High-pressure investigations under CO/H2 of rhodium complexes containing hemispherical diphosphites

Article abstract of DOI:10.1002/chem.201001610

The two rhodium complexes [Rh(acac)(L^R)] (L^R=(S,S)-5, 11,17,23-tetra-tert-butyl-25,27-di(OR)-26,28-bis(1,1'-binaphthyl-2, 2'-dioxyphosphanyloxy)calix[4]arene; 6: R=benzyl, 7: R=fluorenyl), each based on a hemispherical chelator forming a pocket about the metal centre upon chelation, are active in the hydroformylation of 1-octene and styrene. As expected for this family of diphosphanes, both complexes resulted in remarkably high selectivity towards the linear aldehyde in the hydroformylation of 1-octene (l/b≈15 for both complexes). Linear aldehyde selectivity was also observed when using styrene, but surprisingly only 6 displayed a marked preference for the linear product (l/b=12.4 (6) vs. 1.9 (7)). A detailed study of the structure of the complexes under CO or CO/H₂ in toluene was performed by high-pressure NMR (HP NMR) and FT-IR (HP-IR) spectroscopies. The spectroscopic data revealed that treatment of 6 with CO gave [Rh(acac)(CO) (I·¹-L^benzyl)] (8), in which the diphosphite behaves as a unidentate ligand. Subsequent addition of H₂ to the solution resulted in a well-defined chelate complex with the formula [RhH(CO)₂(L^benzyl)] (9). Unlike 6, treatment of complex 7 with CO only led to ligand dissociation and concomitant formation of [Rh(acac)(CO)₂], but upon addition of H₂ a chelate complex analogous to 9 was formed quantitatively. In both [RhH(CO)₂(L ^R)] complexes the diphosphite adopts the bis-equatorial coordination mode, a structural feature known to favour the formation of linear aldehydes. As revealed by variable-temperature NMR spectroscopy, these complexes show the typical fluxionality of trigonal bipyramidal [RhH(CO)₂(diphosphane)] complexes. The lower linear selectivity of 7 versus 6 in the hydroformylation of styrene was assigned to steric effects, due to the pocket in which the catalysis takes place being less adapted to accommodate CO or larger olefins and, therefore, possibly leading to facile ligand decoordination. This interpretation was corroborated by an X-ray structure determination carried out for 7. Rhodium in confinement: As revealed by high-pressure NMR/IR spectroscopic studies, the reaction of rhodium complexes containing hemispherical diphosphites with CO/H₂ leads to trigonal bipyramidal intermediates in which the phosphorus atoms exclusively occupy equatorial sites (see figure). The resulting metal confinement selectively drives olefin hydroformylation reactions to form aldehydes that best fit the cavity. Copyright

Full text of DOI:10.1002/chem.201001610

FULL PAPER
DOI: 10.1002/chem.201001610
High-Pressure Investigations under CO/H of Rhodium Complexes
2
Containing Hemispherical Diphosphites
[
a]
[a]
[b]
[c]
David Sꢀmeril,* Dominique Matt,* Loꢁc Toupet, Werner Oberhauser,* and
[
c]
Claudio Bianchini
Abstract: The two rhodium complexes
ture of the complexes under CO or
CO/H2 in toluene was performed by
high-pressure NMR (HP NMR) and
FT-IR (HP-IR) spectroscopies. The
spectroscopic data revealed that treat-
analogous to 9 was formed quantita-
R
R
R
[Rh
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(acac)(L )] (L =(S,S)-5,11,17,23-
tively. In both [RhH(CO) (L )] com-
2
tetra-tert-butyl-25,27-di(OR)-26,28-
plexes the diphosphite adopts the bis-
equatorial coordination mode, a struc-
tural feature known to favour the for-
mation of linear aldehydes. As re-
vealed by variable-temperature NMR
spectroscopy, these complexes show
the typical fluxionality of trigonal bi-
bis(1,1’-binaphthyl-2,2’-dioxyphospha-
nyloxy)calix[4]arene; 6: R=benzyl, 7:
R=fluorenyl), each based on a hemi-
spherical chelator forming a pocket
about the metal centre upon chelation,
are active in the hydroformylation of 1-
octene and styrene. As expected for
this family of diphosphanes, both com-
plexes resulted in remarkably high se-
lectivity towards the linear aldehyde in
the hydroformylation of 1-octene (l/b
ment of
6
with CO gave [Rh-
1
benzyl
A
H
U
G
R
N
U
G
)] (8), in which the
diphosphite behaves as a unidentate
ligand. Subsequent addition of H2 to
the solution resulted in a well-defined
pyramidal [RhH(CO) (diphosphane)]
2
chelate complex with the formula
complexes. The lower linear selectivity
of 7 versus 6 in the hydroformylation
of styrene was assigned to steric effects,
due to the pocket in which the catalysis
takes place being less adapted to ac-
commodate CO or larger olefins and,
therefore, possibly leading to facile
ligand decoordination. This interpreta-
tion was corroborated by an X-ray
structure determination carried out for
benzyl
[RhH(CO)2
A
H
U
G
R
N
U
G
)] (9). Unlike 6,
treatment of complex 7 with CO only
led to ligand dissociation and concomi-
ꢀ
15 for both complexes). Linear alde-
tant formation of [Rh
ACHTUNGTNERNU(GN acac)(CO) ], but
2
hyde selectivity was also observed
when using styrene, but surprisingly
only 6 displayed a marked preference
for the linear product (l/b=12.4 (6) vs.
upon addition of H a chelate complex
2
Keywords: calixarenes
·
confine-
ment · NMR spectroscopy · hydro-
formylation · bite angle · rhodium
1.9 (7)). A detailed study of the struc-
7
.
