Chiral phosphonite, phosphite and phosphoramidite η6-arene- ruthenium(ii) complexes: Application to the kinetic resolution of allylic alcohols

Article abstract of DOI:10.1039/c0dt00140f

The synthesis and characterization of chiral arene-ruthenium complexes [RuCl₂(η⁶-arene){(R)-PR(binaphthoxy)}] (arene = benzene (1), p-cymene (2), mesitylene (3); R = Ph (a), OPh (b), piperidyl (c)) are described. Derivatives 1-3 have been employed to promote the kinetic resolution of allylic alcohols through a redox-isomerization process. As a general trend, the best selectivities are attained with the more sterically hindered catalysts i.e. those containing p-cymene or mesitylene ligands. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00140f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Chiral phosphonite, phosphite and phosphoramidite g6-arene-ruthenium(II)
complexes: application to the kinetic resolution of allylic alcohols†‡
Mariano A. Ferna´ndez-Zu´mel, Beatriz Lastra-Barreira, Marcus Scheele, Josefina D´ıez, Pascale Crochet* and
Jose´ Gimeno*
Received 15th March 2010, Accepted 1st June 2010
First published as an Advance Article on the web 21st July 2010
DOI: 10.1039/c0dt00140f
6
The synthesis and characterization of chiral arene-ruthenium complexes [RuCl2(h -arene){(R)-PR-
(binaphthoxy)}] (arene = benzene (1), p-cymene (2), mesitylene (3); R = Ph (a), OPh (b), piperidyl (c))
are described. Derivatives 1–3 have been employed to promote the kinetic resolution of allylic alcohols
through a redox-isomerization process. As a general trend, the best selectivities are attained with the
more sterically hindered catalysts i.e. those containing p-cymene or mesitylene ligands.
Introduction
The catalytic redox-isomerization of allylic alcohols represents
a useful synthetic process to generate aldehydes or ketones
(Scheme 1).1 The best performances for this transformation, in
Scheme 2 Kinetic resolution of allylic alcohols.
terms of both activity and selectivity, have been obtained with
catalytic systems based on iron, ruthenium, rhodium and iridium
complexes.1–2 However, despite the extensive studies reported
on this reaction, its asymmetric version, a potential route to
chiral complex [Rh{(R)-BINAP}(MeOH)2][ClO4] (e.e. = 91%).4b
Nevertheless, this procedure presents a series of major drawbacks:
optically active carbonyl compounds with a stereogenic center
(i) a very long◦reaction time is required (14 days), (ii) a low
in a- (R3 π CHR1R2) or b-position (R1 π R2), still remains almost
temperature (0 C) must be maintained throughout the process,
unexplored.3
and (iii) a low yield in the enantio-enriched allylic alcohol is
obtained (27%). Hence, the development of a selective metal-
catalyzed resolution of allylic alcohols, easy to carry out, remains
a challenge.
During the last years, our research group has explored the
catalytic activity of different arene-ruthenium(II) complexes in the
redox-isomerization of allylic alcohols,6 finding that phosphite,
Scheme 1 Redox-isomerization of allylic alcohols.
6
phosphinite and phosphonite derivatives of the type [RuCl2(h -
Another asymmetric process, also based on this particular
p-cymene)(PR3)] are particularly efficient to promote this trans-
formation under extremely smooth reaction conditions.6b,c With
these precedents in mind, we decided to investigate the catalytic
behaviour of similar chiral complexes in the kinetic resolution of
allylic alcohols. In particular, we focused our interest on arene-
ruthenium(II) derivatives containing monodentate phosphonite-,
phosphite- or phosphoramidite-ligands derived from binaphthol.
We must note that, during the last two decades, this type of
ligands has been successfully employed in a huge number of highly
selective asymmetric catalytic processes.7 Thus, in the present
work, we describe the synthesis of new chiral arene-ruthenium(II)
complexes with P-donor ligands a–c (Fig. 1)8 and a evaluation of
their capacity to promote the kinetic resolution of allylic alcohols.
transformation and even less investigated, is the kinetic resolution
of allylic alcohols.4,5 In this case, the chiral catalyst employed
preferably converts one enantiomer of the allylic alcohol into a
ketone, affording enantio-enriched solutions of the other isomer
(Scheme 2).
