Reactions of the metallocene dichlorides [M(Cp)2Cl2] (M = Zr, Hf) and [Ti(MeCp)2Cl2] with the pyridine-2,6-dicarboxylate(−2) ligand: Synthesis, spectroscopic characterization and X-ray structures of the products

The reactivity pattern of the 16-electron species [M(Cp)2Cl2] (M = Zr, Hf; Cp− = η5-C5H5−) and [Ti(MeCp)2Cl2] (MeCp− = η5-C5H4CH3−) towards the dipicolinate(−2) (dipic2−) 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 dipic2− 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 dipic2− 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 dipic2− ligand.

Graphical abstractThe 16-electron species [MIV(η5-C5H4R)2Cl2] (M = Zr, Hf and R = H; M = Ti, R = CH3) react with the dipicolinate(−2) ligand under mild and convenient conditions to give the shown, 18-electron [MIV(η5-C5H4R)2(dipic)] products, which have been characterized by single-crystal, X-ray crystallography and spectroscopic (IR, 1H NMR) techniques.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Bis(η5-cyclopentadienyl)(dipicolinato)zirconium(IV). ► Bis(η5-cyclopentadienyl)(dipicolinato)hafnium(IV). ► Bis(η5-methylcyclopentadienyl)(dipicolinato)titanium(IV). ► Reactivity of Group 4 metallocene dichlorides.