Application of P-stereogenic aminophosphine phosphinite ligands in asymmetric hydroformylation

Article abstract of DOI:10.1002/(SICI)1521-3765(20000417)6:8<1496::AID-CHEM1496>3.0.CO;2-8

New chiral aminophosphine phosphinite ligands with a stereogenic center at the aminophosphine phosphorus atom were prepared based on (R,S)-ephedrine as the chiral auxiliary and backbone. Substituents at the chiral aminophosphine as well as at the phosphinite phosphorus atom were varied. These new ligands were applied to the rhodium-catalyzed asymmetric hydroformylation of vinyl arenes. The enantiomeric excess reached up to 77%. ¹H and ³¹P NMR studies of the Rh complexes under syngas pressure reveal that [HRh(CO)₂(P/P)] complexes with the NP* moiety in an axial position are responsible for enantioselectivity.

Full text of DOI:10.1002/(SICI)1521-3765(20000417)6:8<1496::AID-CHEM1496>3.0.CO;2-8

FULL PAPER
Application of P-Stereogenic Aminophosphine Phosphinite Ligands in
Asymmetric Hydroformylation
Regine Ewalds,[b] Eva B. Eggeling,[a] Alison C. Hewat,[a] Paul C. J. Kamer,[c]
Piet W. N. M. van Leeuwen,[c] and Dieter Vogt*[a]
Abstract: New chiral aminophosphine phosphinite ligands with a stereogenic center
at the aminophosphine phosphorus atom were prepared based on (R,S)-ephedrine as
the chiral auxiliary and backbone. Substituents at the chiral aminophosphine as well
Keywords: aminophosphine ´ asym-
as at the phosphinite phosphorus atom were varied. These new ligands were applied
metric hydroformylation ´ catalysts
to the rhodium-catalyzed asymmetric hydroformylation of vinyl arenes. The
´ P ligands ´ phosphinite ´ rhodium
enantiomeric excess reached up to 77%. 1H and 31P NMR studies of the Rh
complexes under syngas pressure reveal that [HRh(CO)2(P^P)] complexes with the
NP* moiety in an axial position are responsible for enantioselectivity.
metrical phosphine phosphites based on a chiral binaphtha-
lene backbone. The ligands used by Babin and van Leeuwen
Introduction
Aldehydes are among the most versatile building blocks in
synthetic organic chemistry. A huge variety of functionalized
compounds are available on this basis. Access to enantiomeri-
cally pure aldehydes from cheap olefinic substrates through
asymmetric catalysis has therefore attracted enormous inter-
est, spurred by the recent achievements made in this field.[1, 2]
For many years, the platinum catalyst systems activated with
tin chloride and modified by diphosphine ligands, as described
by Stille,[3] were the only systems to give high enantiomeric
excess (ee). These systems, however, suffer from low regio-
selectivity and large amounts of undesired byproducts as well
as from racemization of the product due to the Lewis acidity
of the promoter. In the rhodium-catalyzed reaction, the
standard C2-symmetrical diphosphine ligands lead to moder-
ate to low enantioselectivity, but high regio- and chemo-
selectivity. The breakthrough in this field came with the work
reported by Takaya and Nozaki,[4] and the results of Babin and
van Leeuwen.[2, 5] In the first case the ligands are CS-sym-
are C2-symmetrical diphosphites based on a chiral 2,4-
pentanediol backbone.
At a first glance, these two types of ligands seem to be quite
different, since the phosphine phosphite (R,S)-BINAPHOS 1
adopts an equatorial ± axial coordination in the catalytically
active hydrido-rhodiumcarbonyl complex (structure a),[4]
whereas the diphosphite 2 coordinates in a bis-equatorial
fashion (structure b).[2]
[a] Prof. D. Vogt, E. B. Eggeling, A. C. Hewat
Laboratory of Inorganic Chemistry and Catalysis
Eindhoven University of Technology, P.O. Box 513
5600 MB Eindhoven (The Netherlands)
Fax : (‡ 40)245-5054
E-mail: d.vogt@tue.nl
[b] Dr. R. Ewalds
Ciba, Division Additives AD 4.21, WS 2093.3.15
P.O. Box 1130, 4133 Pratteln 1 (Switzerland)
In situ NMR studies reveal that in both cases there is just
one active hydridocarbonyl species present in solution under
syngas pressure. This seems to be the key feature in control-
ling efficient chirality transfer, resulting from the conforma-
tionally more flexible rhodium systems compared with
[c] Prof. Dr. P. W. N. M. van Leeuwen, Dr. P. C. J. Kamer
Institute of Molecular Chemistry
University of Amsterdam, Nieuwe Achtergracht 166
1018 WV Amsterdam (The Netherlands)
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Chem. Eur. J. 2000, 6, No. 8

1496±1504
platinum catalysts. Only the combination of controlling the
coordination mode of the ligand and differentiation between
the two remaining possible coordination sites will give rise to
high enantioselectivity. The coordination mode is efficiently
controlled by the preferred chelation bite angle of the ligand.
For BINAPHOS this is about 908, while larger bite angles
>1008 result for the diphosphites.
Once the coordination mode of the ligand as well as the
complex geometry and conformation are defined, efficient
differentiation of the possible coordination sites is crucial. In
order to accomplish this, it should be helpful to bring the
center of chirality as close to the metal as possible. After our
success with P-chiral ligands in the asymmetric hydrovinyla-
tion reaction,[6] we decided to design new P-chiral chelating
ligands for use in asymmetric hydroformylation.
We report here on the synthesis of new diastereomerically
pure aminophosphine phosphinites 6 that possess a stereo-
genic center at the nitrogen bound phosphorus atom and their
application in the asymmetric hydroformylation of vinyl-
arenes. Changing the electronic nature of the substituents in
the phosphinite and aminophosphine moieties results in dif-
ferent coordination behavior of the ligands. This was studied
by in situ high-pressure NMR techniques. The results obtained
illustrate the power of a stereogenic phosphorus atom to
control enantioselectivity in the hydroformylation reaction.
meric purity. Deprotection is accomplished by refluxing the
borane adduct in diethylamine. The products can be purified
by simple flash chromatography over basic alumina
(Scheme 1).
The absolute configuration of the aminophosphine phos-
phorus atom could not be assigned, but the diastereomeric
excess was shown to be ꢀ92% de by 31P{1H} NMR spec-
troscopy. The route presented here allows the very variable
synthesis of a large number of P-chiral ligands of this type. As
was already shown by Petit and Mortreux, the aminophos-
phine phosphinite ligand family provides an enormous
potential for variation and ligand fine-tuning for a number
of transition metal catalyzed reactions.[9, 10] With the intro-
duction of a stereogenic center at the phosphorus atom, the
possibilities for variation are even larger. On the basis of
( )-ephedrine the ligands 6a ± 6i listed in Table 1 were
prepared.[11]
Table 1. Prepared aminophosphine phosphinite and phosphite ligands.
Ligand
R
Ar
6a
6b
6c
CH3
CH3
CH3
Ph
Results and Discussion
4-CH3-C6H5
3,5-(CF3)2C6H3
[7]
Â
Ligand synthesis: Following a route described by Juge et al.,
6d
CH3
the borane-protected hydroxy aminophosphines 4 were
prepared in high diastereomeric purity.[8] Starting from
bis(diethylamino)phenyl phosphine with ( )-(R,S)-ephedrine
as auxiliary, the borane-protected 1,3,2-oxazaphospholidines
3 can be obtained in high yields and diastereoselectivities
(Scheme 1). Ring opening of the oxazaphospholidines with an
organolithium reagent results in exclusive cleavage of the
P O bond to give the hydroxy compounds 4. These inter-
mediates represent ideal starting materials to produce a whole
series of chelating ligands by conversion with a chlorophos-
phine in the presence of a base. The final products are
obtained in good yields and with a high degree of diastereo-
6e
6 f
6g
6h
6i
n-Bu
n-Bu
n-Bu
Ph
Ph
4-CH3-C6H5
3,5-(CF3)2C6H3
Ph
Ph
1-naphth
Hydroformylation experiments: The diastereomerically pure
P-chiral aminophosphine phosphinite ligands have been used
in the rhodium-catalyzed asymmetric hydroformylation of
styrene, other vinyl arenes, and vinyl acetate. The catalysts
were prepared in situ by adding
the chelating ligands L to
[(acac)Rh(CO)2] as the catalyst
precursor. By converting the
precursor complex with the
chelating ligands, the CO was
immediately replaced and
bright yellow solutions formed.
