New C2-symmetric diphosphite ligands derived from carbohydrates: Effect of the remote stereocenters on asymmetric catalysis

Article abstract of DOI:10.1002/adsc.200600654

The synthesis of new modular chiral diphosphite ligands with C ₂-symmetry and carbohydrate backbone is reported. We also report here the synthesis of the corresponding rhodium complexes [Rh(COD)(L)]BF₄ (L = diphosphite). All these sp

Full text of DOI:10.1002/adsc.200600654

FULL PAPERS
DOI: 10.1002/adsc.200600654
New C2-Symmetric Diphosphite Ligands Derived from Carbo-
hydrates: Effect of the Remote Stereocenters on Asymmetric
Catalysis
M. Rosa Axet,a Jordi Benet-Buchholz,b Carmen Claver,a,* and Sergio Castillónc,*
a
Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcelli Domingo s/n, 43007 Tarragona, Spain
Fax : (+34)-97-755-9563; e-mail: carmen.claver@urv.cat
Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain
Departament de Química Analítica i Química Orgànica, Facultat de Química, Universitat Rovira i Virgili, Marcelli
b
c
Domingo s/n, 43007 Tarragona, Spain; e-mail: sergio.castillon@urv.cat
Received: December 31, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The synthesis of new modular chiral di- centres in positions 2 and 5 of the tetrahydrofuran
phosphite ligands with C2-symmetry and carbohy- ring of the diphosphite ligands were observed to
drate backbone is reported. We also report here the have a considerable influence on the results obtained
synthesis of the corresponding rhodium complexes in the rhodium-catalysed hydroformylation and hy-
[Rh(COD)(L)]BF4 (L=diphosphite). All these spe- drogenation reactions. Thus, the configuration of the
A
cies have been characterised in solution by NMR major isomer obtained in the hydroformylation reac-
spectroscopy and in some cases in the solid state by tion may be controlled by changing the configuration
X-ray diffraction. The solution structures of the hy- of these stereocentres.
dridorhodiumcarbonyl
species
[RhH(CO)2(L)],
where L=diphosphites 12a–14a, 12b, have been
studied using high-pressure NMR spectroscopy. The Keywords: asymmetric catalysis; carbohydrates; di-
configuration and substitution of the remote stereo- phosphites; hydroformylation; hydrogenation
Introduction
2 proved to function as a pseudoenantiomer of 1 pro-
viding the opposite enantiomer in the asymmetric hy-
In homogeneous asymmetric catalysis based on transi- drogenation of prochiral olefins.[4]
tion metals, the design of new ligands is, perhaps, the
During the last years we have focused in the use of
most crucial step to achieve the highest levels of reac- furanose derivatives of C1-symmetry as ligands in
tivity and selectivity. One of the simplest ways of ob- asymmetric catalysis. Some of these ligands have been
taining chiral ligands is to transform natural chiral
compounds, thus making optical resolution proce-
dures unnecessary. This fact, that can be considered
an advantage from a synthetic point of view, is also
one limitation for catalytic purposes, since only one
enantiomer is accessible. However, this limitation
may be partially overcome by using the so-called
pseudoenantiomer ligands as will be shown in this
contribution. Carbohydrate derivative ligands have
many advantages: they are readily available, highly
functionalised, and they may be systematically modi-
fied.[1] Some carbohydrate derivative ligands are
showed in Figure 1. The pyranoside diphosphinite li-
gands 1 were successfully used in rhodium-catalysed
asymmetric hydrogenation of enamido acids,[2] and
Figure 1. Representative carbohydrate derivative ligands (1–
nickel-catalysed hydrocyanation of alkenes.[3] Ligand 5) with pyranoid and furanoid skeleton.
Adv. Synth. Catal. 2007, 349, 1983 – 1998
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1983

M. Rosa Axet et al.
FULL PAPERS
successfully applied in metal-catalysed asymmetric re-
actions providing excellent results in rhodium-cata-
lysed asymmetric hydrogenation, asymmetric hydro-
formylation or palladium-catalysed asymmetric allylic
substitution.[1] Particularly interesting are the catalytic
results obtained in the rhodium-catalysed asymmetric
hydroformylation of vinylarenes with C1-symmetric
diphosphites derived from carbohydrates, 3 (R=
methyl) (Figure 1),[5,6] which are some of the best re-
ported so far.[7,8] Both the S and the R enantiomers
can be obtained with excellent regio- and enantiose-
lectivity (91%, 98%) under mild reaction conditions.
The configuration of the stereocenters (C-3, C-5) had
remarkable effects on the enantioselectivity of the hy-
droformylation reactions as was shown through the
characterisation of the solution structures of the hy-
dridorhodium diphosphite dicarbonyl intermediates
[RhH(CO)2(L)].[5,6] Complexes containing ligands 4
and 5 were used in the asymmetric hydrogenation of
prochiral olefins also leading to excellent results[9–11]
Recently, palladium nanoparticles stabilized by ligand
3 (R=H) were used in the allylic alkylation reaction
providing an excellent kinetic resolution.[12]
Ligands with C2-symmetry are in general prepared
from d-mannitol. Reetz et al.[13] reported the use of
diphosphites 6 in the asymmetric hydrogenation of
acetoamidoacrylic acid derivatives achieving enantio-
selectivities up to 98%. Other remarkable C2-sym-
metric ligands, derived from mannitol, successfully ap-
plied in asymmetric hydrogenation are the 2,5-disub-
stitued phospholane ligands (Duphos derivatives) 7
and 8[14] and the related DIOP,[15] analogue. These 2,5-
disubstitued phospholane ligands have recently been
identified as excellent ligands for the rhodium-cata-
lysed asymmetric hydroformylation providing high
turnover rates and enantioselectivities for styrene,
allyl cyanide, vinyl acetate[16] and [2.2.1]-bicyclic ole-
fins.[17]
Figure 2. C2-Symmetric ligands 6–11. Ligands 6–10 were ob-
tained from carbohydrates.
We have recently reported the synthesis of C2-sym-
metric diphosphinite ligands 9 and 10 derived from
carbohydrates with a furanoid backbone.[18] These li-
gands were used in the rhodium-catalysed asymmetric
hydrogenation of olefins. The use of ligands 9 and 10
(Figure 2) in the hydrogenation of enamido esters Figure 3. New C2-symmetric diphosphite ligands 12–14.
considerably improves the enantioselectivity in com-
parison with the results obtained with ligand 11,[19]
which does not have substituents in the remote ster- gands because, instead the rigid bicycle of the xylose
eocentres. Since the configuration of carbon bonded and glucose derivatives, they contain substituents in
to the phosphinite function is similar in all these li- positions 2 and 5 of the sugar backbone. This fact
gands, this result reveals a remarkable influence of allows us to study the influence on the enantioselec-
the substituents in positions 2 and 5 of the tetrahydro- tivity of different substituents present at C-2 and C-5,
furan ring.
and the configuration of these positions. We also
In order to know more about this remote effect in report here the synthesis of the corresponding rhodi-
asymmetric catalysis, we present here the preparation um cationic complexes containing the chiral ligands
of a new family of diphosphite ligands 12–14 (Fig- 12–14 and their application in the rhodium-catalysed
ure 3). These ligands present important differences in asymmetric hydroformylation of vinylarenes and hy-
respect to the previous C1-symmetric phosphite li- drogenation of methyl acetamidoacrylate.
1984
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New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
Results and Discussion
Synthesis of Diphosphite Ligands with Carbohydrate
Backbone
Diphosphite ligands 12–13 were synthesised from the
diols 17 and 21, respectively, which in turn were pre-
pared in a straightforward manner from d-glucos-
amine and d-glucitol, respectively (Scheme 1 and
Scheme 2).
Thus, tetrol 16 was prepared from d-glucosamine
following reported procedures.[18] To study the steric
effect of the groups in positions 2 and 5 we selected a
silyloxymethyl and a methyl groups. The reaction of
16 with tert-butyldiphenylchlorosilane (TBDPSCl) af-
forded the diol 17 in high yield, resulting from the se-
lective protection of the primary alcohols. To obtain
Scheme 3. Synthesis of (3R,4R)-3,4-dihydroxytetrahydrofur-
an derivative ligands 14a, b.
the diol 17’ with a methyl group at positions 2 and 5, tosylated[20] and then treated with LiAlH4 to afford
the primary hydroxy groups of 16 were selectively di- compound 17ꢀ (Scheme 1).[18,20] Diols 17 and 17’ were
treated with phosphorochloridites 18a–c, synthesised
in situ by standard procedures,[21,22] to give the corre-
sponding diphosphites 12a–c and 12’a, b in moderate
to good yields (31–72%).
