Structure cristalline du complexe [FeCp((-)DIOP)I] analyse conformationnelle du cycle de chelation de la (-)diop

Synthesis of a functional C2-symmetrical bidentate diphenylphosphonite DIOP derivative and its conversion into the corresponding pi-acidic bis(pentafluorophenyl) and bis(p-tetrafluoropyridyl) compounds

The reaction of a C2-symmetric diiodo compound, 1,4-dideoxy-1,4-diiodo-2,3,-O-isopropyliden-L-threitole, with [K([18]crown-6)]P(CN)2 led to the generation of a corresponding bidentate dicyanophosphorus derivative. The in situ reaction with excess methanol and phenol yielded the corresponding bidentate dimethyl- and diphenylphosphonites, respectively. The isolated liquids were characterized by multinuclear NMR spectroscopy, elemental analysis, and mass spectrometry. The bidentate diphenylphosphonite ligand (a diphenoxyphosphane derivative) represents one of the very few functional bidentate phosphane derivatives: a DIOP [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis(methylene)]bis(diphenylphosphane) modification, in which the phenyl groups at the phosphorus atoms are replaced by functional phenoxy groups. Treatment of the bidentate diphenylphosphonite derivative with C6F5MgBr and p-C5NF4MgBr allowed the isolation and full characterization of the comparable bidentate bis(pentafluorophenyl) and bis(p-tetrafluoropyridyl)phosphanes. The ligand properties of the novel bidentate ligand systems were evaluated through the synthesis and vibrational investigation of their tetracarbonyl-molybdenum and cyclopentadienyl-iron complexes. The pi acidity of the synthesized ligands increases in the order methoxy-<phenoxy-<pentafluorophenyl-<p-tetrafluoropyridyl phosphane.

Chiral C(2)-symmetric ligands with 1,4-dioxane backbone derived from tartrates: syntheses and applications in asymmetric hydrogenation

Chiral 1,4-diphenylphosphines 5-7 as well as thioether 8 were synthesized from tartrates employing Ley's "BDA" and "Dispoke" methodologies as the key step. Rhodium(I) complexes with 5-7 are efficient catalysts for the asymmetric hydrogenation of beta-substituted enamides and MOM-protected beta-hydroxyl enamides, which furnished chiral amines or beta-amino alcohols with 94-->99% ee. These results indicated that the 1,4-dioxane backbone in the ligands having the general structure 2 played an important role in stabilizing metal-ligand chelate conformation. Higher enantioselectivities with ligand 2 were achieved compared with the analogous ligands having the general structure 1.