Air-stable racemization catalysts for the dynamic kinetic resolution of secondary alcohols

Article abstract of DOI:10.1021/jo071065o

(Chemical Equation Presented) The substitution of a carbonyl ligand with PPh₃ in cyclopentadienylruthenium dicarbonyl complexes produces a new class of recyclable alcohol racemization catalysts. The catalysts are active at room temperature under aerobic conditions in the presence of silver oxide. Furthermore, the catalysts are compatible with the use of a lipase and isopropenyl acetate for the dynamic kinetic resolution (DKR) of secondary alcohols under ambient conditions.

Full text of DOI:10.1021/jo071065o

Air-Stable Racemization Catalysts for the Dynamic Kinetic
Resolution of Secondary Alcohols
Soo-Byung Ko, Baskar Baburaj, Mahn-Joo Kim,* and Jaiwook Park*
Department of Chemistry, Pohang UniVersity of Science and Technology (POSTECH),
San 31 Hyojadong, Pohang, Kyungbuk 790-784, Korea
pjw@postech.ac.kr
ReceiVed May 21, 2007
The substitution of a carbonyl ligand with PPh3 in cyclopentadienylruthenium dicarbonyl complexes
produces a new class of recyclable alcohol racemization catalysts. The catalysts are active at room
temperature under aerobic conditions in the presence of silver oxide. Furthermore, the catalysts are
compatible with the use of a lipase and isopropenyl acetate for the dynamic kinetic resolution (DKR) of
secondary alcohols under ambient conditions.
Introduction
limitation that the yield cannot exceed 50% for the desired
product. Dynamic kinetic resolution (DKR), in which KR is
coupled with the catalytic racemization of alcohol substrates,
is a solution to overcome the limitation.4 A number of Rh, Ir,
and Ru complexes have been tested for the racemization of
secondary alcohols.5 However, only a few of them have been
successfully incorporated in chemoenzymatic DKR.6 Recently,
our group has reported that aminocyclopentadienyl ruthenium
complex 1 can be combined with lipase or subtilisin to convert
racemic secondary alcohols into the optically pure (R)- and (S)-
acetates at room temperature, respectively (Scheme 1).7
Enantiomerically pure secondary alcohols are important chiral
building blocks in asymmetric synthesis.1 Many asymmetric
transformations have been developed for preparing enantio-
merically pure compounds by using chiral transition-metal
complexes2 or enzymes.3 However, the resolution of racemic
mixtures is still the most common process to prepare enantio-
merically pure compounds on industrial scales. Enzymatic
kinetic resolution (KR) of secondary alcohols is one of the most
potent industrial processes. However, the KR has the intrinsic
(1) (a) Laumen, K.; Breitgoff, D.; Schneider, M. P. J. Chem. Soc., Chem.
Commun. 1988, 1459. (b) Sheldon, R. A. Chirotechnology, Industrial
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2001, 30, 321. (g) Koh, J. H.; Jeong, H. M.; Park, J. Tetrahedron Lett.
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10.1021/jo071065o CCC: $37.00 © 2007 American Chemical Society
Published on Web 08/10/2007
6860
J. Org. Chem. 2007, 72, 6860-6864

Kinetic Resolution of Secondary Alcohols
SCHEME 1. Chemoenzymatic DKR of Secondary Alcohols
SCHEME 2. Synthesis of Phosphine- or
Phosphite-Substituted Ruthenium Complexes
TABLE 1. Catalytic Racemization of (S)-1-Phenylethanol with
Catalyst 4 in the Aira
Ba¨ckvall and co-workers have also reported a highly efficient
ruthenium complex 2 for the DKR of secondary alcohols at room
temperature.8 However, the DKR with 1 or 2 requires anaerobic
conditions due to the formation of air-sensitive intermediates
and, therefore, are not suitable for use under ambient conditions.
