New chiral oxazoline based-rhodium(I) catalysts: Synthesis, characterisation, heterogeneisation and applications

Article abstract of DOI:10.1016/j.jorganchem.2005.10.016

New chiral oxazoline-based rhodium(I) homogeneous and heterogeneous catalysts have been prepared and fully characterised through ¹H and ¹³C NMR, CP-MAS NMR and XPS. The method used for anchoring the catalyst onto silica was found par

Full text of DOI:10.1016/j.jorganchem.2005.10.016

Journal of Organometallic Chemistry 691 (2006) 741–747
www.elsevier.com/locate/jorganchem
New chiral oxazoline based-rhodium(I) catalysts:
Synthesis, characterisation, heterogeneisation and applications
*
*
Nathalie Debono, Laurent Djakovitch , Catherine Pinel
Institut de Recherches sur la Catalyse, CNRS UPR 5401, 2, Avenue Albert Einstein, 69626 Villeurbanne, France
Received 4 August 2005; received in revised form 3 October 2005; accepted 6 October 2005
Available online 18 November 2005
Abstract
New chiral oxazoline-based rhodium(I) homogeneous and heterogeneous catalysts have been prepared and fully characterised
1
through H and 13C NMR, CP-MAS NMR and XPS. The method used for anchoring the catalyst onto silica was found particularly
suitable, since the organometallic complexes remained unchanged over the procedure. The catalysts exhibited a moderate activity and
enantioselectivity in hydrogenation of C@O and C@C double bond.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Bis(oxazoline); Pyridino-oxazolines; Chiral rhodium(I)-complexes; Tethered catalysts; Hydrogenation
1. Introduction
oxazoline ligands have been developed giving more stable
catalysts, however few applications were reported [10–14].
While successful, the use of chiral nitrogen based cata-
lysts remains limited in the fine chemical industry mainly
due to the tedious separation and recycling of these homo-
geneous complexes. These difficulties can be overcome by
the development of heterogeneous catalysts based on the
oxazoline ligands. Several methods have been applied to
immobilise the bis(oxazoline) ligands onto organic poly-
mers or inorganic supports.
The first example was reported by Mayoral et al. in 1997
[15]. The authors used electrostatic interactions between an
anionic support, i.e. a clay, and a cationic copper (II)
bis(oxazoline) complex for cyclopropanation reactions
[16,17]. Latter, the same authors reported the copolymerisa-
tion of allyl- or styryl-modified bis(oxazoline) ligands as an
interesting alternative method [18,19]. Following these pio-
neering works, several authors reported the grafting of chi-
ral bis(oxazoline) ligands on organic polymers (ArgoGel
[20], PEG [21,22]), or on metal oxides [23–27]. On the con-
trary, very few reports concern, the heterogeneisation of
chiral pyridine-oxazoline based complexes [28–30].
Enantioselective catalysis became one of the most effi-
cient methodologies for asymmetric organic synthesis of
biologically relevant natural or synthetic molecules in fine
chemistry and related disciplines.
Based on the pioneering Pfaltz works related to the syn-
thesis of the C2-symmetric semicorrins, the chemistry of
C2-symmetric chiral bis(oxazoline) ligands and of their cor-
responding transition-metal complexes, have received dur-
ing the last decades a great attention through their
successful applications in asymmetric catalysis of numerous
reactions [1]. Since the early 1990s, chiral bis(oxazoline)
complexes have been successfully applied to carbon–car-
bon coupling reactions such as the Diels–Alder reactions
[2,3] or the cyclopropanation reactions [4], to aziridination
reactions [5], hydrosilylations [6], oxidations [7] or reduc-
tions [8,9]. Usually, high conversions and enantioselectivi-
ties were observed. Recently, new chiral pyridino-
*
Corresponding authors. Tel.: +33 4 72 44 53 81; fax: +33 4 2 44 53 99
These supported bis(oxazoline)-based catalysts were
tested successfully in cyclopropanations, Diels–Alder
reactions, aziridination or hydrosilylation reaction but no
(L. Djakovitch).
E-mail addresses: Laurent.Djakovitch@catalyse.cnrs.fr (L. Djako-
vitch), Catherine.pinel@catalyse.cnrs.fr (C. Pinel).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.10.016

742
N. Debono et al. / Journal of Organometallic Chemistry 691 (2006) 741–747
successful example of reduction have been reported in the
literature.
