Chemistry Reference
In-Depth Information
R
1
R
2
PPh
2
PPh
2
PPh
2
PPh
2
R
1
R
2
(
S
)-
8
:R
1
=TMS;R
2
=H
(
S
)-
9
:R
1
= P(O)(OH)
2
;R
2
=H
(
S
)-4,4'diamBINAP; R
1
=CH
2
NH
2
;R
2
(
S
)-
7
=H
(
S
)-5,5'-diamBINAP; R
1
=H;R
2
=CH
2
NH
2
(
S
)-
10
:R
1
=C
6
F
13
;R
2
=H
(
S
)-
11:
R
1
=H;R
2
=C
6
F
13
SO
3
Na
R
1
2
P
P
PPh
2
PPh
2
R
2
2
NH
2
+
Br
-
SO
3
Na
(
S
)
-Digm
-BINAP: R
1
=R
2
=
H
2
N
H
(
S
)-BINAP-4-SO
3
Na
(
S
)-PEG-BINAP: R
1
= MeO(CH
2
CH
2
O)
n
-
CO(CH
2
)
3
CONH, R
2
=NH
2
Figure 7.4.
Examples of BINAP analogues with substituents on the backbone or the phosphorus
atom.
While great achievement was obtained in developing chelating-bidentated ligands,
monodentated phosphines had almost disappeared even though one of the very fi rst
successful chiral phosphorus ligands CAMP was one of these. Feringa, de Vries, and
others recently demonstrated that monophosphorus ligands can deliver excellent per-
formance in asymmetric hydrogenation. The MonoPhos ligand family, easily synthesized
from BINOL in two steps, exhibited up to 99% ee in the Rh-catalyzed hydrogenation
of dehydroamino acids and aryl enamides [38]. Two modifi ed monophosphorus ligands
SIPHOS [39] and
55
[40] with more rigid backbones were also developed by Zhou and
Zhang, respectively (Fig. 7.10). The discovery of the Crabtree's catalyst opened up a
new fi eld for the development of chelating chiral P,N-ligands for asymmetric hydrogena-
tion [41]. A very successful example was demonstrated by Pfaltz and coworkers on their
PHOX ligands [42]. These chelating aryl phosphane and oxazoline ligands achieved
exceptionally good results in the Ir-catalyzed hydrogenation of unfunctionalized alkenes,
