SYNTHESIS AND PROPERTIES OF AN OPTICALLY-ACTIVE HELICAL BIS-COBALTOCENIUM ION

The optically active helical bis-cobaltocenium salt 6 is synthesized, as are two related monocobaltocenium salts, 29 and 30. The structure o f 6 is analyzed by X-ray diffraction, which shows that the metals are separated by 8.49 angstrom. Reducing 6 either electrochemically or wit h K(Hg) produces species that absorb near 920 nm, but the absorption i s not an intervalence transition. It originates instead from isolated Co(II) centers. This is demonstrated by the reduction product of 29, w hich has only one cobalt, also absorbing at a similar wavelength (lamb da(max) = 957 nm). The optical and ESR spectra imply that the unpaired electron in monoreduced 6 is largely localized on cobalt and that dir educed 6 is essentially a Co(II)Co(II) diradical. The difference betwe en two Co(III)/Co(II) reduction potentials of 6, 130 mV, is shown to b e appropriate for a conjugated dimetallocene with metals so distant. C rystal data for 6: M = 1275.02; orthorhombic, space group P2(1)2(1)2(1 ); Z = 4; a = 11.560(4), b = 12.244(3), and c = 41.349(17) angstrom; V = 5852.5 angstrom3; R = 0.1137 for 4653 reflections having F(o) great er-than-or-equal-to nsigma(F(o)) (n = 7.5).