Abstract
The electronic structures and the electron transfer behavior of (m-pyrazine)Cr2(CO)10 and of (m-pyrazine)(CpMn(CO)4)2 (I) (Cp = h5-C5H5, h5-C5H4CH3, h5-C5(CH3)5) have been studied by electron spectroscopy, cyclic voltammetry, and high-resoln. ESR of the corresponding anion radicals. This combination of techniques allowed us to characterize the lowest unoccupied complex orbital as ligand-centered and the first electronic transition as a metal-to-ligand charge-transfer process. However, in agreement with their pronounced light sensitivity, another close and apparently photoreactive excited state is indicated by the unexpectedly small g values of the anion radicals, I-.bul., of the binuclear Mn(I) complexes. While the persistence of these anion radical complexes increases with the no. of Me substituents at the cyclopentadienyl rings due to less facile cleavage of Cp-, the reverse stability sequence has been obsd. for the photochem. induced ligand dissocn. A comparison of the binuclear organometallic complexes with related Fe(II), Ru(II), Os (II), and Ir(III) species suggests some similarity between the Mn(I) and Ru(II) systems according to a diagonal relationship. Inclusion of mononuclear Mn(I) compds. in the electrochem. and ESR studies reveals facile exchange processes such as the rapid formation of the more stable binuclear anion radicals upon redn. On the other hand, the oxidn. of all Mn(I)-pyrazine complexes was irreversible in DMF due to an ECE mechanism yielding solvent complexes of CpMn(CO)2. on SciFinder(R)
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