Diastereoselective oxidative addition of allyl chloride to planar-chiral cyclopentadienyl-ruthenium complexes

Article abstract of DOI:10.1021/om049616d

The reaction of planar-chiral cyclopentadienyl - ruthenium complexes with allyl chloride at room temperature resulted in the diastereoselective formation of π-allyl - ruthenium complexes, in which the chirality at the Ru center depended on the substituent

Full text of DOI:10.1021/om049616d

Organometallics 2004, 23, 3763-3765
3763
Dia ster eoselective Oxid a tive Ad d ition of Allyl Ch lor id e
to P la n a r -Ch ir a l Cyclop en ta d ien yl-Ru th en iu m
Com p lexes
Yuji Matsushima, Kiyotaka Onitsuka,* and Shigetoshi Takahashi
The Institute of Scientific and Industrial Research, Osaka University,
8-1 Mihogaoka, Ibaraki, Osaka 567-0047, J apan
Received May 27, 2004
Summary: The reaction of planar-chiral cyclopentadi-
enyl-ruthenium complexes with allyl chloride at room
temperature resulted in the diastereoselective formation
of π-allyl-ruthenium complexes, in which the chirality
at the Ru center depended on the substituent at the
4-position of the cyclopentadienyl group. Epimerization
at the Ru center of π-allyl complexes at 90 °C suggested
that the diastereoselectivity was under kinetic control.
ethyl carbonate. However, no reaction took place and
the starting materials were recovered. In the reaction
with 1,3-diphenyl-2-propenyl chloride, the starting ma-
terials were consumed, but we could not confirm the
structure of the products. We next examined the reac-
tion using allyl chloride with no substituents.
Treatment of the Cp′Ru complex 1a with 10 equiv of
allyl chloride in acetone at room temperature led to the
formation of a π-allyl complex (2a ) in 83% yield (eq 1).5,6
Enantioselective allylic substitution is a representa-
tive asymmetric reaction catalyzed by transition-metal
complexes because of its high productivity and applica-
tion in the total synthesis of a variety of biologically
important molecules.1 Although Pd-based catalysts have
been widely used in enantioselective allylic substitution,
recent studies have shown that other transition metals
can be used with efficiencies similar to or better than
those of Pd catalysts.2,3 Recently, we reported the first
example of Ru-catalyzed asymmetric allylic substitution
by using planar-chiral cyclopentadienyl (Cp′) com-
plexes.4 To obtain more information on the origin of the
enantioselectivity in these catalytic reactions, we ex-
amined some stoichiometric reactions of planar-chiral
Cp′Ru complexes with allylic compounds. We report
here the reaction of planar-chiral Cp′Ru complexes with
allyl chlorides to give π-allyl complexes with metal-
centered chirality and high diastereoselectivity.
We started our investigation with the reaction of
planar-chiral Cp′Ru complexes (1) with 1,3-diphenylallyl
Since complex 2a has a three-legged piano-stool struc-
ture with different ligands, metal-centered chirality is
generated at the Ru atom.7 Thus, complex 2a consisted
of two diastereomers, and the 31P NMR spectrum
suggested that the ratio was 89% de. The highly
diastereoselective oxidative addition to planar-chiral Cp′
complexes of Rh and Ir has also been reported by other
groups.8 In the differential NOE spectra of the major
product, irradiation of the methyl signal at the 4-posi-
tion on the Cp′ ring gave rise to NOE signals of the allyl
protons at the anti position, whereas the NOE signal
that was assignable to one of the two syn allylic protons
was observed upon irradiation of the methyl signal at
the 2-position of the Cp′ group.9 These results clearly
(1) For recent reviews, see: (a) Sesay, S. J .; Williams, J . M. J . Adv.
Asymmetric Synth. 1998, 3, 235. (b) Trost, B. M.; Lee, C. In Catalytic
Asymmetric Synthesis, 2nd ed.; Ojima, I., Ed.; VCH: New York, 2000;
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(2) Mo and W catalysts: (a) Lloyd-J ones, G. C.; Pfaltz, A. Angew.
Chem., Int. Ed. Engl. 1995, 34, 462. (b) Trost, B. M.; Hachiya, I. J .
Am. Chem. Soc. 1998, 120, 1104. (c) Glorius, F.; Pfaltz, A. Org. Lett.
1999, 1, 141. (d) Belda, O.; Kaiser, N.-F.; Bremberg, U.; Larhed, M.;
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F. K.; Bremberg, U.; Larhed, M.; Moberg, C.; Hallberg, A. Angew.
