Unusual neutral ligand coordination to arsenic and antimony trifluoride

The preparations and spectroscopic characterisation of the hydrolytically unstable As(III) complexes, [AsF3(OPR3)(2)] (R = Me or Ph) and [AsF3{Me2P(O)CH2P(O)Me-2}] are described and represent the first examples of complexes of AsF3 with neutral ligands. The crystal structure of [AsF3{Me2P(O)CH2P(O)Me-2}] contains dimers with bridging diphosphine dioxide, but there are also long contacts between the dimers to neighbouring phosphine oxide groups, completing a very distorted six-coordination at arsenic and producing a weakly associated polymer structure. The reaction of AsF3 with OAsPh3 affords Ph3AsF2, and no arsine oxide complex was formed. Reaction of SbF3 with OER3 (R = Me or Ph, E = P or As), Me2P(O)CH2P(O)Me-2 and Ph2P(O)(CH2)(n)P(O)Ph-2 (n = 1 or 2) in MeOH produces [SbF3(OER3)(2)], [SbF3{Me2P(O)CH2P(O)Me-2}] and [SbF3{Ph2P(O)(CH2)(n)P(O)Ph-2}] respectively. The X-ray structures reveal that the complexes contain square pyramidal SbF3O2 cores with apical F and cis disposed pnictogen oxides. However, whilst [SbF3(OER3)(2)] (R = Ph: E = P or As; R = Me: E = As) and [SbF3{Ph2P(O)CH2P(O)Ph-2}] are monomeric, [SbF3{Me2P(O)CH2P(O)Me-2}] is a dimer with bridging diphosphine dioxides producing a twelve-membered ring, and [SbF3{Ph2P(O)(CH2)(2)P(O)Ph-2}] is a chain polymer with diphosphine dioxide bridges. In the OAsR3 reactions with SbF3, R3AsF2 are also formed. Notably the Sb-O(P) bonds are shorter than As-O(P), despite the covalent radii (As < Sb), consistent with very weak coordination of the AsF3. IR and multinuclear (H-1, F-19 and P-31) NMR data are reported and discussed. BiF3 does not react with pnictogen oxide ligands under similar conditions and halide exchange of bismuth chloro complexes with Me3SnF gave BiF3.