More recently, our group has developed air-stable alcohol
racemization catalysts including 3.9 The catalyst 3, however,
requires 1 equiv of potassium phosphate and long reaction time
(20-72 h) for alcohol DKR. We herein report new air-stable
alcohol racemization catalysts that are reusable and highly active
at room temperature. Furthermore, the catalysts are compatible
with enzymes for the DKR of various secondary alcohols at
room temperature in the air.
entry
additive (mol %)
eeb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
Ag2O (10)
Ag2O (5)
9.8
23.5
14.7c
27.4d
9.6
Ag2O (10)
Ag2O (10)
Ag2O (20)
Ag2O (50)
Ag3PO4 (10)
AgOTf (10)
AgNO3 (10)
AgOAc (10)
KOtBu (5)
K3PO4 (10)
K2CO3 (10)
9.5
65.0
98.4
99.0
98.5
0.0e
79.4
99
a (S)-1-Phenylethanol (>99% ee, 0.25 mmol) dissolved in toluene (0.5
mL) was added to a flask containing 4 (4 mol %) and additive, and the
resulting mixture was stirred at 25 °C for 1 h in the air. b The % ee values
were measured by GC equipped with a chiral column. c 2 mol % of 4 was
used. d 1 mol % of 4 was used. e After 30 min, 9.5% of acetophenone was
produced.
Results and Discussion
Synthesis of Alcohol Racemization Catalysts. The previous
alcohol racemization catalysts 1-3 have two carbonyl ligands
in common. However, we expected that substituting a carbonyl
group with a phosphine would lead to development of more
efficient alcohol racemization catalysts by varying the steric and
electronic properties of the phosphine ligand. Thus, phosphine-
substituted derivatives (4-6) were prepared on the basis of the
known synthetic method for (η5-Ph5C5)Ru(CO)(PPh3)Br (5b).10
The known method requires high reaction temperature (150 °C)
and long reaction time (15 h) to give 5a-c only in 50-68%
yields. Meanwhile, the use of trimethylamine N-oxide improved
the reaction remarkably. The substitution reactions took place
more rapidly (15 min) even under milder conditions (25 °C) to
give better yields (65-96%) (Scheme 2).
Catalytic Racemization of Secondary Alcohols. The ru-
thenium complexes 4-6 were tested on the catalytic racemiza-
tion of (S)-1-phenylethanol (Table 1). Contrary to our hope, all
of the newly synthesized ruthenium complexes did not show
any activity in alcohol racemization without base. However, we
expected the generation of active species from these ruthenium
complexes with a proper base, and then eventually found Ag2O,
which has been used as a base in coupling reactions11-13 and
in the preparation of silver alkoxide complexes.14 The optical
purity of 1-phenylethanol was 9.8% ee after 1 h of reaction
with 4 mol % of 4 and 10 mol % of Ag2O in toluene, and the
racemization was completed in 1.5 h at room temperature in
(6) (a) Mart´ın-Matute, B.; Ba¨ckvall, J.-E. Curr. Opin. Chem. Biol. 2007,
11, 226. (b) Kim, M.-J.; Ahn, Y.; Park, J. Bull. Korean Chem. Soc. 2005,
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J. Curr. Opin. Chem. Biol. 2002, 13, 578. (h) Huerta, F. F.; Minidis, A. B.
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D. Curr. Opin. Biotechnol. 2000, 11, 565. (j) Dijksman, A.; Elzinga, J. M.;
Li, X.-Y.; Arends, I. W. C. E.; Sheldon, R. A. Tetrahedron: Asymmetry
2000, 13, 879. (k) Gihani, M. T. E.; Williams, J. M. J. Curr. Opin. Chem.
Biol. 1999, 3, 11. (l) Stu¨rmer, R. Angew. Chem. Int. Ed. 1997, 36, 1173.
(m) Reetz, M. T.; Schimossek, K. Chima 1996, 50, 668.
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Kim, M.-J.; Park, J. J. Org. Chem. 2004, 69, 1972. (b) Kim, M.-J.; Chung,
Y. I.; Choi, Y. K.; Lee, H. K.; Kim, D.; Park, J. J. Am. Chem. Soc. 2003,
125, 11494. (c) Choi, J. H.; Kim, Y. H.; Nam, S. H.; Shin, S. T.; Kim,
M.-J.; Park, J. Angew. Chem. Int. Ed. 2002, 41, 2373.
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J.-E. Chem. Eur. J. 2006, 12, 225. (b) Mart´ın-Matute, B.; Edin, M; Boga´r,
K.; Kaynak, F. B.; Ba¨ckvall, J.-E. J. Am. Chem. Soc. 2005, 127, 8817. (c)
Mart´ın-Matute, B.; Edin, M.; Boga´r, K.; Ba¨ckvall, J.-E. Angew. Chem.,
Int. Ed. 2004, 43, 6535.
