Triruthenium carbonyl clusters derived from chiral aminooxazolines: Synthesis and catalytic activity

Article abstract of DOI:10.1039/b517758h

Treatment of [Ru₃(CO)₁₂] with the chiral aminooxazolines (+)-2-amino-(4R)-phenyl-2-oxazoline (H₂amphox), (+)-2-amino-(4R,5S)-indanyl-2-oxazoline (H₂aminox) and (+)-2-(2′-anilinyl)-(4R,5S)-indanyl-2-oxazoline (H₂aninox) in THF at reflux temperature, affords the complexes [Ru₃(-H)( ₃-κ²-Hox-N,N)(CO)₉] (H₂ox = H₂amphox, 1; H₂aminox, 2) and [Ru₃(-H)(- κ²-Haninox-N,N)(CO)₉] (3). In all cases, the activation of an N-H bond has occurred and the resulting amido fragment spans an edge of the metal triangle, while the N atom of the oxazoline ring is attached to the remaining metal atom (as in 1 and 2), or to one of the metal atoms of the bridged edge (as in 3). The use of 1-3 as catalyst precursors in the asymmetric hydrogen-transfer reduction of acetophenone and in the asymmetric cycloaddition of cyclopentadiene and acroleine is reported. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b517758h

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Triruthenium carbonyl clusters derived from chiral aminooxazolines:
synthesis and catalytic activity
Javier A. Cabeza,a Iva´n da Silva,a Ignacio del R´ıo,*a Robert A. Gossage,*b Daniel Miguelc and Marta Sua´reza
Received 15th December 2005, Accepted 6th March 2006
First published as an Advance Article on the web 14th March 2006
DOI: 10.1039/b517758h
Treatment of [Ru3(CO)12] with the chiral aminooxazolines (+)-2-amino-(4R)-phenyl-2-oxazoline
(H2amphox), (+)-2-amino-(4R,5S)-indanyl-2-oxazoline (H2aminox) and (+)-2-(2ꢀ-anilinyl)-
(4R,5S)-indanyl-2-oxazoline (H2aninox) in THF at reflux temperature, affords the complexes
[Ru3(l-H)(l3-j2-Hox-N,N)(CO)9] (H2ox = H2amphox, 1; H2aminox, 2) and [Ru3(l-H)(l-j2-
Haninox-N,N)(CO)9] (3). In all cases, the activation of an N–H bond has occurred and the resulting
amido fragment spans an edge of the metal triangle, while the N atom of the oxazoline ring is attached
to the remaining metal atom (as in 1 and 2), or to one of the metal atoms of the bridged edge (as in 3).
The use of 1–3 as catalyst precursors in the asymmetric hydrogen-transfer reduction of acetophenone
and in the asymmetric cycloaddition of cyclopentadiene and acroleine is reported.
Introduction
A main focus of interest in current synthetic chemistry is
the preparation of novel chiral metal catalysts for asymmetric
processes.1 In contrast with the vast amount of mono- and
binuclear chiral complexes reported to date, transition metal
clusters containing chiral ligands are scarce.2–5 Apart from a
triruthenium derivative of levamisole6 and from a few triruthenium
Fig. 1 Carbonyl clusters derived from 2-aminopyridines.
and triosmium clusters with the chiral atropisomeric ligand (+)-
2,2ꢀ-diamino-1,1ꢀ-binaphthalene (H2binam),7 the remaining exam-
ples of chiral triruthenium clusters reported so far correspond to
species containing mono- or bidentate chiral phosphane ligands.
These latter complexes have been used as catalyst precursors in
asymmetric isomerization,4 hydroformylation5 or hydrogenation3
of unsaturated substrates. In most catalytic reactions, however,
the catalyst precursors have been prepared in situ and their nature
remains unknown.3 No other cluster complexes containing chiral
N-donor ligands have been reported to date.
small number of cluster complexes containing N-donor chiral
ligands known to date, prompted us to investigate the reactiv-
ity of [Ru3(CO)12] with chiral aminooxazoline ligands. Chiral
oxazolines and bis(oxazolines) are versatile ligands that are
easily prepared and thus have been used in a wide range of
asymmetric processes.14,15 The ligands chosen for this study are
(+)-2-amino-(4R)-phenyl-2-oxazoline (H2amphox), (+)-2-amino-
(4R,5S)-indanyl-2-oxazoline (H2aminox) and (+)-2-(2ꢀ-anilinyl)-
(4R,5S)-indanyl-2-oxazoline (H2aninox) (Fig. 2). The first two
contain an amino fragment in the oxazoline ring, while the amino
fragment of H2aninox is located on the phenyl ring.