[
a] Dr. D. Sꢀmeril, Dr. D. Matt
Introduction
Laboratoire de Chimie Inorganique et Catalyse
Institut de Chimie UMR 7177 CNRS
Universitꢀ de Strasbourg
Spatial confinement can strongly influence the catalytic
properties of an organometallic species.
[1–11]
Embedding a
6
7008 Strasbourg Cedex (France)
Fax : (+33)368851637
E-mail: dsemeril@chimie.u-strasbg.fr
dmatt@chimie.u-strasbg.fr
catalytic centre in a molecular pocket, cleft or cage not only
provides a way to efficiently protect the metal unit towards
deactivation but also enables selective stabilisation of transi-
tion states that drive the reaction towards specific prod-
[
b] Dr. L. Toupet
Groupe Matiꢁre Condensꢀe et Matꢀriaux, UMR 6626 CNRS
Universitꢀ de Rennes 1
[12–14]
ucts.
When the pocket possesses receptor properties, it
3
5042 Rennes Cedex (France)
may also function as a substrate-selecting unit that leads to
shape-selective catalysis.
[15,16]
[
c] Dr. W. Oberhauser, Dr. C. Bianchini
Istituto di Chimica dei Composti OrganoMetallici CNR
via Madonna del Piano, 10
In recent work we have shown that calix-diphosphites 1–
, which all have two bulky (S,S)-1,1’-binaphthalene-2,2’-
5
5
0019, Sesto Fiorentino, Firenze (Italy)
dioxy moieties, form highly regioselective hydroformylation
catalysts with [Rh(acac)(CO) ]. The observed high linear al-
Fax : (+39)555225203
E-mail: werner.oberhauser@iccom.cnr.it
AHCTUNGTRENNUNG
2
dehyde selectivities were attributed to a substantial metal
confinement after complexation, which orientates the reac-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001610.
Chem. Eur. J. 2010, 16, 13843 – 13849
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
13843

tion towards the formation of linear Rh–alkyl intermediates
[17–20]
regardless of the olefin used.
Two geometrical features
make the formation of a molecular pocket about the rhodi-
um effective: 1) the large ligand bite angle, which induces a
bending of two symmetrically-sited naphthyl fragments to-
wards the complexed rhodium centre, and 2) the presence of
two calixarene lower rim substituents that behave as a non-
bonding pincer unit. From the pioneering studies of van
Leeuwen et al. on large-bite-angle diphosphanes, it has
become apparent that high selectivities towards linear alde-
hydes usually rely on the capacity of the bidentate ligand to
form trigonal bipyramidal (TBP) hydrido carbonyl inter-
mediates in which both phosphorus atoms occupy equatorial
positions. In these complexes, the metal site becomes most
effective and consequently favours the formation of a linear
Scheme 1. Hydroformylation of a-olefins catalyzed by complexes 6 and 7.
tion of 1-octene. The catalytic runs were performed in tolu-
ene at 508C under a p ACHTUNGTERNN(UNG CO/H ) total pressure of 21 bar.
2
Using a CO/H ratio of 1:2 gave considerably higher turn-
2
over frequencies (TOFs) than with 1:1 or 2:1 mixtures, the
regioselectivity remaining practically unchanged (Table 1,
entries 1–3). This observation is unsurprising because for
Rh
ACHTUNGTRENNUNG( n-alkyl) complex rather than the corresponding
Table 1. Rhodium-catalyzed hydroformylation of 1-octene and styrene
using complexes 6 and 7.
[21–23]
branched analogue.
However, prediction of the relative
[a]
disposition of the P atoms in the catalytic TBP intermedi-
ates is not easy, and it has also been shown that bis-equato-
rial coordination is not compulsory for high selectivity.
[b]
Entry [Rh] p(CO)/
Conv.
[%]
TOF
Isomer
[%]
Aldehydes l/b
p(H
2
)
l
b
[24]
[%] [%]
The stereochemistry of the hydrido carbonyl species formed
under hydroformylation conditions with the above hemi-
spherical diphosphites is not known to date, nor is the ease
with which the key intermediates are formed. In an attempt
to understand the origin of efficiency of rhodium complexes
derived from such ligands, we have examined the behaviour
1-octene
1
2
3
4
6
6
6
7
2:1
1:1
1:2
1:2
1.0
6.8
38.8
18.1
10
70
390
180
1.0
1.2
4.6
1.1
trace
–
94.4 5.6
93.5 6.5
93.1 6.9
16.8
14.5
13.5
styrene
5
6
6
7
1:2
1:2
23.1
8.1
230
80
–
–
92.5 7.5
65.1 34.9 1.9
12.4
of complexes 6 and 7 under H /CO by using combined high-
2
pressure NMR/FT-IR spectroscopic techniques for this pur-
pose. We anticipated that metal confinement would be more
efficient with the ligand containing the O-benzyl substitu-
ents than with that bearing the less flexible O-fluorenyl
groups. The relevance of high-pressure NMR and IR studies
for the understanding of regioselectivity in hydroformylation
[a] General conditions: olefin (5 mmol), [Rh] (2 mmol), olefin/Rh=2500,
(CO/H total =21 bar, T=508C, toluene/n-decane (15:0.5 mL), 2.5 h. The
p
A
H
U
G
R
N
N
2
)
conversions were determined by GC by using decane as an internal stan-
À1 À1
dard. [b] TOFs were expressed in mol(converted olefin)mol(Rh)
h .
