Correlation analysis of the interconversion and nitrogen loss reactions of aryl pentazenes and pentazoles derived from aryl diazonium and azide ions

The pathways for the reaction of aryldiazonium cations with azide anion to arylazide and nitrogen are explored using the B3LYP/6‐311+G(d) method. CCSD(T) calculations were performed on the RN 5 (R = H, OH, Cl, CN) counterparts to verify the appropriateness of this density functional theory method to cases involving NN bond breaking. As in our prior MP2/6‐31G(d) study, a pathway to direct formation of aryl pentazole in a concerted reaction was not found. Transition state structures were calculated for the cyclization reaction of 24 aryl pentazenes in the E configuration and syn conformation (Es) to pentazoles and for the loss of N 2 from the Es, Ea (anti), and Za pentazenes and from pentazoles. Correlations were found between activation energies and both reaction energies and Hammett values for 24 aryl N 5 cases. The activation energies for competing cyclization and N 2 loss from Es pentazenes were both ca. 4 kcal/mol. The barriers for loss of N 2 from Ea and Za pentazenes are both ca. 20 kcal/mol. The lowering of the barriers in the Es configuration is attributed to the nucleophilic assistance of the in‐plane lone pair on the N1 atom and in‐plane aromaticity. Competition between N 2 loss from, and cyclization of the Es pentazene may provide for a synthesis of hitherto unknown arylpentazoles with electron withdrawing groups. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009