Dynamic asymmetric catalysis by diphenylphosphinoferrocene (DPPF)-nickel complexes through control of axial chirality by chiral diamines

Article abstract of DOI:10.1021/ol016968x

(matrix presented) The enantio- and diastereomerically pure metal complexes of a chirally dynamic diphenylphosphinoferrocene (DPPF) ligand are obtained through coordination of enantiopure diaminobinaphthyl (DABN) to control the axial chirality of DPPF-Pt,

Full text of DOI:10.1021/ol016968x

ORGANIC
LETTERS
2002
Vol. 4, No. 1
99-101
Dynamic Asymmetric Catalysis by
Diphenylphosphinoferrocene
(DPPF)−Nickel Complexes through
Control of Axial Chirality by Chiral
Diamines
Koichi Mikami* and Kohsuke Aikawa
Department of Applied Chemistry, Tokyo Institute of Technology,
Tokyo 152-8552, Japan
kmikami@o.cc.titech.ac.jp
Received October 29, 2001
ABSTRACT
The enantio- and diastereomerically pure metal complexes of a chirally dynamic diphenylphosphinoferrocene (DPPF) ligand are obtained
through coordination of enantiopure diaminobinaphthyl (DABN) to control the axial chirality of DPPF−Pt, −Pd, and −Ni complexes. The DPPF−
Ni catalyst with DABN affords higher enantioselectivity and catalytic efficiency than those attained by the Pd or Pt counterparts and [Ni{(R)-
dabn}](SbF6)2 without DPPF ligand.
The choice of a central metal and design of a chirally stable
ligand are key issues in the development of asymmetric
catalysts for organic reactions to establish high enantiose-
lectivity and catalyst efficiency.1 Ferrocenylbisphosphine
ligands,2 such as (R)-N,N-dimethyl-1-[(S)-1′,2-bis(diphe-
nylphosphino)ferrocenyl]ethylamine [(R)-(S)-BPPFA]3 have
been used as chirally stable ligands with appendages of chiral
centers. By contrast, chirally dynamic diphenylphosphino-
ferrocene (DPPF) ligands without center and planar chirality
have never been used as ligands for chiral metal complexes.
Herein, we report the asymmetric catalysis with DPPF ligand
through control, by a chiral diamine, of dynamic axial
chirality not only in the DPPF-Pd and -Pt catalysts but
also in DPPF-Ni catalyst (Scheme 1),4 the central metal of
which is rarely used in asymmetric Lewis acid catalysts.5
First of all, a variety of chiral diols and diamines were
examined to coordinate to dicationic Pd and Pt complexes
with DPPF ligand (DPPF-Pd(SbF6)2, DPPF-Pt(SbF6)2) to
(1) (a) Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H. ComprehensiVe
Asymmetric Catalysis; Springer: Berlin, 1999; Vols. 1-3. (b) Transition
Metals for Organic Synthesis; Beller, M., Bolm, C., Eds.; VCH: Weiheim,
1998. (c) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley:
New York, 1994. (d) Brunner, H.; Zettlmeier, W. Handbook of Enantiose-
lectiVe Catalysis; VCH: Weiheim, 1993. (e) Catalytic Asymmetric Synthesis;
Ojima, I., Ed.; VCH: New York, 1993, 2000; Vols. I and II. (f) Kagan, H.
B. ComprehensiVe Organic Chemistry; Pergamon: Oxford, 1992; Vol. 8.
(g) Asymmetric Catalysis; Bosnich, B., Ed.; Martinus Nijhoff Publishers:
Dordrecht, 1986.
(2) Ferrocenes; Togni, A., Hayashi, T., Eds.; VCH: Weinheim, 1995.
Kagan, H. B.; Riant, O. In AdVances in Asymmetric Synthesis, Hassner,
A., Ed.; JAI Press: London, Vol. 2, pp 189-235, 1997. Richards, C. J.;
Locke, A. J. Tetrahedron: Asymmetry 1998, 9, 2377. Metallocene; Togni,
A.; Halterman, R. L., Eds.; Wiley-VCH: Weinheim, 1998.
(3) Hayashi, T.; Ohno, A.; Lu, S.; Matsumoto, Y.; Fukuyo, E.; Yanagi,
K. J. Am. Chem. Soc. 1994, 116, 4421-4226 and references therein. For
leading references, see: Deng, W.; You, S.; Hou, X.; Dai, L.; Yu, Y.; Xia,
W.; Sun, J. J. Am. Chem. Soc. 2001, 123, 6508-6519.
10.1021/ol016968x CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/15/2001

