Ruthenium complexes containing chiral N-donor ligands as catalysts in acetophenone hydrogen transfer - New amino effect on enantioselectivity

Article abstract of DOI:10.1002/ejic.200500515

New p-cymene ruthenium species containing chiral amino alcohols (1-3), primary (4-7) and secondary (8, 9) amino-oxazolines, were tested as catalysts in the hydrogen transfer of acetophenone, using 2-propanol as the hydrogen source. A remarkable effect on the enantioselectivity, but also on the activity, was observed depending on the amino-type oxazoline, Ru/8 and Ru/9 being low active and nonselective catalytic systems, in contrast to their primary counterpart Ru/5. Complexes containing amino-oxazolines (10-12) were prepared and fully characterized, both in solution and in solid state. The X-ray structure was determined for (S_Ru,R_C)-10. The diastereomeric ratios observed for complexes 10 and 11 were determined by ¹H NMR and confirmed by means of structural modeling (semi-empirical PM3(tm) level). DFT theoretical calculations for the transition states involved in the hydrogen transfer process proved the important differences in their relative populations, which could justify the enantioselectivity divergences observed between primary and secondary amino-oxazoline ruthenium systems. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500515

FULL PAPER
Ruthenium Complexes Containing Chiral N-Donor Ligands as Catalysts in
Acetophenone Hydrogen Transfer – New Amino Effect on Enantioselectivity
Montserrat Gómez,*[a] Susanna Jansat,[a] Guillermo Muller,[a] Gabriel Aullón,[a] and
Miguel Angel Maestro[b]
Keywords: Ruthenium / Chiral N-donors / Asymmetric catalysis / NMR spectroscopy / Density functional calculations
New p-cymene ruthenium species containing chiral amino
alcohols (1–3), primary (4–7) and secondary (8, 9) amino-
oxazolines, were tested as catalysts in the hydrogen transfer
of acetophenone, using 2-propanol as the hydrogen source.
A remarkable effect on the enantioselectivity, but also on the
activity, was observed depending on the amino-type oxazol-
The diastereomeric ratios observed for complexes 10 and 11
were determined by 1H NMR and confirmed by means of
structural modeling (semi-empirical PM3(tm) level). DFT
theoretical calculations for the transition states involved in
the hydrogen transfer process proved the important differ-
ences in their relative populations, which could justify the
ine, Ru/8 and Ru/9 being low active and nonselective cata- enantioselectivity divergences observed between primary
lytic systems, in contrast to their primary counterpart Ru/5.
Complexes containing amino-oxazolines (10–12) were pre-
pared and fully characterized, both in solution and in solid
state. The X-ray structure was determined for (SRu,RC)-10.
and secondary amino-oxazoline ruthenium systems.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
Chiral hydrogen transfer of prochiral ketones catalyzed
by transition metals has emerged as a convenient methodol-
ogy to give enantiomerically pure secondary alcohols, based
on the simplicity of the process and the safety of the rea-
gents.[1]
From a mechanistic point of view, three alternatives have
been proposed for metal-catalyzed hydrogen transfer of
ketones (Scheme 1): i) direct transfer of a hydrogen atom
Scheme 1. Key species involved in the three main mechanisms [con-
certed (a) and (c), and stepwise (b)] of metal-catalyzed hydrogen
transfer (spectator ligands on the metal have been omitted for clar-
ity).
The efficient catalytic system described by Noyori and
of the alcohol to the carbonyl carbon through a concerted co-workers, Ru/TsDPEN (TsDPEN=N-(p-tolylsulfonyl)-
process involving a six-membered cyclic transition state (a), 1,2-diphenylethylendiamine), suggests the requirement of
a
mechanism accepted for Al-catalyzed Meerwein- amino groups in order to achieve high activities.[4,5] Other
Ponndorf-Verley reductions and generally for main group related works showed similar trends.[6] In order to under-
elements;[2] ii) stepwise mechanism through the formation stand the reaction pathway, theoretical studies have been
of a hydride metal intermediate and the migratory insertion reported on the basis of the ruthenium complex structures
of a C=O into a M–H bond (b), a mechanism suggested for and their reactivity, for systems containing primary and sec-
rhodium() and ruthenium free-arene systems;[3] and iii) a ondary amines.[7] These systems are in agreement with a
concerted mechanism where a proton and a hydride are metal–ligand bifunctional mechanism.
simultaneously transferred to the unsaturated substrate (c),
We previously tested p-cymene ruthenium systems con-
a mechanism proposed by Noyori for the Ru arene deriva- taining chiral bis(oxazolines) as catalysts in the acetophe-
tives.[4]
none reduction processes, in particular in hydrogenation
transfer.[8] Moderated enantiomeric excesses were obtained
(ee up to 38%), and the best chiral auxiliaries were found
among those containing two carbon spacers between both
oxazoline fragments. As stated above, the presence of NH2
or NH groups in the auxiliaries is fundamental for catalytic
reactivity.[4b] For that reason, and following our research
with oxazoline ligands,[9] we proposed to use primary (4–7)
[a] Departament de Química Inorgànica, Universitat de Barcelona,
Martí I Franquès 1-11, 08028 Barcelona, Spain
Fax: +34-93-4907725
E-mail: montserrat.gomez@qi.ub.es
[b] Departamento de Química Fundamental, Universidade da Co-
ruña,
Campus da Zapateira, s/n, 15071 A Coruña, Spain
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M. Gómez, S. Jansat, G. Muller, G. Aullón, M. A. Maestro
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and secondary (8–9) amino-oxazolines in order to improve cerning the relative energies of the corresponding transition
the results previously obtained (Figure 1). The amino states responsible for the hydrogen transfer from catalytic
alcohol precursors of the corresponding oxazolines were species to the prochiral ketone.
