Chemistry Reference
In-Depth Information
R
R
t
Bu
P
P
H
P
P
R
R
H
t
Bu
47a
R= iPr ( 82% ee)
47b
R= Ph ( 94% ee)
48
(94% ee)
R
R
O
O
O
N
N
N
R=
H
Ph
P
P
N
O
O
R
R
49
(82% ee)
Figure 10.9.
Bis - phosphacycles
47
-
49
. Enantioselectivities are shown in brackets.
PPh
2
N
O
P
O
50
Figure 10.10.
Phopshite - phosphoroamidite ligand
50
.
Recently, Zhang and coworkers developed a new phosphine-phosphoroamidite
ligand
50
based on BINAPHOS (Fig. 10.10). This ligand provided excellent enantiose-
lectivities (up to 99%) in the Rh-catalyzed hydroformylation of several vinylarenes [23].
Several heterodonor ligands containing a phosphite moiety have been developed with
little success (Fig. 10.11 ) [24] .
Recently, van Leeuwen and Reek reported the template-induced formation of chelat-
ing heterobidentate ligands by the selective self-assembly of two different monodentate
ligands on a rigid bis-zinc(II)-salphen template with two identical binding sites (Fig.
10.12) [25]. These templated heterobidentate ligands induce much higher enantioselec-
tivities (up to 72% ee, ligand
60
) in the rhodium-catalyzed asymmetric hydroformylation
of styrene than any of the corresponding homobidentate ligands or nontemplated mixed
ligand combinations (up to 13% ee).
