Tantalum(V) fluoride complexes of thio- and seleno-ether ligands and a comparison with the TaX5 (X = Cl or Br) analogues

Reaction of TaF5 with SMe2 and RS(CH2)2SR (R = Me, Et or iPr) in anhydrous CH2Cl2 solution produce colourless, extremely moisture sensitive crystals of [TaF4(SMe2)4][TaF6] and [TaF4{RS(CH2)2SR}2][TaF6] respectively, which contain eight-coordinate cations and octahedral anions, whereas TaF5 reacts with neat SR2 (R = Me or Et) to form six-coordinate [TaF5(SR2)]. Very unstable [TaF5(SeMe2)] and [(TaF5)2{μ-MeSe(CH2)2SeMe}] were isolated with the selenoether ligands and also contain six-coordinate tantalum species. Selected complexes of TaCl5 and TaBr5 have been prepared for comparison. The complexes have been characterised by IR, UV/visible and 1H and 19F{1H} NMR spectroscopies, and X-ray crystal structures are reported for [TaF4{MeS(CH2)2SMe}2][TaF6], [(TaCl5)2{μ-MeSe(CH2)2SeMe}] and [TaCl5(SeMe2)].

Synthesis and characterisation of the very rare examples of TaF5 complexes with soft donor ligands are reported, and the properties compared to analogues with TaCl5 and TaBr5.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and characterisation of a series of neutral, soft donor (S or Se) complexes of tantalum pentafluoride.
► The first structurally characterised soft donor (thioether) complexes of TaF5.
► Comparisons of the chemistry of TaF5 with TaCl5 and TaBr5 with neutral S and Se ligands.
► Both six- and eight-coordination are found in TaF5 adducts, whereas TaCl5/TaBr5 favour six-coordination.