During the last decade, our research group has thoroughly
studied the synthesis and reactivity of carbonyl clusters derived
from 2-aminopyridines.8,9 Most of these clusters are trinuclear
and contain a face-capping ligand that results from the activation
of an N–H bond, to give an edge-bridging amido fragment and a
hydride ligand, and from the coordination of the pyridine N atom
to the remaining metal atom (Fig. 1). Some of these complexes have
been recognized as catalytic precursors for the hydrogenation,10,11
dimerization,12 polymerization12 and hydroformylation13 of se-
lected alkynes.
The considerable experience of our group in the prepara-
tion and study of the above mentioned derivatives, and the
aDepartamento de Qu´ımica Orga´nica e Inorga´nica, Instituto de Qu´ımica
Organometa´lica “Enrique Moles”, Universidad de Oviedo-CSIC, E-33071,
Oviedo, Spain. E-mail: irc@fq.uniovi.es; Fax: 34 985103446
Fig. 2 The ligands H2amphox, H2aminox and H2aninox.
We describe herein the synthesis of trinuclear derivatives of
the types [Ru3(l-H)(l2,j2-Hox-N,N)(CO)9] and [Ru3(l-H)(l3,j2-
Hox-N,N)(CO)9] (H2ox = a generic aminooxazoline ligand).
These compounds represent the first examples of triruthenium
clusters containing oxazoline ligands. These complexes have been
bThe David Upton Hill Laboratory of Inorganic Chemistry, 6 University
Avenue, Elliott Hall, Department of Chemistry, Acadia University, Wolfville,
NS B4P 2R6, Canada. E-mail: rgossage@acadiau.ca
c
´
Area de Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad de Val-
ladolid, E-47071, Valladolid, Spain
2450 | Dalton Trans., 2006, 2450–2455
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tested as catalyst precursors in asymmetric transfer hydrogenation
and in a Diels–Alder reaction. The coordination chemistry of
aminooxazolines has not been studied previously, although related
amidooxazoline derivatives have been described.16
Results and discussion
Syntheses of compounds 1–3
Treatment of [Ru3(CO)12] with 1.2 equiv. of H2amphox or
H2aminox in THF at reflux temperature afforded, after chro-
matographic work-up, the trinuclear derivatives [Ru3(l-H)(l3-
j2-Hamphox-N,N)(CO)9] (1) and [Ru3(l-H)(l3-j2-Haminox-
N,N)(CO)9] (2), respectively (Scheme 1). Their trinuclear nature
and the presence of one equiv. of the ligand were clearly evidenced
from their elemental analyses and mass spectra, which showed
peaks corresponding to the molecular ions. The IR spectra of
both complexes in the carbonyl stretching region are identical, and
reflect only the presence of terminal CO ligands. These IR spectra
resemble that of [Ru3(l-H)(l3-j2-ampy-N,N)(CO)9] (H2ampy =
2-amino-6-methylpyridine),17 suggesting an analogous ligand ar-
rangement.
Fig. 3 Molecular view of 1. Ellipsoids are drawn at the 30% probability
level.
binds a Ru atom through the N atom of the oxazoline ring, while
the amido fragment bridges the other two metal atoms. A hydride
ligand spans the same metallic edge as the amido fragment. The
cluster shell is completed with nine terminal CO ligands.
A molecular plot of compound 2 is displayed in Fig. 4. The
ligand disposition in 2 is identical to that described above for
1. In both cases, the stereochemistry of the original oxazoline
ligand is maintained in the metal complex. The coordination of
the oxygen atom in the oxazoline ring was not observed in either
case. These two structures are analogous to that reported for
Scheme 1 Synthesis of compounds 1 and 2.