Tetrol 20 was obtained from d-glucitol (19) follow-
ing a reported procedure.[23] Primary alcohols were
also protected by reaction with TBDPSCl to give
compound 21. The 2,5-dimethyl derivative 21’ was ob-
tained by selective ditosylation of 20 and further re-
duction with LiAlH4 (Scheme 2).[18,20] Treatment of 21
and 21’ with phosphorochloridites 18a, b[21,22] gave the
corresponding diphosphites 13a, b and 13’a, b in mod-
erate to good yields (32–92%).
The diphosphite ligands 14a, b, which do not con-
tain substituents in positions 2 and 5 were also pre-
pared by reaction of (3R,4R)-3,4-dihydroxytetrahy-
drofuran 22[24] with phosphorochloridites 18a, b[21,22] in
75 and 25% yield, respectively (Scheme 3).
Scheme 1. Synthesis of 2,5-anhydro-d-mannitol derivative li-
gands 12a–c and 12’a, b.
The structures of diphosphite ligands 12–14 were
determined by one-dimensional 1H,13C{1H} and
31P{1H}NMR. The signals were readily assigned by
using bidimensional COSY and HSQC techniques.
The 31P{1H}NMR spectrum of ligands 12–14 showed a
single signal, located between 140 and 147 ppm, char-
acteristic of a phosphite function. However, between
1
3–5 ppm of the H NMR spectra of ligands 12–14 ap-
peared signals characteristic of second-order spectra,
as a consequence of the existence of AA’BB’X2X’2
(12–13) or AA’BB’X3X’3 (12’–13’) spin systems.
The crystal structure of diphosphite ligand 12a was
determined by X-ray diffraction. Monocrystals of 12a
suitable for X-ray diffraction were obtained by slow
diffusion of hexane into a CH2Cl2 solution of the
ligand. The ligand crystallises as a solvate containing
two molecules of n-hexane in the elementary cell.
The central five-membered ring has a twisted confor-
mation (Figure 4 and Figure 5). This ligand was found
to crystallise as a racemic twin (74:16).
Scheme 2. Synthesis of 2,5-anhydro-l-iditol derivative li-
gands 13a, b and 13’a, b.
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M. Rosa Axet et al.
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um complexes 23–25 was elucidated by NMR spec-
troscopy techniques. The NMR spectra of the com-
plexes at 258C show that they retain the C2-symmetry
in solution. In the 31P{1H}NMR spectrum, only one
signal appeared between 127 and 136 ppm (JP-Rh
=
253–256 Hz). The chemical shift and coupling con-
stant values are in agreement with those observed for
related cationic diphosphite rhodium complexes.[10,11]
1
The H and 13C NMR chemical shifts were similar to
those of the free ligands, and the 1,5-cyclooctadiene
ligand showed two groups of signals between 4.65 and
5.88 ppm, and between 1.94 and 2.34 ppm for the me-
thynic and methylenic groups, respectively. The mon-
onuclearity of the complexes was confirmed by
MALDI spectra, which in all cases showed molecular
ions corresponding to the cation [Rh
(COD)(L)]+ (L=
A
Figure 4. Structure model (ellipsoids at 50% probability
level) of ligand 12a. Counterions, solvates and hydrogen
atoms have been omitted for the sake of clarity.
12a–c, 12’a–b, 13a, 13’a and 14a, b).
Monocrystals of the complexes [Rh
(12a)]BF4 (23a) and [Rh(COD)(13’a)]BF4 (24’a) were
obtained by slow diffusion of hexane into a CH2Cl2
solution of the complex. Compound [Rh(COD)-
(12a)]BF4 (23a) crystallises as a cation together with a
A
A
N
ACHTREUNG
AHCTREUNG
AHCTREUNG
À
BF4 anion (Figure 6 and Figure 7). The rhodium
atom is coordinated in a slightly distorted square
planar geometry with a mean deviation from the
plane of 0.101 Š. The distances between the metal
atom and the centres of the double bonds at the cy-
clooctadiene rings are: 2.17 Š and 2.18 Š. The five-
membered ring has a twisted conformation. This com-
pound crystallises as a single enantiomer in a pure
chiral structure. Compound [Rh
N
N
(24’a) crystallises with two independent cations in the
elementary cell (Figure 8, Figure 9, Figure 10 and
Figure 5. Structure model showing a lateral view of the
ligand 12a.
Synthesis of the Rhodium Complexes
Rhodium complexes [Rh
L=diphosphite ligands 12–14 and COD=cycloocta-
diene, were prepared by reacting [Rh(COD)2]BF4
A
AHCTREUNG
with ligands 12a–c, 12’a, b, 13a, 13’a and 14a, b, re-
spectively (Scheme 4). All complexes were isolated as
air-stable coloured solids. The structure of the rhodi-
Figure 6. Structure model (ellipsoids at 50% probability
level) of [Rh
N
N
and hydrogen atoms have been omitted for the sake of clari-
ty.
Scheme 4. Synthesis of cationic rhodium complexes 23–25.
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New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
Figure 10. Lateral view of [Rh
N
N
ecule A.
Figure 7. Lateral view of the complex [Rh
(23a).
N
N
Figure 8. ORTEP diagram of [Rh
N
N
molecule A. Counterions, solvates and hydrogen atoms have
been omitted for the sake of clarity.
Figure 11. Lateral view of [Rh
N
N
ecule B.
Figure 11). The independent cations detected in the
crystal cell differ in their conformation. In molecule
A, the five-membered ring has a twisted conformation
and in molecule B this ring has an envelope confor-
mation. The seven-membered ring formed by the
metal atom also shows different folding in molecules
A and B. For molecule B, the folding of this seven-
membered ring is more pronounced. In both mole-
cules the rhodium atom is coordinated in a slightly
distorted square planar geometry. In molecule A, the
mean deviation from the plane is 0.041 Š and in mol-
ecule B the mean deviation from plane is 0.081 Š.
The distances between the metal atom and the centres
of the double bonds at the cyclooctadiene rings are in
molecule A: 2.22 Š and 2.20 Š and in molecule B:
Figure 9. ORTEP diagram (ellipsoids at 50% probability
level) of [Rh
N
N
ions, solvates and hydrogen atoms have been omitted for
the sake of clarity.
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M. Rosa Axet et al.
FULL PAPERS
were observed. The initial solution was analysed by
1
31P and H NMR spectroscopy. Later the NMR tube
was pressurised with syngas (20 bar) and heated at
1
808C for 30 min and the 31P and H NMR spectra
were then recorded. Finally the NMR tube was
shaken for 15 h at 808C and NMR spectra were again
recorded.
Figure 12. Equatorial-equatorial (ee) and equatorial-axial
(ea) [RhH(CO)2(L)] species.
Initially, the displacement of two carbon monoxide
2.25 Š and 2.26 Š. This complex crystallises in a pure molecules by the diphosphite ligands yields the [Rh-
chiral structure. (acac)(L)] complexes which, after a short time under
The distances and angles measured for this species hydroformylation conditions, evolved to the species
are similar to those previously described for the rho- [Rh(acac)(CO)(L)] with characteristic rhodium-
dium-diphosphinite complex 9 (X=H) (Figure 2), phosphorus coupling constants (ca. 300 Hz)
AHCTREUNG
AHCTREUNG
where the diphosphinite ligand has the same furano- (Scheme 5).[30,31] We observed these species in all
side backbone.[18]
cases except for ligands 12a and 12b, which directly
formed the hydridorhodiumdicarbonyl complexes
[RhH(CO)2(L)] from [Rh(acac)(L)]. After a reaction
G
High-Pressure NMR Study
time of 15 h the solution was analysed at room tem-
perature and, in all cases, stable [RhH(CO)2(L)] com-
The
hydridorhodium
diphosphite
complexes plexes were exclusively obtained. This was confirmed
[RhH(CO)2(L)] (L=bidentate ligand) are generally by the presence in the 31P{1H} NMR spectrum of a
considered to be the resting state in the hydroformy- doublet around 155 ppm (JP-Rh =230 Hz) and in the
lation reaction.[8,25–27] It is generally assumed that they 1H NMR spectrum of a signal at À10 ppm. Small
have a trigonal-bipyramidal structure. Two isomeric amounts of the phosphonate, signal at 10 ppm in the
structures of these complexes can be formed with a 31P{1H} NMR spectrum, were also detected.
coordinated bidentate ligand (Figure 12). The pres-
ence of only one active diastereoisomeric hydridorho-
diumcarbonyl species with bidentate ligands is pre- Structural Assignments
sumably the key to an efficient control of the chirality
transfer.[28] These two isomeric structures can be The 31P{1H} NMR chemical shifts (in ppm) and the
easily distinguished by NMR, since the complexes coupling constants (in Hertz) of [RhH(CO)2(L)] (L=
with ee (equatorial-equatorial) coordination show 12a–14a, 12b) complexes are summarised in Table 1.
