Homoleptic phenolate complexes of zirconium(iv): syntheses and structural characterization of the first six coordinate complexes

Abstract

Homoleptic phenolate complexes of zirconium, [Na(THF)₂]₂[Zr(OC₆H₄-2-Cl)₆] and [NH₂(CH₃)₂]₂[Zr(OC₆H₄-2-Cl)₆]·2THF, were synthesized and fully characterized. To our knowledge, these complexes are the first examples for homoleptic six coordinated phenolate complexes of zirconium. Anaerobic reaction of zirconium tetrachloride with six equivalents of sodium 2-chlorophenolate afforded [Na(THF)₂]₂[Zr(OC₆H₄-2-Cl)₆] in excellent isolated yields. The geometry of the ZrO₆ core is octahedral with some distortion due to interactions of the sodium cations with oxygen atoms of the 2-chlorophenolate groups. The sodium cations are bound to five oxygen atoms: three to 2-chlorophenolate groups and two to THF. The coordination sphere is completed by interaction with chloride substituents of three 2-chlorophenolate ligands. A second example of a six coordinate complex of zirconium, [NH₂(CH₃)₂]₂[Zr(OC₆H₄-2-Cl)₆]·2THF, was synthesized by the reaction of zirconium tetrakis(dimethylamino) with six or four equivalents of 2-chlorophenol. The ZrO₆ core adopts a distorted octahedral geometry. Distortion is caused by hydrogen bonding between the dimethylammonium cation and the oxygen atom of one 2-chlorophenolate ligand. ¹H- and ¹³C-NMR spectroscopy revealed that [NH₂(CH₃)₂]₂[Zr(OC₆H₄-2-Cl)₆]·2THF decomposes in solution. These observations illustrate the profound influence that weaker secondary interactions to the donor atoms can have on metal coordination geometry.