phosphites the rate-determining step is the addition of the
olefin to the hydrido–rhodium–bis-carbonyl intermediate, a
step that becomes more easy by
[24–28]
has been emphasised recently by several authors.
reducing the relative carbon
[29]
monoxide pressure.
Note,
however, that the observed
higher activities induced by the
higher partial H2 pressure
cannot be explained by stan-
dard kinetics, which predict that
a 30% increase in the partial
H2 pressure would at most
double the rate. A possible ex-
planation for the observed ab-
normal activity increase is the
existence of an equilibrium be-
tween the active hydrido car-
bonyl species and an inactive
[
RhL(CO) ] dimer, the propor-
2 2
Results and Discussion
tion of which decreases on ap-
plying higher H pressures. This interpretation has already
2
[30,31]
The following catalytic study was exclusively based on the
use of complexes 6 and 7 in the hydroformylation reaction
of 1-octene and styrene (Scheme 1). We began these investi-
gations by assessing the two complexes in the hydroformyla-
been proposed (for other systems) by other authors.
The CO/H ratio of 1:2 was then used for all further tests.
Under these conditions 6 and 7 led to comparable linear/
branched (l/b) aldehyde ratios of 14.5 and 13.5, respectively,
2
13844
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Chem. Eur. J. 2010, 16, 13843 – 13849

Rhodium Complexes Containing Hemispherical Diphosphites
FULL PAPER
with the catalyst activity being two times higher with the
sterically less encumbered ligand 2 (Table 1, entry 3 vs. 4).
When performing the runs with styrene, the linear aldehyde
again turned out to be the major product with the benzyl-
substituted complex 6, but with 7 a significant drop in activi-
ty and selectivity was observed (Table 1, entries 5 and 6).
The latter observation suggests that the expanded fluorenyl
walls may strongly interact with bulkier olefins under cata-
lytic conditions, thereby leading to catalytic intermediates
different to those obtained with
The above observations led us to investigate the nature of
the species formed under catalytic conditions by using NMR
spectroscopy. The following NMR experiments were per-
formed in a sapphire tube under pressure. Applying a CO
pressure of 7 bar to a solution of 6 in [D ]toluene readily led
8
1
to the formation of [Rh
A
H
U
G
R
N
U
G
A
H
U
G
E
N
N
Figure 2). The unidentate nature of 2 in this complex was in-
3
1
1
ferred from the corresponding P{ H} NMR spectrum,
1
which showed a doublet centred at d=141.7 ppm ( J-
smaller olefins.
To get some insight into the
structural peculiarities of 7, we
completed the above investiga-
tions by determining the solid-
state structure of 7·hexane·
methyl-2-pentane. This study
revealed that the unit cell con-
Scheme 2. Formation of complexes 8 and 9 starting from 6.
Figure 1. Solid-state structure of 7 showing the confinement of the rhodi-
um atom (dark grey sphere). Only one of the two molecules present in
the unit cell is shown. Hydrogen atoms have been omitted from the left
view, but are shown in the CPK representation on the right. Selected
bond lengths [ꢃ] and angles [8]: RhÀO1 2.069(6), RhÀO2 2.071(6), RhÀ
P2 2.178(2), Rh1ÀP1 2.209(3); O1-Rh-O2 89.8(3), O1-Rh-P2 83.30(19),
O2-Rh-P2 165.2(2), O1-Rh-P1 167.6(2), O2-Rh-P1 86.2 (2), P2-Rh-P1
1
03.11(9). Complex 7 crystallised with solvent molecules, which are not
shown for clarity.
tains two structurally very similar molecules. In both, the
metal ion sits deeply inside the pocket delineated by two
naphthyl units and the two fluorenyl groups (Figure 1). The
distances between the rhodium atom and the closest
neighbouring aromatic carbon atoms (which belong to naph-
thyl units) are remarkably short at around 3.5 ꢃ. The high
steric pressure exerted on the metal by the surrounding
pocket is best seen in the non-zero dihedral angle between
the acac plane and the PMP plane, 16.08 in molecule 1 and
3
1
1
Figure 2. P{ H} NMR (sapphire tube, [D ]toluene, 81.01 MHz) spectra
8
of 6 under CO (7 bar) and CO/H
b) 6+CO; c) 6+CO/H , RT; d) 6+CO/H
2
(1:2; 21 bar). a) Compound 6 only;
, 408C; e) 6+CO/H , 508C.
