Isostructural phosphine-phosphite ligands in rhodium-catalyzed asymmetric hydroformylation

Article abstract of DOI:10.1021/om100250r

Isostructural phosphine-phosphite ligands 7-10 have been synthesized from the condensation of chiral 3,3′-bis(trialkylsilyl)-2,2′-bisnaphthol phosphorochloridites and phenol-phosphanes 3-6. These ligands were evaluated as chiral inducers in the rhodium-catalyzed asymmetric hydroformylation reaction (AHF) of vinyl acetate and a series of styrene derivatives. The highest enantioselectivity, 78% ee, was observed in the AHF of vinyl acetate using phenylphosphino-based ligand 10. A direct correlation between the enantioselectivity and the Hammett constant σ of the substituent in the substrates was found (4-Me-styrene, 15% ee; styrene, 23% ee; 4-Cl-styrene, 51% ee) under mild reaction conditions for phenylphosphole-based ligand 8. Several rhodium-hydride and rhodium-acyl complexes were prepared and characterized by HP-NMR and HP-IR spectroscopy. Rhodium-hydride complexes of the formula [HRh(L)(CO)₂] A with ligands 7, 8, and 10 were found to be highly conformationally fluxional in solution. The reaction of 4-Cl-styrene with rhodium-hydride complexes of ligands 7 and 8 gave the corresponding rhodium-acyl derivatives [(RCO)Rh(CO)₂(L)] E. A comparative analysis of the spectroscopic properties of these rhodium-acyl complexes revealed that [(RCO)Rh(CO)₂(7)] was more conformationally labile than [(RCO)Rh(CO)₂(8)].

Full text of DOI:10.1021/om100250r

4440 Organometallics 2010, 29, 4440–4447
DOI: 10.1021/om100250r
Isostructural Phosphine-Phosphite Ligands in Rhodium-Catalyzed
Asymmetric Hydroformylation
Franco Doro, Joost N. H. Reek, and Piet W. N. M. van Leeuwen*
Van’t Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Nieuwe Achtergracht 166
1018 WV Amsterdam, The Netherlands
Received March 31, 2010
Isostructural phosphine-phosphite ligands 7-10 have been synthesized from the condensation of
chiral 3,30-bis(trialkylsilyl)-2,20-bisnaphthol phosphorochloridites and phenol-phosphanes 3-6.
These ligands were evaluated as chiral inducers in the rhodium-catalyzed asymmetric hydroformyla-
tion reaction (AHF) of vinyl acetate and a series of styrene derivatives. The highest enantioselectivity,
78% ee, was observed in the AHF of vinyl acetate using phenylphosphino-based ligand 10. A direct
correlation between the enantioselectivity and the Hammett constant σ of the substituent in the
substrates was found (4-Me-styrene, 15% ee; styrene, 23% ee; 4-Cl-styrene, 51% ee) under mild
reaction conditions for phenylphosphole-based ligand 8. Several rhodium-hydride and rhodium-acyl
complexes were prepared and characterized by HP-NMR and HP-IR spectroscopy. Rhodium-
hydride complexes of the formula [HRh(L)(CO)2] A with ligands 7, 8, and 10 were found to be highly
conformationally fluxional in solution. The reaction of 4-Cl-styrene with rhodium-hydride com-
plexes of ligands 7 and 8 gave the corresponding rhodium-acyl derivatives [(RCO)Rh(CO)2(L)]
E. A comparative analysis of the spectroscopic properties of these rhodium-acyl complexes revealed
that [(RCO)Rh(CO)2(7)] was more conformationally labile than [(RCO)Rh(CO)2(8)].
Introduction
with computational studies, characterization of catalyst-
substrate adducts, and kinetic studies.2-5 A specific case is
the Rh-catalyzed asymmetric hydroformylation (AHF) of
styrenes, the enantioselective step of which has been demon-
strated by computational means to be influenced by these
low-energy forces involved in the interaction between the
phenyl groups of the ligand (chiral inducer) and the phenyl
groups of the substrate.5
Our group has contributed significantly to the under-
standing of the mechanisms that determine the selectivity
in transition metal catalyzed transformations, such as the
Rh-catalyzed hydroformylation of linear and internal alkenes.6,7
We have shown that ligands with a wide bite angle induce very
high regioselectivities in the Rh-catalyzed hydroformylation
of linear alkenes into linear aldehydes.8 Conversely, the em-
ployment as catalysts of encapsulated phosphine-containing
Rh complexes allows the regioselective transformation of
internal alkenes into branched aldehydes.9,10
The mechanistic understanding of the induction of chi-
rality in a metal-mediated asymmetric transformation is
essential for developing more selective catalysts.1 For a given
class of electronically similar ligands, the enantio-discrimi-
nation is known to be primarily derived from steric effects
that either favor or disfavor the formation of the enantiomer
resulting from the lowest energy transition state (TS) in the
enantio-determining step of a particular reaction. However,
other types of interactions might be involved in the enantio-
inductive step such as hydrogen bonding, π-π stacking, or
C-H/π interaction.2,3 These interactions could convey a
certain degree of stabilization into key catalytic intermedi-
ates, bringing parts of the molecule that would normally stay
far apart for purely steric reasons in close proximity, thus
strongly affecting the geometry of the TS.4 The determina-
tion of the type and magnitude of substrate-ligand interac-
tions involved in the enantioselective step of an asymmetric
process is very difficult. This issue has so far been addressed
The AHF of substituted alkenes is a particularly challen-
ging reaction owing to the difficulty in controlling the regio-
and enantioselectivity concomitantly. Chiral ligands bearing
*To whom correspondence should be addressed. E-mail: P.W.N.M.
vanLeeuwen@uva.nl.
(1) Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H., Eds. Comprehensive
Asymmetric Catalysis I-III: Spinger: New York, 1999.
(2) Ma, L.; Jiao, P.; Zhang, Q.; Du, D.-M.; Xu, J. Tetrahedron:
Asymmetry 2007, 18 (7), 878–884.
(6) van Leeuwen, P. W. N. M. Homogeneous catalysis: Understanding
the Art; Kluwer Academic Pubblishers: Dordrecht, 2004; Chapter 8.
(7) van Leeuwen, P. W. N. M.; Claver, C., Eds. Rhodium Catalyzed
Hydroformylation; Kluwer Academic Pubblishers: Dordrecht, 2000.
(8) Rivillo, D.; Gulyas, H.; Benet-Buchholz, J.; Escudero-Adan,
E. C.; Freixa, Z.; van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed.
2007, 46 (38), 7247–7250.
(3) Malkov, A. V.; Mariani, A.; MacDougall, K. N.; Kocovsky, P.
Org. Lett. 2004, 6 (13), 2253–2256.
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1991, 113 (19), 7177–7183.
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2008, 37 (2), 247–262.