J
P-H <10 Hz, and JP-P =250 Hz whereas for trans coor- These complexes showed somewhat broadened dou-
dinated phosphite, ea (equatorial-axial) complex blets at room temperature in the 31P{1H} NMR spec-
J
P-H =180–200 Hz and JP-P =70 Hz.[28–31] To obtain in- tra. These broad signals suggest a fluxional process on
formation about these species, we studied the solution the NMR time scale.[25] The doublets appeared be-
1
structures of the hydridorhodium diphosphite dicar- tween 152.7 and 158.1 ppm with JRh-P coupling con-
bonyl species [RhH(CO)2(L)], where L=diphosphites stants between 230.0 and 234.1 Hz. These large JRh-P
1
12a–14a, 12b, through high-pressure NMR spectrosco- coupling constants indicate that the ligands coordi-
py. Under typical hydroformylation conditions, [Rh- nate in an equatorial-equatorial fashion in the trigo-
G
form to trigonal bipyramidal hydridorhodium diphos- In the H NMR spectrum the hydride signal was de-
1
phites (Scheme 5).[28]
tected at d=À10 ppm. The JRh-H coupling constants
2
The complexes were prepared by adding one equiv- were in the range of 2.0 to 3.8 Hz and the JP-H cou-
alent of diphosphite ligands 12a–14a, 12b to a tolu- pling constants were between 2.0 and 9.0 Hz. These
ene-d8 solution containing [Rh
(acac)(CO)2]. In all small phosphorus-hydrogen coupling constants
cases a fast change of colour and displacement of CO (<10 Hz) explain that the hydride signal appears as a
Scheme 5. Formation of [RhH(CO)2(L)] from [Rh(acac)(CO)2] and diphosphites 12a–14a, 12b (L).
G
1988
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New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
Table 1. Selected 1H and 31P{1H} NMR data for
Table 2. Selected 1H and 31P{1H} NMR data for
[RhH(CO)2(L)] (L=12a–14a, 12b) complexes at low tem-
perature.[a]
[RhH(CO)2(L)] complexes.[a]
[c]
1JRh-P
[c]
1JRh-H
[c]
2JP-H
Ligand d (31P)[b]
d (1H)[b]
[c]
[c]
[c]
Ligand d (31P)[b]
1JRh-P1 1JRh-P2 2JP-P
T
12a
12b
12’a
13a
13’a
14a
152.70 (d) À9.93 (br t) 231.9
2.0
3.4
2.7
2.9
3.8
3.4
2.0
3.9
3.8
3.1
3.9
9.0
[8C]
155.33 (d) À9.91 (q)
155.43 (d) À10.14 (q)
158.09 (d) À9.85 (q)
155.27 (d) À10.05 (q)
230.0
231.6
233.6
234.1
12a
161.56
(dd)
148.21
(dd)
270.9
230.2
302.2 À100
12b
12’a
153.92 (broad)
Unresolved
À80
156.40 (d) À10.24 (dt) 232.6
164.42
(dd)
153.62
(dd)
269.3
230.1
232.6
240.4
305.1 À100
[a]
Prepared in toluene-d8 by adding 1.1 equivalents of
ligand to the [Rh(acac)(CO)2] solution, 15 h. at 808C
13a
160.30
(dd)
156.75
(dd)
314.2 À80
AHCTREUNG
under 20 bars of syn gas.
13’a
14a
157.49 (broad d)
158.68 (broad d)
238.6
233.5
-
-
À100
À80
[b]
[c]
1
31P and H NMR spectra recorded in toluene-d8 using a
10-mm high-pressure NMR tube. Chemicals shifts d in
ppm (multiplicity).
Coupling constants in Hz.
[a]
Prepared in toluene-d8 by adding 1.1 equivalents of
ligand to the [Rh(acac)(CO)2] solution, 15 h. at 808C
ACHTREUNG
under 20 bars of syn gas.
[b]
[c]
1
31P and H NMR spectra recorded in toluene-d8 using a
10-mm high-pressure NMR tube. Chemicals shifts d in
ppm (multiplicity).
Coupling constants in Hz.
quadruplet in most of the cases, except for the com-
plex containing ligands 12a and 14a. In the case of
ligand 14a a doublet of triplets was observed in the
hydride region and indicates a cis configuration be-
tween the phosphorus atoms and the hydride ligand.
Low Temperature Studies
As a consequence of the C2-symmetry of the ligands,
the phosphorus atoms are equivalent in the free
ligand. However, this is not the case for the hydrido-
rhodiumcarbonyl
diphosphite
complexes
[RhH(CO)2(L)] (L=12–14), where, although both
phosphorus atoms are coordinated in an equatorial-
equatorial fashion to the rhodium centre, the complex
has a C1-symmetry. The fact that only one doublet is
observed in the 31P{1H} NMR spectrum indicates that
either the chemical shifts of both atoms accidentally
coincide or that they exchange rapidly on the NMR
time scale.[28–31] An NMR study of the hydridorho-
diumcarbonyl species was performed at low tempera-
1
ture in the presence of CO and H2. Selected H and
31P{1H} NMR data for [RhH(CO)2(L)] complexes at
low temperature are summarised in Table 2.
The behaviour of these species strongly depends on
the structure of the diphosphite ligands. Complexes
[RhH(CO)2(L)] where L=12a, 12b and 12’a, derived
from 2,5-anhydro-d-mannitol, all showed similar be-
haviour. When the temperature was decreased, broad-
ening of the resonance of the 31P{1H} NMR and in the
Figure 13. Selected regions of the 1H and 31P{1H} NMR spec-
tra of the complex [RhH(CO)2(12’a)] formed from the pre-
cursor [Rh(acac)(CO)2] in the presence of ligand 12’a under
hydroformylation conditions (15 h at 808C and 20 bar of syn
gas) in toluene-d8. a) Spectrum recorded at room tempera-
ture and b) spectrum recorded at À1008C.
AHCTREUNG
AHCTREUNG
1
hydride region of the H NMR spectra was observed.
The signals of the 31P{1H} NMR for complexes
[RhH(CO)2(L)], where L=12a and 12’a, were re-
solved at À1008C (Figure 13). Two doublets of dou-
blets in the 31P{1H} NMR spectrum were detected: around 230 Hz, and JP-P around 300 Hz, indicated
2
one signal at ca. d=160, and the other at d=150. The that the ligand was coordinated in an equatorial-equa-
1
1
coupling constants, JRh-P1 around 270 Hz and JRh-P2 torial fashion. The hydride region of the 1H NMR
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M. Rosa Axet et al.
FULL PAPERS
cies was previously reported with ligands that form
seven-membered rings with the metal.[28,30,31] These
new carbohydrate derivative ligands 12–14 were
therefore expected to show similar coordination.
However, this was not observed for ligands 12–14,
which coordinate in an equatorial-equatorial fashion
1
2
(corroborated by the large JRh-P and JP-P coupling
2
constants and small JP-H coupling constants, observed
in the NMR spectra). This coordination may be due
to the rigidity of the ligands due to the presence of
the tetrahydrofuran backbone.
Hydroformylation of Vinylarenes
The chiral diphosphites 12–14 were used as ligands in
the rhodium-catalysed asymmetric hydroformylation
of styrene and related prochiral olefin. The catalyst
was prepared in situ. The diphosphite ligand was
added to a solution of [Rh(acac)(CO)2] (acac=acetyl-
G
acetonate) in toluene followed by the addition of the
substrate. Afterwards the solution was introduced in
an autoclave and pressurised with CO/H2. The results
of the asymmetric hydroformylation of styrene are
given in Table 3 and Table 4. Neither hydrogenated
nor polymerised products were observed.
The conditions were optimised with ligands 12a–c
(Table 3). An Rh/L ratio of 1/2 was found to be ap-
propriate in order to increase the enantioselectivity in
comparison to an Rh/L ratio of 1/1, although the ac-
tivity decreases under these conditions. (Table 3, en-
tries 3 vs. 4 and 9 vs. 11). This may be explained by
Figure 14. Selected regions of the 1H and 31P{1H} NMR spec-
tra of the complex [RhH(CO)
A
cursor [Rh(acac)(CO)2] in the presence of ligand 13a under
ACHTREUNG
hydroformylation conditions (15 h at 808C and 20 bar of syn
gas) in toluene-d8. a) Spectrum recorded at room tempera-
ture and b) spectrum recorded at À808C.
spectrum was not resolved and exhibited a broad the formation of the species [RhH(CO)4] at low Rh/L
signal at this temperature.
