Homo- and heterobimetallic azines derived from ferrocene and cyrhetrene: Synthesis, structural characterization and electrochemical studies

A new series of asymmetrical heterobimetallic azines [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)–C(R) = N–N[dbnd]C(R¹)-(η⁵-C₅H₄)Re(CO)₃}] (1–3) and symmetrical homobimetallic cyrhetrenyl azines [{(η⁵-C₅H₄)–C(R) = N}Re(CO)₃]₂ (4, 5) have been synthesized and were spectroscopically characterized by FT-IR, NMR, EI-MS and cyclic voltammetry. The molecular structures of 1 and 4 were determined using single-crystal X-ray diffraction technique. Based on the oxidation potential of the ferrocenyl units and the high degree of planarity of the [(C₅H₄)–C(H) = N–N[dbnd]C(H)-(C₅H₄)] system in complex 1, we inferred electronic communication between the electron-withdrawing cyrhetrenyl groups through the π-conjugated azine bridge. The compounds display an (E,E)-configuration about the >C[dbnd]N- bond, an s-trans conformation for the N–N bond and an anti-conformation for the two organometallic fragments.