Reactions of Os-3(CO)(10)(mu-H)(2)with 1,8-bis(ferrocenyl)octatetrayne yield products involving cyclizations and trans-hydrogenation of alkyne groups

摘要

The reaction of 1,8-bis(ferrocenyl)octatetrayne (1) with Os-3(CO)(10)(mu-H)(2) (2) yielded three new osmium cluster complexes containing two electroactive ferrocenyl groups: Os-3(CO)(9)-(mu(3),eta(2)-FcCCHC(4)COCdrop) (4); and (mu(3),eta(3)-FcCCHC(4)COCdropCFe)(mu-H) (3); Os-3(CO)(10)(mu(3),eta(2)-E-FcCHCHC(2)Os(6)(CO)(20)(mu(3),mu(3)-eta(2)-eta (2)-E,E-FcCHCHC(2)-C(2)CHCHFc) (5). All three compounds were characterized by IR, H-1 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. [References: 23]