As far as we are aware, only two studies on this kinetic resolution
reaction have been reported to date. The first one, involving in
situ generated [RhCl{(-)-DIOP}] catalyst, allowed the generation
of (S)-enantio-enriched 3-buten-2-ol with extremely low enan-
tiomeric excess (1.09%).4a An improved selectivity was reached
in the kinetic resolution of 4-hydroxy-2-cyclopentenone using the
Departamento de Qu´ımica Orga´nica e Inorga´nica, Instituto Universitario de
Qu´ımica Organometa´lica “Enrique Moles” (Unidad Asociada al CSIC),
Facultad de Qu´ımica, Universidad de Oviedo, E-33071, Oviedo, Spain.
E-mail: crochetpascale@uniovi.es, jgh@uniovi.es; Fax: 34 985103446;
Tel: 34 985105076
† Dedicated to the memory of Jose´ Manuel Concello´n Gracia.
‡ Electronic supplementary information (ESI) available: X-Ray diffraction
data and details on catalytic experiments. CCDC reference numbers
769455 (1a), 769456 (1b), 769457 (3b) and 769458 (3c). For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt00140f
Fig. 1 Structure of (R)-enantiomer of the ligands a–c.
7780 | Dalton Trans., 2010, 39, 7780–7785
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Results and discussion
Synthesis and characterization of the phosphonite-, phosphite- and
phosphoramidite-complexes 1–3
6
Treatment of the benzene dimer [{RuCl(m-Cl)(h -benzene)}2]9
with a slight excess of ligands a–c in dichloromethane at room
temperature gives rise to the selective formation of the cor-
6
responding mononuclear derivatives [RuCl2(h -benzene)(L)] (L
= a (1a), b (1b), c (1c)), which were isolated in good yields
(Scheme 3). Similarly, the p-cymene and mesitylene analogues,
6
6
[RuCl2(h -p-cymene)(L)] (L = a (2a), b (2b), c (2c)) and [RuCl2(h -
mesitylene)(L)] (L = a (3a), b (3b), c (3c)), respectively, have been
6
prepared starting from the dimeric precursors [{RuCl(m-Cl)(h -
p-cymene)}2]10 and [{RuCl(m-Cl)(h -mesitylene)}2]11 (Scheme 3).
6
All these arene-ruthenium(II) derivatives have been synthesized
both in racemic ((rac)-1–3) and optically pure forms ((R)-1–3)
using ligands a–c as a racemic mixture ((rac)-a–c) or as their (R)-
enantiomer ((R)-a–c), respectively.
6
Fig.
2
ORTEP-type view of the structure of [RuCl2(h -C6H6)(a)]
1
4
(1a· CH2Cl2). Thermal ellipsoids are drawn at the 10% probabil-
ity level. Hydrogen atoms and CH2Cl2 molecule are omitted for
◦
˚
clarity. Selected bond lengths (A) and angles ( ): Ru–C* 1.7110(4),
Ru–Cl(1) 2.3904(14), Ru–Cl(2) 2.3980(11), Ru–P 2.2659(11); C*–Ru–Cl(1)
125.43(4), C*–Ru–Cl(2) 126.38(3), C*–Ru–P 131.86(3), Cl(1)–Ru–Cl(2)
88.38(5), Cl(1)–Ru–P 86.00(4), Cl(2)–Ru–P 84.37(4). C* denotes the
centroid of the arene ring C(27)–C(32).
Scheme 3 Synthesis of complexes 1–3.
Compounds 1–3, isolated as air-stable orange–brown solids,
have been characterized by means of standard spectroscopic
1
1
techniques (31P{ H}, 1H and 13C{ H} NMR) as well as elemental
analysis, with all data fully consistent with the proposed formu-
lations. In particular, the 31P{ H} NMR spectra for 1–3 show a
1
unique singlet signal at d 177.8–181.7 (a), 129.8–135.3 (b) and
139.9–147.8 ppm (c), the chemical shift observed falling within
the expected range for a coordinated phosphonite, phosphite and
phosphoramidite, respectively.12
The molecular structures of 1a,13 1b, 3b and 3c have been un-
ambiguously confirmed by means of X-ray diffraction.14 ORTEP
plots are shown in Fig. 2, 3, 4 and 5, respectively, and selected
bonding parameters appear in the captions. For all the derivatives,
the geometry around the ruthenium atom can be described as
a distorted octahedron, with the arene ligand occupying three
coordination sites. The values of the interligand angles Cl(1)–Ru–
Cl(2), Cl(1)–Ru–P(1) and Cl(2)–Ru–P(1), and those between the
6
Fig.
