Chiral pyridylamino-ruthenium(ii) complexes: Synthesis, structure and catalytic properties in Diels-Alder reactions

Article abstract of DOI:10.1039/b802381f

Half-sandwich complexes [(η⁶-arene)RuCl(pyam)][SbF ₆] (pyam = L_n = N-(2-pyridylmethyl)-(R)-1-phenylethylamine (L₁), N-(2-pyridylmethyl)-(R)-1-naphthylethylamine (L₂), N-(2-quinolylmethyl)-(R)-1-naphthylethylamine (L₃), N-(2-pyridylmethyl)-(R)-1-cyclohexylethylamine (L₄), N-(2-pyridylmethyl)-(1R,2S,4R)-1-bornylamine (L₅)) have been synthetised and characterised. Treatment of these compounds with AgSbF ₆ generates dicationic complexes [(η⁶-arene)Ru(pyam) (H₂O)]²⁺ which act as enantioselective catalysts for the Diels-Alder reactions of methacrolein and cyclopentadiene. The catalytic reactions occur quickly at room temperature with good exo: endo selectivity (from 84: 16 to 98: 2) and moderate enantioselectivity (up to 74% ee). The molecular structures of the chloride complexes (R_Ru,S _N,R_C)-[(η⁶-p-MeC₆H ₄iPr)RuClL₁][SbF₆], (R_Ru,S _N,S_C2)-[(η⁶-p-MeC₆H ₄iPr)RuClL₅][SbF₆], and that of the aqua complex (R_Ru,S_N,S_C2)-[(η⁶-p- MeC₆H₄iPr)RuL₅(H₂O)][SbF ₆]₂, were determined by X-ray diffractometric methods. The distinctive variations observed in the molecular structures of these complexes only concern the puckering parameters of the metallacycle and the relative disposition of substituents within this ring. A clear trend to localise the most steric demanding substituents at equatorial positions is evident from the structural study. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b802381f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Chiral pyridylamino-ruthenium(II) complexes: synthesis, structure and
catalytic properties in Diels–Alder reactions†
Daniel Carmona,* M. Pilar Lamata,* Fernando Viguri, Ricardo Rodr´ıguez, Fernando J. Lahoz, Isabel T.
Dobrinovitch and Luis A. Oro
Received 12th February 2008, Accepted 2nd April 2008
First published as an Advance Article on the web 14th May 2008
DOI: 10.1039/b802381f
6
Half-sandwich complexes [(g -arene)RuCl(pyam)][SbF6] (pyam = Ln =
N-(2-pyridylmethyl)-(R)-1-phenylethylamine (L1), N-(2-pyridylmethyl)-(R)-1-naphthylethylamine (L2),
N-(2-quinolylmethyl)-(R)-1-naphthylethylamine (L3), N-(2-pyridylmethyl)-(R)-1-cyclohexylethylamine
(L4), N-(2-pyridylmethyl)-(1R,2S,4R)-1-bornylamine (L5)) have been synthetised and characterised.
Treatment of these compounds with AgSbF6 generates dicationic complexes
6
[(g -arene)Ru(pyam)(H2O)]2+ which act as enantioselective catalysts for the Diels–Alder reactions of
methacrolein and cyclopentadiene. The catalytic reactions occur quickly at room temperature with
good exo : endo selectivity (from 84 : 16 to 98 : 2) and moderate enantioselectivity (up to 74% ee). The
6
molecular structures of the chloride complexes (RRu ,SN,RC)-[(g -p-MeC6H4iPr)RuClL1][SbF6],
6
(RRu ,SN,SC2)-[(g -p-MeC6H4iPr)RuClL5][SbF6], and that of the aqua complex
6
(RRu ,SN,SC2)-[(g -p-MeC6H4iPr)RuL5(H2O)][SbF6]2, were determined by X-ray diffractometric methods.
The distinctive variations observed in the molecular structures of these complexes only concern the
puckering parameters of the metallacycle and the relative disposition of substituents within this ring. A
clear trend to localise the most steric demanding substituents at equatorial positions is evident from the
structural study.
C2-symmetry, and L3 represents a good leaving group, usually
Introduction
a solvent molecule. In particular, we have shown the ability
of R-Prophos–Rh(III),12 –Ir(III),13 phosphinooxazoline–Rh(III),
The Diels–Alder (DA) reaction is one of the most powerful con-
–Ir(III),14 –Ru(II), and –Os(II)15,16 and pyridylimino–Ir(III),17
–
struction processes in organic synthesis, specially for the formation
of molecules containing up to four contiguous stereogenic centres.
For this reason there has been much research on the development
of enantioselective versions of this reaction. In this context, very
impressive results have been reported for enantioselective DA
reactions catalysed by chiral Lewis acids.1 Among the numerous
chiral Lewis acid catalysts described so far, in terms of activity,
selectivity and catalyst stability, especially interesting are those
developed by the groups of Narasaka (Ti–TADDOLates)2 and
Evans (Cu–bis(oxazolines))3 successfully employed for enantio-
control in the DA reaction of 3-alkenoyl-1,2-oxazolidin-2-one as
dienophile, and the borane compounds prepared by Corey4 and
Yamamoto,5 excellent catalysts for the asymmetric DA reaction of
a,b-unsaturated aldehydes as dienophiles.
Our work in this area has focused on the development of
one-point-binding half-sandwich catalysts. Recently, cationic half-
sandwich complexes of general formula [(g -ring)M(L1L2)*L3]n+
have been used as chiral catalysts in enantioselective DA reactions
by the groups of Ku¨ndig,6–7 Faller,8 Davies,9–11 and by ourselves.12–19
In these compounds, the metal belongs to Group 8 or 9 (Fe, Ru,
Os, Rh, Ir), the chiral chelate ligand (L1L2)*, with P,P-, P,N-
, N,N-, N,O-, or P,O- sets of donor atoms, possesses C1 or
Rh(III), and –Ru(II)18 complexes to act as catalysts, for the DA
reaction between methacrolein and cyclopentadiene. In general,
moderate to good inductions were obtained. Moreover, we have
recently proved that whereas for the pyridylimino–iridium com-
5
plexes [(g -C5Me5)Ir(pyridylimine)(H2O)][SbF6]2 enantioselectivi-
ties up to 46% were achieved, for the closely related pyridylamino
5
(pyam) compounds [(g -C5Me5)Ir(pyam)(H2O)][SbF6]2, enantios-
electivities of up to 72% were obtained.20 Taking into account these
results, we planned to test pyridylamino–ruthenium complexes of
6
general formula [(g -arene)Ru(pyam)(H2O)][SbF6]2 as catalysts for
the enantioselective DA reactions.
In the present paper we report the preparation of new chloride
6
complexes of formula [(g -arene)RuCl(pyam)][SbF6] (1–7) which
6
are precursors of the aqua solvates [(g -arene)Ru(pyam)(H2O)]-
[SbF6]2 (8–14) (Scheme 1) and the use of the latter complexes
as catalysts for the above mentioned Diels–Alder reaction. The
molecular structural details of three representative complexes,
determined by X-ray diffraction methods, are also discussed.
n
Results and discussion
Preparation of the chloride complexes 1–7
Departamento de Qu´ımica Inorga´nica, InstitutoUniversitario de Cata´lisis
Homoge´nea, Instituto de Ciencia de Materiales de Arago´n, Universidad de
Zaragoza-Consejo Superior de Investigaciones Cient´ıficas, 50009, Zaragoza,
Spain
† CCDC reference numbers 678437–678439. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b802381f
At room temperature the dimers21 [{(g -arene)RuCl}2(l-Cl)2]
6
(arene = p-MeC6H4iPr, C6H6, C6Me6) react, in methanol, in
the presence of NaSbF6, with stoichiometric amounts of the
corresponding pyridylamine L1–L5 (Scheme 1), to give the new
3328 | Dalton Trans., 2008, 3328–3338
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slowly isomerises and, after 2 months, a mixture highly enriched in
3b is recovered (3a : 3b : 3c : 3d, 2 : 94 : 2 : 2). In refluxing methanol
all the cations isomerise with no apparent decomposition. The
invariable composition achieved after 24 h of treatment is also
collected in the Experimental section. On the other hand, due
to the different solubility in methanol, it has proved possible to
obtain diastereomers 1a, 3a and 5a, in essentially complete optical
purity (>98% by 1H NMR).
The complexes were characterised by IR and NMR spec-
troscopy, elemental analysis and from the crystal structure de-
termination for compounds 1a and 5a. In all cases, the 1H
NMR spectroscopic data were consistent with the presence of
6
the g -arene group and the chelate pyridylamine ligand in a 1 :
1 ratio. Stereochemical assignments were accomplished through
NOE experiments. A general feature is the absence of NOE
between the NH and C*H protons which is consistent with an
anti conformation for these protons around the N–C* bond. This
conformation has been suggested as an structural constant in all
the molecular structures of half-sandwich complexes containing
pyridylamine ligands, determined until now by X-ray diffraction
methods.20 The stereochemical assignment can be accomplished
assuming that the anti rotamer is also the most favoured in
solution. Thus, for example, while irradiation of Ha (Fig. 1) induces
enhancement of the methyl of the p-cymene ligand in complexes 1a
and 5a, it does not alter this methyl group in 3a and 7a. Conversely,
when Hb was irradiated, NOE enhancements were encountered in
the methyl substituent of the p-cymene ligand in 3a and 7a, but
not in 1a and 5a. Moreover, while the irradiation of the Hc or Hd
induces enhancement of the methyl group of the amine ligand (Mea
for the bornylamine ligand L5) in complexes 1a, 3a, and 5a, NOE
enhancements were encountered in the naphthyl protons of the
amine ligand, when the Hd proton of complex 7a was irradiated.
