Complexes of molybdenum(VI) oxide tetrafluoride and molybdenum(VI) dioxide difluoride with neutral N- and O-donor ligands

[MoOF 4 (MeCN)], prepared from reaction of MoF 6 with (Me 3 Si) 2 O in anhydrous MeCN solution, reacts with the neutral O-donor ligands, thf, Ph 3 PO, Me 3 PO, dmf and dmso, (L) in a 1:1 molar ratio under rigorously anhydrous conditions to form six-coordinate [MoOF 4 (L)], which have been characterised by microanalysis, IR, 1 H, 19 F{ 1 H} and 95 Mo NMR spectroscopy. In the presence of moisture the major products are [MoO 2 F 2 (L) 2 ], which can be made directly by reaction of [MoOF 4 (L)] with a further equivalent of L and (Me 3 Si) 2 O. [MoOF 4 (MeCN)] and 2,2′-bipyridyl produce the insoluble [MoOF 4 (bipy)], which is probably 7-coordinate. Ph 3 AsO is quantitatively converted to Ph 3 AsF 2 by [MoOF 4 (MeCN)], and soft ligands, including Me 2 S, Me 3 P and Me 3 As, reduce the oxide fluoride on contact. Unstable [MoO 2 F 2 (MeCN) 2 ] has also been prepared and the X-ray structure of [MoO 2 F 2 (MeCN) 2 ]·MeCN is reported. X-ray crystal structures are reported for [MoOF 4 (Ph 3 PO)], [MoO 2 F 2 (Ph 3 PO) 2 ], [MoO 2 F 2 (Me 3 PO)(H 2 O)] and [Mo 2 O 4 F 2 (μ-F) 2 (Me 3 PO) 2 ]. Comparisons with the corresponding chemistries of WOF 4 and WO 2 F 2 are described.