Persistent Metal Bis(Hexafluoroacetylacetonato) Complexes Featuring a 2,2′-Bipyridine Substituted Triarylamminium Radical Cation

Herein, we describe the preparation of a 2,2′-bipyridine derivative containing a redox-active N,N′-(4,4′-dimethoxydiphenylamino) substituent (1), which readily coordinates M(hfac)₂ salts [M = Mn (2), Ni (3), Cu (4)] to generate stable, neutral, and pseudo-octahedral coordination complexes, which have been fully characterized. Cyclic voltammetry and spectroelectrochemical measurements on complexes 2−4 indicate stable one-electron oxidation processes, and the formation of persistent radical cation complexes. The neutral complexes (M = Mn or Ni) were subject to one-electron oxidation with NOPF₆ in acetonitrile, and magnetic moments of the resulting solutions were obtained using the Evans method at different temperatures. Our experimental results suggest that the first reported ferromagnetically coupled metal−triarylamminum radical cation complex is obtained when M = Mn²⁺, and antiferromagnetic coupling results when M = Ni²⁺. These results are supported by results from density functional theory calculations, which indicate that a π spin polarization mechanism for magnetic exchange coupling is operative in singly oxidized complexes, 2−4.