Effects of Metal Coordination on the π‑System of the 2,5-Bis-{(pyrrolidino)-methyl}-pyrrole Pincer Ligand

Pincer complexes of 2,5-bis­{(pyrrolidino)-methyl}-pyrrole
with
group 14 elements such as germanium, tin, and lead were prepared and
fully characterized by X-ray single-crystal analysis, NMR spectroscopy,
and mass spectrometry. The structures of the complexes were analyzed
and compared to the free and the lithiated ligand to gain insight
into the effects of metal coordination on the aromatic system. A further
aspect was to elaborate the capability of group 14 metals to interact
with the pyrrole π-system. Therefore, electronic structure calculations
were carried out with group 14 complexes to better understand the
bonding situation and the trends among the group. The changes in the
aromaticity of the pyrrole ring upon coordination have been rationalized
according to the interaction of the π-system with the metal.
The unusual short bond distance observed between germanium and the
coordinated pyrrole nitrogen was also assessed.