Under hydroformylation condi-
tions the active catalyst
[HRh(L)(CO)2] was formed
readily. In all experiments an
excess of the ligand was used
to avoid the formation of
[HRh(CO)4], which is a highly
active but achiral hydroformy-
lation catalyst.
Scheme 1. Diastereoselective route to aminophosphine phosphinite and phosphite ligands containing
stereogenic P atom.
a
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FULL PAPER
The results obtained in the asymmetric hydroformylation of
styrene are summarized in Table 2. The substituents on the
phosphorus atoms of the phosphinite and aminophosphine
moieties were varied in order to study their influence on the
catalyst activity and selectivity. The highest enantioselectiv-
ities are obtained with ligands bearing no substituent or an
electron-donating group on the phenyl groups in the OPAr2
moiety (Entries 1, 2, 5, and 6). Lowering the electron density
on the OPAr2 phosphorus atom by introducing electron-
withdrawing groups or changing the phosphinite into a
phosphite group significantly decreases the enantioselectivity
(Entries 3, 4, and 7).
Increasing the syngas pressure from 20 to 60 bar CO/H2
(1:1) had a negative effect both on activity and enantioselec-
tivity. It was expected that increasing the pressure would have
a negative effect on the activity, since dissociation of CO and
coordination of the olefin is commonly regarded as the rate-
determining step.[13] It was shown by Buisman et al. for the
asymmetric hydroformylation of styrene using diphosphite
ligands, that an increased hydrogen partial pressure has a
negative influence on the enantioselectivity.[2c] However, this
effect is not very pronounced in the systems studied here.
In order to obtain high enantiomeric excess, it is essential to
apply a larger excess of ligand (4 equiv with respect to Rh).
Also at lower L/Rh ratios, [HRh(CO)4] can be formed.
In contrast to the results obtained with diphosphites, the
preformation time of the catalyst with the new AMPP ligands
had only little or no influence on the catalyst performance.
This is in accordance with our NMR studies, which indicate
that the active species, [HRh(L)(CO)2], is formed rapidly in
the presence of syngas.
Table 2. Hydroformylation of styrene with [HRh(L)(CO)2], L ˆ 6a ± 6i.[a]
Entry
Ligand
TON
iso:n [%][b]
ee [%][c]
1
2
3
4
5
6
7
8
9
6a
6b
6c
6d
6e
6 f
6g
6h
6i
39
41
104
12
71
44
244
302
151
98:2
98:2
95:5
97:3
98:2
98:2
95:5
92:8
80:20
75
71
32
58
75
73
46
10
10
After the promising results we obtained in the hydro-
formylation of styrene, which gave an ee of up to 77% in
2-phenylpropanal and high selectivity to the branched alde-
hyde (98:2), we applied the new P-chiral AMPP ligands in the
hydroformylation of other vinyl derivatives (see Table 3).
[a] 17.4 mmol styrene; 20 mL toluene; styrene /Rh ˆ 500; p(CO/H ) ˆ 20 bar;
2
1
CO/H2 ˆ 1:1; Tˆ 508C; t ˆ 20 h; L:Rh ˆ 3:1; [Rh] ˆ 1.74 mmol L
.
[b] Selectivity to branched and linear aldehyde. [c] Determined by chiral
GC after reduction of the aldehyde and conversion to the trifluoroacetate.
Table 3. Hydroformylation of vinylic substrates with [HRh(L)(CO)2], L ˆ
6a.[a]
Entry
Substrate
TON
iso:n [%][b]
ee [%]
For the electron-withdrawing CF3 substituents, the activity
increased by a factor of 2 ± 5 (Entries 3 and 7). Changing the R
substituent on the chiral phosphorus atom from methyl to n-
butyl did not change the stereoselectivity or activity of the
catalyst. The introduction of a 1-naphthyl group resulted in a
considerable decrease in enantioselectivity to only 10%,
which was also observed for ligand 6h without a stereogenic
center at the phosphorus atom (Entries 8 and 9). Apart from
ligand 6i (Entry 9) the regioselectivity to the branched
aldehyde 2-phenylpropanal always exceeds 90% as is ex-
pected for styrene and similar kind of substrates.[12] In all cases
the configuration of the major stereoisomer of the 2-phenyl-
propanal was determined to be S. This was accomplished by
comparing the retention times from gas chromatography
(GC) with a sample obtained with the ligand (R,S)-BINA-
PHOS, for which the absolute configuration of the product is
described to be always R. Under our reaction conditions (see
footnotes in Table 2) the enantiomeric excess (ee) obtained
with (R,S)-BINAPHOS is 92%.
10
20
92:8
58
11[c]
76
98:2
71
12
13
20
23
98:2
64
62
82:18
[a] 17.4 mmol styrene; 20 mL toluene; styrene/Rh ˆ 500; p(CO/H2) ˆ
20 bar; CO/H2 ˆ 1:1; Tˆ 508C; t ˆ 20 h; L:Rh ˆ 3:1; [Rh] ˆ
1.74 mmolL 1. [b] Selectivity to branched and linear aldehyde. [c] Tˆ
408C.
The 4-bromo-styrene derivative shows a considerably high-
er reactivity, even when the temperature is 108C lower
(Entry 11). The ee obtained is also slightly higher than for the
other substrates and is comparable with that found for
styrene.
For ligand 6a the influence of different reaction parameters
on the performance of the catalyst system was examined.
Lowering the reaction temperature from 608C to 408C
increases the ee from 50% to 77%. On the other hand, the
activity decreases by a factor of 10. Temperatures higher than
608C caused deterioration of the catalyst system and the ee
was reduced to almost zero at 808C. The brown color of the
reaction mixture after reaction indicated that rhodium
carbonyl clusters had been formed, probably due to decom-
position of the ligand. However, at 608C the ligand is stable.
Conversion can be completed by applying longer reaction
times without loss of enantioselectivity.
Structures of hydroformylation catalysts in solution: The
catalysts were prepared in situ by treating the precursor
complex [Rh(acac)(CO)2] with the appropriate amount of
ligand (Scheme 2).
On mixing solutions of [Rh(acac)(CO)2] and ligands 6a ±
6i, displacement of CO was observed immediately. Bright
yellow solutions were formed, and IR and
31P NMR spec-
troscopy showed that both carbonyl ligands had been removed
and the phosphorus ligands formed a chelate with the
rhodium center. In the 31P{1H} NMR spectra of the complexes,
a doublet of doublets occurred in addition to the signals of the
free ligand. Spectra of the solutions prepared with a 1:1 ratio
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Aminophosphine Phosphinite Ligands
1496±1504
are the signals of the free ligand, which is present in excess.
Two broad double doublets at d ˆ 82.1 (PN, 1J(NP-Rh) ˆ 123 Hz,
1
2J(NP-PO) ˆ 15 Hz), and 121.1 (PO, J(OP-Rh) ˆ 216 Hz) are as-
signed to the dinuclear complex D.[14]
Complex C gives rise to a doublet of doublets at d ˆ 94.5
1
2
(PN, J(NP-Rh) ˆ 112 Hz, J(NP-PO) ˆ 17 Hz), and 130.4 (PO,
1J(OP-Rh) ˆ 157 Hz). These assignments are confirmed by cor-
relation of the peak integration areas of the signals. In the
31P,1H NMR spectrum, only the signal of the PN moiety of the
hydrido complex shows further splitting, due to a large
Scheme 2. In situ preparation of catalysts.
2
coupling J(NP-H) ˆ 118 Hz with the axial hydride in a trans
of [Rh(acac)(CO)2] and ligand only contain the signals of the
[(L)Rh(acac)] complex indicating that the complex formation
is quantitative.
position. Large J(P-H) constants have been reported before for
hydrogen and phosphorus with a trans relation at a rhodium
center.[4a, 15] In the coupled spectrum, there is no indication of
a species with a PO moiety trans to the hydride. The signal of
the PO is slightly broadened due to the small cis coupling
(2J(OP-H) ˆ 12 Hz). In the 1H NMR spectrum, the hydride
signal is a doublet of pseudo triplets resulting from the large
Characterization of [HRh(L)(CO)2] complexes: The
[HRh(L)(CO)2] complexes were generated in situ by treating
[Rh(acac)(CO)2] with two equivalents of ligand at 408C under
a syngas pressure of 50 bar (CO/H2 ˆ 1:1) over three hours.
