Neutral p-cymene ruthenium complexes with P-stereogenic monophosphines. New catalytic precursors in enantioselective transfer hydrogenation and cyclopropanation

Article abstract of DOI:10.1016/j.jorganchem.2011.09.015

A family of eight neutral, pseudotetrahedral piano-stool ruthenium complexes C, of the type [RuCl₂(p-cymene)(PArPhR)] (Ar = 1-naphthyl, 9-phenanthryl and 2-biphenylyl; R = Me, i-Pr, OMe, -CH₂SiMe ₃ and -CH₂SiPh₃) have been prepared and characterised, including the X-ray crystal structure for C6 (Ar = 2-biphenylyl; R = i-Pr). These complexes catalyse the asymmetric hydrogen transfer reaction of acetophenone in refluxing 2-propanol in the presence of potassium tert-butoxyde, reaching full conversions and up to 45% ee after 24 h towards the S enantiomer of 1-phenylethanol. Cationic complexes formed upon treatment of C with one equivalent of AgSbF₆ or (Et₃O)PF₆ are active in the cyclopropanation reaction of styrene and α-methylstyrene by ethyl diazoacetate. Low to moderate conversions (up to 58%), diastereoselectivities (up to 40% de), and moderate enantioselectivities (up to 69% ee) have been found. For both reactions, bulky complexes and C6 in particular lead to the best results.

Full text of DOI:10.1016/j.jorganchem.2011.09.015

Journal of Organometallic Chemistry 696 (2012) 4221e4228
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Journal of Organometallic Chemistry
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Neutral p-cymene ruthenium complexes with P-stereogenic monophosphines.
New catalytic precursors in enantioselective transfer hydrogenation and
cyclopropanation
,
a,
Arnald Grabulosa a, Alberto Mannu a, Antonio Mezzetti b , Guillermo Muller
**
*
a Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain
b Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093, Zürich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
A family of eight neutral, pseudotetrahedral piano-stool ruthenium complexes C, of the type [RuCl2(p-
cymene)(PArPhR)] (Ar ¼ 1-naphthyl, 9-phenanthryl and 2-biphenylyl; R ¼ Me, i-Pr, OMe, eCH2SiMe3
and eCH2SiPh3) have been prepared and characterised, including the X-ray crystal structure for C6
(Ar ¼ 2-biphenylyl; R ¼ i-Pr). These complexes catalyse the asymmetric hydrogen transfer reaction of
acetophenone in refluxing 2-propanol in the presence of potassium tert-butoxyde, reaching full
conversions and up to 45% ee after 24 h towards the S enantiomer of 1-phenylethanol. Cationic
complexes formed upon treatment of C with one equivalent of AgSbF6 or (Et3O)PF6 are active in the
Received 28 July 2011
Received in revised form
7 September 2011
Accepted 21 September 2011
Keywords:
Ruthenium
cyclopropanation reaction of styrene and
a-methylstyrene by ethyl diazoacetate. Low to moderate
P-stereogenic monophosphines
Arene complexes
Asymmetric catalysis
Transfer hydrogenation
Cyclopropanation
conversions (up to 58%), diastereoselectivities (up to 40% de), and moderate enantioselectivities (up to
69% ee) have been found. For both reactions, bulky complexes and C6 in particular lead to the best
results.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
alkylation [15] and less prone to secondary interactions such as
those found in supposedly monodentate phosphoramidites [16,17].
Ruthenium is nowadays one of the most intensively used metals
in homogeneous catalysis [1e4], due in part to cheaper price
compared to other noble metals such as rhodium and palladium
and to the wide span of reactions catalysed by Ru(II) complexes,
many of them in enantioselective fashion. The most important
example is arguably the reduction of ketones by Ru/BINAP and Ru/
BINAP/diamine systems, via hydrogenation or transfer hydrogena-
tion [5e7]. Another important transformation is the cyclo-
propanation reaction [8,9], catalysed by Ru(II) complexes mainly of
nitrogen ligands. A common feature of the ligands used in both
transformations is that they are either bi- or polydentate [10]. In
contrast, monodentate ligands [11e13] are still infrequent in ster-
eoselective ruthenium catalysis. In this work we explore the
potential of simple [RuCl2(p-cymene)(P*)] complexes in enantio-
selective hydrogen transfer and cyclopropanation, using a set of
monodentate P-stereogenic ligands, previously described to be
active in both Pd-catalysed hydrovinylation [14] and allylic
2. Synthesis
The required P-stereogenic ligands 1e8 (Scheme 1) were
prepared following the Jugé-Stephan method [18] as described
previously [14,15,19] and obtained as optically pure white solids or
colourless oils. Free phosphinites 3 and 5 were also obtained by
standard deboronation of the corresponding phosphiniteeboranes
[20] and their characterisation is given in the experimental part.
Following the usual method [21e23], neutral ruthenium p-
cymene complexes C1eC8 were easily prepared in moderate to
good yields by splitting the ruthenium p-cymene chloride dimer
[24], dissolved in dichloromethane, with two equivalents of the
monophosphorus ligand (Scheme 2).
The reactions were essentially complete after 1 h, as judged by
31P NMR spectroscopy. The isolated compounds C were red to
brown air-stable solids, soluble in dichloromethane but not in
hexane or pentane, whose full characterisation was in agreement
with the expected structures. 31P NMR spectra (see experimental
part and supplementary material) of complexes bearing phos-
phines presented singlets whose chemical shift was displaced
downfield compared to the free ligands. In contrast, the value of the
* Corresponding author. Tel.: þ34 934039140; fax: þ34 934907725.
