Access to 1,2,3-triphospholide ligands by reduction of di-tert-butyldiphosphatetrahedrane†

Di-tert-butyldiphosphatetrahedrane (tBuCP)₂ (A) is a reactive tetrahedral molecule which may serve as a source of new phosphaorganic molecules and ligands. However, the redox chemistry of this compound has not yet been investigated. Here, we show that the reduction of A with alkali metals (AM = Li, Na, K, Rb and Cs) affords 1,2,3-triphospholides [AM(crown ether)][1,2,3-P₃C₂tBu₂] (1–5, [AM(crown ether)] = [Li([12]crown-4)₂]⁺, [Na([15]crown-5)₂]⁺, [K([18]crown-6)]⁺, [Rb([18]crown-6)]⁺, and Cs⁺) with 1,3-diphospholides [AM(crown ether)][1,3-P₂C₃tBu₃] (6–10) formed as by-products. The potassium salt 3 was isolated on a preparative scale, allowing for reactivity studies. Transmetalation with iron(II) and ruthenium(II) chlorides yielded the sandwich complexes [Cp*M(η⁵-1,2,3-P₃C₂tBu₂)] (11, M = Fe; 12, M = Ru, Cp* = C₅Me₅) featuring η⁵-coordinated triphospholide ligands. Treatment of 3 with [Cp₂Fe][BAr₄^F] or [H(Et₂O)₂BAr₄^F] (BAr₄^F = B{C₆H₃(CF₃)₂}₄) afforded the polyphosphorus compound tBu₄C₄P₆ (13), which presumably results from the dimerisation of a 1,2,3-triphospholyl radical intermediate (1,2,3-P₃C₂tBu₂)˙ (3˙). Tetracyclic 13 is closely structurally related to an isomer of the hydrocarbon hypostrophene (C₁₀H₁₀).