Stabilisation of [WF5]+ and WF5 by Pyridine: Facile Access to [WF5(NC5H5)3]+ and WF5(NC5H5)2

The enhanced reactivity of [WF5](+) over WF6 has been exploited to access a neutral derivative of elusive WF5. The reaction of WF6(NC5H5)(2) with [(CH3)(3)Si(NC5H5)][O3SCF3] in CH2Cl2 results in quantitative formation of trigonal-dodecahedral [WF5(NC5H5)(3)](+), which has been characterised as its [O3SCF3](-) salt by Raman spectroscopy in the solid state and variable-temperature NMR spectroscopy in solution. The salt is susceptible to slow decomposition in solution at ambient temperature via dissociation of a pyridyl ligand, and the resultant [WF5(NC5H5)(2)](+) is reduced to WF5(NC5H5)(2) in the presence of excess C5H5N, as determined by F-19 NMR spectroscopy. Pentagonal-bipyramidal WF5(NC5H5)(2) was isolated and characterised by X-ray crystallography and Raman spectroscopy in the solid state, representing the first unambiguously characterised WF5 adduct, as well as the first heptacoordinate adduct of a transition-metal pentafluoride. DFT-B3LYP methods have been used to investigate the reduction of [WF5(NC5H5)(2)](+) to WF5(NC5H5)(2), supporting a two-electron reduction of W-VI to W-IV by nucleophilic attack and diprotonation of a pyridyl ligand in the presence of free C5H5N, followed by comproportionation to W-V.