Chem., Int. Ed. 2000, 39, 3596. (f) Trost, B. M.; Dogra, K.; Hachiya, I.;
Emura, T.; Hughes, D. L.; Krska, S.; Reamer, R. A.; Palucki, M.;
Yasuda, N.; Reider, P. J . Angew. Chem., Int. Ed. 2002, 41, 1929. (g)
Hughes, D. L.; Palucki, M.; Yasuda, N.; Reamer, R. A.; Reider, P. J . J .
Org. Chem. 2002, 67, 2762. (h) Trost, B. M.; Dogra, K. J . Am. Chem.
Soc. 2002, 124, 7256. (i) Belda, O.; Moberg, C. Acc. Chem. Res. 2004,
37, 159.
(3) Rh and Ir catalysts: (a) J anssen, J . P.; Helmchen, G. Tetrahedron
Lett. 1997, 38, 8025. (b) Bartels, B.; Helmchen, G. Chem. Commun.
1999, 741. (c) Bartels, B.; Garc´ıa-Yebra, C.; Rominger, F.; Helmchen,
G. Eur. J . Inorg. Chem. 2002, 2569. (d) Ohmura, T.; Hartwig, J . F. J .
Am. Chem. Soc. 2002, 124, 15164. (e) Hayashi, T.; Okada, A.; Suzuka,
T.; Kawatsura, M. Org. Lett. 2003, 5, 1713. (f) Lo´pez, F.; Ohmura, T.;
Hartwig, J . F. J . Am. Chem. Soc. 2003, 125, 3426. (g) Fischer, C.;
Defieber, C.; Suzuki, T.; Carreira, E. M. J . Am. Chem. Soc. 2004, 126,
1628.
(5) (a) Albers, M. O.; Liles, D. C.; Robinson, D. J .; Shaver, A.;
Singleton, E. Organometallics 1987, 6, 2347. (b) Nagashima, H.; Mukai,
K.; Shiota, Y.; Yamaguchi, K.; Ara, K.; Fukahori, T.; Suzuki, H.; Akita,
M.; Morooka, Y.; Itoh, K. Organometallics 1990, 9, 799. (c) Kondo, T.;
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14, 1945. (d) Ru¨ba, E.; Simanko, W.; Mauthner, K.; Soldouzi, K. M.;
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1999, 18, 3843. (e) Kondo, H.; Yamaguchi, Y.; Nagashima, H. Chem.
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hashi, S. J . Am. Chem. Soc. 2001, 123, 10405.
10.1021/om049616d CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/08/2004

3764 Organometallics, Vol. 23, No. 16, 2004
Communications
Ta ble 1. Rea ction of Ru th en iu m Com p lexes 1 w ith
Allyl a n d Meth a llyl Ch lor id es
entry complex
substrate
product yield/%a de/%a,b
1
2
3
4
5
6
1a
1b
1c
1a
1b
1c
allyl chloride
allyl chloride
allyl chloride
methallyl chloride
methallyl chloride
methallyl chloride
2a
2b
2c
3a
3b
3c
83
75
81
83
74
53
89 (I)
94 (I)
80 (II)
96 (I)
98 (I)
60 (II)
a
b
Determined by 31P NMR. The structure of the major product
is given in parentheses; see eq 1.
suggested that the π-allyl group coordinates to the Ru
atom in an endo fashion with a configuration of SCpSRu
/
R
CpRRu (I).
Reactions of complexes 1b,c, which have phenyl and
tert-butyl groups at the 4-position on the Cp′ ring
instead of a methyl group as in 1a , also gave π-allyl
complexes 2b,c with high diastereoselectivity, respec-
tively (Table 1). Whereas the configuration of the major
isomer of complex 2b was SCpSRu/RCpRRu (I), the major
F igu r e 1. Molecular structure of complex 3a -I. Hydrogen
atoms and PF6 counteranion are omitted for clarity.
isomer of complex 1c had a configuration of SCpRRu
/
-
R
CpSRu (II). Reactions of complexes 1a -c with methallyl
chloride gave the π-methallyl complexes 3a -c, respec-
tively. The configuration at the Ru atom in the major
isomer of complex 3c was opposite to those of complexes
3a ,b. Similar phenomena were observed in ligand
exchange reactions of planar-chiral Cp′Ru complexes
with an iodide ligand.9b The molecular structure of the
major isomer of π-methallyl complex 3a -I was unequivo-
cally established by X-ray analysis (Figure 1).10 As
predicted from the NOE spectrum, the orientation of the
π-methallyl group was endo and the configuration was
absolute configuration of the products varied according
to the substituent at the 4-position on the Cp′ ring of
complex 1. Since the π-allyl complex is known to be an
intermediate in catalytic allylic substitutions,5,11 the
present results strongly suggest that the stereochem-
istry in the catalytic reactions must depend on the
chirality at the Ru center in π-allyl complexes.
