A twist on Hellwinkel’s salt, [P(2,2′-biphenyl)2]+[P(2,2′-biphenyl)3]–

Treating PCl₅ with C₁₂H₈Li₂, generated from either C₁₂H₁₀, C₁₂H₈Br₂, or C₁₂H₈I₂, affords three products in different ratios depending on the source of the lithiated biphenyl. Hellwinkel’s salt [P(C₁₂H₈)₂][P(C₁₂H₈)₃] ([1][2]) and another product [P(C₁₂H₈)(C₂₄H₁₆)][P(C₁₂H₈)₃] ([1′][2]) were obtained by reacting PCl₅ with 2,2′-dilithiobiphenyl [Route A: 2.5 equiv.; obtained from biphenyl, n-BuLi, and TMEDA; Route B: 3.0 equiv.; obtained from 2,2′-diiodobiphenyl and n-BuLi; Route C: 4.0 equiv.; obtained from 2,2′-dibromobiphenyl and n-BuLi]. The synthesis, isolation, and characterization of the chiral spiro-compound [1′][2] and the characterization of the pentavalent phosphorane [P(C₁₂H₈)₂(C₁₂H₉)] (3) are reported. The complex [1′][2] was characterized by ³¹P{¹H} NMR spectroscopy, X-ray crystallography, and mass spectrometry. The pentavalent compound (3) was characterized by ³¹P{¹H} NMR spectroscopy and X-ray crystallography.