Silylene
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.[1] Most examples feature amido (NR2) or alkyl/aryl groups.[2][3]
Silylenes have been proposed as reactive intermediates. They are carbene analogs.[4]
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:[5]
- 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 Template:Chem name:[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 Template:Val which is close to diffusion control.
See also
- Carbene analogs
- N-heterocyclic silylene
- Silenes, R2Si=SiR2
- Silylium ions, protonated silylenes
References
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