also tested (1–3). In order to rationalize the catalytic results
found, a structural study of ruthenium complexes was car-
ried out, both in solution (by means of NMR spectroscopy)
and in solid state (by means of X-ray diffraction). The dia-
Results and Discussion
stereomeric distributions observed in solution were con-
firmed by structural modeling (PM3(tm) level). In addition,
a theoretical study (DFT level) was also carried out con-
Synthesis of Chiral Amino-Oxazoline Ligands
The optically pure amino-oxazolines 4 and 5 recently re-
ported in the literature were prepared in one and three
steps, respectively.[10] The standard Zn-catalyzed condensa-
tion of anthranilonitrile with the appropriated amino
alcohol, followed for the synthesis of 4,[10b] gave low yields
for 5 and 6 (less than 30% after three days of reaction). But
better results were obtained when the cyclization process
took place under basic conditions in a mixture of glycerol
and ethylenglycol in a one-step process (Scheme 2),[11] in
contrast to the three-step synthetic route from isatoic anhy-
dride.[10c] The one-pot synthesis gave a mixture of the ex-
pected oxazoline and the corresponding amide (oxazoline/
amide 85:15 for 5 and 1:1 for 6), which were separated by
aqueous extractions (the oxazoline remains in the organic
phase). The pure amide derived from -valinol can be trans-
formed to the corresponding oxazoline 5 by substitution of
the hydroxyl group with p-tolylsulfonyl chloride and cycli-
zation under basic conditions (0.5  NaOH, in H2O/MeOH
1:1) at room temperature for two days. The oxazoline 7 was
easily obtained by silylation of 6 with SiClMe3 in excellent
yield. The secondary amine ligands, 8 and 9, were obtained
in two different synthetic ways. Ligand 8 was prepared from
the primary amino-oxazoline 5 following the procedure de-
scribed previously in the literature.[12] But analogous meth-
odology using methyl iodide in place of p-toluenesulfonyl
Figure 1. Chiral amino alcohols (1–3) and amino-oxazolines (4–9). chloride failed to give 9, which was isolated in good yield
Scheme 2. Synthesis of primary (5–7) and secondary (8–9) chiral amino-oxazolines.
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Ruthenium Complexes as Catalysts in Acetophenone Hydrogen Transfer
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in two steps, reacting dimethyl sulfate with the lithium de- Cl(1) = 2.62 Å and Namino(1)–H(1B)···Nox(2) = 2.79 Å,
rivative of 5 (Scheme 2).
shorter than the expected van der Waals separations
(3.0 Å),[16] and consistent with hydrogen bonds.[17,18] These
distances are significantly shorter than for H(1A):
Ruthenium Complexes
N
amino(1)–H(1A)···Cl(1) = 2.85 Å and Namino(1)–H(1A)···
Nox(2) = 3.30 Å (the hydrogen positions were calculated,
not found in the difference Fourier map). It is also signifi-
cant that the nitrogen–axial hydrogen distance (N–H(1B) =
0.862 Å) is shorter than the nitrogen–equatorial hydrogen
one (N–H(1A) = 0.869 Å), as observed for other related
compounds.[5b]
The cationic complexes 10, 11 and 12, of general formula
[RuCl(p-cymene)(κ2-N,N-L)]Cl (where L = 4, 5 and 8,
respectively) were synthesized from the dimeric p-cymene
precursor and the appropriated amino-oxazoline
(Scheme 3). Complexes 10 and 11 were obtained as a mix-
ture of two diastereomers, since the ruthenium chiral center
formed upon coordination of optically pure oxazoline li-
gand: (SRu,RC)- + (RRu,RC)-10 and (SRu,SC)- + (RRu,SC)-
11, as observed for analogous arene Ru complexes contain-
ing pyridino-oxazolines.[13] In solution, complex 12 shows
at least three isomers, probably due to the N stereocenter.
The complexes were fully characterized both in solid state
and solution.
Figure 2. Molecular structure and atom labeling scheme for the
cation of (SRu,RC)-10. Hydrogen atoms, except H1A, H1B, and the
chloride contra-anion have been omitted for clarity.
Table 1. Selected bond lengths [Å] and angles [°] for (SRu,RC)-10
(with esd’s in parentheses).
Ru(1)–N(2)
Ru(1)–N(1)
Ru(1)–Cl(1)
2.110(7)
2.135(6)
2.401(2)
2.168(8)
2.177(8)
2.184(8)
2.209(8)
2.212(8)
2.225(9)
80.5(3)
Ru(1)–C(17)
Ru(1)–C(13)
Ru(1)–C(16)
Ru(1)–C(14)
Ru(1)–C(15)
Ru(1)–C(12)
N(2)–Ru(1)–N(1)
N(2)–Ru(1)–Cl(1)
N(1)–Ru(1)–Cl(1)
83.2(2)
83.7(2)
Scheme 3. Synthesis of ruthenium complexes (10–12) containing
amino-oxazolines (4, 5, 8).
Conductivity measurements in acetonitrile for complexes
Single crystals of 10 were obtained by slow diffusion of 10 and 11 show the existence of 1:1 electrolytes in solution
hexane over a chloroform/dichloromethane solution of the (about 50 Ω–1 cm2 mol–1).[19] The highest peak of positive
complex (Figure 2). Selected bond lengths and angles are FAB mass spectra corresponds to the cation [RuCl(p-cy-
listed in Table 1. The absolute configuration of the ruthe- mene)L]+ (L = 4 for 10; L = 5 for 11).
nium stereocenter is SRu [according to the priority sequence
1H NMR spectra for both ruthenium complexes indicate
η6-arene Ͼ Cl Ͼ Nox(1) Ͼ Namino(2)].[14] The complex the existence of two isomers in about 5:1 and 2:1 ratios for
adopts a distorted three-legged “piano stool” geometry. 10 and 11, respectively. For complex 10 many signals ap-
The ruthenium atom is η6-coordinated to the p-cymene unit peared overlapped and consequently a complete assignment
(calculated distance between the planar arene group and for both isomers was not possible, in contrast to complex
metal is 1.66 Å), and the other three positions are occupied 11 (see Experimental section for NMR spectroscopic data).
by the two nitrogen (from the bidentated ligand) and chlo- The Namino-coordination of the oxazoline ligand in 11 is
rine atoms. The bond distances and angles are quite similar proven by the different chemical shifts of the two N–H pro-
to those for the known analogous ruthenium complexes.[15] tons, for each isomer, analogously to Ru arene complexes
It is interesting to note the short intramolecular nonbonded containing amino alcohols.[20] The difference between both
distances of one amino hydrogen atom (H1B) with the ox- chemical shifts (more than 5 ppm) stands out, due to the
azoline nitrogen and chlorine atoms: Namino(1)–H(1B)··· intramolecular hydrogen bond between one N–H and the
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chlorine atom coordinated to the metal (see above, X-ray stereomers. In Figure 3, calculated formation enthalpies
discussion). As mentioned above, the diastereomers are due versus the dihedral angle defined by C(methyl of p-cy-
to the two chiral centers, the oxazoline carbon stereocenter mene)–p-cymene ring–ruthenium–chlorine are plotted for
(R or S for 4 or 5, respectively), and the Ru atom. These both isomers of each complex 10 and 11. For the epimer in
isomers are exchanged at a low rate in solution, because no which the ethyl or isopropyl oxazoline group points toward
isomeric composition change was observed in the nonco- the arene [(SRu,RC)-10 and (RRu,SC)-11, respectively],
ordinating solvent (CDCl3) in the temperature range higher energy intermediates are observed than for the other
studied (223–298 K). When a 2-propanol solution of 11 was isomer [(RRu,RC)-10 and (SRu,SC)-11, respectively]. In ad-
treated at 60 °C for three hours, slight changes in the dia- dition, these hills show higher energy for (RRu,SC)-11 than
stereomeric composition were detected (ratio of both iso- for (SRu,RC)-10, due to the more important steric hindrance
mers about 2.5:1).
of the isopropyl than the ethyl group.
