# Silylene

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{{Chembox
|Name           = generic silylene
|Watchedfields  = changed
|ImageFile      = Silylene.svg
|ImageFile1     = Silylene-3D-vdW.png
|ImageCaption   = Simplest silylene has R=Hydrogen
|verifiedrevid  = 464391717
|IUPACName      = Silylene
|SystematicName = Silylidene<ref>{{BlueBook2013|rec=71.2.2.1}}</ref>
|OtherNames     = Hydrogen silicide(−II)<br />Silicene
|Section1       = {{Chembox Identifiers
|CASNo            = 13825-90-6
|PubChem          = 6327230
|ChemSpiderID     = 4885758
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|SMILES           = [SiH2]
|StdInChI         = 1S/H2Si/h1H2
|StdInChI_Ref     = {{stdinchicite|correct|chemspider}}
|StdInChIKey      = XMIJDTGORVPYLW-UHFFFAOYSA-N
|StdInChIKey_Ref  = {{stdinchicite|correct|chemspider}}
}}
|Section2       = {{Chembox Properties
| H = 2 | Si = 1
}}
}}

'''Silylene''' is a [chemical compound](/source/chemical_compound) with the formula SiR<sub>2</sub> (R = H).  It is the [silicon](/source/silicon) analog of [carbene](/source/carbene). Silylenes decomposes rapidly when condensed. 

'''Silylenes''' are formal derivatives of silylene with its hydrogens replaced by other substituents.<ref>{{cite journal |doi=10.1021/cr900093s |title=Stable Heavier Carbene Analogues |year=2009 |last1=Mizuhata |first1=Yoshiyuki |last2=Sasamori |first2=Takahiro |last3=Tokitoh |first3=Norihiro |journal=Chemical Reviews |volume=109 |issue=8 |pages=3479–3511 |pmid=19630390 }}</ref> Most examples feature amido (NR<sub>2</sub>) or organyl groups.<ref name=HR>{{cite journal |doi=10.1021/om7007869|title=The Chemistry of Aluminum(I), Silicon(II), and Germanium(II) |year=2008 |last1=Nagendran |first1=Selvarajan|last2=Roesky|first2=Herbert W.|journal=Organometallics|volume=27|issue=4|pages=457–492}}</ref><ref name=denk1>{{cite journal |doi=10.1021/ar950192g|title=Stable Silylenes|year=2000|last1=Haaf|first1=Michael|last2=Schmedake|first2=Thomas A.|last3=West|first3=Robert|journal=Accounts of Chemical Research|volume=33|issue=10|pages=704–714|pmid=11041835}}</ref>

Silylenes have been proposed as [reactive intermediate](/source/reactive_intermediate)s. They are [carbene analog](/source/carbene_analog)s.<ref>{{cite book |doi=10.1002/0470857250.ch43 |chapter=Silylenes |year=1998 |last1=Gaspar |first1=Peter |last2=West |first2=R. |title=The Chemistry of Organic Silicon Compounds |series=The Chemistry of Functional Groups |volume=2 |issue=1 |pages=2463–2568 |isbn=0471967572 }}</ref>

==Synthesis and properties==
Silylenes have been generated by [thermolysis](/source/thermolysis) or [photolysis](/source/photolysis) of [polysilane](/source/polysilane)s, by [silicon](/source/silicon) atom reactions ([insertion](/source/insertion_reaction), [addition](/source/addition_reaction) or abstraction), by [pyrolysis](/source/pyrolysis) of [silane](/source/silane)s, or by [reduction](/source/redox) of 1,1-dihalosilane.  It has long been assumed that the conversion of metallic Si to tetravalent silicon compounds proceeds via silylene intermediates:
:Si + Cl<sub>2</sub> → SiCl<sub>2</sub>
:SiCl<sub>2</sub> + Cl<sub>2</sub> → SiCl<sub>4</sub>
Similar considerations apply to the [direct process](/source/direct_process), the reaction of [methyl chloride](/source/methyl_chloride) and bulk silicon.

