- Chiral molybdenum(VI) and tungsten(VI) 2′-pyridinyl alcoholate complexes. Synthesis, structure and catalytic properties in asymmetric olefin epoxidation
-
A new class of chiral molybdenum(VI) and tungsten(VI) complexes of the type MO2L*2 (M = Mo, W; L* = chiral 2′-pyridinyl alcoholate), available through several synthetic pathways, and their catalytic behavior in the asymmetric epoxidation of unfunctionalized olefins are reported. MO2Cl2, MO2(acac)2, and Na2[MO4] (M = Mo, W) served as starting materials for the synthesis of the chiral molybdenum(VI) or tungsten(VI) complexes, respectively. The new oxo complexes were fully characterized including X-ray crystallographic analyses. The chiral 2′-pyridinyl alcoholate ligands were derived from either (-)-menthone, (-)-fenchone, (-)-camphor or (+)-camphor. For catalytic runs in the enantioselective epoxidation, trans-methylstyrene was used as model substrate and tert-butylhydroperoxide as the oxidant. The molybdenum complexes exhibit good catalytic activity and substantial optical induction. By way of contrast, the analogous tungsten complexes have low activities at comparable optical yields.
- Herrmann, Wolfgang A.,Haider, Joachim J.,Fridgen, J?rg,Lobmaier, Gerhard M.,Spiegler, Michael
-
-
Read Online
- Highly diastereoselective synthesis of new optically active aminoalcohols in one step from (+)-camphor and (-)-fenchone
-
New optically active aminoalcohols have been prepared from CeCl3-activated (+)-camphor and (-)-fenchone and N-functionalized organolithium compounds. The aminoalcohols obtained catalyze the addition of diethylzinc to benzaldehyde in high yields
- Genov, Miroslav,Kostova, Kalina,Dimitrov, Vladimir
-
-
Read Online
- Chiral bis(oxazoline) and pyridyl alcoholate dioxo-molybdenum(VI) complexes: Synthesis, characterization and catalytic examinations
-
A group of chiral molybdenum(VI) complexes comprising MoO2Cl2L**, MoO2Cl(THF)L* and MoO2L*2 [L** = chiral bis(oxazoline) and L* = chiral 2′-pyridyl alcoholate] have been prepared in good yields by reaction of the solvent substituted complex MoO2Cl2(THF)2 with one or two equivalents of chiral ligand. Optically active aminoalcohols (L*) were obtained by reaction of the appropriate organolithium compound with (-)-menthone, (+)-8-phenylisomenthone, (-)-8-phenylmenthone, (+)-camphor and (-)-thujone. The molybdenum complexes were characterized by multinuclear NMR (1H, 13C, 17O, 95Mo) spectroscopy, IR spectroscopy and elemental analysis. 95Mo-NMR data reflected the donor capability of the organic ligands, whereas 1H-NMR and IR data were comparatively indifferent to the changes in the Lewis base ligand. The complexes were evaluated as catalysts for the asymmetric epoxidation of trans-β-methylstyrene by tert-butylhydroperoxide. The bis(oxazoline) complexes showed good catalytic activity but had low optical yields. Complexes of the type MoO2Cl(THF)L* (L* = chiral 2′-pyridyl alcoholate) also exhibited high catalytic activity and enantiomeric excesses of up to 23%. The corresponding MoO2L*2 alcoholate complexes were considerably less active with comparable optical yields.
- Kühn, Fritz E.,Santos, Ana M.,Lopes, André D.,Gon?alves, Isabel S.,Rodríguez-Borges, José E.,Pillinger, Martyn,Rom?o, Carlos C.
-
p. 207 - 217
(2007/10/03)
-