Coordination Chemistry of Amine Bis(phenolate) Titanium Complexes: Tuning Complex Type and Structure by Ligand Modification

The coordination chemistry of titanium(IV) complexes of amine bis(phenolate) ligands was investigated by
synthesizing various types of complexes and analyzing them specroscopically and structurally. Steric effects of
tridentate [ONO]- and tetradentate [ONNO]-type ligands were studied by reacting the ligand precursors with
titanium tetra(isopropoxide). [ONNO]-type ligands featuring an amine donor located on a pendant arm led to
octahedral bis(isopropoxide) complexes, regardless of the steric bulk around the metal. Several such complexes
having varying steric crowding were thus synthesized. On the other hand, steric effects were found to play a
major role in determining the complex constitution when [ONO]-type ligands, featuring no side donor, were
involved. Relatively sterically undemanding ligands led to octahedral bis(homoleptic) complexes, whereas increased
steric bulk resulted in the formation of pentacoordinate bis(isopropoxide) complexes. These pentacoordinate
complexes readily lead to bis(heteroleptic) complexes by reaction with nonsterically demanding [ONO]- and
[ONNO]-type ligand precursors. In the latter case the sidearm nitrogen remains uncoordinated to the metal. The
bis(isopropoxide) complexes of the [ONNO]-type ligands may also lead to bis(heteroleptic) complexes, however,
these reactions are much slower.