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. Most examples feature amido (NR2) or alkyl/aryl groups.
Silylenes have been proposed as reactive intermediates. They are carbene analogs.
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 → SiCl4Similar 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:5
SiCl2(CH3)2 + 2 K → Si(CH3)2 + 2 KClThe 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)3A room-temperature isolable N-heterocyclic silylene is N,N′-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene:6
The α-amido centers stabilize silylenes by π-donation. The dehalogenation of diorganosilicon dihalides is a widely exploited.7
Related reactions
In one study diphenylsilylene is generated by flash photolysis of a trisilane:8
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
References
Mizuhata, Yoshiyuki; Sasamori, Takahiro; Tokitoh, Norihiro (2009). "Stable Heavier Carbene Analogues". Chemical Reviews. 109 (8): 3479–3511. doi:10.1021/cr900093s. PMID 19630390. /wiki/Doi_(identifier) ↩
Nagendran, Selvarajan; Roesky, Herbert W. (2008). "The Chemistry of Aluminum(I), Silicon(II), and Germanium(II)". Organometallics. 27 (4): 457–492. doi:10.1021/om7007869. /wiki/Doi_(identifier) ↩
Haaf, Michael; Schmedake, Thomas A.; West, Robert (2000). "Stable Silylenes". Accounts of Chemical Research. 33 (10): 704–714. doi:10.1021/ar950192g. PMID 11041835. /wiki/Doi_(identifier) ↩
Gaspar, Peter; West, R. (1998). "Silylenes". The Chemistry of Organic Silicon Compounds. The Chemistry of Functional Groups. Vol. 2. pp. 2463–2568. doi:10.1002/0470857250.ch43. ISBN 0471967572. 0471967572 ↩
Skell, P. S.; Goldstein, E. J. (1964). "Dimethylsilene: CH3SiCH3". Journal of the American Chemical Society. 86 (7): 1442–1443. doi:10.1021/ja01061a040. /wiki/Doi_(identifier) ↩
Denk, Michael; Lennon, Robert; Hayashi, Randy; West, Robert; Belyakov, Alexander V.; Verne, Hans P.; Haaland, Arne; Wagner, Matthias; Metzler, Nils (1994). "Synthesis and Structure of a Stable Silylene". Journal of the American Chemical Society. 116 (6): 2691–2692. doi:10.1021/ja00085a088. /wiki/Doi_(identifier) ↩
Driess, Matthias; Yao, Shenglai; Brym, Markus; Van Wüllen, Christoph; Lentz, Dieter (2006). "A New Type of N-Heterocyclic Silylene with Ambivalent Reactivity". Journal of the American Chemical Society. 128 (30): 9628–9629. doi:10.1021/ja062928i. PMID 16866506. /wiki/Doi_(identifier) ↩
Moiseev, Andrey G.; Leigh, William J. (2006). "Diphenylsilylene". Journal of the American Chemical Society. 128 (45): 14442–14443. doi:10.1021/ja0653223. PMID 17090011. /wiki/Doi_(identifier) ↩