Self-Assembly of Heterobimetallic Neutral Macrocycles Incorporating Ferrocene Spacer Groups: Spectroelectrochemical Analysis of the Double Two-Electron Oxidation of a Molecular Rectangle

Two Pt4−Fe2 mixed-metal neutral assemblies, 4 and 5, incorporating four bis(triethylphosphine)platinum(II) centers, two flexible bridging 1,1‘-ferrocenedicarboxylates, and two rigid 2,9-phenanthrenediyl (4) or 1,8-anthracenediyl (5) bridges, have been synthesized. X-ray characterization of 4 and 5 reveals the formation of discrete and highly symmetrical heterobimetallic neutral species possessing a rhomboidal and rectangular shape, respectively. The rectangular molecules, 5, could be reversibly oxidized in two two-electron steps, separated by 0.21 V. Spectroelectrochemistry in the UV−vis−NIR region confirms the ferrocene groups as primary oxidation sites; however, the intermediate 52+ is EPR silent even at 4 K due to enhanced EPR relaxation involving the oxidizable 1,8-anthracenediyl linkers.