** Corresponding author. Tel.: +41 44 632 61 21; fax: +41 44 632 13 10.
E-mail address: guillermo.muller@qi.ub.es (G. Muller).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.09.015

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A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
Scheme 1. P-stereogenic ligands.
chemical shift was almost unchanged in the case of complexes C3
and C5, bearing phosphinite ligands. 1H and 13C NMR spectra pre-
sented the anticipated features (see experimental part and
supplementary material). As expected due to the non-symmetric
environment produced by the stereogenic phosphorus, the p-
cymene aromatic ring presented four distinct aromatic proton
resonances in the 1H spectra and six distinct carbon resonances in
the 13C spectra for most of the complexes. Another feature is the
non-equivalence of the diastereotopic methyl groups of the iso-
propyl fragment in the p-cymene, both in 1H and 13C NMR spectra.
A single crystal X-ray structure determination was carried out
for complex C6. As expected, the complex has a distorted octahe-
dral structure with the typical piano-stool pseudotetrahedral
geometry around the Ru atom with the h6 coordination of the
phenyl ring of p-cymene. The unit cell contains two crystallo-
graphically distinct molecules of the complex (I and II), whose
ORTEP view is displayed in Fig. 1. In both structures the imaginary
line defined by the chloro ligands and the line passing through the
phosphine, has an average distance of 2.173 Å whereas for the
second the value increases to 2.227 Å. Two slightly different RueCl
distances are also observed. The distances are in general similar to
other related complexes [22,24e34] although the RueP distance is
longer for C6. The average value of the PeRueCl angles is 91.74ꢀ and
for the CleRueCl moiety the angle is 85.22ꢀ. The first value is larger
and the second smaller compared to other [Ru(p-cymene)(P)Cl2]
complexes (P ¼ phosphine) [24e34] and even compared to an
analogous complex with a bulky phosphoramidite [22]. This data
points out the rather bulky character of the phosphine ligand in C6.
3. Hydrogen transfer
There is some precedent [13,35,36] that neutral [RuCl2(h6
-
arene)P] (P ¼ monodentate phosphorus ligand) complexes are
active in hydrogen transfer from alcohols to ketones. To the best of
our knowledge, however, up to date only achiral phosphines have
been used. Therefore the optically pure complexes C presented here
could be interesting precatalysts in enantioselective hydrogen
transfer from 2-propanol to acetophenone, which is the model
substrate for this reaction (Scheme 3).
Hydrogen transfer reactions were performed in refluxing 2-
propanol (82 ꢀC), which was both the solvent and the hydrogen
donor in the presence of t-BuOK [37]. The catalyst/t-BuOK/aceto-
phenone ratio was 1/10/100. The solutions of the complexes were
activated (without addition of acetophenone) for 30 min at 82 ꢀC
before the addition of acetophenone. The plot of the conversion to
1-phenylethanol vs. time for several complexes C is given in Fig. 2
and the plot of the ee of 1-phenylethanol vs. time is given in
Fig. 3. Numerical data can be found in the supplementary material.
Fig. 2 shows that all complexes are active in reducing aceto-
phenone, reaching almost full conversion after 24 h. In spite of that,
important differences in activity are clearly observed. The activity
order is C6 [ C2 > C1 z C4 [ C3 z C5. Indeed, with C6 full
conversion is achieved after only 8 h. Surprisingly, Fig. 3 shows that
the enantioselectivity follows exactly the same order. Although the
ee value is higher and rather unreliable at low reaction times, it
stabilises to a slightly lower value. Only precursor C6 gives
substituted C carbons of the
h
6-coordinated phenyl ring are
approximately parallel, which is a common feature of this type of
complexes. The main difference between structures I and II is
simply that the h6-coordinated p-cymene ring is rotated by 180ꢀ.
For this reason, only some distances and angles of structure I will be
commented.
The structure confirms the expected absolute configuration of
the coordinated stereogenic phosphorus atom (R). The average of
the six RueCp-cymene distances is 2.209 Å. These distances can be
divided into two groups featuring relatively short and long bonds.
The first one, corresponding to the carbon atoms closer to the
a
moderate ee of around 45%, whereas C2 provides 1-
phenylethanol with just below 20% ee. In both cases the absolute
configuration of the product is S. The rest of the catalysts give very
poor enantioselectivities. The results described here suggest that
both activity and enantioselectivity are affected by the same factors
for the systems described.
Since the best results were obtained with precursor C6, a run at
lower temperature was performed with the aim of increasing the
Scheme 2. Synthesis of neutral Ru(p-cymene) complexes.

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
4223
Fig. 1. ORTEP view (thermal ellipsoids drawn at the 30% probability level) of molecules I (left) and II (right) of complex C6. Hydrogen atoms have been omitted for clarity. Distances
(Å) and angles (deg) for I: Ru(1)eCl(1), 2.4160(19); Ru(1)eCl(2), 2.4248(19); Ru(1)eP(1), 2.4336(19); P(1)eRu(1)eCl(1), 90.07(7); P(1)eRu(1)eCl(2), 93.41(7); Cl(1)eRu(1)eCl(2),
85.22(7). For II: Ru(2)eCl(4), 2.413(2); Ru(2)eCl(3), 2.4107(19); Ru(2)eP(2), 2.4180(19); P(2)eRu(2)eCl(4), 92.25(7); P(2)eRu(2)eCl(3), 91.84(7); Cl(4)eRu(2)eCl(3), 84.20(7).
enantioselectivity. After activation of the catalytic system at 82 ꢀC
for 1 h the temperature was lowered to 40 ꢀC and acetophenone
was added. Under these conditions, the reaction was much slower,
reaching only 44% conversion at 24 h and 56% at 48 h. The reaction
did not reach full conversion at this temperature, indicating that
the catalyst slowly deactivates over time [13]. The enantiose-
lectivity was only marginally better at low conversions: 55% ee at
13% conversion (6 h reaction time) and 44% ee at 24 h, a result
almost identical to the reaction performed at 82 ꢀC.
