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j
Scheme 2 One pot synthesis of [Rh(nbd)(L )].
potential ligands increases geometrically with each new chloro-
phos or silylmethylphosphine component, opens up the possi-
bility of applying HTE methods to diphosphine synthesis and
Fig. 3 (a) Crystal structure of 3j. Thermal ellipsoids are plotted at 50% catalyst screening in a way that previously, have only been applied
4
probability. Hydrogen atoms and the BF counterion have been omitted for
to monophos ligands. This is currently under investigation as is
the mechanism of the ligand formation reaction.
clarity. The two molecules in the asymmetric unit have the same orientation
hence only one is shown for clarity. Selected bond lengths (Å) and angles (1):
Rh1–P1 2.2839(7), Rh1–P2 2.3198(7), P1–C1 1.841(3), P2–C1 1.846(3),
We thank EPSRC for supporting this work with a student-
P1–Rh1–P2 72.84(3), P1–C1–P2 95.68(13). (b) Quandrant diagram of 3j, where ships to ELH.
shaded area represents a blocked quadrant.
Notes and references
1
2
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3
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6
7
8
Fig. 4 (a) Crystal structure of 4d. Thermal ellipsoids are plotted at 50%
probability. Hydrogen atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (1): Pt–Cl1 2.3572(8), Pt–Cl2 2.3657(8), Pt–P1 2.1620(9),
Pt–P2 2.2596(8), P1–C1 1.798(3), P2–C1 1.866(3), P1–Pt–P2 73.74(3), P1–C1–P2
9 M. van den Berg, A. J. Minnaard, E. P. Schudde, J. van Esch, A. H. M.
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1
1539–11540.
1
0 J. G. de Vries and C. J. Elsevier, The Handbook of Homogeneous
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Hydrogenation, Wiley-VCH, 2008.
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area represents a blocked quadrant.
1
1
2
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8
(F in Fig. 1). The mean planes through M–P–P–C have rms
deviations of 0.035/0.049 Å in 3j and 0.003 Å in 4d showing that
the chelates are almost planar (see Fig. 3 and 4). It is evident
from Fig. 4 that the upper left quadrant is blocked in the L
d
complex (and presumably the same would be the case for all the
ligands La–f) while Fig. 3 shows lower left quadrant is blocked in
the in L complex (and presumably the same would be the case
j
for all the ligands Lg–j). Therefore, the absolute configurations
of the products of asymmetric hydrogenation (Table 1) conform
to the quadrant rule.
The remarkable efficiency of the ligand synthesis (Scheme 1)
coupled with the ready removal of the volatile chlorosilane
1
075–1084; (h) W. Chen, F. Spindler, B. Pugin and U. Nettekoven,
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3 I. D. Gridnev and T. Imamoto, Acc. Chem. Res., 2004, 37, 633–644.
1
by-product suggested that a one-pot procedure may be feasible. 14 I. D. Gridnev, T. Imamoto, G. Hoge, M. Kouchi and H. Takahashi,
J. Am. Chem. Soc., 2008, 130, 2560–2572.
j
This was carried out according to Scheme 2 for L and the pro-
1
5 (a) A. H. Hoveyda, A. W. Bird and M. A. Kacprzynski, Chem. Commun.,
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duct tested for asymmetric hydrogenation of MAA. The 97% ee
that was obtained compares favourably with the 98% ee recorded
with the isolated complex (Table 1).
2
2
1
6 R. den Heeten, B. H. G. Swennenhuis, P. W. N. M. van Leeuwen, J. G.
de Vries and P. C. J. Kamer, Angew. Chem., Int. Ed., 2008, 47, 6602–6605.
The simplicity and generality of the chlorosilane elimination
route shown in Scheme 1 to C
1
-symmetric, C
1
-backboned, 17 (a) L. Lefort, J. A. F. Boogers, A. H. M. de Vries and J. G. de Vries,
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optically pure diphos ligands has been demonstrated by varying
the nature of the two P-reagents. The success of the one-pot
procedure (Scheme 2), coupled with the fact that the number of
de Vries and J. G. de Vries, Top. Catal., 2006, 40, 185–191.
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