1,3-Dialkyltriazenyl radicals: their electron spin resonance spectra. Electronic configuration, and addition to trialkyl phosphites

Abstract

The 1,3-dialkyltriazenyl radicals R[graphic omitted]R, in which R = CH₃, CD₃, Prⁱ, or Bu^t, have been generated in solution from the parent triazenes and studied by e.s.r. spectroscopy. The triazenyl radicals exhibit large hyperfine splitting from the central nitrogen, smaller splitting from two equivalent alkylated nitrogens, and characteristically low g factors of ca. 2.0020. These spectroscopic parameters are as expected for a σ-radical, in which the SOMO is in the NNN plane, and this electronic configuration is supported by the results of semiempirical molecular orbital calculations. Dialkyltriazenyl radicals add to trialkyl phosphites to give the cyclic triazyl radicals (A), which may be regarded as ‘spin-labelled’ phosphoranes. The same [graphic omitted] radicals are produced by cyclisation of dialkyltriazeno(trialkoxy)phosphoranyl radicals (R²O)₃PN(R¹)NNR¹. The e.s.r. spectra of the spin-labelled phosphoranes exhibit temperature-dependent lineshape effects which are attributed to exchange of apical and equatorial nitrogen ligands, and an activation energy of 22 kJ mol^–1 for this exchange was obtained by computer simulation of the spectra for (A; R¹= Bu^t, R²= Me).