beta-Silylcarbenes from isolable diazosilanes

Area of Science:

• Organic Chemistry
• Organosilicon Chemistry
• Reaction Mechanisms

Background:

• Diazocompounds are versatile synthetic intermediates.
• Understanding carbene reactivity is crucial for organic synthesis.
• The role of silicon in stabilizing reactive intermediates is an area of ongoing research.

Purpose of the Study:

• To synthesize and characterize a novel silyl-substituted diazocompound.
• To investigate the thermal and photochemical decomposition pathways of the diazocompound.
• To elucidate the mechanism of carbene formation and subsequent reactions, including migration events.

Main Methods:

• Synthesis of 2-tert-butyldimethylsilyl-1-phenyldiazoethane via manganese dioxide oxidation.
• Thermal and Rh(II)-catalyzed decomposition in cyclohexane and methanol.
• Photochemical decomposition in methanol.
• Kinetic studies and solvent isotope effect measurements.
• Computational studies (HF/6-31G and B3LYP/6-31G) for geometry optimization and energy calculations.

Main Results:

• Isolation of the novel diazocompound 2-tert-butyldimethylsilyl-1-phenyldiazoethane.
• Major product of thermal/Rh(II) decomposition in cyclohexane is 1-tert-butyldimethylsilyl-1-phenylethylene, indicating preferential 1,2-silyl migration.
• Decomposition in methanol yields alkene and methyl ether, suggesting a beta-silyl carbocation intermediate and protonation by methanol.
• Photochemical decomposition primarily yields the alkene.
• Computational studies show carbenes are not energy minima at B3LYP/6-31G, rearranging via silyl migration.

Conclusions:

• The study successfully synthesized and characterized a novel diazocompound.
• Preferential 1,2-silyl migration over 1,2-hydrogen migration is a key feature of the intermediate carbene.
• Evidence supports the involvement of beta-silyl carbocation intermediates in methanolysis.
• Computational results suggest facile rearrangement of carbenes via silyl migration, contrasting with experimental trapping observations.