Taken together all these NOE observations, an R configuration at
ruthenium and an S configuration at nitrogen can be assigned to
complexes 1a and 5a, an SRu SN configuration to 3a and an RRu RN
to 7a. Following a similar reasoning an RRu SN configuration was
assigned to isomers 2a and 3b.
Scheme 1 Complex numbering scheme.
6
pyridylamino compounds [(g -arene)RuClLn][SbF6] in 78–95%
chemical yield. During the formation of the chloride complexes,
the ruthenium and the amine nitrogen become chiral centres and,
as the chiral pyridylamine ligand is enantiopure (RC for L1–
L4 and 1R,2S,4R for L5), the new compounds are prepared
as diastereomeric mixtures of up to four diastereomers, RRu SN,
SRu RN, SRu SN, RRu RN, depending on the configuration adopted by
the metal and nitrogen atoms.22 In most cases, mixtures of the four
diastereomers are obtained. The composition of these mixtures
is gathered in the Experimental section. The isomer ratio was
obtained from accurate integration of corresponding Ha or Hh
proton signals (for proton labelling, see Chart 1). Labels a, b, c,
and d arrange the diastereomers by yield percentage; label a refers
to the major component and d to the least abundant one.
At room temperature, in acetone, both the ruthenium and
nitrogen atoms are configurationally stable, the composition of the
mixtures remaining unchanged for days. As an exception, pure 3a
The CD spectra of these complexes are compatible with
the above-assigned configurations at ruthenium atom. Thus,
Chart 1 Labelling of the ligands for NMR assignments.
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Fig. 2 Selected NOE for the aqua complexes.
Fig. 1 Selected NOE for chloride complexes.
the main features of pure or highly enriched mixtures in the
RRu distereomers 1a, 3b or 5a, are two maxima with positive
Cotton effect centred within the ranges 310–345 and 415–420 nm.
Moreover, the CD spectra of pure 3a, and 3b (94% purity) display
a pseudo-enantiomorphic relationship, showing that the major
contribution to the spectra most probably corresponds to the metal
chromophore.
Fig. 3 Molecular structure of complex 1a. Only hydrogens bonded to the
chiral N(2) and C(17) atoms are included in the drawing.
Preparation of the solvated complexes 8–14
At room temperature, the chloride complexes 1–7 react with
AgSbF6 to give diastereomeric mixtures of the solvated com-
6
pounds [(g -arene)RuLn(H2O)][SbF6]2 (see Scheme 1).
The aqua complexes were characterized by IR and NMR
spectroscopy, elemental analysis and from the crystal structure
determination of compound 12a. The IR spectra show absorptions
in the 3400–3650 and 1650–1690 cm−1 regions, and, in most
cases, the 1H NMR spectra show peaks, in the 5.6–7.5 ppm
range, both characteristics assignable to the presence of coordi-
nated water. Stereochemical assignments have been accomplished
through NOE experiments. As stated above, the absence of NOE
between the NH and C*H protons is consistent with an anti
conformation around the N–C* bond. Following the method
detailed above for the parent chlorides, we have assigned the
RRu SN and RRu RN configuration to the most abundant isomer 12a
and 14a, respectively.22 The existence of NOE between NH (12a)
or C*H (14a) and the water protons corroborates the assigned
configuration (Fig. 2).
Fig. 4 Molecular structure of diastereomer 5a. Only hydrogens of the
chiral N(2) and C(17) atoms have been represented.
6
geometries. A g -p-MeC6H4iPr group occupies three fac positions,
and the chelating amine ligand and one chlorine atom (1a, 5a)
or one water molecule (12a) complete the coordination sphere
of the metal. The absolute configuration of the metal centre is
R in all the three complexes, according with the ligand priority
6
sequence g -arene > Cl/O > N(py) > N(am). Similarly, after
Molecular structure of the diastereomers 1a, 5a and 12a
metal coordination, the aminic nitrogen atom also becomes chiral,
showing in the three molecules an S absolute configuration.22
As a general structural feature, most of the relevant metal-to-
ligand bond distances are similar in both chloride complexes, 1a
and 5a, and comparable to those observed in the isoelectronic
Ir(III) complexes [Cp*IrCl(pyam)]+ (pyam = L1 or L5)20 or those
Single crystals of the complexes were grown by slow diffusion of
diethyl ether into acetone (1a and 5a) or dichloromethane (12a)
solutions. Molecular representations of the cations are depicted in
Fig. 3–5 and selected structural parameters are listed in Table 1.
All the three cationic complexes exhibit “three-legged piano-stool”
3330 | Dalton Trans., 2008, 3328–3338
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reported in the closely related pyridylimine complexes.17,18
As it was observed in these cases, the different electronic nature
of the two coordinated nitrogen atoms, pyridinic (N(1)) or aminic
(N(2)), originates substantial differences in the Ru–N bond
distances, with those of the pyridinic nitrogens being shorter
than those of the aminic analogues (see Table 1). Most probably,
the easy accessibility of the p orbitals of the pyridine ring could
contribute to a reinforcement of the Ru–N(1) bond through an
additional p interaction with the occupied metal d-orbitals.23
These differences in the Ru–N bond interactions have a clear
effect on the other side of the metal coordination sphere causing
statistically different Ru–C(arene) bond lengths (in the range
◦
˚
Table 1 Selected bond distances (A) and angles ( ) for complexes 1a, 5a
and 12a
1a
2.3841(16)
5a
2.3934(10)
12a
2.131(4)
Ru–Cl/O
Ru–N(1)
Ru–N(2)
Ru–C(1)
Ru–C(2)
Ru–C(3)
Ru–C(4)
Ru–C(5)
2.090(5)
2.167(5)
2.204(7)
2.176(7)
2.207(7)
2.247(6)
2.170(6)
2.148(6)
1.681(3)
1.315(9)
1.363(9)
1.468(9)
1.463(8)
1.519(7)
82.53(15)
83.28(14)
127.80(11)
77.5(2)
2.089(4)
2.154(4)
2.218(4)
2.189(4)
2.206(4)
2.241(5)
2.185(5)
2.198(4)
1.6903(19)
1.350(5)
1.344(6)
1.508(6)
1.478(6)
1.510(5)
84.64(9)
82.93(10)
128.68(7)
76.58(14)
130.52(13)
134.30(11)
124.7(3)
115.8(3)
115.2(4)
108.8(4)
106.8(2)
118.8(3)
114.1(3)
0.46(12)
2.012(6)
2.136(5)
2.162(7)
2.158(6)
2.183(6)
2.208(7)
2.170(6)
2.164(6)
1.664(3)
1.371(7)
1.334(7)
1.510(8)
1.476(7)
1.486(7)
86.49(18)
80.39(17)
130.44(15)
76.63(19)
127.94(17)
135.49(17)
126.7(4)
118.3(5)
113.4(6)
109.2(5)
106.8(3)
120.5(4)
111.8(5)
1.39(16)
Ru–C(6)
Ru–GGa
˚
N(1)–C(11)
N(1)–C(15)
C(15)–C(16)
N(2)–C(16)
N(2)–C(17)
Cl/O–Ru–N(1)
Cl/O–Ru–N(2)
Cl/O–Ru–GGa
N(1)–Ru–N(2)
N(1)–Ru–GGa
N(2)–Ru–GGa
Ru–N(1)–C(11)
Ru–N(1)–C(15)
N(1)–C(15)–C(16)
N(2)–C(16)–C(15)
Ru–N(2)–C(16)
Ru–N(2)–C(17)
C(16)–N(2)–C(17)
Arene/M–Ga
2.148–2.247(6) A for 1a, for instance). The shortest Ru–C(arene)
bond distances (C(5) and C(6) in both structures) are always
localised in a pseudo–trans disposition to the aminic nitrogen, the
donor atom with the lowest structural trans influence.24
The coordination of the water molecule in 12a develops a
remarkable shortening of the Ru–N and Ru–G bond distances if
compared with its parent chloride complex 5a. This shortening
is more apparent in the ruthenium–pyridine bond length which
130.38(18)
135.78(18)
124.4(5)
116.1(4)
115.6(6)
111.2(5)
108.3(3)
120.6(4)
111.8(5)
1.34(19)
˚
changes from a rough value of 2.09 A in the chloro complexes
˚
1a and 5a, to 2.012(6) A in 12a. This is a particular behaviour
that markedly differs from the structural data observed in the
closely related pyridylamine Ir(III) complexes; in this case, two
chloride/water related complexes, [Cp*IrX(L1)]n+ (X = Cl−
or H2O; L1 = N-(2-pyridylmethyl)-(R)-1-phenylethylamine),
have been also described, but no significant differences have
been observed neither in the Ir–N bond distances, nor in
the Ir–Cp* separation.20 The Ru–O bond distance in 12a,
a G represents the centroid of the aromatic p-cymene ring. Arene/M–G
represents the angle formed by the normal to the arene ring and the M–G
vector.
˚
2.131(4) A, is slightly shorter than those reported for other similar
Ru(II) cationic compounds of the type [(g -arene)Ru(N,Nꢀ-
6
L)(H2O)]n+, such as [(g -C6Me6)Ru(bpy)(H2O)]2+ 2.153(2) A,
6
25
˚
[(g -C6H3Me3)Ru(N,Nꢀ-L)(H2O)]2+
(N,Nꢀ-L
=
2,2-bis(2-
6
11
6
ꢀ
2+
˚
oxazolinyl)propane) 2.160(10) A, [(g -C6H6)Ru(N,N -L)(H2O)]
(N,Nꢀ-L
=
2,2-bis(4(R)-phenyl-1,3-oxazolon-2-yl)propane
2.161(8) A, or the dinuclear [(g -p-MeC6H4iPr)2Ru2(N,Nꢀ-
26
6
˚
L)(H2O)2]3+ (N,Nꢀ-L = 2,5-(2,2ꢀ-bis(6-methylpyridine))pirazolate)
27
˚
2.153(5) A. This Ru–O bond length is also shorter than the
Ir–O separation observed in the isoelectronic related Ir(III)
complexes, [Cp*IrL1(H2O)]2+ 2.145(6) A, [Cp*Ir(bpy)(H2O)]2+
20
˚
28
or [Cp*Ir(R,R-dach)(H2O)]2+ (R,R-dach
=
˚
2.1542(6) A,
29
˚
1R,2R-1,2-diaminocyclohexane) 2.180(7) A.
