Science of Synthesis

Negishi, E.-i.; Takahashi, T., Science of Synthesis, (2003) 2, 807.

Selective introduction of only one cyclopentadienyl ligand on zirconium or hafnium is relatively difficult. Since the reaction of zirconium(IV) or hafnium(IV) chloride with lithium cyclopentadienide does not give pure mono(η5-cyclopentadienyl) complexes, various alternative methods have been developed. In contrast, selective introduction of three η5-cyclopentadienyl ligands to give tris(η5-cyclopentadienyl) complexes is easy. Even though four cyclopentadienyl ligands can be simultaneously bonded to zirconium, only three of them can be attached to the metal in a η5 mode; the fourth ligand only coordinates to zirconium in a η1 mode.

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