In complexes 2 and 3, epimerization between I and
II did not take place at room temperature but did occur
at higher temperature. Heating a nitromethane solution
of complex 2c (I/II ) 10/90) at 90 °C for 6 h changed
the I/II ratio to 66/34. Although the solution of complex
2c (I/II ) 66/34) was left to stand at room temperature
for a long time, the ratio of the isomers did not change
at all. These results suggest that the diastereoselectivity
in the oxidative addition of allyl chlorides is under
kinetic control, as was also supported by the experi-
mental finding that the diastereoselectivity of complex
2c decreased to 42% de in the reaction of complex 1c
with allyl chloride at 40 °C.
S
CpSRu/RCpRRu. In the catalytic allylic substitution, the
(6) The preparation of 2a is as follows: to a solution of complex 1a
(136 mg, 0.2 mmol) in acetone (2 mL) was added allyl chloride (160
µL, 2.0 mmol), and the mixture was stirred for 36 at room
h
temperature. After the addition of diethyl ether, the resulting orange
precipitate was collected and washed several times with diethyl ether
to give complex 2a (112 mg, 83%). IR (cm-1, KBr): 1741 (νCdO). FAB
MS: m/z 527 (M - PF6-). Anal. Calcd for C25H27ClF6O2P2Ru: C, 44.69;
H, 4.05; Cl, 5.28. Found: C, 44.79; H, 4.31; Cl, 5.20. Data for the major
product 2a -I are as follows. 1H NMR (acetone-d6, 600 MHz): δ 7.82-
7.45 (m, 10H, Ph), 6.48 (s, 1H, Cp′ H5), 6.29 (s, 1H, Cp′ H3), 5.06 (ddd,
1H, J ) 7.7, 11.3, 24.2 Hz, OCH2), 4.72 (dd, 1H, J ) 2.5, 11.3 Hz, allyl
H4), 4.54-4.51 (m, 1H, allyl H1), 4.10-4.09 (m, 1H, allyl H2), 3.96-
3.91 (m, 1H, OCH2), 3.56-3.50 (m, 1H, CH2P), 3.31-3.26 (m, 1H, allyl
H3), 2.75 (d, 1H, J ) 10.7 Hz, allyl H5), 2.23 (d, 3H, J ) 1.4 Hz, Cp′
Me2), 1.96 (s, 3H, Cp′ Me4). 13C NMR (CD3NO2, 150 MHz): δ 165.4
(CdO), 135.8-126.8 (Ph), 125.2 (Cp′ C1), 108.1 (Cp′ C4), 104.1 (Cp′ C3),
99.5 (allyl C2), 93.7 (Cp′ C2), 89.9 (Cp′ C5), 70.6 (allyl C1), 65.4 (allyl
C3), 62.2 (d, J ) 5 Hz, CH2O), 21.4 (d, J ) 40 Hz, CH2P), 13.1 (Cp′
Me2), 12.9 (Cp′ Me4). 31P NMR (acetone-d6, 160 MHz): δ 34.1. Data
for the minor product 2a -II are as follows. 31P NMR (acetone-d6, 160
MHz): δ 25.3. See the Supporting Information for the assignment of
the signals due to the allyl groups in 1H and 13C NMR.
Next, we examined the reactivity of π-allyl complexes
with amine. The reaction of complex 2a -I, which was
isolated as a diastereomerically pure sample from a
mixture with 2a -II, with 1.1 equiv of triethylamine in
acetone at room temperature resulted in the formation
of an olefin complex (4a ) in 82% yield (eq 2), while the
(7) For recent reviews, see: (a) Brunner, H. Eur. J . Inorg. Chem.
2001, 905. (b) Ganter, C. Chem. Soc. Rev. 2003, 32, 130. (c) Faller, J .
W.; Parr, J .; Lavoie, A. R. New J . Chem. 2003, 899.
(8) (a) Mobley, T. A.; Bergman, R. G. J . Am. Chem. Soc. 1998, 120,
3253. (b) Kataoka, Y.; Shibahara, A.; Saito, Y.; Yamagata, T.; Tani, K.
Organometallics 1998, 17, 4338. (c) Kataoka, Y.; Iwato, Y.; Yamagata,
T.; Tani, K. Organometallics 1999, 18, 5423. (d) Kataoka, Y.; Naka-
gawa, Y.; Shibahara, A.; Yamagata, T.; Mashima, K.; Tani, K.