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r
pubs.acs.org/Organometallics
Published on Web 09/30/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 20, 2010 4441
Scheme 1. Synthesis of Phosphine 3a
Figure 2. Structures of phenyl-dibenzophosphole I and phenyl-
phenoxaphosphine II.
a EVE = ethyl vinyl ether or 1-ethoxyethoxy group. Key: (i) 1 equiv
TMEDA, 1 equiv BuLi, Et2O/hexane, 0 °C to rt, overnight; (ii) 1.1 equiv
10-chloro-2,8-dimethylphenoxaphosphine, 0 °C, 3 h; (iii) PPTS, ethanol/
CH2Cl2, reflux. Overall yield: 52%.
synthesis of phosphine-phosphite ligands with defined
stereoelectronic properties. Phenoxaphosphine 3, which
consists of two equivalent aryl groups fused together, was
prepared starting from (1-ethoxyethoxy)benzene 1. Metala-
tion of 1 with n-butyllithium, in the presence of TMEDA,
followed by reaction with 10-chloro-2,8-dimethylphenoxa-
phosphine gives 2, which after deprotection affords phenox-
aphosphine 3 (Scheme 1).
Dibenzophosphine 4 was prepared following an experi-
mental procedure analogous to that of phosphine 3. The
synthesis of enantiopure phosphine (R)-5 was performed fol-
lowing an experimental procedure previously reported.19
Triarylphosphine 6, which does not suffer from any strain,
completes the series (Figure 1).
Benzo-fused phosphole I is a slightly aromatic P-heterole
by virtue of the high inversion barrier of the phosphorus
pyramid, which prevents flattening (Figure 2). Although this
phosphine is, overall, isostructural with phenoxaphosphine II,
there are some structural features, relevant for our studies,
that differ considerably.
Figure 1. Structures of phenol-phosphine compounds.
phosphine and phosphite moieties are the ligands of choice in
the Rh-catalyzed AHF.11-16 Enantioselectivities around
90% were reported for the first time by Babin and Whiteker
using bulky diphosphites.15 Another successful ligand for
this transformation is represented by (R,S)-Binaphos, which
gives an ee higher than 90%.17 This ligand and its deriva-
tives,18 however, give relatively low regioselectivities. Chiral
diphosphite ligands, instead, induce high regioselectivities
and moderate to high ee.11,14-16
In this paper we report on the synthesis of a series of
conformationally constrained phosphine-phosphite ligands
and their evaluation in the AHF of electronically different
styrene derivatives at various reaction conditions. These
ligands, upon coordination to a metal precursor, differ
exclusively in the orientation of the P-aryl groups protruding
toward the metal center. A trend between the electronic
properties of the substrate and the orientations of the P-aryl
groups of the ligand was found. In order to find additional
proof on this particular issue, we studied the coordination
chemistry of our chiral inducers. Notably, we discovered that
all corresponding catalytic initiators, characterized by high-
pressure NMR and FT IR spectroscopy, are conformationally
fluxional under the reaction conditions. The structural mod-
ification of these species, achieved by preparing substrate-
containing complexes of increasing internal steric hindrance,
enabled us to examine their conformational behavior and to
extract indirectly valuable information regarding a possible
aryl-aryl interaction in the AHF.
A comparative crystallographic analysis of phosphines
I and II shows that the central five-membered ring of phos-
phole I has an envelope conformation, with phosphorus
22
˚
deviating about 0.12 A from the four-C-atom plane.
Analogously, phenyl-phenoxaphosphine II contains a
central ring with a boat-like conformation due to the phos-
˚
phorus and oxygen deviations of 0.22 and 0.18 A on the same
side of the plane.20 Another relevant feature of the phenyl-
dibenzophosphole is the dihedral angle between the plane
described by the C atoms of the central ring and the adjacent
fused aromatic rings, which fall in the range 1.1-3.0°. In the
case of the phenoxaphosphine the two fused aromatic rings
have a dihedral angle of 15.0°.20-22 Thus, a major difference
between phenyl-dibenzophosphole and phenyl-phenoxa-
phosphine lies in the higher degree of planarity of the
three-ring system of the former.
The corresponding phosphine-phosphite ligands were
prepared by condensation of phenol-phosphines with chiral
binol chlorophosphites of different steric bulk, in the pre-
sence of triethylamine (Figure 3).23 The 31P{1H} NMR
spectrum of 7 clearly displays a doublet at -66.6 and 140.1
ppm with a JP-P of 23 Hz, which stems from the 31P-31P
through-space coupling. The 31P{1H} NMR spectroscopic
analysis of ligands 8-10 shows a similar pattern of signals.
2. Asymmetric Hydroformylation of Substituted Alkenes.
AHF experiments were carried out with vinyl acetate and
styrene derivatives as substrates, using complexes [Rh(acac)L]
Results and Discussion
1. Ligands: Syntheses and Structural Features. A series of
aryl-phosphines 3-6 were used as building blocks for the
(11) Klosin, J.; Landis, C. R. Acc. Chem. Res. 2007, 40 (12), 1251–
1259.
(12) Cobley, C. J.; Klosin, J.; Qin, C.; Whiteker, G. T. Org. Lett. 2004,
6 (19), 3277–3280.
(13) Clark, T. P.; Landis, C. R.; Freed, S. L.; Klosin, J.; Abboud,
K. A. J. Am. Chem. Soc. 2005, 127 (14), 5040–5042.
(14) Gual, A.; Godard, C.; Claver, C.; Castillon, S. Eur. J. Org. Chem.
2009, No. 8, 1191–1201.
(15) Babin, J. E.; Whiteker, G. T. PCT Int. Appl. WO 93/03830 1992.
(16) Buisman, G. J. H.; van der Veen, L. A.; Klootwijk, A.; de Lange,
W. G. J.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Vogt, D.
Organometallics 1997, 16 (13), 2929–2939.
(19) Doro, F.; Lutz, M.; Reek, J. N. H.; Spek, A. L.; van Leeuwen, P.
W. N. M. Eur. J. Inorg. Chem. 2008, No. 8, 1309–1317.
(20) Mann, F. G.; Millar, I. T.; Powell, H. M.; Watkin, D. J. J. Chem.
Soc., Perkin Trans. 2 1976, No. 12, 1383–1385.
(21) Nyulaszi, L.; Holloczki, O.; Lescop, C.; Hissler, M.; Reau, R.
Org. Biomol. Chem. 2006, 4 (6), 996–998.
(22) Alyea, E. C.; Ferguson, G.; Gallagher, J. F. Acta Crystallogr.
Sect. C: Cryst. Struct. Commun. 1992, 48, 959–961.
(23) Deerenberg, S.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
(17) Sakai, N.; Mano, S.; Nozaki, K.; Takaya, H. J. Am. Chem. Soc.
1993, 115 (15), 7033–7034.
(18) Zhang, X.; Yan, Y. J. Am. Chem. Soc. 2006, 128, 7198–7202.
Organometallics 2000, 19 (11), 2065–2072.

4442 Organometallics, Vol. 29, No. 20, 2010
Doro et al.
Figure 3. Structures of phosphine-phosphite ligands L.