2
1
118 Hz J(H-PN) coupling and two couplings J(H-Rh) and
2J(H-PO) both with a value of 12 Hz (Figure 2).
The resulting complexes were characterized by H and 31P
1
NMR, and IR spectroscopy. The NMR spectra were recorded
at 303 K under a syngas pressure of 20 bar CO/H2 (1:1).
In principle, three different isomeric mononuclear hydrido
rhodium complexes A ± C with a trigonal bipyramidal struc-
ture can be formed.
Figure 2. Hydride region of the 1H NMR spectrum of [HRh(L)(CO)2],
L ˆ 6a.
It turned out that in the case of ligands giving rise to high
enantiomeric excesses (6a, 6b, 6e, and 6 f), only two species
are formed under these conditions. In addition to a catalyti-
cally inactive dinuclear carbonyl-bridged complex D, only
species C with the PN moiety in the axial position and the PO
moiety bound in the equatorial position is observed. Figure 1
shows the 31P{1H} NMR and the 31P,1H NMR spectra for
ligand 6a. The two singlets at d ˆ 50.7 (PN) and 113.9 (PO)
Similar results have been described by Pottier with the
EPHOS ligand 6h. They also showed that there is only one
hydride species present in solution containing NP in axial and
OP in equatorial positions, as well as a dinuclear complex.[16]
The important point is that both ligands 6a and 6h show the
same coordination mode, while in 9a the aminophosphine
phosphorus atom represents an additional homochiral stereo-
genic center. Complex 9h gives an ee of only 10% under our
reaction conditions, whereas 9a gives 77%.
This clearly demonstrates the importance of the additional
chirality at the phosphorus atom. From this point of view, the
chiral phosphorus atom bearing one relatively small and one
larger group gives rise to efficient stereodifferentiation of the
two possible coordination sites. This also explains why the
P-chiral ligand 6i with two substituents similar in shape gives
poor enantioselectivity.
Figure 1. 31P{1H} NMR (lower trace) and 31P,1H NMR spectra (upper
trace) of [HRh(L)(CO)2], L ˆ 6a, at 20 bar (CO:H2 ˆ 1:2) and 303 K;
L:Rh ˆ 2:1.
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D. Vogt et al.
FULL PAPER
The catalytically inactive dinuclear complex D is in
equilibrium with the hydrido complex C under the NMR
experimental conditions. This was shown by varying the
hydrogen partial pressure as well as by lowering the rhodium
complex concentration during the measurements.
ligands bearing electron-withdrawing groups in the phosphin-
ite part show a mixture of several different species in solution.
The signals obtained in the 31P NMR under syngas pressure
are very broad, indicative of a fluctional behavior of the
complexes.[5c] By using ligand 6g, however, four sets of signals
were obtained that were interpreted as a mixture of all four
possible complexes A ± D present in solution under these
conditions. Signals remained broad and unresolved for ligands
6c, 6d, and 6g on cooling down to 223 K. By introducing
electron-withdrawing groups in the phosphinite part, the
donor character is decreased and the acceptor ability is
increased. When the two different phosphorus atoms in the
ligand have similar electronic properties, there is no longer a
preference for either an axial or an equatorial mode of
coordination.
Increasing the hydrogen partial pressure from 10 bar
(P(CO/H ) ˆ 20 bar, CO:H2 ˆ 1:1) to 20 and 40 bar caused the
2
ratio of complexes D:C to vary from 17:1 to 2.5:1 and 2:1,
respectively. A similar effect was observed by lowering the
complex concentration from 51 mmolL 1 to 33 mmolL 1 at a
syngas pressure of 20 bar (CO:H2 ˆ 1:1).[14] This increased the
amount of the active hydride from the initial 17:1 ratio to 3.5:1
D:C. After releasing the syngas pressure from the NMR tube,
only the dinuclear complex D remained as could be seen from
the 31P NMR spectrum and no hydride was observed in the
1H NMR spectrum. The IR spectrum of this solution shows a
Conclusions
Aminophosphine phosphinite ligands derived from
( )-ephedrine with a stereogenic center at the aminophos-
phine phosphorus atom are successful ligands in the asym-
metric hydroformylation of styrene and other vinylic sub-
strates. High enantioselectivity (up to 77%) and high
selectivity to the branched aldehydes (up to 98%) is obtained
under mild reaction conditions (40 ± 508C, 20 bar CO/H2).
The results highlight that the presence of the additional
stereogenic center at the aminophosphine phosphorus atom
increases the enantioselectivity significantly. Investigation of
the hydrido rhodium complexes under syngas pressure by
NMR and IR spectroscopy showed that the actual structure of
these complexes has a great influence on the enantioselectiv-
ity. Ligands that give high eeꢁs coordinate in a stable axial/
equatorial manner, with the aminophosphine moiety in the
axial position of the trigonal bipyramidal complex. We assign
this species to be responsible for good enantioselection. The
ligands, which form seven-membered ring chelates with a
flexible ligand backbone, prefer bite angles of about 908 and
hence equatorial/axial coordination. By changing the elec-
tronic properties of the phosphinite part to become more
electron-accepting, the complexes become fluctional and the
eeꢁs drop considerably. It is therefore evident that in order to
control the complex configuration and conformation, the two
phosphorus atoms must have different donor/acceptor prop-
erties. This is the case for the ligands 6a, 6b, 6e, and 6 f. Once
the complex configuration is defined, differentiation between
the two remaining coordination sites should be brought about.
For the new AMPP ligands, this task is achieved by the chiral
phosphorus atom bearing two different substituents. It is
evident that these should be different in size and shape. In the
case of the (R,S)-BINAPHOS ligand, the differentiation is
achieved by the fixed conformation of the (S)-binaphthalene
part of the phosphite, which efficiently shields one coordina-
tion site.
1
band at 1788 cm that results from the bridging CO groups
1
and a band at 1988 cm , which is typical for a terminal CO
group. This is also in agreement with the C2-symmetrical
structure we assigned for D from the 31P NMR data.
Since the rhodium concentrations for the NMR experi-
ments were about 30 times higher than those of the catalytic
1
1
reactions (51 mmolL versus 1.74 mmolL ), we also per-
formed high pressure in situ IR spectroscopy. At a rhodium
1
concentration of 1.74 mmolL under a syngas pressure of
20 bar (CO:H2 ˆ 1:1) at 323 K there was no indication for
bridging CO groups. The spectrum shows three bands in the
1
carbonyl and hydride region at 2021, 1994, and 1943 cm
(Figure 3).
Figure 3. In situ IR spectrum of [HRh(L)(CO)2], L ˆ 6a (L:Rh ˆ 2:1),
323 K. A) 20 bar (CO:H2 ˆ 1:1). B) 20 bar (CO:D2 ˆ 1:1).
1
The band at 2021 cm could be assigned to the Rh H
vibration by replacing CO/H2 with CO/D2. The two bands at
1
1994 and 1943 cm remained unchanged, while the band at
1
2021 cm disappeared. This underlines the results of the
NMR experiments, that there is no bis-equatorial complex
present because these would lead to frequency shifts of the
carbonyl bands upon the exchange.[17]
In contrast to the behavior described for the ligands 6a, 6b,
6e, and 6 f that gives rise to high enantiomeric excess, the
So far, the activity of the catalyst systems with our P-chiral
AMPP ligands is too low for practical purposes. Based on the
encouraging results obtained by using this new type of ligands,
work is in progress to make use of this concept for more active
and stable catalysts.
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Chem. Eur. J. 2000, 6, No. 8

Aminophosphine Phosphinite Ligands
1496±1504
(CO/H2 ˆ 1:1) and pressurized to 50 bar. After 3 h at 408C the autoclave
was cooled and depressurized and the solution was transferred into the
NMR tube, which was immediately pressurized again to the appropriate
pressure and analyzed.
Experimental Section
General: All manipulations were carried out under an atmosphere of dry
argon using standard Schlenk techniques. The argon was deoxygenated by
BASF catalyst R-3-11 and dried over molecular sieves (Linde 4 Š).
