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 RN5 (R = H, OH, Cl, CN) counterparts to verify the appropriateness of this density functional theory method to cases involving N=N 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 N2 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 N5 cases. The activation energies for competing cyclization and N2 loss from Es pentazenes were both ca. 4 kcal/mol. The barriers for loss of N2 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 N2 loss from, and cyclization of the Es pentazene may provide for a synthesis of hitherto unknown arylpentazoles with electron withdrawing groups.