Unusual neutral ligand coordination to arsenic and antimony trifluoride

Abstract

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)Me₂}] are described and represent the first examples of complexes of AsF₃ with neutral ligands. The crystal structure of [AsF₃{Me₂P(O)CH₂P(O)Me₂}] 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)Me₂ and Ph₂P(O)(CH₂)_nP(O)Ph₂ (n = 1 or 2) in MeOH produces [SbF₃(OER₃)₂], [SbF₃{Me₂P(O)CH₂P(O)Me₂}] and [SbF₃{Ph₂P(O)(CH₂)_nP(O)Ph₂}] 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)Ph₂}] are monomeric, [SbF₃{Me₂P(O)CH₂P(O)Me₂}] is a dimer with bridging diphosphine dioxides producing a twelve-membered ring, and [SbF₃{Ph₂P(O)(CH₂)₂P(O)Ph₂}] 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 (¹H, ¹⁹F and ³¹P) 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.