Synthesis and Characterization of Redox-Active Mononuclear Fe(κ²‑dppe)(η⁵‑C₅Me₅)‑Terminated π‑Conjugated Wires

Several new redox-active Fe­(κ2-dppe)­(η5-C5Me5) arylacetylide complexes featuring pendant ethynyl (Fe­(κ2-dppe)­(η5-C5Me5)­[{CC­(1,4-C6H4)}nCCH] (1b–d; n = 1–3), Fe­(κ2-dppe)­(η5-C5Me5)­[CC­(1,3-C6H4)­CCH] (2)) or ethenyl (Fe­(κ2-dppe)­(η5-C5Me5)­[CC­(1,4-C6H4)­CHCH2] (3)) groups have been synthesized and characterized under their Fe­(II) and Fe­(III) states. In contrast to the known ethynyl Fe­(III) complex [Fe­(κ2-dppe)­(η5-C5Me5)­(CCH)]­[PF6] (1a[PF6]), most of the new Fe­(III) derivatives turned out to be kinetically stable in solution. A consistent picture of the electronic structure of the latter complexes in both redox states emerged from experimental data and DFT calculations. This study revealed that beyond the first 1,4-phenylene ring, modification or extension of the carbon-rich linker using (4-phenylene)­ethynylene spacers will have only a minor influence on their electronic properties in their ground state, while still maintaining some (weak) electronic interaction along the carbon-rich backbone.