3
ORTEP-type view of the structure of [RuCl2(h -C6H6)(b)]
1
2
(1b· CH2Cl2). Thermal ellipsoids are drawn at the 10% probabil-
ity level. Hydrogen atoms and CH2Cl2 molecule are omitted for
clarity. Selected bond lengths (A) and angles (◦): Ru–C* 1.7038,
˚
Ru–Cl(1) 2.3975(13), Ru–Cl(2) 2.3968(13), Ru–P 2.2540(13); C*–Ru–Cl(1)
124.49(4), C*–Ru–Cl(2) 127.53(4), C*–Ru–P 128.92(4), Cl(1)–Ru–Cl(2)
87.34(5), Cl(1)–Ru–P 90.17(5), Cl(2)–Ru–P 85.10(5). C* denotes the
centroid of the arene ring C(27)–C(32).
6
centroid (C*) of the h -arene ring and the legs lie in the expected
unit) being now located near the chlorine atoms. During the
catalytic experiments (see below), these chloride ligands are
removed to allow the substrate coordination and the proximity
of the chiral unit may enhance the selectivity of the process.
range for pseudo-octahedral three-legged piano-stool ruthenium
complexes.15 As a general trend, the C*–Ru–P(1) angle is slightly
larger than the C*–Ru–Cl(1) and C*–Ru–Cl(2) ones, probably to
minimize the steric hindrance between the large phosphine and
arene ligands.
Kinetic resolution of allylic alcohols promoted by complexes 1–3
The most relevant structural features of these complexes
concern the position of the binaphthoxy unit. Thus, in 1a and
1b, which contain the less sterically hindered arene ligand (i.e.
benzene), the binaphthoxy moiety points towards the arene.
In contrast, probably due to steric grounds, in the mesitylene
compounds, 3b and 3c, the binaphthoxy unit is oriented towards
the opposite direction, the chiral fragment (i.e. the binaphthoxy
In a first step, we compared the activities and selectivities of all
the chiral complexes (R)-1–3 in the kinetic resolution of 1-phenyl-
2-propen-1-ol (Table 1). The catalytic reactions were performed at
45 ◦C using 4 mmol of substrate, 1 mol% of ruthenium catalyst, 2
mol% of KOtBu16,17 and 20 mL of THF, and both conversions and
enantiomeric excesses of the remaining alcohol were monitored by
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Table 1 Kinetic resolution of 1-phenyl-2-propen-1-ol promoted by com-
plexes (R)-1–3a
Catalyst [arene]
t/h
Alcoholb,c (%)
e.e.c (%)
Phosphonite catalysts
1a [benzene]
2.6
3
0.33
44
48
45
0
13(S)
15(S)
2a [p-cymene]
3a [mesitylene]
Phosphite catalysts
1b [benzene]
2b [p-cymene]
3b [mesitylene]
2.9
0.25
4.9
48
45
50
15(S)
17(S)
16(S)
6
Fig.
4
ORTEP-type view of the structure of [RuCl2(h -1,3,5-
C6H3Me3)(b)] (3b). Thermal ellipsoids are drawn at the 10% probability
Phosphoramidite catalysts
1c [benzene]
level. Hydrogen atoms are omitted for clarity. Selected bond lengths
3.9
7
20
46
47
90
4(S)
6(S)
0
◦
˚
(A) and angles ( ): Ru–C* 1.740(12), Ru–Cl(1) 2.4106(18), Ru–Cl(2)
2.3894(18), Ru–P 2.2372(16); C*–Ru–Cl(1) 125.9(9), C*–Ru–Cl(2)
125.0(6), C*–Ru–P 128.5(3), Cl(1)–Ru–Cl(2) 87.20(8), Cl(1)–Ru–P
89.62(6), Cl(2)–Ru–P 87.97(7). C* denotes the centroid of the arene ring
C(27)–C(32).
2c [p-cymene]
3c [mesitylene]
a Reactions carried out at 45 ◦C using 4 mmol of 1-phenyl-2-propen-1-ol,
1 mol% of the indicated catalyst, 2 mol% of KOtBu and 20 mL of THF.
b Allylic alcohol remaining. c Determined by GC, absolute configuration
of the major enantiomer indicated in parentheses.
Table 2 Kinetic resolution of other allylic alcohols promoted by com-
plexes (R)-2b and (R)-3ba
Ar
Catalyst
t/h
Alcoholb,c (%)
e.e.c (%)
4-ClC6H4
4-BrC6H4
4-MeOC6H4
1-Naphthyl
2b
3b
2b
3b
2b
3b
2b
3b
2.5
8
1.5
5
3.5
7
2.5
2.5
50
48
49
48
55
49
56
50
8(S)
10(S)
12(S)
8(S)
11(S)
10(S)
11(S)
16(S)
a Reactions carried out at 75 ◦C using 4 mmol of indicated allylic alcohol,
1 mol% of 2b or 3b, 2 mol% of KOtBu and 20 mL of THF. b Allylic
alcohol remaining. c Determined by GC, absolute configuration of the
major enantiomer indicated in parentheses.
