Abstract
The first series of complexes of niobium(v) oxide trifluoride, [NbOF3(OPR3)2] (R = Me or Ph), [NbOF3(dppmO2)] (dppmO2 = Ph2P(O)CH2P(O)Ph2), [NbOF3(dmso)2], [NbOF3(tmeda)] (tmeda = Me2N(CH2)2NMe2) and [NbOF3(diimine)] (diimine = 2,2'-bipy, 1,10-phen) have been prepared, either by reaction of the corresponding complexes of NbF5 and hexamethyldisiloxane (HMDSO) in CH2Cl2-MeCN solution, or directly from NbF5, ligand and HMDSO. They were characterised by IR, (1)H, (31)P{(1)H} and (19)F{(1)H} NMR spectroscopy, and X-ray crystal structures are reported for [NbOF3(OPR3)2] (R = Me or Ph) and [NbOF3(dppmO2)]. Complexes of NbOCl3, [NbOCl3(OPPh3)2], [NbOCl3(dppmO2)], [NbOCl3(dppeO2)] (dppeO2 = Ph2P(O)(CH2)2P(O)Ph2), [NbOCl3(tmeda)] and [NbOCl3(diimine)] were made from NbCl5 and HMDSO in MeCN (which forms [NbOCl3(MeCN)2] in situ), followed by addition of the neutral ligand. Their properties are compared with the oxide fluoride analogues. X-ray structures are reported for [NbOCl3(dppmO2)], [NbOCl3(dppeO2)], [NbOCl3(tmeda)] and [NbOCl3(2,2'-bipy)]. The synthesis and spectroscopic characterisation of [MF5L] (M = Nb or Ta; L = OPR3, OAsPh3) and [MF4(diimine)2][MF6] are also described, and the key properties of the four series of complexes compared.
Highlights
The fluorides and oxide fluorides of early transition metals in high oxidation states are strong Lewis acids and form a substantial range of complexes with F− and with hard N- or O-donor ligands, whilst their more limited chemistry with soft donor ligands (P, S etc.) sometimes includes redox chemistry at the metal centre and oxidation/fluorination of the heteroatom donor, in addition to adduct formation.[1]
Within Group V, the coordination chemistry of the oxide fluorides VOF3,2 and VO2F2,3 has been studied in some detail recently, whilst that of VF5 is completely unexplored
Similar behaviour was observed with VO2F,3 and the niobium system seems to be a further example of the metal centre preferring to form oxide/fluoride bridges rather than coordinate to weak, neutral donor groups.[1]
Summary
The fluorides and oxide fluorides of early transition metals in high oxidation states are strong Lewis acids and form a substantial range of complexes with F− and with hard N- or O-donor ligands, whilst their more limited chemistry with soft donor ligands (P, S etc.) sometimes includes redox chemistry at the metal centre and oxidation/fluorination of the heteroatom donor, in addition to adduct formation.[1]. The complexes [NbOF3(OPMe3)2] and [NbOF3(dppmO2)] were prepared to [NbOF3(OPPh3)2], but all attempts to obtain [NbOF3(OAsPh3)2] gave mixtures containing [NbF5(OAsPh3)], [NbF6]− and Ph3AsF2 (identified based upon in situ 19F and 93Nb NMR spectra).
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