Structures and electrocommunication between ferrocenyl groups in osmium cluster complexes of 1,8-bis(ferrocenyl)octatetrayne

The reaction of Os-3(CO)(11)(NCMe), 1, with 1,8-bis(ferrocenyl)octatetrayne, 3, has yielded four new products: Os-3(CO)(10)(mu (3)-eta (2)-Fc-C-2-C equivalent toC-C equivalent toC-C equivalent toC-Fc), 4; Os-3(CO)(10)(mu (3)-eta (2)-Fc-C equivalent toC-C-2-C equivalent toC-C equivalent toC-Fc), 5; Os-3(CO)(11)(mu (3)-eta (4)-Fc-C-4-C equivalent toC-C equivalent toC-Fc), 6; and Os-6(CO)(21)- (Fc-C-2-C-3-COC-C equivalent toC-Fc), 7. Compounds 4 and 5 were obtained in better yields from the reaction of Os-3(CO)(10)(NCMe)(2), 2, with 3, which also yielded a new hexaosmium compound, Os-6(CO)(20)(mu (6)-eta (4)-Fc-C equivalent toC-C-2-C equivalent toC-C-2-Fc), 8, formed by the addition of 2 equiv of 2 to 3. All five products were characterized by IR, H-1 NMR, and single-crystal X-ray diffraction analysis. Compounds 4 and 5 are isomers containing a triply bridging bis(ferrocenyl)octatetrayne ligand coordinated to a triangular triosmium cluster via different alkyne groups along the tetrayne chain. Compound 6 contains an open triosmium cluster coordinated in a parallel fashion to two adjacent triple bonds of the tetrayne chain of 3. Compound 7 contains two triosmium clusters. One is open and the other is a closed triangle. A CO ligand was coupled to the tetrayne to form a five-membered heterocycle and a ferrocenyl carbocation along the C-8-chain. Compound 8 crystallized in two modifications. In both forms the molecular structure contains two closed triosmium clusters with triply bridging alkyne units coordinated to each cluster from the first and third alkyne groups of the tetrayne chain of 3. In one crystal form each cluster has a bridging CO ligand. In the other modification there are no bridging CO ligands. The redox potentials of the ferrocenyl groups in 4, 5, and 8 are very the closely spaced, DeltaE(p) = 0.05 V, DeltaE(p) = 0.02 V, and DeltaE(p) = 0.03 V, respectively, suggesting that there is very little electrocommunication between them, but compound 6 shows two resolved one-electron redox processes, DeltaE(p) = 0.14 V, indicating that there may be significant electrocommunication in this case. This is attributed to greater interactions in the pi -orbtial network in the ligand 3 induced by coordination to the metal atoms.