For the [RhH(CO)2(13a)] complex, where diphos-
T
phite ligand 13a is derived from 2,5-anhydro-l-iditol, Table 3. Rhodium-catalysed hydroformylation of styrene
using diphosphites 12a and 12b.[a]
the decrease in the temperature also led to broaden-
ing of the signals in the 31P{1H} and in the hydride
Entry L
Rh/ t
L
T
% con- % regio-
% ee
1
region of the H NMR spectra. The 31P{1H} NMR was
[h] [8C] version[b] selectivity[c]
better resolved at À808C, an eight-line spectrum for
1
2
3
4
12a
1/1 15 60
1/2 15 40
1/1 48 25
1/2 48 25
99
57
>99
77
78
96
93
97
97
79
88
93
95
94
93
95
79
20 (S)
41 (S)
20 (S)
46 (S)
42 (S)
24 (S)
28 (S)
30 (S)
30 (S)
25 (S)
39 (S)
37 (S)
0
phosphorus atoms was observed. This arises from an
1
1
12a
12a
12a
ABX system where JRh-P1 and JRh-P2 are very close,
230 and 240 Hz, and the signals appeared at 160.30
and 156.75 ppm with a phosphorus-phosphorus cou-
pling constant of 314.2 Hz (Figure 14). These coupling
constants indicated an equatorial-equatorial coordina-
tion mode.
5
6
7
8
12a[d] 1/2 48 25
12b 1/1 15 60
12b 1/1 15 40
12b 1/2 15 40
12b 1/1 48 25
12b[d] 1/1 48 25
12b 1/2 48 25
12b 1/4 48 25
85
99
99
64
>99
99
97
61
99
In the variable temperature study of the hydrido-
rhodiumdicarbonyl complexes with ligands 13’a and
14a only a slight broadening of the doublet in the cor-
responding 31P{1H} at À808C was observed. This indi-
cates that the fluxional process at this temperature is
not completely stopped, suggesting a lower energy
barrier than in the case of ligands 12a, 12b, 12’a and
13a.
9
10
11
12
13
12c
1/1 15 60
[a]
Substrate/Rh=200, styrene 2.7 mmol, [Rh
(acac)(CO)2]
0.0135 mmol, P=20 bar, 15 mL toluene P(CO/H2)=1.
% conversion of styrene determined by GC.
% of 2-phenylpropanal
AHCTREUNG
[b]
[c]
[d]
The equatorial-axial coordination mode in the
trigonal bipyramidal hydridorhodium-dicarbonyl spe-
P(CO)=10, P(H2)=20.
1990
asc.wiley-vch.de
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 1983 – 1998

New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
Table 4. Rhodium-catalysed hydroformylation of styrene
using diphosphites 12–14.[a]
haviour was unexpected since these ligands are less
sterically demanding. The catalysts that contain li-
gands 12a,b and 13a,b, which have OTBDPS groups
in positions 2 and 5, have slightly higher activity than
those containing ligands 14a,b (Table 4, entries 1, 2
and 5, 6 vs. 9, 10). Unexpectedly, the catalytic systems
Rh/12’a,b were the most actives, while the catalytic
systems Rh/13’a,b, were found to be the less actives
(Table 4, entries 3, 4 and 7, 8).
In all cases, the regioselectivity in the branched al-
dehyde was higher than 90%, and in some cases it
was even higher than 95%. These values are in agree-
ment with those obtained with other rhodium-diphos-
phite system ligands containing biphenyl moiet-
ies.[10,11,28,32]
Entry
L
% conversion[b]
% regio-
% ee
selectivity[c]
1
2
3
4
5
6
7
8
9
10
12a
12b
12’a
12’b
13a
13b
13’a
13’b
14a
14b
57
64
98
98
57
40
33
25
43
38
96
93
93
94
95
98
96
94
>99
94
41 (S)
30 (S)
14 (R)
19 (R)
22 (R)
43 (R)
17 (S)
18 (S)
26 (R)
34 (R)
[a]
Substrate/Rh=200, Rh/L=0.5, styrene 2.7 mmol, [Rh-
(acac)(CO)2] 0.0135 mmol, P=20 bar, 15 mL toluene, P-
(CO/H2)=1, T=408C, reaction time: 15 h
% conversion of styrene determined by GC.
% of 2-phenylpropanal.
In general, the enantiomeric excesses obtained with
ligands 12–14 in the rhodium-catalysed hydroformyla-
tion of styrene were moderate (up to 46%). However,
ligands 12a and 13b showed higher enantioselectivi-
ties than other previously reported with diphosphite
ligands derived from 1,2-diols.[22,30] This can be related
ACHTREUNG
ACHTREUNG
[b]
[c]
ratios, which is known to be a highly active achiral hy- to the fact that they exclusively coordinate in equato-
droformylation catalyst.[28] However, a further in- rial-equatorial fashion in the hydridorhodiumdicar-
crease of the Rh/L ratio (1/4) was not found to en- bonyl complexes. We have also observed that the
hance the regioselectivity or the enantioselectivity value and the sense of the enantiomeric excess were
(Table 3, entries 11 vs. 12), indicating that only a low strongly affected by the configuration and substituents
excess of free ligand is needed in order to avoid the of the ligand backbone.
formation of [RhH(CO)4] species. Concerning the
A comparison of the results obtained with ligands
effect of the partial pressure of hydrogen, we ob- 12a–b with 12c (Table 3, entries 1, 6 and 13) showed
served no improvement in the activity, the regioselec- that these systems have similar activities and regiose-
tivity or the enantioselectivity when the H2/CO ratio lectivities. However, no enantioselectivity was ob-
was changed to 2 at total pressure of 30 bar (Table 3, served when ligand 12c was used. This indicates that
entries 4 vs. 5 and 9 vs. 10). In previous studies using bulky substituents are needed in ortho-positions of
rhodium systems containing diphosphite ligands with the biphenyl moieties if asymmetric induction is to be
C1-symmetry have shown a different behaviour, in- obtained. This behaviour was also observed in other
creasing the activity with the partial pressure of hy- systems containing diphosphite ligands with the same
drogen.[6] The fact that the activity did not increase biphenyl moieties.[10,11,28,32] In ligands containing me-
when the partial pressure of hydrogen was increased thoxy groups in the para-positions of the biphenyl
suggests that the rate-determining step is not the hy- moieties (ligands 13b–14b) an increase in the enantio-
drogenolysis. As was expected, lower temperatures selectivity and a decrease the activity were observed
led to a decrease in the activity, thus the reaction in comparison with the corresponding ligands with
time was increased to 48 h at 258C in order to have tert-butyl groups in the para-positions of the biphenyl
comparable conversions to those obtained at 408C for moieties (e.g., Table 4, entries 5 vs. 6). Similar behav-
15 h (e.g., Table 3, entries 7 vs. 10). A slight increase iour has also been observed in other carbohydrate de-
in the enantioselectivities (Table 3, entries 2 vs. 4 and rivative diphosphite ligands.[10,11,28,32] The behaviour of
8 vs. 11) was also observed when the temperature was ligand 12b was an exception, since when it was used,
decreased.
the activity revealed to be higher and the enantiose-
For comparative purposes, ligands 13–14 were lectivity lower than ligand 12a.
tested under conditions that gave the optimum com-
The enantioselectivities were higher when bulky
promise between enantioselectivities and reaction substituents were presents in positions 2 and 5 of the
rates; i.e., Rh/L=1/2, PCO/H2 =20 bar (1/1) and T= tetrahydrofuran ring. This is the case of ligands 12a, b
408C. The results are given in Table 4.
and 13a, b (where X=OTBDPS) which reached en-
A comparison of the conversions obtained with dif- antiomeric excesses up to 43% (Table 4, entries 1, 2
ferent catalysts that incorporate ligands derived from and 5, 6, respectively, see also Figure 15). Unexpect-
mannitol 12, iditol 13 and dihydroxytetrahydrofuran edly, the enantioselectivities were the lowest when a
14, showed that the systems containing ligands 14 methyl group was in positions 2 and 5 of the tetrahy-
were less active (Table 4, entries 9 and 10). This be- drofuran ring, 12’a, b and 13’a, b (Table 4, entries 3, 4
Adv. Synth. Catal. 2007, 349, 1983 – 1998
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1991

M. Rosa Axet et al.
FULL PAPERS
Table 5. Rhodium-catalysed hydroformylation of different
vinylarenes using diphosphite 12a.[a]
Entry Substrate
% con-
% regio-
% ee
version[b] selectivity[c]
1
2
57
60
96
97
41 (S)
49 (S)
3
34
96
96
94
60 (S)
18 (S)
4
[a]
Substrate/Rh=200, Rh/L=0.5, substrate 2.7 mmol, [Rh-
(acac)(CO)2] 0.0135 mmol, P=20 bar, (CO/H2)=1,
A
P
ACHTREUNG
Figure 15. Enantioselectivity values and configuration of the
major enantiomer obtained in the hydroformylation of sty-
rene using Rh/12–14 catalytic systems.