6
Fig.
5
ORTEP-type view of the structure of [RuCl2(h -1,3,5-
C6H3Me3)(c)] (3c). Thermal ellipsoids are drawn at the 10% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths (A)
˚
and angles (◦): Ru–C* 1.73(2), Ru–Cl(1) 2.4165(16), Ru–Cl(2) 2.3917(16),
Ru–P 2.2618(11); C*–Ru–Cl(1) 127.7(4), C*–Ru–Cl(2) 124.7(3), C*–Ru–P
130.5(6), Cl(1)–Ru–Cl(2) 87.82(7), Cl(1)–Ru–P 84.94(6), Cl(2)–Ru–P
87.03(6). C* denotes the centroid of the arene ring C(26)–C(31).
above). As the P-donor ligands are concerned, those complexes
containing the phosphite b are the most selective.
GC analyses of aliquots. Under these conditions, all the catalysts
are able to promote the redox-isomerization of 1-phenyl-2-propen-
1-ol into 1-phenylpropan-1-one, reacting preferably with the R
enantiomer. By this way, enantio-enriched solutions of the S
isomer, albeit with low e.e. values (Table 1), are generated.18 As
a general trend, the best enantioselectivities are attained with
catalysts containing the more sterically demanding arene ligands,
i.e. p-cymene and mesitylene.19 This behavior is probably related
with the orientation of the chiral fragment in these derivatives (see
The metal-promoted resolution processes have been extended
to other allylic alcohols with different aromatic substituents on
the C(1) carbon, using catalysts 2b and 3b (Table 2). However,
these substrates were revealed to be less reactive than 1-phenyl-
2-propen-1-ol and required increasing the temperature reaction
to 75 ◦C. Once again, phosphite-complexes 2b and 3b convert
preferably the R enantiomers, furnishing the remaining S allylic
alcohol albeit with low e.e. values.
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Preparation of [RuCl2(g6-C6H6){(rac)-b}] ((rac)-1b)
Conclusions
Following the same procedure (rac)-1b was prepared as a brown
In summary, the synthesis and structural characterization of
new chiral phosphonite, phosphite and phosphoramidite arene-
ruthenium(II) complexes have been presented. These species
belong to the scarce examples of catalytic systems able to promote
the kinetic resolution of allylic alcohols through an isomerization
reaction,4 nevertheless the enantioselectivities obtained were by
far lower that those reached through other kinetic resolution
processes.20 The relative orientation of the chiral binapthoxy unit
respectively to the arene ligand seems to govern the selectivity
of the catalysts. Studies focused on the synthesis and catalytic
behavior of more structurally rigid tethered arene-ruthenium
complexes, containing a chiral phosphite pendant, are currently
under way in our laboratory.
6
solid, using 0.136 g (0.271 mmol) of [{RuCl(m-Cl)(h -C6H6)}2]
and 0.246 g of ligand (rac)-b (0.602 mmol). Yield: 0.276 g (78%).
1
1
31P{ H} NMR, CD2Cl2, d 129.8 (s). H NMR, CD2Cl2, d 8.07–
6.92 (m, 17 H, ArH), 5.56 (s, 6 H, C6H6). 13C{ H} NMR, CD2Cl2,
1
d 151.7 (d, 2JPC = 13.6, C–O), 148.8 (d, 2JPC = 12.8, C–O), 147.0
(d, 2JPC = 7.2, C–O), 132.4–121.0 (m, Caromatic), 91.0 (d, 2JPC = 5.6,
C6H6). Anal. Calc. for C32H23Cl2O3PRu: C, 58.37; H, 3.52. Found:
C, 58.59; H, 3.67%.
Preparation of [RuCl2(g6-C6H6){(R)-b}] ((R)-1b)
Prepared through the same procedure using optically pure ligand
(R)-b. Yield: 81%. aD = -94◦ (c = 0.245 in CH2Cl2, at 20 ◦C).
Experimental
Preparation of [RuCl2(g6-C6H6){(rac)-c}] ((rac)-1c)
The manipulations were performed under an atmosphere of dry
nitrogen using vacuum-line and standard Schlenk techniques.
Solvents were dried by standard methods and distilled under
nitrogen before use. All reagents were obtained from commercial
Following the same procedure (rac)-1c was prepared as a brown
6
solid, using 0.110 g (0.220 mmol) of [{RuCl(m-Cl)(h -C6H6)}2]
and 0.195 g of ligand (rac)-c (0.488 mmol). Yield: 0.249 g (87%).