The activation of an N–H bond of the amino fragment was
1
clearly pointed out by the H NMR spectra of both complexes,
which showed a singlet resonance in the high field region
(−11.10 ppm for 1 and −11.09 ppm for 2), indicating the presence
of a hydride ligand, and a broad signal at 5.62 ppm for 1 and
1
5.57 ppm for 2, which correspond to the N–H proton. The 13C{ H}
NMR spectra of both complexes showed the presence of nine
terminal CO ligands and indicated the absence of C-metalation.
The absolute configurations of 1 and 2 were unambiguously
determined by X-ray diffraction methods. A selection of bond
lengths for both complexes is given in Table 1. For comparison
purposes, the same labelling scheme is used where possible. Fig. 3
shows a view of complex 1. The structure of 1 consists of a Ru3
triangle face-capped by the Hamphox ligand in such a way that it
˚
Table 1 Selected interatomic distances (A) in compounds 1–3
1
2
3
Ru(1)–Ru(2)
Ru(1)–Ru(3)
Ru(2)–Ru(3)
Ru(1)–N(1)
Ru(1)–N(2)
Ru(2)–N(1)
Ru(3)–N(2)
2.7528(11)
2.7773(9)
2.7600(9)
2.173(5)
—
2.159(5)
2.137(4)
2.7684(6)
2.7633(5)
2.7753(5)
2.142(3)
—
2.133(3)
2.170(3)
2.7819(9)
2.7950(12)
2.8238(12)
2.120(4)
2.123(3)
2.169(4)
—
Fig. 4 Molecular view of 2. Ellipsoids are drawn at the 30% probability
level.
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[Ru3(l-H)(l3-j2-ampy-N,N)(CO)9],17 in which an amido fragment
and a hydride atom bridge the same edge of the cluster, while the
third Ru atom is attached to the pyridine nitrogen atom.
When [Ru3(CO)12] was treated with 1.2 equiv. of H2aninox
under the same conditions as those described above for 1 and
2, the trinuclear derivative [Ru3(l-H)(l-j2-Haninox-N,N)(CO)9]
(3, Scheme 2) was obtained. The IR spectrum of 3 in the carbonyl
stretching region varies from that of 1 and 2, pointing to a different
ligand disposition. Its 1H NMR spectrum again showed a singlet
resonance at −12.03 ppm, indicating the presence of a hydride
ligand, and a broad signal at 6.69 ppm, attributable to an NH
fragment.
the high regio- and enantioselectivity observed in their synthesis
allowed us to undertake a study of some catalytic applications.
Catalytic activity
For the study of the asymmetric catalytic properties of 1–3, we
chose two well-known processes, i.e., the asymmetric hydrogen
transfer hydrogenation of acetophenone (Scheme 3) and the
[4 + 2]-cycloaddition reaction of cyclopentadiene and acroleine
(Scheme 4).
Scheme 3 Asymmetric hydrogenation of acetophenone.
Scheme 2 Synthesis of compound 3.
Scheme 4 Asymmetric Diels–Alder reaction.
The atom connectivity in 3 was unambiguously determined
by X-ray diffraction. A molecular plot of 3 is shown in Fig. 5.
A selection of bond distances is given in Table 1. The structure
consists of a metallic triangle in which two of the three Ru atoms
are attached to the Haninox ligand, in such a way that the amido
fragment spans the Ru(1)–Ru(2) edge, while the oxazoline ring
coordinates to Ru(1) through the N(2) atom. A hydride ligand
spans the same edge as the NH fragment. The cluster shell is
completed with nine terminal carbonyl ligands.
The different coordination behaviour observed for the H2aninox
ligand, which bridges only two of the three metal atoms and
chelates one of them through its two nitrogen atoms, is favoured by
the formation of a six-membered ring in 3. In contrast, the Ham-
phox and Haminox ligands would render highly constrained four-
membered rings when acting as chelating agents; consequently,
they prefer to adopt a face-capping disposition similar to that
observed in compounds 1 and 2.
