Synthesis of the first chiral bidendate bis(trifluoromethyl)phosphane ligand through stabilization of the bis(trifluoromethyl)phosphanide anion in the presence of acetone

摘要

Lewis acid/Lewis base adduct formation of the P(CF3)(2)(-) ion and acetone leads to a reduced negative hyperconjugation and, therefore, limits the C-F bond activation. The resulting increased thermal stability of the P(CF3)2- ion in the presence of acetone allows selective substitutions and enables the synthesis of the first example of a chiral, bidentate bis(trifluoromethyl)phosphane ligand: a DIOP derivative, [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis(methylene)]bis(diphenyl- phosphane), in which the phenyl groups at the phosphorus atoms are replaced by strong electron-withdrawing trifluoromethyl groups. The resulting high electron-acceptor strength of the synthesized bidentate (CF3)(2)P ligand is demonstrated by a structural and vibrational study of the corresponding tetracarbonyl-molybdenum complex. The stabilization of the P(CF3)(2)(-) ion in the presence of acetone is based on the formation of a dynamic Lewis acid/Lewis base couple, (CF3)(2)PC(CH3)(2)O-. Although there is no spectroscopic evidence for the formation of the formulated alcoholate ion, the intermediate formation of (CF3)(2)PC(CH3)(2)O- could be proved through the reaction with (CF3)(2)PP(CF3)(2), which yields the novel phosphane-phosphinite ligand (CF3)(2)PC(CH3)(2)OP(CF3)(2). This ligand readily forms square-planar Pt(II) complexes upon treatment with solid PtCl2.