1
31P{ H} NMR, CDCl3, d 144.7 (s). 1H NMR, CDCl3, d 8.04–7.23
6
suppliers with the exception of compounds [{RuCl(m-Cl)(h -
arene)}2],9–11 ligands a–c,8 1-(4-chlorophenyl)prop-2-en-1-ol,21
1-(4-bromophenyl)prop-2-en-1-ol,22 1-(4-methoxyphenyl)prop-2-
en-1-ol21 and 1-(naphthalen-1-yl)prop-2-en-1-ol,22 which were
prepared following the method reported in the literature. NMR
spectra were recorded on a Bruker DPX300 instrument at
300 MHz (1H), 121.5 MHz (31P) or 75.4 MHz (13C) using SiMe4
or 85% H3PO4 as standards. DEPT experiments have been carried
out for all the compounds reported in this paper. Optical rotations
(aD) were measured on a Perkin–Elmer 343 polarimeter at the
wavelength of the yellow sodium D line (589 nm). The C, H and
N analyses were carried out with a Perkin–Elmer microanalyzer.
GC and GC/MSD measurements were made on a Hewlett–
Packard HP6890 apparatus (Supelco Beta-DexTM 120 column, 30
m, 250 mm or Gamma-DexTM 225 column, 30 m, 250 mm) and
an Agilent 6890 N apparatus coupled to a 5973 mass detector
(HP-1MS column, 30 m, 250 mm), respectively.
(m, 12 H, ArH), 5.41 (s, 6 H, C6H6), 3.31–3.28 (m, 4 H, NCH2),
1
1.61–1.21 (m, 6 H, CH2). 13C{ H} NMR, CD2Cl2, d 149.6 (d,
2
2JPC = 13.6, C–O), 148.2 (d, JPC = 6.4, C–O), 132.7–121.2 (m,
2
2
Caromatic), 90.3 (d, JPC = 4.8, C6H6), 46.8 (d, JPC = 3.2, NCH2),
3
26.3 (d, JPC = 4.8, NCH2CH2), 24.4 (s, CH2). Anal. Calc. for
C31H28Cl2NO2PRu: C, 57.33; H, 4.35; N, 2.16. Found: C, 57.49;
H, 4.42; N, 2.07%.
Preparation of [RuCl2(g6-C6H6){(R)-c}] ((R)-1c)
Prepared through the same procedure using optically pure ligand
(R)-c. Yield: 84%. aD = -144◦ (c = 0.200 in CH2Cl2, at 20 ◦C).
Preparation of [RuCl2(g6-p-cymene){(rac)-a}] ((rac)-2a)
Following the same procedure (rac)-2a was prepared as a orange
6
solid, using 0.317 g (0.518 mmol) of [{RuCl(m-Cl)(h -p-cymene)}2]
and 0.451 g of ligand (rac)-a (1.15 mmol). Reaction time: 1 h.
Preparation of [RuCl2(g6-C6H6){(rac)-a}] ((rac)-1a)
1
Yield: 0.654 g (91%). 31P{ H} NMR, CDCl3, d 181.7 (s). 1H NMR,
6
A slurry of 0.288 g of [{RuCl(m-Cl)(h -C6H6)}2] (0.576 mmol) and
CDCl3, d 8.00–7.15 (m, 17 H, ArH), 5.50 and 5.37 (both d, 1 H
each, 3JHH = 6.4, cymene), 5.15 and 4.58 (both d, 1 H each, 3JHH
= 5.8, cymene), 2.82 (m, 1 H, CHMe2), 2.09 (s, 3 H, Me), 1.23
0.502 g of ligand (rac)-a (1.28 mmol) in 40 mL of dichloromethane
was stirred for 24 h at room temperature. The resulting red solution
was then filtered through Kieselguhr and evaporated to dryness.
The brown solid was washed three times with a 1 : 3 mixture of
diethyl ether–hexane and vacuum-dried. Yield: 0.666 g (90%).
3
3
(d, 3 H, JHH = 6.9, CHMe), 1.18 (d, 3 H, JHH = 6.8, CHMe).
