Abstract
Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO2. In the first complex 1[NiIIL]0, the octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second 1[NiIILH]2+ 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-CCO2 bond and the oxidation state of the central Ni atom. It was found that in the [NiLH] complex, the central atom is reduced to Ni0 and/or NiI and is thus able to bind CO2 via a single σ bond. In addition, the two-electron reduced 3[NiL]2− species also shows an affinity forwards CO2.
Highlights
IntroductionThe catalytic reduction of carbon dioxide to C1 chemicals (or even to liquid fuels, e.g., methanol) is receiving considerable attention
The catalytic reduction of carbon dioxide to C1 chemicals is receiving considerable attention
We focus on the oxidation state of the central Ni atom and the N-CCO2 bond
Summary
The catalytic reduction of carbon dioxide to C1 chemicals (or even to liquid fuels, e.g., methanol) is receiving considerable attention. Several recent reviews describe the electrocatalytic and/or photocatalytic reduction of CO2 using different molecular catalytic systems [1,2,3,4,5,6,7]. Many of these utilize expensive 4d and 5d transition metals, such as Ru, Rh, Pd, Re, Os, or Ir with bipyridine [8,9,10] or phosphate-like ligands [11,12,13,14]. Binuclear Cu(II) tetraazacyclotetradecane units show affinity forwards carboxylates, which could be a further interesting option for a CO2 reduction strategy [27,28,29,30,31]
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