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O
Base
(COD)
*
[Ir(COD)
L*
Cl]
K3
Ir
P
K4
O
L
K1
N
Nu
Ar
Ar
R
OCOOMe
R
+
R
R
Nu
(COD)
HNu
(COD)
O
O
Ir
Ir
*
*
P
P
O
O
-
N
N
H
3
COCO
2
Ar
Ar
Ar
Ar
K5
K6
Scheme 8B.78.
Catalytic cycle of the allylic substitution using Ir complexes of phosphoramidite
ligands with
all - S
- confi guration (
L59 - L63
) as catalysts.
reversible and endergonic. The product complexes
K6
were observed (NMR) as a
mixture of diastereomers. The ratio of the diastereoisomers was in remarkably good
agreement with the ratio of the enantiomers of the isolated product. Accordingly, the
reaction
K5
→
K6
probably proceeds via a late transition state.
The catalytic cycle and the structures of the intermediates seem to be fairly stable
against variations. This is inferred from the observation that all allylic substitutions cata-
lyzed by (phosphoramidite)Ir complexes follow the general rule described by Scheme
8B.78 concerning absolute confi gurations of the products.
8B.7.1.5.3. Variation of the Phosphoramidite Framework
The modular construction of
phosphoramidite ligands is an important asset of this class of compounds. The most
important variants have already been presented in Figure 8B.33. Further important
aspects are discussed with reference to the following general formula:
X
R'
H
3
C
O
PN
R
O
R'
(a) For the binaphthalene derivatives with axial and central chirality (
L59 - L62
),
diastereoisomers with the (a
S
,
S
,
S
) and the (a
S
,
R
,
R
) confi guration, or their enan-
tiomers, that is, with
l -
or
u -
confi guration, are possible. Investigations for ligands