2
2
2
AHCTUNGTRENNUGN( Rh,P)=297 Hz) and a singlet at d=123.3 ppm assigned to
the coordinated and the dangling phosphite arms, respec-
tively. The formulation of 8 was further confirmed by the
presence of a single strong CO stretching band at n˜ =
2
0.58 in molecule 2. The averaged ligand bite angle is 102.78.
Interestingly, these geometrical features are similar to those
found in the recently reported complex [Rh(acac)(1)]
PMP=101.58; acac/PMP tilt angle=16.38). The fluorenyl
À1
A
H
U
G
R
N
U
G
2010 cm in the IR spectrum (measured at 7 bar). The IR
[19]
(
spectrum of 8 also revealed the presence of the coordinated
acac ligand. Complex 8 was stable in the absence of CO be-
cause bubbling of nitrogen into a solution of the complex
did not modify its P NMR spectrum.
On pressurizing the above sapphire tube with hydrogen at
planes of 7 adopt an orientation that is roughly parallel to
the calixarene axis, thereby minimising the steric repulsion
between these groups and the naphthyl units. As a result,
the rhodium atom is sterically more confined than in [Rh-
3
1
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(acac)(1)].
14 bar to apply a p(CO)/p(H ) ratio similar to the one that
2
led to the highest TOFs in the catalytic tests, complex 9
Chem. Eur. J. 2010, 16, 13843 – 13849
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13845

D. Sꢀmeril, D. Matt, W. Oberhauser et al.
slowly formed (Scheme 2 and Figure 2). Here, unlike in 8,
diphosphite 2 shows bidentate coordination, which could be
inferred from the appearance of a doublet at d=144.1 ppm
paratus. On heating the solution to 508C, full conversion of
8 into 9 occurred readily. Prolonged heating of a solution of
9 did not result in the formation of new species.
1
31
1
(
J
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(Rh,P)=246 Hz) in the P{ H} NMR spectrum. Hydride
To prove that complex 9 displays dynamic behaviour in
solution, the NMR probe was gradually cooled to À808C.
1
formation was observed in the H NMR spectrum, which ex-
2
31
hibited a triplet centred at d=À8.28 ppm with a
coupling constant of 5.8 Hz (J(Rh,H)=0 Hz). The small J-
(P,H) coupling constant is in accord with a hydride cis-dis-
posed with respect to the P atoms. Although complex 9 for-
J
A
H
U
G
R
N
U
G
Upon cooling, the peak seen in the P NMR spectrum at
2
A
H
U
G
E
N
N
high temperature first broadened, then coalesced near
3
1
1
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
À208C. At À808C, the P{ H} NMR spectrum (Figure 4)
3
1
mally has C symmetry, its P NMR spectrum shows an A X
1
2
instead of an ABX pattern. This is indicative of a fluxional
process similar to that described by van Leeuwen et al. for
related TBP complexes that contain flexible diphosphites
[
32]
(
vide infra). The IR spectrum of complex 9 showed two
À1
strong absorption bands at n˜ =2063 and 1965 cm . The
presence of two carbonyl ligands could be deduced from the
31
13
1
room-temperature P, C, and H NMR spectra of complex
measured after the latter had been synthesised in a sepa-
9
1
3
rate experiment by using C-enriched (99%) carbon mon-
oxide (Figure 3). Therefore, the above data are in agreement
with the formation of a dynamic, trigonal bipyramidal com-
plex with equatorially positioned phosphorus atoms and a
3
1
1
Figure 4. P{ H} NMR ([D
8
]toluene) spectra of 9 at a) 25, b) À10, and
c) À808C.
[29,32–34]
1
hydride occupying an apical coordination site.
It is
gave a well-resolved ABX spin system (d =143.5 ppm, J-
(Rh,P)=238 Hz,
ACTHNGUTRENNUG( Rh,P)=241, J ACHTNUGTRENNUNG
A
2
1
worth noting that the conversion of complex 8 into 9 oc-
curred considerably faster in the HP-IR cell than in the
NMR tube owing to more efficient stirring in the former ap-
A
H
U
G
R
N
U
G
JACHTUNGTRENNUNG
2
revealed a broad unresolved signal centred at d=À7.85 ppm
2
(
not shown). The observed J
A
H
U
G
R
N
U
G
cal for phosphorus atoms occupying equatorial sites in a
TBP species.
1
In addition, a low-temperature H NMR spectrum was ac-
quired in the presence of a 2:1 H /CO mixture that con-
2
1
3
tained C-enriched (99%) CO. The hydride region showed
a doublet of a broad signal, in accord with a hydrido ligand
2
trans to a carbonyl ligand ( J
A
H
U
G
E
N
N
(H,C)=40 Hz, see the Support-
ing Information). Overall, these findings indicate that the
fluxionality of 9 can be frozen out at low temperatures and
that the two exchanging species (which cannot be distin-
guished spectroscopically) have phosphorus atoms occupy-
ing exclusively equatorial coordination sites. These observa-
tions are consistent with the equatorial–equatorial phospho-
rus exchange proposed by van Leeuwen et al., which occurs
in TBP [RhH(diphosphite)(CO) ] complexes that contain
2
[35]
diphosphites with a long P–P link (Scheme 3). These re-
sults also corroborate earlier studies by Muetterties
[36,37]
et al.
