EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides
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The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium, gallium and indium trichlorides with phenyl azides containing a variety of substituents. Analysis of the spectra showed that 4-methoxy-, 3-methoxy- and 2-methoxyphenyl azides all gave ‘dimer’ radical cations [ArNHC6H4NH2]+• and trimers [ArNHC6H4NHC6H4NH2]+• followed by polymers. 4-Azidobenzonitrile, with its electron-withdrawing substituent, did not react. In general the aromatic azides appeared to react most rapidly with AlCl3 but this reagent tended to generate much polymer. InCl3 was the least reactive group 13 halide. DFT computations of the radical cations provided corroborating evidence and suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposed.
Bencivenni , G , Cesari , R , Nanni , D , El Mkami , H & Walton , J C 2010 , ' EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides ' , Beilstein Journal of Organic Chemistry , vol. 6 , pp. 713-725 . https://doi.org/10.3762/bjoc.6.84
Beilstein Journal of Organic Chemistry
© 2010 Bencivenni et al; licensee Beilstein-Institut. This is an Open Access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: (http://www.beilstein-journals.org/bjoc)
DescriptionFunding: The authors thank EaStChem and the EPSRC (UK Basic Technology Programme grant GR/S85726/01) for financial assistance. We also acknowledge financial support from MIUR, Italy (2008 PRIN funds for ‘Properties and reactivity of free radicals in complex environments and their role in oxidative processes and in organic synthesis’).
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