Scheme 1. Dynamic Chirality Control of DPPF Ligand
Figure 1. ORTEP drawing of [Pd{(P)-dppf}{(R)-dabn}]-(OTf)2.
provide single diastereomeric complexes. Unfortunately,
chiral diols such as binaphthols (BINOLs) and their deriva-
tives did not coordinate to the dicationic DPPF-Pd and -Pt
complexes. More coordinating diamines such as diphenyl-
ethylenediamine (DPEN), diaminobinaphthyl (DABN), and
3,3′-dimethyldiaminobinaphthyl (DM-DABN) did coordinate
to control axial chirality of DPPF-Pd and -Pt complexes,
giving the single diastereomers within seconds (Scheme 2),6
In sharp contrast to the biphenylphosphine (BIPHEP)-
Pd and -Pt complexes, the present DPPF counterparts are
chirally stable only as the complexes with chirality controllers
(X-*-X) (Scheme 1). In turn, the present DPPF complexes
are chirally dynamic9 and subjected to more facile chirality
control by chiral diamines than the BIPHEP complexes.
These DPPF-Pd10 and -Pt complexes with diamine
controllers were examined as asymmetric catalysts for
carbon-carbon bond forming reactions such as ene reactions.
A variety of diamines were examined for the asymmetric
ene reaction of ethyl glyoxylate and R-methylstyrene (Table
1). The complex with DPEN hardly catalyzed the glyoxylate-
Scheme 2
(6) We denote the dppf chirality in terms of descriptors of chirality sense
of a helix: (P) plus, clockwise; (M) minus, counterclockwise.
(7) (P)-DPPF-Pd(SbF6)2/(R)-DABN: 1H NMR (CD2Cl2, 300 MHz) δ
4.21 (br, 4H), 4.52 (br s, 2H), 4.58 (br s, 2H), 4.66 (br s, 2H), 4.85 (br s,
2H), 6.73 (d, J ) 9.0 Hz, 2H), 6.91 (d, J ) 8.7 Hz, 2H), 7.30 (t, J ) 8.1
Hz, 2H), 7.39-7.44 (m, 4H), 7.54-7.67 (m, 8H), 7.76-7.81 (m, 4H), 7.85-
7.94 (m, 6H), 8.05 (d, J ) 8.1 Hz, 2H), 8.11 (d, J ) 9.0 Hz, 2H).
(8) The single-crystal growth was carried out in a hexane/dichloromethane
mixed solvent at room temperature. X-ray crystallographic analysis was
performed with a Bruker SMART 1000 diffractometer (graphite mono-
chromator, Mo KR radiation, λ ) 0.71073 Å). Crystal data for [Pd{(P)-
dppf}{(R)-dabn}](OTf)2‚2CH2Cl2: C58H48Cl4FeN2O6P2PdS, dark red, crys-
tal dimension 0.51 × 0.36 × 0.25 mm3, orthorhombic, space group P21, a
) 14.0774(6) Å, b ) 13.2027(5) Å, c ) 15.4943(7) Å, V ) 2879.6(2) Å3,
Z ) 2, Fcalcd ) 1.630 gcm-3, µ(Mo KR) ) 0.95 cm-1, Τ ) 100 Κ. 15753
e.g., 31P NMR (CDCl3) (P)-DPPF-Pd(SbF6)2/(R)-DABN,
39.1 ppm.7 The (P)/(R)-configuration of the DPPF-M/DABN
diastereomer was determined by X-ray analysis of a single
crystal of [Pd{(P)-dppf}{(R)-dabn}](OTf)2 complex obtained
from dichloromethane-hexane (Figure 1).8
reflections were independent and unique, and 767 with I > 2σ(I) (2 θmax
)
31.5°) were used for the solution of the structure. The non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included but not refined.
R ) 0.0444, wR2 ) 0.1218. Crystallographic data (excluding structure
factors) for the structure reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication
N lo. CCDC-173071. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, U.K. (Fax:
(+44) 1223-336-033. E-mail deposit@ccdc.cam.ac.uk) Selective bond
lengths [Å], bond angles [deg] and torsion angles [deg]: Pd1-P1 2.3036-
(9), Pd1-P2 2.2904(9), Pd1-N1 2.169(3), Pd1-N2 2.152(3); P1-Pd1-
P2 94.87(3), N1-Pd1-N2 83.53(11): C1-C10-C11-C20 65.92, P1-
C33-C42-P2 34.86.
(9) For spectroscopic characteristics of DPPF-Pt(CH2SiMe2R)2 com-
plexes, see: Kelly, R. D.; Young, G. B. Polyhedron 1989, 8, 433-435.
Ankianiec, B. C.; Young, G. B. Polyhedron 1991, 12, 1411-1421.
(10) [Pd(dppf)(PhCN)2](BF4)2: Oi, S.; Kashiwagi, E.; Terada, E.; Ohuchi,
K.; Inoue, Y. Tetrahedron Lett. 1996, 37, 6351-6354.
(4) Crystal structures of DPPF-M complexes. Pt(dppf)Cl2: Clemente,
A.; Corain, B.; Longato, B.; Tiripicchio-Camellini, M.; Pilloni, G. Inorg.
Chim. Acta 1986, 115, L9-11. Pd(dppf)Cl2: Hayashi, T.; Konishi, M.;
Kobori, Y.; Kumada, M.; Higuchi, T.; Hirotsu, K. J. Am. Chem. Soc. 1984,
106, 158-163. Ni(dppf)Cl2: Casellato, U.; Ajo, D.; Valle, G.; Corain, B.;
Longato, B.; Graziani, R. J. Crystallogr. Spectrosc. Res. 1988, 18, S83-
S90.
(5) (a) Kanemasa, S.; Oderanotoshi, Y.; Sakaguchi, S.; Yamamoto, H.;
Tanaka, J.; Wada, E.; Curran, D. P. J. Am. Chem. Soc. 1998, 120, 3074-
3088. (b) Iwasa, S.; Tsushima, S.; Shimada, T.; Nishiyama, H. Tetrahedron
Lett. 2001, 42, 6715-6717.
100
Org. Lett., Vol. 4, No. 1, 2002

