Diphenylamine-Substituted Osmanaphthalyne Complexes: Structural, Bonding, and Redox Properties of Unusual...

Diarylamine-substituted osmanaphthalyne complexes that feature two redox centers linked by the rigid skeleton of the metallacycle (C^C⁺ ), specifically, [OsCl₂ (PPh₃ )₂ {(C^C⁺ )NAr₂ }][BF₄ ^- ] (Ar=Ph (1 a), p-MeOPh (1 b)) and their open-ring precursors [OsHCl₂ (PPh₃ )₂ {(≡C-C(PPh₃ ⁺ )=CHPh)NR₂ }][BF₄ ^- ] (Ar=Ph (2 a), p-MeOPh (2 b)), were successfully synthesized and characterized by ¹ H, ¹³ C, and ³¹ P NMR spectroscopy, ESI-MS, and elemental analysis. The solid-state molecular structures of complexes 1 a and 2 a were ascertained by single-crystal X-ray diffraction. The Os≡C bond length in both complexes 1 a and 2 a fell within the range reported for similar osmanaphthalynes and osmium carbyne complexes, respectively. The structural parameters determined for complex 1 a, which were successfully reproduced by theoretical calculations, point to a π-delocalized metallacycle structure. The purple color of compounds 1 a and b was explained by the diarylamine→Os(metallacycle) charge-transfer absorption in the visible region. The neutral, one-electron-oxidized and one-electron-reduced states of compounds 1 a, b, and a reference complex that lacked the diarylamine substituent, [OsCl₂ (PPh₃ )₂ {(C^C⁺ )}][BF₄ ^- ] (1'), were investigated by cyclic and square-wave voltammetry, UV/Vis/NIR spectroelectrochemistry, and DFT calculations. The spin density in singly oxidized complexes [1 a]⁺ and [1 b]⁺ predominantly resided on the aminyl segment, with osmium involvement controlled by the diphenylamine substitution. Spin density in stable, singly-reduced [1']^- was distributed mainly over the osmanaphthalyne metallacycle.