Mononuclear Rhodium(II) and Iridium(II) Complexes Supported by Tetradentate Pyridinophane Ligands

The tetradentate ligands N,N'-dialkyl-2,11-diaza[3,3] (2,6)pyridinophane ((R)N4, where R = Me or tBu) were employed to synthesize and fully characterize [((R)N4)M-I(COD)(+) complexes (M = Rh or Ir; COD = cyclooctadiene). Interestingly, these complexes exhibit accessible oxidation potentials and can generate detectable [((R)N4)M-II(COD)](2+) complexes, which were characterized by electron paramagnetic resonance and high-resolution electrospray ionization mass spectrometry. Moreover, a rare mononuclear [((Me)N4)Rh-II(COD)](2+) complex was isolated and crystallographically characterized, allowing for a direct comparison with its rhodium(I) analogue. The detailed characterization of such paramagnetic rhodium (II) and iridium(II) complexes enables further investigation of their redox reactivity.