Table 1. Effect of Chirality Controller in Glyoxylate-Ene
Table 2. Asymmetric Glyoxylate-Ene Reaction Using Ni
Reaction
Complexes
of the steric shielding effect by the 3,3′-dimethyl groups
(entries 4 vs 7).
Thus, the Ni complexes prepared with chirally dynamic
DPPF ligand can be used as highly enantioselective catalysts
for the carbon-carbon bond forming reaction. Indeed, the
efficacy of DPPF ligand is highlighted by the higher
enantioselectivity and catalytic activity compared to those
obtained with diphenylphosphinoethane (DPPE) and diphe-
nylphosphinopropane (DPPP) ligands (Scheme 3).
ene reaction (entry 1). By using DABN, the catalytic
activities of Pd and Pt complexes were increased to give
virtually quantitative yields (entries 1 vs 2 and 3). DM-
DABN provided an increased level of enantioselectivity but
lower chemical yield (entry 4). H8-DABN gave low selectiv-
ity and yield (entry 5). Though in low enantioselectivities,
the present examples represent a rarely precedented example
of the DPPF ligand for asymmetric catalysts even in the well-
studied Pd and Pt complexes.
Scheme 3. Effects of Phosphine Ligands on Ni Complexes
To attain higher enantioselectivity, the more Lewis acidic
Ni with higher coordination number was examined as the
central metal. Significantly, DPPF-Ni complexes were found
to exhibit higher levels of enantioselectivity in the glyoxylate-
ene reaction (Table 2).11 These Ni complexes gave virtually
quantitative yields and high levels of enantioselectivity at
room temperature (entries 1 and 4). The catalyst without
DPPF ligand gave lower enantioselectivity (entry 2). At 0
°C, a decrease in chemical yield was observed down to 14%
yield (entry 5). However, even at higher reaction temperature
(60 °C), an equally high level of enantioselectivity was
obtained along with the quantitative yield (entry 6). Signifi-
cantly, the choice of the counteranion is critical to obtain
high enantioselectivity and chemical yield; the perchlorate
counterpart gave chemical yield and enantioselctivity lower
than those obtained with the hexafluoroantimonate complex
(entries 1 vs 3). DM-DABN as a controller gave lower
chemical yield and enantioselectivity, presumably because
In summary, we have reported that asymmetric catalysis
can be established even by the use of chirally dynamic ferro-
cenyl DPPF ligands through facile control of axial chirality.
Furthermore, those Ni complexes of the DPPF ligand
associated with the DABN controller afford high levels of
enantioselectivity and chemical yield for in situ asymmetric
catalysis of the carbon-carbon bond forming reaction.
Acknowledgment. We are grateful to Dr. Kenji Yoza
and Mr. Kazuyoshi Kitajima in Nippon Brucker Co. for
X-ray analysis. We are also grateful to Prof. Masahiro Terada
of Tohoku University for his useful discussion. This work
was financially supported by the Ministry of Education,
Science, Sports and Culture of Japan (nos. 09238209 and
10208204).
(11) Typical Experimental Procedure (Table 2). To a solution of NiCl2-
(dppf) (0.02 mmol, 5 mol % of alkene) and AgSbF6 (0.04 mmol) in CH2-
Cl2 (2 mL) was added (R)-DABN (0.022 mmol) at room temperature under
argon atmosphere. After the mixture was stirred at room temperature for 1
h, ethyl glyoxylate (0.5 mmol) and alkene (0.4 mmol) were added and stirred
for 24 h. The reaction mixture was directly loaded onto a silica gel column
and eluted with hexane/AcOEt (3:1) to give the ene product as an colorless
oil.
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