1
The H NMR spectrum for 12 shows the existence of at
least three isomers in a ratio of about 4:1:1 at room tem-
perature. A complete assignment could be done only for the
major isomer. At lower temperatures (temperature range
studied: 298–233 K), the signals corresponding to the minor
isomers became larger and the relative ratio could not be
determined. Upon coordination of the amino nitrogen
atom (NHR, R = ptolylsulfonyl) to the ruthenium, a new
stereocenter is formed, which could be the factor responsi-
ble for the presence of more isomers: (SRu,SC,RN)-12,
(SRu,SC,SN)-12, (RRu,SC,RN)-12, and (RRu,SC,SN)-12.
In order to evaluate the relative isomer stability for com-
plexes 10 and 11, semi-empirical optimizations [PM3(tm)
level] were carried out for both isomers of each complex.[21]
The energy difference between the two diastereomers is
1.029 and 0.685 kcalmol–1 for 10 and 11, respectively, the
most stable isomers being (RRu,RC)-10 and (SRu,SC)-11.
The Boltzmann species distribution (about 6:1 and 3:1 for
10 and 11, respectively, at 298 K) is in good accordance
with the ratio observed in the 1H NMR spectra (see above).
For both cases, the most stable diastereomer corresponds
to the configuration at the Ru atom, that leads to the ox-
azoline substituent at the stereocenter pointing away from
the arene group. To prove the steric hindrance between p-
Ru-Catalyzed Enantioselective Hydrogen Transfer of
Acetophenone
The Ru/amino alcohol (1–3) and Ru/amino-oxazoline (4–
9) catalytic systems were tested in the asymmetric transfer
hydrogenation of acetophenone (I), using 2-propanol as the
hydrogen source under basic conditions (Scheme 4).[22] The
catalytic results are summarized in Table 2. The catalyses
were performed with in situ prepared catalyst precursor,
[Ru2Cl4(p-cymene)2], and the corresponding chiral ligand,
in a Ru/L* ratio 1:2. In the absence of tBuOK, Ru/L* sys-
tems were inactive. Conversions of acetophenone (I) and
enantiomeric excesses of 1-phenylethanol (II) were moni-
tored during the catalytic reaction by GC.
Scheme 4. Hydrogen transfer of acetophenone (I) catalyzed by Ru/
L* systems (L* = 1–9).
Concerning the catalytic behavior of Ru/amino alcohols
cymene and the remaining ligands, the rotation effect (entries 1–5), the β-monosubstituted amino alcohols, 1 and
around the Ru-arene axis has been considered for both dia- 2, are more active than the α,β-disubstituted one, 3 (entries
Figure 3. Plot of calculated enthalpies (kcalmol–1) vs dihedral angle “C(methyl of p-cymene)–p-cymene ring–ruthenium–chlorine” [°] for
complexes 10 and 11.
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Ruthenium Complexes as Catalysts in Acetophenone Hydrogen Transfer
Table 2. Asymmetric hydrogen transfer of acetophenone catalyzed by chiral ruthenium systems, Ru/L* (L* = 1–9).[a]
FULL PAPER
Entry
L*
I/Ru
Time (h)
Conv. (%)[b]
ee II (%)[b]
TOF (h–1) (%)
1
2
3
4
1
2
2
3
3
4
5
5
5
6
6
7
8
8
8
9
9
100/1
100/1
20/1
100/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
20/1
1.5
1.5
0.5
24
72
24
1.5
24
72
1.5
24
1.5
1.5
24
89
80
92
0
17
20
53
75
33
9
41
95
3
63
92
12
42
12 (R)
32 (S)
32 (S)
–
33 (S)
43 (R)
45 (S)
45 (S)
79 (S)
n.d.
2.0
71 (S)
nd
0
0
0
59
53
37
–
0.2
0.2
7.0
0.6
0.1
5
6[c]
7
8
9
10
11[c]
12[c]
13
14
15[c]
16
17[c]
1.2
0.3
0
0.5
0.3
1.6
0.3
72
1.5
24
0
[a] Results from duplicated experiments. Ru/L*/tBuOK 1:2:3. See Scheme 4. [b] Conversions based on the substrate I and enantiomeric
excesses (absolute configuration in parenthesis) determined by GC. [c] Reaction monitored up to 120 h, being conversion and enantio-
selectivity constants.
1 and 2 vs 4 and 5), in contrast to the results observed with
α,β-dialkyl-substituted amino alcohols.[20] In our case the
introduction of a second alcohol function leads to a dra-
matic activity decrease, but with an asymmetric induction
similar to ligand 2 (entries 2 and 5). The selectivity of Ru/
1 and Ru/2 systems is independent of the acetophenone/
ruthenium ratio (entries 2 and 3). When the ruthenium-to-
ligand ratio was 1:1, the catalytic behavior did not change,
proving that the catalytic species are active without the li-
gand excess in the reaction medium that was observed pre-
viously for other ligands.[23]
Amino-oxazolines 4 and 5 are less active but more selec-
tive than the corresponding amino alcohols 1 and 2 (entries
6 and 7 vs 1 and 2, respectively). Also, oxazoline 6 is more
selective than 3 (entry 11 vs 5), and, in turn, the silyl oxaz-
oline 7 is more active than 6 (entry 12 vs 10 and 11), the
Scheme 5. Dehydrogenative oxidation of rac-II catalyzed by the Ru/
Ru/7 system being the most active oxazoline catalyst tested.
These results indicate a “poison” effect of the alcohol
group, both for the amino alcohol 3 and the oxazoline de-
rivative 6. In addition, we observe that the catalytic activity
and selectivity are highly influenced by the substitution de-
gree of the oxazoline heterocycle (7, α,β-disubstituted ox-
azoline, is more active and affords better enantiomeric ex-
cesses than 4 and 5, β-monosubstituted oxazolines), as re-
ported for α,β-dialkyl-substituted amino alcohols.[20]
We note that only the Ru/5 catalytic system leads to an
increase of enantiomeric excess (up to 79%) at long reaction
times, together with a conversion decrease (entries 8 and 9).
This proves the reversibility of the transfer hydrogenation,
as stated by Noyori.[4a,24] In order to verify this kinetic reso-
lution, the dehydrogenative oxidation of rac-II with acetone
was carried out under similar conditions as those described
5 system.
