Site-selective ligand exchange on a heteroleptic Ti(IV) complex towards stepwise multicomponent self-assembly

Abstract

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 stepwise synthetic route.