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

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 I-III and the diphosphine (C6H3F2-2,6)(2)PCH2CH2P(C6H3F2-2,6)(2) have been prepared and their spectroscopic properties compared with those of the analogous complexes of the pentafluorophenylphosphines PPhx(C6F5)(3-x) (x=0-2) and the diphosphine (C6F5)(2)PCH2CH2P(C6F5)(2). The structures of trans-[PtCl2(PEt3){PPhx(C6H3F2-2,6)(3x)}] (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.