New chiral phosphine-phosphite ligands in the enantioselective rhodium-catalyzed hydroformylation of styrene

Article abstract of DOI:10.1021/om990760m

A series of chiral phosphine-phosphite ligands 1a-g have been synthesized from monophosphines 2-4, enantiomerically pure propene oxide or styrene oxide, and 3,3′,5,5′-tetra(tert-butyl)-2,2′-bisphenol phosphorochloridite or enantiomerically pure 3,3′-bis(tri> methylsilyl)-2,2′-binaphthol phosphorochloridites. These phosphine-phosphites have been used in the rhodium-catalyzed asymmetric hydroformylation of styrene. The structures of the active catalysts, [HRh(L-L)(CO)₂] complexes (L-L = ligands 1a-g), have been studied using high-pressure NMR and IR spectroscopy. The obtained spectroscopic data show that the ligands coordinate in an equatorial-apical fashion to the rhodium center with the phosphine in apical position. Systematic variation in configuration of the stereocenters at both the ligand bridge and the phosphine moiety revealed a remarkable cooperative effect on the selectivity of the hydroformylation reaction. Under mild reaction conditions ee's of 63% and regioselectivities up to 92% toward 2-phenylpropanal were obtained (25-60°C, 20 bar of syn gas CO:H₂ [1:1]) for ligands 1. The absolute configuration of the product is governed by the stereogenic center of the backbone of the ligand. There is a large cooperative effect, however, from the phosphine moiety. Spectroscopic data, in combination with the obtained results in catalysis, suggest that phosphine-phosphite ligands (L-L) containing the conformationally flexible and axially chiral biphenyl moiety exist predominantly as single atropisomers in the HRh(L-L)(CO)₂ complexes. Comparison of the bisphenol and binaphthol substituents suggests that the high enantiomeric excesses obtained with the former are caused by the preferential formation of the most selective diastereomer.

Full text of DOI:10.1021/om990760m

Organometallics 2000, 19, 2065-2072
2065
New Ch ir a l P h osp h in e-P h osp h ite Liga n d s in th e
En a n tioselective Rh od iu m -Ca ta lyzed Hyd r ofor m yla tion
of Styr en e
Sirik Deerenberg, Paul C. J . Kamer, and Piet W. N. M. van Leeuwen*
Institute for Molecular Chemistry, University of Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands
Received September 28, 1999
A series of chiral phosphine-phosphite ligands 1a -g have been synthesized from
monophosphines 2-4, enantiomerically pure propene oxide or styrene oxide, and 3,3′,5,5′-
tetra(tert-butyl)-2,2′-bisphenol phosphorochloridite or enantiomerically pure 3,3′-bis(tri-
methylsilyl)-2,2′-binaphthol phosphorochloridites. These phosphine-phosphites have been
used in the rhodium-catalyzed asymmetric hydroformylation of styrene. The structures of
the active catalysts, [HRh(L-L)(CO)2] complexes (L-L ) ligands 1a -g), have been studied
using high-pressure NMR and IR spectroscopy. The obtained spectroscopic data show that
the ligands coordinate in an equatorial-apical fashion to the rhodium center with the
phosphine in apical position. Systematic variation in configuration of the stereocenters at
both the ligand bridge and the phosphine moiety revealed a remarkable cooperative effect
on the selectivity of the hydroformylation reaction. Under mild reaction conditions ee's of
63% and regioselectivities up to 92% toward 2-phenylpropanal were obtained (25-60 °C, 20
bar of syn gas CO:H2 [1:1]) for ligands 1. The absolute configuration of the product is governed
by the stereogenic center of the backbone of the ligand. There is a large cooperative effect,
however, from the phosphine moiety. Spectroscopic data, in combination with the obtained
results in catalysis, suggest that phosphine-phosphite ligands (L-L) containing the
conformationally flexible and axially chiral biphenyl moiety exist predominantly as single
atropisomers in the HRh(L-L)(CO)2 complexes. Comparison of the bisphenol and binaphthol
substituents suggests that the high enantiomeric excesses obtained with the former are
caused by the preferential formation of the most selective diastereomer.
In tr od u ction
In general, chiral diphosphine-Rh(I) complexes show
high catalytic activity and chemoselectivity. The enan-
tiomeric excesses obtained so far, however, do not exceed
60%.12 Chiral diphosphite-Rh(I) complexes show high
enantioselectivities,13,14 but the scope is limited. Takaya
et al. have reported a hydroformylation catalyst precur-
sor based on [Rh(acac)(CO)2] modified with a chiral
phosphine-phosphite ligand, BINAPHOS,15,16 which
combines the advantages of both ligand types; high ee’s
were obtained in the hydroformylation of styrene and
other olefins, combined with excellent chemo- and
regioselectivity.17
Hydroformylation is an important and thus exten-
sively studied industrial process.1-4 Improvement of
rates and selectivities and mechanistic aspects receive
a great deal of attention.5,6 Asymmetric hydroformyla-
tion is a potentially powerful synthetic tool for the
synthesis of several chiral building blocks that can be
used as precursors for high-value-added compounds
such as pharmaceuticals, agrochemicals, flavors, and
fragrances.7-11
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88-89.
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Mol. Catal. A 1995, 104, 17-85.
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A., Eds.; Springer-Verlag: New York, 1996; pp 29-90.
(5) van Leeuwen, P. W. N. M.; van Santen, R. A. In Surface Science
and Catalysis; Moulijn, J . A., Ed.; 1993; Vol. 79.
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tallics 1997, 16, 2981-2986.
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1986, 42, 4095.
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ity 1991, 3, 355.
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10.1021/om990760m CCC: $19.00 © 2000 American Chemical Society
Publication on Web 04/22/2000