Given that compounds C are saturated 18-electron complexes,
a dissociative process has to take place in order to generate
ruthenium hydride species thought to be the active catalysts
[38e43]. In addition, the dependence of activity and enantiose-
lectivity on the phosphorus ligand points out that the active species
do not decoordinate the chiral ligand [42]. Considering these two
facts it is possible to conceive different activation mechanisms to
generate the catalytic species as depicted in Scheme 4.
acetophenone (Fig. 4) suggests the presence of a very well-defined
catalytic mechanism.
4. Cyclopropanation
Following previous studies with Ru/phosphoramidite ligands
[16,17,22] the performance of complexes C as precatalysts in
cyclopropanation of styrene and
a-methylstyrene by controlled
decomposition of ethyl diazoacetate was explored (Scheme 5).
Ethyl diazoacetate (EDA) slowly decomposes transferring a car-
bene unit to the chiral Ru complex, forming a metallic carbene [44],
which cyclopropanates the substrate. The formation of such
metallic carbenes from saturated 18-electron precursors C requires
the decoordination of one or more ligands. Although thermal
decoordination of the p-cymene unit has been suggested for similar
complexes [45], the most common method is the formation of
cationic unsaturated 16 electron species by abstracting one of the
chloride ligands [17,22]. Therefore, the conditions to generate
active species in the cyclopropanation of styrene were screened
with complex C6 and several halide abstractors (Table 1).
A reasonable route from the starting complexes C to the hydride
species comprises three steps: substitution of one of the chloride
ligands by the in situ generated isopropoxyde anion (I), b-hydride
elimination (II) and acetophenone coordination (III). Mechanisti-
cally, each of these steps must involve an unsaturated intermediate,
which can be generated either by direct chloride decoordinations
(path A) [35,40,41,43] or by hapticity reduction (from h6 to h4 or
Entries 1 and 2 show that neutral complexes C are almost cata-
lytically inactive, a fact that was expected since they are saturated
18 eꢁ compounds bearing no labile ligands. Upon activation by
halide scavenger salts with uncoordinating anions, catalytic activity
from h h
6 to 2) [43] of the p-cymene fragment as suggested for other
systems (path B) [13,38,39,43].
These activation mechanisms, although speculative, can explain
some of the experimental observations. Basic phosphines would
stabilise the cationic unsaturated complexes better, whereas bulky
ligands would favour the decoordination of the first and second
chloride anions and the change of the hapticity of the p-cymene
fragment. That would explain why catalysts C2 and C6, both bearing
a phosphine with the basic and relatively bulky isopropyl group,
give the more active catalysts whereas C3 and C5, with less basic
and not so bulky phosphinite ligands provide more sluggish
catalysts.
Regardless of the mechanism, the almost perfect linearity of
the plots of the reduction process at moderate conversions of
Fig. 2. Conversion of acetophenone vs. time in hydrogen transfer. Complex
C
(6 ꢂ 10ꢁ3 mmol) was dissolved in 3 ml of a 0.02 M solution of potassium tert-butoxyde
in 2-propanol. After stirring for 30 min at 82 ꢀC a solution of acetophenone (0.06 M,
10 ml) in 2-propanol was added.
Scheme 3. Catalytic hydrogen transfer.

4224
A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
Fig. 4. Conversion of species vs. time in hydrogen transfer of acetophenone in the
presence of complex C1. The crosses and the triangles represent each of the enantio-
mers of 1-phenylethanol.
Fig. 3. Enantiomeric excess of 1-phenylethanol vs. time in hydrogen transfer of
acetophenone.
enantioselectivity is observed at 20 h (entry 9 vs. entry 10). This fact,
observed previously in other systems [22], can be due to unselective
catalysis by achiral Ru species originated by degradation of the
catalyst. Most of the catalysts give better enantioselectivity results
for the cis diastereomers, but this is not general (entries 1, 2 and 9). A
remarkable feature is that complexes bearing phosphines with the
2-biphenylyl group (entries 9e14) favour the (R,R) enantiomer of
the trans diastereomers but the contrary happens for the other
catalysts. A surprising fact is the very low enantioselectivity of
complex C7 (entries 11 and 12), bearing a phosphine with the 2-
biphenylyl group compared to C6 and C8 (entries 8, 9, 13 and 14).
was observed, following the order (Et3O)PF6 > AgSF6 > TlPF6. As
(Et3O)PF6 (Meerwein’s salt) provides both the higher activity and
enantioselectivity, it was selected as a reagent of choice to activate
the precursors. Under the same conditions, the other complexes C
were tested in the cyclopropanation of styrene and a-methylstyr-
ene. The results obtained for these two substrates are listed in
Table 2 and Table 3 respectively.
In general, conversions and yields remain low for styrene,
reaching the maximum value of 29% in entry 14 at 20 h. The
comparison between the values at 3 and 20 h indicates that the
catalysts decompose over the time to inactive species. Entries 1e10
show that the diastereoselectivity is approximately 2:3 in favour of
the trans diastereomers regardless of the catalyst and on the time.
For the bulky silylated phosphines of complexes C7 and C8 (entries
11e14) the cis:trans ratio increases slightly to approximately 1:2.
Enantioselectivity ranges from low to moderate. The best results are
obtained with complexes C2 and C6 bearing phosphines with an
isopropyl group (entries 3, 4, 9 and 10) and with C8, containing
a very bulky silylated phosphine (entries 13 and 14). The best result
is obtained with complex C6 at 3 h, although a severe decrease in
It is known that a-methylstyrene often gives better results in
cyclopropanation compared to unsubstituted styrene due to the
more electron rich nature of the former [17]. The data from the table
confirm this expectation. Conversions and yields are higher, reaching
or surpassing the 50% mark (entries 2, 4, 6, 8 and 10). The different
steric requirements of a-methylstyrenecauses that in this case the cis
diastereomers of the cyclopropanated products are favoured. Like for
styrene, though, the diastereoselectivity is only modest, reaching
a 7:3 ratio for catalyst C6 (entry 5). The enantioselectivity also
Scheme 4. Generation of RueH catalysts from precursors C.

