Y. Zhang et al. / Journal of Organometallic Chemistry 696 (2011) 709e714
Me Me Ph2
713
3.2. Synthesis of [{(R)-1-[1-(dimethylamino)ethyl]-2-naphthyl-C,N}
Me
P
N
O
P
{1,1-bis (diphenylphosphino)-ethylene monoxide-P,O}]-palladium
(II) perchlorate, (R)-6
+
PPh2
OMe
Ph2P
PPh2
Pd
7a
+
P
Ph2
-
Ph2
ClO4
9
A mixture of 1-bis(diphenylphosphino)ethane monoxide 5
(0.843 g, 2.044 mmol) and (R)-1 (0.994 g, 2.045 mmol) in
dichloromethane (60 mL) was stirred at room temperature for 2 h.
After removal of the organic solvent, the complex (R)-6 was isolated
8a
Scheme 2. Liberation of optically active bisphosphine monoxide ligand 8a.
as yellow solid, 1.837 g (99% yield). [
a
]
þ22 (c 0.5, CH2Cl2);
D
Mp158 ꢁC (dec.). Anal. Calcd. for C40H38ClNO5P2Pd:C, 58.8; H, 4.7; N,
signals were identical with those observed for the minor product
7b. Hence, it could be confirmed that 7b was indeed the minor
product of the original asymmetric synthesis and the liberated bis-
phosphine monoxide 8a is indeed optically pure.
In conclusion, two converging synthetic pathways sharing
a common metal template promoted asymmetric hydroalkoxylation
and oxidation process have been illustrated for the synthesis of
chiral bis-phosphine monoxide ligands. These ligands are currently
being evaluated for catalytic potential in various organic synthetic
scenarios.
1.7. Found: C, 58.3; H, 4.7; N, 1.4. 31P NMR (CDCl3)
d 35.7, 49.3
(JPP ¼ 64.4 Hz); 1H NMR (CDCl3)
d
1.88 (d, 3H, CHMe, 3JHH ¼ 6.2 Hz),
3
2.94 (s, 6H, NMe2), 4.48 (qn, 1H, JHH
¼
4JPH ¼ 6.2 Hz, CHMe),
6.28e6.44 (m, 2H, CCH2), 6.89e7.78 (m, 26H, aromatics).
3.3. Hydroalkoxylation reaction. Isolation of complex 7a
A mixture of (R)-6 (1.000 g, 1.225 mmol), triethylamine (0.124 g,
1.225 mmol) and methanol (2 mL) was stirred in benzene (50 mL)
at room temperature for 6 h. The solvent was removed and complex
7a was obtained from dichloromethane and diethyl ether as
3. Experimental
colorless crystals, 0.623 g (60% yield). [
a
]
þ14 (c 0.5, CH2Cl2);
D
Reactions involving air-sensitive compounds were performed
under an inert atmosphere of argon using standard Schlenk tech-
niques. Solvents were dried and freshly distilled according to stan-
dard procedures and degassed prior to use when necessary. The 1H
and 31P{1H} NMR spectra recorded at 25 ꢁC on Bruker ACF 300 and
500 MHz spectrometers. Optical rotations were measured on the
specified solution in a 0.1 dm cell at 20 ꢁC with a PerkineElmer
model 341 polarimeter. Elemental analyses were performed by the
staff in the Elemental Analysis Laboratory of the Division of Chem-
ical and Biological Chemistry of Nanyang Technological University.
Melting points were measured using the SRS Optimelt Automated
Melting Point System, SRS MPA100.
The chiral palladium complexes bis(acetonitrile) [(S)-1-[1-
(dimethylamino)ethyl]-2-phenyl-C, N]-palladium(II) perchlorate
((R)-1) [32] were prepared according to literature methods.
Caution! All perchlorate salts should be handled as potentially
explosive compounds.