The apparently anomalous Ru–O bond length could be ratio-
nalized assuming that all these chelate N,Nꢀ-L groups are better
electron donors than our pyridylbornylamine (L5) ligand, and
consequently a higher positive charge on the metal atom will be
present in 12a, if compared to the above referred complexes. An
evaluation of the estimated partial charges on the metal atom
and the Mulliken populations on the Ru–O and Ru–N bonds has
been carried out by the extended Hu¨ckel approach30 for 12a, for
its parent chloride compound 5a and for the related bipyridine
Fig. 5 Molecular representation of the solvated complex 12a. Only
hydrogens of the N(2) and C(17) chiral atoms and those of the coordinated
water molecule are represented.
6
complex [(g -C6Me6)Ru(bpy)(H2O)]2+ (Table 2). In accordance
Table 2 Calculated partial charges on the ruthenium atom and Mulliken populations30
Complex
Ru
Ru–O/Ru–Cl
Ru–N(py)
Ru–N(am)
0.331
6
[(g -p-MeC6H4iPr)Ru(L5)(H2O)]2+ (12a)
0.841
0.712
0.675
0.228
0.193
0.378
0.426
0.405, 0.402
0.378
6
[(g -C6Me6)Ru(bpy)(H2O)]2+
6
[(g -p-MeC6H4iPr)RuCl(L5)]2+ (5a)
0.304
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with our proposal, the calculated values clearly show the relative
highest partial charge for the Ru atom in 12a (+0.841) and,
consequently, the highest Mulliken population for the Ru–O bond
is also observed in this complex (0.228 e−).
formation of the RRu SN diastereomer in the pyridylbornylamine
complexes (94% 5a and 90% 12a; see the Experimental section).
Another relevant structural motif that should be discussed
in relation to the NMR behaviour of these complexes is the
conformation observed around the N(2)–C(17) single bond. The
determined values for the Ru–N(2)–C(17)–C(18) torsion angles
are identical in the bornyl-substituted complexes (61.3(4) 5a
and 60.3(6)◦ 12a) and very similar to that observed for the
corresponding Ru–N(2)–C(17)–C(19) parameter (54.4(6)◦) in 1a.
These preferred conformations are a consequence, as reported for
Only minor differences have been observed in the metal
coordination bond angles of the three complexes and between
these complexes and their Ir(III) or pyridylimino analogues; the
bonding parameters of the chelating ligand (N(1)–C(15)–C(16)–
N(2)) are also comparable to other related complexes.17,18,20 The
unique bond parameter within the chelate ligand that shows a
significant deviation from ideal values concerns the Ru–N(2)–
C(17) bond angle (in the range 118.8–120.6(4)◦) which reflects the
greater steric requirements of the aminic R substituent (a phenyl
moiety in 1a, and a bornyl group in 5a and 12a).
Excepting the above commented dissimilarities related to water
coordination in 12a—and its consequences on Ru–N bond
distances—the most relevant differences among these complexes
are associated with conformational parameters of the metallacycle
Ru–N(1)–C(15)–C(16)–N(2) and the localisation of the diverse
ring substituents. The geometric limitations, due to the presence
of the aromatic N(1)–C(15) bond within the ring, restrict the
puckering of this metallacycle towards an ideal envelope, having
the aminic N(2) atom slightly out of the envelope plane. In fact,
n
other related [(g -arene)M(N,Nꢀ-L)Cl]+ complexes (M = Os, Rh
or Ir),32 of the different steric demands of the groups bonded
to chiral C(17) which make the smallest ligand, H(17), to be
preferably situated towards the bulkiest p-cymene ligand, and
the anti conformation (H(17) vs. H(2 N)) generally most stable
for these complexes. In fact, this anti conformation seems to be
an structural constant also maintained in solution (see above)
and could be of great use as a reference for configuration
assignment.20
Examining the intramolecular non-bonding distances, a partic-
ular aspect, common to the three complexes, merits a comment.
All the geometric parameters obtained in the solid state evidenced
(Table 3) the presence of a clear CH–p interaction between
hydrogens of the p-cymene ligand and the aromatic phenyl (1a)
or pyridine (5a and 12a) rings.33,34 These weak but attractive
interactions seem to be maintained in solution, at least for 1a,
as supported by 1H MNR data, since one of the signals of the aro-
matic hydrogens of the p-cymene ligand resonates at an anomalous
high field (d 4.80 ppm), clearly displaced from the remaining ones
(d 5.41, 5.75 or 5.93 ppm). The presence or absence of these CH–p
bonds may affect the relative energies of different intermediates
and hence affect the catalytic stereoselectivity observed for this
type of chiral half-sandwich complexes.
◦
˚
Cremer and Pople parameters (q2 = 0.363(6) A, φ2 = −37.7(9)
(1a); q2 = 0.471(4) A, φ2 = −27.1(5)◦ (5a); q2 = 0.460(5) A,
φ2 = −22.9(8)◦ (12a) characterise the metallacycles as a clear
envelope E5 (1a) or as mixed twist/envelope structures E5+1T5
(5a and 12a).31 The puckering amplitudes are appreciably larger
˚
˚
˚
for bornyl derivatives (mean 0.465(3) A), most likely reflecting
the greater steric requirements of the bornyl substituent, but
being smaller than those observed in analogous Ir(III) or Rh(III)
complexes containing the bulkier pentamethylcyclopentadienyl
20,32
˚
ligand (values in the range 0.502(4)–0.540(7) A.
As previously described for Os(II), Ir(III) or Rh(III)
analogues,20,32 these complexes show a clear tendency to localise
both steric-demanding substituents—arene and the R groups of
the amine—at equatorial positions of the metallacycle. This can
be figured out from the low values of the torsion angles relating
the two corresponding axial groups at Ru and N(2) atoms (Cl/O–
Ru–N(2)–H(2 N) −1.49 (1a), 8.0 (5a) and 11.1◦ (12a)), which also
prove the relative spatial proximity of aminic hydrogens to the
chloride or the water ligands. This trend—that is more evident
as the size of the R substituent increases—is at the source of
the relative preference to stabilize diastereomers having inverted
configurations at the metal and the aminic nitrogen, both in the
solid state and in solution. In our case, the equilibrium molar ratio
measured in solution clearly shows a greater tendency towards the
The most relevant intermolecular interaction detected concerns
complex 12a and involves the formation of two hydrogen bonds
between the coordinated water molecule and the oxygen of a
symmetry related [1 − x, 1/2 + y, 3/2 − z] solvation diethylether
˚
molecule (O(1) · · · O(2) 2.578(6), H(1w) · · · O(2) 2.30 A, O(1)–
H(1w) · · · O(2) 99.6◦) or a fluoride atom of a SbF6 anion
−
(symmetry operation for F(5): x, 1 + y, z; O(1) · · · F(5) 2.821(6),
◦
˚
H(2w) · · · F(5) 1.99 A, O(1)–H(2w) · · · F(5) 164.4 ). This interac-
tion through hydrogen bond formation of the coordinated water
molecule seems to be also a common behaviour for aqua-solvated
half-sandwich complexes, as all related previously-characterized
complexes exhibit in the solid state a similar hydrogen bonding
system, involving a good hydrogen bond-acceptor anion or
solvation molecule (another water molecule in most cases).11,12,20,35
Table 3 Geometric parameters for the intramolecular CH–p interactions detecteda
Complex
Datm
Dpln
Dlix
Dliy
D(H · · · G)
c /◦
1a
2.76 (H(3) · · · C(24))
2.59 (H(9C) · · · C(15))
2.81 (H(7) · · · N(1))
2.63
2.56
2.76
−0.65
0.10
−0.10
0.49
0.35
0.53
2.66
2.80
3.01
11.2
25.0
23.0
5a
12a
a Datm = distance between the hydrogen and the closest atom of the p ring. Dpln = distance to the mean-plane of the aromatic p ring. Dlix and Dliy
=
values defining the projection of the hydrogen atom on the p ring (see ref. 33). D(H · · · G) = distance between the hydrogen and the centroid of the p ring (all
˚
distances expressed in A). c = angle between the vector H–G and the normal to the aromatic ring mean-plane.
3332 | Dalton Trans., 2008, 3328–3338
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Catalytic Diels–Alder reactions
derivative preferentially affords the RC2 enantiomer, the more basic
and sterically demanding arene, C6Me6, gives the SC2 enantiomer
in good ee (entries 17–19). Unfortunately, the explanation of these
results is not straightforward.
6
Solvated complexes [(g -arene)Ru(pyam)(H2O)]2+ are active cata-
lysts for the DA reaction between methacrolein and cyclopentadi-
ene. Table 4 collects the most representative results. A low catalyst
loading (5 mol%) and a 6 : 1 cyclopentadiene–methacrolein molar
ratio were used. In general, complexes are quite active giving con-
versions greater than 90% at room temperature, in a few minutes.
Indeed, together with the pyridyloxazoline complexes reported by
Davies et al.,10 they are the most active half-sandwich ruthenium
complexes in DA reactions reported so far. The reactions proceed
with the usually high exo selectivity (from 84 : 16 to 98 : 2) and
enantioselectivity up to 74% ee. These results place them, among
the most selective half-sandwich ruthenium catalysts with N,N-
ligands until now studied. Only some pyridyloxazoline complexes,
In summary, taking into account that up to four diastere-
6
omers of the presumably active methacrolein complex7,10,15 [(g -
arene)RuLn(methacrolein)]2+ could be formed, no direct evident
conclusions can be drawn from the obtained data. The observed
switch on the absolute configuration of the product suggests that
the distribution of active and diversely selective diastereomeric
catalysts is strongly affected by the temperature.
