Site-Selective Ligand Exchange on a Heteroleptic Ti-IV Complex Towards Stepwise Multicomponent Self-Assembly

A series of heteroleptic [Ti1(2)X](-) complexes have been selectively constructed from a mixture of Ti-IV ions, a pyridyl catechol ligand (H(2)1; H(2)1 = 4-(3-pyridyl)catechol), and various bidentate ligands (HX) in the presence of a weak base, in addition to a previously reported [Ti1(2)(acac)](-) (acac = acetylacetonate) complex. Comparative studies of these Ti-IV complexes revealed that [Ti1(2)(trop)](-) (trop = tropolonate) is much more stable than the [Ti1(2)(acac)](-) complex, which allows the replacement of acac with trop on the [Ti1(2)(acac)](-) complex. This Ti-IV-centered site-selective ligand exchange reaction also takes place on a heteronuclear Pd-II-Ti-IV ring complex with the preservation of the Pd-II-centered coordination structures. Intra- and intermolecular linking between two Ti-IV centers with a flexible or a rigid bis-tropolone bridging ligand provided a tetranuclear and an octanuclear Pd-II-Ti-IV complex, respectively. These higher-order structures could be efficiently constructed only through a step-wise synthetic route.