Synthesis and reactions of the co-ordinatively unsaturated hexafluorobut-2-yne complex [WBr2(CO)(CF3CCCF3)2]. The crystal and molecular structure of [{W[C(CF3)C(CF3)P(OEt)2O](µ-Br)(CO)(CF3CCCF3)}2]

Abstract

Reaction of [{WBr₂(CO)₄}₂] with CF₃CCCF₃ in pentane affords the bis(alkyne) complex [WBr₂(CO)(CF₃CCCF₃)₂](1) in which the carbonyl ligand appears to function as a σ-donor ligand only, according to i.r. data. Complex (1) reacts with P(OMe)₃ and P(OEt)₃ to give dimeric complexes [{W[C(CF₃)C(CF₃)P(OR)₂O](µ-Br)(CO)(CF₃CCCF₃)}₂] containing a novel vinylphosphonate ligand resulting from a Michaelis–Arbuzov type elimination of alkyl bromide. The structure of the complex with R = Et has been determined by X-ray analysis. Four centrosymmetric molecules occupy a monoclinic cell with a= 24.068(2), b= 8.440(2), c= 25.197(2)Å, β= 121.50(1)°, space group I2/a(no. 15, C⁶_2h), and R= 0.036 for 2 872 reflections. The tungsten co-ordination is octahedral with mutually cis carbonyl and σ-alkenyl carbon atoms both trans to µ-Br groups, and with phosphate O trans to a four-electron donor η²-CF₃CCCF₃. The bonding in the novel vinylphosphonate W[C(CF₃)C(CF₃)P(OEt)₂O] chelate ring is discussed.