Preparation of organozirconium aromatic compounds in mixed aqueous-organic solvents: X-ray structures of [Cp2ZrCl(μ2-O′,O′′C-C6H5)], [(CpZr)3(μ2-O′,O′′C-C6H3Cl2)3(μ3-OH)(μ2-OH)3](Cl2C6H3COO)2, and [(CpZr)3(μ2-O′,O′′C-C6H4Cl)3(μ3-OH)(μ2-OH)3]Cl2·CH2Cl2

A new and facile method is presented for the synthesis of zirconocene carboxylate compounds, in which zirconocene dichloride (Cp2ZrCl2) is dissolved in 1 M aqueous HCl solution and the requisite ligand is dissolved in an organic solvent. Five such compounds [Cp2ZrCl(μ2-O′,O′′C-C6H5)] (1), [Cp2ZrCl(μ2-O′,O′′C-C6H3Cl2)] (2), [Cp2Zr(μ2-O′,O′′C-C6H3(OH)Cl)2] (3), [Cp2Zr(μ2-O′,O′′C-C6H3(OH)(NO2))2] (4), and [Cp2Zr(μ2-O′,O′′C-C6H(OH)Cl3)2] (5) have been obtained by this method. The effect of pH on the stability of Cp2ZrCl2 in 1 M HCl solution has been investigated by UV/vis spectrophotometry and 1H NMR spectrometry. The results showed that the aqueous Cp2ZrCl2 solutions became less stable with increasing pH, liberating cyclopentadiene. Accordingly, at higher pH (∼7), two trinuclear zirconium monocyclopentadienyl compounds, [(CpZr)3(μ2-O′,O′′C-C6H3Cl2)3(μ3-OH)(μ2-OH)3](Cl2C6H3COO)2 (6) and [(CpZr)3(μ2-O′,O′′C-C6H4Cl)3(μ3-OH)(μ2-OH)3]Cl2·CH2Cl2 (7), were obtained. All compounds 1–7 have been characterized by FT-IR, 1H NMR spectra and elemental analysis. In all of the compounds, the aromatic acid acts as a bidentate ligand in coordinating to the zirconium; both chelating and bridging modes are observed. X-ray crystallographic studies on 1, 6, and 7 have revealed that the geometries at zirconium are distorted octahedral in 6 and 7, and distorted trigonal-bipyramidal in 1.

Graphical abstractInvestigation of the pH dependence of the stability of Cp2ZrCl2 in aqueous solutions has shown that the synthesis of bis(cyclopentadienyl)zirconium carboxylate compounds requires a low pH (∼0), whereas that of compounds containing a core of three mono(cyclopentadienyl)zirconium units complexed to aromatic carboxylates proceeds at higher pH (∼7).Figure optionsDownload full-size imageDownload as PowerPoint slide