15 mL toluene, T=408C, reaction time=15 h.
% conversion of substrate determined by GC.
% branched aldehyde.
[b]
[c]
and 7, 8, respectively). It could be expected that li-
gands 14, which have no substituents in positions 2
Finally, the diphosphite ligand 12a was used in the
and 5 of the tetrahydrofuran ring, provide the lowest rhodium-catalysed hydroformylation of various substi-
enantiomeric excess because they are the more flexi- tuted vinylarenes. The results are summarised in
ble ligands. Nevertheless the enantiomeric excesses Table 5. The presence of a fluoro substituent in the
were in between the enantioselectivities obtained para-position of the substrate (Table 5, entry 2) did
with ligands 12–13 and 12’–13’ (Table 4, entries 9 and not affect the activity or the regioselectivity. If we
10).
compare these results with those obtained in the hy-
It must be noted that the configuration of the droformylation of styrene (Table 5, entry 1), a slight
major enantiomer produced during the catalysis is increase in the enantioselectivity [41% ee (S) to 49%
governed by both the nature of the substituents and ee (S)] is observed. When a methoxy group is intro-
the configuration of the remote stereocentres in posi- duced in the para-position the enantioselectivity is en-
tions 2 and 5 of the tetrahydrofuran ring (Table 4, hanced to 60% ee (S) (Table 5, entry 3), but the activ-
Figure 15). Thus, comparing the hydroformylation re- ity is lower. Unexpectedly, the hydroformylation of 2-
sults obtained by using ligands 12 and 13 (X= vinylnaphthalene with diphosphite 12a evolved with
OTBDPS) (Table 4, entries 1 and 2 vs. 5 and 6) it can high activity but very low enantioselectivity, 18% ee
be observed that the enantiomeric excesses were very (S) (Table 5, entry 4). In all cases, the sense of the
close but with opposite senses. Similar behaviour was asymmetric induction was the same as that the ob-
observed for ligands 12’ and 13’ (X=H) (Table 4, en- served in the styrene hydroformylation. We can con-
tries 3 and 4 vs. 7 and 8). However, ligands with the clude that the introduction of substituents in the para-
same configuration in positions 2 and 5 of the tetrahy- position of the substrate affects both the conversion
drofuran ring, this is ligands 12–12’ and 13–13’, and the enantioselectivity. The fact that the best re-
showed an opposite enantiomeric induction (e.g., sults were obtained in the rhodium-catalysed hydro-
Table 4, entries 5 and 6 vs. 7 and 8). The effect of the formylation of p-methoxystyrene agrees with previous
remote stereocentres on the enantioselectivity has report in the literature.[26]
previously been observed in the asymmetric hydroge-
nation reaction of enamido esters using diphosphinite
ligands 8–10 (Figure 2), which have a similar back- Rhodium-Catalysed Hydrogenation of Methyl
bone.[18] It can be suggested that the influence of the Acetamidoacrylate
remote stereocentres on the chiral induction can be
due to the interaction of chains at positions 2 and 5 We have shown that the related diphosphinite ligands
with the biphenyl moieties of the phosphites, which 9–11 with the same furanoside backbone (Figure 2)[18]
are ultimately responsible for the chirality transfer. It showed very high activities in the asymmetric hydro-
is known that the sterically hindered biphenyl moiet- genation of methyl acetamidoacrylate (total conver-
ies of chiral diphosphites preferentially adopt one sion in 5 min at 1 bar of hydrogen pressure and room
configuration, that can change by the interaction with temperature). Moreover, diphosphite ligands derived
chains in positions 2 and 5.[25,28]
from carbohydrates showed very high enantioselectiv-
1992
asc.wiley-vch.de
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 1983 – 1998

New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
tivity increased significantly when the reaction was
carried out in dichloromethane/methanol mixture
(Table 6, entries 1 vs. 3). On the other hand, an in-
crease in hydrogen pressure enhanced the conversion
but had a little effect on the enantioselectivity
(Table 6, entries 1 and 7 vs. 2 and 8, respectively).
The previously described diphosphinite ligands,
with the same furanoside backbone (Figure 2),[18]
showed very high activities in the asymmetric hydro-
genation of methyl acetamidoacrylate using mild con-
ditions, whereas the related diphosphite ligands 12–14
showed lower activities in more drastic conditions
(10 bar of pressure and room temperature).
This may be due to the greater steric hindrance of
the diphosphite ligands (ligand 12c, without substitu-
ents in the biphenyl moieties, showed higher activities
than the rest of the related diphosphites) and also to
the fact that the diphosphite ligands are less basic
than the diphosphinite ligands, since greater basicity
favours the oxidative addition of hydrogen which is
the rate- and enantioselectivity-determining step of
this reaction. On the other hand, in all cases the enan-
tioselectivity of the Rh/diphosphite systems was much
lower than with the corresponding Rh/diphosphinite
system.
Scheme 6. Hydrogenation of methyl acetamidoacrylate with
[Rh(COD)(L)]BF4 catalytic system.
ACHTREUNG
Table 6. Hydrogenation of methyl acetamidoacrylate using
[Rh(L)
A
Entry
Ligand
Conversion [%][b]
% ee[b]
1
2
3
4
5
6
7
8
12a
7
0
12a[c]
12a[d]
12b
61
41
6
10 (R)
45 (R)
8 (R)
57 (R)
16 (R)
19 (R)
34 (R)
0
12c
>99
21
59
74
81
20
26
17
12’a
12’a[c]
12’b
13a
13’a
14a
9
10
11
12
6 (S)
13 (R)
6 (R)
14b
[a]
Conditions: 2.5 mL CH2Cl2, Rh: 2.5”10À6 mol, Rh/sub-
strate=1/100, room temperature, P(H2)=10 bar.
% conversion of substrate and enantiomeric excess deter-
mined by GC.
[b]
[c]
[d]
Conditions: 5 mL CH2Cl2, Rh=5”10À6 mol, Rh/sub-
strate=1/100, room temperature, P(H2)=50 bar.
Solvent=CH2Cl2/CH3OH (1/1).
Conclusions
New diphosphite ligands (12–14) with C2-symmetry
and a tetrahydrofuran backbone were synthesised in
ities in asymmetric hydrogenation.[9] In order to probe moderate to good yields starting from d-glucosamine,
the activity of the complexes [Rh
25) in the asymmetric hydrogenation reaction, they ionic complexes containing diphosphite ligands of
were used as catalyst precursors in the hydrogenation general formula [Rh(COD)(L)]BF4, (L=12a–c,
of methyl acetamidoacrylate (Scheme 6). The results 12’a,b, 13a, 13’a and 14a–b) were prepared by reacting
are summarised in Table 6. [Rh(COD)2]BF4 with the respective ligands. The
(COD)(L)]BF4 (23– d-glucitol and (2S,3S)-diethyl tartrate. Rhodium cat-
AHCTREUNG
AHCTREUNG
Activities were low for all the complexes tested, structures of 12a, 23a and 24’a were proved unambig-
and a reaction time of at least 15 h was required to uously by single crystal X-ray diffraction.
attain full conversion in the best cases. The most
The intermediate species in hydroformylation with
active catalytic system was the one with ligand 12c diphosphite ligands 12a, 12b, 12’a, 13a, 13’a and 14a
(Table 6, entry 5). The enantioselectivities were also were studied by high pressure NMR spectroscopy.
2
poor and the major enantiomer, when the enantio- The small JP-H coupling constants (2.0 to 9.0 Hz) and
1
meric excesses were substantial, was always R. The re- the large JRh-P coupling constants (230.0 to 234.1 Hz)
sults were also best with the catalytic system [Rh- indicate that the ligands coordinate in an equatorial-
A
N
in the biphenyl moieties, and this may explain the dorhodiumcarbonyl species. The low temperature
higher activity of the catalytic system containing this study of the hydridorhodiumcarbonyl species under
ligand. The enantiomeric excesses obtained show that hydroformylation conditions detected that the phos-
substitution in the biphenyl moieties has a negative phorus atoms were non-equivalent, indicating the C1-
effect on the enantioselectivity. Similar behaviour has symmetry of these complexes.
previously been observed for related xylose deriva-
This new series of diphosphite ligands has been ap-
plied to the rhodium-catalysed asymmetric hydrofor-
tives ligands with bulky diphosphites.[11]
In all cases we obtained better results, in activity mylation of styrene and related substituted vinylar-
and enantioselectivity, when dichloromethane was enes. High regioselectivities to the branched aldehyde
used as a solvent. Complex [Rh
N
N
an exception since the activity and the enantioselec- 46% ee) were obtained in styrene hydroformylation.
