RIGID BENT BRIDGES BETWEEN CYCLOPENTADIENYLMETAL FRAGMENTS - IRON DERIVATIVES OF THE 4,8-ETHANO-2,4,6,8-TETRAHYDRO-SYM-INDACENE-2,6-DIYL DIANION

From the reaction of the 4,8-ethano-2,4,6,8-tetrahydro-s-indacene-2,6-diyl dianion (L) and cyclopentadienyl (Cp) anion with iron (II) chloride the bridged ferrocenes syn, syn-CpFeLFeCp (4), syn,anti-CpFeLFeCp (5), and all-syn-CpFeLFeLFeCp (6) were obtained. The structures of 4-6, including syn, anti isomerism, were deduced from their H-1 and C-13 NMR and mass spectra. X-ray crystal analyses were carried out for 4 and 5 (4, monoclinic, P2(1)/n, a = 8.665 (1) angstrom, b = 7.724 (1) angstrom, c = 26.286 (2) angstrom, beta = 97.82 (1)-degrees, R(w) = 0.028 for 235 refined parameters and 3107 observables; 5.0.5C6H6, monoclinic, P2(1)/n, a = 6.087 (1) angstrom, b = 41.475 (4) angstrom, c = 7.995 (1) angstrom, beta = 96.58 (1)-degrees, R(w) = 0.074 for 262 refined parameters and 2219 observables). They showed that both molecules are rather distorted, leading to Fe-Fe distances which are almost 0.5 angstrom longer than those expected for an idealized geometry. In the cyclic voltammograms of 4-6 separate waves indicated that the ferrocene units were oxidized at different potentials. These potentials were shown to depend on the number of bridges and CpFe+ fragments next to the ferrocene unit under study. The separation of the potentials reflected the metal-metal interaction.