Synthesis, spectroscopic and structural characterization of the first mixed fluoro-bromo group 4 organometallic complex [{CpZrF₂Br}₄] (Cp = C₅Me₅)

Abstract

[{CpZrF₂Br}₄] is conveniently prepared in high yield from the reaction of [{CpZrF₃}₄] with four equivalents of Me₃SiBr. In contrast the reaction of [{CpZrF₃}₄] with Me₃SiI under identical reaction conditions leads to a mixture of [CpZrI₃] and unreacted [{CpZrF₃}₄]. The crystal structure of [{CpZrF₂Br}₄] has been determined by X-ray diffraction studies. The compound crystallizes in the orthorhombic crystal system [a = 9.325(1), b = 23.483(3), c = 27.016(5) Å , α = β =γ = 90°, space group Ibam, Z = 4]. The tetrameric core structure of [{CpZrF₂Br}₄] contains four zirconium atoms linked by alternating single and triple fluorine bridges. One terminal bromine atom is bonded to each zirconium. ¹H and ¹⁹FNMR spectroscopic data and structural features of the title compound are compared with those for the mixed fluoro-chloro complexes [{CpZrF₂Cl}₄], [{CpZrF₂Cl}₂{CpZrFCl₂}₂] and the trifluoro complex [{CpZrF₃}₄].