Organometallics 2004, 23, 2095.
(9) (a) Onitsuka, K.; Ajioka, Y.; Matsushima, Y.; Takahashi, S.
Organometallics 2001, 20, 3274. (b) Matsushima, Y.; Onitsuka, K.;
Takahashi, S. Dalton 2004, 547.
(10) Crystallographic data for 3a -I: formula C26H29ClF6O2P2Ru, fw
) 685.97, monoclinic, space group P21/c (No. 14), a ) 10.992(5) Å, b )
17.793(6) Å, c ) 14.320(4) Å, â ) 101.13(3)°, V ) 2747(1) Å3, Z ) 4,
dcalcd ) 1.658 g cm-3, -75 °C, ω-2θ scan, 6° < 2θ < 55°, µ(Mo KR) )
8.48 cm-1, R (Rw) ) 0.065 (0.089) for 343 parameters against 4620
reflections with I > 3.0σ(I) out of 6310 unique reflections (Rint ) 0.178)
by the full-matrix least-squares method, GOF ) 1.12.

Communications
Organometallics, Vol. 23, No. 16, 2004 3765
Sch em e 1. P ossible Str u ctu r e of Com p lex 4a
of 4a was warmed at room temperature, a mixture of
two diastereomers in 38% de, which is the same
selectivity as in the reaction at room temperature, was
obtained, suggesting that the olefin complex 4 was in
an equilibrium state at room temperature. As shown
in Scheme 1, there are four possible structures for
complex 4. Each of them can be generated by the
epimerization at the Ru center (a) and the face flip of
the olefin ligand (b). Although we tried to determine the
stereochemistry of complex 4 by spectral analyses such
as NOE experiments and 2D NMR, no useful informa-
tion was obtained. However, the facile face flip of the
olefin ligand was known in chiral CpRe complexes, in
which the configuration at the chiral metal center did
not change.12 Thus, complex 4 likely consists of 4-I and/
or 4-III.
In summary, we have described the diastereoselective
formation of π-allyl-Ru complexes by the oxidative
addition of allyl chloride to planar-chiral Cp′Ru com-
plexes under kinetic control. These results should
provide useful information for understanding the mech-
anism of asymmetric allylic substitution catalyzed by
planar-chiral Cp′Ru complexes. Further studies are now
in progress.
a
Legend: (a) epimerization at the Ru center; (b) face flip of
the olefin ligand.
Ta ble 2. Rea ction of Ru th en iu m Com p lexes 2-I
w ith Tr ieth yla m in e
entry
complex
temp/°C
product
yield/%a
de/%a
1
2
3
4
5
6
7
8
2a -I
2a -I
2a -I
2a -I
2b-I
2b-I
2b-I
2b-I
20
0
-40
-78
20
0
-40
-78
4a
4a
4a
4a
4b
4b
4b
4b
82
94
>99
>99
96
98
97
>99
38
71
>99
>99
42
51
92
>99
Ack n ow led gm en t. This work was supported in part
by a Grant-in-Aid for Scientific Research from the
Ministry of Education, Science, Sports and Culture and
by the Tokuyama Science Foundation (K.O.). Y.M. is
grateful for a J SPS Fellowship for J apan J unior Scien-
tists. We thank the members of the Material Analysis
Center, ISIR, Osaka University, for spectral measure-
ments, X-ray diffraction, and microanalyses.
a
Determined by 31P NMR.
reaction with dipropylamine gave a complex mixture.
Although we could not isolate complex 4a from the
reaction mixture, the structure was confirmed on the
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details and full characterization data for complexes 2
and 3, and a CIF file giving crystallographic data for complex
3a -I. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
basis of comparison of the H NMR spectrum to that of
an analogous Ru complex.5d The 31P NMR spectrum of
complex 4a suggested that the diastereoselectivity was
38% de. A similar reaction of diastereomerically pure
2b-I gave an olefin complex (4b) in 96% yield with 42%
de. When the reaction was performed at lower temper-
ature, the yield and diastereoselectivity were increased
(Table 2). For example, the reaction of complex 2a -I at
-40 °C produced a single diastereomer of complex 4a .
However, when the solution of the single diastereomer
OM049616D
(11) (a) Zhang, S.-W.; Mitsudo, T.; Kondo, T.; Watanabe, Y. J .
Organomet. Chem. 1993, 450, 197. (b) Morisaki, Y.; Kondo, T.; Mitsudo,
T. Organometallics 1999, 18, 4742.
(12) For a review, see: Gladysz, J . A.; Boone, B. J . Angew. Chem.,
Int. Ed. Engl. 1997, 36, 551.