Structural and electronic impact of fluorine in the ortho positions of triphenylphosphine and 1,2-bis(diphenylphosphino)ethane; a comparison of 2,6-difluorophenyl- with pentafluorophenyl-phosphines

Abstract

The new fluorine-containing phosphines PPh₂(C₆H₃F₂-2,6) I and PPh(C₆H₃F₂-2,6)₂ II were synthesized in high yield from C₆H₃BrF₂-2,6 and PPh₂Cl or PPhCl₂. Phosphines I, II and the previously reported P(C₆H₃F₂-2,6)₃ III have been structurally characterized by single-crystal X-ray diffraction. A range of transition metal complexes of IIII and the diphosphine (C₆H₃F₂-2,6)₂PCH₂CH₂P(C₆H₃F₂-2,6)₂ have been prepared and their spectroscopic properties compared with those of the analogous complexes of the pentafluorophenylphosphines PPh_x(C₆F₅)_3  x (x = 02) and the diphosphine (C₆F₅)₂PCH₂CH₂P(C₆F₅)₂. The structures of trans-[PtCl₂(PEt₃){PPh_x(C₆H₃F₂-2,6)_3  x}] (x = 2, 1 or 0), trans-[MCl(CO){PPh(C₆H₃F₂-2,6)₂}₂] (M = Rh or Ir), trans-[IrCl(CO){P(C₆H₃F₂-2,6)₃}₂] and trans-[PtCl₂{PPh(C₆H₃F₂-2,6)₂}₂] have been determined by single-crystal X-ray diffraction. The spectroscopic and structural data indicate that the 2,6-difluorophenylphosphines are more basic than the analogous pentafluorophenylphosphines and exert a similar or slightly smaller steric influence.