Synthesis, Structure, and Electrochemistry of Osmametallocenophanes with Different Ring Size † ,1

The reaction of the bis(triflates) [η5-C5H4(CH2) n OTf]2M (n = 3, M = Fe (4a), Ru (5a); n = 4, M = Fe (4b), Ru (5b); n = 6, M = Fe (4c), Ru (5c)), which are obtained from the bis(alcohols) [η5-C5H4(CH2) n OH]2M (2a − c, 3a − c) and (CF3SO2)2O in the presence of pyridine, with Na2[Os(CO)4] in dimethyl ether results in the formation of the novel osmametallocenophanes [η5-C5H4(CH2) n Os(CO)4(CH2) n C5H4-η5]M (6a − c, 7a − c). The structures of 6b (n = 4, M = Fe) and 7c (n = 6, M = Ru) were investigated by X-ray structural analyses. In a similar way the bis(rhenium) complexes [η5-C5H4(CH2) n Re(CO)5]2M (8a − c, 9a − c) were made accessible from the bis(triflates) 4a − c and 5a − c and Na[Re(CO)5] in THF. The dependence of the redox behavior of the metallocene unit in the osmametallocenophanes 6a − c and 7b,c on the metal−metal distance was examined by means of cyclic voltammetry. The obtained results were compared with those of the bis(alcohols) 2a − c and 3a − c and the bis(rhenium) complexes 8a − c and 9a − c. The ferrocenes are characterized by a reversible one-electron oxidation, whereas the ruthenocenes feature an irreversible two-electron process accompanied by a chemical reaction. A consistent through-space effect of the spacer-bound substituents on the redox potential is observed in the case of the ferrocenes.