Ni Oxidation State and Ligand Saturation Impact on the Capability of Octaazamacrocyclic Complexes to Bind and Reduce CO.

Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO. In the first complex [], the octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second [] one, the macrocycle is saturated with hydrogens. One and two-electron reductions are described using Mulliken population analysis, quantum theory of atoms in molecules, localized orbitals, and domain averaged fermi holes, including the characterization of the Ni-C bond and the oxidation state of the central Ni atom. It was found that in the [] complex, the central atom is reduced to Ni and/or Ni and is thus able to bind CO via a single σ bond. In addition, the two-electron reduced [] species also shows an affinity forwards CO.