19F NMR spectroscopy as useful tool for determining the structure in solution of coordination compounds of MF 5 (M = Nb, Ta)

Abstract

The salts [S(NMe 2) 3][MF 6] (M = Nb, 2a; M = Ta, 2b) and [S(NMe 2) 3][M 2F 11] (M = Nb, 2c; M = Ta, 2d) have been prepared by reacting MF 5 (M = Nb, 1a; M = Ta, 1b) with [S(NMe 2) 3][SiMe 3F 2] (TASF reagent) in the appropriate molar ratio. The solid state structure of 2b has been ascertained by X-ray diffraction. The 1:1 molar ratio reactions of 1a with a variety of organic compounds (L) give the neutral adducts NbF 5L [L = Me 2CO, 3a; L = MeCHO, 3b; L = Ph 2CO, 3c; L = tetrahydrofuran (thf), 3d; L = MeOH, 3e; L = EtOH, 3f; L = HOCH 2CH 2OMe, 3g; L = Ph 3PO, 3h; L = NCMe, 3i] in good yields. The complexes MF 5L [M = Nb, L = HCONMe 2, 3j; M = Nb, L = (NMe 2) 2CO, 3k; M = Ta, L = (NMe 2) 2CO, 3l; M = Nb, L = OC(Me)CH CMe 2, 3m] have been detected in solution in admixture with other unidentified products, upon 2:1 molar reaction of 1 with the appropriate reagent L. The ionic complexes [NbF 4(tht) 2][NbF 6], 4a, and [NbF 4(tht) 2][Nb 2F 11], 4b, have been obtained by combination of tetrahydrothiophene (tht) and 1a, in 1:1 and 2:3 molar ratios, respectively. The treatment of 1 with a two-fold excess of L leads to the species [MF 4L 4][MF 6] [M = Nb, L = HCONMe 2, 5a; M = Ta, L = HCONMe 2, 5b; M = Nb, L = thf, 5c; M = Ta, L = thf, 5d; M = Nb, L = OEt 2, 5e]. The new complexes have been fully characterised by NMR spectroscopy. Moreover, the revised 19F NMR features of the known compounds MF 5L [M = Ta, L = Me 2CO, 3n; M = Ta, L = Ph 2CO, 3o; M = Ta, L = MePhCO, 3p; M = Ta, L = thf, 3q; M = Nb, L = CH 3CO 2H, 3r; M = Nb, L = CH 2ClCO 2H, 3s; M = Ta, L = CH 2ClCO 2H, 3t], TaF 4(acac), TaF 4(Me-acac) and [TaF(Me-acac) 3][TaF 6] (Me-acac = methylacetylacetonato anion) are reported.