Stabilisation of [WF5 ]+ and WF5 by Pyridine: Facile Access to [WF5 (NC5 H5 )3 ]+ and WF5 (NC5 H5 )2.

The enhanced reactivity of [WF5 ]+ over WF6 has been exploited to access a neutral derivative of elusive WF5 . The reaction of WF6 (NC5 H5 )2 with [(CH3 )3 Si(NC5 H5 )][O3 SCF3 ] in CH2 Cl2 results in quantitative formation of trigonal-dodecahedral [WF5 (NC5 H5 )3 ]+ , which has been characterised as its [O3 SCF3 ]- 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 (NC5 H5 )2 ]+ is reduced to WF5 (NC5 H5 )2 in the presence of excess C5 H5 N, as determined by 19 F NMR spectroscopy. Pentagonal-bipyramidal WF5 (NC5 H5 )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 (NC5 H5 )2 ]+ to WF5 (NC5 H5 )2 , supporting a two-electron reduction of WVI to WIV by nucleophilic attack and diprotonation of a pyridyl ligand in the presence of free C5 H5 N, followed by comproportionation to WV .