Secondary amino-oxazolines, N-(p-tolylsulfonyl)- and N-
methyl-amino-oxazoline (8 and 9, respectively), were some-
what less active than the analogous primary amino-oxazo-
line 5 (entries 14 and 17 vs 8), and what is more significant,
they did not induce asymmetry (entries 13–17). Then a pri-
mary amine moiety and not a secondary amine function in
the ligand appears essential for the enantioselectivity. This
is something that has not been observed before and is only
mentioned for indanol amino alcohol derivatives.[6c]
Theoretical Calculations
Assuming that the Ru-catalyzed hydrogen transfer pro-
above for the direct process (Scheme 5). After 48 h at room cess involves a concerted transfer of both proton and hy-
temperature, 46% of acetophenone was formed, achieving dride, a six-membered transition state may be responsible
an enantiomeric excess for 1-phenylethanol up to 50% (S); for the ketone reduction by means of a double hydrogen
then (R)-II dehydrogenates faster than the (S)-II enanti- transfer from Ru–H and N–H bonds towards the prochiral
omer.
substrate, as postulated by Noyori.[7a,25] This concerted
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mechanism for Ru complexes containing bidentated N-do-
For prochiral substrates, like the acetophenone, the enan-
nor ligands, in particular oxazolinyl (Nox)-amino(NHR) li- tiomeric enhancement of the chiral alcohol formed depends
gands, is represented in Figure 4.
on the way that the ketone enantioface approaches the me-
tal–hydride intermediate (see transition states depicted in
Figure 5). In order to understand the enantioselectivity dif-
ferences observed with our catalytic systems containing
substituted (NHR for ligands 8 and 9) and nonsubstituted
(NH2 for 4–7) amino groups, theoretical calculations at
DFT level were carried out for the corresponding transition
states (see below). In the hydride model structure 13 (Fig-
ure 5), the substituent on the oxazoline stereocenter is a
methyl group with S absolute configuration. The energy dif-
ference between both optimized diastereomers was
0.59 kcalmol–1 (Boltzmann distribution, 73:27), the SRu be-
ing the most stable isomer, where the oxazoline substituent
at the stereocenter points away from the arene group, analo-
gously to the related prepared chloro complexes 10 and 11
(see above).
The calculated transition states are labeled as TS-RII-13
or TS-SII-13 depending on the 1-phenylethanol enantiomer
afforded (Figure 5). Their relative stability of four transition
states are determined by an equilibrium between weak hy-
drogen interactions of the type C–H···Ar. Our calculations
show that the two most stable states produce the R alcohol
(relative energies are 0.0 and +1.2 kcalmol–1), whereas the
relative S alcohol states are higher in energy (+1.6 and
+2.5 kcalmol–1). Concerning the transition states related to
the 13 hydride species, the Boltzmann distribution (298 K)
for their four transition states leads to a calculated enantio-
meric excess for the secondary alcohol II of about 40% in
the R isomer (Figure 6), in agreement with the catalytic re-
sults obtained with the analogous amino-oxazolines con-
Figure 4. Catalytic cycle for Ru-catalyzed hydrogen transfer of
ketones through a concerted mechanism.
Figure 5. Optimized hydride species 13 (SRu-13 and RRu-13) and the transition states involved in the hydrogenation of acetophenone used
in the DFT study.
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Ruthenium Complexes as Catalysts in Acetophenone Hydrogen Transfer
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taining an ethyl and isopropyl instead of the methyl group in Figure 5). For these states, only the two axial related spe-
(ligands 4 and 5).
cies were taken into account because of the topological ar-
rangement for hydrogen transfer to the prochiral ketone in
the transition state (Figure 5). As depicted in Figure 7, the
isomers TS-SRu-14 are less stable than the other two, poss-
ibly due to steric repulsions, having an energy higher than
10 kcalmol–1 and higher than the related TS-RRu-14. For
this reason they do not play any role in our catalytic system
(Figure 8). Consequently, only the lowest transition states,
TS-RII,RRu-14 and TS-SII,RRu-14, participate in the hydro-
genation reaction and the small energy gap between the two
forms is responsible for a decrease of enantiomeric excess
(calculated ee = 26%). In contrast, in the related transition
states of 13, the largest populations corresponded to the
transition states loading to the R enantiomers, explaining
the selectivity trends observed for Ru catalytic systems con-
taining primary and secondary amino-oxazolines (see Cata-
lytic section).
Figure 6. Energy profile for minima of compound model 13, and
their generated transition states (Figure 5) for the reaction with
acetophenone, depending on the relative orientation of prochiral
ketone. Relative populations of transition states are shown accord-
ing to the Boltzmann distribution at 298 K.
Figure 8. Schematic representation of the transition states TS-14.
The steric repulsions between hydrocarbon groups for TS-SRu-14
(left) are missing in analogous TS-RRu-14 (right).
The good correlation observed between experimental
and calculated data for the Ru systems containing primary
amino ligands led us to calculate the relative population
of the transition states involved with Ru species containing
secondary amino-oxazoline 9 (transition states labeled as 14
Conclusions
We used modular chiral N-donor ligands in order to
study the fine effects on the transfer hydrogenation of ace-
tophenone catalyzed by Ru arene systems. An important
influence on selectivity was found to depend on the nature
of the amino group: secondary amino ligands (8–9) do not
induce enantioselectivity, in contrast to their analogous pri-
mary derivative (5). In order to rationalize these results, a
structural and mechanistic study was proposed. The synthe-
sis and full characterization of complexes containing pri-
mary (10 and 11) and secondary (12) oxazolinyl-amino li-
gands was carried out. The NMR spectroscopic data show
the presence of isomers due to the new sterocenters (Ru and
also N for 12) generated upon coordination of the ligands
(4, 5, and 8) to the metal. The relative populations found
by modeling structures (PM3(tm) level) are in agreement
with the diastereomeric ratios observed by NMR spec-
troscopy. The enantioselectivity loss observed for secondary
amines relative to the analogous primary ligands can be
justified by the theoretical data obtained (DFT studies) for
the transition states proposed for the arene ruthenium sys-
tems involved in the hydrogen transfer of prochiral ketones.
Figure 7. Relative stabilities of Ru transition states involved in the
acetophenone hydrogen transfer containing primary (13) and sec-
ondary (14) oxazolinyl-amines. Relative populations are shown as
Figure 5 and zero level is taken from the TS-RII,RRu isomer.
Eur. J. Inorg. Chem. 2005, 4341–4351
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4347

M. Gómez, S. Jansat, G. Muller, G. Aullón, M. A. Maestro
FULL PAPER
ture and washed with a saturated aqueous solution of NH4Cl and
extracted with dichloromethane (3×15 mL). The organic extracts
were dried with anhydrous Na2SO4. Solvent elimination under low
pressure gave the product as a yellow oil. Yield: 0.640 g (57%). IR
Experimental Section
General Remarks: All compounds were prepared under purified ni-
trogen using standard Schlenk and vacuum-line techniques. The
solvents were purified by standard procedures and distilled under
nitrogen.[26] (R)-(+)-2-Aminobutanol (Fluka), -valinol (Aldrich),
and [RuCl(p-cymene)(µ-Cl)]2 (Aldrich) were used without previous
purification. Ligand 4[10b] was prepared as described previously.