Table 1. Asymmetric Hydroformylation of Vinyl Acetate and
Styrene with [Rh(acac)(CO)2]/La
Table 2. Asymmetric Hydroformylation of Styrene Derivatives
with [Rh(acac)(CO)2]/La
entry
substrate
L
conv, % branched, % ee, %
entry
substrate
L
conv, % branched, %
ee, %
1
2
3
4
5
6
7
8
vinyl acetateb,c (R)-7
60
>99
>99
>99
40
98
15
98
94
8 (R)
19 (-)
3 (S)
20 (þ)
22 (R)
17 (-)
78 (S)
44 (þ)
1
2
3
4
5
6
7
4-Me-styreneb
4-Cl-styrene
(R)-7
(R)-7
14 (-)
11 (-)
17 (þ)
18 (þ)
15 (þ)
38 (þ)
12 (þ)
styrene
vinyl acetateb
styrene
(R)-7
(S)-8
(S)-8
(R,S)-9
(R,S)-9
>99
>99
>99
>99
>99
>99
96
96
94
97
94
97
96
95
4-OMe-styrene (S)-8
4-Me-styreneb
4-Cl-styrene
4-Me-styreneb
4-Cl-styrene
(S)-8
(S)-8
(R)-10
(R)-10
vinyl acetateb
styrene
93
96
95
vinyl acetateb,c (R)-10
styrene
(R)-10
a Reaction conditions: T = 60 °C, 20 bar H2/CO, [substrate0]/[Rh] =
1000, [Rh] = 1.00 mM, [L]/[Rh] = 5, time = 20 h, internal standard =
decane, solvent = toluene. b Internal standard = undecane.
a Reaction conditions: T = 60 °C, 20 bar H2/CO = 1:1, [substrate0]/
[Rh] = 1000, [Rh] = 1.00 mM, [L]/[Rh] = 5, time = 20 h, internal
standard=decane, solvent=toluene (0.5 mL). b Internal standard=
heptane. c [L]/[Rh] = 8.
Table 3. Asymmetric Hydroformylation of Styrene Derivatives
with [Rh(acac)(CO)2]/La
formed in situ as catalyst precursors. In the presence of syn-
gas these catalyst precursors are converted quantitatively to
species [HRh(L)(CO)2], which are the actual initiators of the
reaction. The factors that govern the regio- and enantiopurity of
the aldehyde formed by a particular catalyst are several:
temperature, gas pressure, and solvent.24 Preliminary screen-
ings were performed using vinyl acetate and styrene, which
are benchmark substrates for this reaction. These substrates
were evaluated with catalysts bearing ligands 7-10 using
toluene at 60 °C. Table 1 shows that ligand 10 outperforms
all other ligands tested in terms of enantioselectivity with
respect to both substrates. The highest ee obtained with this
ligand is 78% for the AHF of vinyl acetate. For the other
ligands 7-9, the observed enantioselectivity is poor. A high
branched/linear ratio (b/l) could be achieved in all experi-
ments, thus ruling out the presence of ligand-free Rh com-
plexes during the catalysis.25-27
In order to study the involvement of an electronic effect, a
series of styrene derivatives were screened: 4-methoxystyrene
(-0.27), 4-methylstyrene (-0.17), styrene (0.0), and 4-chloro-
styrene (þ0.23) (in parentheses are the Hammett constant
σ values). The catalytic results obtained by employing
ligands 7, 8, and 10, in the AHF of these alkenes displayed
only marginal changes in ee and regioselectivities com-
pared to unsubstituted styrene (Table 2). The only excep-
tion to this trend is given by the low enantioinduction
attained in the AHF of 4-Cl-styrene (entry 7, Table 2),
which might be caused by partial racemization of the cor-
responding aldehyde.
entry
substrate
L
conv, % branched, %
ee, %
1
2
3
4
5
6
7
8
4-OMe-styrene (R)-7
8
96
17 (-)
19 (-)
22 (-)
12 (-)
33 (þ)
39 (þ)
33 (þ)
55 (þ)
52 (þ)
52 (þ)
47 (þ)
4-Me-styreneb
styrene
(R)-7
(R)-7
(R)-7
(S)-8
(S)-8
(S)-8
10
10
97
98
4-Cl-styrene
4-Me-styreneb
styrene
4
3
12
12
16
14
94
94
94
99
97
99
4-Cl-styrene
4-OMe-styrene (R)-10
9
10
11
4-Me-styreneb
styrene
4-Cl-styrene
(R)-10
(R)-10
(R)-10
a Reaction conditions: T = 25 °C, 20 bar H2/CO = 1:1, [substrate0]/
[Rh] = 1000, [Rh] = 1.00 mM, [L]/[Rh] = 5, time = 20 h, internal
standard=decane, solvent=toluene. b Internal standard=undecane.
All ligands respond differently to a drop in reaction
temperature, although consistently within the substrate set.
Ligand 7 does not benefit from a lower reaction temperature,
with ee’s below 20% in all the runs. Ligand 10 performs
better in terms of ee (þ10%) with all the substrates tested,
while for 8 this beneficial effect is even larger (Table 3).
Ligands 7, 8, and 10 induce similar ee’s, regardless of the
electronic properties of the substrates tested. This can be
illustrated nicely if the ee’s are plotted against the type of
substrate, in increasing order of σ (Figure 4).
To ascertain the role of the reaction media, we screened all
substrates in solvents of different polarity and polarizability.
The difference in performance between 7 and 8 in DCM is
very striking, with 8 capable of transforming 4-Cl-styrene
with ee’s up to 51% (entry 8, Table 4) and 7 inducing, at best,
an ee of 16% (entry 4, Table 4). Ligand 10 gave ee’s in THF
and DCM similar to the ones obtained in toluene, indicating
that the solvent is not playing a role in this case.
(24) Breault, G. A.; Hunter, C. A.; Mayers, P. C. J. Am. Chem. Soc.
1998, 120 (14), 3402–3410.
(25) Lazzaroni, R.; Settambolo, R.; Caiazzo, A. Catal. Met. Com-
plexes 2000, 22, 15–33.
(26) Garland, M.; Bor, G. Inorg. Chem. 1989, 28 (3), 410–413.
(27) Liu, G. W.; Volken, R.; Garland, M. Organometallics 1999,
18 (17), 3429–3436.
The plot of the ee’s versus the electronic properties of the
substrates, for reactions carried out in dichloromethane,

Article
Organometallics, Vol. 29, No. 20, 2010 4443
shows clearly that in the case of ligand 8 the ee increases
with σ (Figure 5). The enantioselectivity induced by ligands 7
and 10 is not affected by any of the reaction factors that
were varied (solvent, temperature). The difference in
performance between isostructural 7 and 8 is therefore
ascribed exclusively to the different level of planarity of
the P-phenyl groups in the phosphorus-based hetero-
cycles.20,22 The fact that ligands featuring DBP, as donor
groups, are superior in terms of ee induced to the ones
having phenoxaphosphino moieties was already demon-
strated by Knowles et al. for DIOP-based ligands.28 The
authors, however, could not rationalize this difference
of performance since according to their studies, based
exclusively on a qualitative analysis of the orientation of
the phenyl groups, it would have been logical to obtain the
same level of ee for both DBP and phenoxaphosphino-
based DIOP ligands.
3. Spectroscopic Characterization of Catalytic Intermedi-
ates in the Asymmetric Hydroformylation Reaction. Isostruc-
tural ligands 7 and 8 clearly respond differently to the
changes in temperature and solvent in the catalytic experi-
ments depicted above. The strong influence of the Hammett
parameter observed for the latter ligand strongly hints
toward a synergy of effects between ligand and substrate.
