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.