Organometallics
Communication
(13) (a) Osborn, J. A.; Schrock, R. R. J. Am. Chem. Soc. 1971, 93,
determination of the enantiomeric excesses. This material is
3089. (b) Fischer, C.; Thede, R.; Drexler, H.-J.; Konig, A.; Baumann,
̈
W.; Heller, D. Chem. Eur. J. 2012, 18, 11920.
(14) Interestingly, the hydrogenation product from reaction of 4d
and ligand 3a (which contains an (Ra)-phosphite fragment; entry 4,
Table 1) had the same configuration as those obtained from ligands 3b
and 3d containing the (Sa)-phosphite fragment (entry 4, Table 1).
This observation suggests a substrate- and ligand-dependent
mechanistic scenario in the hydrogenations involving ligand 3a.
However, any mechanistic rationalizations about processes with low
enantioselectivity (e.g., 8% ee in entry 4, Table 1) should be made
judiciously.
(15) The ligands with an (Ra)-phosphite fragment (3a,c) led to the
(R)-, (S)-, and (R)-configured products of 6a−c, respectively. This
stereochemistry implies incorporation of the CHO and H groups into
the Si-alkene face (differences in the CIP R or S prefixes arise from
changes in the CIP priority rules and not from attack at the other
enantiotopic face of the alkene).
AUTHOR INFORMATION
■
Corresponding Author
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the MINECO (Grant CTQ2011-28512),
the DURSI (Grant 2009SGR623) and the ICIQ Foundation
for financial support.
REFERENCES
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(1) See Wassenaar, J.; Reek, J. N. H. Org. Biomol. Chem. 2011, 9,
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(6) The term bite-angle refers to the angle formed between the metal
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(10) For selected examples of highly efficient ligands containing the
chiral tert-butyl(methyl)phosphino fragment, see: (a) Imamoto, T.;
Watanabe, J.; Wada, Y.; Masuda, H.; Yamada, H.; Tsuruta, H.;
Matsukawa, S.; Yamaguchi, K. J. Am. Chem. Soc. 1998, 120, 1635.
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(11) Compound 1 was prepared using slightly modified procedures
from the following publications: (a) Genet, C.; Canipa, S. J.; O’Brien,
P.; Taylor, S. J. Am. Chem. Soc. 2006, 128, 9336. (b) Carbone, G.;
O’Brien, P.; Hilmersson, G. J. Am. Chem. Soc. 2010, 132, 15445.
(12) See the Supporting Information for details.
D
dx.doi.org/10.1021/om500378b | Organometallics XXXX, XXX, XXX−XXX