₂Si(H)−Si(CH₃)₃

A room-temperature isolable N-heterocyclic silylene is N,N′-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene:^[7]

Synthesis of an isolable silylene.

The α-amido centers stabilize silylenes by π-donation. The dehalogenation of diorganosilicon dihalides is a widely exploited.^[8]

Related reactions

Decamethylsilicocene is an example of a silylene.^[3]

In one study diphenylsilylene is generated by flash photolysis of a trisilane:^[9]

In this reaction diphenylsilylene is extruded from the trisila ring. The silylene can be observed with UV spectroscopy at 520 nm and is short-lived with a chemical half-life of two microseconds. Added methanol acts as a chemical trap with a second order rate constant of 1.3×10¹⁰ mol⁻¹ s⁻¹ which is close to diffusion control.

See also

• Carbene analogs
• N-heterocyclic silylene
• Silenes, R₂Si=SiR₂
• Silylium ions, protonated silylenes