Reactions of Os3(CO)10(μ-H)2 with 1,8-Bis(ferrocenyl)octatetrayne Yield Products Involving Cyclizations and Trans-Hydrogenation of Alkyne Groups

Abstract

The reaction of 1,8-bis(ferrocenyl)octatetrayne (1) with Os3(CO)10(μ-H)2 (2) yielded three new osmium cluster complexes containing two electroactive ferrocenyl groups: Os3(CO)9(μ3,η3-FcCCHC4COC⋮CFc)(μ-H) (3); Os3(CO)10(μ3,η2-E-FcCHCHC2−C⋮C−C⋮CFc) (4); and Os6(CO)20(μ3,μ3-η2-η2-E,E-FcCHCHC2−C2CHCHFc) (5). All three compounds were characterized by IR, 1H NMR, and single-crystal X-ray diffraction analyses. In compound 3, the tetrayne chain was coupled to a CO ligand and cyclized to form an eight-membered heterobicycle containing two five-membered rings that bridges a closed cluster of three osmium atoms. Compound 4 contains one triangular triosmium cluster. Compound 5 contains two triangular triosmium clusters. In both 4 and 5, both the hydride ligands were transferred from the cluster to an alkyne group to form an olefinic group with E-stereochemistry. A mechanism for trans-hydrogenation at a bimetallic site is proposed. Cyclic and differential pulse voltammetric measurements show two reversible one-electron oxidation peaks for compounds 3 and 4 for their inequivalent ferrocenyl groups. Compound 5 shows only one two-electron oxidation for the two ferrocenyl groups, indicating no significant electrocommunication between them.