Asymmetric hydrogenation of acetophenone. The catalysis re-
sults are summarized in Table 2. Reactions were carried out in
refluxing isopropanol, using 0.025 mmol of catalyst and 5 mmol
of acetophenone (0.5% of catalyst with respect to the ketone).
Potassium hydroxide (0.34 M solution in isopropanol) was used
as co-catalyst in a 4 : 1 ratio with respect to the catalyst.
No reaction was observed when the free aminooxazoline ligands
were used as pre-catalysts (Table 2, entry 2). When [Ru3(CO)12] was
used as the pre-catalyst in the presence of the oxazoline ligands,
the conversion was always lower than 5%, suggesting that these
species do not catalyse this process in an effective way (entries
3–5). However, when compounds 1–3 were used as pre-catalysts,
quantitative conversion was observed after 10 h, the most active
catalyst being the H2aninox derivative 3, which afforded a TOF
of 200 h−1 (entries 6–8). The ee values observed were similar in all
cases, the highest being 20% for complex 1.
Complexes 1–3 are the first cluster complexes containing oxazo-
line ligands and they also represent rare examples of metal clusters
containing N-donor chiral ligands. Their easy preparation and
In this process, the catalysis is assumed to follow the hydride
route mechanism, in which the pre-catalyst would react with
Fig. 5 Molecular view of 3. Ellipsoids are drawn at the 30% probability level.
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Table 2 Asymmetric hydrogenation of acetophenone
t/h TOFa/h−1 Conv. (%) ee (%)
yields mixtures of products that result in moderate conversions
and no enantiomeric excesses. The low activity observed for
compounds 1–3 in this process prevented us from attempting to
improve the ee by lowering the temperature.
It is well established that the use of ancillary ligands which
bind the three metal atoms often prevents cluster fragmentation
during catalytic reactions.10,11,20 However, it has also been proven
that some trinuclear complexes having edge-bridging ligands lead
to mononuclear catalytic species.21 Without kinetic data, the
nuclearity of the real catalytic species involved in the reactions
described in this contribution cannot be unequivocally assigned.
Entry Pre-catalyst
1
2
3
4
5
—
H2ox
24
24
—
—
—
—
—
—
—
3
4
5
99
99
99
62
72
51
—
—
—
—
[Ru3(CO)12] + H2amphox 10
[Ru3(CO)12] + H2aminox 10
[Ru3(CO)12] + H2aninox 10
—
6
1
2
3
1
2
3
10 144
10 160
10 200
20(S)
19(S)
18(S)
18(S)
15(S)
16(S)
7
8
9b
10b
11b
10
10
10
65
85
91
a TOF at t = 10 min. b No KOH added.
Conclusions
The first examples of trinuclear clusters containing oxazoline-
type ligands are described. Compounds 1–3 represent three of
the few examples of triruthenium carbonyl clusters containing
chiral N-donor ligands known so far. These complexes catalyse
efficiently the hydrogen-transfer asymmetric hydrogenation of
acetophenone, although the ees obtained are low. However, these
complexes present low activity when used as catalyst precursors
in an asymmetric Diels–Alder reaction. No previous examples of
the use of trinuclear species as catalyst precursors for these two
processes have been reported.
the KOH to generate an active species which contains at least
one hydride ligand. This hydride ligand would be subsequently
transferred to the acetophenone.18 Since compounds 1–3 already
contain a hydride ligand, we performed the catalytic reactions
under the same conditions but without KOH (Table 2, entries
9–11). In this case, however, the processes were slower, resulting
in lower conversions and TOF, while the enantiomeric excesses
observed were in the same range. This lower activity can be
explained by assuming that the role played by the KOH is not
only to generate a hydride ligand but also to create a vacant
coordination site that facilitates the interaction of the incoming
substrate with the active hydride species. The nucleophilic attack
of a hydroxy group onto a coordinated carbonyl ligand to generate
CO2 and a hydride species is a well documented process.19
Experimental
General Data
Solvents were dried over sodium diphenyl ketyl (hydrocarbons,
THF) or CaH2 (dichloromethane, isopropanol) and distilled
under nitrogen prior to use. The reactions were carried out
under nitrogen, using Schlenk vacuum line techniques, and
were routinely monitored by solution IR spectroscopy (car-
bonyl stretching region) and spot TLC. (+)-2-Amino-(4R)-
phenyl-2-oxazoline (H2amphox),22 (+)-indanyl-2-amino-(4R,5S)-
2-oxazoline (H2aminox)23 and (+)-indanyl-2-(2ꢀ-anilinyl)-(4R,
5S)-2-oxazoline (H2aninox)23 were prepared as previously re-
ported. IR spectra were recorded in solution on a Perkin-Elmer
Paragon 1000 FT spectrophotometer. 1H NMR spectra were run
on a Bruker DPX-300 instrument, at room temperature, using
the dichloromethane solvent resonance as internal standard (d =
5.30). Microanalyses were obtained from the University of Oviedo
Analytical Service. FAB-MS were obtained from the University of
Santiago de Compostela Mass Spectrometric Service; data given
refer to the most abundant molecular ion isotopomer.
