Self-Assembly Reactions To Form Multinuclear Zirconium(III) and Titanium(III) Complexes with Imidazole Derivatives as Bridging Ligands

Self-assembly reactions with low valent early transition metals, leading to neutral multinuclear complexes are rare. Mostly late transition metals like Pt, Pd or Ru together with N-heterocycles or O-donor-based ligands are used to form supramolecular coordination complexes. This paper reports on self-assembly reactions of low valent titanocene and zirconocene units and five-membered N-heterocycles as bridging ligands. These reactions lead to novel molecular triangles and rectangles with the metal centers marking the vertices. Five different imidazole derivatives and four different metallocene precursors were used. For the first time, molecular triangles and architectures with zirconocene as vertex units through self-sorting effects are reported. Less sterically demanding substituents lead to the formation of molecular rectangles, whereas more sterically demanding substituents, e.g. Cp*-ligands on the metal centers or phenyl groups on the bridging ligands lead to the formation of molecular triangles. The synthesis and properties of these air and moisture sensitive compounds are shown and discussed, and their molecular structures and geometries in the solid state were determined by single-crystal X-ray diffraction.