Early observations of silylenes involved generation of dimethylsilylene by dechlorination of [dimethyldichlorosilane](/source/dimethyldichlorosilane):<ref>{{cite journal |doi=10.1021/ja01061a040|title=Dimethylsilene: CH<sub>3</sub>SiCH<sub>3</sub>|year=1964|last1=Skell|first1=P. S.|last2=Goldstein|first2=E. J.|journal=Journal of the American Chemical Society|volume=86|issue=7|pages=1442–1443}}</ref>
:SiCl<sub>2</sub>(CH<sub>3</sub>)<sub>2</sub> + 2 K → Si(CH<sub>3</sub>)<sub>2</sub> + 2 KCl
The formation of dimethylsilylene was demonstrated by conducting the dechlorination in the presence of [trimethylsilane](/source/trimethylsilane): the [trapped](/source/chemical_trap) product being pentamethyldisilane:
:Si(CH<sub>3</sub>)<sub>2</sub> + HSi(CH<sub>3</sub>)<sub>3</sub> → (CH<sub>3</sub>)<sub>2</sub>Si(H)−Si(CH<sub>3</sub>)<sub>3</sub>

A room-temperature isolable [''N''-heterocyclic silylene](/source/N-heterocyclic_silylene) is {{chem name|''N'',''N''′-di-''tert''-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene}}:<ref>{{cite journal |doi=10.1021/ja00085a088|title=Synthesis and Structure of a Stable Silylene|year=1994|last1=Denk|first1=Michael|last2=Lennon|first2=Robert|last3=Hayashi|first3=Randy|last4=West|first4=Robert|last5=Belyakov|first5=Alexander V.|last6=Verne|first6=Hans P.|last7=Haaland|first7=Arne|last8=Wagner|first8=Matthias|last9=Metzler|first9=Nils|journal=Journal of the American Chemical Society|volume=116|issue=6|pages=2691–2692}}</ref>
thumb|center|Synthesis of an isolable silylene.

The α-amido centers stabilize silylenes by π-donation. The dehalogenation of diorganosilicon dihalides is a widely exploited.<ref>{{cite journal |doi=10.1021/ja062928i|title=A New Type of ''N''-Heterocyclic Silylene with Ambivalent Reactivity|year=2006|last1=Driess|first1=Matthias|last2=Yao|first2=Shenglai|last3=Brym|first3=Markus|last4=Van Wüllen|first4=Christoph|last5=Lentz|first5=Dieter|journal=Journal of the American Chemical Society|volume=128|issue=30|pages=9628–9629|pmid=16866506}}</ref>

==Related reactions==
[[File:Decamethylsilicocene.png|thumb|upright|left|[Decamethylsilicocene](/source/Decamethylsilicocene) is an example of a silylene.<ref name=HR/>]]In one study diphenylsilylene is generated by [flash photolysis](/source/flash_photolysis) of a trisilane:<ref>{{cite journal |doi=10.1021/ja0653223|title=Diphenylsilylene|year=2006|last1=Moiseev|first1=Andrey G.|last2=Leigh|first2=William J.|journal=Journal of the American Chemical Society|volume=128|issue=45|pages=14442–14443|pmid=17090011}}</ref>

:400px|Diphenylsilylene

In this reaction diphenylsilylene is extruded from the trisila ring. The silylene can be observed with [UV spectroscopy](/source/UV_spectroscopy) at 520&nbsp;nm and is short-lived with a [chemical half-life](/source/chemical_half-life) of two [microsecond](/source/microsecond)s. Added [methanol](/source/methanol) acts as a [chemical trap](/source/chemical_trap) with a [second order rate constant](/source/second_order_rate_constant) of {{val|1.3e10|u=mol<sup>−1</sup> s<sup>−1</sup>}} which is close to diffusion control.

==See also==
*[Carbene analogs](/source/Carbene_analogs)
*[''N''-heterocyclic silylene](/source/N-heterocyclic_silylene)
*[Silenes](/source/Silenes), R<sub>2</sub>Si=SiR<sub>2</sub>
*[Silylium ion](/source/Silylium_ion)s, protonated silylenes

==References==
{{Reflist}}

Category:Inorganic silicon compounds
Category:Free radicals
Category:Octet-deficient functional groups

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Adapted from the Wikipedia article [Silylene](https://en.wikipedia.org/wiki/Silylene) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Silylene?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.