[4 + 2]-Cycloaddition of cyclopentadiene and acroleine. The
results are collected in Table 3. Reactions were carried out in
dichloromethane at room temperature, dissolving 0.025 mmol
of metal complex (5% with respect to acroleine), 3 mmol of
cyclopentadiene and 0.5 mmol of acroleine. Me3NO (0.025 mmol)
was used as the CO abstractor.
The reaction proceeded in the absence of catalyst to afford the
final adduct with an endo to exo ratio of ca. 80 : 20 and a ca.
20% conversion after 2 h (Table 3, entry 1). No significant changes
were observed in conversion nor in regioselectivity when the chiral
ligands (entry 2) or when [Ru3(CO)12] in the presence of the chiral
oxazolines (entries 3–5) were used as catalyst precursors.
When compounds 1–3 were employed (entries 6–8), conversions
went up to 80% after 2 h, with a TOF of 25 h−1 at a reaction time
of 10 min. Unfortunately, no enantiomeric excesses were obtained
in any case. It seems that the use of Me3NO as the CO abstractor
Table 3 Asymmetric cycloaddition of cyclopentadiene and acroleine
Entry
Pre-catalyst
TOFa/h−1
Conv.b (%)
Endo : exo
ee (%)
1
2
3
4
5
6
7
8
—
H2ox
—
—
—
—
—
20
22
25
19
19
18
18
20
77
74
80
79 : 21
80 : 20
81 : 19
80 : 20
79 : 21
86 : 14
88 : 12
90 : 10
—
—
—
—
—
—
—
—
[Ru3(CO)12] + H2amphox
[Ru3(CO)12] + H2aminox
[Ru3(CO)12] + H2aninox
1
2
3
a TOF at t = 10 min. b t = 2 h.
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Syntheses
removal (65 mg, 58%). Calcd for C19H10N2O10Ru3 (729.50): C,
31.28; H, 1.38; N, 3.84. Found: C, 31.40; H, 1.39; N, 3.72. FAB-
MS (m/z): 731 [M+]. IR (CH2Cl2): mCO = 2082 (m), 2051 (s), 2030
(vs), 1996 (s, br), 1960 (w, sh) cm−1. 1H NMR (CD2Cl2): d 7.64 (d,
J = 6.0 Hz, 1 H; CH), 7.40–7.32 (m, 3 H; CH), 5.80 (td, J = 7.9,
3.5 Hz, 1 H; CH), 5.57 (s, br, 1 H, NH), 4.95 (d, J = 7.9 Hz, 1 H;
CH), 3.53 (dd, J = 17.8, 7.9 Hz, 1 H; CH), 3.12 (dd, J = 17.8,
[Ru3(l-H)(l3-j2-Hamphox-N,N)(CO)9] (1).
