Dipyrrolyldiketonato Titanium(IV) Complexes from Monomeric to Multinuclear Architectures: Synthesis, Stability, and Liquid-Crystal Properties.

Dipyrrolyldiketone ligands (H) are used with Ti(OPr) to afford monomeric titanium(IV) complexes displaying the general formula -[Ti()(OPr)]. The H ligands employed consist of two dipyrrolyldiketone compounds (H and H) and three diphenyl-substituted analogues (H-H). The behavior of these octahedral [Ti()(OPr)] species in solution was investigated by H NMR at variable temperatures. Dynamic phenomena were evidenced, and the activation parameters associated with these processes (Δ, Δ, and Δ) were retrieved. [Ti()(OPr)] complexes are precursors for the formation of high-nuclearity aggregates whose structures depend on the substituents on the diketone backbone. The crystal structures of monomeric ([Ti()(OPr)]; is the 1,3-diphenyl-1,3-propanedionato ligand) and [Ti()(OEt)]), dimeric ([Ti()(μ-O)]), and tetrameric ([Ti()(μ-O)]) species have been established, and the origin of this structural diversity is discussed. The solid-state optical properties of several complexes were determined and interpreted with the help of DFT calculations. Finally, the dinuclear complex [Ti()(μ-O)] was synthesized, where ligand incorporates six long alkyl chains (CH). This complex shows rich mesomorphic properties, with an original room-temperature plastic crystal phase followed by a hexagonal columnar liquid-crystalline phase.