Solvents were freshly distilled under argon atmosphere and dried by
standard procedures. Air and moisture sensitive solutions and reagents
were handled by using syringe techniques. Catalytic experiments under
pressure were carried out in 75 mL stainless steel autoclaves equipped with
a magnetic stirring bar. NMR spectra were acquired on Bruker AC300 and
Bruker DPX300 spectrometer. Chemical shifts are referenced to internal
or external TMS (1H, 13C, respectively), or external 85% H3PO4 (31P). 31P
and 13C NMR spectra were measured 1H decoupled unless otherwise
stated. IR spectra were recorded on a Nicolet 5130-FT-IR spectrometer
and processed with the OMNIC software. Chemicals were purchased from
Fluka and Aldrich. Styrene was distilled under argon atmosphere after
drying over CaH2. All other substrates were distilled prior to use and stored
under argon at 308C. 2-Methoxy-6-vinylnaphthalene was dissolved in
toluene and filtered over neutral alumina. The syngas used was mixed in
house in a 1:1 ratio from 3.0 quality CO and H2. The phosphorus
compounds PhP(NEt2)2,[18] Cl2P(NEt2),[18] ClP(3,5-(CH3)2-C6H3)2,[19] and
Ligand Preparation
(XP,4S,5R)-2,5-Diphenyl-3,4-dimethyl-1,3,2-oxazaphospholidine-2-borane
(3): This compound was prepared according to a procedure reported by
Juge.[7] (R,S)-Ephedrin (37 mmol, 6.08 g) was azeotropically dried by three
Â
cycles of dissolving in toluene and evaporating. It was then dissolved in
toluene (180 mL) together with fresh distilled PhP(NEt2)2. The mixture
was refluxed for 18 h, during which the diethylamine was removed from the
top of the reflux condenser. To assure complete conversion, the reaction
mixture was degassed three times in between by means of vacuum. The
mixture was allowed to cool to room temperature and a solution of BH3 ´
CS2 (0.074 mmol, 36.8 mL of a 2m solution in toluene) was added. After
stirring at room temperature for 12 h, the solvent was removed in vacuum
to yield a viscous oil. The crude product was recrystallized from methanol
(30 mL) at 208C. Yield: 82% (30.3 mmol, 8.58 g). Mp: 988C; de ꢀ 95%
1
(31P{1H} NMR); 31P NMR (CDCl3): d ˆ 133.4 (q, J(P-B) ˆ 65.8 Hz);
13C NMR (CDCl3): d ˆ 136.8 ± 127.2 (C arom), 84.8 (OCHPh), 59.2
(NCH(CH3)), 29.8 (NCH3), 14.1 (CHCH3); 1H NMR (CDCl3): d ˆ 7.78 ±
[19]
ClP(4-CH3-C6H3)2 were prepared by literature procedures. Elemental
3
7.19 (m, 10H; arom), 5.52 (dd, 3J ˆ 3.0 Hz, J(H-P) ˆ 6.0 Hz, 1H; OCHPh),
analyses were performed on a Carlo Erba CHN-Analyzer 1106. Gas
chromatographic analyses for styrene, 4-methoxy styrene, 2-methoxy-6-
vinylnaphthalene, and 4-bromo styrene were run on a Siemens Sichromat 2
apparatus (split/splitless injector, 25 m Ultra 2 column, carrier gas
101.3 kPa N2, FID detector). The analyses for vinyl acetate were run on
the same apparatus, but with a different capillary column (50 m Pona (HP),
carrier gas 152 kPa He). The integration system HP 3359 was used for all
GC analyses. Enantiomeric excess for styrene, 4-methoxy styrene, and
4-bromo styrene was determined after reduction of the aldehydes and
conversion to the corresponding trifluoroacetates. For styrene and 4-bromo
styrene the trifluoro acetates are analyzed on a 25 m Lipodex E cyclo-
dextrin column (carrier gas 50.6 kPa H2). For 4-methoxy styrene a 25 m FS-
3
3.64 ± 3.57 (m, 1H; NCH(CH3), 2.60 (d, J(H-P) ˆ 11.0 Hz, 3H; NCH3), 0.75
3
(d, J ˆ 6.5 Hz, CH(CH3)), 1.6 ± 0.4 (brm, 3H; BH3).
(XP,1R,2S)-2-N-Methyl-N-(methylphenylphosphinoborane)-2-amino-1-
phenylpropane-1-ol (4a): The oxazaphospholidine 3 (18 mmol, 5.02 g) was
dissolved in THF (60 mL) in a Schlenk flask equipped with a rubber
septum. At 788C MeLi (20 mmol, 25.1 mL of a 0.8 m solution in diethyl
ether) was introduced dropwise through a syringe. After complete addition
the mixture was stirred for an additional 2 h at 788C and was allowed to
warm to room temperature overnight. The reaction was monitored by TLC
(5% EtOAc/toluene (v/v), Rf ˆ 0.20, starting material Rf ˆ 0.55). The
reaction mixture was hydrolyzed with water (20 mL) and the THF was
removed in vacuum. The mixture was taken up in CH2Cl2 (20 mL) and
separated, and the aqueous phase was extracted with CH2Cl2. The
combined and dried (MgSO4) organic phases were evaporated to dryness.
Yield: 97% (17.5 mmol, 5.30 g) of a white powder; de ꢀ 95% (31P{1H}
NMR); 31P NMR (CDCl3): d ˆ 66.7 66.0 (m); 13C NMR (CDCl3): d ˆ
141.6 ± 125.8 (C arom), 76.5 (OCHPh), 57.0 (NCH(CH3)), 27.9 (NCH3), 13.1
Cyclodex
b I/P column (carrier gas 81 kPa H2) was used, and for
2-acetoxypropanal from vinyl acetate, which was analyzed without
derivatization, a 50 m b I/P (7%) column (carrier gas 141.8 kPa H2) was
used. For the enantiomer analyses in all cases a Carlo Erba 2300 apparatus
was used (split/splitless injector, FID detector). For 2-methoxy-6-vinyl-
naphthalene the enantiomeric excess was determined from the alcohol
after reduction with LiAlH4 using HPLC on a (S,S)-Whelk-O 1 (4 Â
250 mm) column with cyclohexane/iso-propanol (95:5) as eluent (303 K,
UV detector).
1
1
(CH(CH3)), 10.2 (d, J(C-P) ˆ 41.0 Hz, PCH3); H NMR (CDCl3): d ˆ 7.42 ±
7.00 (m, 10H; arom), 4.67 (d, 3J ˆ 7.2 Hz, 1H; OCH(Ph)), 3.98 (dq, 3J ˆ
3
3
7.2 Hz, J ˆ 6.7 Hz, 1H; NCH(CH3)), 2.40 (d, J(H-P) ˆ 7.8 Hz, 3H; NCH3),
2.32 (brs, 1H; OH), 1.45 (d, 2J(H-P) ˆ 8.9 Hz, 3H; PCH3), 1.17 (d, 3J ˆ 6.7 Hz,
3H; CH(CH3)), 2.0 ± 0.1 (brm, 3H; BH3).
Hydroformylation experiments: In a typical experiment, the autoclave was
heated to 608C, dried under reduced pressure for about 1 h, and filled with
argon. The catalyst precursor [Rh(acac)(CO)2] (0.035 mmol) and the ligand
(0.104 mmol, P/Rh ratio of 3) were each dissolved in toluene (5 mL). After
mixing and stirring for 15 min the solution was transferred into the
autoclave by syringe. The autoclave was purged three times with syngas
(CO/H2 ˆ 1:1), pressurized to the appropriate initial pressure, and put into
a preheated bath. In runs with separate catalyst preformation the mixture
was stirred for the appropriate time (1 h or 15 h). Styrene (2.0 mL,
17.4 mmol in 5 mL of toluene, total solvent volume 20 mL) was introduced
into the autoclave and the reaction mixture was stirred for the desired time.
The autoclave was then cooled, depressurized, and vented with argon. A
weighed amount of standard (1.50 g) was added and the reaction mixture
was directly distilled under high vacuum into a dry ice trap to remove the
catalyst. A sample was analyzed by GC. For measuring the enantiomeric
excess a sample of the distilled reaction mixture was dropped to a
suspension of LiAlH4 in diethyl ether under ice cooling. This reaction
mixture was stirred at room temperature for additional 3 h and quenched
with water. The mixture was extracted three times with diethyl ether. The
combined organic layers were dried over sodium sulfate, and the solvent
was removed under reduced pressure. The residue was dissolved in
dichloromethane and trifluoroacetic acid anhydride was added at room
temperature. After removing the solvent, the resulting trifluoroacetate was
distilled in vacuum and analyzed on a chiral GC column.
