Formation of cationic monocyclopentadienyl metal(IV) compounds following halide abstraction from [M(η5-C5H5)Cl3(MeCN)2](M = Zr or Hf): crystal and molecular structure of [Hf(η5-C5H5)(MeCN)6][SbCl6]3·CH2Cl2

Abstract

Treatment of [M(η⁵-C₅H₅)Cl₃(MeCN)₂](M = Zr or Hf) with antimony(V) chloride in acetonitrile solution provides a convenient route to cationic monocyclopentadienyl metal(IV) species following halide abstraction. The hexachloroantimonate(V) salts [M(η⁵-C₅H₅)Cl₂(MeCN)₃][SbCl₆], [M(η⁵-C₅H₅)Cl(MeCN)₄][SbCl₆]₂ and [M(η⁵-C₅H₅)(MeCN)₆][SbCl₆]₃ have been isolated and characterised by micro-analytical and spectroscopic (IR, ¹H NMR) data. The presence of geometrical isomers in solution is discussed. The structure of [Hf(η⁵-C₅H₅)(MeCN)₆][SbCl₆]₃·CH₂Cl₂ has been established by X-ray crystallographic studies: monoclinic, space group P2₁/n, a= 22.627(7), b= 18.956(8), c= 22.699(7)Å, β= 98.80(7)°. The structure shows two independent [Hf(η⁵-C₅H₅)(MeCN)₆]³⁺ cations, six [SbCl₆]^– anions and two lattice solvent (CH₂Cl₂) molecules. The two cations show equivalent dimensions within experimental error and feature a seven-co-ordinate, pentagonal-bipyramidal metal geometry in which the cyclopentadienyl ligand occupies an axial position: Hf–C_ring 2.38(2)–2.53(2)(molecule 1) and 2.43(2)–2.51 (2)Å(molecule 2).