NMR spectra were recorded with Varian XL-500 (1H, standard
SiMe4), Varian Gemini (1H, 200 MHz; 13C, 50 MHz; standard
SiMe4), Bruker DRX 250 (13C, 62.9 MHz, standard SiMe4), and
Mercury 400 (1H, 400 MHz; 13C, 100 MHz, standard SiMe4) spec-
trometers, using CDCl3 as solvent, unless stated otherwise. Chemi-
cal shifts were reported downfield from standards. IR spectra were
recorded with a Nicolet 520 FTIR spectrometer. FAB mass chro-
matograms were obtained on a Fisons V6-Quattro instrument. The
GC analyses were performed on a Hewlett–Packard 5890 Series II
gas chromatograph (50 m Ultra 2 capillary column) with a FID
detector. Enantiomeric excesses were determined by GC on a FS-
cyclodex-β-I/P column. Optical rotations were measured on a Per-
kin–Elmer 241MC spectropolarimeter. Conductivities were ob-
tained on a Radiometer CDM3 conductimeter. Elemental analyses
were carried out by the Serveis Cientifico-Tècnics de la Universitat
de Barcelona in an Eager 1108 microanalyzer.
(NaCl): ν = 3466 (N–H), 3415 (O–H), 3309 (N–H), 1633 (C=N),
˜
1
1261 (C–O) cm–1. H NMR (200 MHz, CDCl3; multiplicity, coup-
ling constants in Hz, and relative integration in parentheses): 7.81
(dd, 7.9, 0.6, 1 H), 7.24 (m, 3 H), 6.70 (m, 5 H), 6.07 (br. s, 2 H),
4.39 (d, 7, 1 H), 4.26 (pq, 3.6, 1 H), 3.94 (pdd, 11.5, 3.7, 1 H), 3.74
(dd, 11.2, 4.0, 1 H), 2.61 (br. s, 1 H) ppm. 13C NMR (50 MHz,
CDCl3): 164.8 (C), 148.6 (C), 140.8 (C), 132.4 (CH), 129.9 (CH),
128.8 (CH), 128.2 (CH), 125.6 (CH), 116.4 (CH), 115.9 (CH), 108.8
(C), 80.9 (CH), 64.1 (CH2) ppm. MS (FAB positive) m/z 267 ([M –
H]+). [α]2D5 (1×10–3 , CHCl3) = +59.3.
(+)-(3ЈS,4ЈS)-2-(3Ј-Phenyl-4Ј-trimethylsilyloxymethyl-3Ј,4Ј-dihy-
drooxazol-2Ј-yl)aniline (7): Compound 6 (0.330 g, 1.23 mmol), imi-
dazole (0.175 g, 2.58 mmol), DMAP (6.6 mg, 5.3×10–2 mmol), and
SiClMe3 (0.132 g, 1.22 mmol) were successively introduced in a
Schlenk. The solids were dissolved in 50 mL of freshly distilled
chloroform, and the resulting mixture was stirred for 24 h at room
temperature. The evolution of the reaction was followed by thin-
layer chromatography (hexane/ethyl acetate, 2:1). When the reac-
tion was over, the organic phase was treated successively with
10 mL of saturated aqueous solution of sodium hydrogenocarbon-
ate and 10 mL of a saturated aqueous solution of brine, and the
organic extracts were then dried with anhydrous Na2SO4. After
solvent evaporation, the resulting oil was purified by column
chromatography on silica using a mixture of hexane/ethyl acetate
(2:1) as eluent. The product was obtained as a white solid. Yield:
(+)-(4ЈS)-2-(4Ј-Isopropyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)aniline (5):
-Valinol (0.743 g, 7.20 mmol), 2-aminobenzonitrile (0.500 g,
4.23 mmol), and potassium carbonate (0.054 g, 0.39 mmol) were
successively introduced in a Schlenk, followed by a solution of glyc-
erol (5 mL) in dry ethylene glycol (9 mL). The resulting mixture
was brought to 105 °C under nitrogen. The disappearance of the
nitrile was followed by thin-layer chromatography (hexane/ethyl
acetate, 3:1). After 24 h, the reaction was complete. Two new spots
appeared on the thin layer, which were further identified as the
amide for the high Rf and the oxazoline for the low Rf one (15:85
respectively, determined by GC analysis). The mixture was cooled
to room temperature and then poured over crushed ice. The re-
sulting white solid was filtered, dissolved in dichloromethane and,
after several extractions with water, the organic phases were dried
with anhydrous Na2SO4. Solvent elimination under low pressure
0.372 g (89 %). IR (KBr): ν = 3408 (N–H), 3276 (N–H), 1635
˜
(C=N), 1261 (C–O) cm–1 1H NMR (200 MHz, CDCl3; multi-
.
plicity, coupling constants in Hz, and relative integration in paren-
theses): 7.67 (pdd, 7.9, 1.5, 2 H), 7.16 (m, 4 H), 6.58 (d, 8.6, 2 H),
6.54 (pt, 7.6, 1 H), 5.97 (br. s, 2 H), 5.29 (d, 6.0, 1 H), 4.15 (m, 1
H), 3.83 (dd, 10.4, 4.2, 1 H), 3.55 (pdd, 10.1, 7.3, 1 H), –0.02 (s, 9
H) ppm. 13C NMR (50 MHz, CDCl3): 164.2 (C), 148.8 (C), 141.5
(C), 132.2 (CH), 129.8 (CH), 128.6 (CH), 127.9 (CH), 125.0 (CH),
116.0 (CH), 115.6 (CH), 108.9 (C), 81.6 (CH), 77.2 (CH), 64.9
(CH2), 0.1 (CH3) ppm. C19H25N2O2Si (341.5): calcd. C 67.03, H
7.05, N 8.23; found C 67.69, H 7.11, N 8.30. MS (FAB positive)
m/z 340 ([M]+). Melting point: 153 °C. [α]2D5 (1×10–3 , CHCl3) =
+30.7.
gave the product as a white solid. Yield: 0.860 g (80%). IR (KBr):
ν = 3395 (N–H), 3261 (N–H), 1640 (C=N), 1255 (C–O) cm–1. H
1
˜
NMR (250 MHz, CDCl3; multiplicity, coupling constants in Hz,
and relative integration in parentheses): 7.67 (pdd, 8.8, 1.6, 1 H),
7.19 (pt, 7.4, 1 H), 6.69 (m, 2 H), 6.13 (br. s, 2 H), 4.32 (ppd, 8.6,
7, 1 H), 4.11 (m, 1 H), 4.00 (t, 7.3, 1 H), 1.81 (m, 1 H), 1.03 (d,
6.8, 3 H), 0.93 (d, 6.8, 3 H) ppm. 13C NMR (50 MHz, CDCl3):
163.4 (C), 148.5 (C), 131.8 (C), 129.5 (CH), 115.9 (CH), 115.5
(CH), 109.1 (CH), 72.9 (CH), 68.7 (CH2), 33.2 (CH), 19.1 (CH3),
18.6 (CH3) ppm. C12H16N2O (204): calcd. C 70.58, H 7.84, N
13.72; found C 70.29, H 8.02, N 13.74. MS (FAB positive) m/z 204
([M]+). Melting point: 103 °C. [α]2D5 (1×10–3 , CHCl3) = +19.8.