(XP,1R,2S)-2-N-Methyl-N-(n-butylphenylphosphinoborane)-2-amino-1-
phenylpropane-1-ol (4b): This compound was prepared by the procedure
described for 4a. The oxazaphospholidine 3 (5.30 mmol, 1.51 g) in THF
(40 mL) was converted with n-BuLi (5.83 mmol, 2.8 mL of a 2.1m solution
in hexane). The reaction was monitored by TLC (5% EtOAc/toluene (v/v),
Rf ˆ 0.29). Yield: 97% (5.14 mmol, 1.77 g) of a colorless oil; de ꢀ 95%
(31P{1H} NMR); 31P NMR (CDCl3): d ˆ 71.4 ± 70.7 (m); 13C NMR (CDCl3):
d ˆ 141.5 ± 124.2 (C arom), 77.4 (OCH(CH3)), 57.0 (NCH(CH3)), 28.1
(C(CH3)), 24.2 ± 23.0 ((CH2)3), 12.6 (NCH3), 11.9 (H3C(CH2)3); 1H NMR
(CDCl3): d ˆ 7.40 ± 7.23 (m, 10H; arom), 4.80 (d,3J ˆ 6.0 Hz, 1H;
3
3
OCH(Ph)), 4.02 ± 3.90 (dq, J ˆ 6.0 Hz, J ˆ 6.9 Hz, 1H; NCH(CH3)), 2.53
3
(d, J(H-P) ˆ 7.8 Hz, 3H; NCH3), 1.80 ± 1.34 (m, 7H; P(CH2)3, OH), 1.15 (d,
3
3J ˆ 6.9 Hz, 3H; CH(CH3)), 0.91 (t, J ˆ 6.9 Hz, 3H; CH2CH3), 1.80 ± 0.32
(brm, 3H; BH3).
(XP,1R,2S)-2-N-Methyl-N-(1-naphthylphenylphosphinoborane)-2-amino-
1-phenylpropane-1-ol (4c): In a 100 mL Schlenk flask equipped with a
rubber septum, sec-BuLi (19 mmol, 16.56 mL of a 1.165m solution in
diethyl ether) in diethyl ether (10 mL) was cooled to 788C. A solution of
1-bromonaphthalene (23 mmol, 4.79 g) in diethyl ether (10 mL) was added
dropwise by using syringe. During addition, the naphthyllithium precipi-
tated as a white solid. The reaction was monitored by TLC (5% EtOAc/
toluene (v/v), Rf (bromonaphthalene) ˆ 0.65) and upon complete conver-
sion of the bromonaphthalene, THF (20 mL) was added to the mixture. The
oxazaphospholidine 3 (17 mmol, 5.00 g) was dissolved in THF (30 mL) in a
second flask and cooled to 788C. The suspension of naphthyllithium
was transferred by using syringe and added slowly in order to keep the
Preparation of [HRhL(CO)2] complexes and NMR measurements: In a
typical experiment a dried 13 mL autoclave was filled with [Rh(acac)-
(CO)2] (0.0922 mmol), ligand (0.191 mmol, ligand to Rh ratio of 2), and
[D8]toluene (1.8 mL). The autoclave was purged three times with syngas
Chem. Eur. J. 2000, 6, No. 8
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0608-1501 $ 17.50+.50/0
1501

D. Vogt et al.
FULL PAPER
temperature at 788C. After the addition was complete, the mixture was
allowed to warm to room temperature overnight. The mixture was
hydrolyzed with water (30 mL), and the THF was removed in vacuum.
The remaining suspension was mixed with CH2Cl2 (20 mL) and separated,
and the aqueous layer was extracted with CH2Cl2 (3 Â 10 mL). The
combined organic layers were washed with brine and dried over Na2SO4.
Evaporation of the solvent gave the product 4c as a pale yellow, highly
viscous oil, which was further purified by column chromatography (5%
EtOAc/toluene (v/v), Rf ˆ 0.31). Yield: 61% (10.37 mmol, 4.42 g) of a
colorless viscous oil; de ꢀ 95% (31P{1H} NMR); 31P NMR (CDCl3): d ˆ 71.5
(m); 13C NMR (CDCl3): d ˆ 143.7 ± 124.5 (C arom), 78.5 (OCHPh), 57.0
(NCH(CH3)), 28.1 (NCH3), 13.9 (CH(CH3)); 1H NMR (CDCl3): d ˆ 7.40 ±
7.23 (m, 10H; arom), 5.01 (d, 3J ˆ 3.7 Hz, 1H; OCH(Ph)), 4.53 (dq, 3J ˆ
(XP,1R,2S)-2-N-Methyl-N-(methylphenylphosphino)-2-amino-1-phenyl-1-
(di-{[3,5-bis-(trifluoromethyl)phenyl]}phosphinoxy)propane (6c): This
compound was prepared by the procedure described for 6a. Compound
4a (1.7 mmol, 0.50 g) and ClP(3,5-(CF3)2C6H3)2 (1.9 mmol, 0.91 g) were
converted in the presence of triethylamine (5.0 mmol, 0.51 g). Yield: 96%
(1.63 mmol, 1.21 g) of 5c as a highly viscous pale yellow oil; de ꢀ 95%
(31P{1H} NMR); 31P NMR (C6D6): d ˆ 106.6 (s, PO), 69.1 (m, PN); 19F NMR
(C6D6): d ˆ 63.2 (d, J ˆ 13.5 Hz); 13C NMR (C6D6): d ˆ 144.4 ± 121.5 (C
arom), 87.8 (OCHPh), 57.2 (NCH(CH3)), 28.1 (NCH3), 15.9 (CH(CH3)),
1
11.1 (PCH3); H NMR (CDCl3): d ˆ 7.85 ± 6.59 (m, 16H; arom), 4.76 (dd,
3
3J ˆ 8.0 Hz, J(H-PO) ˆ 9.3 Hz, 1H; OCH(Ph)), 4.38 (m, 1H; NCH(CH3)),
3
3
2.25 (d, J(H-PN) ˆ 8.1 Hz, 3H; NCH3), 1.46 (d, J ˆ 8.8 Hz, 3H; CH(CH3)),
3
1.31 (d, J(H-PN) ˆ 6.5 Hz, 3H; PCH3), 2.00 ± 0.50 (brm, 3H; BH3).
3
3
3.7 Hz, J ˆ 6.6 Hz, 1H; NCH(CH3)), 2.65 (d, J(H-P) ˆ 7.5 Hz, 3H; NCH3),
Deprotection of the borane adduct 5c (1.6 mmol, 1.20 g) in triethylamine
(20 mL) afforded 6c as a viscous colorless oil. Yield: 96% (1.54 mmol,
1.13 g); de ˆ 92% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 104.9 (s, PO), 51.3
(s, PN); 19F NMR (C6D6): d ˆ 63.2 (d, J ˆ 13.5 Hz); 13C NMR (C6D6): d ˆ
144.1 ± 122.1 5 (C arom), 87.7 (OCHPh), 57.2 (NCH(CH3)), 28.2 (NCH3),
15.9 (CH(CH3)), 10.8 (PCH3); 1H NMR (C6D6): d ˆ 7.95 ± 6.65 (m, 16H;
arom), 4.87 (dd, 3J ˆ 7.9 Hz, 3J(H-PO) ˆ 8.6 Hz, 1H; OCH(Ph)), 3.93 (dq, 3J ˆ
7.9 Hz, 3J ˆ 7.2 Hz, 1H; NCH(CH3)), 2.19 (d, 3J(H-PN) ˆ 3.3 Hz, 3H; NCH3),
3
1.97 (brs, 1H; OH), 1.33 (d, J ˆ 6.6 Hz, 3H; CH(CH3)), 2.36 ± 0.91 (brm,
3H; BH3).
