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

Abstract

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 C_3v 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.