(11) O-Alkylation of alcohols: (a) Sureshan, K. M.; Shashidhar, M. S.
Tetrahedron Lett. 2000, 41, 4185. (b) Das, T.; Shashidhar, M. S. Carbohydr.
Res. 1997, 297, 243. (c) Banerjee, T.; Srikantiah, S. M. Tetrahedron Lett.
1994, 35, 8053. (d) Stevens, P. G. J. Am. Chem. Soc. 1932, 54, 3732.
(12) Monoprotection of symmetrical diols: (a) Bouzide, A.; Sauve´, G.
Org. Lett. 2002, 4, 2329. (b) Bouzide, A.; LeBerre, N.; Sauve´, G.
Tetrahedron Lett. 2001, 42, 8781. (c) Bouzide, A.; Sauve´, G. Tetrahedron
Lett. 1997, 38, 5945.
(13) Pd-catalyzed coupling reaction: (a) Lightfoot, A. P.; Twiddle, S. J.
R.; Whiting, A. Synlett 2005, 529. (b) Chen, H.; Deng, M.-Z. J. Org. Chem.
2000, 65, 4444. (c) Chen, H.; Deng, M.-Z. Org. Lett. 2000, 2, 1649. (d)
Uenishi, J.; Beau, J.-M.; Armstrong, R. W.; Kishi, Y. J. Am. Chem. Soc.
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J. Org. Chem, Vol. 72, No. 18, 2007 6861

Ko et al.
TABLE 2. Catalytic Racemization of (S)-1-Phenylethanol with
TABLE 3. Catalytic Racemization of Secondary Alcohols Using 5b
and Ag2Oa
Other Ru Complexesa
entry
catalyst
solvent
toluene
t (h)
eeb (%)
>99
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
none
1
2a
3
10.0
5.0
5.0
5.0
1.5
2.0
1.0
1.0
10.0
10.0
10.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
benzene
THF
5.1
40.6
52.4
4
0.0 (40.0)c
5a
5b
5c
6a
6b
6c
5b
5b
5bd
5b
5b
5b
5b
0.0 (48.0)c
0.0 (32.0)c
0.0 (29.1)c
97.6
89.0
98.2
0.0
0.0
0.0
20.8
74.8
82.1
97.6
THF
CH2Cl2
acetone
EtOAc
CH2dCHOAc
a (S)-1-Phenylethanol (>99% ee, 0.25 mmol) dissolved in toluene (0.5
mL) was added to a flask containing catalyst (4 mol %) and Ag2O (10 mol
%), and the resulting mixture was stirred at 25 °C in the air. b The % ee
values were measured after 1 h by GC equipped with a chiral column. c The
% ee values in parentheses were measured after 30 min. d 5b and Ag2O
recovered from the ninth reuse were employed.
the air (entry 1). Decreasing the amount of 4 decreased the
racemization rate (entries 3 and 4), but increasing the amount
of Ag2O more than 10 mol % did not increase the rate (entries
5 and 6). Silver phosphate was helpful for the racemization,
although its efficiency was much lower than that of Ag2O (entry
7). Other silver salts such as AgOTf, AgOAc, and AgNO3,
however, were ineffective for the racemization with 4 under
the same conditions (entries 8-10). The racemization with 4
and potassium tert-butoxide was completed in 30 min, but 4
was decomposed during the racemization and 9.5% of acetophe-
none as side product was produced (entry 11). Other bases such
as K3PO4 and K2CO3 did not help 4 in racemizing the alcohol
(entries 12 and 13).
Ag2O was tested for the racemization with other ruthenium
complexes, 1-6 (Table 2). Ag2O alone did not racemize the
alcohol (entry 1) and was not so effective on the racemization
with 1-3 (entries 2-4). The racemization with 5b or 5c was
faster than that with 4 (entries 7 and 8), whereas the racemization
with ruthenium chloride complex 5a, trimethyl phosphine
complex 6a, triphenyl phosphite complex 6b, or trimethyl
phosphite complex 6c was slower than that with 4 (entries 6
and 9-11). According to the ee values obtained after 30 min
(entries 5-8), there might be no induction period for the
racemization with 4 or 5. Among solvents tested, benzene and
tetrahydrofuran (THF) were as effective as toluene, while
dichloromethane was less effective (entries 12-15). Acetone
and ethyl acetate (EtOAc) hindered the racemization signifi-
cantly (entries 16 and 17). In particular, vinyl acetate, which is
a popular acyl donor for enzymatic acylation, inhibited the
racemization almost completely (entry 18). Meanwhile, it is
noticeable that 5b and Ag2O can be recovered and reused at
least 10 times without activity loss (entry 14).15
a The mixture of alcohol (0.25 mmol), 5b (4 mol %), and Ag2O (10 mol
%) in toluene (0.5 M) was stirred in the air. b Determined by GC. c Measured
by HPLC equipped with a chiral column. d Determined by GC after
conversion to 2-octyl acetate.