on the dynamics of five-coordinate TBP metal–
3
1
13
1
Figure 3. Room-temperature
P,
C and H NMR (sapphire tube,
1
3
[
D
8
]toluene, 81.01 MHz) spectra of 9 obtained under 99% CO. Impor-
tant data inferred from these spectra: P NMR: d=139.2 ppm (dt, J-
3
1
1
Scheme 3. Equatorial–equatorial phosphorus exchange in TBP [RhH(ca-
lix-diphosphite)(CO) ] complexes that contain long P–P links. In these
2
13
1
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(Rh,P)=249,
J
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(P,C)=21 Hz); C NMR: d=192.88 ppm (dt,
(P,C)=21.0 Hz); H NMR: d=À8.20 ppm (tt,
J
A
H
U
G
R
N
U
G
2
2
1
2
2
6
0.4,
J
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
J
A
H
U
G
R
N
U
G
dynamics each CO ligand is alternately cis and trans bonded with respect
to the hydrido ligand.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(P,H)=4.8 Hz).
13846
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Chem. Eur. J. 2010, 16, 13843 – 13849

Rhodium Complexes Containing Hemispherical Diphosphites
FULL PAPER
phosphane complexes. It is worth noting that in the pro-
posed exchange mechanism each carbonyl ligand alternately
occupies an apical and an equatorial position. Consistent
1
3
with these dynamics, the C NMR spectrum that was ob-
13
tained under C-enriched CO shows a symmetrical carbonyl
signal at room temperature (actually a doublet of triplets
1
2
with
J ACHTUNGTRENNUNG( Rh,C)=60.4, J ACHTUNRTGENNUNG( P,C)=21.0 Hz). It is worth noting
here that the proposed fluxionality is different from a hypo-
thetical exchange mechanism restricted to a 1808 rotation of
the diphosphite about its intrinsic C axis. In this case, in
2
fact, two distinct carbonyl signals would appear in the room-
temperature C NMR spectrum.
To summarise, the above NMR spectroscopy studies dem-
onstrate that, under catalytic conditions, hemispherical di-
3
1
1
13
Figure 5. P{ H} NMR (sapphire tube, [D
8
]toluene, 81.01 MHz) spectra
(1:2; 21 bar).
, RT; d) 7+CO/H , 508C;
of fluorenyl complex 7 under CO (7 bar) and CO/H
a) Compound 7 only; b) 7+CO; c) 7+CO/H
e) 7+CO/H , 608C.
2
2
2
2
phosphite
2
leads exclusively to
a
pentacoordinate
[
RhH(CO) (diphosphite)] intermediate that adopts a bis-
2
equatorial P,P coordination mode.
cannot accommodate a double chelate structure owing to
strong interactions between the CO ligand and the rigid flu-
orenyl moieties. Upon addition of hydrogen (14 bar, 25–
508C), hydrido dicarbonyl complex 10 then slowly formed
(Figure 5). Full conversion into 10 only occurred after heat-
ing the solution at 608C (Scheme 4 and Figure 5). At this
The above reactions, which were carried out in an NMR
tube with 6, were repeated in the presence of 1-hexene
3
1
(
olefin/Rh=145). The P NMR spectrum acquired at 508C
just after addition of CO revealed the exclusive formation
of complex 8. Subsequent addition of hydrogen gave 9, with
no other product being detected. After 1 h the solution was
analysed by GC, which revealed the formation of a mixture
of linear and branched aldehydes in a l/b ratio of 49. It is
worth noting that when this reaction was repeated in an au-
toclave, similar regioselectivities were obtained.
3
1
1
temperature, the P{ H} NMR spectrum of compound 10
1
showed an unique doublet centred at d=144.1 ppm ( J-
AHCTUNGTRENNUNG( Rh,P)=246 Hz). The bis-equatorial coordination mode of
1
the diphosphite ligand was again inferred from the H NMR
spectrum, which showed a broad hydride signal with a small
2
A second series of experiments was run with fluorenyl
complex 7. The room-temperature P NMR spectrum of
J AHCTUNGTERNNUNG( P,H) coupling constant (<2 Hz, unresolved signal). The
3
1
dynamics of 10 are similar to those outlined above for 9.
3
1
this complex in [D ]toluene showed a doublet at d=
Thus, as for 9, the P NMR spectrum of complex 10
measured at À508C displayed an ABX spin system, as ex-
8
1
1
26.1 ppm ( J
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(Rh,P)=327 Hz). After pressurizing the solu-
tion with CO (7 bar), decoordination of diphosphite 4 with
concomitant formation of [Rh(acac)(CO) ] was observed
Scheme 4 and Figure 5). This latter complex, which did not
form in the experiments performed with 6, was un-
ambiguously characterized by its IR spectrum, which
pected for a C -symmetrical molecule undergoing slow ex-
1
1
A
H
N
R
N
U
G
change (d =147.2 ppm; d =144.1 ppm with
247, J AHCUTNGTRENNUN(G Rh,P )=246, and J AHCTUNGTRENNNU(G A,B)=246 Hz). When the acti-
B
J ACHTUNGERTNNUNG( Rh,P )=
A
2
A
B
1
2
(
vation of 7 with CO/H was repeated in the presence of 1-
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
hexene, the same rhodium carbonyl intermediates as those
formed in the absence of olefin were observed. At the end
of these experiments, aldehydes had formed with a l/b ratio
of 3. Thus, the proportion of linear aldehyde here is consid-
erably lower than that obtained
À1 [38]
showed two stretching bands at n˜ =2082 and 2011 cm .
