Synthesis and equilibria in solutions of hafnium fluoro complexes with phosphoryl-containing bases Ph3PO, Bu3PO, and (Me2N)3PO

Abstract

The composition and equilibria in solutions of the products of reaction of HfF₄(dmso)₂ with monodentate phosphoryl-containing bases L = Ph₃PO, Bu₃PO, and (Me₂N)₃PO in CH₂Cl₂ are studied by ¹⁹F NMR. Octahedral molecular complexes cis-[HfF₄L₂] and minor amounts of trans-[HfF₄L₂] and fac-[HfF₃L₃]⁺ cations were the main products for all ligands. The oxytrifluoride complex (μ-O)[HfF₃(Bu₃PO)₂]₂ and the [HfF₅(Bu₃PO)]^– anion were identified in the case of Bu₃PO. The conclusion about the formation of the hafnium oxytrifluoro complex was verified via hydrolysis of the product of reaction between HfF₄ and Ph₃PO upon exposure to air. As a result, (μ-O)[HfF₃(Ph₃PO)₂]₂ were detected; fine-structure ¹⁹F NMR resonance lines were obtained and the spin–spin coupling constant J_FF was measured for the first time. Hydrolysis via adding a Bu₄NOH solution in i-PrOH to the HfF₄L₂ solutions in CH₂Cl₂ did not yield the expected zirconium oxyfluoro complexes with the smaller number of fluorine atoms. Due to deeper hydrolysis, equilibrium in fluoride complexes shifted towards species with higher fluorine contents, [ZrF₅L]^– and [ZrF₆]^2–, resulting in the formation of Hf(O)_x(OH)_у(i-PrOH)_z complexes that were not observed in the ¹⁹F NMR spectra and the substitution of the released fluoride ions for molecular ligands in HfF₄L₂ complexes.