Syntheses, structural characterisation and electronic structures of ferrocenyl-osmafuran heterobinuclear organometallic complexes

Abstract

The heterobinuclear complex OsCl₂(PPh₃)₂[CHC(PPh₃)CFcO] (Fc = (C₅H₄)Fe(C₅H₅)) (1) in which the two metal centers were connected by the skeleton of the osmafuran and cyclopentadienyl was synthesized via a one-pot reaction of OsCl₂(PPh₃)₃ and FcCOCCH in high yield. Three derivatives (Os(η²-OCOO)(PPh₃)₂[CHC(PPh₃)CFcO] (2), Os(NCS)₂(PPh₃)₂[CHC(PPh₃)CFcO] (3), and OsCl₂(dppb)[CHC(PPh₃)CFcO] (dppb = Ph₂P(CH₂)₄PPh₂) (4)) were obtained by the ligand substitution reactions of complex 1 with different reagents (Cs₂CO₃ (2), NaSCN (3) and dppb (4)), respectively. All of these complexes were characterized by NMR spectroscopy and elemental analysis and the structures of complexes 1, 3 and 4 were further confirmed by single crystal X-ray diffraction. Their electrochemical properties were studied by cyclic voltammetry and square wave voltammetry. The first redox wave was ascribed to the couple Os(II)/Os(III). All of these complexes exhibit two redox processes with a large peak separation. However, UV-Vis-NIR combined with theoretical calculation clearly indicated that (1) the Os center plays a major role in the one-electron oxidation process of heterobinuclear complexes 1–4 and the osmafuran could be better described as a carbene ligand; (2) the electronic communication between the Os and Fe center is absent, and the osmafuran with the electron-withdrawing phosphonium substituent actually functioned as an insulating bridge.