Metallocene complexes of iron and cobalt derived from the 4,4 '-bis(eta(5)-cyclopentadienyl)octafluorobiphenyl ligand

The reaction of decafluorobiphenyl with 10 equiv of sodium cyclopentadienid e (NaCp) in THF (65 degrees C, 2 h) afforded 4,4'-bis(cyclopentadienyl)octa fluorobiphenyl (1) as a mixture of double-bond isomers in 72% yield after w orkup and purification. Subsequent treatment with sodium hydride in THF (25 degrees C, 6 h) afforded disodium 4,4'-bis(cyclopentadienyl)octafluorobiph enyl (2). Reaction of NaCp, ligand 2, and FeBr2 (21:1:10 mol ratio) in THF afforded mostly ferrocene as well as the diiron complex CpFe(eta(5)-C5H4-4, 4'-C6F4C6F4-eta(5)-C5H4)FeCp (3), the Linear triiron complex Cp[Fe(eta(5)-C 5H4-4,4'-C6F4C6F4-eta(5)-C5H4)](2)FeCp (4), and the linear tetrairon comple x Cp[Fe(eta(5)-C5H4-4,4'-C6F4C6F4-eta(5)-C5H4)](3)FeCp (5), which were isol ated by liquid chromatography. Solution voltammetric analysis of 3 showed a single, reversible two-electron oxidation at +200 mV, 4 showed two reversi ble oxidations (2:1 ratio) at +180 and +372 mV, respectively, and 5 showed two reversible oxidations (2:2 ratio) at +192 and +382 mV, respectively tal l vs Cp2Fe\Cp2Fe+). A similar reaction of NaCp, ligand 2, and CoBr2 in THF was worked up with air and dilute aqueous HCl followed by aqueous KPF6 to a fford a mixture of cobaltocenium hexafluorophosphates from which [Cp2Co]+PF 6- and the dicobalt complex [CpCo(eta(5)-C5H4-4,4'-C6F4C6F4-eta(5)-C5H4)CoC p](2+)[PF6-](2) (6) were isolated by liquid chromatography. CV analysis of 6 showed a single, reversible Co-II\Co-III wave at +232 mV relative to Cp2C o\(CpCo+)-Co-2. These voltammetric data suggest that no significant electro nic communication exists between two metals bridged by this conjugated diba sic ligand (2). A crystal structure of diiron complex 3 demonstrated the co nformational preferences of the CpC6F4C6F4Cp ligand in the solid state with respective torsional angles of 37.5 degrees, 50.1 degrees, and 32.1 degree s.