Conclusions
6
[(g -arene)Ru(pymox)(H2O)]2+, reported by Davies et al. give
6
Cationic half-sandwich complexes of the type [(g -
better enantioselectivity (up to 83% ee).10 On the other hand,
large improvements in both rate and enantioselectivity have been
obtained, with respect to the closely related pyridylimine catalysts
arene)RuCl(pyam)][SbF6], that incorporate chiral pyridylamine
6
ligands, are prepared from the corresponding dimers [{(g -
arene)RuCl}2(l-Cl)2] as a mixture of up to four diastereomers.
6
[(g -p-MeC6H4iPr)Ru(pyridylimine)(H2O)][SbF6]2.18 Among the
Abstraction of the chloride affords the new aqua complexes
6
pyam ligands employed the pyridylnaphthylamine L2 ligand gave
the best results in terms of activity and enantioselectivity (entries
4–6 and 14–19).
Lowering the reaction temperature has very little effect on
the exo : endo ratio. However, this change produces, in most
cases, a remarkable switch on the absolute configuration of the
product. Thus, for example, while, at room temperature, the
pyridylnaphthylamine complex 9 gives a 52% ee in the SC2 aldehyde
product, at −50 ◦C, a 40% ee in the RC2 enantiomer was obtained
(entries 4 and 6).
[(g -arene)Ru(pyam)(H2O)][SbF6]2.
Most of the structural parameters involving the metal-to-ligand
bonds and those of the chelating ligands showed only minor
differences. The distinctive variations in the molecular structures
of these complexes concern the puckering parameters of the Ru–
N(py)–CH–CH2–NH(am) metallacycle and the relative localisa-
tion of substituents within this ring. As previously described, these
complexes showed a clear tendency to localise the most sterically-
demanding substituents (arene and the R groups of the amine) at
equatorial positions of the metallacycle; this trend becomes more
evident as the size of these moieties increase. Also as a consecuence
of steric requirements, the anti conformation of the N(am)–C*
single bond results an structural constant, maintained both in
solution and in the solid state.
On the other hand, to investigate the stereoelectronic influence
6
of the g -arene ligand, the benzene 13 and hexamethylbenzene
14 derivatives, with the pyridylnaphthylamine ligand L2, were
tested as catalyst precursors (entries 14–19). Whereas the benzene
Table 4 Enantioselective Diels–Alder reactions of methacrolein with cyclopentadiene catalysed by rhutenium complexes 8–14
Entry
Catalyst precursor
Temperature/◦C
Time/h
Yield (%)
Isomer ratio (exo : endo)
eea (%)
1
2
3
4
5
6
7
8
9
12
11
12
13
14
15
16
17
18
19
8
8
RT
0.5
24
96
0.17
24
96
0.5
192
0.25
8
144
0.5
24
94
90
92
93
91
92
92
78
87
88
92
91
81
96
92
73
96
96
95
90 : 10
90 : 10
91 : 9
91 : 9
91 : 9
92 : 8
93 : 7
96 : 4
84 : 16
92 : 8
91 : 9
89 : 11
95 : 5
89 : 11
91 : 9
93 : 7
95 : 5
97 : 3
98 : 2
37(S)
25(R)
37(R)
52(S)
30(R)
40 (R)
33 (S)
36(R)
4(S)
20(S)
24 (S)
10(S)
40(R)
6(R)
−20
−50
RT
−20
−50
RT
8
9
9
9
10
10
11
11
11
12
12
13
13
13
14
14
14
−20
RT
−20
−50
RT
−20
RT
1
24
120
0.25
20
−20
−50
RT
37(R)
37(R)
48(S)
69(S)
74(S)
−20
−50
96
a R and S assignments refers to the R or S at C2 enantiomer of the 2-methylbicyclo[2.2.1]hept-5-ene-2-carbaldehyde adduct.
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All the solvates are active catalysts for the DA reaction
between methacrolein and cyclopentadiene with good exo : endo
diastereoselectivity and up to 74% ee. The enantioselectivity is
highly dependent on the nature of the arene and pyridylamine
ligands and, in most cases, a switch of the absolute configuration of
the products was observed on lowering the reaction temperature.
C, 44.1; H, 4.2; N, 3.9. IR (Nujol, cm−1): m(NH) 3280(w), 3200 (w),
m(CN) 1600 (m), m(SbF6) 285 (s). 1H NMR ((CD3)2CO, d) 2a: 0.73
(d, JHH = 6.9 Hz, 3H, MeMeCH), 1.05 (d, JHH = 7.0 Hz, 3H,
MeMeCH), 1.60 (s, 3H, Me of p-cymene), 1.88 (d, JHH = 6.5 Hz,
3H, MeC*), 2.34 (psp, 1H, MeMeCH), 4.54 (d, JAB = 5.7 Hz, 1H,
HAHB), 4.79 (d, 1H, AB part of an ABX system, JAB = 14.3, Hz,
Hd), 5.11 (m, 1H, AB part of an ABX system, Hc), 5.25 (d, 1H,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
JA B = 6.1 Hz, HA HB ), 5.68 (d, 1H, HA HB ), 5.80 (d, 1H, HAHB),
Experimental
6.10 (m, 1H, Ha), 7.6–8.2 (m, aromatic protons), 8.50 (d, JHH
=
8.7 Hz, 1H, Hi or Hj), 9.08 (d, JHH = 5.8 Hz, 1H, Hh). 2b: 1.22
(d, JHH = 7.0 Hz, 3H, MeMeCH), 1.24 (d, JHH = 7.3 Hz, 3H,
MeMeCH), 1.78 (d, JHH = 6.5 Hz, 3H, MeC*), 2.24 (s, 3H, Me
All solvents were dried over appropriate drying agents, distilled
under nitrogen and degassed prior to use. All preparations have
been carried out under nitrogen. Infrared spectra were obtained as
Nujol mulls with a Perkin-Elmer 783 or 1330 spectrophotometer.
Carbon, hydrogen and nitrogen analyses were performed using
a Perkin-Elmer 240 B microanalyzer. 1H NMR spectra were
recordered on a Varian UNITY 300 spectrometer (299.95 MHz)
or a Brucker AV-400 (400.16 MHz). Chemical shifts are expressed
in ppm upfield from SiMe4. CD spectra were measured in acetone
or dichloromethane (ca. 5 × 10−4 mol L−1 solutions) in a 1 cm
path length cell by using a Jasco-710 apparatus. NOEDIFF and
1H correlation spectra were obtained using standard procedures.
The ligands L1–L5, were prepared using literature procedures.36
of p-cymene), 9.19 (d, JHH = 5.3 Hz, 1H, Hh). 2c: 0.95 (d, JHH
=
7.0 Hz, 3H, MeMeCH), 1.12 (d, JHH = 9.8 Hz, 3H, MeMeCH),
1.69 (d, JHH = 4.4 Hz, 3H, MeC*), 1.80 (s, 3H, Me of p-cymene),
9.30 (d, JHH = 5.3 Hz, 1H, Hh). 2d: 1.18 (d, JHH = 7.0 Hz, 3H,
MeMeCH), 1.29 (d, JHH = 6.9 Hz, 3H, MeMeCH), 2.27 (s, 3H,
Me of p-cymene), 9.10 (d, JHH = 5.9 Hz, 1H, Hh).
Complex 3. Yield: first fraction, 36%, 3a; second fraction,
45%, 3a : 3b : 3c : 3d molar ratio, 30 : 30 : 30 : 10. Equilibrium
molar ratio: 3a : 3b : 3c : 3d, 29 : 32 : 13 : 32. Anal. calcd for
C32H34N2ClF6RuSb: C, 46.9; H, 4.2; N, 3.4. Found: C, 47.0; H
4.2; N, 3.4. IR (Nujol, cm−1): m(NH) 3280 (m), m(CN) 1600 (m),
m(SbF6) 285 (s). CD (Me2CO), [H]k values of maxima and minima
(k, nm), 3a: −13000 (350), −1700 (390), −2300 (430); 3a : 3b : 3c :
3d molar ratio, 2 : 94 : 2 : 2. +15200 (345), +5500 (385), +14500
Preparation of [(g6-arene)RuClLn][SbF6] (1–7)
6
A mixture of [{(g -arene)RuCl}2(l-Cl)2] (0.5 mmol), NaSbF6
(1.0 mmol) and the appropriate pyridylamine ligand (1.0 mmol) in
methanol (10 mL) was stirred for 14 h. During this time, complexes
1, 3 and 5 precipitated, and were filtered off and recrystallised
from dichloromethane–diethyl ether solutions. The filtrate, or
the reaction mixture for the remaining complexes, was vacuum-
evaporated to dryness. The resulting residue was extracted with
dichloromethane (15 mL) and the solution partially concentrated
under reduced pressure. Slow addition of diethyl ether gave orange
solids, which were filtered off, washed with diethyl ether and air-
dried.
