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Triplet diphenylcarbenes protected by o-Aryl groups
Kyoko Monguchi1, Tetsuji Itoh, Katsuyki Hirai
1Chemistry Department for Materials, Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan.
Journal of the American Chemical Society
|September 24, 2004
Summary
Diphenyldiazomethanes photolysis primarily yields fluorenes via singlet carbene attack. Triplet carbenes were observed at low temperatures, but room temperature reactions showed different transient species, suggesting alternative pathways for fluorene formation.
Area of Science:
- Photochemistry
- Organic Chemistry
- Spectroscopy
Background:
- Diphenyldiazomethanes are precursors to diphenylcarbenes.
- Carbene reactivity is crucial in organic synthesis and photochemistry.
- Understanding carbene reaction mechanisms requires advanced characterization techniques.
Purpose of the Study:
- To characterize photochemically generated diphenylcarbenes.
- To elucidate the reaction mechanism leading to fluorene formation.
- To investigate the influence of reaction conditions and substituents on carbene behavior.
Main Methods:
- Photolysis of diphenyldiazomethanes in various matrices and solutions.
- Electron Spin Resonance (ESR) and UV/Vis spectroscopy at low temperatures.
- Laser Flash Photolysis (LFP) at room temperature.
- Product analysis and kinetic studies.
Main Results:
- Fluorenes are the exclusive products under typical conditions.
- ESR and UV/Vis spectroscopy identified triplet carbenes at low temperatures.
- LFP at room temperature revealed different transient species, distinct from low-temperature observations.
- Substituents on the phenyl rings showed minimal impact on the reaction pathway.
Conclusions:
- Fluorene formation likely proceeds through singlet carbene attack on the ortho-phenyl ring, followed by hydrogen shifts.
- Triplet carbenes can also be trapped by the ortho-phenyl ring, contributing to fluorene formation.
- Reaction conditions significantly influence the observed carbene species and reaction pathways.
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