(XP,1R,2S)-2-N-Methyl-N-(methylphenylphosphino)-2-amino-1-phenyl-1-
(diphenylphosphinoxy)propane (6a): In a 50 mL Schlenk flask equipped
with a rubber septum, compound 4a (3.5 mmol, 1.06 g) and triethylamine
(7.34 mmol, 0.78 g) were dissolved in toluene (15 mL) and cooled to
208C. A solution of freshly distilled ClPPh2 in toluene (5 mL) was slowly
added by using syringe. The resulting suspension was allowed to warm to
room temperature overnight and the ammonium salt was filtered off over a
3 cm pad of Celite. The solvent was evaporated, and the residue dried in
high vacuum. Yield: 92% (3.22 mmol, 1.57 g) of 5a as a highly viscous
colorless oil; de ꢀ 95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 113.8 (s, PO),
68.3 (m, PN); 13C NMR (C6D6): d ˆ 142.7 ± 125.7 (C arom), 86.4 (OCHPh),
3
1.38 (d, 3J ˆ 7.2 Hz, 3H; CH(CH3)), 1.31 (d, J(H-PN) ˆ 6.3 Hz, 3H; PCH3).
(XP,1R,2S)-2-N-Methyl-N-(methylphenylphosphino)-2-amino-1-phenyl-1-
(1,3,2-dioxa-[d,f]-dibenzo-phosphepinoxy)propane (6d): This compound
was prepared by the procedure described for 6a. Compound 4a (1.3 mmol,
0.40 g) and 2,2'-biphenylphosphorchloridite (1.5 mmol, 0.37 g) were con-
verted in the presence of triethylamine (3.0 mmol, 0.41 g). Yield: 81%
(1.05 mmol, 0.55 g) of 5d as a white solid; de ꢀ 95% (31P{1H} NMR); 31P
NMR (C6D6): d ˆ 145.4 (s, PO), 68.1 ± 67.5 (m, PN); 13C NMR (C6D6): d ˆ
149.4 ± 121.2 (C arom), 79.5 (OCHPh), 63.7 (NCH(CH3)), 30.3 (NCH3),
15.3 (CH(CH3)), 12.0 (PCH3); 1H NMR (C6D6): d ˆ 7.48 ± 6.76 (m, 18H;
58.3 (NCH(CH3)), 28.3 (CH(CH3)), 15.6 (NCH3), 11.1 (PCH3); 1H NMR
3
(C6D6): d ˆ 7.67 ± 6.80 (m, 20H; arom), 4.88 (dd, 3J ˆ 8.7 Hz, J(H-PO)
ˆ
8.7 Hz, 1H; OCH(Ph)), 4.72 (dq, 3J ˆ 8.7 Hz, 3J ˆ 8.7 Hz, 1H; NCH(CH3)),
1.96 (d, 3J(H-PN) ˆ 8.4 Hz, 3H; NCH3), 1.30 (d, 3J(H-PN) ˆ 6.6 Hz, 3H; PCH3),
3
3
arom), 5.48 (dd, 3J ˆ 6.6 Hz, J(H-PO) ˆ 9.6 Hz, 1H; OCH(Ph)), 4.33 (dq,
1.14 (d, J ˆ 8.7 Hz, 3H; CH(CH3)), 2.27 ± 0.76 (brm, 3H; BH3).
3
3J ˆ 6.6 Hz, 3J ˆ 8.1 Hz, 1H; NCH(CH3)), 2.19 (d, J(H-PN) ˆ 8.7 Hz, 3H;
For deprotection the borane adduct 5a (0.68 mmol, 0.33 g) was dissolved in
diethylamine (20 mL) and heated to 558C for 15 h. The reaction was
monitored by 31P NMR. After quantitative removal of the BH3 the mixture
was evaporated to dryness and the residue was taken up in a hexane/
toluene mixture (2 mL, 1:1). The amine ± borane adduct was removed by
filtration over basic alumina. Evaporation and drying in high vacuum
afforded the product 6a. Yield: 84% (0.57 mmol, 0.27 g) of a colorless
highly viscous oil; de ꢀ 95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 113.9 (s,
PO), 50.7 (s, PN); 13C NMR (C6D6): d ˆ 143.2 ± 126.3 (C arom), 85.4
(OCHPh), 63.9 (NCH(CH3)), 28.9 (NCH3), 16.0 (CH(CH3)), 11.3 (PCH3);
1H NMR (C6D6): d ˆ 7.75 ± 6.77 (m, 20H; arom), 4.94 (dd, 3J ˆ 8.7 Hz,
3J(H-PO) ˆ 8.7 Hz, 1H; OCH(Ph)), 3.97 (dq, 3J ˆ 8.7 Hz, 3J ˆ 6.0 Hz, 1H;
NCH(CH3)), 2.05 (d, 3J(H-PN) ˆ 3.6 Hz, 3H; NCH3), 1.45 (d, 3J(H-PN) ˆ 6.6 Hz,
3
3
NCH3), 1.15 (d, J ˆ 8.1 Hz, 3H; CH(CH3)), 1.13 (d, J(H-PN) ˆ 6.1 Hz, 3H;
PCH3), 2.00 ± 0.80 (brm, 3H; BH3).
Deprotection of the borane adduct 5d (1.1 mmol, 0.55 g) in triethylamine
(20 mL) afforded 6d as a white solid. Yield: 82% (0.90 mmol, 0.44 g); de ꢀ
95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 149.2 (s, PO), 49.9 (s, PN);
13C NMR (C6D6): d ˆ 149.3 ± 121.1 (C arom), 79.2 (OCHPh), 63.8
(NCH(CH3)), 29.9 (NCH3), 14.9 (CH(CH3)), 11.2 (PCH3); 1H NMR
3
(C6D6): d ˆ 7.19 ± 6.66 (m, 18H; arom), 5.27 (dd, 3J ˆ 8.5 Hz, J(H-PO)
ˆ
8.5 Hz, 1H; OCH(Ph)), 3.56 (dq, 3J ˆ 8.5 Hz, 3J ˆ 6.6 Hz, 1H; NCH(CH3)),
3
3
2.01 (d, J(H-PN) ˆ 3.9 Hz, 3H; NCH3), 1.29 (d, J ˆ 6.6 Hz, 3H; CH(CH3)),
3
1.08 (d, J(H-PN) ˆ 6.3 Hz, 3H; PCH3).
(XP,1R,2S)-2-N-Methyl-N-(n-butylphenylphosphino)-2-amino-1-phenyl-1-
(diphenylphosphinoxy)propane (6e): This compound was prepared by the
procedure described for 6a. Compound 4b (1.5 mmol, 0.50 g) and ClPPh2
(1.7 mmol, 0.37 g) were converted in the presence of triethylamine
(3.4 mmol, 0.34 g). Yield: 78% (1.33 mmol, 0.60 g) of 5e as a colorless,
highly viscous oil; de ꢀ 95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 112.1 (s,
PO), 71.1 (m, PN); 13C NMR (C6D6): d ˆ 141.9 ± 126.4 (C arom), 85.8
(OCHPh), 64.0 (NCH(CH3)), 28.3 (NCH3), 27.05 (CH2CH2CH3), 26.7
3
3H; PCH3), 1.16 (d, J ˆ 6.0 Hz, 3H; CH(CH3)).
(XP,1R,2S)-2-N-Methyl-N-(methylphenylphosphino)-2-amino-1-phenyl-1-
[di-(4-methyl-phenyl)phosphinoxy]propane (6b): This compound was
prepared by the procedure described for 6a. Compound 4a (3.8 mmol,
1.15 g) and ClP(4-CH3C6H4)2 (4.2 mmol, 1.04 g) were converted in the
presence of triethylamine (8.4 mmol, 0.85 g). Yield: 82% (3.12 mmol,
1.60 g) of 5b as a highly viscous colorless oil; de ꢀ 95% (31P{1H} NMR); 31
P
(PCH2CH2), 23.3 (CH(CH3)), 15.5 (CH2CH3), 12.7 (PCH2); 1H NMR
NMR (C6D6): d ˆ 114.4 (s, PO), 68.4 (m, PN); 13C NMR (C6D6): d ˆ 141.1 ±
125.6 (C arom), 86.3 (OCHPh), 58.4 (NCH(CH3)), 28.4 (NCH3), 21.2
(PhCH3), 15.6 (CH(CH3)), 11.1 (PCH3); 1H NMR (C6D6): d ˆ 7.68 ± 6.86
3
(C6D6): d ˆ 7.50 ± 6.92 (m, 20H; arom), 4.83 (dd, 3J ˆ 8.0 Hz, J(H-PO)
ˆ
8.0 Hz, 1H; OCH(Ph)), 4.17 (dq, 3J ˆ 8.0 Hz, 3J ˆ 6.6 Hz, 1H; NCH(CH3)),
3
3
(m, 18H; arom), 4.93 (dd, 3J ˆ 8.4 Hz, J(H-PO) ˆ 8.4 Hz, 1H; OCH(Ph)),
2.39 (d, J(H-PN) ˆ 7.8 Hz, 3H; NCH3), 1.89 ± 1.31 (m, 6H; (CH2)3), 1.26 (d,
3J ˆ 6.6 Hz, 3H; CH(CH3)), 0.90 (t, 3J ˆ 7.1 Hz, 3H; CH2CH3), 1.89 ± 0.30
(brm, 3H; BH3).