3). The racemizations of 1-(4-methoxyphenyl)ethanol, 1-(4-
chlorophenyl)ethanol, and indanol were slower than that of
1-phenylethanol (entries 1-4). In particular, the racemization
of 1-(4-chlorophenyl)ethanol was 8 times slower (entry 3).
However, increasing reaction temperature can increase the rate
(entries 6-8). 1-Phenyl-1,2-ethanediol was also racemized
successfully. It is remarkable that aliphatic alcohols such as
3-phenyl-2-propanol, 4-phenyl-2-butanol, and 2-octanol can be
racemized with rates comparable to those for benzylic alcohols
under the same conditions (entries 9-11).
Dynamic Kinetic Resolution of Secondary Alcohols. The
activities of 2b, 4, and 5a-c were compared in the DKR of
1-phenylethanol in the air (Table 4) with Candida antarctica
lipase B (CALB) as the lipase and isopropenyl acetate as the
acyl donor. The DKR with 2b requires potassium tert-butoxide
to activate 2b and also requires sodium carbonate to maintain
its activity during the DKR.8c The product yield is only 60% in
the DKR with 2b (entry 1) and in that with 5b and 10 mol %
of Ag2O under aerobic conditions after 15 h (entry 2). Addition
of base such as Na2CO3 did not improve the yield (entry 3).
Interestingly, however, increasing the amount of Ag2O to 1
equiv completed the DKR in 6 h to give (R)-1-phenylethyl
acetate in 98% (entry 4). After the DKR, the catalysts could be
recovered, but additional Ag2O was required for the next use.
The DKR with 5c was as successful as that with 5b (entry 5),
while those with 5a and 4 were not completed in 6 h (entries 6
and 7).
The catalyst system, 5b and Ag2O, was employed for the
racemization of various secondary alcohols in the air (Table
(15) The yields of racemic 1-phenylethanol in the reuse: 2nd, 99 %;
3rd, 99 %; 4th, 98 %; 5th, 98 %; 6th, 98 %; 7th, 99 %; 8th, 98 %; 9th,
98 %.
6862 J. Org. Chem., Vol. 72, No. 18, 2007

Kinetic Resolution of Secondary Alcohols
TABLE 4. DKR of 1-Phenylethanol in the Aira
SCHEME 3. Reported Mechanism for Ru-Catalyzed
Racemization of Secondary Alcohol
entry
1
catalyst
additive (mol %)
t (h)
yieldb,c (%)
eed (%)
2b
KOtBu (5)
15
60
>99
Na2CO3 (100)
Ag2O (10)
Ag2O (10)
2
3
5b
5b
15
15
60
60
>99
>99
Na2CO3 (100)
Ag2O (100)
Ag2O (100)
Ag2O (100)
Ag2O (100)
4
5
6
7
5b
5c
5a
4
6
6
6
6
98 (95)
96 (92)
85
>99
>99
>99
>99
89
a A mixture of alcohol (1.0 mmol), ruthenium catalyst (4 mol %), Ag2O,
Novozym-435 (8 mg), and isopropenyl acetate (2.0 mmol) in toluene (3.2
mL) was stirred at 25 °C in the air. b Determined by GC. c Numbers in
parentheses show isolated yields. d Determined by GC equipped with a chiral
column.