A solution of
[Ru3(CO)12] (100 mg, 0.156 mmol) and (+)-2-amino-(4R)-phenyl-
2-oxazoline (30.5 mg, 0.187 mmol) in THF (30 mL) was stirred
at reflux temperature for 20 min. The colour changed from yellow
to orange. The solution was concentrated under reduced pressure
to ca. 3 mL and the residue was set onto a silica gel column
(2 × 15 cm) packed in hexane. Elution with hexane afforded a
small amount of unreacted [Ru3(CO)12]. Elution with hexane–
dichloromethane (8 : 1) afforded an orange band from which
compound 1 was obtained as an orange solid after solvent removal
(70 mg, 63%). Calcd for C18H10N2O10Ru3 (717.48): C, 30.13; H,
1.40; N, 3.90. Found: C, 30.62; H, 1.46; N, 3.83. FAB-MS (m/z):
719 [M+]. IR (CH2Cl2): mCO = 2082 (m), 2051 (s), 2030 (vs), 1996
(s, br), 1960 (w, sh) cm−1. 1H NMR (CD2Cl2): d 7.50–7.35 (m, 5 H;
CH), 5.62 (s, br, 1 H, NH), 5.06 (t, J = 9.5 Hz, 1 H; CH), 4.59 (t,
J = 9.5 Hz, 1 H; CH), 4.54 (t, J = 9.5 Hz, 1 H; CH), −11.10 (s,
1
3.5 Hz, 1 H; CH) −11.09 (s, 1 H; l-H). 13C{ H} NMR (DEPT,
CD2Cl2): d 207.8, 205.7, 204.1, 203.2, 201.8, 200.5, 197.4, 195.5,
194.7 (9 CO); 181.3, 139.8, 137.4 (3 C); 130.3, 127.8, 126.9, 125.5,
87.8, 74.6 (6 CH); 39.7 (CH2).
[Ru3(l-H)(l-j2-Haninox-N,N)(CO)9] (3).
A
solution of
[Ru3(CO)12] (100 mg, 0.156 mmol) and (+)-indanyl-2-(2ꢀ-anilinyl)-
(4R,5S)-2-oxazoline (47 mg, 0.187 mmol) in THF (30 mL) was
stirred at reflux temperature for 2.5 h, whereupon the colour
changed from yellow to orange. The solution was concentrated
under reduced pressure to ca. 3 mL and the residue was set onto
a silica gel column (2 × 15 cm) packed in hexane. Elution with
hexane afforded a small amount of unreacted [Ru3(CO)12]. Elution
with hexane–dichloromethane (4 : 1) afforded a yellow band from
which compound 3 was obtained as a yellow solid after solvent
removal (85 mg, 67%). Calcd for C25H14N2O10Ru3 (805.59): C,
37.27; H, 1.75; N, 3.47. Found: C, 37.90; H, 1.86; N, 3.27. FAB-
MS (m/z): 807 [M+]. IR (CH2Cl2): mCO = 2086 (m), 2048 (vs),
2004 (s, br), 1986 (m, sh), 1972 (w, sh), 1933 (w) cm−1. 1H NMR
(CD2Cl2): d 8.21 (t, J = 5.5 Hz, 1 H; CH), 7.90 (d, J = 6.6 Hz, 1 H;
CH), 7.47–7.36 (m, 5 H; CH), 7.05 (t, J = 6.6 Hz, 1 H; CH), 6.69
(s, br, 1 H, NH), 6.08 (d, J = 7.4 Hz, 1 H; CH), 5.52 (ddd, J =
7.4, 7.2, 3.6 Hz, 1 H; CH), 3.79 (dd, J = 17.9, 3.6 Hz, 1 H; CH),
1 H; l-H). 13C{ H} NMR (DEPT, CD2Cl2): d 206.4, 205.1, 204.1,
1
202.9, 202.0, 200.5, 198.7, 197.3, 195.4 (9 CO); 181.3, 136.4 (2 C);
128.4, 128.2 (×2), 127.3 (×2), 68.7 (6 CH); 77.4 (CH2).
[Ru3(l-H)(l3-j2-Haminox-N,N)(CO)9] (2).
