Tris(2-pyridyl)phosphine as a versatile ligand for pnictogen acceptors

We report cationic complexes of arsenic and antimony with the tris(2-pyridyl)phosphine ligand. Chloride ion abstraction from AsCl3 using TMSOTf in the presence of the ligand gives [P(Pyr)3As][OTf]3, in which the trication adopts a C3v symmetric cage structure. The reaction proceeds via the intermediate [P(Pyr)3AsCl][OTf]2, which undergoes chloride exchange to give [P(Pyr)3As][OTf]3 and [P(Pyr)3AsCl2][OTf]. The rearrangement reaction has been supported by the isolation of the antimony mono fluoride derivative [P(Pyr)3SbF][OTf]2. The asymmetric axial lone pairs in derivatives of [P(Pyr)3Pn]3+ are electronically separated. The HOMO−1 (for arsenic) and HOMO (for antimony) represent the major contribution to the phosphine lone pair indicating the possibility for nucleophilic behaviour despite the +3 charge. Less accessible is the HOMO−7, which represents the lone pair at arsenic or antimony, respectively.