1
(420). H NMR ((CD3)2CO, d) 3a: 0.88 (d, JHH = 6.8 Hz, 3H,
MeC*), 1.13 (d, JHH = 6.8 Hz, 3H, MeMeCH), 1.22 (d, JHH
=
6.8 Hz, 3H, MeMeCH), 1.86 (s, 3H, Me of p-cymene), 2.79 (m,
1H, MeMeCH), 4.84 dd (1H, AB part of an ABX system, JAB
=
17.9 Hz, JAX = 6.7 Hz, Hc), 5.13 (d, 1H, AB part of an ABX
system, Hd), 5.42 (q, JHH = 6.8 Hz, 1H, Ha), 5.87 (d, JAB = 6.1 Hz,
1H, HAHB), 6.18 (m, 3H, HAHB), 7.38 (bd, JHH = 5.9 Hz, 1H, Hb),
7.5–8.3 (m, aromatic protons), 7.90 (d, JHH = 7.1 Hz, 1H, Hi or
Hj), 8.16 (d, JHH = 6.1 Hz, 1H, Hi or Hj), 8.73 (d, JHH = 8.3 Hz,
1H), 9.09 (d, JHH = 8.8 Hz, 1H, Hh). 3b: 0.27 (d, JHH = 6.6 Hz, 3H,
MeMeCH), 1.01 (d, JHH = 7.1 Hz, 3H, MeMeCH), 1.52 (s, 3H,
Me of p-cymene), 1.92 (d, JHH = 6.3 Hz, 3H, Me of MeC*), 2.22
(psp, 1H, MeMeCH), 5.19 d (1H, AB part of an ABX system,
JAB = 12.4, Hz, Hd), 5.2 (m, 1H, Hb), 5.46 (m, 1H, AB part of
an ABX system, Hc), 6.20 (m, HAHB), 6.25 (m, 1H, Ha), 7.57 (t,
JHH = 7.6 Hz, 1H), 7.68 (t, JHH = 7.1 Hz, 1H), 7.80 (m, 1H, Hi),
8.12 (d, JHH = 8.1 Hz, 1H), 8.17 (d, JHH = 8.3 Hz, 1H), 8.57 (d,
Complex 1. Yield: first fraction, 18%, 1a; second fraction, 72%,
1a : 1b : 1c : 1d molar ratio, 26 : 28 : 26 : 20. Equilibrium molar ratio:
1a : 1b : 1c : 1d, 78 : 4 : 0 : 18. Anal. calcd for C24H30N2ClF6RuSb: C,
40.1; H, 4.2; N, 3.9. Found: C, 40.1; H 4.3; N, 3.9. IR (Nujol, cm−1):
m(NH) 3210 (w), m(CN) 1600 (m), m(SbF6)285(s). CD(Me2CO), 1a,
[H]k values of maxima, minima and nodes (k, nm); +12400 (325),
0 (350), −2500 (360), 0 (375), +8000 (420). 1H NMR ((CD3)2CO,
d) 1a: 0.85 (d, JHH = 7.0 Hz, 3H, MeMeCH), 1.10 (d, JHH = 7.0 Hz,
3H, MeMeCH), 1.76 (d, 3H, JHH = 6.6 Hz, Me of MeC*), 1.78
(s, 3H, Me of p-cymene), 2.49 (psp, 1H, MeMeCH), 4.53 (m, 1H,
Hb), 4.58 (pt, 1H, AB part of an ABX system, JAB = 11.8 Hz, Hd),
4.80 (d, JAB = 5.9 Hz, 1H, HAHB), 4.94 (d, 1H, AB part of an
JHH = 8.5 Hz, 1H, Hj), 8.70 (d, JHH = 8.3 Hz, 1H), 8.83 (d, JHH
8.8 Hz, 1H). 3c: 8.40 (d, JHH = 8.1 Hz, 1H). 3d: 0.92 (d, JHH
7.1 Hz, 3H, MeMeCH), 8.55 (d, JHH = 9.8 Hz, 1H), 8.96 (d, JHH
8.8 Hz, 1H).
=
=
=
Complex 4. Yield: 80%, 4a : 4b : 4c molar ratio, 35 : 35 : 30.
Equilibrium molar ratio: 4a : 4b : 4c, 42 : 42 : 16. Anal. calcd for
C24H36N2ClF6RuSb: C, 39.8; H 5.0; N, 3.9. Found: C, 39.6; H, 5.0;
N, 3.6. IR (Nujol, cm−1): m(NH) 3280 (w), 3200(w), m(CN) 1600
ꢀ
ꢀ
ABX system, Hc), 5.14 (m, 1H, Ha), 5.41 (d, 1H, JA B = 6.2 Hz,
ꢀ
ꢀ
ꢀ
ꢀ
HA HB ), 5.75 (d, 1H, HA HB ), 5.93 (d, 1H, HAHB), 7.3–7.7 (m,
aromatic protons), 7.57 (pt, JHH = 6.2 Hz, 1H, Hg), 7.62 (d, JHH
7.0 Hz, 1H, Hi), 7.74 (d, JHH = 7.9 Hz, 1H, He), 8.07 (pt, JHH
7.8 Hz, 1H, Hf), 9.05 (d, JHH = 5.7 Hz, 1H, Hh). 1b: 9.11 (d, JHH
=
=
=
1
(m), m(SbF6) 285 (s). H NMR ((CD3)2CO, d) 4a, 4b: 1.13, 1.22,
1.33, 1.41 (d, 3H, MeMeCH), 1.65 (d, 3H, Me of MeC*), 2.19, 2.21
(s, 3H, Me of p-cymene), 2.68 (psp, 1H, MeMeCH), 4.50 (m, 1H,
Hb), 4.51, 4.68 (m,1H, AB part of an ABX system, Hc or Hd), 4.65
(d, JHH = 6.0 Hz, 1H, HAHB), 5.66 (d, JHH = 5.8 Hz, 1H, HAHB),
5.79 (d, JHH = 6.0 Hz, 1H, HAHB), 5.82 (d, JHH = 6.0 Hz, 1H,
HAHB), 5.91 (d, JHH = 6.5 Hz, 1H, HAHB), 6.01 (d, JHH = 6.6 Hz,
5.5 Hz, 1H, Hh). 1c: 9.28 (d, JHH = 5.7 Hz, 1H, Hh). 1d: 9.05 (d,
JHH = 5.7 Hz, 1H, Hh).
Complex 2. Yield: 95%, 2a : 2b : 2c : 2d molar ratio, 42 : 22 :
22 : 14. Equilibrium molar ratio: 2a : 2b : 2c : 2d, 49 : 17 : 14 : 20.
Anal. calcd for C28H32N2ClF6RuSb: C, 43.7; H, 4.2; N, 3.6. Found:
3334 | Dalton Trans., 2008, 3328–3338
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1H, HAHB), 6.03 (d, JHH = 6.3 Hz, 1H, HAHB), 9.07 (d, JHH
=
to dryness, and the addition of diethyl ether gave orange oils.
Vigorous stirring in diethyl ether affords orange–brown solids.
5.4 Hz, 1H, Hh). 4c: 1.12 (d, JHH = 6.8 Hz, 3H, MeMeCH), 1.48
(d, JHH = 6.6 Hz, 3H, MeMeCH), 2.25 (s, 3H, Me of p-cymene),
9.13 (d, JHH = 6.6 Hz, 1H, Hh).
Complex 8. Yield: 65%, 8a : 8b : 8c : 8d molar ratio, 47 : 28 :
1
14 : 11. H NMR ((CD3)2CO, d) 8: 0.88 (d, JHH = 6.8 Hz, 3H,
Complex 5. Yield: first fraction, 54%, 5a : 5b : 5c molar ratio,
46 : 23 : 31; second fraction, 24%, 5a : 5b : 5c : 5d molar ratio, 26 :
36 : 8 : 30. Equilibrium molar ratio: 5a : 5b : 5c : 5d, 94 : 2 : 2 : 2.
Anal. calcd for C26H38N2ClF6RuSb: C, 41.5; H, 5.0; N, 3.7. Found:
C, 41.4; H 5.2; N, 3.7. IR (Nujol, cm−1): m(NH) 3280 (w), 3200 (w),
m(CN) 1600 (m), m(SbF6) 285 (s). CD (Me2CO), 5a : 5b : 5c : 5d
molar ratio, 94 : 2 : 2 : 2, [H]k values of maxima, minima and nodes
(k, nm); +20000 (310), 0 (345), −4500 (365), 0 (380), +9000 (415).
1H NMR ((CD3)2CO, d) 5a: 0.92 (s, 3H, Mea), 1.06 (s, 3H, Meb),
1.11 (d, JHH = 6.9 Hz, 3H, MeMeCH), 1.20 (d, JHH = 6.9 Hz, 3H,
MeMeCH), 1.28 (s, 3H, Mec), 2.20 (s, 3H, Me of p-cymene), 2.62
(m, 1H, Hi), 2.73 (psp, 1H, MeMeCH), 3.60 (m, 1H, Hb), 4.23 (t,
1H, JHH = 9.3 Hz, Ha), 4.58 (m, 1H, AB part of an ABX system,
Hd), 4.77 (dd, 1H, AB part of an ABX system, JAB = 15.8 Hz,
JAX = 3.8 Hz, Hc), 5.83 (d, JAB = 6.0 Hz, 1H, HAHB), 5.89 (d, 1H,
MeMeCH), 1.05 (d, JHH = 7.1 Hz, 3H, MeMeCH), 1.15 (d, JHH
=
7.1 Hz, 3H, MeMeCH), 1.18 (d, JHH = 6.8 Hz, 3H, MeMeCH),
1.26 (d, JHH = 6.8 Hz, 3H, MeMeCH), 1.40 (d, JHH = 6.8 Hz,
3H, MeMeCH), 1.76, 1.79 (d, 3H, MeC*), 1.78, 2.27, 2.28, 2.37
(s, 3H, Me of p-cymene), 6.88, 6.94, 7.18, 7.25 (s, H2O), 7.2–8.3
(m, aromatic protons), 9.42 (d, J = 6.1 Hz, Hh, 8a), 9.44 (d, J =
6.1 Hz, Hh, 8c), 9.46 (d, J = 6.1 Hz, Hh, 8b), 9.59 (d, J = 6.1 Hz,
Hh, 8d).