The homogeneous complexes ½RhðIÞ-PyOx-CODꢀþ
½BF4ꢀꢁ ð4Þ, ½RhðIÞ-BoxPh-CODꢀþ½BF4ꢀꢁ ð5Þ, and ½RhðIÞ-
BoxOH-CODꢀþ½BF4ꢀꢁ ð6Þ were fully characterised through
NMR spectra, IR, [a]D and elemental analysis. IR spectra
(film) show the characteristic mC@N band at 1643–
1653 cmꢁ1, in good agreement with values reported in the
literature for structurally close bis(oxazoline) complexes
[35,36]. 13C NMR spectra of the complexes 4–6 gave a sig-
nal at 168–172 ppm corresponding to the C@N of the oxaz-
oline ring. The presence of THF was observed by NMR
(1H: 1.78 and 3.67 ppm; 13C: 25.6 and 67.9 ppm), for the
complexes prepared from the bis-oxazoline ligands. Consid-
We previously reported the reduction of phenyl-alkyl
ketones by transfer hydrogenation catalysed by chiral
bis(oxazoline) transition metal complexes [31]. Encouraged
by these results, we investigated further the development of
heterogeneous catalysts for enantioselective reduction
based on the C2-symmetric bis(oxazoline) ligands.
In the present contribution, we describe the preparation
of the different homogeneous and heterogeneous complexes
and the characterisation of new homogeneous and silica
supported chiral bis(oxazoline)- and pyridino-oxazoline-
rhodium(I) complexes. The first results achieved with the
different catalysts for the hydrogenation of prochiral car-
bonyl and olefinic compounds are reported.
1
ering the H integration, one molecule of THF was proba-
bly enclosed into the crystal net of the complex 5 during the
removal of the solvent. Such phenomenon was not observed
with the PyOx corresponding complex 4, but was already
reported in the literature for rhodium complexes [37].
2. Results and discussion
1
All other signals of the H and 13C NMR spectra were
The chiral pyridine-oxazoline ligand (PyOx) 1 was pre-
pared from the commercial picolinic acid and (S)-phenyl-
glycinol following the 4 steps procedure reported by
Meyers et al. [32] in 36% overall yield. The chiral bis(oxaz-
oline) ligand 2 (BoxPh) and 3 (BoxOH) were synthesised
from the diethylmalonimidate dihydrochloride and the
commercial (S)-phenylglycinol or (1S, 2S)-2-amino-1-phe-
nylpropane-1,3-diol, respectively, in CH2Cl2 according to
a procedure reported by Aggarwal et al. [33] in good yields.
The corresponding rhodium(I) complexes ½RhðIÞ-PyOx-
CODꢀþ½BF4ꢀꢁ ð4Þ, ½RhðIÞ-BoxPh-CODꢀþ½BF4ꢀꢁ ð5Þ and
½RhðIÞ-BoxOH-CODꢀþ½BF4ꢀꢁ ð6Þ were prepared from the
cationic precursor [Rh(I)(COD)(THF)2]+[BF4]ꢁ in dry
THF in excellent isolated yields (>89%) (Scheme 1) [34].
attributed to the cyclooctadienyl and bis(oxazoline) ligands
coordinated to the rhodium(I) centre. More specifically, the
1H NMR spectra of rhodium(I) complexes show signal cor-
responding to the bridging CH2 group of the BOX moiety
as a singlet at 4.05 ppm for 5 and 3.99 ppm for 6, suggest-
ing a C2-symmetry in these complexes [38].
In order to achieve the heterogeneisation of 5 onto silica
(SiO2), the chiral bis(oxazoline) ligand 2 was functionalised
at the bridging CH2 carbon by introduction of a tris(eth-
oxy)silyl-alkyl chain (Scheme 2). 1H and 13C NMR spectra
of the resulting ligand (C3BoxPh) 7 indicate that the C2-
symmetry of the bis(oxazoline) moiety is not disordered
by such modification. The corresponding rhodium(I)
complex [Rh(I)-C3BoxPh-COD]+[BF4]ꢁ (8) was obtained
O
N
-
, BF4
4
N
Rh
N
Ph
1
2
N
O
Ph
O
O
Ph
N
N
O
N
N
Ph
Ph
[Rh(COD)(THF)2]BF4
-
, BF4 , nTHF
5
Rh
Ph
O
O
O
Ph
Ph
HOH2C
Ph
CH2OH
HOH2C
N
N
O
N
3
-
, BF4 , nTHF
6
Rh
N
O
HOH2C
Ph
Scheme 1. Synthesis of the chiral rhodium(I) complexes 4–6.

N. Debono et al. / Journal of Organometallic Chemistry 691 (2006) 741–747
743
following the procedure described above starting from the
crude substrate 7 and was used in further steps without
purification.
Typically, such binding energies can be assigned to Rh(I)
species [40,41]. The close values observed for both homoge-
neous and grafted complexes would indicate that the sphere
coordination around the metallic center is the same in the
two rhodium catalysts 5 and 9. Since NMR characterisation
of 5 confirmed the expected structure for the {[Rh(I)-BoxPh-
COD]+[BF4]ꢁ} complex, we assume that both complexes
have the same coordination properties (ligand field) and that
the rhodium centre is in the same oxidation state 1+. These
results, together those issued from the characterisation by
13C CP-MAS NMR of the catalyst 9, indicate that the rho-
dium complex {[Rh(I)-C3BoxPh-COD]+[BF4]ꢁ} (8) was
not altered during the grafting procedure.
