Two diphosphines bearing an ethynylene and a 1,2-phenylene linkers between the sterically crowded triarylphosphine moieties have been synthesized by employing Sonogashira and Suzuki-Miyaura couplings as key reactions, respectively. Intramolecular interactions between the two phosphine moieties were studied by UV–Vis spectroscopy and cyclic voltammetry. The UV–Vis spectrum of the ethynylene bridged diphosphine exhibits visible absorption in longer wavelength than that of the 1,2-phenylene bridged derivative reflecting lower LUMO spreading over the diphenylacetylene moiety. On the other hand, the cyclic voltammogram of the 1,2-phenylene bridged diphosphine shows larger difference of the first and the second oxidation potentials reflecting larger positive charge repulsion upon oxidation. The trend observed in the UV–Vis absorptions is similar to that of the structurally related diamines, whereas the voltammograms show the opposite trend, or dependence on the distance between the redox centers, reflecting the limited π-conjugation of the triarylphosphines.
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