(+)-(4ЈS)-2-(4Ј-Isopropyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)-N-(p-tolyl-
sulfonyl)aniline (8): Stirring a solution of 5 (0.100 g, 0.49 mmol)
and p-tolylsulfonyl chloride (0.160 g, 0.84 mmol) in dichlorometh-
ane with an aqueous solution of KOH (0.049 g, 0.89 mmol) for 8 h
gave a white solid, which was filtered off and purified by column
chromatography on silica using hexane/ethyl acetate (5:1) as eluent.
Yield: 0.134 g (77%). IR (KBr): ν = 3389 (N–H), 1637 (C=N), 1341
˜
(S=O), 1163 (S=O) cm–1. 1H NMR (200 MHz, CDCl3; multiplicity,
coupling constants in Hz, and relative integration in parentheses):
12.54 (br. s, 1 H), 7.66 (d, 8.2, 2 H), 7.62 (m, 2 H), 7.26 (ptd, 7.8,
1.4, 2 H), 6.91 (ptd, 7.9, 1.0, 1 H), 4.28 (dd, 8.6, 7.4, 1 H), 4.06 (m,
1 H), 3.98 (m, 1 H), 2.26 (s, 3 H), 1.73 (m, 1 H), 0.98 (d, 6.6, 3 H),
0.88 (d, 6.6, 3 H) ppm. 13C NMR (50 MHz, CDCl3): 164.8 (C),
142.5 (C), 137.8 (C), 135.4 (C), 132.3 (CH), 129.4 (CH), 129.1
(CH), 127.1 (CH), 122.1 (CH), 117.6 (CH), 72.3 (CH), 69.5 (CH2),
33.1 (CH), 18.8 (CH3), 18.6 (CH3) ppm. C19H22N2O2S (342): calcd.
C 63.68, H 6.14, N 7.81; found C 63.78, H 6.53, N 7.60. MS (FAB
positive) m/z 340 ([M]+). Melting point : 129 °C. [α]2D5 (1×10–3 ,
CHCl3) = +82.1.
(+)-(3ЈS,4ЈS)-2-(3Ј-Phenyl-4Ј-hydroxymethyl-3Ј,4Ј-dihydrooxazol-
2Ј-yl)aniline (6): (1S,2S)-2-Amino-1-phenyl-1,3-propanediol
(1.201 g, 7.20 mmol), 2-aminobenzonitrile (0.500 g, 4.23 mmol),
and potassium carbonate (0.054 g, 0.39 mmol) were successively in-
troduced in a Schlenk, followed by a solution of glycerol (5 mL) in
dry ethylene glycol (9 mL). The resulting mixture was brought to
105 °C under nitrogen. The disappearance of the nitrile was fol-
lowed by thin-layer chromatography (hexane/ethyl acetate, 3:1).
The reaction was complete after 36 h. Two new spots appeared on
the thin layer, which were further identified as the amide for the
high Rf and the oxazoline for the low Rf one (1:1 respectively, deter-
mined by GC analysis). The mixture was cooled to room tempera-
(4ЈS)-2-(4Ј-Isopropyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)-N-(methyl)aniline
(9): Compound 5 (0.150 g, 0.73 mmol) was dissolved in 10 mL of
4348
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 4341–4351

Ruthenium Complexes as Catalysts in Acetophenone Hydrogen Transfer
FULL PAPER
THF. The resulting mixture was cooled to –78 °C under nitrogen.
After 30 min, nBuLi (0.55 mL, 0.88 mmol) was introduced in the
Schlenk, followed by a solution of Me2SO4 (0.111 g, 0.88 mmol) in
THF (3 mL). The resulting mixture was warmed to room tempera-
ture. The reaction was complete after 18 h. Two new spots appeared
on the thin layer, which were further identified as the product for
the high Rf and the oxazoline 5 for the low Rf one (70:30 respec-
tively, determined by GC analysis). The mixture was dissolved in
dichloromethane and after several extractions with an aqueous sat-
urated solution of NH4Cl and water, the organic phases were dried
with anhydrous Na2SO4. The resulting oil was purified by column
chromatography on silica using hexane/ethyl acetate (20:1) as elu-
ent. Solvent elimination under low pressure gave the product as a
yellow oil. Yield: 0.116 g (73%). IR (KBr) = 3265 (N–H), 3171 (N–
1.5, 1 H), 7.58 (m, 1 H), 7.30 (t, 7.5, 1 H), 5.89 (br. s, 2 H), 5.79
(d, 6.0, 1 H), 5.65 (d, 6.0, 1 H), 5.01 (d, 11.0, 1 H), 4.86 (pt, 9.5, 1
H), 4.70 (m, 1 H), 4.52 (m, 2 H), 2.84 (m, 1 H), 2.60 (m, 1 H), 1.84
(s, 3 H), 0.93 (d, 7.5, 3 H), 0.59 (d, 6.5, 3 H) ppm. 13C NMR
(CDCl3, 100 MHz) δ = major isomer: 164.2 (C), 142.1 (C), 134.7
(C), 128.7 (CH), 126.7 (CH), 124.7 (CH), 119.4 (CH), 107.2 (CH),
84.4 (CH), 84.1 (CH), 81.1 (CH), 80.6 (CH), 71.4 (CH2), 69.4
(CH2), 31.2 (CH), 28.3 (CH), 22.1 (CH), 21.2 (CH), 19.7 (CH3),
18.2 (CH3), 15.0 (CH3) ppm. δ minor isomer: 163.3 (C), 142.7 (C),
134.7 (C), 130.8 (CH), 126.8 (CH), 123.7 (CH), 118.7 (CH), 97.2
(CH), 84.0 (CH), 79.0 (CH), 78.3 (CH), 77.5 (CH), 69.5 (CH2),
66.0 (CH2), 30.9 (CH), 28.8 (CH), 23.3 (CH), 19.8 (CH3), 18.1
(CH3), 14.9 (CH3) ppm. C22H30Cl2N2ORu (475): calcd. C 51.76, H
5.88, N 5.49, Cl 13.90; found C 51.29, H 6.00, N 5.25, Cl 13.40.