In most cases the semi-quantitative XPS analysis of the
catalysts gave results in good agreement with the expected
structure, generally close to those obtained from elemental
analyses (Table 1). The N/Rh atomic ratios calculated
from these analyses were used to confirm both the struc-
tures and the purities of the rhodium catalysts. If for the
homogeneous catalyst 5, both the XPS and the elemental
analyses gave values in agreement with the expected struc-
ture (respectively, 1.7 and 2.0; expected 2.0), those obtained
for the heterogeneous catalysts 9 show higher N/Rh ratio
(respectively, 4.5 and 3.6) indicating that some free
bis(oxazoline) ligand is present at the silica surface proba-
bly due to partial decomplexation during the grafting pro-
cedure. Extensive washing of the heterogeneous catalyst 9
assured the absence of free complex.
Anchoring of 8 was performed by treatment of a suspen-
sion of activated silica in dichloromethane to give the heter-
ogeneous catalysts {[Rh(I)-C3BoxPh-COD]+[BF4]ꢁ}@SiO2
(9). At this stage, a new chiral centre was created but
according to previous report, modification at this carbon
did not affect the enantiocontrol of the reaction [39]. The
success of the covalent anchoring was assessed by analytical
and spectroscopic characterisations (NMR and XPS) of the
resulting solids. According to the chꢁem1 ical analyses (C, H,
N and Rh), 0.12–0.14 mmolcomplex g were grafted on the
silica support, in good agreement with results usually
reported in the literature for such preparations [24,26,27].
13C CP-MAS NMR spectra of the supported homogeneous
catalyst {[Rh(I)-C3BoxPh-COD]+[BF4]ꢁ}@SiO2 (9) was in
good agreement with the expected structure containing
the oxazoline ring bearing a C3-pendant chain and the
cyclooctadienyl ligand. The signals observed at 19 and
51 ppm were attributed to residual CH3CH2O group linked
to the bridging silicon atom at the silica surface. According
to Corma et al., [26] this observation would attest that the
{[Rh(I)-C3BoxPh-COD]+[BF4]ꢁ} complex 8 is grafted onto
the support by two Si–O–Si links (see Fig. 1).
X-ray photoelectron spectroscopy (XPS) has been used
for qualitative and quantitative characterisation of the
homogeneous and heterogeneous catalysts 5 and 9. The
binding energies for the [Rh]-3d5/2 as well as the atomic
ratio of N/Rh are summarized in Table 1. A binding energy
of 285 eV of the C1s level was used as internal standard.
The position of the Rh3d5/2 peaks of the homogeneous 5
and grafted 9 complexes were observed at 308.85 and
308.80 eV, respectively, with a slightly larger width in the
case of the latter one (Fig. 2).
We reported previously the use of bisoxazoline-Rh com-
plex 6 in the transfer hydrogenation of acetophenone. Low
conversion (22%) and ee (16%) were achieved [31].
Alternatively, the homogeneous Rh(I)-catalysts 4–6 were
evaluated for the enantioselective hydrogenation of C@O
and C@C bonds. These catalysts exhibited very low activity
towards the hydrogenation of a-acetamido cinnamic acid
Si(OEt)3
Ph
Si(OEt)3
O
O
N
N
[Rh(COD)(THF)2]BF4
THF, 0˚C to r.t., 24h
1/ BuLi, THF, 0˚C
O
O
O
O
, BF4-, nTHF
Rh
N
N
N
N
2/ I(CH2)3Si(OEt)3, 0˚C to r.t.
8
Ph
Ph
Ph
Ph
Ph
2
7
activated SiO2
CH2Cl2, 24h, r.t.
OEt
Si
Ph
O
N
SiO2
, BF4-, nTHF
Rh
N
O
Ph
9
Scheme 2. Preparation of the heterogeneous catalyst 9.

744
N. Debono et al. / Journal of Organometallic Chemistry 691 (2006) 741–747
OEt
Si
Ph
O
O
N
N
SiO2
, BF4-, nTHF
Rh
Ph
9
200
150
100
50
0
ppm
Fig. 1. CP MAS 13C NMR of the heterogeneous catalyst 9.
Table 1
molRh). Except for phenyl ethanol, for which low eeÕs were
observed (<10%), racemic products were analyzed.
The heterogeneous {[Rh-C3BoxPh-COD]+[BF4]ꢁ}@
SiO2 catalyst 9 was evaluated for the hydrogenation of the
methyl acetoacetate. Using only 0.06 mol% Rh, a reasonable
conversion of 24% within 6 h was obtained, corresponding
to the unexpected TON of 800 mol/molRh, giving again the
racemic product.
