ELECTRON DELOCALIZATION IN MIXED-VALENCE BIFERROCENIUM SALTS - NUCLEAR MAGNETIC-RESONANCE CONTACT SHIFT STUDIES

1′,6′-Diethenylbiferrocenium triiodide (6) was prepared, and the intramolecular electron-transfer rate was determined. The X-ray structure of 1′,6′-diethenylbiferrocene at 300 K has been determined: monoclinic, P21/n, a = 5.7977 (4) Å, b = 17.2970 (20) Å, c = 9.1994 (13) Å, and β = 90.210 (15)°; ρcalcd = 1.520 g cm−3, Z = 2, RF = 0.04, and RwF = 0.03. The 1H and 13C NMR contact shifts have been observed for a series of mixed-valence biferrocenium triiodides. Analysis of the sign of contact shifts suggests that the electron delocalization is based on competing σ and π delocalization mechanisms. It appears that the σ skeleton in the delocalization of spin density is strongly favored in the cyclopentadienyl moiety. The unpaired spin delocalization in π-type orbitals is found to predominate in the fulvenide moiety. © 1990, American Chemical Society. All rights reserved.