SCHEME 4. Proposed Mechanism for Racemization of
Secondary Alcohol with 5b and Ag2O
TABLE 5. DKR of Secondary Alcoholsa
addition, interestingly, the silver oxide recovered from the
racemization was the same as the original silver oxide and did
not show any sign for the formation of silver bromide in the
XRD analysis.16 With these observations, it is hard to propose
a persuasive mechanism for the racemization with our catalyst
system. However, it has been shown that a ruthenium alkoxide
(7a or 7b) is formed during the racemization with 2b by the
aid of a strong base such as potassium tert-butoxide (Scheme
3).8b The alkoxides 7a and 7b are in equilibrium through the
formation of ruthenium hydride complex 8 and through alcohol
exchange. Thus, the analogous alkoxide complex 9 would be
formed from 5b and silver oxide. In this reaction silver oxide
acts as the base for the deprotonation of an alcohol (Scheme
4). The equilibrium far shifted to 5b and silver oxide can explain
the failure to detect 9 and alkoxide intermediates.
a A mixture of alcohol (1.0 mmol), 5b (4 mol %), Ag2O (1.0 mmol),
Novozym-435 (8 mg), and isopropenyl acetate (2.0 mmol) in toluene (3.2
mL) was stirred at 25 °C in the air. b Determined by GC equipped with a
chiral column. c Numbers in parentheses show isolated yields. d Determined
by HPLC equipped with a chiral column.
Dynamic Kinetic Resolution of Various Secondary Alco-
hols. On the basis of the results obtained from the DKR of
1-phenylethanol, 5b was selected as the racemization catalyst
and applied to the DKRs of various secondary alcohols (Table
5). The catalyst system was effective for aliphatic alcohols as
well as for benzylic alcohols. 1-(Naphthalen-1-yl)ethanol and
1-(naphthalen-2-yl)ethanol were converted into the correspond-
ing (R)-acetates (>99% ee), respectively, in excellent yields
(entries 1 and 2). The DKR of 1-(p-chlorophenyl)ethanol was
also successful, whereas 1-(4-methoxyphenyl)ethanol gave the
corresponding (R)-acetate only in 75% yield due to the side
reaction producing 1-(4-methoxyphenyl)ethanone (entries 3 and
4). 3-Phenyl-2-propanol and 2-octanol were also transformed
successfully into the corresponding (R)-acetates (99% ee) in 93%
and 96% yield, respectively, although a longer reaction time
(20 h) was needed (entries 5 and 6).
Conclusion
In summary, we have synthesized a new class of air-stable
and recyclable alcohol racemization catalysts and demonstrated
that they are applicable to the DKR of aliphatic alcohols as
well as benzylic ones at room temperature. The catalysts are
readily synthesized from the corresponding ruthenium dicar-
bonyl complexes through simple ligand-substitution reactions.
The efficiency of the catalysts in the DKR is comparable to
that of the parent ruthenium dicarbonyl complexes. In contrast
to the dicarbonyl complexes, however, our catalysts do not
require the strong base such as potassium tert-butoxide to be
activated for alcohol racemization and DKR and are stable
during the DKR under aerobic conditions.
Studies for the Role of Silver Oxide. To get a clue for the
role of silver oxide, a mixture of 1-phenylethanol, 5b, and Ag2O
in methylene chloride-d2 was subjected to NMR experiments
(1H, 13C, and 31P). However, no intermediate was detected, and
only the resonance peaks for 1-phenylethanol and 5b were
observed during the racemization of 1-phenylethanol.16 In
Experimental Section
Synthesis of [2,3,4,5-Ph4(η5-C4CNHiPr)]Ru(CO)(Cl)(PPh3) (4).
In a 100 mL flask equipped with a grease-free high-vacuum
(16) See the Supporting Information.
J. Org. Chem, Vol. 72, No. 18, 2007 6863

Ko et al.
stopcock were dissolved [2,3,4,5-Ph4(η5-C4CNHiPr)]Ru(CO)2Cl
(200 mg, 0.323 mmol) and triphenylphosphine (93.2 mg, 0.355
mmol) in dry CH2Cl2 (5 mL). After the flask was filled with argon
and closed, trimethylamine N-oxide (48.5 mg, 0.646 mmol)
dissolved in acetonitrile (2 mL) was slowly added to the first
solution and stirred for 15 min at room temperature. The resulting
solution was concentrated and chromatographed on silica gel
column to give a red solid 4 (260 mg, 94% yield). Mp: >180 °C
CDCl3): δ 207.1 (d, Jcp ) 23.9 Hz, CO), 136.0-127.3 (48
resonances, aromatic), 103.8 (C of Cp). 31P NMR (121 MHz,
CDCl3): δ 42.66 (s) external std. H3PO4 in D2O. IR (KBr, cm-1):
γ(CO) 1940 (s). MS (FAB, m/z): 964.0 [M+]. Anal. Calcd for
C54H40IOPRu: C, 67.29; H, 4.18. Found: C, 67.10; H, 4.36.
