Abstract
The syntheses of the extremely moisture sensitive, neutral [MF5(PR3)] (M = Nb or Ta, R = Me or Ph) and [MF5(AsR′3)] (R′ = Me or Et), from reaction of the ligands with MF5 in anhydrous diethyl ether solution are reported. Attempts to isolate analogous complexes with SbMe3 were unsuccessful. The products are characterised by IR and mutinuclear NMR (1H, 19F{1H}, 31P{1H} and 93Nb) spectroscopic studies. These are the first examples of six-coordinate phosphine or arsine complexes of the Group 5 pentafluorides. The ionic species, trans-[MF4(PMe3)2][MF6], are obtained from diethyl ether solution of [MF5(PMe3)] containing excess PMe3 and similarly characterised. All complexes are extremely moisture and oxygen sensitive and decomposed by many common solvents. In solution in toluene the [MF5(PMe3)] (M = Nb or Ta) and [MF5(AsR′3)] are extensively dissociated at ambient temperatures. The [MF5(PPh3)] dissolve in CH2Cl2 with decomposition to form [PPh3H][MF6]. Attempts to isolate phosphine complexes of NbOF3 were unsuccessful.
Highlights
Niobium and tantalum pentafluorides are very strong, hard Lewis acids which form complexes with many neutral donor ligands; the commonest stoichiometries are the six-coordinate [MF5L] (L = monodentate ligand) and the ‘‘self ionisation’’ products [MF4L2][MF6] and [MF4L4][MF6] with six- and eight-coordinate cations, respectively [1]. Both types of complex with O, N- and S-donor ligands have been well characterised in recent studies [1,2,3,4], and we reported very recently [5] the first complexes with neutral bidentate phosphorus or arsenic donor ligands, [MF4(diphosphine)2][MF6] (M = Nb or Ta, diphosphine = o-C6H4(PMe2)2, Me2P(CH2)2PMe2, Et2P(CH2)2PEt2 or o-C6H4(PPh2)2) and the diarsine analogues [MF4(o-C6H4(AsMe2)2)2][MF6]
These were prepared by reaction of the appropriate MF5 with the Group 15 donor ligand in anhydrous MeCN, and spectroscopic and X-ray structural data showed that they all contain distorted eightcoordinate cations and regular octahedral anions
We report the successful synthesis of several new complexes of the pentafluorides with PR3 and AsR3 ligands, providing the first directly synthesised examples with sixcoordinate metal centres containing these soft donor pnictogen ligands
Summary
Niobium and tantalum pentafluorides are very strong, hard Lewis acids which form complexes with many neutral donor ligands; the commonest stoichiometries are the six-coordinate [MF5L] (L = monodentate ligand) and the ‘‘self ionisation’’ products [MF4L2][MF6] and [MF4L4][MF6] with six- and eight-coordinate cations, respectively [1] Both types of complex with O-, N- and S-donor ligands have been well characterised in recent studies [1,2,3,4], and we reported very recently [5] the first complexes with neutral bidentate phosphorus or arsenic donor ligands, [MF4(diphosphine)2][MF6] (M = Nb or Ta, diphosphine = o-C6H4(PMe2), Me2P(CH2)2PMe2, Et2P(CH2)2PEt2 or o-C6H4(PPh2)2) and the diarsine analogues [MF4(o-C6H4(AsMe2)2)2][MF6]. We report the successful synthesis of several new complexes of the pentafluorides with PR3 and AsR3 ligands, providing the first directly synthesised examples with sixcoordinate metal centres containing these soft donor pnictogen ligands
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