New diphosphoramidite rhodium complexes for asymmetric hydrogenation
H
cyclohex), 2.26–2.19 (mbr, 2H, Hcod), 1.96–1.90 (mbr, 2H, Hcod),
1
1
1
1
1
.88–1.84 (mbr, 2H, Hcyclohex), 1.60–1.49 (mbr, 2H, Hcyclohex),
.49–1.42 (mbr, 2H, Hcyclohex). C{ H} NMR (75 MHz, CDCl ) δ
3
13
1
47.66 (Car(q)), 146.92 (Car(q)), 132.39 (Car(q)), 131.67 (Car(q)),
31.36 (Car(q)), 128.40 (Car), 126.93 (Car), 126.77 (Car), 125.91 (Car),
21.30 (Car), 105.71 (Ccod), 105.63 (Ccod), 58.90 (C*cyclohex), 36.12
Scheme 3. Hydrogenation of 2-methyl acetamidoacrylate derivatives
catalyzed rhodium(I) complexes [Rh(cod)(R,R,Ra,Ra)-L1] 1, [Rh(cod)(R,R,
Sa,Sa)-L2] 2 and [Rh(cod)(R,R)-L3] 3.
31
1
(Ccyclohex), 31.06 (Ccod), 29.29 (Ccod), 25.05 (Ccyclohex). P{ H} NMR
1
(122 MHz, CDCl ) δ 136.66 (d, J
= 220 Hz). Anal. Calcd for
3
RhP
C H BF N O P Rh: calcd C 62.33; H 4.65; N 2.69; found: C
54
48
4 2 4 2
62.42; H 4.69; N 2.75.
Table 3. Asymmetric hydrogenation results for methyl 2-
4
[Rh(cod)(L3)]BF 3
acetamidoacrylate derivatives 6 and 7 with complexes [Rh(cod)(L1)]
1
4
a
BF
4
1, [Rh(cod)(L2)]BF
4
2 and [Rh(cod)(L3)]BF
4
3
Yield 111 mg, 94%. H NMR (300 MHz, CDCl
3
) δ 7.10 (d, J = 3 Hz,
4
4
Har, 2H), 7.03 (d, J = 3 Hz, Har, 2H), 6.71 (d, J = 3 Hz, Har, 2H),
.65 (d, J = 3 Hz, Har, 2H), 5.75 – 5.64 (mbr, 2H, Hcod), 5.43–
Entry
Catalyst Pressure (bar)
Conversion (%)
ee (%)
4
6
5.35 (mbr, 2H, Hcod), 3.86 (s, 6H, OMe), 3.84 (s, 6H, OMe), 3.25
Methyl 2-acetamidoacrylate
(
4
1
sbr, NH, 2H), 3.12–3.08 (mbr, 2H, H*cyclohex), 2.39–2.21 (mbr,
H, Hcod), 2.20–2.04 (mbr, 4H, Hcod), 1.63 (s, 18H, tBu), 1.60 (s,
8H, tBu), 1.58–1.53 (mbr, 2H, Hcyclohex), 1.52–1.46 (mbr, 2H,
1
2
3
4
5
6
1
1
2
2
2
3
1
20
1
99
100
<5
99
76.6 (R)
74.7 (R)
—
H
H
cyclohex), 1.12–1.07 (mbr, 2H, Hcyclohex), 1.05–1.00 (mbr, 2H,
5
84.8 (R)
87.0 (S)
51.1 (S)
13
1
cyclohex). C{ H} NMR (75 MHz, CDCl
ar(q)), 156.46 (Car(q)), 141.67 (Car(q)), 141.58 (Car(q)), 132.68 (Car
q)), 132.25 (Car(q)), 131.82 (Car(q)), 115.63 (Car), 115.03 (Car), 114.59
3
) δ 157.47 (Car(q)), 156.63
20
10
100
8
(C
(
(Z)-Methyl 2-acetamido-3-phenylacrylate
(C
ar), 114.36 (Car), 107.73 (Ccod), 104.61 (Ccod), 60.64 (C*cyclohex),
7
8
9
1
1
1
1
2
2
3
1
20
1
100
100
87
77.8 (R)
72.1 (R)
61.7 (S)
65.7 (S)
53.7 (S)
5
(
{
5.99 (COMe), 55.91 (COMe), 35.76 (CtBuq), 34.56 (Ccyclohex), 32.34
31
C
tBu), 32.09 (CtBu), 30.33 (Ccod), 29.91 (Ccod), 24.56 (Ccyclohex).
P
1
1
H} NMR (122 MHz, CDCl
3
) δ 135.26 (d, JRhP = 243 Hz). Anal. Calcd
0
1
5
100
27
for C58
5
4 2 8 2
H80BF N O P
Rh: calcd C 58.79; H 6.81; N 2.36; found: C
5
8.83; H 6.85; N 2.40.
a
Substrate/Rh = 1000, 25°C, 20 h. Conversion and ee values were
determined by GC.