13C{ H} NMR, CD2Cl2, d 149.7 (d, 2JPC = 12.8, C–O), 148.1 (d,
1
2JPC = 7.2, C–O), 133.8–118.1 (m, Caromatic), 108.8 (d, 2JPC = 1.6, C
cymene), 106.2 (d, 2JPC = 2.4, C cymene), 94.0 (d, 2JPC = 4.0, CH
1
1
31P{ H} NMR, CD2Cl2, d 181.0 (s). H NMR, CD2Cl2, d 8.18–
7.21 (m, 17 H, ArH), 5.40 (s, 6 H, C6H6). 13C{ H} NMR, CD2Cl2,
1
2
2
cymene), 92.7 (d, JPC = 10.3, CH cymene), 86.4 (d, JPC = 3.2,
CH cymene), 83.6 (s, CH cymene), 30.6 (s, CHMe2), 22.4 and 21.7
(both s, CHMe2), 18.2 (s, Me). Anal. Calc. for C36H31Cl2O2PRu:
C, 61.89; H, 4.47. Found: C, 62.03; H, 4.40%.
d 149.8 (d, 2JPC = 13.2, C–O), 148.1 (d, 2JPC = 7.8, C–O), 132.7–
2
118.2 (m, Caromatic), 90.5 (d, JPC = 3.6, C6H6). Anal. Calc. for
C32H23Cl2O2PRu: C, 59.82; H, 3.61. Found: C, 60.05; H, 3.76%.
Preparation of [RuCl2(g6-C6H6){(R)-a}] ((R)-1a)
Preparation of [RuCl2(g6-p-cymene){(R)-a}] ((R)-2a)
Prepared through the same procedure using optically pure ligand
Prepared through the same procedure using optically pure ligand
(R)-a. Yield: 88%. aD = -91◦ (c = 0.222 in CH2Cl2, at 20 ◦C).
(R)-a. Yield: 88%. aD = -84◦ (c = 0.248 in CH2Cl2, at 20 ◦C).
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Preparation of [RuCl2(g6-p-cymene){(rac)-b}] ((rac)-2b)
CH mesitylene), 18.1 (s, Me). Anal. Calc. for C35H29Cl2O2PRu: C,
61.41; H, 4.27. Found: C, 61.33; H, 4.13%.
Following the same procedure (rac)-2b was prepared as a orange
6
solid, using 0.208 g (0.339 mmol) of [{RuCl(m-Cl)(h -p-cymene)}2]
Preparation of [RuCl2(g6-mesitylene){(R)-a}] ((R)-3a)
and 0.308 g of ligand (rac)-b (0.753 mmol). Reaction time: 1 h.
1
Yield: 0.363 g (75%). 31P{ H} NMR, CDCl3, d 130.7 (s). 1H NMR,
Prepared through the same procedure using optically pure ligand
(R)-a. Yield: 93%. aD = -26◦ (c = 0.253 in CH2Cl2, at 20 ◦C).
CD2Cl2, d 8.10–6.95 (m, 17 H, ArH), 5.68 and 5.31 (both d, 1 H
each, 3JHH = 6.2, cymene), 5.41 and 5.00 (both d, 1 H each, 3JHH
= 5.9, cymene), 2.86 (m, 1 H, CHMe2), 2.08 (s, 3 H, Me), 1.26
Preparation of [RuCl2(g6-mesitylene){(rac)-b}] ((rac)-3b)
1
and 1.20 (both d, 3 H each, 3JHH = 6.9, CHMe2). 13C{ H} NMR,
Following the same procedure (rac)-3b was prepared as a or-
CD2Cl2, d 151.8 (d, 2JPC = 12.6, C–O), 148.7 (d, 2JPC = 13.2, C–
O), 148.2 (d, 2JPC = 7.2, C–O), 132.6–115.5 (m, Caromatic), 110.6 (d,
6
ange solid, using 0.095 g (0.163 mmol) of [{RuCl(m-Cl)(h -
mesitylene)}2] and 0.148 g of ligand (rac)-b (0.362 mmol). Reaction
2
2JPC = 3.0, C cymene), 104.0 (d, JPC = 2.4, C cymene), 92.7 (d,
1
time: 4 h. Yield: 0.159 g (70%). 31P{ H} NMR, CDCl3, d 135.3
2JPC = 6.6, CH cymene), 91.6 (d, 2JPC = 9.0, CH cymene), 88.1 (d,
1
(s). H NMR, CDCl3, d 8.05–7.05 (m, 17 H, ArH), 4.94 (s, 3 H,
2
2JPC = 4.8, CH cymene), 87.0 (d, JPC = 4.2, CH cymene), 30.7
1
C6H3Me3), 2.17 (s, 9 H, C6H3Me3). 13C{ H} NMR, CD2Cl2, d
(s, CHMe2), 22.2 and 21.7 (both s, CHMe2), 18.4 (s, Me). Anal.