Mp195 ꢁC (dec.). Anal. Calcd. for C41H42ClNO6P2Pd:C, 58.0; H, 5.0; N,
1.7. Found: C, 57.4; H, 5.1; N, 1.6. 31P NMR (CDCl3)
d 43.8, 58.6
(JPP ¼ 30 Hz); 1H NMR (CDCl3)
d
2.12 (d, 3H, CHMe, 3JHH ¼ 6.2 Hz),
2.79 (s, 3H, OMe), 3.06 (s, 3H, NMeax), 3.16 (d, 3H, JPH ¼ 3.2 Hz,
3
NMeeq), 3.40 (m, 2H, CH2OMe), 4.58 (qn, 1H, JHH
¼
4JPH ¼ 6.2 Hz,
CHMe), 4.70 (m, 1H, CHCH2OMe), 6.57e8.39 (m, 26H, aromatics).
3.4. Liberation of bis-phosphine monoxide 8a
A mixture of 7a (0.103 g, 0.121 mmol) and diphenylphosphino
ethane (0.048 g, 0.120 mmol) was stirred in dichloromethane at room
temperature for 15 min. The resulting yellowish mixture was passed
through a silicagel chromatographic column using dichloromethane-
acetoneaseluent. Removalofsolvent under reduced pressure gave 8a
as air-sensitive yellowish solid, 0.040 g (75% yield), [
a]D þ40.9 (c 0.1,
CH2Cl2). 31P NMR (CDCl3)
(CDCl3)
d
ꢀ15.2, 33.7 (JPP ¼ 67.0 Hz); 1H NMR
d
2.69 (s, 3H, OMe), 3.36e3.47 (m, 2H, CH2OMe), 5.30e5.32
(m, 1H, CHCH2OMe), 7.29e7.80 (m, 20H, aromatics).
3.1. Synthesis of 1,1-bis(diphenylphosphino)-ethylene monoxide, 5
3.5. X-ray crystal structure determinations of complexes (R)-6
A
mixture of 1,1-bis(diphenylphosphino)ethylene (1.982 g,
5.000 mmol) and hydrogen peroxide (0.170 g, 5.000 mmol) in
dichloromethane (80 mL) was stirred at room temperature for 2 h.
The solvent was removed under reduced pressure. This material
was chromatographed on a silica gel column with ethyl acetate-
dichloromethane (1:3 v/v) as the eluent, giving the bis-phosphine
monoxide 5 as yellowish solid: 1.072 g (52% yield). Mp112e113 ꢁC.
Crystal data and a summary of the crystallographic analyses are
given in Table 2. Diffraction data were collected at the Nanyang
Technological University using a Bruker X8 Apex diffractometer
with Mo Ka radiation (graphite monochromator). All non-H atoms
were refined anisotropically, while Hydrogen atoms were intro-
duced at a fixed distance from the carbon atoms and were assigned
fixed thermal parameters. The absolute configurations of the chiral
complexes were determined unambiguously using the Flack
parameter [33].
Anal. Calcd. for C26H22P2O:C, 75.7; H, 5.4. Found: C, 75.3; H, 5.6. 31
P
NMR (CDCl3)
d
ꢀ12.2, 29.0 (JPP ¼ 83.5 Hz); 1H NMR (CDCl3)
d 6.06
2
(ddd, 1H, CHH0, JH H ¼ 1.3 Hz, JP H ¼ 39.6 Hz, JPH ¼ 8.0 Hz), 6.96
0
0
2
(ddd, 1H, CHH0, JHH ¼ 1.3 Hz, JPH ¼ 22.3 Hz, JP H’ ¼ 11.6 Hz),
0
0
0
7.19e7.76 (m, 20H, aromatics).
Acknowledgements
We are grateful to Nanyang Technological University for sup-
porting this research and the research scholarships to Y. Z. and Y. D.
8a
1
+
(R)-
7a
Me
Me
Me
Me
Me
Me
N
N
NCMe
NCMe
O
P
P
Ph2
OMe
+
+
Appendix A. Supplementary material
Pd
Pd
8a
+
Ph2
-
-
CCDC 779850 contains the supplementary crystallographic data
for complex (R)-6. These data can be obtained free of charge from
ClO4
ClO4
10
1
(S)-
Scheme 3. Re-complexation studies for confirmation of optical purity.
Zhang, Yi
