Conformational equilibria of 2,5-bis(1-phenyliminoethyl)pyrazine anion radical, bpip˙–. An electron paramagnetic resonance/electron–nuclear double resonance study of bpip˙–, (bpip˙–)(RMg+)2, and of the related anion radical of N-tert-butylpyridine-2-carbaldimine (But-pyca)

EPR and ENDOR spectra were obtained for the anion radical forms of But-pyca (N-tert-butylpyridine-2-carbaldimine) and of the new symmetrical bis-chelate ligand bpip [2,5-bis(1-phenyliminoethyl)pyrazine]. The spin distribution of both species reflects the mixed imine/azine composition of the ‘α-diimine’ chelate moieties. In the absence of coordinating electrophiles, bpi˙– displays ENDOR-detectable conformational equilibria, presumably between s-cis/s-cis, s-cis/s-trans and s-trans/s-trans isomers. Bpip reacts with MgR2, R = 2-tolyl, in an electron-transfer fashion to form an organomagnesium radical complex.