In such a scenario, we would envisage a special interaction
between the aromatic P-rings of the phosphole and the
phenyl group of the styrene derivatives. To address this
issue, the coordination properties of these ligands were
studied under the actual catalytic conditions,21,29,30 em-
ploying high-pressure analytical techniques such as HP
NMR and HP IR spectroscopy.31
3.1. Rhodium-Hydride Species. Phosphine-phosphite li-
gands 7-10 were reacted, in excess, with [Rh(CO)2(acac)] to
form exclusively complexes [Rh(L)(acac)] 11-14. The NMR
data are in agreement with a bidentate coordination of the
phosphine-phosphite ligand with a cis disposition of the
donor groups. Complex [Rh(L)(acac)] is transformed in the
presence of syn-gas into a species of the type [HRh(L)(CO)2] A.
The analysis of the FT IR spectra showed, for all the
systems studied, absorptions of the carbonyl ligands around
2000 cm-1 (Table 5).23 Experiments of deuterium/hydrogen
exchange were carried out showing no shift of the absorp-
tions, thus indicating that the CO ligands are coordinated
equatorially to the Rh center. Complexes of type Aea-Aae
with ligand L coordinating in an equatorial-axial (ea) or
axial-equatorial (ae) fashions are in agreement with these
spectroscopic data.23
Figure 4. Plot of the ee’s versus σ. Reaction conditions: see
Table 3.
Table 4. Asymmetric Hydroformylation of Styrene Derivatives
with [Rh(acac)(CO)2]/La
entry
substrate
L
conv, % branched, % solvent ee, %
1
2
3
4
5
6
7
8
9
4-OMe-styrene (R)-7
4-Me-styreneb (R)-7
9
98
DCM 7 (-)
DCM 5 (-)
DCM 12 (-)
DCM 16 (-)
styrene
4-Cl-styrene
4-Cl-styrene
(R)-7
(R)-7
(R)-7
15
6
5
98
96
94
THF
3 (-)
4-Me-styreneb (S)-8
DCM 15 (þ)
DCM 23 (þ)
DCM 51 (þ)
THF 20 (þ)
styrene
4-Cl-styrene
(S)-8
(S)-8
5
4
3
95
93
98
94
99
99
98
99
99
4-OMe-styrene (S)-8
(S)-8
10 4-Cl-styrene
11 4-OMe-styrene (R)-10
12 4-Me-styreneb (R)-10
13 styrene (R)-10
14 4-Cl-styrene (R)-10
15 4-OMe-styrene (R)-10
3
THF
9 (þ)
15
20
20
24
4
DCM 55 (þ)
DCM 54 (þ)
DCM 55 (þ)
DCM 52 (þ)
THF 57 (þ)
a Reaction conditions: T = 25 °C, 20 bar H2/CO = 1:1, [substrate0]/
[Rh]=1000, [Rh]=1.00 mM, [L]/[Rh]=5, time=20 h, internal standard=
decane. b Internal standard = undecane.
Complexes Aea and Aae are not distinguishable with IR
spectroscopy.31 Each absorption in the terminal CO region
of the IR spectra corresponds to the symmetric and anti-
symmetric stretching modes of two equatorially coordinated
CO ligands; the asymmetric stretch is usually of higher
Figure 5. Plot of the ee versus σ. Reaction conditions: as Table 4,
solvent = dichloromethane.
Figure 6. Structures of rhodium complexes formed in situ.
Table 5. 31P NMRa and IRb Data for Complexes [HRh(L)(CO)2] A
J{P-Rh} δ PO J{PO-H} J{PO-Rh} J{P-P} δ H
133 159 95 218 69 -9.3
L
δ P
J{P-H}
J{H-Rh}
ν CO
ν CO
7
8
10
-21
76
10
2025
2030
2021
1986
1989
1981
18.2
69
133
168
69
220
81
-9.3
8
a C6D6 (2 mL), T = 20 °C. b T = 25 °C, 20 bar H2/CO = 1:1, [Rh] = 1.8 mM, [L]/[Rh] = 5, solvent = cyclohexane (15 mL).

4444 Organometallics, Vol. 29, No. 20, 2010
Doro et al.
Figure 7. Possible structures of rhodium complexes: after addition of substrate.
energy (higher wavenumbers). The Rh-H vibration was not
observed in the spectra. These rhodium-hydride complexes
were also prepared in a pressurized sapphire tube to confirm
the formation of the above-mentioned species by NMR
spectroscopy. In the case of 10 the 1H NMR spectrum shows
a signal at -9.3 ppm attributed to the hydride of a hydri-
dorhodium species. The average coupling constant of JP-H
and JPO-H corresponds to 69 Hz, giving rise to a triplet. This
is a value typical of complexes Aea-Aae being present in
approximately 1:1 ratio and interconverting rapidly, via a
hydride movement, on the NMR time scale.32 The same
explanation applies to 7. The bulkiness of these ligands dis-
favors the formation of complexes of type B (Figure 6).
3.2. Rhodium Acyl Species. The rhodium-hydride species
A, described in the previous section, are highly fluxional. The
internal steric hindrance of these species is clearly not
sufficient to hamper conformational rearrangements in solution.
The reaction of a substrate with catalytic initiators [HRh-
(L)(CO)2] A is expected to increase the internal bulkiness of
the newly formed complexes. A typical experimental procedure
for the formation of substrate-containing catalytic inter-
mediates consists in reacting the preformed complex [HRh-
(7)(CO)2], in presence of syn-gas, with the desired substrate
(4-Cl-styrene).31 The formation of the new rhodium carbonyl
species is monitored by FT IR. Within a few seconds after the
addition of the substrate, the rhodium-hydride complex is
converted into another species; this is clearly indicated by the
appearance of four new bands in the terminal carbonyl area
of the IR spectrum (1975, 1998, 2015, 2031 cm-1). No
absorptions were detected in the area of carbonyl bridge
frequencies, thus ruling out the presence of rhodium-carbonyl
dimers.33
Figure 8. FT-IR monitoring of catalytic species: (a) hydro-
rhodium A, 20 bar H2/CO; (b) introduction of substrate, argon;
(c) 20 bar H2/CO, time = 0 min; (d) 19 bar H2/CO, time = 10 h;
(e) 18 bar H2/CO, time = 35 h. Reaction conditions: T = 25 °C,
substrate = 4-Cl-styrene, [substrate0]/[Rh] = 60, L = 7, [Rh] =
1.8mM, [L]/[Rh] =5, solvent =cyclohexane (15 mL). (*) Aea-ae;
(club) Eae-ea; (spade) (2-(4-Cl-phenyl)propanal)/(3-(4-Cl-
phenyl)propanal)/4-Cl-styrene; (b) 4-Cl-styrene; (() (2-(4-Cl-
phenyl)propanal)/(3-(4-Cl-phenyl)propanal). Intensities of the
absorbance for complexes A-E are in the range 0.15-0.25 A.
The resting state of the catalyst is dictated by the rate-
limiting step of the overall catalytic cycle, which could be
either the alkene coordination/insertion step or the Rh-acyl
hydrogenolysis.6,7 The corresponding resting states are 18-
electron metal complexes saturated with molecules of CO;
see species A in Figure 6 and species E in Figure 7.6,7,26,27
Figure 9. Section of the IR spectra series. Reaction conditions:
see Figure 7, L = 8.
Species C and E are expected to give absorptions at similar
frequencies in the terminal carbonyl area of the IR spectrum,
in the period immediately following the addition of the
substrate.
