Photo- and thermal-induced multistructural transformation of 2-phenylazolyl chelate boron compounds.

Ying-Li Rao, Hazem Amarne, Leanne D Chen, Matthew L Brown, Nicholas J Mosey, Suning Wang

Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6.

Journal of the American Chemical Society 2013 Mar 6

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The new N,C-chelate boron compounds B(2-phenylazolyl)Mes2 [Mes = mesityl; azolyl = benzothiazolyl (1a), 4-methylthiazolyl (2a), benzoxazolyl (3a), benzimidazolyl (4a)] undergo an unprecedented multistructural transformation upon light irradiation or heating, sequentially producing isomers b, c, d, and e. The dark isomers b generated by photoisomerization of a undergo a rare thermal intramolecular H-atom transfer (HAT), reducing the azole ring and generating new isomers c, which are further transformed into isomers d. Remarkably, isomers d can be converted to their diastereomers e quantitatively by heating, and e can be converted back to d by irradiation at 300 nm. The structures of isomers 1d and 1e were established by X-ray diffraction. The unusual HAT reactivity can be attributed to the geometry of the highly energetic isomers b and the relatively low aromaticity of the azole rings. The boryl unit plays a key role in the reversible interconversion of d and e, as shown by mechanistic pathways established through DFT and TD-DFT calculations.

Citation

Ying-Li Rao, Hazem Amarne, Leanne D Chen, Matthew L Brown, Nicholas J Mosey, Suning Wang. Photo- and thermal-induced multistructural transformation of 2-phenylazolyl chelate boron compounds. Journal of the American Chemical Society. 2013 Mar 6;135(9):3407-10