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.