Complex 9. Yield: 61%, 9a : 9b : 9c : 9d molar ratio, 52 : 23 :
16 : 9. Anal. calcd for C28H34N2OF12RuSb2.H2O: C, 33.45; H, 3.6;
N, 2.8. Found: C, 33.0; H, 3.8; N, 2.6. IR (Nujol, cm−1): m(H2O)
3650–3400 (br), 1690(m), m(NH) 3240 (w), m(CN) 1610 (w), m(SbF6)
1
285 (s). H NMR ((CD2Cl2), d) 9a: 0.76 (d, JHH = 6.8 Hz, 3H,
MeMeCH), 0.98 (d, JHH = 7.1 Hz, 3H, MeMeCH), 1.90 (d, JHH
=
6.5 Hz, 3H, Me of MeC*), 2.17 (s, 3H, Me of p-cymene), 2.68 (psp,
1H, MeMeCH), 3.78 (d,1H, AB part of an ABX system, JAB
17.2 Hz, Hc or Hd), 4.10 (m, 1H, AB part of an ABX system, Hd or
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
JA B = 6.2 Hz, HA HB ), 6.00 (d, 1H, HA HB ), 6.11 (d, 1H, HAHB),
7.62 (pt, JHH = 6.5 Hz, 1H, Hg), 7.79 (d, JHH = 7.8 Hz, 1H, He),
8.08 (pt, JHH = 7.8 Hz, 1H, Hf), 9.08 (d, JHH = 5.6 Hz, 1H, Hh).
5b: 9.03 (d, JHH = 4.9 Hz, 1H, Hh). 5c: 9.15 (d, JHH = 5.1 Hz, 1H,
Hh). 5d: 9.10 (d, JHH = 5.1 Hz, 1H, Hh).
=
ꢀ
ꢀ
Hc), 4.66 (d, JAB = 5.9 Hz, 1H, HAHB), 5.44 (d, JA B = 6.2 Hz, 1H,
ꢀ
ꢀ
ꢀ
ꢀ
HA HB ), 5.63 (d, 1H, HA HB ), 5.79 (d, JAB = 6.6 Hz, 1H, HAHB),
6.9–8.4 (m, aromatic protons), 9.21 (d, JHH = 5.4 Hz, 1H, Hh). 9b:
1.12 (d, JHH = 6.8 Hz, 3H, MeMeCH), 1.26 (d, JHH = 6.4 Hz, 3H,
MeMeCH), 1.55 (s, 3H, Me of p-cymene), 1.84 (d, JHH= 6.5 Hz,
Complex 6. Yield: 90%, 6a : 6b : 6c : 6d molar ratio, 34 : 29 :
22 : 15. Equilibrium molar ratio: 6a : 6b : 6c : 6d, 51 : 9 : 25 :
15. Anal. calcd for C24H24N2ClF6RuSb: C, 40.4; H, 3.4; N, 3.9.
Found: C, 39.9; H 3.7; N, 4.2. IR (Nujol, cm−1): m(NH) 3285 (w),
3200 (m), m(CN) 1610 (m), m(SbF6) 290 (s). 1H NMR ((CD3)2CO,
d) 6a: 1.94 (d, 3H, JHH = 6.6 Hz, Me of MeC*), 5.46 (s, 6H, C6H6),
9.10 (d, JHH = 5.6 Hz, 1H, Hh). 6b: 1.98 (d, 3H, JHH = 6.8 Hz, Me
of MeC*), 6.30 (s, 6H, C6H6), 9.13 (d, JHH = 5.4 Hz, 1H, Hh). 6c:
1.85 (d, 3H, JHH = 6.4 Hz, Me of MeC*), 6.24 (s, 6H, C6H6), 9.20
(d, JHH = 5.5 Hz, 1H, Hh). 6d: 1.69 (d, 3H, JHH = 6.8 Hz, Me of
MeC*), 5.41 (s, 6H, C6H6), 9.33 (d, JHH = 5.5 Hz, 1H, Hh).
Complex 7. Yield: 92%, 7a : 7b : 7c molar ratio, 44 : 36 : 20.
Equilibrium molar ratio: 7a : 7b : 7c, 54 : 26 : 20. Anal. calcd
for C30H36N2ClF6RuSb: C, 45.1; H, 4.5; N, 3.5. Found: C, 45.0; H
4.4; N, 3.4. IR (Nujol, cm−1): m(NH) 3285 (w), 3200 (m), m(CN)
1610 (m), m(SbF6) 290 (s). 1H NMR ((CD3)2CO, d) 7a: 1.66 (d, 3H,
3H, MeC*), 9.33 (d, JHH = 5.4 Hz, 1H, Hh). 9c: 9.23 (d, JHH
=
1
5.9 Hz, 1H, Hh). 9d: 9.31 (d, JHH = 5.9 Hz, 1H, Hh). H NMR
((CD3)2CO), d) 9a: 0.84 (d, JHH = 7.1 Hz, 3H, MeMeCH), 1.00 (d,
JHH = 6.9 Hz, 3H, MeMeCH), 1.90 (d, JHH= 6.6 Hz, 3H, MeC*),
2.35 (s, 3H, Me of p-cymene), 2.35 (psp, 1H, MeMeCH), 4.98 (d,
ꢀ
ꢀ
ꢀ
ꢀ
JAB = 5.7 Hz, 1H, HAHB), 5.83 (d, JA B = 6.4 Hz, 1H, HA HB ),
ꢀ
ꢀ
6.01 (d, 1H, HA HB ), 6.07 (d, JAB = 6.6 Hz, 1H, HAHB), 6.99 (s,
H2O), 7.2–8.7 (m, aromatic protons), 9.50 (d, JHH = 5.5 Hz, 1H,
Hh). 9b: 1.99 (d, JHH= 6.1 Hz, 3H, MeC*), 7.05 (s, H2O), 9.58 (d,
JHH = 5.5 Hz, 1H, Hh). 9c: 7.08 (s, H2O,), 9.48 (d, JHH = 5.5 Hz,
1H, Hh). 9d: 7.14 (s, H2O), 9.67 (d, JHH = 5.5 Hz, 1H, Hh).
Complex 10. Yield: 81%, 10a : 10b : 10c molar ratio, 34 : 33 :
33. Anal. calcd for C32H36N2OF12RuSb2: C, 37.1; H, 3.5; N, 2.7.
Found: C, 37.0; H, 3.5; N, 2.6. IR (Nujol, cm−1): m(H2O) 3650–3400
(br), 1650(s), m(NH) 3240 (w), m(CN) 1600 (m), m(SbF6) 285 (s). 1H
NMR ((CD2Cl2), d) 10: 0.29 (d, JHH = 6.8 Hz, 3H, MeMeCH),
0.88 (d, JHH = 6.8 Hz, 3H, MeMeCH), 0.94 (d, JHH = 7.1 Hz, 3H,
JHH = 6.6 Hz, Me of MeC*), 2.28 (s, 18H, C6Me6), 3.65 (d, JAB
=
16.6 Hz, 1H, AB part of an ABX system, Hd), 4.24 (dd, 1H, JAx
=
5.4 Hz, AB part of an ABX system, Hc), 4.83 (m, 1H, Ha), 5.21 (m,
1H, Hb), 6.71 (d, JHH = 7.8 Hz, 1H, He), 6.91 (d, JHH = 8.8 Hz, 1H,
Hj or Hi), 7.0–8.7 (m, aromatic protons), 7.98 (d, JHH = 7.3 Hz,
1H, Hi or Hj), 8.79 (d, JHH = 5.1 Hz, 1H, Hh). 7b: 1.83 (d, 3H,
JHH = 6.3 Hz, Me of MeC*), 2.28 (s, 18H, C6Me6), 3.9 (m, 2H, Hc
and Hd), 5.50 (m, 1H, Ha), 8.41 (d, JHH = 8.7 Hz, 1H, Hi or Hj),
8.67 (d, JHH = 5.4 Hz, 1H, Hh). 7c: 1.96 (d, 3H, JHH = 6.4 Hz, Me
of MeC*), 8.75 (bd, 1H, Hh).
MeMeCH), 1.02 (d, JHH = 6.8 Hz, 3H, MeMeCH), 1.13 (d, JHH
=
6.8 Hz, 3H, MeMeCH), 1.20 (d, JHH = 6.8 Hz, 3H, MeMeCH),
1.85 (d, JHH = 6.2 Hz, 3H, MeC*), 1.92 (d, JHH = 6.2 Hz, 3H,
MeC*) 1.27, 2.12, 2.14 (s, 3H, Me of p-cymene), 2.38, 2.55 (psp,
1H, MeMeCH), 6.8–8.8 (m, aromatic protons). ((CD3)2CO, d) 10:
0.37 (d, JHH = 6.9 Hz, 3H, MeMeCH), 0.94 (d, JHH = 6.9 Hz, 3H,
MeMeCH), 0.99 (d, JHH = 6.9 Hz, 3H, MeMeCH), 1.07 (d, JHH
=
6.9 Hz, 3H, MeMeCH), 1.20 (d, JHH = 6.9 Hz, 3H, MeMeCH),
1.30 (d, JHH = 6.9 Hz, 3H, MeMeCH), 1.96 (d, JHH = 6.4 Hz, 3H,
MeC*), 2.00 (d, JHH = 6.6 Hz, 3H, MeC*), 1.49, 2.21, 2.27 (s, 3H,
Me of p-cymene), 7.2–9.2 (m, aromatic protons).