A solution of
[Ru3(CO)12] (100 mg, 0.156 mmol) and (+)-indanyl-2-amino-
(4R,5S)-2-oxazoline (32.6 mg, 0.187 mmol) in THF (30 mL) was
stirred at reflux temperature for 30 min, whereupon the colour
changed from yellow to orange. The solvent was removed under
reduced pressure to ca. 3 mL and the residue was set onto a silica
gel column (2 × 15 cm) packed in hexane. Elution with hexane
afforded a small amount of unreacted [Ru3(CO)12]. Elution with
hexane–dichloromethane (7 : 1) afforded a yellow band from which
compound 2 was obtained as a bright yellow solid after solvent
1
−12.03 (s, 1 H; l-H). 13C{ H} NMR (DEPT, CD2Cl2): d 207.0,
206.1, 205.5, 202.9, 200.9, 198.9, 198.0, 192.3, 184.0 (9 CO); 161.9,
Table 4 Selected crystal, measurement and refinement data for compounds 1–3
1
2
3
Formula
C18H10N2O10Ru3
717.49
Orthorhombic
P212121
C19H10N2O10Ru3
729.50
Orthorhombic
P212121
C25H14N2O10Ru3
805.59
Orthorhombic
P212121
Formula weight
Crystal system
Space group
˚
a/A
8.579(3)
7.466(1)
7.758(3)
˚
b/A
13.436(6)
19.870(8)
2290.5(16)
4
1376
2.081
15.525(3)
19.898(4)
2306.4(7)
4
1400
2.101
17.703(7)
19.581(8)
2689(2)
˚
c/A
3
˚
V/A
Z
4
F(000)
1560
1.990
Mo Ka (0.71073)
1.722
Dc/g cm−3
˚
Radiation (k/A)
Mo Ka (0.71073)
2.008
Mo Ka (0.71073)
1.996
l/mm−1
Crystal size/mm
Temperature/K
0.22 × 0.21 × 0.10
0.30 × 0.24 × 0.23
0.34 × 0.10 × 0.07
296(2)
296(2)
293(2)
h limits/◦
1.83 to 23.31
−9/9, −14/14, −22/22
14753
3303
3177
SADABS
0.818/0.687
306/0
1.086
0.0228
1.66 to 23.27
−8/8, −17/17, −22/22
15461
3316
3278
SADABS
0.819/0.629
316/0
1.030
0.0147
1.55 to 23.25
−8/8, −19/19, −21/21
17278
3872
3683
SADABS
0.886/0.713
359/0
1.047
0.0212
Min/max h, k, l
Collected reflections
Unique reflections
Reflections with I > 2r(I)
Absorption correction
Max/min transmission
Parameters/restraints
GOF on F2
R1 (on F, I > 2r(I))
wR2 (on F2, all data)
0.0525
0.0367
0.0495
−3
˚
Max/min Dq/e A
0.303/−0.375
0.224/−0.215
0.488/v0.352
−0.03(4)
Absolute structure parameter
−0.05(4)
−0.04(3)
2454 | Dalton Trans., 2006, 2450–2455
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161.7, 140.2, 139.2, 113.4 (5 C); 133.5, 130.7, 129.7, 127.7, 126.2,
125.6, 124.7, 122.6, 81.8, 81.7 (10 CH); 38.6 (CH2).
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Hydrogen transfer reactions
All reactions were carried out in Schlenk tubes under nitrogen, us-
ing magnetic stirrers and thermostated oil baths. Isopropanol was
used as solvent. Acetophenone was distilled under nitrogen prior
to use. In a typical experiment, the metal complex (0.025 mmol),
KOH (0.1 mmol, solution 0.34 M in isopropanol) and 20 mL of
isopropanol were introduced in a Schlenk tube and the mixture
was heated to reflux temperature. After 10 min, acetophenone
(5 mmol) was added. Conversions and enantiomeric excesses were
determined by GC, using a chiral GAMMA-DEX fused-silica cap-
illary column (0.25 mm id) and p-xylene as the internal standard.
3 P. Homanen, R. Persson, M. Haukka, T. A. Pakkanen and E.
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M. G. Sa´nchez-Vega, Organometallics, 2003, 22, 1519.
8 For a review on the reactivity of triruthenium carbonyl clusters derived
from 2-aminopyridines, see: J. A. Cabeza, Eur. J. Inorg. Chem., 2002,
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9 For recent articles uncovered by ref. 8, see: (a) J. A. Cabeza, I. del R´ıo,
S. Garc´ıa-Granda, V. Riera and M. Sua´rez, Organometallics, 2002, 21,
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Sua´rez, Organometallics, 2002, 21, 5055; (c) J. A. Cabeza, I. del R´ıo, M.