We attempted to form species type C by following a
procedure reported by Moser et al., which consists in pre-
paring a rhodium-hydride A in the presence of syn-gas
(spectrum a, Figure 8), purging the reaction medium with
an inert gas (Ar) for 1 h, and adding the substrate.34 How-
ever, upon removing the syn-gas from the medium, the
absorptions corresponding to terminal carbonyl groups of
(28) Hobbs, C. F.; Knowles, W. S. J. Org. Chem. 1981, 46 (22), 4422–
4427.
(29) Rubio, M.; Suarez, A.; Alvarez, E.; Bianchini, C.; Oberhauser,
W.; Peruzzini, M.; Pizzano, A. Organometallics 2007, 26 (25), 6428–
6436.
(30) Robert, T.; Abiri, Z.; Wassenaar, J.; Sandee, A. J.; Romanski, S.;
€
Neudorfl, J.-M.; Schmalz, H.-G.; Reek, J. N. H. Organometallics 2010,
29, 478–483.
(31) Kamer, P. C. J.; van Rooy, A.; Schoemaker, G. C.; van Leeuwen,
P. W. N. M. Coord. Chem. Rev. 2004, 248 (21-24), 2409–2424.
(32) Buisman, G. J. H.; van der Veen, L. A.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M. Organometallics 1997, 16 (26), 5681–5687.
(33) Moasser, B.; Gladfelter, W. L.; Roe, D. C. Organometallics 1995,
14 (8), 3832–3838.
(34) Moser, W. R.; Papile, C. J.; Brannon, D. A.; Duwell, R. A.;
Weininger, S. J. J. Mol. Catal. 1987, 41 (3), 271–292.

Article
Organometallics, Vol. 29, No. 20, 2010 4445
Figure 10. Variation of the absorbance of CO frequency of the mixture of aldehydes ((2-(4-Cl-phenyl)propanal)/(3-(4-Cl-phenyl)-
propanal)) (left) and intermediates E, A, G (right) over time. Reaction conditions: see Figure 8, L = 8.
complex [HRh(7)(CO)2] in the IR spectra disappeared
(spectrum b, Figure 7). The addition of the substrate (Cl-
styrene) did not bring any change to the spectra. Complex
[HRh(7)(CO)2] is probably not stable in the absence of
syn-gas, thus forming insoluble Rh carbonyl oligomers or other
dormant species. Only when syn-gas (20 bar) was reintro-
duced did the four absorptions corresponding to the terminal
carbonyl groups of the rhodium acyl species E appear (spectra
c and d, Figure 8). When the substrate was completely
consumed, the resting state of the catalyst reverted to the
initial rhodium-hydride complex (spectrum e, Figure 8).
In this case, the carbonyl absorptions of complexes Eae
and Eea, contrary to the corresponding rhodium-hydride A,
did not coincide at the same wavenumbers. The frequency of
the CO absorptions is related to the CO-Rh-CO angle; thus
we deduce that the replacement of a hydride in species Aae
and Aea by an acyl moiety in the corresponding species E
might affect differently the internal steric hindrance of the
latter species. Unfortunately, it was not possible to individ-
uate the acyl carbonyl absorptions, which are known to have
a lower intensity than the terminal carbonyl absorptions,
probably because they are hidden in the noise of the
spectra.31
The same study was conducted with ligand 8. Despite the
poor solubility of this ligand in cyclohexane, the correspond-
ing complex [Rh(8)(acac)] is highly soluble. The absorbance
of the two CO bands (1998 and 2022 cm-1), assigned to
species E, did not show any change of intensity in the first
10 h (Figures 9 and 10). A new species G (2051 cm-1) is
formed during the course of the reaction, which could
correspond to a complex in which ligand 8 is coordinated
to the rhodium center only via the phosphite moiety.35 Its
importance is considered negligible since a hypothetical
participation of these species in the transformation of the
styrene derivatives tested would induce very low ee.11
Two possible scenarios exist that are consistent with this
picture: two isomeric complexes Eae-Eea are formed, and
their absorptions overlap, or only one of the two isomers is
formed. As ligand 8 is isostructural with ligand 7 and given
that ligand 7 led to the formation of the two isomers Eae-
Eea, with absorptions well resolved, the latter option is the
most plausible one. The IR spectroscopic study of the in situ
coordination behavior of ligand 10 displayed only broad
absorptions, which could not be successfully analyzed.
of ligand 8 in the AHF showed a direct correlation between
the ee and the electronic-withdrawing properties of the sub-
stituent in the substrate (4-Me-styrene, 15% ee; styrene, 23%
ee; 4-Cl-styrene, 51% ee) under mild reaction conditions
(T = 25 °C, P = 20 bar syn-gas, solvent = dichloromethane).
Under the same reaction conditions, isostructural ligand 7
failed to show a similar behavior.
Complexes [HRh(L)(CO)2] A with ligands 7 and 8 have
been prepared, and they were found to be highly conforma-
tionally fluxional in solution. These catalytic species have
been subsequently reacted with 4-Cl-styrene at room tem-
perature to form substrate-containing rhodium acyl species
of the formula [(RCO)Rh(CO)2(L)] E. The formation of
these complexes was monitored by in situ IR spectroscopy.
The IR data revealed that compound [(RCO)Rh(CO)2(7)] is
present in two isomeric forms. The structure elucidation of
intermediate [(RCO)Rh(CO)2(8)] was considerably more
complex. We postulate on the basis of structural analogies
between ligand 7 and 8 that the rhodium-acyl complex of the
latter is present in solution as only one isomer.
In view of the Hammett dependency between substrate
and ligand observed in catalysis with ligand 8, we speculate
that an aryl-aryl π-π interaction might be involved in the
conformational stabilization of intermediate [(RCO)Rh-
(CO)2(8)].
Experimental Part
General Procedures. All chemical manipulations were carried
out under an argon atmosphere using standard Schlenk techni-
ques. Solvents were dried by standard procedures and freshly
distilled under a nitrogen atmosphere. Triethylamine was dis-
tilled from CaH2 under nitrogen. 10-Chloro-2,8-dimethylpheno-
xaphosphine,36 5-chloro-5H-benzo[b]phosphindole,37 and (R/S)-
bis(trimethylsilyl)binol chlorophosphite38 were prepared as
reported in the literature. (1-Ethoxyethoxy)benzene (1)39 was
prepared following an experimental procedure previously de-
scribed. All other reagents were purchased from commercial
suppliers and used as received. The styrene derivatives and
1-octene were filtered freshly over basic alumina prior to use.
NMR spectra were recorded at 295 K on a Varian Gemini 300
spectrometer operating at 300.07 MHz (1H), 121.47 MHz (31P),
and 75.46 MHz (13C) unless otherwise stated. Chemical shifts
are quoted with reference to Me4Si (1H) and 85% H3PO4 (31P).
The optical rotations were measured using a Perkin-Elmer 241-MC
polarimeter. High-resolution mass spectra were measured on a
Conclusions
(36) van der Veen, L. A.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
Organometallics 1999, 18 (23), 4765–4777.
(37) Teunissen, H. T.; Hansen, C. B.; Bickelhaupt, F. Phosphorus,
Sulfur Silicon Relat. Elem. 1996, 118, 309–312.
(38) Buisman, G. J. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
Tetrahedron: Asymmetry 1993, 4 (7), 1625–1634.
