Novel 2,2′-bipyridine containing two (η2-dppe)(η5-C5Me5)Fe–CC– redox-active units with an exceptionally spatially demanding substitution pattern

Abstract

Synthetic approaches to 6,6′-disubstituted-2,2′-bipyridine ligands bearing two redox active (η²-dppe)(η⁵-C₅Me₅)Fe–CC– moieties are described. The target complex 6,6′-{(η²-dppe)(η⁵-C₅Me₅)Fe–CC}₂(2,2′-bipyridine) (6) was obtained in 79% yield as an orange powder from the reaction between the iron chloride (η²-dppe)(η⁵-C₅Me₅)Fe–Cl (9) and the 6,6′-bis(trimethylsilylethynyl)-2,2′-bipyridine (14) in the presence of KF and KPF₆ in a 3 : 1 methanol/THF mixture. When reacted with 2 equiv. of [(C₅H₅)₂Fe][PF₆], 6 provided the stable bis-iron(III) complex 6[PF₆66]₂22 in 89% yield which was characterized by an X-ray crystal structure. The substitution pattern of the novel metallo-ligand 6 is so spatially demanding that it does not react with CuCl, [Cu(CH₃CN)₄][PF₆] and PtCl₂, even in drastic conditions. Nevertheless, compound 6 reacts smoothly with ZnCl₂ to provide the zinc adduct ZnCl₂2(6), the spectroscopic properties of which evidence the Lewis acidic character of zinc dichloride.