(η5-Ph5Cp)Ru(CO)(Br)(PMe3) (6a). From (η5-Ph5C5)Ru(CO)2-
Br (200 mg, 0.292 mmol), trimethylphosphine (36 µL, 0.350 mmol),
and trimethylamine N-oxide (43.8 mg, 0.584 mmol) was obtained
orange-brown solid 6a (139 mg, 65% yield). Mp: 220-223 °C
1
dec. H NMR (300 MHz, CDCl3): δ 7.70-7.68 (m, 2H), 7.45-
1
7.39 (m, 6H), 7.32-7.02 (m, 20H), 6.97-6.90 (m, 3H), 6.60 (t, J
) 7.6 Hz, 2H), 6.48 (d, J ) 7.7 Hz, 2H), 3.40 (d, J ) 8.0 Hz, 1H),
3.17 (m, 1H), 0.94 (d, J ) 6.1 Hz, 3H), 0.63 (d, J ) 6.1 Hz, 3H).
13C NMR (75 MHz, CDCl3): δ 206.8 (d, Jcp ) 23.2 Hz, CO), 137.7
(C1 of Cp), 135.0-126.9 (42 resonance, aromatic), 99.9, 96.3 (C
3, 4 of Cp), 82.9, 80.7 (C 2, 5 of Cp), 45.6, 25.8, 24.5. 31P NMR
(121 MHz, CDCl3): δ 42.39 (s) external std. H3PO4 in D2O. IR
(KBr, cm-1): γ(CO) 1933 (s). MS (FAB, m/z): 854.0 [M+ + 1].
Anal. Calcd for C51H43ClNOPRu: C, 71.78; H, 5.08; N, 1.64.
Found: C, 71.79; H, 5.09; N, 1.87.
dec. H NMR (300 MHz, CDCl3): δ 7.16-7.02 (m, 25H), 1.60
(d, JPH ) 9.7 Hz, 9H). 13C NMR (75 MHz, CDCl3): δ 204.3 (d,
Jcp ) 24.0 Hz, CO), 132.7, 132.0, 127.5, 102.8, (C of Cp), 18.4 (d,
JCP ) 35.0 Hz). 31P NMR (121 MHz, CDCl3): δ 6.98 (s) external
std H3PO4 in D2O. IR (KBr, cm-1): γ(CO) 1942 (s). MS (FAB,
m/z): 731.9 [M+ + 1]. Anal. Calcd for C39H34BrOPRu: C, 64.11;
H, 4.69. Found: C, 64.37; H, 4.71.
(η5-Ph5Cp)Ru(CO)(Br)[P(OPh)3] (6b). From (η5-Ph5C5)Ru(CO)2-
Br (200 mg, 0.292 mmol), triphenyl phosphite (115 µL, 0.438
mmol), and trimethylamine N-oxide (43.8 mg, 0.584 mmol) was
obtained yellow solid 6b (273 mg, 97% yield). Mp: 180-181 °C
(η5-Ph5Cp)Ru(CO)(Cl)(PPh3) (5a). From (η5-Ph5C5)Ru(CO)2-
Cl (300 mg, 0.470 mmol), triphenylphosphine (136 mg, 0.517
mmol), and trimethylamine N-oxide (70.6 mg, 0.940 mmol) was
obtained red solid 5a (390 mg, 95% yield). Mp: >190 °C dec. 1H
NMR (300 MHz, CDCl3): δ 7.47-7.41 (m, 6H), 7.31-7.28 (m,
3H), 7.14-7.06 (m, 11H), 6.88 (t, J ) 7.8 Hz, 10H), 6.78 (d, J )
7.8 Hz, 10H). 13C NMR (75 MHz, CDCl3): δ 206.5 (d, Jcp ) 26.1
Hz, CO), 134.8-127.4 (48 resonances, aromatic), 103.4 (C of Cp).
31P NMR (121 MHz, CDCl3): δ 40.61 (s) external std. H3PO4 in
D2O. IR (KBr, cm-1): γ(CO) 1943 (s). MS (FAB, m/z): 872.4
[M+] Anal. Calcd for C54H40ClOPRu: C, 74.34; H, 4.62. Found:
C, 74.38; H, 4.65.