XPS analysis of homogeneous complex 5 and heterogeneous catalyst 9
Complex
Binding energy (eV) Rh 3d5/2
Atomic ratio N/Rha
5
308.85
308.8
307.5
309.2
1.7 (2)
3.5 (4.6)
9
9 after H2
9 after HTR
a
Calculated from XPS analysis (calculated from elemental analysis).
The XPS binding energies observed for the used hetero-
geneous rhodium catalyst 9 at 307.3 eV accounting for the
formation of metallic Rh(0) species [42], indicating that the
rhodium(I) complex 8 was reduced during the hydrogena-
tion reaction. The rhodium(0) species precipitated, most
probably, onto the silica support during the reaction.
Reduction of nitrogen-containing rhodium complex under
even under hydrogen pressure. At atmospheric pressure, the
methyl tiglate was slowly hydrogenated. Increasing the pres-
sure yielded total conversion but gave only racemic product
mixture (Table 2). Low to moderate conversions were
observed for the hydrogenation of acetophenone or methyl
acetoacetate corresponding to modest TON (<50 mol/
5-RhBoxPh
9-RhBox/SiO2
325
320
315
Binding energy (eV)
Fig. 2. XPS analysis of the homogeneous catalyst 5 and heterogeneous catalyst 9.
310
305
300

N. Debono et al. / Journal of Organometallic Chemistry 691 (2006) 741–747
745
Table 2
precipitated onto the support surface, those being not
enantioselective for the hydrogenation reaction. These
nitrogen-based complexes are preferably used in transfer
hydrogenation involving reaction conditions more favour-
able to their stability.
Hydrogenation in the presence of homogeneous Rh(I)-catalysts 4–6
Catalyst
O
O
O
O
O
OMe
OMe
4. Experimental
Conversion
(%)a (ee) (%)
Conversion (%)b
Conversion (%)
All preparations, manipulations and reactions were car-
ried out under argon (Schlenk techniques), including the
transfer of the catalysts to the reaction vessel. All glassware
was base- and acid-washed and oven dried.
4
6
5
13 (10)
76 (7)
63 (6)
50
30
41
100 (20 bar, 30 ꢁC) 31
(1 bar, r.t.)
100 (20 bar, 30 ꢁC) 10
(1 bar, r.t.)
96 (20 bar, 30 ꢁC)
THF was distilled under argon before use over sodium
from purple benzophenone ketyl and CH2Cl2 and CHCl3
were distilled over CaH2. Silica Aerosil 200 was agglomer-
ated prior to use by treatment with water. After evapora-
tion and drying at 120 ꢁC for 3 days the resulting
material was crushed and sieved to give a selected fraction
with a particle size of 40–60 mesh. BET of a silica sample
dehydroxylated at 500 ꢁC under 10ꢁ5 mmHg for 6 h gave
the following characteristics: specific surface = 204
4 m2/g. The organometallic precursor [Rh(I)(COD)-
(THF)2]+[BF4]ꢁ was prepared according to the literature
[34].
Solution NMR spectra were recorded with a Bruker AM
250 spectrometer (1H NMR were referenced to the residual
protio-solvent: CDCl3, d = 7.25 ppm; 13C NMR were ref-
erenced to the C-signal of the deutero solvent: CDCl3,
d = 77 ppm). Solid-state 13C-CP-MAS NMR spectra were
recorded on a Bruker DSX 300 or DSX 500 spectrometer.
13C NMR were arbitrarily referenced to the internal aro-
matic signal of the phenyl-ring substituent on the oxazoline
ring at 128 ppm. The absolute rhodium content of the cat-
alysts was determined by ICP-AES from a solution
obtained by treatment with a mixture of H2SO4 and
HNO3 and HCl in a Teflon reactor at 250–300 ꢁC. XPS
measurements were recorded on an ESCALAB 250 spec-
trometer equipped with a Al–K source (1486.6 eV). The
measurements of the binding energies were referred to the
characteristic C1s peak of the carbon fixed at the generally
accepted value of 285.0 eV.
a
200 mg of acetophenone, 1 mol% Rh/S, 10 mL MeOH, 10 bar H2, r.t.
200 mg of methyl acetoacetate, 1 mol % Rh/S, 10 mL MeOH, 20 bar
b
H2, 30 ꢁC.
nitrogen pressure was previously reported in the literature
in the presence of diamine ligand [43]. Excess of ligand
may prevent this decomplexation.
Such reduction of the rhodium has not been observed
when the catalyst 9 was used in transfer hydrogenation
(iPrOH, tBuOK) [44]. Under those conditions, Rh3d5/2
peak at 309.2 eV was detected for the used catalyst 9
accounting for the remaining presence of Rh(I)-species on
the silica support.
The absence of enantioselectivity can be clearly corre-
lated to the lack stability of the different rhodium com-
plexes under hydrogenation reaction conditions. These
results are coherent with the formation of metallic rhodium
during the reaction as observed by the apparition of black
colour after hydrogenation. The higher activity observed
for the supported complex 8 can be attributed to a good
dispersion of the precipitated metallic rhodium particles
during the reaction onto the silica support, rather than rho-
dium agglomeration in the reaction media as probably
observed for the homogeneous catalysts 4–6.