Adv. Synth. Catal. 2007, 349, 1983 – 1998
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1993

M. Rosa Axet et al.
FULL PAPERS
HP 5890A gas chromatograph (split/splitless injector, J&W
Scientific, Permabond L-Chirasil-Val, 25 m. column, internal
diameter 0.25 mm., carrier gas: 100 kPa He, F.I.D. detector).
Single crystal X-ray diffraction structure determinations
were carried out using a Bruker-Nonius diffractometer
equipped with a APPEX 2 4 K CCDarea detector, a FR591
rotating anode with MoKa radiation, Montel mirrors as mon-
ochromator and a Kryoflex low temperature device (T=
100 K), fullsphere data collection omega and phi scans. Pro-
grams used: Data collection Apex2V. 1.0–22 (Bruker-
Nonius 2004), data reduction Saint+ Version 6.22 (Bruker-
Nonius 2001) and absorption correction SADABS V. 2.10
(2003). Crystal structure solution was achieved using direct
methods as implemented in SHELXTL Version 6.10 [G. M.
Sheldrick, Universtität Gçttingen (Germany), 2000] and vi-
sualised using XP program. Missing atoms were subsequent-
ly located from difference Fourier synthesis and added to
the atom list. Least-squares refinement on F2 using all mea-
sured intensities was carried out using the program
SHELXTL Version 6.10 [G. M. Sheldrick, Universtität Gçt-
tingen (Germany), 2000]. All non-hydrogen atoms were re-
fined including anisotropic displacement parameters.
In the rhodium-catalysed p-methoxystyrene hydrofor-
mylation the system containing ligand 12a reached
60% ee which is one of the higher enantioselectivity
reported using diphosphites derived from 1,2-diols.
We can conclude that the use of strained and hin-
dered backbones can increase the enantioselectivities
of rhodium systems containing diphosphites derived
from 1,2-diols in comparison to previously reported
data. The configuration and substitution of the
remote stereocentres in positions 2 and 5 of the tetra-
hydrofuran ring were observed to have a considerable
influence on the enantioselectivity. The most signifi-
cant result is that changing the configuration of these
stereocentres can control the configuration of the
major isomer obtained in the hydroformylation reac-
tion.
Rhodium complexes bearing diphosphite ligands
were tested in the asymmetric hydrogenation of
methyl acetamidoacrylate. The conversions and the
enantioselectivities were much lower than those ob-
tained with the corresponding phosphinites, and were
mainly influenced by the substitution in the biphenyl
moiety and by the configuration of the remote centres
in positions 2 and 5 of the tetrahydrofuran ring.
Synthesis of the Ligands; General Procedure for
Synthesising Diphosphites from the Corresponding
Diols
To a solution of the diol (0.5 mmol)[18] which had previously
been azeotropically dried with toluene (3”1 mL), in dry and
degassed toluene (5 mL) was added dry pyridine
(2.0 mmol). After cooling to 08C, the mixture was slowly
added to a solution of phosphorochlorohydrite (2.2 mmol),
synthesised in situ by standard procedure,[21,22] in dry and de-
gassed toluene (6 mL) and dry pyridine (2.2 mmol). The
mixture was allowed to warm to room temperature and
stirred overnight. The mixture was then filtered to eliminate
the pyridine salts, and the filtrate was concentrated to dry-
ness. The white foam obtained was purified by chromato-
graphic techniques.
Experimental Section
General Methods
All syntheses were performed using standard Schlenk tech-
niques under argon atmosphere. Solvents were purified by
standard procedures. Compounds 15–17, 19–21 and 22[18]
and phosphorochloridites 18[21,22] were prepared by methods
described previously. All other reagents were used as re-
ceived. Elemental analyses were performed on a Carlo Erba
1
EA-1108 instrument. H, 13C{1H} and 31P{1H} NMR spectra
were recorded on a Varian Gemini 400 MHz spectrometer.
Chemical shifts are relative to SiMe4 (1H and 13C) as internal
standard or H3PO4 (31P) as external standard. All NMR
spectral assignments were determined by COSY and HSQC
spectra. Hydroformylation reactions were carried out in a
Berghof 100-mL. stainless steel autoclave. Gas chromato-
graphic analyses were run on a Hewlett–Packard HP 5890 A
instrument (split/splitless injector, J&W Scientific, HP-5,
25 m column, internal diameter 0.25 mm, film thickness
0.33 mm, carrier gas: 150 kPa He, F.I.D. detector) equipped
with a Hewlett–Packard HP3396 series II integrator. Enan-
tiomeric excesses of hydroformylation reactions were mea-
sured after oxidation of the aldehydes to the corresponding
carboxylic acids on a Hewlett–Packard HP 5890A gas chro-
matograph (split/splitless injector, J&W Scientific, FS-Cyclo-
dex b-I/P 50 m column, internal diameter 0.2 mm, film thick-
3,4-Bis-O-[(3,3’,5,5’-tetra-tert-butyl-1,1’-biphenyl-2,2’-diyl)-
phosphite]-1,6-di-O-(tert-butyldiphenylsilyl)-2,5-anhydro-d-
mannitol (12a): The synthesis of 12a was carried out in ac-
cordance with the general procedure from 0.3 g (0.47 mmol)
of diol 17 in 5 mL of dry and degassed toluene and 0.2 mL
(2.4 mmol) of dry pyridine, and 2.1 mmol of phosphoro-
chlorohydrite 18a in 6 mL of toluene and 0.2 mL (2.4 mmol)
of pyridine. The reaction mixture was purified by flash
column chromatography (eluent: toluene Rf =0.9) to afford
12a as a white solid; yield: 0.22 g (31%)
Single crystal X-ray diffraction: Crystals of 12a were ob-
tained by slow diffusion of hexane into a solution of 12a in
dichloromethane. Empirical formula: C106H154O9.5P2Si2, for-
mula weight: 679.36, temperature: 100(2) K, wavelength:
0.71073 Š, crystal system: monoclinic, space group: P21, unit
cell dimensions: a=14.6938(11) Š, b=24.842(2) Š, c=
ness 0.33 mm, carrier gas: 100 kPa He, F.I.D. detector). The 15.0146(12) Š, b=109.112(2)8, V=5178.6(7) Š3, Z=2, den-
absolute configuration was determined by comparing of re-
tention times with optically pure (S)-(+)-2-phenylpropionic
and (R)-(À)-2-phenylpropionic acids. Hydrogenation reac-
tions were carried out in a Parr 450-mL multiple reaction
vessel autoclave. Conversion and enantiomeric excesses of
the reaction crude were measured on a Hewlett–Packard
sity (calculated): 1.089 Mg/m3, m (Mo-Ka): 0.118 mmÀ1, crys-
tal size: 0.40”0.40”0.40 mm3, theta range for data collec-
tion: 2.81 to 36.888, reflections collected: 86383, independ-
ent reflections: 46995 [R(int)=0.0401], absorption correc-
G
tion: SADABS (Bruker-Nonius), refinement method: full-
matrix least-squares on F2, data/restraints/parameters:
1994
asc.wiley-vch.de
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 1983 – 1998

New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
46995/1/1125, goodness-of-fit on F2: 1.018, final R indices
[I>2 sigma(I)]: R1=0.0719, wR2=0.2001, R indices (all
data): R1=0.0933, wR2=0.2190, absolute structure parame-
ter: 0.16(5), largest diff. peak and hole: 1.050 and
À0.584 eŠÀ3. The ligand crystallises as a solvate with two
(0.40 mmol) of diol 21 in 4 mL of dry and degassed toluene
and 0.1 mL (1.6 mmol) of dry pyridine were treated with
1.6 mmol of phosphorochlorohydrite 18b dissolved in 4 mL
of toluene and 0.1 mL (1.6 mmol) of pyridine. After the
work-up the obtained residue was purified by flash column
chromatography (eluent: toluene Rf =0.6) to afford 13b as a
white solid; yield: 0.18 g (32%).
molecules of n-hexane and two disordered positions of
1
water (in total
=
molecule of water without hydrogen
2
3,4-Bis-O-[(3,3’,5,5’-tetra-tert-butyl-1,1’-biphenyl-2,2’-diyl)-
phosphite]-1,6-dideoxy-2,5-anhydro-l-iditol (13’a): The syn-
thesis of 13’a was carried out in accordance with the general
procedure from 0.075 g (0.57 mmol) of diol 21’ in 5 mL of
dry and degassed toluene and 0.25 mL (2.9 mmol) of dry
pyridine, and 2.3 mmol of phosphorochlorohydrite 18a dis-
solved in 6 mL of toluene and 0.25 mL (2.9 mmol) of pyri-
dine. The mixture was stirred overnight, the salts were fil-
tered and the white foam was purified by flash column chro-
matography (eluent: toluene Rf =0.9) to afford 13’a as a
white solid; yield: 0.53 g (92%).
