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)].