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
4225
improves compared to styrene, reaching a value close to 70% at low
conversion for C6 (entry 5). The more enantioselective catalysts, in
parallel to styrene cyclopropanation, are C6 and C8, bearing 2-
biphenylyl groups (entries 5, 6, 9 and 10). In contrast, C2 (entries 3
and 4) is very unselective. Like in the case of styrene, a degradation of
stereoselectivity as the reaction progresses is observed.
Scheme 5. Catalytic cyclopropanation.
Table 1
Catalytic cyclopropanation of styrene by ethyl diazoacetate in the presence of C6 and several halide abstractors.
Entry
Abstractor
Time h
Conversiona%
Yielda%
cis:transa
e.e. (%)a
cis
trans
1b
2b
3
4
5
6
7
8
e
3
20
3
20
3
20
3
20
1
2
7
21
5
19
12
26
0.6
0.7
6.0
18.3
3.0
9.7
37:63
43:57
40:60
38:62
38:62
32:68
46:54
42:48
e
e
e
e
e
AgSbF6
AgSbF6
TlPF6
TlPF6
(Et3O)PF6
(Et3O)PF6
27.8 (1S,2R)
8.8 (1S,2R)
e
21.8 (1R,2R)
5.5 (1R,2R)
e
z0
57.8 (1S,2R)
37.0 (1S,2R)
z0
58.9 (1R,2R)
31.2 (1R,2R)
10.6
21.7
Catalyst preparation: complex C6 (24 mmol) and the halide abstractor (24e26 mmol) were dissolved in 1 ml of CH2Cl2 and stirred at room temperature for 14 h and filtered.
Catalytic runs: the internal standard and styrene (0.48 mmol) were added to the flask containing the catalyst solution. Ethyl diazoacetate (0.48 mmol), dissolved in 1 ml of
CH2Cl2, was added over a period of 6 h by an automatic syringe pump. The results are the average of at least two runs.
a
Results from GC analysis.
The precatalyst was C1.
b
Table 2
Catalytic cyclopropanation of styrene.
Entry
Precursor
Time h
Conversiona
%
Yielda
%
cis:transa
e.e. (%)a
cis
trans
1
2
3
4
5
6
7
8
C1
C1
C2
C2
C3
C3
C4
C4
C6
C6
C7
C7
C8
C8
3
20
3
20
3
20
3
20
3
20
3
20
3
11
23
16
32
20
38
8
18
12
26
9
7.4
15.1
11.7
26.1
5.8
19.5
5.4
12.6
10.6
21.7
7.4
43:57
43:57
43:57
41:59
46:54
44:56
43:57
43:57
42:58
42:58
35:65
35:65
35:65
33:67
4.6 (1S,2R)
6.5 (1S,2R)
38.4 (1S,2R)
22.2 (1S,2R)
9.7 (1S,2R)
10.8 (1S,2R)
7.4 (1S,2R)
8.3 (1S,2R)
57.8 (1S,2R)
37.0 (1S,2R)
8.2 (1S,2R)
3.8 (1S,2R)
24.4 (1S,2R)
25.4 (1S,2R)
12.4 (1S,2S)
11.1 (1S,2S)
22.6 (1S,2S)
22.0 (1S,2S)
2.9 (1S,2S)
5.4 (1S,2S)
7.2 (1S,2S)
6.9 (1S,2S)
58.9 (1R,2R)
31.2 (1R,2R)
5.7 (1R,2R)
z0
9
10
11
12
13
14
23
9
29
21.0
8.6
29.0
8.6 (1R,2R)
8.5 (1R,2R)
20
Catalyst preparation: complex C (24
m
mol) and Et3OPF6 (26 mmol) were dissolved in 1 ml of CH2Cl2 and stirred at room temperature for 14 h and filtered. Typical catalytic run:
The internal standard (n-decane) and styrene (0.48 mmol) were added to the flask containing the catalyst solution. Ethyl diazoacetate (0.48 mmol), dissolved in 1 ml of CH2Cl2,
was added over a period of 6 h by an automatic syringe pump. The results are the average of at least two runs.
a
Results from GC analysis.
Table 3
Catalytic cyclopropanation of
a
-methylstyrene.
Time h
Entry
Precursor
Conversiona
%
Yielda
%
cis:transa
e.e. (%)a
cis
trans
1
2
3
4
5
6
7
8
9
10
C1
C1
C2
C2
C6
C6
C7
C7
C8
C8
3
20
3
20
3
20
3
20
3
18
52
25
56
33
58
19
50
14
41
15.2
49.3
24.6
55.7
33.0
58.0
18.0
46.6
14.0
41.0
69:31
67:33
64:36
62:38
71:29
68:32
63:37
59:41
69:31
62:38
3.7 (cis-I)
3.4 (cis-I)
10.4 (trans-I)
10.2 (trans-I)
14.8 (trans-I)
20.8 (trans-I)
68.6 (trans-II)
52.9 (trans-II)
23.1 (trans-II)
11.7 (trans-II)
60.9 (trans-II)
28.0 (trans-II)
13.7 (cis-II)
21.1 (cis-II)
66.5 (cis-I)
58.7 (cis-I)
37.5 (cis-I)
24.8 (cis-I)
60.8 (cis-I)
40.7 (cis-I)
20
Catalyst preparation: complex C (24
mmol) and Et3OPF6 (26 mmol) were dissolved in 1 ml of CH2Cl2 and stirred at room temperature for 14 h and filtered. Typical catalytic run:
The internal standard (n-dodecane) and a-methylstyrene (0.48 mmol) were added to the flask containing the catalyst solution. Ethyl diazoacetate (0.48 mmol), dissolved in
1 ml of CH2Cl2, was added over a period of 6 h by an automatic syringe pump. The results are the average of at least two runs.
a
Results from GC analysis, I and II simply refer to the order of elution of each enantiomer in the chromatographic analysis.