Calc. for C36H31Cl2O3PRu: C, 60.51; H, 4.37. Found: C, 60.70; H,
4.48%.
2
2
151.6 (d, JPC = 6.9, C–O), 149.3 (d, JPC = 8.0, C–O), 148.4 (d,
2JPC = 12.3, C–O), 132.7–120.3 (m, Caromatic), 108.4 (d, 2JPC = 3.2,
2
C mesitylene), 86.2 (d, JPC = 6.4, CH mesitylene), 18.6 (s, Me).
Anal. Calc. for C35H29Cl2O3PRu: C, 60.01; H, 4.17. Found: C,
60.23; H, 4.09%.
Preparation of [RuCl2(g6-p-cymene){(R)-b}] ((R)-2b)
Prepared through the same procedure using optically pure ligand
Preparation of [RuCl2(g6-mesitylene){(R)-b}] ((R)-3b)
(R)-b. Yield: 79%. aD = -65◦ (c = 0.215 in CH2Cl2, at 20 ◦C).
Prepared through the same procedure using optically pure ligand
Preparation of [RuCl2(g6-p-cymene){(rac)-c}] ((rac)-2c)
(R)-b. Yield: 74%. aD = -18◦ (c = 0.255 in CH2Cl2, at 20 ◦C).
Following the same procedure (rac)-2c was prepared as a orange
Preparation of [RuCl2(g6-mesitylene){(rac)-c}] ((rac)-3c)
6
solid, using 0.183 g (0.299 mmol) of [{RuCl(m-Cl)(h -p-cymene)}2]
and 0.266 g of ligand (rac)-c (0.664 mmol). Reaction time: 1 h.
Following the same procedure (rac)-3c was prepared as a or-
1
Yield: 0.258 g (61%). 31P{ H} NMR, CDCl3, d 147.8 (s). 1H NMR,
6
ange solid, using 0.179 g (0.306 mmol) of [{RuCl(m-Cl)(h -
CDCl3, d 8.08–7.31 (m, 12 H, ArH), 5.50 and 5.44 (both d, 1 H
mesitylene)}2] and 0.300 g of ligand (rac)-c (0.751 mmol). Reaction
each, 3JHH = 5.9, cymene), 5.32 and 4.69 (both d, 1 H each, 3JHH
=
1
time: 4 h. Yield: 0.297 g (70%). 31P{ H} NMR, CD2Cl2, d 139.9
1
5.6, cymene), 3.26 (broad s, 4 H, NCH2), 2.88 (m, 1 H, CHMe2),
(s). H NMR, CD2Cl2, d 8.04–7.17 (m, 12 H, ArH), 5.09 (s, 3
2.12 (s, 3 H, Me), 1.37–0.90 (m, 6 H, CH2), 1.20 (d, 3 H, 3JHH
=
H, C6H3Me3), 3.34–2.75 (broad s, 4 H, NCH2), 2.27 (s, 9 H,
3
1
6.8, CHMe), 1.11 (d, 3 H, JHH = 6.9, CHMe). 13C{ H} NMR,
1
C6H3Me3), 1.51–1.31 (m, 6 H, CH2). 13C{ H} NMR, CD2Cl2,
CDCl3, d 149.8 (d, 2JPC = 12.6, C–O), 148.5 (d, 2JPC = 6.0, C–O),
2
2
d 149.5 (d, JPC = 4.8, C–O), 149.4 (d, JPC = 12.0, C–O),
2
2
132.8–121.3 (m, Caromatic), 108.9 (d, JPC = 2.4, C cymene), 103.7
134.8–121.5 (m, Caromatic), 108.3 (s, C mesitylene), 85.0 (d, JPC
(d, 2JPC = 2.4, C cymene), 92.3 (d, 2JPC = 4.8, CH cymene), 90.6
2
3
= 5.6, CH mesitylene), 46.7 (d, JPC = NCH2), 26.4 (d, JPC
= 6.4, NCH2CH2), 24.6 (s, CH2), 18.6 (s, Me). Anal. Calc. for
C34H34Cl2NO2PRu: C, 59.05; H, 4.96; N, 2.03. Found: C, 59.25;
H, 4.08; N, 2.09%.
2
2
(d, JPC = 9.6, CH cymene), 89.1 (d, JPC = 5.4, CH cymene),
85.7 (d, 2JPC = 3.0, CH cymene), 44.7 (d, 2JPC = 2.4, NCH2), 30.5
(s, CHMe2), 26.4 (d, 3JPC = 5.4, NCH2CH2), 24.6 (d, 4JPC = 1.2,
CH2), 22.2 and 21.2 (both s, CHMe2), 18.3 (s, Me). Anal. Calc. for
C35H36Cl2NO2PRu: C, 59.58; H, 5.14; N, 1.99. Found: C, 59.43;
H, 5.25; N, 2.04%.
