{{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 with the formula SiR<sub>2</sub> (R = H). It is the silicon analog of 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 intermediates. They are carbene analogs.<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 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 + 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, the reaction of methyl chloride and bulk silicon.
Early observations of silylenes involved generation of dimethylsilylene by dechlorination of 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: the trapped 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 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 is an example of a silylene.<ref name=HR/>]]In one study diphenylsilylene is generated by 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 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 {{val|1.3e10|u=mol<sup>−1</sup> s<sup>−1</sup>}} which is close to diffusion control.
==See also== *Carbene analogs *''N''-heterocyclic silylene *Silenes, R<sub>2</sub>Si=SiR<sub>2</sub> *Silylium ions, protonated silylenes
==References== {{Reflist}}
Category:Inorganic silicon compounds Category:Free radicals Category:Octet-deficient functional groups