4.60 (dq, 3J ˆ 8.4 Hz, 3J ˆ 6.6 Hz, 1H; NCH(CH3)), 2.08 (s, 3H; PhCH3),
3
2.01 (d, J(H-PN) ˆ 8.4 Hz, 3H; NCH3), 2.00 (s, 3H; PhCH3), 1.33 (d, 3J ˆ
3
6.6 Hz, 3H; CH(CH3)), 1.15 (d, J(H-PN) ˆ 8.7 Hz, 3H; PCH3), 2.00 ± 0.80
Deprotection of the borane adduct 5e (1.14 mmol, 0.60 g) in triethylamine
(brm, 3H; BH3).
(20 mL) afforded 6e as
a colorless highly viscous oil. Yield: 84%
(0.96 mmol, 0.49 g); de ꢀ 95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ
112.6 (s, PO), 62.2 (s, PN); 13C NMR (C6D6): d ˆ 141.8 ± 126.3 (C arom),
85.8 (OCHPh), 64.1 (NCH(CH3)), 28.3 (NCH3), 27.1 (CH2CH2CH3), 26.6
Deprotection of the borane adduct 5b (0.7 mmol, 0.38 g) in triethylamine
(15 mL) afforded 6b as a viscous colorless oil. Yield: 62% (0.43 mmol,
0.23 g); de ꢀ 95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 114.3 (s, PO), 52.1
(s, PN); 13C NMR (C6D6): d ˆ 140.6 ± 126.3 (C arom), 85.3 (OCHPh), 64.1
(NCH(CH3)), 28.9 (NCH3), 19.9 (PhCH3) 16.0 (CH(CH3)), 11.3
(PCH3); 1H NMR (C6D6): d ˆ 7.08 ± 6.65 (m, 18H; arom), 5.29 (dd, 3J ˆ
(PCH2CH2), 23.3 (CH(CH3)), 15.5 (CH2CH3), 12.7 (PCH2); 1H NMR
(C6D6): d ˆ 7.75 ± 6.77 (m, 20H; arom), 4.98 (dd, 3J ˆ 8.7 Hz, J(H-PO)
ˆ
3
8.7 Hz, 1H; OCH(Ph)), 4.05 (dq, 3J ˆ 8.7 Hz, 3J ˆ 5.7 Hz, 1H; NCH(CH3)),
3
3
3
3
3
2.16 (d, J(H-PN) ˆ 3.6 Hz, 3H; NCH3), 1.52 (d, J ˆ 5.7 Hz, 3H; CH(CH3)),
7.5 Hz, J(H-PO) ˆ 9.6 Hz, 1H; OCH(Ph)), 3.57 (dq, J ˆ 6.6 Hz, J ˆ 9.6 Hz,
3
3
1.85 ± 1.20 (m, 6H; (CH2)3), 0.92 (t, J ˆ 6.9 Hz, 3H; CH2CH3).
1H; NCH(CH3)), 2.02 (s, PhCH3), 2.01 (d, J(H-PN) ˆ 3.9 Hz, 3H;
3
3
NCH3), 1.30 (d, J(H-PN) ˆ 6.6 Hz, 3H; CH(CH3)), 1.08 (d, J ˆ 6.3 Hz, 3H;
PCH3).
(XP,1R,2S)-2-N-Methyl-N-(n-butylphenylphosphino)-2-amino-1-phenyl-1-
[di-(4-methyl-phenyl)phosphinoxy]propane (6 f): This compound was
1502
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0608-1502 $ 17.50+.50/0
Chem. Eur. J. 2000, 6, No. 8

Aminophosphine Phosphinite Ligands
1496±1504
prepared by the procedure described for 6a. Compound 4b (3.8 mmol,
1.30 g) and ClP(4-CH3C6H4)2 (4.2 mmol, 1.04 g) were converted in the
presence of triethylamine (8.4 mmol, 0.85 g). Yield: 76% (2.89 mmol,
1.60 g) of 5 f as a pale yellow, highly viscous oil; de ꢀ 95% (31P{1H} NMR);
31P NMR (C6D6): d ˆ 114.1 (s, PO), 68.3 (m, PN); 13C NMR (C6D6): d ˆ
141.2 ± 125.6 (C arom), 86.3 (OCHPh), 58.4 (NCH(CH3)), 28.4 (NCH3),
27.05 (CH2CH2CH3), 26.7 (PCH2CH2), 23.3 (CH(CH3)), 15.5 (CH2CH3),
12.7 (PCH2); 1H NMR (C6D6): d ˆ 7.50 ± 6.92 (m, 18H; arom), 4.83 (dd,
amine (4.9 mmol, 0.50 g). Yield: 83% (1.83 mmol, 1.10 g) of 5i as a highly
viscous, colorless oil. It turned out that during synthesis a scrambling of the
BH3 group occurred between the PN and the newly introduced PO
terminus. 31P NMR (C6D6): d ˆ 111.2 (s, POÞNP(BH3)), 107.0
((BH3)POÞNP), 71.8 (m, POÞNP(BH3)), 58.7 (s, (BH3)POÞNP). The
1
13C NMR and H NMR spectra show a mixture of compounds.
Deprotection of the borane adduct 5i (1.8 mmol, 1.07 g) in triethylamine
(20 mL) afforded 6i as
a highly viscous, colorless oil. Yield: 95%
3
3J ˆ 8.0 Hz, J(H-PO) ˆ 8.0 Hz, 1H; OCH(Ph)), 4.17 (dq, 3J ˆ 8.0 Hz, 3J ˆ
(1.71 mmol, 0.99 g); de ˆ 93% (31P{1H} NMR); 31P NMR (C6D6): d ˆ
3
111.8 (s, PO), 57.6 (s, PN); 13C NMR (C6D6): d ˆ 141.8 ± 124.1 (C arom),
6.6 Hz, 1H; NCH(CH3)), 2.33 (d, J(H-PN) ˆ 6.0 Hz, 3H; NCH3), 2.26 (s,
3H; PhCH3), 2.20 (s, 3H; PhCH3), 1.89 ± 1.31 (m, 6H; (CH2)3), 1.26 (d, 3J ˆ
6.6 Hz, 3H; CH(CH3)), 1.16 (d, 3J ˆ 9.0 Hz, 3H; CH(CH3)), 0.83 (t, 3J ˆ
6.0 Hz, 3H; CH2CH3), 2.00 ± 0.20 (brm, 3H; BH3).
85.7 (OCHPh), 64.4 (NCH(CH3)), 30.5 (NCH3), 15.8 (CH(CH3)); 1H NMR
(C6D6): d ˆ 8.22 ± 6.60 (m, 27H; arom), 4.85 (dd, 3J ˆ 7.5 Hz, J(H-PO)
ˆ
3
7.5 Hz, 1H; OCH(Ph)), 4.12 (dq, 3J ˆ 7.5 Hz, 3J ˆ 6.0 Hz, 1H; NCH(CH3)),
3
3
2.29 (d, J(H-PN) ˆ 3.0 Hz, 3H; NCH3), 1.43 (d, J(H-PN) ˆ 6.0 Hz, 3H;
CH(CH3)).