Preparation of [(g6-arene)Ru(Ln)(H2O)][SbF6]2 (8–14)
To a diastereomeric mixture of the corresponding chlorocom-
pound (0.325 mmol) in 25 mL of dichloromethane, 111.7 mg
(0.325 mmol) of AgSbF6 in 1 mL of acetone were added. The
suspension was stirred for 30 min and the AgCl formed was
separated by filtration. The solution was vacuum-evaporated
Complex 11. Yield: 70%, 11a : 11b : 11c : 11d molar ratio, 40 :
30 : 20 : 10. Anal. calcd for C24H38N2OF12RuSb2: C, 30.6; H, 4.1;
N, 3.0. Found: C, 31.0; H, 3.9; N, 2.8. IR (Nujol, cm−1): m(H2O)
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Dalton Trans., 2008, 3328–3338 | 3335
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3650–3400 (br), 1690(s), 1650(s), m(NH) 3240 (w), m(CN) 1613 (m),
an ABX system, JAB = 16.8 Hz, Hd), 3.80 (m, 1H, AB part of an
ABX system, Hc), 4.04 (m, 1H, Ha), 5.08 (m, 1H, Hb), 5.68 (bs,
2H, H2O), 6.75 (d, JHH = 7.3 Hz, 1H), 6.98 (d, JHH = 8.1 Hz, 1H),
7.1–8.2 (m, aromatic protons), 8.91 (d, JHH = 4.9 Hz, 1H, Hh).
14b: 1.93 (d, 3H, JHH = 6.6 Hz, MeC*), 2.23 (s, 18H, C6Me6), 5.50
(bs, 1H, Hb), 5.76 (bs, 2H, H2O), 8.80 (d, JHH = 9.9 Hz, 1H, Hh).
1H NMR ((CD3)2CO, ∂) 14a: 1.89 (d, 3H, JHH = 6.6 Hz, MeC*),
2.43 (s, 18H, C6Me6), 3.81 (d, 1H, AB part of an ABX system,
JAB = 16.8 Hz, Hd), 4.35 (bd, 1H, AB part of an ABX system, Hc),
4.35 (m, 1H, Ha), 5.75 (m, 1H, Hb), 7.15 (d, JHH = 7.6 Hz, 1H, Hj
or Hi), 7.25 (s, H2O), 8.02 (d, JHH = 7.8 Hz, 1H, Hi or Hj), 9.22
(d, JHH = 5.6 Hz, 1H, Hh). 14b: 1.90 (m, 3H, MeC*), 2.40 (s, 18H,
C6Me6), 3.97 (d, 1H, AB part of an ABX system, JAB = 16.4 Hz,
Hd), 9.11 (d, JHH = 5.6 Hz, 1H, Hh).
1
1
m(SbF6) 285 (s). H NMR ((CD2Cl2), d) 11: 9.2–9.4 (m, Hh). H
NMR ((CD3)2CO, ∂) 11: 1.11 d, JHH = 6.8 Hz, 3H, MeMeCH),
1.17 (d, JHH = 6.6 Hz, 3H, MeMeCH), 1.19 (d, JHH = 6.6 Hz, 3H,
MeMeCH), 1.21 (d, JHH = 6.9 Hz, 3H, MeMeCH), 1.28 (d, JHH
=
6.8 Hz, 3H, MeMeCH), 1.40 (d, JHH = 6.8 Hz, 3H, MeMeCH),
1.64 (d, JHH = 6.6 Hz, 3H, MeMeCH), 2.22, 2.28, 2.31, 2.36 (s,
3H, Me of p-cymene), 6.94, 6.99, 7.04, 7.50 (s, H2O), 9.40 (d, J =
5.5 Hz, Hh, 11b), 9.45 (d, J = 5.7 Hz, Hh, 11c), 9.55 (d, J = 5.3 Hz,
Hh, 11d), 9.63 (d, J = 5.5 Hz, Hh, 11a).
Complex 12. Yield: 65%, 12a : 12b : 12c molar ratio in CD2Cl2,
90 : 7 : 3. Anal. calcd for C26H40N2OF12RuSb2: C, 32.2; H, 4.1;
N, 2.9. Found: C, 32.7; H 4.3; N, 2.7. IR (Nujol, cm−1): m(H2O)
3650–3400 (br), 1680(s), 1650(s), m(NH) 3240 (w), m(CN) 1610 (m),
m(SbF6) 285 (s). CD (Me2CO), 12a : 12b : 12c molar ratio, 90 : 7 :
3, [H]k values of maxima, minima and nodes (k, nm); +5000 (310),
0 (330), −4000 (360), 0 (380), +8000 (425). 1H NMR (CD2Cl2, d)
12a: 0.97 (s, 3H, Mec), 1.10 (d, JHH = 6.6 Hz, 3H, MeMeCH),
1.11 (s, 3H, Mea), 1.13 (d, JHH = 6.6 Hz, 3H, MeMeCH), 1.28 (s,
3H, Meb), 1–2 (m, 7H, bornyl), 2.15 (s, 3H, Me of p-cymene), 2.50
(psp, 1H, MeMeCH), 2.73 (m, 1H, Hi), 3.07 (m, 1H, Hb), 4.07 (t,
1H, JHH = 9.5 Hz, Ha), 4.26 (m, 1H, AB part of an ABX system,
Hd), 4.55 (dd, 1H, AB part of an ABX system, JAB = 15.7 Hz,
JAX = 3.8 Hz, Hc), 5.42 (bs, H2O), 5.80 (s, 2H, HAHB), 5.83 (d,
Crystal structure determinations
Single crystals of the complexes were mounted on a glass fibber
and intensity data were collected at low temperature (173 K for 1a,
150 K for 5a, and 100 K for 12a) on a CCD Bruker SMART APEX
diffractometer with graphite-monochromated Mo Ka radiation
◦
˚
(k = 0.71073 A) using x rotations (0.3 ).† Instrument and crystal
stability were evaluated by measuring equivalent reflections at
different times; no significant decay was observed. Crystal data for
1a (from 7924 reflections, 2.3 < h < 27.2◦): C24H30ClF6N2RuSb,
monoclinic, space group P21; a = 9.4680(11), b = 10.7280(12),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
JA B = 6.4 Hz, 1H, HA HB ), 5.93 (d, 1H, HA HB ), 7.60 (d, JHH
=
=
7.8 Hz, 1H, He), 7.68 (t, JHH = 6.5 Hz, 1H, Hg), 8.06 (td, JHH
◦
3
˚
˚
c = 13.8827(16) A, b = 109.2470 (10) , V = 1331.3(3) A , Z =
2, Dc = 1.793 Mg m−3, l(Mo Ka) = 1.740 mm−1; crystal size
0.24 × 0.22 × 0.15 mm; max. 2h = 57.5◦; 16173 measured
reflections, 6286 unique (Rint = 0.0722). Crystal data for 5a
(from 1290 reflections, 5.0 < h < 21.0◦): C26H38ClF6N2RuSb,
monoclinic, space group P21; a = 11.9604(8), b = 10.8946(7), c =
7.9 Hz, JHH = 1.4 Hz, 1H, Hf), 9.15 (d, JHH = 5.6 Hz, 1H, Hh).
12b: 9.22 (d, JHH = 5.6 Hz, 1H, Hh). 12c: 8.82 (d, JHH = 5.6 Hz,
1H, Hh). 1H NMR ((CD3)2CO, d) 12a: 0.95 (s, 3H, Mec), 1.11 (d,
JHH = 6.4 Hz, 3H, MeMeCH), 1.12 (s, 3H, Mea),1.19 (d, JHH
=
6.8 Hz, 3H, MeMeCH), 1.32 (s, 3H, Meb), 1–2 (m, 7H, bornyl),
2.23 (s, 3H, Me of p-cymene), 2.75 (psp, 1H, MeMeCH), 3.07 (m,
1H, Hi), 3.78 (m, 1H, Hb), 4.46 (t, 1H, JHH = 9.5 Hz, Ha), 4.69 (m,
1H, AB part of an ABX system, Hd), 4.92 (dd, 1H, AB part of an
ABX system, JAB = 15.7 Hz, JAX = 3.7 Hz, Hc), 6.2–6.4 (m, 4H,
p-cymene), 7.25 (bs, H2O), 7.77 (t, JHH = 6.4 Hz, 1H, Hg), 7.92 (d,
JHH = 8.0 Hz, 1H, He), 8.21 (t, JHH = 5.6 Hz, 1H, Hf), 9.45 (d,
JHH = 5.6 Hz, 1H, Hh). 12b: 7.30 (s, H2O), 9.69 (d, JHH = 5.4 Hz,
1H, Hh). 12c: 7.15 (s, H2O), 9.50 (bd, 1H, Hh).
◦
3
˚
˚
12.1915(8) A, b = 116.7890 (10) , V = 1418.10(16) A , Z = 2, Dc =
1.758 Mg m−3, l(Mo Ka) = 1.637 mm−1; crystal size 0.28 × 0.22 ×
0.20 mm; max. 2h = 53.0◦; 6991 measured reflections, 4478 unique
(Rint = 0.0232). Crystal data for 12a (from 3337 reflections, 2.3 <
h < 21.2◦): C26H40F12N2ORuSb2. C4H10O. CH2Cl2, orthorhombic,
˚
space group P212121; a = 10.395(3), b = 11.073(3), c = 36.007(9) A,
3
−3
˚
V = 4144.5(19) A , Z = 4, Dc = 1.808 Mg m , l(Mo Ka) =
1.867 mm−1; crystal size 0.25 × 0.22 × 0.11 mm; max. 2h = 57.1◦;
27547 measured reflections, 9745 unique (Rint = 0.0659).
Complex 13. Yield: 82%, 13a : 13b : 13c : 13d molar ratio, 39 :
25 : 23 : 13. Anal. calcd for C24H26N2OF12RuSb2.H2O: C, 30.4;
H, 3.0; N, 3.0. Found: C, 30.2; H 3.1; N, 3.0. IR (Nujol, cm−1):
m(H2O) 3650–3400 (br), 1690(s), m(NH) 3235 (w), m(CN) 1614 (m),
Data were integrated with Bruker SAINT-PLUS software.37 Ab-
sorption corrections were applied by using SADABS program.38
Structures were solved by direct methods and completed by sub-
sequent difference Fourier techniques. Anisotropic displacement
parameters were used for all non-hydrogen non-disordered atoms.
