Diphenylamine‐Substituted Osmanaphthalyne Complexes: Structural, Bonding, and Redox Properties of Unusual Donor–Bridge–Acceptor Systems

Diarylamine‐substituted osmanaphthalyne complexes that feature two redox centers linked by the rigid skeleton of the metallacycle (C^C + ), specifically, [OsCl 2 (PPh 3 ) 2 {(C^C + )NAr 2 }][BF 4 − ] (Ar=Ph ( 1 a ), p ‐MeOPh ( 1 b )) and their open‐ring precursors [OsHCl 2 (PPh 3 ) 2 {(≡C−C(PPh 3 + )=CHPh)NR 2 }][BF 4 − ] (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, [OsCl 2 (PPh 3 ) 2 {(C^C + )}][BF 4 − ] ( 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.