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A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
5. Conclusions
residue was purified by column chromatography (alumina, toluene)
to yield the title product as colourless oil. Yield: 0.60 g (90%).
1H NMR (300.1 MHz, CDCl3),
(ppm): 3.78 (d, 3H, J ¼ 14.1 Hz),
Ruthenium complexes with monodentate phosphorus ligands
are competent systems for hydrogen transfer and cyclo-
propanation. Good activities, leading to full conversions, are ob-
tained in hydrogen transfer of acetophenone whereas the
enantioselectivity is moderate at best. The active catalyst seems
a well-defined single species whose discrimination ability does not
appear to change with the temperature. In cyclopropanation, the
complexes show low activity and low to moderate stereoselectivity.
It seems that for both reactions the phosphines must have
a relatively bulky alkyl group since those with methyl or methoxy
give very low enantioselectivities. For the systems examined the
best catalysts, both in activity and stereoselectivity, contain the 2-
biphenylyl group in the phosphine [46], in parallel to previous
results in Pd-catalysed hydrovinylation [14] and allylic alkylation
[15]. The optical induction, although far from satisfactory with the
phosphines used, stems only from a single stereogenic phosphorus
atom of a simple Horner phosphine [47]. These results show that it
is possible to generate interesting new catalytic systems with
a ratio Ru/P-stereogenic phosphine ¼ 1/1. Therefore it seems
plausible to obtain good results with other bulky phosphines
bearing P-stereogenic atoms, a chiral motif hardly ever used in
ruthenium-catalysed reactions [47e51].
d
7.35e8.32 (m, 12H, Ar). 13C{1H} NMR (62.9 MHz, CDCl3),
d(ppm):
57.3 (d, CH3, JCP ¼ 20.7 Hz), 125.1e141.0 (m, C, CH, Ar). 31P{1H} NMR
(101.1 MHz, CDCl3),
d(ppm): þ113.4.
6.2. (R)-methoxy(9-phenanthryl)phenylphosphine, 5
The same procedure used to prepare 3 was followed. Starting
from (R)-methoxy(9-phenanthryl)phenylphosphine-borane [20]
(0.66 g, 2.0 mmol), the title product was obtained as a colourless
oil. Yield: 0.23 g (37%).
1H NMR (250.1 MHz),
d
(ppm): 3.79 (d, 3H, J ¼ 14.2 Hz),
7.29e8.69 (m, 14H, Ar). 13C{1H} NMR (100.0 MHz),
d(ppm): 57.6 (d,
CH3, JCP ¼ 21.4 Hz), 122.8e140.7 (m, C, CH, Ar). 31P{1H} NMR
(101.1 MHz),
d(ppm): þ114.4.
6.3. Dichloro(
h
6-p-cymene)[(R)-methyl(1-naphthyl)
phenylphosphine]ruthenium(II), C1
Ruthenium p-cymene dimer (0.490 g, 0.8 mmol) and phosphine
1 (0.400 g, 1.6 mmol) were dissolved in 10 ml of dichloromethane
and left stirring for 1 h. The solvent was removed and the brownish
found was suspended in diethyl ether. The solid was filtrated and
washed with diethyl ether and pentane. Yield: 0.490 g (60%).
6. Experimental section
IR
(CeH), 2940
1435, 1387, 1280, 893, 804, 799, 780, 750, 689, 453. 1H NMR
(250.1 MHz),
n
(cmꢁ1): 3061
(CeH), 2924
n
(CeH), 3044
n
(CeH), 2964
n(CeH), 2952
All compounds were prepared under a purified nitrogen or
argon atmosphere using standard Schlenk and vacuum-line tech-
niques. The solvents were purified by standard procedures and
distilled under nitrogen. 1H, 13C, and 31P NMR spectra were recor-
ded using the following spectrometers: Varian XL-500, Mer-
400 MHz, Varian Inova 300 and Bruker DRX-250, using CDCl3 as
a solvent. Chemical shifts were reported downfield from standards.
IR spectra were recorded using Nicolet Impact 400 and Avatar 330
spectrometers. FAB mass chromatograms were obtained on
a Fisons V6-Quattro instrument.
n
n
n
(CeH), 2871
n(CeH), 1503, 1489, 1470,
d(ppm): 0.71 (d, 3H, J ¼ 6.9 Hz), 0.89 (d, 3H, J ¼ 7.0 Hz),
1.91 (s, 3H), 2.12 (d, 3H, J ¼ 10.7 Hz), 2.52e2.61 (m,1H), 4.97e5.05 (m,
2H), 5.18 (d,1H, J ¼ 6.3 Hz), 5.36 (d,1H, J ¼ 6.2 Hz), 7.29e8.21 (m,12H,
Ar). 13C{1H} NMR (50.0 MHz),
d
(ppm): 14.8 (d, CH3, JCP ¼ 35.5 Hz),
17.6 (s, CH3), 20.4 (s, CH3), 22.4 (s, CH3), 30.0 (s, CH), 82.8 (d, CH,
JCP ¼ 4.6 Hz), 87.7 (d, CH, JCP ¼ 2.7 Hz), 88.6 (d, CH, JCP ¼ 7.3 Hz), 91.8
(d, CH, JCP ¼ 5.9 Hz), 95.0 (s, C) 107.5 (s, C),124.6e135.4 (m, C, CH, Ar).