A series of closely related phosphine-phosphite ligands
7-10 were synthesized and evaluated in the AHF of styrene
derivatives under different reaction conditions. The employment
(39) Mueller, C.; Ackerman, L. J.; Reek, J. N. H.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2004, 126 (45), 14960–
14963.
(35) van der Slot, S. C.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.;
Iggo, J. A.; Heaton, B. T. Organometallics 2001, 20 (3), 430–441.

4446 Organometallics, Vol. 29, No. 20, 2010
Doro et al.
JEOL IMS-SX/SX102A. Gas chromatography analyses were
run on a Shimadzu GC-17A apparatus (split/splitless injector,
J&W Scientific, DB-1 J&W 30 m column, film thickness 3.0 μm,
carrier gas 70 kPa He, FID detector) equipped with a Hewlett-
Packard data system (Chrom-Card). Chiral GC separation was
conducted on an Interscience Focus-Trance GC Ultra (FID
detector). High-pressure FT-IR experiments were performed in
a stainless steel 50 mL autoclave equipped with an INTRAN
window (ZnS), a mechanical stirrer, a temperature controller,
and a pressure transducer. The in situ IR spectra were recorded
on a Nicolet 510 FT-IR spectrophotometer.
10-(2-(1-Ethoxyethoxy)phenyl)-2,8-dimethyl-10H-phenoxapho-
sphine (2). To a solution of (1-ethoxyethoxy)benzene (1) (4.0 g,
24.10 mmol) and TMEDA (26.51 mmol, 2.62 mL) in 300 mL of
diethyl ether/hexane (1:2) was added dropwise a solution of
n-butyllithium in hexane (2.5 M, 26.51 mmol, 10.6 mL) at 0 °C,
and the reaction mixture was allowed to stir overnight at room
temperature. The resultant orange solution was cooled to 0 °C,
and subsequently 10-chloro-2,8-dimethyl-10H-phenoxaphosphine
(7.0 g, 26.60 mmol) was slowly added with a spatula. The re-
action mixture was slowly warmed to room temperature and
allowed to stir for 5 h. The color of the solution changed from
orange to colorless with the formation of a precipitate (LiCl).
The solution was canulated into another Schlenk tube, and the
solvent was removed under vacuum. The crude of reaction was
dissolved in CH2Cl2 and washed with a deoxygenated aqueous
0.1 M HCl solution. The crude product is an orange oil, which
after filtration over silica (eluent: CH2Cl2) and removal of the
solvent under vacuum is obtained as colorless, sticky oil (7.3 g,
18.62 mmol, 77%). 1H NMR (CDCl3): δ 1.17 (t, 3J = 6.9 Hz,
3H), 1.51 (d, 3J = 5.4 Hz, 3H), 2.33 (s, 6H, Me), 3.39 (m, 1H),
3.75 (m, 1H), 5.52 (q, 3J = 5.4 Hz, 1H), 6.66 (m, 1H), 6.78 (m,
1H), 7.00-7.30 (m, 6H), 7.44 (t, 3J = 7.8 Hz, 2H) ppm. 31P{1H}
NMR (CDCl3): δ -62.6 ppm.
all volatiles were evaporated under vacuum to leave a white,
viscous oil. The product was filtered over silica (eluent: CH2Cl2),
and the solvent was removed under vacuum to yield a white solid
(1.8 g, 6.5 mmol, 43%). 1H NMR (CDCl3): δ 5.92 (s, 1H, OH),
6.76 (t, 3J = 7.5 Hz, 1H), 6.86 (m, 1H), 6.95 (t, 3J = 7.5 Hz, 1H),
7.25 (m, 1H), 7.36 (m, 2H), 7.52 (t, 3J = 7.5 Hz, 2H), 7.8 (m, 2H),
8.01 (d, 3J = 6.9 Hz, 2H) ppm. 13C{1H} NMR (CDCl3): δ 116.1,
121.31-121.35, 122.04, 128.11-128.17, 129.31, 130.95, 131.11,
131.99, 133.43-133.51, 141.36, 143.86-143.89, 159.64-159.75
ppm. 31P{1H} NMR (202.3 MHz; CDCl3): δ -28.1 ppm.
HRMS, FABþ: m/z calcd for C18H13O2P 276.0704; found
277.0786 [M þ H]þ.
(R)-4-(2-(2,8-Dimethyl-10H-phenoxaphosphan-10-yl)phenoxy)-
2,6-bis(trimethylsilyl)dinaphtho[2,1-d:10,20-f][1,3,2]dioxaphosphepine,
(R)-(7). Compound 3 (0.10 g, 0.32 mmol) was azeotropically
dried with toluene (3 ꢀ 5 mL) and dissolved in toluene (20 mL).
Next NEt3 (0.1 mL) was added and the solution was allowed to
stir 30 min at rt. Subsequently the solution was cooled to -20 °C,
and a solution of 4-chlorodinaphtho[2,1-d:1020-f][1,3,2]dioxapho-
sphepine (0.38 mmol) in toluene (5 mL) was added dropwise.
The reaction mixture was allowed to stir overnight at room
temperature. The solution was canulated into another Schlenk
tube, and the solvent was removed under vacuum. Filtration
over a short pad of neutral alumina (eluent: dichloromethane)
and subsequent evaporation of the volatiles yielded the product
as a white foam (0.17 g, 0.22 mmol, 69%). [R]25 = þ51.9 (c
D
0.76, CHCl3). 1H NMR (500 MHz; CD2Cl2): δ 0.60 (s, 9H), 0.68
(s, 9H), 2.24 (s, 3H), 2.35 (s, 3H), 6.77 (m, 1H), 6.84 (m, 1H), 6.93
(t, 3J = 7.5 Hz, 1H), 7.04 (t, 3J = 7.5 Hz, 1H), 7.13 (d, 3J = 8.5 Hz,
1H), 7.18 (d, 3J = 8.5 Hz, 1H), 7.26 (d, 3J = 10 Hz, 1H),
7.26-7.66 (m, 9H), 8.11 (d, 3J = 8.5 Hz, 2H), 8.34 (s, 1H), 8.41
(s, 1H) ppm. 13C{1H} NMR (125.7 MHz; CD2Cl2): δ 0.16, 0.37,
20.68-20.70, 117.26, 117.51, 117.84, 117.92, 120.57-120.67,
122.63, 123.70-123.74, 124.62, 125.17, 125.28, 125.43, 126.58,
126.84, 127.02-127.13, 128.63-128.76-128.76-128.86, 130.14,
131.30, 131.64-131.76, 131.99, 132.16, 132.93, 133.02, 133.11-
133.18, 133.27, 133.47, 134.16, 134.46, 135.59, 135.70, 135.88,
135.98, 137.67, 151.66, 152.52-152.56, 153.81-153.97-154.09,
154.83 ppm. 31P{1H} NMR (202.3 MHz; CD2Cl2): δ -66.6 (d,
JP-P = 23 Hz), 140.1 (d, JP-P = 23 Hz) ppm. HRMS, FABþ:
m/z calcd for C46H44O4P2Si2 778.2253; found 779.2344 [M þ H]þ.
(S)-4-(2-(5H-Benzo[b]phosphindol-5-yl)phenoxy)-2,6-bis(tri-
methylsilyl)dinaphtho[2,1-d:10,20-f][1,3,2]dioxaphosphepine, (S)-(8).
