100993-02-0Relevant articles and documents
Chiral molybdenum(VI) and tungsten(VI) 2′-pyridinyl alcoholate complexes. Synthesis, structure and catalytic properties in asymmetric olefin epoxidation
Herrmann, Wolfgang A.,Haider, Joachim J.,Fridgen, J?rg,Lobmaier, Gerhard M.,Spiegler, Michael
, p. 69 - 79 (2000)
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.
Chiral bis(oxazoline) and pyridyl alcoholate dioxo-molybdenum(VI) complexes: Synthesis, characterization and catalytic examinations
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)
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.