H), 2959 (C–H), 1636 (C=N), 1253 (C–O) cm–1 1H NMR MS (FAB positive): m/z calcd. for C22H30ClN2ORu [M+]: 439.6;
.
(200 MHz, CDCl3; multiplicity, coupling constants in Hz, and rela-
tive integration in parentheses): 8.31 (br. s, 1 H), 7.63 (dd, 7.9, 1.8,
1 H), 7.23 (m, 1 H), 6.53 (m, 2 H), 4.21 (dd, 8.4, 7.0, 1 H), 4.03
(m, 1 H), 3.90 (q, 7.0, 1 H), 2.85 (d, 4.8, 3 H), 1.69 (m, 1 H), 0.94
(d, 6.6, 3 H), 0.84 (d, 6.6, 3 H) ppm. 13C NMR (50 MHz, CDCl3):
163.6 (C), 149.8 (C), 132.2 (CH), 129.6 (CH), 113.9 (CH), 109.6
(CH), 108.3 (C), 72.8 (CH), 68.3 (CH2), 33.1 (CH), 29.4 (CH3),
19.0 (CH3), 18.5 (CH3) ppm. MS (FAB positive) m/z 218 ([M]+).
Chloro-(η6-p-cymene)-[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)-
aniline-N,N]ruthenium(II) Chloride (10): [RuCl(p-cymene)(µ-Cl)]2
(102 mg, 0.166 mmol) and 4 (63.5 mg, 0.33 mmol) were dissolved
in dichloromethane (18 mL) and stirred at room temperature for
8 h. The solvent was then removed and the residue washed with
diethyl ether. The product was recrystallized from dichloromethane
and diethyl ether, giving an orange solid. Yield: 0.156 g (95%). IR
(KBr) = 3414 (N–H), 3052 (N–H), 1630 (C=N), 1293 (C–O) cm–1.
1H NMR (250 MHz, CDCl3, 233 K; multiplicity, coupling con-
stants in Hz, and relative integration in parentheses) δ = major
isomer: 9.84 (d, 10.0, 1.6, 2 H), 8.61 (d, 7.5, 1 H), 7.60 (m, 2 H),
7.31 (m, 1 H), 5.78 (br. s, 2 H), 5.69 (br. s, 2 H), 5.58 (br. s, 2 H),
4.86 (pt, 11.2, 1 H), 4.68 (br. s, 1 H), 4.29 (m, 1 H), 2.28 (br. s, 1
H), 2.07 (br. s, 1 H), 1.64 (s, 3 H), 0.95 (m, 9 H) ppm. δ minor
isomer: 8.52 (d, 12.5, 1 H), 7.74 (d, 7.5, 1 H), 5.05 (m, 1 H), 2.54
(m, 1 H) ppm. 13C NMR (63 MHz, CDCl3) δ = major isomer: 163.9
found 439.0. Melting point: 243 °C. Molar conductivity (c =
0.001 , acetonitrile): 50 Ω–1 cm2 mol–1.
Chloro-(η6-p-cymene)-[(4ЈS)-2-(4Ј-isopropyl-3Ј,4Ј-dihydrooxazol-2Ј-
yl)-N-(p-tolylsulfonyl)aniline-N,N]ruthenium(II
)
Chloride
(12):
[RuCl(p-cymene)(µ-Cl)]2 (9.6 mg, 0.015 mmol) and 8 (11.3 mg,
0.031 mmol) were dissolved in dichloromethane (4 mL) and stirred
at room temperature for 8 h. The solvent was then removed and
the residue washed with diethyl ether. The product was recrys-
tallized from dichloromethane and diethyl ether, giving an orange
solid. Yield: 0.019 g (99%). IR (KBr) = 3245 (N–H), 1634 (C=N),
1
1267 (SO2), 1099 (SO2) cm–1. H NMR (500 MHz, CDCl3, 298 K;
multiplicity, coupling constants in Hz, and relative integration in
parentheses) δ = major isomer: 9.49 (br. s, 1 H), 8.30 (d, 8.0, 1 H),
7.60 (d, 7.0, 1 H), 7.58 (t, 7.8, 1 H), 7.37 (d, 6.5, 2 H), 7.32 (m, 1
H), 7.23 (q, 6.7, 2 H), 6.84 (m, 3 H), 6.26 (m, 3 H), 6.25 (d, 6.0, 1
H), 6.10 (d, 5.5, 1 H), 5.37 (d, 4.5, 1 H), 5.22 (d, 4.5, 1 H), 4.30 (t,
12.2, 1 H), 4.23 (d, 11.5, 1 H), 4.13 (d, 10.0, 1 H), 3.94 (d, 12.0, 1
H), 2.31 (m, 1 H), 1.23 (s, 3 H), 1.24 (m, 1 H), 0.98 (d, 6.5, 6 H),
0.85 (d, 6.0, 6 H), 0.29 (s, 3 H) ppm. C29H36Cl2N2O3RuS (664.6):
calcd. C 52.41, H 5.45, N 4.21, S 4.82; found C 52.80, H 5.60, N
4.00, S 4.95. MS (FAB positive): m/z calcd. for C29H36ClN2O3RuS
[M+]: 629.20; found 629.00.
Ruthenium-Catalyzed Hydrogen Transfer of Acetophenone: The pre-
(C), 135.1 (CH), 129.7 (CH), 126.8 (CH), 123.6 (CH), 119.4 (CH), cursor ([Ru(p-cymene)Cl(µ-Cl)]2, 1.8 mg, 3×10–3 mmol) and ligand
107.1 (CH), 97.9 (CH), 83.8 (CH), 81.3 (CH), 73.9 (CH), 67.9 (12×10–3 mmol) were dissolved in a solution (2 mL, 0.012 ) of
(CH2), 31.0 (CH), 26.9 (CH2), 18.2 (CH3), 9.9 (CH3) ppm. tBuOK in 2-propanol at room temperature for 30 min. Then a solu-
C21H28Cl2N2ORu (496.4): calcd. C 50.70, H 5.63, N 5.63, Cl 14.26;
tion of acetophenone in 2-propanol (2 mL, 0.06 ) was added. The
found C 50.94, H 5.49, N 5.78, Cl 14.20. MS (FAB positive): m/z reaction was performed at room temperature under nitrogen, moni-
calcd. for C21H28ClN2ORu [M+]: 460.2; found 460.3. Melting
point: 232 °C. Molar conductivity (c = 0.001 , acetonitrile):
47 Ω–1 cm2 mol–1.
tored by GC. When the Ru/substrate ratio was 1:100, the precursor
(1.8 mg, 3×10–3 mmol) and ligand (12×10–3 mmol) were dissolved
in a solution of tBuOK in 2-propanol (10 mL, 0.012 ) at room
temperature for 30 min. Then a solution of acetophenone in 2-pro-
panol (10 mL, 0.06 ) was added. The reaction was performed at
room temperature under nitrogen, monitored by GC.
