Reactions of the metallocene dichlorides [M(Cp) 2Cl 2] (M = Zr, Hf) and [Ti(MeCp) 2Cl 2] with the pyridine-2,6-dicarboxylate(−2) ligand: Synthesis, spectroscopic characterization and X-ray structures of the products

Abstract

The reactivity pattern of the 16-electron species [M(Cp) 2Cl 2] (M = Zr, Hf; Cp − = η 5-C 5H 5 −) and [Ti(MeCp) 2Cl 2] (MeCp − = η 5-C 5H 4CH 3 −) towards the dipicolinate(−2) (dipic 2−) ligand under mild (ambient temperature) and convenient (aerobic reactions, aqueous media) conditions have been investigated. The syntheses, molecular structures and spectroscopic (IR, 1H NMR) characterization are reported for the 18-electron products [Zr(Cp) 2(dipic)] ( 1), [Hf(Cp) 2(dipic)] ( 2) and [Ti(MeCp) 2(dipic)] ( 3). The dipic 2− ion behaves as N,O,O′-chelating ligand in the three complexes, while the centroids of the Cp − ( 1, 2) and MeCp − ( 3) rings formally occupy the fourth and fifth coordination sites about the central metal. The two identical/very similar bite angles of only ∼70° make the dipic 2− ligand particularly suited to form stable metallocene derivatives with 5-coordinate geometry. IR and 1H NMR data are discussed in terms of the known structures and the tridentate chelating mode of the dipic 2− ligand.