General procedure for asymmetric hydrogenation
À3
[
Rh(cod)(P,P)]BF 1–3, (2 × 10 mmol) and 2 mmol of substrate
4
was dissolved in CH Cl2 (2.5–7.5 ml) under argon. The yellow
2
solution was introduced with a syringe into a 100 ml glass-lined,
stainless steel autoclave containing a magnetic stirring bar.
Hydrogen was introduced to the desired pressure and the
reaction mixture was stirred at 25°C for 20 h. Then, the hydrogen
pressure was released and the solution was passed through a
short pad of silica and analyzed by GC.
of hexane a yellow powder was obtained. It was filtered, washed
with hexane and dried in vacuo.
4
[Rh(cod)(L1)]BF 1
1
3
Yield 95.7 mg, 92%. H NMR (300 MHz, CDCl ) δ 8.07 (d, J = 9 Hz,
3
3
3
Har, 4H), 7.98 (d, J = 8 Hz, Har, 4H), 7.55 (d, J = 9, Ho, 4H),
.53–7.51 (mbr, Har, 4H), 7.41 (d, J = 9 Hz, Har, 4H), 7.32
3
7
(
mbr, Har, 4H), 5.89–5.80 (mbr, 2H, Hcod), 5.52–5.45 (mbr, 2H, Hcod),
Conclusions
3
2
2
(
(
(
(
.73 (sbr, 2H, NH), 3.76–3.60 (mbr, 2H, H*cyclohex), 2.56–2.45 (mbr,
H, Hcod), 2.34–2.29 (mbr, 2H, Hcod), 2.30–2.25 (mbr, 2H, Hcod),
.25–2.21 (mbr, 2H, Hcod), 2.10–2.05 (mbr, 2H, Hcyclohex), 1.84–1.76
The cationic Rh(I) complexes [Rh(cod)(P,P)]BF with C -symmetric
4
2
chiral diphosphoramidite ligands containing a chiral diamine
backbone and two atropoisomeric biaryl units have been easily
prepared and fully characterized to be tested as catalysts in the
asymmetric hydrogenation of prochiral benchmark substrates
dimethyl itaconate, methyl 2-acetamidoacrylate and (Z)-methyl-
mbr, 2H, Hcyclohex), 1.53–1.44 (mbr, 2H, Hcyclohex), 1.44–1.39
1
3
1
mbr, 2H, Hcyclohex). C{ H} NMR (75 MHz, CDCl
3
) δ 152.74
C
C
ar(q)), 147.67 (Car(q)), 146.53 (Car(q)), 132.57 (Car(q)), 131.37
ar(q)), 128.40 (Car), 127.36 (Car), 126.82 (Car), 125.81 (Car),
21.30 (Car(ortho)), 105.97 (Ccod), 105.51 (Ccod), 58.20 (C*cyclohex),
1
3
{
2-acetamido-3-phenylacrylate.
3
1
5.63 (Ccyclohex), 31.50 (Ccod), 28.70 (Ccod), 24.42 (Ccyclohex).
P
The rhodium complexes derived from diastereomeric
diphosphoramidite ligands (R,R,R ,R )-L1 and (R,R,S ,S )-L2, which
contain two BINOL (2,2′-dihydroxy-1,1′-binaphthyl) units, can be
successfully applied to asymmetric olefin hydrogenation.
1
1
H} NMR (122 MHz, CDCl
3
) δ 137.04 (d, JRhP = 235 Hz). Anal.
Rh: calcd C 62.33; H 4.65; N 2.69;
found: C, 62.43; H, 4.68; N, 2.74.
a
a
a a
4 2 4 2
Calcd for C54H48BF N O P
An uncommon positive H
was observed in the hydrogenation of dimethyl itaconate catalyzed
by Rh-complex with diphosphoramidite ligand (R,R,S
contains two (S)-binaphthol moieties.
The rhodium complex with ligand L3 in which each BINOL unit
was replaced by two fluxional axially chiral 3,3′-dimethoxy-5,5′-di-
tert-butyldiphenol groups exhibited very low activity as well as
poor asymmetric induction.
2
pressure effect on the enantioselectivity
[
4
Rh(cod)(L2)]BF 2
1
3
Yield 92.6 mg, 89%. H NMR (300 MHz, CDCl
Har, 4H), 8.00 – 7.95 (mbr, Har, 4H), 7.56–7.53 (mbr, Ho, 4H),
.52–7.49 (mbr, Har, 4H), 7.40–7.36 (mbr, Har, 4H), 7.33–7.30
mbr, Har, 4H), 6.03–5.97 (mbr, 2H, Hcod), 5.11–5.04 (mbr, 2H,
cod), 3.99 (sbr, 2H, NH), 3.88–3.81 (mbr, 2H, H*cyclohex), 2.46–2.41
mbr, 2H, Hcod), 2.34–2.30 (mbr, 2H, Hcod), 2.31–2.26 (mbr, 2H,
3
) δ 8.09 (d, J = 9 Hz,
a a
,S )-L2, which
7
(
H
(
Appl. Organometal. Chem. (2014)
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc