Arene derivatives of zirconium(II) and hafnium(II)

Abstract

The anhydrous tetrahalides MX₄(M = Zr or Hf, X = Br or I) were prepared by treating M(BH₄)₄ with dry HX in n-heptane as solvent, followed by sublimation under reduced pressure. The reaction of ZrCl₄ with Al–AlCl₃–aromatic hydrocarbon systems led to solutions containing zirconium(II)–arene complexes. For the case of benzene and hexamethylbenzene (in benzene), solid substances of composition Zr(arene)(AlCl₄)₂ were obtained. On the basis of spectroscopic properties, chemical reactivity, and other data these substances are believed to be zirconium(II) derivatives, with structures similar to those already established for the corresponding titanium (II) complexes. The hexamethylbenzene complex of zirconium(II) can also be obtained by a ligand-synthesis reaction from [Zr(C₆H₆)(AlCl₄)₂] and but-2-yne. Spectroscopic evidence of the existence in solution of the corresponding hafnium(II)–η⁶-arene complexes (arene = toluene or mesitylene) has been obtained. The trinuclear species [Zr₃Cl₆(η⁶-C₆Me₆)₃]ⁿ⁺(n= 1 or 2) were obtained either by Al–AlCl₃ reduction of ZrCl₄(n= 2) or by treatment with water (n= 1) of the zirconium(II)–C₆Me₆–tetrachloroaluminate complex at low temperature.