Here, ligand decoordination arises after formation of the in-
termediate [Rh(acac)(CO)(4)] (not seen), which probably
ACHTUNGTRENNUNG
with complex 6. The relatively
low linear selectivity observed
here is in accord with the obser-
vation that unlike diphosphite
2
, ligand 4 shows a marked ten-
dency to decoordinate, which
would result in unsaturated
and, therefore, unselective rho-
[39]
dium species.
Conclusion
The Rh ACHNTUGRNENUG( acac) complex contain-
ing benzyl-substituted calix-di-
phosphite 2 exclusively forms
Scheme 4. Activation of fluorenyl complex 7 with CO and H
2
.
the
trigonal
bipyramidal
Chem. Eur. J. 2010, 16, 13843 – 13849
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13847

D. Sꢀmeril, D. Matt, W. Oberhauser et al.
hydrido carbonyl complex [RhH(CO) (2)], in which both
phosphorus atoms occupy equatorial coordination sites,
0.57 mL of styrene) and decane (0.50 mL) under nitrogen. Afterwards,
2
the autoclave was flushed twice with syn-gas (CO/H
2
, 1:1 v/v) and the
pressurised with 21 bar of the desired CO/H mixture before being
2
under CO/H at 508C. This particular configuration, which
2
heated at 508C. The reaction progress was monitored by using the gas
consumption. Samples of the catalytic solution were taken regularly and
analyzed by using GC.
results in an effective confinement of the metal in a cleft
formed by two symmetrical naphthyl units, certainly contrib-
utes to a large extent to the high linear aldehyde selectivity
observed. However, this result does not allow one to quanti-
fy the contribution of the pocket effect arising from the
presence of the calixarene Z substituents, which helps to
create a tight envelope about the metal and favours linear
aldehyde selectivity. An equatorial–equatorial configuration
was also observed in complex 10, which was formed under
General procedure for the HP NMR experiments: A solution of [Rh-
A
H
U
G
R
N
U
G
8
]toluene (2 mL) was transferred
3
1
1
1
into the NMR apparatus for acquisition of the P{ H} and H NMR
spectra at RT. Afterwards, the sapphire tube was removed from the
3
1
1
NMR probe and charged with CO (7 bar) at RT, and new P{ H} and
1
H NMR spectra were acquired. The sapphire tube was again removed
from the NMR probe and pressurised with hydrogen (14 bar) before new
measurements were carried out at RT. Finally, the solution was gradually
heated, first to 408C (full conversion was not observed at this tempera-
ture), then to 508C. At this latter temperature, the reaction progress was
CO/H from rhodium acac complex 7 based on ligand 4, but
2
the latter ligand turned out to be a poorer chelating ligand
because temporary decoordination was observed when com-
plex 7 was treated with CO. The latter observation may ac-
count for the weaker regioselectivity obtained with this
ligand in styrene hydroformylation. Overall, this study gives
a good understanding of the way hemispherical diphosphites
may operate for controlling regioselectivity in the hydrofor-
mylation of olefins.
2
monitored until [RhH(CO) (L)] had quantitatively formed (complexes 9
and 10). At the end of these experiments, the sapphire tube was gradual-
ly cooled to À808C to freeze out the dynamics of the hydrido carbonyl
complex formed. Complexes 9 and 10 turned out to be stable at RT for
31
1
1
several days, as verified by P{ H} and H NMR spectroscopy. The above
sequence of experiments was repeated in the presence of 1-hexene
(200 mL, 1.59 mmol), including heating for 1 h at 508C. At the end of this
experiment, the NMR probe was cooled to RT, the gas was vented from
the sapphire tube and the solution was subjected to GC analysis.
General procedure for the HP-IR experiments: [Rh ACTHUNGTRNENUNG( acac)(L)] (6 or 7)
(
0.024 mmol) was dissolved in dichloromethane (26 mL) before being
transferred to the high-pressure IR cell under nitrogen. The IR cell was
pressurized at RT with CO (7 bar) and then introduced into the spec-
trometer. The spectrum was then run. After measurement, the IR cell
was removed from the spectrometer, and charged with hydrogen (14 bar)
at RT, then reintroduced into the spectrometer for a new measurement.
The IR cell was then heated stepwise up to 508C (108C intervals) and
maintained at this temperature for 1 h. At each temperature an IR spec-
trum was acquired. On reaching 508C, IR spectra were acquired at time
intervals of 20 min.
Experimental Section
All samples were prepared in dry solvents and under nitrogen. Ligands 2
and 4 and complexes 6 and 7 were obtained according to previously re-
[
18,19]
ported synthetic procedures.
