Chemistry Reference
In-Depth Information
t
Bu
O
O
P
O
P
O
O
O
O
O
O
O
O
=
,
m
,
l
a
,
b
,
j
,
k
=
O
O
O
P
O
O
P
O
O
t
Bu
24
(1
S
,5
S
,6
R
)
23
p
25
(1
R
,5
R
,6
S
)
(ee'supto16%)
(ee'supto70%)
O
O
Ph
O
P
P
O
O
O
O
O
O
O
O
=
j
,
k
,
l
,
m
,
n
O
(RO)
2
PO
O
OPh
O
P
O
O
P
O
OP(OR)
2
30
(
S
)
ax
(
R
)
ax
(
S
)
ax
(
R
)
ax
26
27
28
29
(ee's up to 36%)
(ee's up to 43%)
O
O
O
O
O
P
O
O
O
O
O
O
j
,
k
j
,
k
=
=
O
O
O
O
O
O
P
O
P
O
O
P
O
O
O
O
31
(ee'supto76%)
32
(ee's up to 76%)
Figure 10.4.
Miscellaneous of diphosphite ligands
23 - 32
. Enantioselectivities are shown in
brackets.
combinations of regio- and enantio-selectivities were therefore obtained with ligands
40a
and
40b
[17]. Recently, ligand
40a
has been successfully applied in the Rh-catalyzed
hydroformylation of vinylfuranes (ee's up to 99%) and vinylthiophenes (ee's up to 93%)
[18] .
The characterization of the rhodium complexes formed under hydroformylation
conditions by NMR techniques and
in situ
IR spectroscopy showed that there is a rela-
tionship between the structure of the [RhH(CO)
2
(BINAPHOS)] species and their enan-
tiodiscriminating performance. Thus, (
R
,
S
) and (
S
,
R
) - BINAPHOS ligands show high
equatorial - xial (
ea
) coordination preference with the phosphite moiety in the axial posi-
tion. Meanwhile, the characterization of the (
R
,
R
) - and (
S
,
S
) - BINAPHOS ligands sug-
gests that there is either a structural deviation of the monohydride complexes from an
ideal TBP structure or an equilibrium between isomers [10a,19].