Chloro-(η6-p-cymene)-[(4ЈS)-2-(4Ј-isopropyl-3Ј,4Ј-dihydrooxazol-2Ј-
yl)aniline-N,N]ruthenium(II) Chloride (11): [RuCl(p-cymene)(µ-Cl)]2
(102 mg, 0.166 mmol) and 5 (67.9 mg, 0.33 mmol) were dissolved
in dichloromethane (18 mL) and stirred at room temperature for
8 h. The solvent was then removed and the residue washed with
diethyl ether. The product was recrystallized from dichloromethane
and diethyl ether, giving an orange solid. Yield: 0.161 g (95%). IR
(KBr) = 3427 (N–H), 3045 (N–H), 1631 (C=N), 1394 (C–O) cm–1.
1H NMR (500 MHz, CDCl3, 298 K; multiplicity, coupling con-
stants in Hz, and relative integration in parentheses) δ = major
isomer: 10.31 (d, 10.0, 1 H), 8.77 (d, 8.0, 1 H), 7.58 (m, 1 H), 7.54
Ruthenium-Catalyzed Dehydrogenation of rac-1-Phenylethanol: The
precursor (1.8 mg of [Ru(p-cymene)Cl(µ-Cl)]2, 3×10–3 mmol) and
ligand 5 (25 mg, 12×10–3 mmol) were dissolved in a solution of
tBuOK in 2-propanol (2 mL, 0.012 ) at room temperature for
30 min. Then an equimolar solution of rac-1-phenylethanol and
acetone in 2-propanol (2 mL, 0.06 ) was added. The reaction was
performed at room temperature under nitrogen, monitored by GC.
(dd, 7.2, 1.5, 1 H), 7.27 (t, 7.5, 1 H), 5.98 (m, 2 H), 5.76 (d, 5.5, 1 X-ray Crystallographic Study: An orange block of 10 was selected
H), 5.62 (d, 6.0, 2 H), 4.58 (dd, 8.0, 6.0, 1 H), 4.52 (m, 2 H), 4.45
(dd, 10.0, 8.0, 1 H), 4.34 (d, 10.0, 1 H), 2.51 (m, 1 H), 2.42 (m, 1
H), 1.92 (s, 3 H), 1.04 (pt, 7.2, 6 H), 0.98 (pt, 7.0, 6 H) ppm. δ
minor isomer: 9.91 (d, 11.0, 1 H), 8.57 (d, 8.0, 1 H), 7.79 (dd, 7.2,
and mounted on a Bruker SMART CCD area detector single-crys-
tal diffractometer with graphite monochromatized Mo-Kα radia-
tion (λ = 0.71073 Å) operating at room temperature. Crystal data
are summarized in Table 3.
Eur. J. Inorg. Chem. 2005, 4341–4351
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4349

M. Gómez, S. Jansat, G. Muller, G. Aullón, M. A. Maestro
FULL PAPER
Table 3. Crystal data for (SRu,RC)-10.
Acknowledgments
(SRu,RC)-10
The authors thank Prof. Santiago Álvarez for constructive dis-
cussions. The authors also wish to thank the Ministerio de Educa-
ción y Ciencia (CTQ2004-01546/BQU and 2002-04033/BQU) and
the Generalitat de Catalunya for financial support. The installation
of the SMART CCD Single-Crystal Diffractometer at the Univer-
sity of A Coruña was supported by the Xunta de Galicia (XUGA
INFRA-97).
Empirical formula
Molecular mass
Crystal size [mm]
Temperature [K]
Crystal system
Space group
C23H29Cl8N2ORu
734.15
0.39×0.09×0.08
298(2)
orthorhombic
P212121
8.881(1)
18.102(2)
20.231(2)
3252.6(5)
4
1.499
1.158
1.51–26.37
19013
6599
R1 = 0.0643
wR2 = 0.1547
1.018
a (Å)
b (Å)
c (Å)
V [Å3]
[1] For reviews see: a) D. Carmona, M. P. Lamata, L. A. Oro, Eur.
J. Inorg. Chem. 2002, 2239; b) M. J. Palmer, M. Wills, Tetrahe-
dron: Asymmetry 1999, 10, 2045; c) G. Zassinovich, G. Mes-
troni, Chem. Rev. 1992, 92, 1051.
[2] C. F. de Graauw, J. A. Peters, H. van Bekkum, J. Huskens, Syn-
thesis 1994, 1007.
[3] a) M. Bernard, V. Guiral, F. Delbecq, F. Fache, P. Sautet, M.
Lemaire, J. Am. Chem. Soc. 1998, 120, 1441; b) J.-E. Backwall,
R. L. Chowdhuri, U. Karlsson, G. Z. Wang, in Perspectives in
Coordination Chemistry (Eds.: A. F. Williams, C. Floriani, G.
Merbach), Verlag Helvetica Chimica Acta, Basel, Switzerland,
1992, p. 463.
[4] a) R. Noyori, S. Hashiguchi, Acc. Chem. Res. 1997, 30, 97; b)
K.-J. Haack, S. Hashiguchi, A. Fujii, T. Ikariya, R. Noyori,
Angew. Chem. Int. Ed. Engl. 1997, 36, 285.
Z
Density (calculated) [Mgm–3]
Absorption coefficient [mm–1]
θ range for data collection [°]
Reflections collected (I Ն 2σ(I))
Independent reflections
Final R indices [I Ͼ 2σ(I)][a]
Final wR2 indices (all data)[a]
Gof on F2
Abs. structure parameter[b]
Largest diff. peak and hole [eÅ–3]
0.05(8)
0.565 and –0.481
2
2 2
2
[a] R1 = Σ||Fo| – |Fc|| / Σ|Fo| and wR2 = {Σ[w(Fo – Fc ) ] / Σ[w(Fo
2]}1/2. [b] H. D. Flack, Acta Crystallogr. Sect. A 1983, 39, 876.
)
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2
scheme employed was w = [σ2(Fo + (0.0997P)2 + 0.4457P] and P
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CCDC-274550 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
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4350
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 4341–4351

Ruthenium Complexes as Catalysts in Acetophenone Hydrogen Transfer
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Received: June 8, 2005
Published Online: September 21, 2005
Eur. J. Inorg. Chem. 2005, 4341–4351
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4351