Soft diphosphine and diarsine complexes of niobium(V) and tantalum(V) fluorides: synthesis, properties, structures and comparisons with the corresponding chlorides

The reactions of the soft diphosphines o-C6H4(PMe2)(2), Me2P(CH2)(2)PMe2, Et2P(CH2)(2)PEt2 or o-C6H4(PPh2)(2) with NbF5 or TaF5 in anhydrous MeCN solution produce [MF4(diphosphine)(2)][MF6] (M = Nb or Ta), which have been characterised by microanalysis, IR, H-1, F-19{H-1}, P-31{H-1} and Nb-93 NMR spectroscopy. X-ray crystal structures are reported for the isomorphous [MF4{o-C6H4(PMe2)(2)}(2)][MF6], which confirm the presence of eight-coordinate (distorted dodecahedral) cations. The corresponding reactions using o-C6H4(AsMe2)(2) produced [MF4{o-C6H4(AsMe2)(2)}(2)][MF6] which were similarly characterised, including by the X-ray structure of [NbF4{o-C6H4(AsMe2)(2)}(2)][NbF6]. These are very rare examples of arsine complexes of high valent metal fluorides. The chloro complexes [NbCl4{o-C6H4(PMe2)(2)}(2)]Cl, [TaCl4{o-C6H4(PMe2)(2)}(2)][TaCl6], [NbCl4{Me2P(CH2)(2)PMe2}(2)][NbCl6] and [MCl4{o-C6H4(AsMe2)(2)}(2)][MCl6] were prepared and their structural and spectroscopic properties compared with the fluoride analogues. Attempts to prepare diphosphine complexes of NbOF3 were unsuccessful, but the NbOCl3 complexes, [{{Me2P(CH2)(2)PMe2}NbOCl3}(2){mu-Me2P(CH2)(2)PMe2}] and [{o-C6H4(PMe2)(2)}NbOCl3(mu-O)NbCl3(CH3CN){o-C6H4(PMe2)(2)}] were obtained. X-Ray structures are also reported for [NbCl4{o-C6H4(PMe2)(2)}(2)]Cl, [NbCl4{o-C6H4(AsMe2)(2)}(2)][NbCl5(OEt)], [NbCl4{o-C6H4(PMe2)(2)}(2)][NbOCl4(CH3CN)], [{{Me2P(CH2)(2)PMe2}NbOCl3}(2){mu-Me2P(CH2)(2)PMe2}] and [{o-C6H4(PMe2)(2)}NbOCl3(mu-O)NbCl3(CH3CN){o-C6H4(PMe2)2}].