Chemistry Reference
In-Depth Information
Me
Me
Pt/L* or Ni/L*
HSiMeCl
2
SiMeCl
2
+
Ph
Ph
1
2
CH
2
Ph
cis
-PtCl
2
(C
2
H
4
)(
3
): 5% ee (
R
)
trans
-NiCl
2
(
3
)
2
:18%ee(
R
)
3
:
P
Me
Ph
Me
Me
Rh
+
/L *(0 .0 5 mol %)
*
+
HSiMe
3
SiMe
3
Ph
Ph
120 C
1
4
H
L* = (
R
)-
3
:7%ee(
R
)
L* = (Î)-diop (
5
): 10% ee (
S
)
O
PPh
2
PPh
2
O
H
(Î)-(
R
,
R
)-diop (
5
)
Scheme 9.2.
SiCl
3
OH
Pd/L*
[O]
+
HSiCl
3
Ph
Ph
Me
Ph
*
Me
*
6
7
8
L*
SiCl
3
Pd
Scheme 9.3.
mops, have been developed and applied to palladium-catalyzed asymmetric hydrosi-
lylation. In the fi rst study reported in 1972, menthyldiphenylphosphine (
9
) and neomen-
thyldiphenylphosphine (
10
) were applied as chiral ligands in the palladium-catalyzed
reaction of styrene with trichlorosilane to afford 1 - (trichlorosilyl) - 1 - phenylethane (
7
) of
34% and 22% ee, respectively [6]. Moderate enantioselectivities (52-65% ee), which
were determined after oxidation of the hydrosilylation product into (
S
) - 1 - phenylethanol
(
8
), were realized by using planar chiral ferrocenylmonophosphine (
R
) - (
S
) - ppfa (
11
) and
chiral (β -
N
- sulfonylaminoalkyl)phosphine (
12
) derived from (
S
) - valinol in the asym-
metric hydrosilylation of styrene [7]. However, heterogenation of palladium catalysts
with (
R
) - (
S
)-ppfa, supported on a Merrifi eld polystyrene resin, turned out to give only
15% ee [8].
A remarkable improvement in enantioselectivity was achieved in palladium-
catalyzed asymmetric hydrosilylation by using axially chiral monophosphine ligands,
mops, having 1,1′-binaphthyl skeleton [9] (Table 9.1). A series of chiral mop derivatives