Moreno, S. Garc´ıa-Granda, M. Pe´rez-Priede and V. Riera, Eur. J. Inorg.
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11 For a review on alkyne hydrogenation mediated by 2-amidopyridine-
bridged triruthenium carbonyl cluster complexes, see: J. A. Cabeza,
J. M. Ferna´ndez-Colinas and A. Llamazares, Synlett, 1995, 579.
12 P. Nombel, N. Lugan, F. Mulla and G. Lavigne, Organometallics, 1994,
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13 P. Nombel, N. Lugan, B. Donnadieu and G. Lavigne, Organometallics,
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14 For reviews on the chemistry of oxazoline ligands and their use in
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15 For reviews on the use of bis(oxazoline) ligands in asymmetric
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16 A. Decken, R. A. Gossage and P. N. Yadav, Can. J. Chem., 2005, 83,
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Asymmetric Diels–Alder reactions
Reactions were carried out using dichloromethane as solvent. Cy-
clopentadiene was freshly obtained from its dimer by distillation.
Acroleine was distilled under nitrogen prior to use. In a typical
experiment, the metal complex (0.025 mmol), cyclopentadiene
(3 mmol, dissolved in 2 mL of dichloromethane), acroleine
(0.5 mmol, dissolved in 2 mL of dichloromethane), Me3NO
(0.025 mmol) and 10 mL of dichloromethane were placed into
a Schlenk tube and the mixture was stirred in a thermostated
bath. Conversion data, the endo : exo ratio and the enantiomeric
excesses were determined by GC using a chiral GAMMA-DEX
fused-silica capillary column (0.25 mm id) and p-xylene as the
internal standard.
X-Ray crystallography
A selection of crystal, measurement and refinement data for
compounds 1–3 is collected in Table 4. Diffraction data were
measured at room temperature on a Bruker AXS SMART 1000
diffractometer, using graphite-monochromated Mo Ka radia-
tion. Semi-empirical absorption corrections were applied with
SADABS.24 Structures were solved by direct methods and refined
by full matrix least-squares against F2 with SHELXTL.25 All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were set in calculated positions and refined as riding atoms. The
molecular plots were made with the PLATON program package.26
The WINGX program system27 was used throughout the structure
determinations.
17 P. L. Andreu, J. A. Cabeza, V. Riera, Y. Jeannin and D. Miguel, J. Chem.
Soc., Dalton Trans., 1990, 2201.
18 (a) A. Aranyos, G. Csjernyik, K. J. Szabo´ and J. E. Ba¨ckvall, Chem.
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19 See, for example: (a) W. Schatz, H. P. Neumann, B. Nuber, B.
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Cabeza, I. del R´ıo, V. Riera and F. Grepioni, Organometallics, 1995,
14, 3124.
CCDC reference numbers 293020–293022.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b517758h
20 J. A. Cabeza, J. M. Ferna´ndez-Colinas, A. Llamazares, V. Riera, S.
Garc´ıa-Granda and J. F. van der Maelen, Organometallics, 1994, 13,
4352.
Acknowledgements
21 J. A. Cabeza, J. M. Ferna´ndez-Colinas, A. Llamazares and V. Riera,
Organometallics, 1992, 11, 4355.
22 G. I. Poos, J. R. Carson, J. D. Rosenau, A. P. Roszkowski, N. M. Kelley
and J. McGowin, J. Med. Chem., 1963, 6, 266.
23 K. M. Button and R. A. Gossage, J. Heterocycl. Chem., 2003, 40, 513.
24 G. M. Sheldrick, SADABS, Empirical Absorption Correction Program,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
25 G. M. Sheldrick, SHELXTL, An Integrated System for Solving,
Refining, and Displaying Crystal Structures from Diffraction Data,
Version 5.1, Bruker AXS Inc., Madison, WI, 1998.
This work was supported by the Spanish MEC-MCyT research
projects BQU2002-2623 (to J.A.C.) and BQU2002-3414 (to D.M.)
and by the Natural Sciences and Engineering Research Council of
Canada (NSERC, research project to R.A.G.).
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27 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
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