Theoretical Assessment of Low-Valent Germanium Compounds as Transition Metal Ligands: Can They Be Better than Phosphines or NHCs?

We analyze the key transition metal ligand properties, σ-donor and π-acceptor ability, ligand-to-metal charge transfer, and steric parameters, using theoretical methods in order to examine 144 synthesized low-valent germanium compounds as potential ligands in homogeneous transition metal catalysis. We compare these features to those of currently widely used ligands (carbenes, phosphines). We find that several low-valent germanium compounds discovered lately, especially Ge(0) and double-donor-stabilized Ge­(II) compounds, can easily outperform phosphine ligands in σ-donor strength or reach the strength of NHCs. We set up a databank in which one can find the most suitable germanium-based ligand to promote different homogeneous catalytic steps. We present the factors behind the favorable features of low-valent germanium compounds, which may help to design new low-valent germanium compounds with enhanced properties in the future.