Zusammenfassung
The reaction of pyrazine or 4,4'-bipyridine radical monoanions with M(CO)6 (M = Mo, W) yielded the stable radical anions of pentacarbonyl complexes which could be identified and analyzed by high-resoln. ESR. When compared with the free ligand anion radicals the paramagnetic complexes show distinct differences: (1) the proton coupling aH is slightly reduced upon complexation, indicating a flow of spin d. to the N centers and, possibly, to the metal carbonyl fragments; and (2) the N consts. aN of the complexes have increased significantly relative to the free anion radicals and metal isotope coupling reveals non-zero spin population at the metal center. The 13C satellite lines suggest a configurationally stable structure with 6-coordinate metal atoms and 2 sets of 8 equatorial and 2 axial carbonyl groups. The stabilized radical anion grouped state of these systems is described by hyperconjugative interaction of the ligand LUMO (p*) with antibonding metal-carbonyl s* orbitals. [on SciFinder(R)]
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