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

Abstract

Several new redox-active Fe(κ 2 -dppe)(η 5 -C 5 Me 5 ) arylacetylide complexes featuring pendant ethynyl (Fe(κ 2 -dppe)(η 5 -C 5 Me 5 )[{C≡C(1,4-C 6 H 4 )} n C≡CH] ( 1b – d; n = 1–3), Fe(κ 2 -dppe)(η 5 -C 5 Me 5 )[C≡C(1,3-C 6 H 4 )C≡CH] ( 2 )) or ethenyl (Fe(κ 2 -dppe)(η 5 -C 5 Me 5 )[C≡C(1,4-C 6 H 4 )CH═CH 2 ] ( 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(κ 2 -dppe)(η 5 -C 5 Me 5 )(C≡CH)][PF 6 ] ( 1a [PF 6 ]), 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.