Preparation of [RuCl2(g6-mesitylene){(R)-c}] ((R)-3c)
Prepared through the same procedure using optically pure ligand
(R)-c. Yield: 67%. aD = -21◦ (c = 0.200 in CH2Cl2, at 20 ◦C). H,
4.40.
Preparation of [RuCl2(g6-p-cymene){(R)-c}] ((R)-2c)
Prepared through the same procedure using optically pure ligand
(R)-c. Yield: 62%. aD = -122◦ (c = 0.200 in CH2Cl2, at 20 ◦C).
General procedure for the catalytic kinetic resolution of allylic
alcohols
Preparation of [RuCl2(g6-mesitylene){(rac)-a}] ((rac)-3a)
Under and inert atmosphere, the allylic alcohol (4 mmol), the
catalyst precursor (1 mol%), potassium tert-butoxide (2 mol%),
and 20 mL of THF were introduced into a Schlenk tube fitted
with a condenser. Then, the mixture was heated at 45 ◦C. The
conversion and the enantiomeric excess of the remaining alcohol
were monitored by GC analyses of aliquots. In the case of 1-
phenyl-2-propen-1-ol, the absolute configuration of the major
enantiomer has been determined by comparison of GC analyses of
commercially available (R)-1-phenyl-2-propen-1-ol. For the other
Following the same procedure (rac)-3a was prepared as a or-
6
ange solid, using 0.257 g (0.440 mmol) of [{RuCl(m-Cl)(h -
mesitylene)}2] and 0.384 g of ligand (rac)-a (0.978 mmol). Reaction
1
time: 4 h. Yield: 0.572 g (95%). 31P{ H} NMR, CDCl3, d 177.8
1
(s). H NMR, CDCl3, d 8.08–6.91 (m, 17 H, ArH), 4.90 (s, 3
1
H, C6H3Me3), 2.11 (s, 9 H, C6H3Me3). 13C{ H} NMR, CD2Cl2, d
148.7 (d, 2JPC = 14.7, C–O), 148.2 (d, 2JPC = 6.7, C–O), 134.8–121.2
(m, Caromatic), 108.5 (d, 2JPC = 2.7, C mesitylene), 84.9 (d, 2JPC = 5.3,
7784 | Dalton Trans., 2010, 39, 7780–7785
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substrates, the assignment of absolute configuration is based on
the sign of optical rotation of the isolated alcohol.22,23
6 (a) V. Cadierno, P. Crochet, S. E. Garc´ıa-Garrido and J. Gimeno, Dalton
Trans., 2004, 3635; (b) P. Crochet, J. D´ıez, M. A. Ferna´ndez-Zu´mel and
J. Gimeno, Adv. Synth. Catal., 2006, 348, 93; (c) P. Crochet, M. A.
Ferna´ndez-Zu´mel, J. Gimeno and M. Scheele, Organometallics, 2006,
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25, 4846; (d) A. E. D´ıaz-Alvarez, P. Crochet, M. Zablocka, C. Duhayon,
Acknowledgements
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Ansell and M. Wills, Chem. Soc. Rev., 2002, 31, 259; (c) A. J. Minnaard,
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This work was supported by Spanish “Ministerio de Educacio´n y
Ciencia” (Projects CTQ2006-084885/BQU and CSD2007-00006
(Consolider Ingenio 2010 program)) and FICYT of Asturias
(Project IB08-036). M. A. F.-Z. and B. L.-B. thank the MEC
(FPU program) and the FICYT (PCTI-Severo Ochoa program),
respectively, for the award of a Ph.D grant and M. S. (from the
University of Hamburg, Germany) thanks the Erasmus Program.
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14 In all the cases, single crystals suitable for X-ray diffraction study were
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´
15 See for example: A. E. D´ıaz-Alvarez, P. Crochet, M. Zablocka, V.
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17 The quantity of base and the temperature chosen for these catalytic
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18 Slightly higher e.e. values, up to 25%, could be attained at higher
conversions.
19 With the exception of catalyst 3c, which presents a very low activity
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ˇ
22 J. Stambasky´, A. V. Malkov and P. Kocˇovsky, J. Org. Chem., 2008, 73,
=
C
5 Note that another kinetic resolution of allylic alcohol, based on C
9148.
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This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 7780–7785 | 7785
©