HP NMR spectroscopic measurements
were carried out by using a Bruker Avance II 200 spectrometer operating
1
31
1
at 200.13 MHz ( H NMR) or 81.01 MHz ( P{ H} NMR). For these ex-
periments, a 10 mm o.d. sapphire tube (Saphikon, Milford, NH, USA)
and a titanium high-pressure charging head (ICCOM-CNR, Sesto-Fioren-
[
40]
tino, Italy) were used. HP-IR experiments were performed in a high-
pressure IR cell (ICCOM-CNR) consisting of 75 mL autoclave
equipped with ZnS windows (4 mm thickness, 8 mm diameter, optical
a
[
34]
path length 0.2 mm). The catalytic solutions were analyzed by using a
Varian 3900 gas chromatograph equipped with a WCOT fused-silica
column (25 mꢄ0.25 mm).
Acknowledgements
X-ray crystallographic data for 7·hexane·methyl-2-pentane: Crystals of
Financial support by the French Agence National de la Recherche (ANR
MATCALACAT) and the Universitꢀ de Strasbourg is gratefully ac-
knowledged. Thanks are also due to the European Commission for fi-
nancing the project (IDECAT, NoE contract no. NMP3-CT-2005-
011730).
7
·hexane·methyl-2-pentane were grown from a solution of the complex in
dichloromethane/hexane/methyl-2-pentane.
¯
C
242
H
226
O
20
P
4
Rh
2
;
r
M =
3
787.96; monoclinic; P1; a=12.7031(4), b=27.156(1), c=32.506(1) ꢃ;
3
À3
b=97.267(3); V=11123.4(6) ꢃ ; Z=2; 1calcd =1.131 mgm ; l
A( MoKa)=
H
U
G
R
N
U
G
À1
0
.71073 ꢃ; m=0.237 cm
;
F
A
H
U
G
R
N
U
G
were collected by using a NONIUS Kappa CCD diffractometer (graphite
MoKa radiation, l=0.71073 ꢃ). The structure was solved by using SIR-
[
1] J. A. A. W. Elemans, E. J. A. Bijsterveld, A. E. Rowan, R. J. M.
Nolte, Chem. Commun. 2000, 2443–2444.
[
41]
9
7, which revealed the non-hydrogen atoms of the molecule. The struc-
[
42]
ture was refined with SHELXL97 using a riding model for hydrogen
[
2] H. Ito, T. Kusukawa, M. Fujita, Chem. Lett. 2000, 598–599.
3] V. F. Slagt, P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek,
Angew. Chem. 2001, 113, 4404; Angew. Chem. Int. Ed. 2001, 40,
atoms; 2437 variables and 37181 observations with I>2.0s(I). R=0.065,
[
À3
R
w
=0.155 and S
w
=0.784, D1<0.889 eꢃ . A major difficulty in structure
determination arose from the tendency of the crystal to desolvate rapidly.
The Alert level A revealed in the checkCIF is mainly due to the disor-
dered hexane and methyl-2-pentane solvent molecules. The difficulty in
locating the solvent molecules may explain the high value of parameter
shift to su ratio and the large voids in the structure. CCDC-718244 (7)
contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallograph-
ic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
4
271–4274.
4] D. Fiedler, R. G. Bergman, K. N. Raymond, Angew. Chem. 2004,
16, 6916–6919; Angew. Chem. Int. Ed. 2004, 43, 6748–6751.
[
[
[
[
1
5] V. F. Slagt, P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek, J.
Am. Chem. Soc. 2004, 126, 1526–1536.
6] C. Jeunesse, D. Armspach, D. Matt, Chem. Commun. 2005, 5603–
5
614.
7] T. S. Koblenz, H. L. Dekker, C. G. de Koster, P. W. N. M. van Leeu-
General procedure for the hydroformylation experiments: The catalytic
runs were carried out in a glass-lined, 100 mL stainless steel autoclave
that contained a magnetic stirring bar. Typically, the autoclave was
wen, J. N. H. Reek, Chem. Commun. 2006, 1700–1702.
[8] J. A. A. W. Elemans, E. J. A. Bijsterveld, A. E. Rowan, R. J. M.
Nolte, Eur. J. Org. Chem. 2007, 751–757.
charged with
a
solution of [Rh
A
H
U
G
R
N
U
G
[9] D. Fiedler, H. van Halbeek, R. G. Bergman, K. N. Raymond, J. Am.
Chem. Soc. 2006, 128, 10240–10252.
(
15.0 mL), olefin (5 mmol, corresponding to ꢀ0.78 mL of 1-octene or
13848
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 13843 – 13849

Rhodium Complexes Containing Hemispherical Diphosphites
FULL PAPER
[
[
[
[
[
10] A. B. C. Deutman, C. Monnereau, J. A. A. W. Elemans, G. Ercolani,
[29] A. van Rooy, P. C. J. Kamer, P. W. N. M. van Leeuwen, K. Goubitz,
J. Fraanje, N. Veldman, A. L. Spek, Organometallics 1996, 15, 835–
847.
[30] A. Castellanos-Pꢆez, S. Castillꢇn, C. Claver, P. W. N. M. van Leeu-
wen, W. G. J. de Lange, Organometallics 1998, 17, 2543–2552.
[31] L. A. van der Veen, P. C. J. Kamer, P. W. N. M. van Leeuwen, Orga-
nometallics 1999, 18, 4765–4777.