3. Conclusion
New homogeneous and heterogeneous chiral rho-
dium-catalysts based onto chiral bis(oxazoline) and pyr-
idino-oxazoline ligands have been prepared and fully
characterised. After anchoring onto inorganic support
(SiO2) the structure of the organometallic {[Rh(I)-C3Box-
Ph-COD]+[BF4]ꢁ} complex 8 remained intact as outlined
by the 13C CP-MAS NMR and XPS analyses.
Gas chromatography was performed on a Shimadzu
14A chromatograph equipped with a FID detector and a
Lipodex A column for the methyl acetoacetate and the
Chirasil Dex CB for the acetophenone. Flash chromatogra-
phy was performed at a pressure slightly greater than
atmospheric pressure using silica (Merck Silica Gel 60,
230–400 mesh). Thin layer chromatography was performed
The activity and selectivity of the homogeneous cata-
lysts were evaluated for the enantioselective hydrogenation
of prochiral C@O and C@C bonds. While the catalysts
gave generally a moderate activity, no significant enanti-
oselectivities were observed.
on Fluka Silica Gel 60 F254.
4.1. Synthesis of the 2-(4R-phenyl-4,5-dihydrooxazoli-2-yl)-
pyridine (1)
This was reasonably attributed to the instability of the
catalysts under the reaction conditions. As shown by
XPS analysis of the used catalyst 9, the rhodium(I) species
are converted to rhodium(0) particles that were probably
A solution of picolinic acid (2.07 g, 16.8 mmoles) in
freshly distilled thionyl chloride (20 mL) was refluxed for
20 h. After cooling, the excess of thionyl chloride was
removed under vacuum to give the corresponding acid

746
N. Debono et al. / Journal of Organometallic Chemistry 691 (2006) 741–747
chloride as a dark red solid. A solution of (R)-phenylgly-
cinol (2.47 g, 18.0 mmoles) and triethylamine (6.8 mL) in
dry chloroform (40 mL) was added dropwise at 0 ꢁC to a
solution of acid chloride in dry chloroform (20 mL). The
mixture is stirred for 20 h at room temperature then thionyl
chloride (12 mL) was added and the solution was refluxed
for 4 h. After cooling, the solution was slowly poured in
ice water (100 mL). After 10 min, the organic layer was col-
lected and washed with brine (40 mL), an aqueous solution
of K2CO3 0.1 M (2 · 50 mL) and brine (40 mL). The
organic layer was dried over Na2SO4 and the solvent was
removed under vacuum. The residue was purified by flash
chromatography eluting with Et2O/heptane (50/50) to give
the ligand as orange viscous oil in 36% yield.
m-C5H4N); 7.93 (m, 1H, o-C5H4N); 7.83 (m, 1H, m-
C5H4N); 7.78 (m, 1H, p-C5H4N); 7.30 (m, 5H, ðCHðC H ÞÞ);
6
5
5.24 (dd, J = 4 Hz, 2 Hz, 1H, CH2O); 5.22 (t, J = 4 Hz,
1H, CH2O); 4.59 (dd, J = 4 Hz, 2 Hz, 1H, NCH); 4.45 (m,
2H, CH(COD)); 4.31 (m, 2H, CH(COD)); 2.38 (m, 4H,
CH2(COD)); 1.90 (m, 4H, CH2(COD)). 13C NMR (CD2Cl2,
62.9 MHz): 172.2 (OCN); 149.9 ðCqðC H NÞÞ; 145.0
5
4
(o-C5H4N); 141.8 (m-C5H4N); 138.4 ðCqðC H ÞÞ; 131.1 (m-
6
5
C5H4N); 129.9 (m-C6H5); 129.8 (p-C5H4N); 127.5 (o-
C6H5); 126.6 (p-C6H5); 83.4 (CH(COD)); 80.1 (CH(COD));
67.4 (CH2(COD)); 29.9 (CH2(COD)). Anal. for C22H24-
N2O4RhBF4 [Found (Calc.)]: C, 49.7 (50.6); H, 4.7 (4.6);
N, 5.3 (5.4); Rh, 19.7 (19.7). [a]D = ꢁ33.6ꢁ (c 0.22, CHCl3).
