2,3‐Bis(diphenylphosphino)‐1,3‐butadien

2,3‐Bis(diphenylphosphino)‐1,3‐butadiene A method for synthesis of the title compound is described, using the readily available 2,3‐bis(diphenylphosphinoyl)‐1,3‐butadiene (1) as the starting material. For the protection of the diene system, 1 is first converted into the 1,4‐dibromo‐ and 1,4‐dichloro derivatives 2a and b, respectively, by addition of Br₂ or Cl₂, respectively. The structure of 2b has been determined by single‐crystal X‐ray diffraction. The molecule has a centrosymmetrical (E)‐configuration. Reduction of the phosphinoyl groups by HSiCl₃(to give the bis(diphenylphosphino)compound 3), followed by removal of the Cl‐atoms using Zn powder, affords the bis(diphenylphosphino)butadiene 4. Compounds 3 and 4 give quaternary phosphonium salts 5 and 6, respectively, on addition of CH₃OSO₂F or CH₃I. The sulfur analogue of 1 is formed on treatment of 4 with elemental sulfur.