Halogen effect on mixed-valence state of biosmocenium(II, IV) salts

• Biosmocenium-Cl adduct and biosmocenium-Br adduct were synthesized.
• The structures of each biosmocenium salt were determined by single crystal X-ray structural analysis.
• The intramolecular electron exchange reaction between OsII and Os IV was observed by 1H NMR.
• The activation energy of the electron exchange reaction was determined.
• The activation energy decreased in the order I > Br > Cl of halogen ligand bonded to Os center.

The mixed-valence biosmocenium(II, IV)–Cl adduct [(C5H5)OsII(μ2-η5:η5-C10H8) (C5H5)OsIVCl]Y(1a:YPF6, 1b:YBF4) and biosmocenium-Br adduct [(C5H5)OsII(μ2-η5:η5-C10H8) (C5H5)OsIVBr]PF6(2) were prepared. The structures of 1b and 2 were determined by single crystal X-ray analysis, and it was found that Os-X bond was fixed on cis position to the other half of osmocenyl moiety. Although 1b and 2 had the trapped-valence state in solid state, valence-detrapping depending on temperature was observed in solution state by using variable-temperature 1H NMR spectroscopy. It was found that intramolecular electron exchange reaction OsII–OIV ⇄ OsIV–OsII occurred accompanied by halogen migration. The activation energy of the reaction was determined. The energy decreased in the order A > 2 > 1a depending on a kind of halogen ligand bonded to Os center, and the tendency can be explained by HSAB theory.

The mixed-valence biosmocenium(II, IV)–Cl adduct [(C5H5)OsII(μ2-η5:η5-C10H8) (C5H5)OsIVCl]Y(1a:YPF6, 1b:YBF4) and biosmocenium-Br adduct [(C5H5)OsII(μ2-η5:η5-C10H8) (C5H5)OsIVBr]PF6(2) were synthesized. Valence-detrapping depending on temperature was observed in solution state by variable-temperature 1H NMR spectroscopy. It was found that intramolecular electron exchange reaction OsII–OIV ⇄ OsIV–OsII occurred accompanied by halogen migration.Figure optionsDownload as PowerPoint slide