title: Titanium-based molecular squares and rectangles: syntheses by self-assembly reactions of titanocene fragments and aromatic N-heterocycles.
abstract: This paper reports on the potential of titanium compounds as building blocks for supramolecular polygons. Self-assembly reactions of low-valent titanocene units and N-heterocyclic bridging ligands lead to novel titanium-based supramolecular squares. Pyrazine (3), 4,4'-bipyridine (4), and tetrazine (5) were used as bridging ligands, and the acetylene complexes [Cp2Ti{eta2-C2(SiMe3)2}] (1) and [(tBuCp)2Ti{eta2-C2(SiMe3)2}] (2) as sources of titanocene fragments. Molecular rectangles can be synthesized by stepwise reduction of the titanocene dichlorides [Cp(2)TiCl2] and [(tBuCp)2TiCl2] and consecutive coordination of two different bridging ligands. The resulting complexes are the first examples of molecular rectangles containing bent metallocene corner units. Single-crystal X-ray analyses of the tetranuclear compounds revealed the geometric properties of the molecular polygons in the solid state. Comparison of bond lengths and angles in coordinated and free ligands reveals the reduced state of the bridging ligand in the low-valent titanium compounds. The syntheses and properties of these novel, highly air- and moisture-sensitive compounds are discussed.
authors.affiliation: Institut für Reine und Angewandte Chemie, Fakultät für Mathematik und Naturwissenschaften, Carl von Ossietzky Universität Oldenburg, Postfach 2503, 26111 Oldenburg, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Kraft
authors.forename: Edith
authors.initials: E
authors.lastname: Hanuschek
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Beckhaus
authors.forename: Detlev
authors.initials: D
authors.lastname: Haase
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Saak
mesh_terms: D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011719:Pyrazines / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D014025:Titanium / Q000737:chemistry*
chemical_list: D006571:Heterocyclic Compounds; D006841:Hydrocarbons, Aromatic; D008024:Ligands; D009942:Organometallic Compounds; D011719:Pyrazines; D011725:Pyridines; C406884:titanocene; D014025:Titanium; C034306:4,4'-bipyridyl