Synthesis, structure, and electrochemistry of osmametallocenophanes with different ring size

The reaction of the bis(triflates) [eta(5)-C5H4(CH2)(n)OTf](2)M (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) [eta(5)-C5H4(CH2)(n)OH](2)M (2a- c, 3a-c) and (CF3SO2)(2)O in the presence of pyridine, with Na-2[Os(CO)(4)] in dimethyl ether results in the formation of the novel osmametallocenopha nes [eta(5)-C5H4(CH2)(n)Os(CO)(4)(CH2)(n)C5H4-eta(5)]M (6a-c, 7a-c). The st ructures 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 [eta (5)-C5H4(CH2)(n)Re(CO)(5)](2)M (8a-c, 9a-c) were made accessible from the b is(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 a nd 7b,c on the metal-metal distance was examined by means of cyclic voltamm etry. 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 ar e characterized by a reversible one-electron oxidation, whereas the rutheno cenes feature an irreversible two-electron process accompanied by a chemica l reaction. A consistent through-space effect of the spacer-bound substitue nts on the redox potential is observed in the case of the ferrocenes.