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Ir-phosphanodihydrooxazole catalyst gives 81% ee (.99% yield)
from the hydrogenation of 10,4a and that the (EBTHI)ZrMe2
system gives 93% ee (86% yield).5 All-in-all our ligands do not
show any promise for practical applications to the tetrasubstituted
olefins.
In summary, we have demonstrated that both cationic Ir- and
Rh-complexes of chiral (iminophosphoranyl)ferrocenes are very
powerful catalysts for asymmetric hydrogenation of a series of
unfunctionalized di- and trisubstituted olefins. Also notable is that
in some cases rhodium complexes may serve as even better
practical catalysts than their iridium counterparts.
5 M. V. Troutman, D. H. Appella and S. L. Buchwald, J. Am. Chem.
Soc., 1999, 121, 4916.
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This work was supported by KOSEF (Grant No. R01-2004-
000-10602-0). Spectral measurements were performed by the
KBSI.
Notes and references
{ Typical procedure for asymmetric hydrogenation is as follows:7
A
solution of 0.5 mmol substrate and 2 mol% of pre-catalyst in 5 mL of
CH2Cl2 (for Ir-catalysis) or MeOH (for Rh-catalysis) was stirred in an
autoclave under 10 bar of hydrogen pressure for 24 h at RT. Work-up
consisted of releasing the gas, evaporating the solvent, followed by
extraction of the hydrogenated product with 3 mL of heptane (HPLC
quality). The solution was applied directly to GC or HPLC for chemical
and optical yield measurements.
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This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 3537–3539 | 3539