International audienceSeveral 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
Several redox-active Fe(κ 2 -dppe)(η 5 -C 5 Me 5 ) arylacetylide complexes (dppe = 1,2-bis(diphenylphosphino)ethane) featuring a pendant ethynyl (1b−d and 2) or ethenyl (3) group have been grafted on oxide-free hydrogen-terminated silicon (Si−H) surfaces through a covalent interfacial Si−C bond. They form densely packed redox-active monolayers. The chargetransfer process between the terminal redox center and the underlying silicon interface was subsequently studied by cyclic voltammetry. The latter turned out to be strongly dependent on the nature of the spacer linking the organometallic end groups to the silicon surface, the highest charge-transfer rates being obtained for monolayers anchored through conjugated and unsaturated spacers. Although the rates measured were among the highest values obtained for redox-active systems grafted to Si− H surfaces, this study nevertheless suggests that the electron tunnelling is not entirely controlling the interfacial charge-transfer process for the shorter linkers tested. In this respect, strategies to improve further the charge-transfer kinetics of the produced redox-active films are briefly discussed.
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