Synthesis and structure of mononuclear titanium complexes containing ansa-aminopyridinato ligands

A series of siloxane-bridged bis(2-aminopyridines) were synthesized from dichlorosiloxanes and 2-aminopyridines in the presence of a base via nucleophilic substitution reactions. They were used, after deprotonation, as dianionic (ansa-aminopyridinato) ligands to stabilize mononuclear titanium complexes with unusual coordination geometries. An X-ray crystal structure analysis of one of the ligands and of a titanium complex proved mononuclearity and provided information about the binding mode of this novel type of ligands. Ethylene polymerization studies showed low activity, remarkable differences between structurally related complexes, and broad molecular weight distributions. Sterically less demanding substituents and a high basicity of the ligand increase polymerization activity.