Experimental procedure as reported for 7 (49%). [R]25D = þ28
2-(2,8-Dimethyl-10H-phenoxaphosphan-10-yl)phenol (3). 10-(2-
(1-ethoxyethoxy)phenyl)-2,8-dimethyl-10H-phenoxaphosphine
(7.3 g, 18.62 mmol) was dissolved in a 3:1 mixture of degassed
ethanol and dichloromethane (80 mL). PPTS (0.19 mmol) was
added, andthe solutionwas heated to65 °C andstirred overnight.
The mixture was allowed to cool, and subsequently the solvent
and all volatiles were evaporated under vacuum to leave a white,
viscous oil. The product was filtered over silica (eluent: CH2Cl2/
pentane, 1:1), and the solvent was removedunder vacuum toyield
1
a white solid (4.05 g, 12.66 mmol, 68%). H NMR (CDCl3): δ
1
2.28 (s, 6H, Me) 6.48 (s br, 1H, OH), 6.75-7.25 (m, 10H) ppm.
13C{1H} NMR (CDCl3): δ 20.83 (-CH3), 115.94-116.04,
117.87, 121.44-121.49, 131.73, 132.09, 133.33, 133.48, 134.22,
134.64-134.75, 153.68, 158.53, 158.76 ppm. 31P{1H} NMR
(CDCl3): δ -70.3 ppm. HRMS, FABþ: m/z calcd for C20H17-
O2P 320.0966; found 321.1045 [M þ H]þ. Anal. Calcd for
C20H17O2P (320.1): C 74.99, H 5.35. Found: C 75.06, H 5.38.
2-(5H-Benzo[b]phosphindol-5-yl)phenol (4). To a solution of
(1-ethoxyethoxy)phenol (2.5 g, 15.0 mmol) and TMEDA (16.5
mmol, 1.63 mL) in 100 mL of diethyl ether/hexane (1:2) was
added dropwise a solution of n-butyllithium in hexane (2.5 M,
16.5 mmol, 6.6 mL) at 0 °C, and the reaction mixture was
allowed to stir overnight at room temperature. The resultant
orange solution was cooled to 0 °C, and subsequently 5-chloro-
5H-benzo[b]phosphindole (3.5 g, 16.0 mmol) was slowly added
with a spatula. The reaction mixture was slowly warmed to
room temperature and allowed to stir 5 h. The color of the
solution changed from orange to colorless with the formation of
a precipitate (LiCl). The solution was canulated into another
Schlenk tube, and the solvent was removed under vacuum. The
crude of reaction was dissolved in CH2Cl2 and washed with a
deoxygenated 0.1 M HClaq solution. The crude product was
subsequently dissolved in a 3:1 mixture of degassed ethanol and
dichloromethane (80 mL). PPTS (0.18 mmol) was added, and
the solution was heated to 65 °C and stirred overnight. The
mixture was allowed to cool, and subsequently the solvent and
(c 5.2, CHCl3). H NMR (500 MHz; CD2Cl2): δ 0.48 (s, 9H),
0.58 (s, 9H), 6.65 (m, 1H), 6.80 (m, 2H), 7.05 (t, 3J = 6.5 Hz, 1H),
7.1-7.35 (m, 6H), 7.36-7.50 (m, 4H), 7.60 (m, 1H), 7.70 (m,
1H), 7.94 (t, 3J = 6.5 Hz, 2H), 8.00 (t, 3J = 6 Hz, 2H), 8.21 (s,
1H), 8.27 (s, 1H) ppm. 13C{1H} NMR (125.7 MHz; CD2Cl2):
δ -0.10, 0.22, 121.21-121.30, 121.55-121.61, 122.48-122.50,
123.48-123.52, 124.70, 125.16-125.27, 126.76-126.82-126.85-
126.91, 127.51-127.56-127.64, 128.47-128.56-128.70-128.77-
128.88, 130.56, 131.13-131.17-131.23-131.39-131.49-131.63,
132.69-132.80, 134.04-134.23, 137.44-137.54, 141.85-141.89,
142.36-142.39, 143.61-143.64, 144.09-144.12, 151.37, 152.30-
152.35, 155.25, 155.42 ppm. 31P{1H} NMR (202.3 MHz;
CD2Cl2): δ -23.2 (d, JP-P = 32.3 Hz), 141.3 (d, JP-P = 32.3 Hz)
ppm. HRMS, FABþ: m/z calcd for C44H40O3P2Si2 734.1991;
found 735.2075 [M þ H]þ.
(R)-4-(10-Phenyl-10H-phenoxaphosphan-1-yloxy)-(S)-2,6-bis-
(trimethylsilyl)dinaphtho[2,1-d:10,20-f][1,3,2]dioxaphosphepine,
(R,S)-(9). Experimental procedure as reported for 7 (65%).
[R]25D = þ26.8 (c 1.41, CHCl3). 1H NMR (500 MHz; CD2Cl2):
δ 0.26 (s, 9H), 0.32 (s, 9H), 6.90-7.05 (m, 7H), 7.07-7.20 (m,
4H), 7.22-7.40 (m, 5H), 7.45 (t, 3J = 7 Hz, 1H), 7.53 (t, 3J =
7 Hz, 1H), 7.96 (d, 3J = 8 Hz, 1H), 8.05 (d, 3J = 8 Hz, 1H), 8.07
(s, 1H), 8.13 (s, 1H) ppm. 13C{1H} NMR (125.7 MHz; CD2Cl2):
δ 0.20, 112.32, 113.89, 115.21-115.31, 117.54, 118.53-118.58,
122.09, 123.46-123.50, 123.81-123.90, 125.13-125.19, 126.66-
126.76-126.78-126.97, 128.32-128.37-128.53-128.58-128.66,

Article
Organometallics, Vol. 29, No. 20, 2010 4447
130.88-130.98-131.11-131.44, 132.41-132.59-132.75-132.84,
134.08-134.07-134.19-134.18, 134.83, 135.13, 137.41, 140.00,
140.20, 151.13, 152.39-152.44, 154.11-154.20-154.24, 154.42,
155.88 ppm. 31P{1H} NMR (202.3 MHz; CD2Cl2): δ -16.9 (d,
rhodium species. The enantiopurity and regioselectivities
were determined by GC without further treating the samples. AHF
of vinyl acetate: the conversion was determined by GC using a
DB-1 (J&W) column (40 °C for 20 min, then ΔT = 20 °C min-1).
Retention times: 5.6 min for vinyl acetate, 6.5 min for acetic acid, 14.2
min for heptane, 22.5 min for 2-acetoxypropanal, and 25.5 min for
3-acetoxypropanal. The enantiomeric purity was determined by
chiral GC using a Chiralsil DEX-CB column (50 °C for
5 min, then ΔT = 6 °C min-1, tR(R) = 7.2 min, tR(S) = 7.6 min).