R. J. M. Nolte, A. E. Rowan, Science 2008, 322, 1668–1671.
11] J. N. H. Reek in Supramolecular Catalysis (Ed.: P. W. N. M. van
Leeuwen), 2008, Wiley-VCH, Weinheim, pp. 199–234.
12] S. Steyer, C. Jeunesse, J. Harrowfield, D. Matt, Dalton Trans. 2005,
1
301–1309.
13] A. Lꢅtzen, Angew. Chem. 2005, 117, 1022–1025; Angew. Chem. Int.
Ed. 2005, 44, 1000–1002.
14] B. Kersting, U. Lehman in Advances in Inorganic Chemistry, Vol. 61
[32] G. J. H. Buisman, L. A. van der Veen, P. C. J. Kamer, P. W. N. M. van
Leeuwen, Organometallics 1997, 16, 5681–5687.
(
Eds.: R. van Eldik, C. D. Hubbard), Elsevier, Amsterdam, 2009,
[33] L. A. van der Veen, M. D. K. Boele, F. R. Bregman, P. C. J. Kamer,
P. W. N. M. van Leeuwen, K. Goubitz, J. Fraanje, H. Schenk, C. Bo,
J. Am. Chem. Soc. 1998, 120, 11616–11626.
[34] C. Bianchini, W. Oberhauser, A. Orlandini, C. Giannelli, P. Frediani,
Organometallics 2005, 24, 3692–3702.
pp. 407–470.
[
[
15] R. Breslow, Chem. Rev. 1988, 88, 1997–2011.
16] M. T. Reetz, S. R. Waldvogel, Angew. Chem. 1997, 109, 870–873;
Angew. Chem. Int. Ed. Engl. 1997, 36, 865–867.
17] D. Sꢀmeril, C. Jeunesse, D. Matt, L. Toupet, Angew. Chem. 2006,
[
[35] G. J. H. Buisman, E. J. Vos, P. C. J. Kamer, P. W. N. M. van Leeuwen,
J. Chem. Soc. Dalton Trans. 1995, 409–417.
1
18, 5942–5946; Angew. Chem. Int. Ed. 2006, 45, 5810–5814.
[
[
18] D. Sꢀmeril, D. Matt, L. Toupet, Chem. Eur. J. 2008, 14, 7144–7155.
19] L. Monnereau, D. Sꢀmeril, D. Matt, L. Toupet, Adv. Synth. Catal.
[36] P. Meakin, J. P. Jesson, F. N. Tebbe, E. L. Muetterties, J. Am. Chem.
Soc. 1971, 93, 1797–1799.
2
009, 351, 1629–1636.
20] L. Monnereau, D. Sꢀmeril, D. Matt, Eur. J. Org. Chem. 2010, 3068–
073.
[37] P. Meakin, E. L. Muetterties, J. P. Jesson, J. Am. Chem. Soc. 1972,
94, 5271–5285.
[38] J. Zhang, X.-Z. Sun, M. Poliakoff, M. W. George, J. Organomet.
Chem. 2003, 678, 128–133.
[
[
3
21] P. W. N. M. van Leeuwen, P. C. J. Kamer, J. N. H. Reek, P. Dierkes,
Chem. Rev. 2000, 100, 2741–2769.
2
[39] Hydroformylation of 1-octene by using [Rh ACHTUNGTERNNGN(U acac)(CO) ] without
[
[
22] Z. Freixa, P. W. N. M. van Leeuwen, Dalton Trans. 2003, 1890–1901.
23] L. A. van der Veen, P. H. Keeven, G. C. Schoemaker, J. N. H. Reek,
P. C. J. Kamer, P. W. N. M. van Leeuwen, M. Lutz, A. L. Spek, Orga-
nometallics 2000, 19, 872–883.
any additional ligand was found to result in l/b ratios of around 2.
Under these conditions a significant drop in activity was also ob-
served.
[40] C. Bianchini, A. Meli, A. Traversi, Ital. Pat. FI A000025, 1997.
[41] A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovaz-
zo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J.
Appl. Crystallogr. 1998, 31, 74–77.
[42] SHELX-97, Program for the refinement of crystal structures, G. M.
Sheldrick, University of Gçttingen (Germany), 1997.
[
[
[
[
[
24] C. B. Dieleman, P. C. J. Kamer, J. N. H. Reek, P. W. N. M. van Leeu-
wen, Helv. Chim. Acta 2001, 84, 3269–3280.
25] P. Uriz, E. Fernꢆndez, N. Ruiz, C. Claver, Inorg. Chem. Commun.
2
000, 3, 515–519.
26] P. C. J. Kamer, A. van Rooy, G. C. Schoemaker, P. W. N. M. van
Leeuwen, Coord. Chem. Rev. 2004, 248, 2409–2424.
27] D. Selent, W. Baumann, K.-D. Wiese, A. Bçrner, Chem. Commun.
2
008, 6203–6205.
28] E. Rafter, D. G. Gilheany, J. N. H. Reek, P. W. N. M. van Leeuwen,
Received: June 8, 2010
ChemCatChem 2010, 2, 387–391.
Published online: October 18, 2010
Chem. Eur. J. 2010, 16, 13843 – 13849
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13849