IR: m(CN) = 1643 cmꢁ1
1H RMN (CDCl3, 250 MHz): 8.68 (dq, J = 4.8 Hz,
{[Rh(I)-BoxPh-COD]+[BF4]ꢁ} (5): yellow solid, 89%
yield, m.p. = 130–135 ꢁC (decomposition) 1H NMR
(CDCl3, 250 MHz): 7.25 (m, 10H, ðCHðC H ÞÞ; 5.01 (dd,
0.8 Hz, 1H, CH
); 8.10 (pseudo dt, J = 7.9 Hz, 1H,
ðC5H4Þ
CH
); 7.74 (td, J = 7.8 Hz, 1.8 Hz, 1H, CH
); 7.36
ðC5H4Þ
ðC5H4Þ
6
5
(ddd, J = 7.6 Hz, 4.9 Hz, 1.1 Hz, 1H, CH
); 7.28 (m,
J = 10.0 Hz, 4.4 Hz, 2H, CHC6H5); 4.96 (dd, J = 9.0 Hz,
9.0 Hz, 2H, CH2OCN); 4.21 (dd, 2H, J = 9 Hz, 4.5 Hz,
CH2OCN); 4.18 (m, 2H, CH(COD)); 4.05 (s, 2H, CCH2C);
3.67 (m, 4H, CH2O(THF)); 3.48 (m, 2H, CH2(COD)); 2.25
(m, 2H, CH2(COD)); 1.78 (m, 4H, CH2CH2O(THF)); 1.62 (m,
2H, CH2(COD)); 1.31 (m, 2H, CH2(COD)). 13C NMR (CDCl3,
62.9 MHz): 168.7 (OCN); 139.6 ðCqðC H ÞÞ; 129.4 (m-C6H5);
ðC5H4Þ
5H, CH
); 5.40 (dd, J = 10.2 Hz, 8.6 Hz, 1H, CH O);
ðC6H5Þ
2
4.84 (dd, J = 10.3 Hz, 8.5 Hz, 1H, CH2O); 4.33 (pseudo t,
J = 8.5 Hz, 1H, CH2CHN). 13C RMN (CDCl3, 62.9
MHz): 163.86 (OCN); 149.75 ðo-CHðC H NÞÞ; 146.65
5
4
ðCqðC H NÞÞ; 141.77 ðCqðC H ÞÞ; 136.68 (CH); 128.78
5
4
6
5
ðm-CHðC H ÞÞ; 127.73 (CH); 126.79 ðo-CHðC H ÞÞ; 125.75
6
5
6
5
6
5
(CH); 124.24 (CH); 75.30 (CH2CHN); 70.33 (CH2). IR :
m(CN) = 1644 cmꢁ1
128.9 (p-C6H5); 126.0 (o-C6H5); 83.1 (CH(COD), J(Rh–C) =
.
12.4 Hz); 80.4 (CH(COD)
,
J(Rh–C) = 12.4 Hz); 77.8
(OCH2); 67.9 (OCH2(THF), CH–C6H5); 30.7 (CH2(COD));
29.3 (CH2(COD)); 27.9 (CCH2C); 25.6 (CH2CH2O(THF)).
Anal. for C35H46N2O4RhBF4 [Found (Calc.)]: C, 56.17
(56.11); H, 6.19; (6.14); N, 3.74 (3.74); Rh, 13.75 (13.75).
4.2. Synthesis of the bis(oxazoline) 2 and 3 [33]
A solution of aminoalcohol (11.9 mmol) and diethyl
malonimidate hydrochloride (5.9 mmol) in dry dichloro-
methane (20 mL) was refluxed for 18 h under argon. At
completion of the reaction (TLC), water (40 mL) was added
and the mixture was extracted by CH2Cl2 (3 · 20 mL). The
combined organic layers were dried over MgSO4 and the
solvent was removed under vacuum to give a brown oil.
The residue was purified by flash chromatography eluting
with CH2Cl2/MeOH (90:10) to give bis(oxazoline).
[a]D = ꢁ143ꢁ (c 0.2, CHCl3). IR: m(CN) = 1647 cmꢁ1
.
{[Rh(I)-BoxOH-COD]+[BF4]ꢁ} (6): yellow solid, 90%
yield, m.p. = 130–135 ꢁC (decomposition). 1H NMR
(CDCl3, 250 MHz): 7.41 (m, 10H, ðCHðC H ÞÞ; 5.76 (d, J =
6
5
4.1 Hz, 2H, CHO); 4.35 (m, 2H, CHN); 4.06 (m, 2H,
CH2OH); 3.99 (s, 2H, CCH2C); 3.88 (m, 2H, CH2OH);
3.75 (m, 10H, CH2O (THF), CH(COD)); 2.58 (m, 4H,
CH(COD)); 1.85 (m, 8H, CH2CH2O(THF)); 1.70 (m, 4H,
CH(COD)).13C NMR (CDCl3, 62.9 MHz): 168.1 (OCN);
137.5 ðCqðC H ÞÞ; 129.6 (m-C6H5); 129.4 (p-C6H5); 125.6 (o-
bis[(4R)-Phenyl-2-oxazoline]methylene (2) was obtained
as orange viscous oil in 57% yield. IR: m(CN) = 1663 cmꢁ1
.
