Synthetic and Structural Study of peri-Substituted Phosphine-Arsines

A series of phosphorus-arsenic peri-substituted acenaphthene species have been isolated and fully characterised, including single crystal X-ray diffraction. Reactions of EBr₃ (E = P, As) with iPr₂PAcenapLi (Acenap = acenaphthene-5,6-diyl) afforded the thermally stable peri-substitution supported donor-acceptor complexes, iPr₂PAcenapEBr₂3 and 4. Both complexes show a strong P→E dative interaction, as observed by X-ray crystallography and ³¹P NMR spectroscopy. DFT calculations indicated the unusual As∙∙∙As contact (3.50 Å) observed in the solid state structure of 4 results from dispersion forces rather than metallic interactions. Incorporation of the excess AsBr₃ in the crystal structure of 3 promotes the formation of the ion separated species [iPr₂PAcenapAsBr]⁺Br^- 5. A decomposition product 6 containing the rare [As₆Br₈]^2- heterocubane dianion was isolated and characterised crystallographically. The reaction between iPr₂PAcenapLi and EtAsI₂ afforded tertiary arsine (BrAcenap)₂AsEt 7, which was subsequently lithiated and reacted with PhPCl₂ and Ph₂PCl to afford cyclic PhP(Acenap)₂AsEt 8 and acyclic EtAs(AcenapPPh₂)₂ 9.