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.