Deprotection of the borane adduct 5 f (0.7 mmol, 0.39 g) in triethylamine
(15 mL) afforded 6 f as a pale yellow, highly viscous oil. Yield: 70%
(0.49 mmol, 0.26 g); de ꢀ 95% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 113.4
(s, PO), 62.2 (s, PN); 13C NMR (C6D6): d ˆ 142.8 ± 121.7 (C arom), 87.1 (m,
OCHPh), 65.6 (m, NCH(CH3)), 29.6 (NCH3), 28.4 (CH2CH2CH3), 28.1
(PCH2CH2), 24.7 (CH(CH3)), 21.2 (PhCH3), 16.8 (CH2CH3), 14.1 (PCH2);
1H NMR (C6D6): d ˆ 7.74 ± 6.84 (m, 18H; arom), 5.03 (dd, 3J ˆ 8.7 Hz,
3J(H-PO) ˆ 8.7 Hz, 1H; OCH(Ph)), 4.07 (dq, 3J ˆ 8.7 Hz, 3J ˆ 6.7 Hz, 1H;
Acknowledgement
This work was supported by the DFG, SFB 380, ªAsymmetrische Synthesen
mit Chemischen und Biologischen Methodenº at the RWTH Aachen and
by the ªCatalysis Network NRWº. R.E. is grateful for a grant from Hoechst
AG. We wish to thank Degussa AG for the generous loan of rhodium
compounds. Financial support by the Fonds der Chemischen Industrie,
VCI, is gratefully acknowledged. Thanks to K. Kupferschläger for
redesigning the titanium valve-head for the sapphire tube.
3
NCH(CH3)), 2.18 (d, J(H-PN) ˆ 3.4 Hz, 3H; NCH3), 2.09 (s, 3H; PhCH3),
2.00 (s, 3H; PhCH3), 1.49 (d, 3J ˆ 6.7 Hz, 3H; CH(CH3)), 1.95 ± 1.20 (m,
3
6H; (CH2)3), 0.91 (t, J ˆ 6.9 Hz, 3H; CH2CH3).
(XP,1R,2S)-2-N-Methyl-N-(n-butylphenylphosphino)-2-amino-1-phenyl-1-
(di-{[3,5-bis-(trifluoromethyl)phenyl]}phosphinoxy)propane (6g): This
compound was prepared by the procedure described for 6a. Compound
4b (1.3 mmol, 0.45 g) and ClP(3,5-(CF3)2C6H3)2 (1.5 mmol, 0.71 g) were
converted in the presence of triethylamine (2.9 mmol, 0.29 g). Yield: 96%
(1.25 mmol, 1.01 g) of 5g as a pale yellow, highly viscous oil; de ꢀ 95%
(31P{1H} NMR); 31P NMR (C6D6): d ˆ 107.1 (s, PO), 72.5 (m, PN); 13C NMR
(C6D6): d ˆ 144.7 ± 121.2 (C arom), 87.0 (OCHPh), 59.3 (NCH(CH3)), 28.3
(NCH3), 27.05 (CH2CH2CH3), 26.7 (PCH2CH2), 23.3 (CH(CH3)), 15.9
[1] a) N. Sakai, S. Mano, K. Nozaki, H. Takaya, J. Am. Chem. Soc. 1993,
Â
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van der Veen, P. C. J. Kamer, P. W. N. M. van Leeuwen, Organome-
tallics 1997, 16, 5681.
1
(CH2CH3), 14.6 (PCH2); H NMR (C6D6): d ˆ 7.95 ± 6.65 (m, 16H; arom),
4.84 (dd, 3J ˆ 8.4 Hz, 3J(H-PO) ˆ 8.4 Hz, 1H; OCH(Ph)), 4.37 (dq, 3J ˆ 8.4 Hz,
3
3J ˆ 6.6 Hz, 1H; NCH(CH3)), 2.40 (d, J(H-PN) ˆ 7.3 Hz, 3H; NCH3), 1.93 ±
1.26 (m, 6H; (CH2)3), 1.37 (d, 3J ˆ 6.6 Hz, 3H; CH(CH3)), 0.91 (t, 3J ˆ
7.0 Hz, 3H; CH2CH3), 2.00 ± 0.20 (brm, 3H; BH3).
Deprotection of the borane adduct 5g (1.30 mmol, 1.01 g) in triethylamine
(20 mL) afforded 6g as a pale yellow, highly viscous oil. Yield: 81%
(1.05 mmol, 0.80 g); de ˆ 94% (31P{1H} NMR); 31P NMR (C6D6): d ˆ 104.9
(s, PO), 60.8 (s, PN); 19F NMR (C6D6): d ˆ 63.2 (s); 13C NMR (C6D6): d ˆ
143.6 ± 120.2 (C arom), 87.1 (OCHPh), 62.9 (NCH(CH3)), 28.8 (NCH3), 27.1
(CH2CH2CH3), 26.6 (PCH2CH2), 23.3 (CH(CH3)), 15.9 (CH2CH3), 12.7
(PCH2); 1H NMR (C6D6): d ˆ 7.85 ± 6.66 (m, 16H; arom), 4.73 (dd, 3J ˆ
3
3
3
8.4 Hz, J(H-PO) ˆ 8.4 Hz, 1H; OCH(Ph)), 3.78 (dq, J ˆ 8.4 Hz, J ˆ 6.6 Hz,
1H; NCH(CH3)), 1.95 (d, 3J(H-PN) ˆ 3.0 Hz, 3H; NCH3), 1.26 (d, 3J ˆ 6.6 Hz,
3H; CH(CH3)), 1.63 ± 1.00 (m, 6H; (CH2)3), 0.78 (t, 3J ˆ 7.2 Hz, 3H;
CH2CH3).
(XP,1R,2S)-2-N-Methyl-N-(diphenylphosphino)-2-amino-1-phenyl-1-(di-
phenylphosphinoxy)propane (6h, EPHOS): The azeotropically dried (3 Â
10 mL toluene) ephedrine (13.7 mmol, 2.27 g) and triethylamine
(40.9 mmol, 4.14 g) were dissolved in toluene (100 mL). At 788C a
solution of ClPPh2 (30.1 mmol, 6.65 g) in toluene (10 mL) was slowly added
by a syringe. The mixture was allowed to warm to room temperature
overnight, and the ammonium salt was filtered off. Evaporation of the
solvent yielded raw 6h 94% (12.9 mmol, 6.8 g) as a yellow, highly viscous
oil. The product was purified by dissolving in hexane/toluene (2:1) and
filtration over carefully dried basic alumina. Evaporation of the solvents
gave 6h as colorless, highly viscous oil. Yield: 84% (11.5 mmol, 5.7 g); 31
P
NMR (C6D6): d ˆ 111.1 (s, PO), 65.3 (s, PN); 13C NMR (C6D6): d ˆ 141.8 ±
126.3 (C arom), 85.8 (OCHPh), 64.3 (NCH(CH3)), 30.5 (NCH3), 15.8
(CH(CH3)); 1H NMR (C6D6): d ˆ 7.75 ± 6.77 (m, 20H; arom), 4.94 (dd, 3J ˆ
3
3
3
8.7 Hz, J(H-PO) ˆ 8.7 Hz, 1H; OCH(Ph)), 3.97 (dq, J ˆ 8.7 Hz, J ˆ 6.0 Hz,
3
3
1H; NCH(CH3)), 2.05 (d, J(H-PN) ˆ 3.6 Hz, 3H; NCH3), 1.45 (d, J(H-PN)
ˆ
[6] R. Bayersdörfer, B. Ganter, U. Englert, W. Keim, D. Vogt, J.
Organomet. Chem. 1998, 552, 183.
3
6.6 Hz, 3H; PCH3), 1.16 (d, J ˆ 6.0 Hz, 3H; CH(CH3)).
Â
Â
(XP,1R,2S)-2-N-Methyl-N-(1-naphthylphenylphosphinoborane)-2-amino-
1-phenyl-1-(diphenylphosphinoxy)propane (6i): This compound was pre-
pared by the procedure described for 6a. Compound 4c (2.2 mmol, 0.92 g)
and ClPPh2 (2.4 mmol, 0.54 g) were converted in the presence of triethyl-
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Â
c) V. Peper, K. Stingl, H. ThümLer, W. Saak, D. Haase, S. Pohl, S. Juge,
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0947-6539/00/0608-1503 $ 17.50+.50/0
1503

D. Vogt et al.
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Â
Â
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Received: July 16, 1999 [F1921]
1504
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Chem. Eur. J. 2000, 6, No. 8