Crystallographic characterisation of arenesulfonyl azides. Structural and kinetic effects induced by ortho- and para-substituents

Abstract

The molecular structures of six arenesulfonyl azides, ArSO₂N₃ (Ar = 4-nitrophenyl, 4-acetylphenyl, 4-methoxyphenyl, 2-nitrophenyl, 2,4,6-triisopropylphenyl or ferrocenyl group), have been characterised by X-ray diffraction studies. The N–N bond lengths are influenced only to a negligible extent by the nature of para-substituents. In contrast, the C–S and S–N distances are sensitive to the electron-withdrawing power of para-substituents and undergo opposing changes. These bond lengths as well as the ν_as(N₃) frequencies of the 4-substituted azides show linear dependencies as a function of Hammett's σ constants, which agree well with earlier results on the relative reactivities of arenesulfonyl azides toward [Pd₂Cl₂(dppm)₂]. The unusual structural properties of o-nitrobenzenesulfonyl azide are attributed to dipole–dipole interactions of the nitro group with the sulfonyl and the azide moieties. Although electronic effects due to para-substituents govern the magnitude of the second-order rate constants, the reactivity of o-nitrobenzenesulfonyl azide seems to be determined by steric interactions.