3,4-Bis-O-[(3,3’-di-tert-butyl-,5,5’-dimethoxy-1,1’-biphenyl-
2,2’-diyl)phosphite]-1,6-dideoxy-2,5-anhydro-l-iditol (13’b):
The synthesis of 13’b was carried out in accordance with the
general procedure from 0.075 g (0.57 mmol) of diol 21’ in
5 mL of dry and degassed toluene and 0.25 mL (2.9 mmol)
of dry pyridine, and 2.3 mmol of phosphorochlorohydrite
18b dissolved in 6 mL of toluene and 0.25 mL (2.9 mmol) of
pyridine. After the work-up the obtained residue was puri-
fied by flash column chromatography (eluent: toluene Rf =
0.5) to afford 13’b as a white solid; yield: 0.53 g (64%).
atoms) in the elementary cell. The measured compound
crystallises as a racemic twin (74:16).
3,4-Bis-O-[(3,3’-di-tert-butyl-5,5’-dimethoxy-1,1’-biphenyl-
2,2’-diyl)phosphite]-1,6-di-O-(tert-butyldiphenylsilyl)-2,5-an-
hydro-d-mannitol (12b): Following the general procedure
0.3 g (0.47 mmol) of diol 17 in 5 mL of dry and degassed tol-
uene and 0.2 mL (2.4 mmol) of dry pyridine were treated
with 2.1 mmol of the phosphorochlorohydrite 18b dissolved
in 6 mL of toluene and 0.2 mL (2.4 mmol) of pyridine. After
the work-up the reaction mixture was purified by flash
column chromatography (eluent: toluene Rf =0.75) to afford
12b as a white solid; yield: 0.28 g (42%).
3,4-Bis-O-[(1,1’-biphenyl-2,2’-diyl)phosphite]-1,6-di-O-
(tert-butyl-diphenylsilyl)-2,5-anhydro-d-mannitol (12c): Fol-
lowing the general procedure 0.25 g (0.40 mmol) of diol 17
in 2.5 mL of dry and degassed toluene and 0.1 mL
(1.6 mmol) of dry pyridine were treated with 1.6 mmol of
phosphorochlorohydrite 18c dissolved in 4 mL of toluene
and 0.1 mL (1.6 mmol) of pyridine. After the work-up the
remaining residue was purified by flash column chromatog-
raphy (eluent: hexane/ethyl acetate 100:2 Rf =0.6) to afford
12c as a white solid; yield: 0.21 g (50%).
3,4-Bis-O-[(3,3’,5,5’-tetra-tert-butyl-1,1’-biphenyl-2,2’-diyl)-
phosphite]-1,6-dideoxy-2,5-anhydro-d-mannitol (12’a): The
synthesis of 12’a was carried out in accordance with the gen-
eral procedure from 0.15 g (1.14 mmol) of diol 17ꢁ in 10 mL
of dry and degassed toluene and 0.5 mL (5.7 mmol) of dry
pyridine and 4.6 mmol of phosphorochlorohydrite 18a dis-
solved in 12 mL of toluene and 0.5 mL (5.7 mmol) of pyri-
dine. After the work-up the obtained residue was purified
by flash column chromatography (eluent: toluene Rf =0.9)
to afford12’a as a white solid; yield: 0.84 g (72%).
3,4-Bis-O-[(3,3’-di-tert-butyl-,5,5’-dimethoxy-1,1’-biphenyl-
2,2’-diyl)phosphite]-1,6-dideoxy-2,5-anhydro-d-mannitol
(12’b): Following the general procedure 0.15 g (1.14 mmol)
of diol 17’ in 10 mL of dry and degassed toluene and 0.5 mL
(5.7 mmol) of dry pyridine were treated with 4.6 mmol of
phosphorochlorohydrite 18b dissolved in 12 mL of toluene
and 0.5 mL (5.7 mmol) of pyridine. After the work-up the
obtained residue was purified by flash column chromatogra-
phy (eluent: toluene Rf =0.9) to afford 12’b as a white solid;
yield: 0.4 g (42%).
(3R,4R)-(À)-3,4-Bis-O-[(3,3’,5,5’-tetra-tert-butyl-1,1’-bi-
phenyl-2,2’-diyl)phosphite]-tetrahydrofuran(14a): Following
the general procedure from 0.15 g (1.44 mmol) of diol 22 in
14 mL of dry and degassed toluene and 0.7 mL (5.7 mmol)
of dry pyridine, were treated with 7 mmol of phosphoro-
chlorohydrite 18a dissolved in 15 mL of toluene and 0.7 mL
(5.7 mmol) of pyridine. After the work-up the obtained resi-
due was purified by flash column chromatography (eluent:
toluene Rf =0.9) to afford 14a as a white solid; yield: 1.00 g
(75%).
3,4-Bis-O-[(3,3’-di-tert-butyl-5,5’-dimethoxy-1,1’-biphenyl-
2,2’-diyl)phosphite]-tetrahydrofuran(14b):
Following the
general procedure 0.15 g (1.14 mmol) of diol 22 in 10 mL of
dry and degassed toluene and 0.5 mL (5.7 mmol) of dry pyri-
dine, were treated with 4.6 mmol of phosphorochlorohydrite
18b dissolved in 12 mL of toluene and 0.5 mL (5.7 mmol) of
pyridine. After the work-up the obtained residue was puri-
fied by flash column chromatography (eluent: toluene Rf =
0.9) to afford 14b as a white solid; yield: 0.3 g (29%).
Synthesis of Rhodium Complexes; General Procedure
3,4-Bis-O-[(3,3’,5,5’-tetra-tert-butyl-1,1’-biphenyl-2,2’-diyl)-
phosphite]-1,6-di-O-(tert-butyldiphenylsilyl)-2,5-anhydro-l-
iditol (13a): Following the general procedure 0.25 g
(0.40 mmol) of diol 21 in 2.5 mL of dry and degassed tolu-
ene and 0.1 mL (1.6 mmol) of dry pyridine were treated
with 1.6 mmol of phosphorochlorohydrite 18a dissolved in
4 mL of toluene and 0.1 mL (1.6 mmol) of pyridine. After
the work-up the obtained residue was purified by flash
column chromatography (eluent: toluene Rf =0.9) to afford
13a as a white solid; yield: 0.25 g (42%).
for Synthesizing [Rh(COD)(L)]BF4, L=Diphosphite
U
The complexes were prepared by adding 1.1 equivalents of
diphosphinite ligand to a solution of [Rh(COD)2]BF4 in the
AHCTREUNG
minimum volume of CH2Cl2. The mixture was then stirred
for 30 min, and the solvent was removed under vacuum. The
residue was washed with dry hexane first and then with dry
ether in order to remove the excess diphosphite and free cy-
clooctadiene. Characterisation details of rhodium complexes
[Rh
12--14 are collected in the Supporting Information.
