Syntheses, Structures, Bonding, and Redox Behavior of 1,4-Bis(ferrocenyl)butadiyne Coordinated Osmium Clusters

Abstract

The reaction of Os3(CO)11(NCMe) (1) with 1,4-bis(ferrocenyl)butadiyne (3) yielded two products: Os3(CO)10(μ3-η2-FcC4Fc) (4) and Os3(CO)11(μ3-η4-FcC4Fc) (5). Compound 4 was obtained in better yield (94%) from the reaction of Os3(CO)10(NCMe)2 (2) with 3 at 67 °C. Compound 4 contains a bis(ferrocenyl)butadiyne ligand coordinated to a triangular triosmium cluster via one of its alkyne groups in a triply bridging fashion. Compound 5 contains an open triosmium cluster with the two C−C triple bonds coordinated in a parallel fashion to the three metal atoms. Compound 2 reacts with 3 at 97 °C to yield the compound Os2(CO)6(μ-η4-FcC2C⋮CFc)2 (6) as a result of cluster fragmentation. Compound 6 exhibits a ferrole-type structure formed by the coupling two molecules of diyne 3. At 97 °C 4 is transformed into the new compound Os3(CO)9(μ3-η2-C⋮CFc)(μ-η2-C⋮CFc) (7), which contains two bridging ferrocenylacetylide ligands formed by cleaving the C−C bond between the two alkyne groups. All four products were characterized by IR, 1H NMR, and single-crystal X-ray diffraction analyses. The two ferrocenyl units in 4, 6, and 7 are inequivalent. The redox potentials of the ferrocenyl groups in 4 are very closely spaced, ΔEp = 0.057 V, suggesting that there is little electrocommunication between them. The redox potentials of the ferrocenyl groups in 6 are widely spaced, probably due to their intrinsic inequivalence. The two ferrocenyl units in 5 are equivalent but show two resolved one-electron redox processes, ΔEp = 0.184 V, which indicates that there is significant electrocommunication between them. This is attributed to greater interactions in the π-orbital network in the ligand 3 induced by coordination to the metal atoms. A molecular orbital model based on a butatrienediyl group is proposed to explain the coordination and π-bonding in the 1,4-bis(ferrocenyl)butadiyne ligand in 5.