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dec. H NMR (300 MHz, CDCl3): δ 7.19-6.92 (m, 40H). 13C
NMR (75 MHz, CDCl3): δ 202.1 (d, Jcp ) 32.8 Hz, CO), 152.2,
132.9, 132.6, 131.2, 129.5, 127.7, 127.5, 124.9, 121.4, 121.3, 104.4
(d, Jcp ) 3.2 Hz, C of Cp). 31P NMR (121 MHz, CDCl3): δ 121.5
(s) external std H3PO4 in D2O. IR (KBr, cm-1): γ(CO) 1978 (s).
Anal. Calcd for C54H40BrO4PRu: C, 67.22; H, 4.18. Found: C,
67.25; H, 4.33.
(η5-Ph5Cp)Ru(CO)(Br)[P(OMe)3] (6c). From (η5-Ph5C5)Ru(CO)2-
Br (200 mg, 0.292 mmol), trimethyl phosphite (52.0 µL, 0.438
mmol), and trimethylamine N-oxide (43.8 mg, 0.584 mmol) was
obtained orange solid 6c (214 mg, 94% yield). Mp: 205-206 °C
(η5-Ph5Cp)Ru(CO)(Br)(PPh3) (5b). From (η5-Ph5C5)Ru(CO)2-
Br (300 mg, 0.440 mmol), triphenylphosphine (127 mg, 0.484
mmol), and trimethylamine N-oxide (66.1 mg, 0.880 mmol) was
obtained red solid 5b (383 mg, 95% yield). Mp: >200 °C dec .1H
NMR (300 MHz, CDCl3): δ 7.47-7.41 (m, 6H), 7.32-7.27 (m,
3H), 7.15-7.05 (m, 11H), 6.88 (t, J ) 7.5 Hz, 10H), 6.79 (d, J )
7.2 Hz, 10H). 13C NMR (75 MHz, CDCl3): δ 206.6 (d, Jcp ) 25.5
Hz, CO), 135.1-127.3 (48 resonances, aromatic), 103.5 (C of Cp).
31P NMR (121 MHz, CDCl3): δ 41.20 (s) external std. H3PO4 in
D2O. IR (KBr, cm-1): γ(CO) 1942 (s). Anal. Calcd for C54H40-
BrOPRu: C, 70.74; H, 4.40. Found: C, 70.73; H, 4.40.
dec. H NMR (300 MHz, CDCl3): δ 7.14-7.00 (m, 25H), 3.70
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(d, JPH ) 11 Hz, 9H). 13C NMR (75 MHz, CDCl3): δ 203.9 (d, Jcp
) 33.8 Hz, CO), 138.0, 133.2, 132.9, 131.7, 130.1, 128.4, 127.5,
127.3, 127.1, 126.2, 104.0 (d, Jcp ) 3.1 Hz, C of Cp), 54.3 (d, JCP
) 7.7 Hz). 31P NMR (121 MHz, CDCl3): δ 136.9 (s) external std.
H3PO4 in D2O. IR (KBr, cm-1): γ(CO) 1954 (s). Anal. Calcd for
C39H34BrO4PRu: C, 60.16; H, 4.40. Found: C, 60.33; H, 4.57.
Acknowledgment. We are grateful for the financial support
from KOSEF (the Center for Integrated Molecular System and
R01-2006-10696-0) and KRF (the BK21 program).
(η5-Ph5Cp)Ru(CO)(I)(PPh3) (5c). From (η5-Ph5C5)Ru(CO)2I
(300 mg, 0.411 mmol), triphenylphosphine (162 mg, 0.616 mmol),
and trimethylamine N-oxide (61.7 mg, 0.822 mmol) was obtained
Supporting Information Available: Experimental procedures,
characterization data, and NMR and XRD studies for racemization
of (S)-1-phenylethanol. This material is available free of charge
via the Internet at http://pubs.acs.org.
1
brown solid 5c (380 mg, 96% yield). Mp: 210 °C dec. H NMR
(300 MHz, CDCl3): δ 7.46-7.40 (m, 6H), 7.30-7.28 (m, 2H),
7.14-7.06 (m, 12H), 6.90-6.81 (m, 20H). 13C NMR (75 MHz,
JO071065O
6864 J. Org. Chem., Vol. 72, No. 18, 2007