[Rh(COD)(12a)]BF4 (23a): Beginning with 0.015 g
(0.036 mmol) of [Rh(COD)2]BF4 in the minimum quantity
A
3,4-Bis-O-[(3,3’-di-tert-butyl-5,5’-dimethoxy-1,1’-biphenyl-
2,2’-diyl)phosphite]-1,6-di-O-(tert-butyldiphenylsilyl)-2,5-an-
hydro-l-iditol (13b): Following the general procedure 0.25 g
A
N
ACHTREUNG
AHCTREUNG
Adv. Synth. Catal. 2007, 349, 1983 – 1998
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1995

M. Rosa Axet et al.
FULL PAPERS
of CH2Cl2, 0.060 g (0.040 mmol) of diphosphite 12a and fol-
lowing the general procedure, 0.054 g (83%) of complex
weight: 2869.13, temperature: 100(2) K, wavelength:
0.71073 Š, crystal system: orthorhombic, space group:
P212121, unit cell dimensions: a=19.1067(15) Š, b=
26.855(2) Š, c=30.828(3) Š, V=15818(2) Š3, Z=4, density
(calculated):1.205 Mg/m3, m (Mo Ka): 0.413 mmÀ1, crystal
size: 0.20”0.04”0.02 mm3, theta range for data collection:
2.50 to 30.738, reflections collected: 209015, independent re-
[Rh
Single crystal X-ray diffraction. Crystals of [Rh
(12a)]BF4 (23a) were obtained by slow diffusion of hexane
into a solution of [Rh(COD)(12a)]BF4 (23a) in dichlorome-
A
ACHTREUNG
AHCTREUNG
ACHTREUNG
A
ACHTREUNG
thane. Empirical formula: C103H140BCl2F4O9.50P2RhSi2, for-
mula weight: 1908.89, temperature: 100(2) K, wavelength:
0.71073 Š, crystal system: orthorhombic, space group:
P212121, unit cell dimensions: a=19.512(3) Š, b=
20.172(3) Š, c=26.249(4) Š, V=10332(3) Š3, Z=4, density
(calculated): 1.227 Mg/m3, m (Mo Ka): 0.332 mmÀ1, crystal
size: 0.20”0.10”0.04 mm3, theta range for data collection:
2.74 to 30.188, reflections collected: 125396, independent re-
flections: 48854 [R(int)=0.0598], absorption correction:
A
SADABS (Bruker-Nonius), refinement method: full-matrix
least-squares on F2, data/restraints/parameters: 48854/0/
1719, goodness-of-fit on F2: 1.068, final R indices [I>
2 sigma(I)]: R1=0.0661, wR2=0.1780, R indices (all data):
R1=0.0867, wR2=0.1923, absolute structure parameter:
0.000(18), largest diff. peak and hole: 1.748 and
À1.039 eŠÀ3. Compound [Rh
N
N
flections: 30370 [R(int)=0.0744], absorption correction:
H
tallises with two independent cations in the elementary cell.
The crystal cell also contains two BF4 anions and four disor-
dered positions of dichloromethane molecules with a total
occupancy of 3. The independently obtained cationic struc-
tures have different conformations. The measured com-
pound crystallises in a pure chiral structure.
SADABS (Bruker-Nonius), refinement method: full-matrix
least-squares on F2, data/restraints/parameters: 30370/14/
1393, goodness-of-fit on F2: 1.013, final R indices [I>2 sig-
ma(I)]:R1=0.0492, wR2=0.1139, R indices (all data): R1=
0.0798, wR2=0.1282, absolute structure parameter:
À0.022(15), largest diff. peak and hole: 1.186 and
À0.973 eŠÀ3.Compound [Rh
U
G
[Rh
A
G
A
(0.062 mmol) of [Rh
AHCTREUNG
of CH2Cl2, 0.068 g (0.068 mmol) of diphosphite 14a and fol-
lowing the general procedure, 0.059 g (75%) of complex
[Rh
A
ACHTREUNG
solid.
[Rh
A
G
ACHTREUNG
[Rh
A
G
G
(0.062 mmol) of [Rh
ACHTREUNG
(0.030 mmol) of [Rh
AHCTREUNG
of CH2Cl2, 0.061 g (0.068 mmol) of diphosphite 14b and fol-
lowing the general procedure, 0.054 g (79%) of complex
of CH2Cl2 and 0.046 g (0.032 mmol) of diphosphite 12b and
following the general procedure, 0.030 g (61%) of complex
[Rh
N
N
[Rh
[Rh
(0.061 mmol) of [Rh
0.074 g (0.067 mmol) of diphosphite 12c and following the
general procedure, 0.054 g (65%) of complex [Rh(COD)-
(12c)]BF4 23c was obtained as a pale yellow solid.
[Rh(COD)(12’a)]BF4 (23’a): Beginning with 0.025 g
(0.062 mmol) of [Rh(COD)2]BF4 in the minimum quantity
A
ACHTREUNG
solid.
A
N
ACHTREUNG
AHCTREUNG
AHCTREUNG
In Situ High-Pressure NMR Experiments; General
Procedure
ACHTREUNG
A
N
ACHTREUNG
In a typical experiment, a sapphire tube (ø10 mm) was filled
AHCTREUNG
under argon with a solution of [Rh
(acac)(CO)2] (2.10À2 m)
G
of CH2Cl2, 0.069 g (0.068 mmol) of diphosphite 12’a and fol-
and ligand (molar ratio PP/Rh=1.1) in toluene-d8 (2 mL).
The solution was analysed and then the HP NMR tube was
purged three times with CO and pressurised to the appropri-
ate pressure of CO/H2. After a reaction time of 15 h during
which the solution was shaken at 808C of temperature, the
solution was analysed. Characterisation details of [Rh-
lowing the general procedure, 0.068 g (81%) of complex
[Rh
[Rh
(0.052 mmol) of [Rh
A
ACHTREUNG
G
A
ACHTREUNG
AHCTREUNG
of CH2Cl2, 0.050 g (0.055 mmol) of diphosphite 12’b and fol-
lowing the general procedure, 0.047 g (76%) of complex
A
[Rh
A
ACHTREUNG
collected in the Supporting Information.
solid.
[Rh
N
G
ACHTREUNG
(0.036 mmol) of [Rh
ACHTREUNG
of CH2Cl2, 0.062 g (0.041 mmol) of diphosphite 13a and fol-
lowing the general procedure, 0.054 g (83%) of complex
HydroformylationExperiments
[Rh
[Rh
(0.062 mmol) of [Rh
A
ACHTREUNG
In a typical experiment, the autoclave was purged three
times with CO. The solution was formed from [Rh-
N
N
ACHTREUNG
AHCTREUNG
(acac)(CO)2] (0.013 mmol), diphosphite (0.015 mmol) and
of CH2Cl2, 0.069 g (0.068 mmol) of diphosphite 13’a and fol-
lowing the general procedure, 0.068 g (81%) of complex
styrene (13 mmol) in toluene (15 mL). The autoclave was
pressurised to the desired pressure. After the desired reac-
tion time, the autoclave was cooled to room temperature
and depressurised. The reaction mixture was analysed by
gas chromatography. The aldehydes obtained from the hy-
droformylation were oxidised to carboxylic acids to deter-
mine the enantiomeric excess.
[Rh
Single crystal X-ray diffraction. Crystals of [Rh
(13’a)]BF4 (24’a) were obtained by slow diffusion of hexane
into a solution of [Rh(COD)(13’a)]BF4 (24’a) in dichlorome-
thane. Empirical formula: C143H210B2Cl6F8O14P4Rh2, formula
A
ACHTREUNG
AHCTREUNG
ACHTREUNG
A
ACHTREUNG
1996
asc.wiley-vch.de
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 1983 – 1998

New C2-Symmetric Diphosphite Ligands Derived from Carbohydrates
FULL PAPERS
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lón, Chem. Eur. J. 2001, 7, 3086–3094; b) M. Diꢂguez,
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2004, 69, 4031–4040.
Hydrogenation Experiments
The experiments were prepared in a multiple reaction vessel
autoclave in a glovebox. After the addition of the substrate
to a solution of [Rh
(COD)(L)]BF4 (2.5”10À3 mmol) in the
A
corresponding solvent (2.5 mL) the autoclave was pressur-
ised to the desired pressure with hydrogen. After the de-
sired reaction time the autoclave was depressurised. The re-
action mixture was analysed by gas chromatography.
[8] a) J. E. Babin, G. T. Whiteker, (Union Carbide Chem.
Plastics Techn. Co.), World Patent WO 93/03839, 1993;
Chem. Abs. 1993, 119, P159872; b) K. Nozaki, N. Sakai,
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Asymmetry 2000, 11, 1097–1108.
Supporting Information
Experimental details for the characterization of all new
compounds and the hydrofomylation and hydrogenation re-
action procedures are collected in the Supporting Informa-
tion. Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supple-
mentary publication no. CCDC 610289–610291. Copies of
the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax.:
(internat.) + 44 1223/336–033; e-mail: deposit@ccdc.cam.
ac.uk].
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Acknowledgements
We thank the Spanish Government, Ministerio de Educación
y
Cultura, (CTQ2004–04412/BQU, CTQ2005–03124 and
Consolider Ingenio 2010,CSD2006–0003) and the Generalitat
de Catalunya (2005SGR007777 and Distinction for Research
Promotion, 2003 C.C.) for their financial support. With the
support of the Departament d’Universitats, Recerca i Societat
de la Informació i del Fons Social Europeu for a FPI grant
(M.R.A.).
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