NHC→SiCl4 : an ambivalent carbene-transfer reagent

Area of Science:

• Organometallic Chemistry
• Silicon Chemistry
• Carbene Transfer Reactions

Background:

• The carbene-transfer reagent (1,3-dimethylimidazolidin-2-ylidene)silicon tetrachloride (NHC→SiCl4) has been utilized in various chemical transformations.
• Understanding the reactivity of NHC→SiCl4 with different Lewis acids is crucial for developing new synthetic methodologies.

Purpose of the Study:

• To investigate the reaction of NHC→SiCl4 with Lewis acidic compounds such as BCl3, BF3·OEt2, and fluorinated silanes.
• To characterize the resulting silicon(IV) cations and explore their potential as precursors for electron-poor silylenes.

Main Methods:

• Reactions were conducted with BCl3, BF3·OEt2, and bis(pentafluoroethyl)silane derivatives in various solvents (acetonitrile, dichloromethane).
• Product characterization involved spectroscopic techniques to identify novel cationic silicon(IV) complexes and carbene transfer products.
• The reactivity towards phosphines was also examined.

Main Results:

• Reaction with BCl3 yielded tetra- and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3]+ and [(NHC)2SiCl3]+ with tetrachloroborate counterions.
• Reaction with BF3·OEt2 resulted in carbene transfer to form NHC→BF3.
• Treatment with bis(pentafluoroethyl)silane derivatives produced cationic silicon(IV) complexes in acetonitrile and carbene transfer products in dichloromethane, including species formed via chloride/hydride metathesis.

Conclusions:

• NHC→SiCl4 exhibits diverse reactivity with Lewis acids, leading to the formation of unique cationic silicon(IV) species.
• The observed carbene transfer and metathesis reactions highlight the versatility of NHC→SiCl4 as a synthetic tool.
• The synthesized compounds show promise as precursors for electron-poor silylenes, expanding the scope of silicon chemistry.