6
5
1H and 13C NMR data are consistent with those reported [4].
bis[(4S,5S) (4-Hydroxymethyl-5-phenyl-2-oxazoline)]meth-
ylene (3) was obtained as a white solid in 62% yield. IR:
C6H5); 85.8 (CH–C6H5); 83.1 (CH(COD), J(Rh–C) =
12.4 Hz); 80.5 (CH(COD)
,
J(Rh–C) = 12.4 Hz); 73.7
(CHN); 67.9 (OCH2(THF)); 65.8 (CH2OH); 30.9 (CH2(COD));
29.5 (CH2(COD)); 28.1 (CCH2C); 25.6 (CH2CH2O(THF)).
Anal. for C37H50N2O6RhBF4 [Found (Calc.)]: C, 56.2
(56.9); H, 6.2 (6.4); N, 3.6 (3.6); Rh, 13.5 (13.2).
1
m(CN) = 1673 cmꢁ1. H and 13C NMR data are consistent
with those reported [33].
4.3. Preparation of homogeneous catalyst 4–6
[a]D = ꢁ87.8ꢁ (c 0.2, CHCl3). IR: m(CN) = 1653 cmꢁ1
.
The pyridine-oxazoline ligand or, the bis(oxazoline)
ligands (0.34 mmol) was added at 0 ꢁC to a solution of
[Rh(COD)(THF)2]+[BF4]ꢁ (150.2 mg, 0.34 mmol) in dry
THF (10 mL). The solution was stirred for 20 h at room
temperature and the solvent was removed under vacuum
to give the expected complex.
4.4. Preparation of the modified ligand bis[4-phenyl-2-
oxazoline]methylene propyltriethoxysilane (7)
n-BuLi (1.9 mL of a solution 2.1 M in n-hexane,
4.1 mmol) was added dropwise at 0 ꢁC to a solution of 2
(1.26 g, 4.1 mmol) in dry THF (60 mL). The solution was
allowed to warm to room temperature and stirred for 3 h.
Then, the 3-iodopropylethoxysilan (1.36 g, 4.1 mmol) was
added drop wise at 0 ꢁC. The mixture was allowed to warm
{[Rh(I)-PyOx-COD]+[BF4] ꢁ} (4): orange solid, 95%
yield, m.p. = 222–228 ꢁC (decomposition). 1H NMR
(CD2Cl2, 250 MHz): 8.16 (td, J = 7.6 Hz, 1.7 Hz, 1H,

N. Debono et al. / Journal of Organometallic Chemistry 691 (2006) 741–747
747
´
[8] M. Gomez, S. Jansat, G. Muller, M.C. Bonnet, J. Breuzard, M.
to room temperature and stirred for 21 h. The solvent was
removed under vacuum. The residue was dissolved in
CH2Cl2 (20 mL) and washed with an aqueous saturated
NH4Cl solution (1 · 20 mL). The organic layer was dried
over Na2SO4 and the solvent evaporated under vacuum to
give the ligand 7 as orange viscous oil in 98% yield.
Lemaire, J. Organomet. Chem. 659 (2002) 186.
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(1991) 232.
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Lett. 43 (2002) 8599–8602.
[14] U. Bremberg, F. Rahm, C. Moberg, Tetrahedron Asym. 9 (1998)
3437–3443.
[15] J.M. Fraile, J.I. Garcia, J.A. Mayoral, T. Tarnai, Tetrahedron Asym.
8 (1997) 2089.
[16] J.M. Fraile, J.I. Garcia, J.A. Mayoral, T. Tarnai, M.A. Harmer, J.
Catal. 186 (1999) 214.
[17] A.I. Fernandez, J.-M. Fraile, J.I. Garcıa, C.I. Herrerıas, J.A.
Mayoral, L. Salvatella, Catal. Commun. 2 (2001) 165.
[18] M.I. Burguete, J.M. Fraile, J.I. Garc-a, E. Garc-a-Verdugo, C.I.
1H NMR (CDCl3, 250 MHz): 7.26 (m, 10H, ðCHðC H ÞÞ);
6
5
5.23 (m, 2H, NCH); 4.64 (m, 2H, OCH2CH); 4.14 (m, 2H,
OCH2CH); 3.79 (m, 7H, OCH2CH3 and NCCHCN); 2.11
(m, 2H, CHCH2CH2); 1.77 (m, 2H, CH2CH2CH2); 1.19
(m, 9H, OCH2CH3); 0.69 (m, 2H, CH2Si). 13C NMR
(CDCl3, 62.9 MHz): 168.57 (C@N); 141.99 ðCqðC H ÞÞ;
6
5
128.30 ðCHðC H ÞÞ; 127.14 ðp-CHðC H ÞÞ; 126.41 ðCHðC H ÞÞ;
6
5
6
5
6
5
´
´
´
74.64 (CH2O); 69.23 (NCH); 57.96 (CH2OSi); 36.93
(NCCHCN); 34.57 (CH2CH2CH2); 17.97 (CH3CH2);
17.41 (CH2CH2CH); 10.52 (CH2Si).