31P{1H} NMR (101.1 MHz),
d(ppm): þ14.5. EA: Calcd. for
Achiral GC analyses for cyclopropanation of styrene and
a
-
C27H29Cl2PRu: C 58.28%, H 5.25%. Found: C 58.15%, H 5.69%.
methylstyrene were performed with an instrument equipped with
an Optima column, 25 m long with He as a carrier gas (100 kPa).
Conditions: 50 ꢀC isotherm for 5 min, then to 200 ꢀC at 5 ꢀC/min.
Data for styrene cyclopropanation: tR (min) styrene, 8.5; n-decane
(internal standard), 12.8; ethyl-cis-2-phenylcyclopropane carbox-
ylate, 26.5; ethyl-trans-2-phenylcyclopropane carboxylate, 27.9.
MS(MALDI) m/e: 485, [MeCleHCl]þ
6.4. Dichloro(h
6-p-cymene)[(R)-(isopropyl)(1-naphthyl)
phenylphosphine] ruthenium(II), C2
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.300 g, 0.49 mmol) and
phosphine 2 (0.289 g, 1.04 mmol), the title product was obtained as
a brown solid. Yield: 0.236 g (41%).
Data for
a-methylstyrene cyclopropanation: tR (min) a-methyl-
styrene, 12.0; n-dodecane (internal standard), 19.6; ethyl-cis-2-
methyl-phenylcyclopropane-1-carboxylate, 26.3; ethyl-trans-2-
methyl-phenylcyclopropane-1-1-carboxylate, 27.6. Chiral GC anal-
yses were carried out in a Supelco Beta Dex 120 column with He as
a carrier gas (1.4 mL/min). Conditions: 120 ꢀC isotherm. Data for
styrene cyclopropanation: tR (min), cis-(1R, 2S), 52.8; cis-(1S,2R),
IR
(CeH), 1507, 1469, 1435, 1387, 1094, 809, 780, 702, 513, 479. 1H
NMR (300.1 MHz), (ppm): 1.03e1.10 (m, 12H), 1.69 (s, 3H),
n
(cmꢁ1): 3047
n(CeH), 2962 n(CeH), 2927 n(CeH), 2870
n
d
2.55e2.64 (m, 1H), 3.65 (s, 1H), 4.74 (d, 2H, J ¼ 5.7 Hz), 4.92 (s, 1H),
55.5; trans-(1R,2R), 62.7; trans-(1S,2S), 64.6. Data for
a-methyl-
5.10 (s, 1H), 7.42e8.50 (m, 12H, Ar). 31P{1H} NMR (121.5 MHz),
styrene cyclopropanation: tR (min), cis-isomers, 39.3 and 41.3;
trans-isomers, 49.7 and 50.9.
d
(ppm): þ30.3. EA: Calcd. for C29H33Cl2PRu: C 59.59%, H 5.69%.
Found: C 59.78%, H 5.34%.
GC analyses of transfer hydrogenation of acetophenone were
performed with an instrument equipped with a chiral FS cyclodex
6.5. Dichloro(h
6-p-cymene)[(S)-methoxy(1-naphthyl)
b
column, 30 m long with He as a carrier gas (100 kPa). Conditions:
phenylphosphine]ruthenium(II), C3
120 ꢀC isotherm. Data: tR (min), acetophenone, 7.0; 1-
phenylethanol, 11.1 (R) and 11.8 (S).
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.345 g, 0.56 mmol) and
phosphinite 3 (0.332 g, 1.24 mmol), the title product was obtained
as a light red solid. Yield: 0.597 g (92%).
6.1. (R)-methoxy(1-naphthyl)phenylphosphine, 3
(R)-methoxy(1-napthyl)phenylphosphine-borane [20] (0.70 g,
2.5 mmol) was dissolved in morpholine (30 ml) and stirred for 14 h
at room temperature. After concentration to dryness, the gummy
IR
(CeH), 2871
776, 743, 695, 538, 509, 481. 1H NMR (300.1 MHz),
n
(cmꢁ1): 3056
n
(CeH), 3045
(CeH), 1507, 1470, 1437, 1387, 1098, 1030, 821, 807,
(ppm): 1.03 (d,
n(CeH), 2960 n(CeH), 2938
n
n
d

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
4227
3H, J ¼ 6.6 Hz), 1.12 (d, 3H, J ¼ 6.6 Hz), 1.75 (s, 3H), 2.73 (m, 1H), 3.56
(d, 3H, J ¼ 11.4 Hz), 4.43 (s, 1H), 5.19 (s, 2H), 5.31 (s, 1H), 7.29e8.32
CH3, JCP ¼ 6.9 Hz), 22.1 (s, CH3), 22.6 (s, CH3), 25.4 (d, CH,
JCP ¼ 22.1 Hz), 29.8 (s, CH), 84.9 (d, CH, JCP ¼ 3.8 Hz), 88.6 (d, CH,
JCP ¼ 5.3 Hz), 89.8 (d, CH, JCP ¼ 5.4 Hz), 89.9 (d, CH, JCP ¼ 3.8 Hz), 97.5
(s, C), 106.9 (s, C), 126.3e146.1 (m, C, CH, Ar). 31P{1H} NMR
(m, 12H, Ar). 3C1H} NMR (62.9 MHz),
d(ppm): 17.6 (s, CH3), 20.9 (s,
CH3), 22.4 (s, CH3), 29.9 (s, CH), 55.9 (d, CH3, JCP ¼ 7.5 Hz), 85.4 (d,
CH, JCP ¼ 4.9 Hz), 90.4 (d, CH, JCP ¼ 3.1 Hz), 90.9 (d, CH, JCP ¼ 6.8 Hz),
92.6 (d, CH, JCP ¼ 6.7 Hz), 97.5 (s, C), 108.9 (s, C), 124.2e133.9 (m, C,
(101.1 MHz),
d(ppm): þ29.2. EA: Calcd. for C31H35Cl2PRu: C 60.98%,
H 5.78%. Found: C 60.46%, H 6.44%. MS(MALDI) m/e: 303, [MeRu(p-
cymene)CleHCl]þ; 339, [MeRu(p-cymene)Cl]þ; 441, [Me(p-cym-
ene)Cl]þ; 575, [MeCl]þ; 580, [MeCleHCl]þ.
