Structural diversity in tris(cyclopentadienyl) complexes of the Group 4 metals: Synthesis of Cp and MeCp complexes of Zr and Hf, and crystallographic characterization of (MeCp)3HfCl and (MeCp)4Zr (MeCp = C5H4CH3)

Previous theoretical studies have predicted structural differences between the tris(cyclopentadienyl) zirconium and hafnium complexes Cp3MX (Cp = C5H5; M = Zr, Hf). Cp3ZrCl can be isolated via the stoichiometric reaction of Cp2ZrCl2 and NaCp, but forming the analogous Hf complex is complicated by ligand redistribution. Partial crystallographic analysis of these two complexes indicates likely structural differences wherein the Zr complex has three η5 Cp ligands (“3-5” structure) while the Hf complex has two η5 Cp ligands and one η1 Cp ligand (“2-5,1-1” structure). The use of C5H4CH3 (MeCp) simplifies both the syntheses and the procurement of suitable crystals. The preparation of a number of MeCp complexes of Zr and Hf is reported along with crystallographic characterization of (MeCp)3HfCl, which has a 2-5,1-1 structure and (MeCp)4Zr, which has a 3-5,1-1 structure.

The complexes Cp3MX (M = Zr, Hf) have been predicted to exhibit different structures when X is a σ-only donor, such as an alkyl, or a weak π-donor, such as a halide. The Zr complexes are predicted to have three η5-Cp ligands (a “3-5” structure) whereas the Hf complexes are predicted to have two η5-Cp and one η1-Cp ligands (a “2-5,1-1” structure). This unusual structural diversity for these elements is explored using the C5H4CH3 (MeCp) ligand, and the structures of (MeCp)3HfCl and (MeCp)4Zr are reported.Figure optionsDownload as PowerPoint slide