´
´
Herrer´ıas, S.V. Luis, J.A. Mayoral, J. Org. Chem. 66 (2001) 8893.
[19] E. Dıez-Barra, J.M. Fraile, J.I. Garcia, E. Garcıa-Verdugo, C.I.
´
´
´
´
´
Herrerıas, S.V. Luis, J.A. Mayoral, P. Sanchez-Verdu, J. Tolosa,
4.4.1. General procedure for anchoring the {[Rh(I)-C3BOX-
COD]+[BF4]ꢁ} complex 8
Tetrahedron Lett. 14 (2003) 773–778.
[20] K. Hallman, C. Moberg, Tetrahedron Asym. 12 (2001) 1475.
[21] R. Annunziata, M. Benaglia, M. Cinquini, F. Cozzi, Eur. J. Org.
Chem. (2001) 1045.
[22] R. Annunziata, M. Benaglia, M. Cinquini, F. Cozzi, G. Pozzi, Eur.
J. Org. Chem. (2003) 1191.
[23] J.K. Park, S.W. Kim, T. Hyeon, B.M. Kim, Tetrahedron Asym. 12
(2001) 2931.
[24] D. Rechavi, M. Lemaire, Org. Lett. 3 (2001) 2493.
[25] D. Rechavi, M. Lemaire, Chem. Rev. 102 (2002) 3467.
The complex 8 was added to a suspension of SiO2 in dry
CH2Cl2 (15 mL/0.1 mmol of 8). The mixture was stirred for
24 h at room temperature. The heterogeneous catalyst 9
was filtered under argon, washed twice with 10 mL of dry
CH2Cl2 and dried under vacuum.
13CCP-MASNMR(75.5 MHz):174(CN);140ðCqðC H ÞÞ;
6
5
128 ðCqðC H ÞÞ; 78 (CH (COD)); 59 (CH2O); 50 (CH3CH2O);
6
5
´
[26] A. Corma, H. Garcıa, A. Moussaif, M.J. Sabater, R. Zniber, A.
41 (CH2CH2CH2); 35 (NCCHCN); 30 (CH2 (COD)); 19
(CH3CH2O); 17 (CH2CH2CH); 13 (CH2Si). Found Anal.:
Rh, 1.38; C, 7.91; H, 1.04; N, 0.87.
Redouane, Chem. Commun. (2002) 1058.
[27] R.J. Clarke, I.J. Shannon, Chem. Commun. (2001) 1936.
[28] K. Hallman, E. Macedo, K. Nordstro¨m, C. Moberg, Tetrahedron
Asym. 10 (1999) 4037–4046.
´
´
[29] A. Cornejo, J.M. Fraile, J.I. Garcıa, E. Garcıa-Verdugo, M.J. Gil,
4.4.2. General procedure for hydrogenation reactions
´
G. Legarreta, S.o.V. Luis, V. Martınez-Merino, J.A. Mayoral, Org.
All hydrogenation reactions were performed in stainless
steel autoclaves equipped with a glass inlet. The substrate
(200 mg) and the catalyst (1 mol %) were dissolved in
10 mL MeOH. The glass inlet was introduced in the auto-
clave that was then purge by series of pressurisation/depres-
surisation under hydrogen before the pressure was set to the
desire value. The reaction was performed at 30 ꢁC for 24 h.
Lett. 4 (2002) 3927.
[30] A. Cornejo, J.M. Fraile, J.I. Garcia, M.J. Gil, C.I. Herrerias, G.
Legarreta, V. Martinez-Merino, J.A. Mayoral, J. Mol. Catal. A:
Chem. 196 (2003) 101.
[31] N. Debono, M. Besson, C. Pinel, L. Djakovitch, Tetrahedron Lett.
45 (2004) 2235.
[32] A.I. Meyers, R.A. Gabel, J. Org. Chem. 47 (1982) 2633.
[33] V.K. Aggarwal, L. Bell, M.P. Googan, P. Jubault, J. Chem. Soc.,
Perkin Trans. I (1998) 2037.
Acknowledgements
[34] M. Beller, H. Trauthwein, M. Eichberger, C. Breindl, T.E. Muller,
¨
A. Zapf, J. Organomet. Chem. 566 (1998) 277.
[35] D. Carmona, J. Ferrer, E. Lalaguna, M. Lorenzo, F.J. Lahoz, S.
Elipe, L.A. Oro, Eur. J. Inorg. Chem. (2001) 259.
[36] Y. Imai, W. Zhang, T. Kida, Y. Nakatsuji, I. Ikeda, Tetrahedron
Asym. 7 (1996) 2453.
`
The authors thank Pierre Delichere for XPS analysis
and discussions and Frederic Lefebvre for 13C-CP-MAS
NMR. N.D. thanks the Ministry of Education for a grant.
´ ´
`
[37] M. Beller, H. Trauthwein, M. Eichberger, C. Breindl, T.E. Muller,
¨
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