CH, Ar). 31P{1H} NMR (121.5 MHz),
C27H30Cl2OPRu: C 56.55%, H 5.27%. Found: C 56.01%, H 5.52%.
d
(ppm): þ116.6. EA: Calcd. for
6.6. Dichloro(
phenylphosphine]ruthenium(II), C4
h
6-p-cymene)[(R)-methyl(9-phenanthryl)
6.9. Dichloro(h
6-p-cymene)[(R)-(2-biphenylyl)(2,2-dimethyl-2-
silapropyl)phenylphosphine] ruthenium(II), C7
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.172 g, 0.281 mmol) and
phosphine 4 (0.186 g, 0.619 mmol), the title product was obtained
as a red solid. Yield: 0.279 g (87%).
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.061 g, 0.099 mmol) and
phosphine 7 (0.069 g, 0.198 mmol), the title product was obtained
as a deep red solid. Yield: 0.060 g (47%).
IR
(CeH), 2839
431. 1H NMR (300.1 MHz),
n
(cmꢁ1): 3053
n
(CeH), 2960
n(CeH), 2938 n(CeH), 2868
n
n
(CeH), 1435, 1096, 1029, 752, 725, 694, 564, 489,
IR
(CeH), 2885
706, 695, 510. 1H NMR (250.1 MHz),
n
(cmꢁ1): 3054
(CeH), 2872
n
(CeH), 2962
n(CeH), 2925 n(CeH), 2896
d
(ppm): 0.89 (d, 3H, J ¼ 6.9 Hz), 0.94 (d,
n
n
n
(CeH), 1434, 1120, 850, 842, 783, 757,
3H, J ¼ 6.9 Hz), 1.92 (s, 3H), 2.25 (d, 3H, J ¼ 10.5 Hz), 2.61e2.66 (m,
1H), 4.95 (d, 1H, J ¼ 5.4 Hz), 5.12e5.18 (m, 2H), 5.33 (d, 1H,
J ¼ 6.0 Hz), 7.17e8.81 (m, 14H, Ar). 13C{1H} NMR (62.9 MHz),
d
(ppm): ꢁ0.18 (s, 9H), 0.65 (d,
3H, J ¼ 6.8 Hz), 1.06 (d, 3H, J ¼ 6.8 Hz), 2.03 (s, 3H), 2.48e2.59 (m,
1H), 4.60 (d, 1H, J ¼ 5.5 Hz), 5.32e5.37 (m, 3H), 6.89e8.71 (m, 14H,
d
(ppm): 15.8 (d, CH3, JCP ¼ 13.3 Hz), 17.7 (s, CH3), 20.9 (s, CH3), 22.4
Ar). 13C{1H} NMR (62.9 MHz),
d(ppm): 1.7 (d, CH3, JCP ¼ 2.5 Hz), 12.1
(s, CH3), 30.1 (s, CH), 83.5 (d, CH, JCP ¼ 4.9 Hz), 88.2 (d, CH,
JCP ¼ 6.4 Hz), 88.4 (d, CH, JCP ¼ 3.4 Hz), 91.3 (d, CH, JCP ¼ 5.5 Hz), 95.3
(s, C), 107.9 (s, C), 122.7e136.0 (m, C, CH, Ar). 31P{1H} NMR
(d, CH2, JCP ¼ 18.4 Hz), 17.2 (s, CH3), 20.0 (s, CH3), 22.9 (s, CH3), 29.7
(s, CH), 85.4 (d, CH, JCP ¼ 4.2 Hz), 86.8 (d, CH, JCP ¼ 3.4 Hz), 87.2 (d,
CH, JCP ¼ 7.5 Hz), 93.4 (d, CH, JCP ¼ 6.0 Hz), 101.3 (s, C), 107.7 (s, C),
126.3e146.1 (m, C, CH, Ar). 31P{1H} NMR (101.1 MHz),
(121.5 MHz),
H 5.15%. Found: C 61.76%, H 5.79%.
d
(ppm): þ16.5. EA: Calcd. for C31H31Cl2PRu: C 61.39%,
d
(ppm): þ24.2. EA: Calcd. for C32H39Cl2PRuSi: C 58.70%, H 6.00%.
Found: C 58.35%, H 6.32%. MS(MALDI) m/e: 347 (24) [MeRu(p-
cymene)Cl2]þ, 577 (14) [MePh]þ.
6.7. Dichloro(h
6-p-cymene)[(S)-methoxy(9-phenanthryl)
phenylphosphine] ruthenium(II), C5
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.203 g, 0.330 mmol) and
phosphinite 5 (0.231 g, 0.720 mmol), the title product was obtained
as a deep red solid. Yield: 0.149 g (36%).
6.10. Dichloro(h
6-p-cymene)[(R)-(2-biphenylyl)(2,2,2-triphenyl-2-
silaethyl)phenylphosphine] ruthenium(II), C8
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.085 g, 0.139 mmol) and
phosphine 8 (0.164 g, 0.307 mmol), the title product was obtained
as a red solid. Yield: 0.169 g (66%).