Most of the hydrogen atoms were included in calculated positions
and refined riding on carbon atoms. Refinement on F2 was carried
out by full-matrix least-squares (SHELXL-97).39 In 1a, four of the
m(SbF6) 289 (s). 1H NMR ((CD3)2CO, d) 13a: 2.00 (d, 3H, JHH
=
6.6 Hz, MeC*), 5.79 (s, 6H, C6H6), 9.50 (d, JHH = 5.6 Hz, 1H,
Hh). 13b: 1.93 (d, 3H, JHH = 6.6 Hz, MeC*), 6.52 (s, 6H, C6H6),
9.60 (m, 1H, Hh). 13c: 2.25 (d, 3H, JHH = 6.6 Hz, MeC*), 6.60 (s,
6H, C6H6), 9.63 (m, Hz, 1H, Hh). 13d: 1.87 (d, 3H, JHH = 6.6 Hz,
MeC*), 6.22 (s, 6H, C6H6).
−
fluorine atoms of the PF6 anion were observed disordered and
refined in two positions with complementary occupancy factors. In
the case of 5a, some of the hydrogens were found from difference
Fourier maps; all were refined with free isotropic displacement
parameters. Two solvent molecules, a dichloromethane and a
diethyl ether, were present in the crystal structure of 12a; hydrogens
of the water molecule were calculated with the subroutine CALC-
OH.40 The absolute configuration for these compounds were
determined on the basis of previously known internal references,
and this assignment was confirmed using the Flack parameter41
Complex 14. Yield: 65%, 14a : 14b molar ratio, 67 : 33. Anal.
calcd for C30H38N2OF12RuSb2: C, 35.5; H, 3.8; N, 2.8. Found: C,
35.5; H 3.9; N, 2.9. IR (Nujol, cm−1): m(H2O) 3650–3400 (br),
1690(s), m(NH) 3280 (w), m(CN) 1613 (m), m(SbF6) 289 (s). CD
(Me2CO), 14a : 14b molar ratio, 67:33, [H]k values of maxima,
minima and nodes (k, nm); +2300 (305), 0 (315), −100 (320), 0
(325), +3000 (335), +7200 (395). 1H NMR (CD2Cl2, d) 14a: 1.69
(bd, 3H, MeC*), 2.25 (s, 18H, C6Me6), 3.63 (d, 1H, AB part of
3336 | Dalton Trans., 2008, 3328–3338
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(0.0011(3) 1a, 0.0010(3) 5a, and −0.038(19) 12a). Conventional
final agreement factors39 were: R1 = 0.0506 (for 5924 reflections
with F2 > 4r(F2)), xR2 = 0.1244 and S = 1.036 for all independent
K. Ishihara, H. Kurihara, M. Matsumoto and H. Yamamoto, J. Am.
Chem. Soc., 1998, 120, 6920; K. Futatsugi and H. Yamamoto, Angew.
Chem., Int. Ed., 2005, 44, 1484.
6 E. P. Ku¨ndig, B. Bourdin and G. Bernardinelli, Angew. Chem., 1994,
106, 1931, (Angew. Chem., Int. Ed. Engl., 1994, 33, 1856); M. E. Bruin
and E. P. Ku¨ndig, Chem. Commun., 1998, 2635; E. P. Ku¨ndig, C. M.
Saudan and F. Viton, Adv. Synth. Catal., 2001, 343, 51; E. P. Ku¨ndig,
C. M. Saudan, V. Alezra, F. Viton and G. Bernardinelli, Angew. Chem.,
Int. Ed., 2001, 40, 4481; V. Alezra, G. Bernardinelli, C. Corminboeuf,
U. Frey, E. P. Ku¨ndig, A. E. Merbach, C. M. Saudan, F. Viton and
J. Weber, J. Am. Chem. Soc., 2004, 126, 4843; J. Rickerby, M. Vallet,
G. Bernardinelli, F. Viton and E. P. Ku¨ndig, Chem.–Eur. J., 2007, 13,
3354.
reflections of 1a; R1 = 0.0257 (for 4347 reflections with F2
>
4r(F2)), xR2 = 0.0637 and S = 1.072 for all reflections of 5a; R1 =
0.0447 (for 6439 reflections with F2>4r(F2)), xR2 = 0.0783 and
S = 0.783 for all reflections of 12a.
Catalysis
A solution of the corresponding complex 8–14 (0.025 mmol) in
2 mL of dry CH2Cl2 was prepared under argon. Methacrolein
(0.5 mmol in 2mL of dry CH2Cl2) and freshly distilled cyclopenta-
diene (3 mmol in 2 mL of dry CH2Cl2) were added consecutively by
syringe. The reaction was monitored by gas chromatography (GC).
Yields and exo : endo ratios were determined by GC analysis. The
reaction mixture was concentrated to ca. 0.3 mL, filtered through
silica and washed with CH2Cl2–hexane: 2 : 1, v/v before the
determination of the enantiomeric purity. Enantiomeric excesses
were determined by integration of the aldehyde proton of both
7 E. P. Ku¨ndig, C. M. Saudan and G. Bernardinelli, Angew. Chem., Int.
Ed., 1999, 38, 1219.
8 J. W. Faller and J. Parr, Organometallics, 2000, 19, 1829; J. W. Faller
and A. Lavoie, J. Orgonamet. Chem., 2001, 630, 17; J. W. Faller and J.
Parr, Organometallics, 2001, 20, 697; J. W. Faller and J. B. Grimmond,
Organometallics, 2001, 20, 2454; J. W. Faller, J. B. Grimmond and D. G.
D’Alliessi, J. Am. Chem. Soc., 2001, 123, 2525; J. W. Faller, A. R. Lavoie
and B. J. Grimmond, Organometallics, 2002, 21, 1662; J. W. Faller and
P. P. Fontaine, Organometallics, 2005, 24, 4132; J. W. Faller and P. P.
Fontaine, J. Organomet. Chem., 2006, 691, 5810.
9 D. L. Davies, J. Fawcett, S. A. Garratt and D. R. Russell, Chem.
Commun., 1997, 1351; A. J. Davenport, D. L. Davies, J. Fawcett, S. A.
Garratt, L. Lad and D. R. Russell, Chem. Commun., 1997, 2347; D. L.
Davies, J. Fawcett, S. A. Garratt and D. R. Russell, J. Organomet.
Chem., 2002, 662, 43; A. J. Davenport, D. L. Davies, J. Fawcett and
D. R. Russell, Dalton Trans., 2004, 1481; A. J. Davenport, D. L. Davies,
J. Fawcett and D. R. Russell, J. Organomet. Chem., 2006, 691, 2221; A. J.
Davenport, D. L. Davies, J. Fawcett and D. R. Russell, J. Organomet.
Chem., 2006, 691, 3445.
1
enantiomers in the H-NMR spectra, using Eu(hfc)3 (0.3 molar
ratio) as a chiral shift reagent. The absolute configuration of the
major adduct was assigned by comparing the sign of [a]D with that
in the literature.42
10 A. J. Davenport, D. L. Davies, J. Fawcett, R. Krafczyk and D. R.
Russell, J. Chem. Soc., Dalton Trans., 2000, 4432.
11 D. L. Davies, J. Fawcett, S. A. Garratt and D. R. Russell,
Organometallics, 2001, 20, 3029.
12 D. Carmona, C. Cativiela, R. Garc´ıa-Correas, F. J. Lahoz, M. P.
Lamata, J. A. Lo´pez, M. P. Lo´pez-Ram de V´ıu, L. A. Oro, E. San
Jose´ and F. Viguri, Chem. Commun., 1996, 1247.
13 D. Carmona, M. P. Lamata, F. Viguri, C. Barba, R. Rodr´ıguez, F. J.
Lahoz, M. L. Mart´ın, L. A. Oro and L. Salvatella, Organometallics,
2007, 26, 6493.
Acknowledgements
We thank the Ministerio de Educacio´n y Ciencia (Grant CTQ
2006-03030/BQU and Grant CSD2006-0015 Consolider Ingenio
2010) and Gobierno de Arago´n (Grupo Consolidado: Catal-
izadores Organometa´licos Enantioselectivos) for financial sup-
port. Marta Salas and M. Trinidad Rodrigo are acknowledged
for experimental assistance.
14 D. Carmona, F. J. Lahoz, S. Elipe, L. A. Oro, M. P. Lamata, F. Viguri,
F. Sa´nchez, S. Mart´ınez, C. Cativiela and M. P. Lo´pez-Ram de V´ıu,
Organometallics, 2002, 21, 5100.
15 D. Carmona, C. Cativiela, S. Elipe, F. J. Lahoz, M. P. Lamata, M. P.
Lo´pez-Ram de V´ıu, L. A. Oro, C. Vega and F. Viguri, Chem. Commun.,
1997, 2351.
16 D. Carmona, C. Vega, N. Garc´ıa, F. J. Lahoz, S. Elipe, L. A. Oro, M. P.
Lamata, F. Viguri and R. Borao, Organometallics, 2006, 25, 1592.
17 D. Carmona, F. J. Lahoz, S. Elipe, L. A. Oro, M. P. Lamata, F. Viguri,
C. Mir, C. Cativiela and M. P. Lo´pez-Ram de V´ıu, Organometallics,
1998, 17, 2986.
18 D. Carmona, C. Vega, C. Cativiela, F. J. Lahoz, S. Elipe, L. A. Oro,
M. P. Lamata, F. Viguri, R. Garc´ıa-Correas, C. Cativiela and M. P.
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19 H. Brunner, F. Henning, M. Weber, D. Carmona and F. J. Lahoz,
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