Styrene derivatives: the conversion was determined by GC using a
DB-1 (J&W) column (70 °C for 1 min, then ΔT1 = 7 °C min-1 to
120 °C and ΔT2 = 13 °C min-1 to 250 °C). Retentions times: tR(4-
OMe-styrene) = 13.8 min, tR(2-(4-MeO-phenyl)propanal) =
16.6 min, tR(3-(4-MeO-phenyl)propanal) = 17.3 min, tR(4-Me-
styrene) = 11.3 min, tR(2-(4-Me-phenyl)propanal) = 14.6 min,
tR(3-(4-Me-phenyl)propanal) = 15.3 min, tR(styrene) = 9.0 min,
tR(2-phenylpropanal) = 12.9 min, tR(3-phenylpropanal) = 13.8 min,
tR(4-Cl-styrene) = 12.7 min, tR(2-(4-Cl-phenyl)propanal) =
15.9 min, tR(3-(4-Cl-phenyl)propanal) = 16.7 min, tR(decane) =
11.4 min, tR(undecane) = 13.1 min. The enantiomeric purity
was determined by chiral GC using a Supelco Beta Dex 225
column (T = 100 °C for 5 min, then ΔT = 4 °C min-1 to 180 °C,
then ΔT = 20.0 °C min-1 to 210 °C, T = 210 °C for 2 min). 2-(4-
MeO-phenyl)propanal: tR(þ) = 20.75 min, tR(-) = 20.91 min.
2-(4-Me-phenyl)propanal: tR(þ) = 14.74 min, tR(-) = 14.86
min. 2-(4-Cl-phenyl)propanal: tR(þ) = 20.51 min, tR(-) =
20.76 min. (T = 100 °C for 5 min, then ΔT = 3 °C min-1 to
150 °C, then ΔT = 50 °C min-1 to 210 °C, T = 210 °C for 2 min):
2-phenylpropanal: tR(þ) = 11.83 min, tR(-) = 12.04 min. All
reactions were performed in duplicate.
HP NMR Experiments. In a typical experiment the sapphire
NMR tube was filled with a solution of Rh(CO)2(acac), ligand,
and C6D6. The tube was purged two times with 10 bar of syn-
gas, pressurized with 20 bar of syn-gas, and heated to 60 °C for
2 h. Next, the tube was allowed to cool to rt and the NMR
spectra were recorded.
HP FT-IR Experiments. In a typical experiment a 50 mL HP
IR autoclave was filled with a solution of Rh(CO)2(acac) (0.0018M),
ligand (0.009 M), and cyclohexane (15 mL). The autoclave was
purged three times with 15 bar of syn-gas, pressurized with
20 bar of syn-gas, and heated to 60 °C. Catalyst formation was
followed in time by FT-IR and was completed within 1 h. After
complete conversion to the hydride rhodium complex the auto-
clave was cooled to room temperature, and a solution of the
substrate (0.2 mL) in cyclohexane (1 mL), previously charged
into the reservoir of the autoclave, was added to the reaction
mixture by overpressure. The IR spectra were recorded at 25 °C
with an acquisition speed of 0.5 scan/s.
JP-P = 35 Hz), 139.9 (d, JP-P = 35 Hz) ppm. HRMS, FABþ:
m/z calcd for C44H40O4P2Si2 750.1940; found 751.2019 [M þ H]þ.
(R)-4-(2-(Diphenylphosphino)phenoxy)-2,6-bis(trimethylsilyl)-
dinaphtho[2,1-d:10,20-f][1,3,2]dioxaphosphepine, (R)-(10). Experi-
mental procedure as reported for 7 (73%). [R]25 = þ46.3
D
1
(c 1.08, CHCl3). H NMR (500 MHz; CD2Cl2): δ 0.44 (s, 9H),
0.45 (s, 9H), 6.74 (m, 1H), 6.90 (m, 1H), 7.03 (t, 3J = 7.5 Hz, 1H),
7.10-7.45 (m, 15H), 7.47 (t, 3J = 7.5 Hz, 1H), 7.51 (t, 3J=7.5Hz,
1H), 8.00 (d, 3J = 8.5 Hz, 1H), 8.05 (d, 3J = 8.5 Hz, 1H), 8.20 (s,
2H) ppm. 13C{1H} NMR (125.7 MHz; CD2Cl2): δ 0.07-0.04-
0.07, 121.27-121.35, 122.39, 123.49-123.44, 124.59, 125.09-
125.205, 125.56, 126.66, 126.80-126.86, 126.99, 128.47-128.50-
128.56-128.69-128.71-128.74-128.92-128.97, 130.23, 131.13,
131.43, 132.83-132.92-132.93, 133.79-133.95-134.05-134.21-
134.31-134.37-134.47, 136.64-136.74-136.79-136.88, 137.37,
151.45-151.47, 152.40-152.44, 154.20, 154.36 ppm. 31P{1H}
NMR (202.3 MHz; CD2Cl2): δ -17.0 (d, JP-P = 35 Hz), 140.0
(d, JP-P = 35 Hz). HRMS, FABþ: m/z calcd for C44H42O3P2Si2
736.2148; found 737.2224 [M þ H]þ.
In Situ Preparation of [Rh(acac)(7)] (11). To a solution of
[Rh(CO)2(acac)] (6.6 mg, 0.026 mmol) in dichloromethane was
added ligand 7 (20.2 mg, 0.026 mmol). After stirring at room
temperature for 1 h, the solvent was evaporated under vacuum
and the solid dissolved in CD2Cl2. 31P{1H} NMR (121.3 MHz;
C6D6): δ 2.7 (dd, JP-P = 103 Hz, JP-Rh = 180 Hz), 138.6 (dd,
J
P-P = 103 Hz, JP-Rh = 308 Hz) ppm.
[Rh(acac)(8)] (12). Experimental procedure as reported for 11.
31P{1H} NMR (121.3 MHz; CD2Cl2): δ 33.9 (dd, JP-P = 106 Hz,
JP-Rh = 170 Hz), 139.8 (dd, JP-P =106Hz,JP-Rh =314Hz) ppm.
[Rh(acac)(9)] (13). Experimental procedure as reported for 11.
31P{1H} NMR (121.3 MHz; C6D6): δ -13.1 (dd, JP-P = 111 Hz,
JP-Rh = 178 Hz), 145.5 (dd, JP-P =111Hz,JP-Rh =300Hz) ppm.
[Rh(acac)(10)] (14). Experimental procedure as reported for
11. 31P{1H} NMR (121.3 MHz; C6D6): δ 39.4 (dd, JP-P = 99 Hz,
JP-Rh = 173 Hz), 145.5 (dd, JP-P =99Hz, JP-Rh = 321 Hz) ppm.
Asymmetric Hydroformylation of Vinyl Acetate and Styrene
Substrates. The catalytic experiments were performed in a
stainless steel 150 mL autoclave equipped with internal stainless
steel trays, which can accommodate 8 or 15 glass reactors (1 mL
total volume for each vial). Prior to use, the vials were equipped
with magnetic stirrer bars and left overnight in an oven at 120 °C.
Stock solutions of [Rh(acac)(CO)2], phosphine-phosphite ligand,
internal standard, and substrates were added in that order to the
vial. The autoclave was purged three times with 10 bar of syn-gas
and then pressurized to the required value. After 20 h reaction time
at the desired temperature, the autoclave was cooled on ice and the
pressure released. The samples were quenched immediately by adding
an excess of P(O-nBu)3 to deactivate hydroformylation-active
Acknowledgment. We would like to thank J. M. Ernsting
for the HP NMR experiments and the University of
Amsterdam for financial support.