IR
(CeH), 1436, 893, 751, 726, 696, 691, 461, 432. 1H NMR
(400.1 MHz),
n
(cmꢁ1): 3056
n(CeH), 2961 n(CeH), 2923 n(CeH), 2869
n
d
(ppm): 1.03 (d, 3H, J ¼ 6.8 Hz), 1.14 (d, 3H, J ¼ 6.4 Hz),
1.74 (s, 3H), 2.75e2.82 (m, 1H), 3.59 (d, 3H, J ¼ 11.6 Hz), 4.45 (s, 1H),
5.17 (d,1H, J ¼ 6.0 Hz), 5.23 (d,1H, J ¼ 5.2 Hz), 5.34 (d,1H, J ¼ 6.4 Hz),
IR
(CeH), 1466, 1427, 1107, 799, 755, 741, 717, 699, 667, 518, 499, 488.
1H NMR (250.1 MHz),
(ppm): 0.95 (d, 3H, J ¼ 6.5 Hz), 1.02 (d, 3H,
J ¼ 6.5 Hz), 1.88 (s, 3H), 2.51e2.63 (m, 1H), 5.19 (s, 1H), 5.31 (s, 3H),
6.75e8.24 (m, 29H, Ar). 13C{1H} NMR (62.9 MHz),
(ppm): 12.2 (d,
n
(cmꢁ1): 3047
n(CeH), 2959 n(CeH), 2924 n(CeH), 2869
n
7.26e8.76 (m, 14H, Ar). 13C{1H} NMR (100.0 MHz),
d(ppm): 17.9 (s,
d
CH3), 21.0 (s, CH3), 22.7 (s, CH3), 30.1 (s, CH), 56.3 (d, CH3,
JCP ¼ 7.7 Hz), 85.4 (s, CH), 90.7 (s, CH), 91.5 (s, C), 93.2 (s, CH), 97.5 (s,
CH), 109.0 (s, C), 122.9e134.2 (m, C, CH, Ar). 31P{1H} NMR
d
CH2, JCP ¼ 24.0 Hz), 17.2 (s, CH3), 21.5 (s, CH3), 22.0 (s, CH3), 29.9 (s,
CH), 85.5 (d, CH, JCP ¼ 6.7 Hz), 85.9 (d, CH, JCP ¼ 4.8 Hz), 89.1 (d, CH,
JCP ¼ 5.0 Hz), 90.1 (d, CH, JCP ¼ 4.2 Hz), 94.5 (s, C), 107.5 (s, C),
(121.5 MHz),
d
(ppm): þ114.9. EA: Calcd. for C31H31Cl2OPRu: C
59.81%, H 5.02%. Found: C 59.58%, H 5.23%. MS(MALDI) m/e: 443,
[Mephenanthryle2H]þ; 551, [MeCleHCl]þ; 579, [MeiPr]þ
126.6e148.0 (m, C, CH, Ar). 31P{1H} NMR(101.1 MHz),
d
(ppm): þ27.4.
EA: Calcd. for C47H45Cl2PRuSi: C 67.13%, H 5.39%. Found: C 69.46%, H
5.80%. MS(MALDI) m/e: 533 (58) [MeRu(p-cymene)CleHCl]þ, 569
(90) [MeCH2SiPh3]þ, 843 (8) [Mþ2H]þ.
6.8. Dichloro(h
6-p-cymene)[(R)-(2-biphenylyl)(isopropyl)phenyl
phosphine]ruthenium(II), C6
The same procedure used in the preparation of C1 was
employed. From the Ru p-cymene dimer (0.171 g, 0.279 mmol) and
phosphine 6 (0.170 g, 0.558 mmol), the title product was obtained
as a brown solid. Yield: 0.227 g (63%). Single crystals, suitable for X-
ray crystallography were obtained by slow diffusion of hexane into
a solution of the complex in dichloromethane, at 4 ꢀC.
6.11. General procedure for the enantioselective transfer
hydrogenation
A
typical transfer hydrogenation run was performed as
follows. Under a nitrogen atmosphere in a schlenk flask, the
ruthenium precursor C (6 ꢂ 10ꢁ3 mmol) was dissolved in 3 ml of
a 0.02 M solution of potassium tert-butoxyde in 2-propanol and
left stirring for 30 min. A solution (0.06 M, 10 ml) of acetophe-
none in 2-propanol was added rapidly by syringe, to give
a 0.046 M solution of acetophenone in 2-propanol. The flask was
heated to the desired temperature. The reaction was monitored
by GC analysis.
IR
(CeH), 1467, 1458, 1444, 1435, 1088, 761, 755, 703, 668, 524, 465.
1H NMR (400.1 MHz),
(ppm): 0.66e0.70 (m, 6H), 1.11 (d, 3H,
n
(cmꢁ1): 3048
n(CeH), 2962 n(CeH), 2925 n(CeH), 2868
n
d
J ¼ 7.2 Hz), 1.19 (d, 3H, J ¼ 7.2 Hz), 2.02 (s, 3H), 2.50e2.60 (m, 1H),
2.85e2.93 (m, 1H), 4.74 (d, 1H, J ¼ 6.0 Hz), 5.13 (d, 1H, J ¼ 6.0 Hz),
5.43e5.47 (m, 2H), 7.11e7.92 (m, 14H, Ar). 13C{1H} NMR
(100.0 MHz),
d(ppm): 18.1 (s, CH3),19.2 (d, CH3, JCP ¼ 2.3 Hz), 20.0 (s,

4228
A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2012) 4221e4228
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a nitrogen-filled glovebox the ruthenium precursor C (0.024 mmol)
and the chloride abstractor were dissolved in 1 ml of dichloro-
methane and stirred for 14 h protected from light. The solution was
filtered through an HPLC filter and transferred to an schlenk flask,
which was closed and taken out of the glovebox. To this flask, the
olefin (0.48 mmol) and the internal standard (n-decane for styrene
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