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Silylene

{{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{{BlueBook2013|rec=71.2.2.1}}

|OtherNames = Hydrogen silicide(−II)
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 SiR2. It is the silicon analog of carbene. Silylene rapidly when condensed.

Silylenes are formal derivatives of silylene with its hydrogens replaced by other substituents.{{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 }} Most examples feature amido (NR2) or alkyl/aryl groups.{{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}}{{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}}

Silylenes have been proposed as reactive intermediates. They are carbene analogs.{{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 }}

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:{{cite journal |doi=10.1021/ja01061a040|title=Dimethylsilene: CH3SiCH3|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}}

: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 {{chem name|N,N′-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene}}:{{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}}

File:DenkSiR2.png

The α-amido centers stabilize silylenes by π-donation. The dehalogenation of diorganosilicon dihalides is a widely exploited.{{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}}

Related reactions

File:Decamethylsilicocene.png is an example of a silylene.]]In one study diphenylsilylene is generated by flash photolysis of a trisilane:{{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}}

:File:Diphenylsilylene.png

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−1 s−1}} which is close to diffusion control.

See also

References

{{Reflist}}

Category:Inorganic silicon compounds

Category:Free radicals

Category:Octet-deficient functional groups