2066 Organometallics, Vol. 19, No. 11, 2000
Deerenberg et al.
Most of the research published to date is dedicated
to ligands having stereogenic elements attached to the
donor atom(s). Ligands having a stereogenic donor atom,
for instance a stereogenic phosphine, are rare, and
DIPAMP is one of the few examples.18 J uge´ et al. have
developed a method for the synthesis of enantiomeri-
cally pure, borane-protected stereogenic phosphines of
the type P(Ph)(R)(Me)(BH3).19 It is a useful chiral
building block, which can be applied in the synthesis of
chiral ligands containing stereogenic P atoms. Following
this method, Mezzetti et al. synthesized (S,S)-Me2Si-
(CH2P(1-Np)(Ph))2, which gave ee’s up to 97.7% in the
catalytic hydrogenation of dehydroamino acids.20 Al-
though high enantioselectivities have been obtained,
catalytic applications of bidentate ligands containing
stereogenic phosphorus atoms are still rare.21-31
we designed a series of chiral phosphine-phosphite
ligands that allowed a systematic approach to study the
asymmetric induction of a ligand in the hydroformyla-
tion reaction.
Previous work in our group and in the literature
shows the possibility of chiral cooperativity between
stereocenters in a ligand. For instance, diphosphite
ligands containing biaryl moieties with bulky substit-
uents show hindered rotation around the biaryl axis.14,17
Although the additional stereocenter originating from
the atropisomeric biaryl substituents may lead to sev-
eral diastereomers, high enantioselectivities are ob-
tained in the hydroformylation reaction. It was found
that the low-energy barrier for interconversion in atrop-
isomers resulted in the formation of a single diastereo-
meric HRh(CO)2(diphosphite) complex. This complex
also gives rise to high enantioselectivities.
Herrmann et al. have published molecular modeling
studies of the BINAPHOS-rhodium complex,32 but the
mechanistic aspects of the asymmetric hydroformylation
reaction are still not understood well enough to be used
for the prediction of the enantioselectivities.
Encouraged by the success of BINAPHOS, the success
of ligands containing stereogenic phosphorus atoms, and
the cooperative effect found in bulky phosphite ligands,
In this paper we describe the synthesis of novel chiral
phosphine-phosphite ligands. The designed ligands
consist of a phosphine moiety with a stereogenic phos-
phorus atom. The configuration of the phosphorus atom
is expected to be important for the course of the catalytic
reaction, since it is in close vicinity of the metal center.
Furthermore, the ligands contain a bridge having a
stereocenter and a bulky phosphite moiety. The stereo-
genic phosphorus moiety, the stereocenter in the back-
bone, and the configuration of the biaryl moiety can
result in several diastereomers. Systematic variation of
the stereocenters provides information about the effect
of the different stereocenters on the enantioselectivity.
The presence of bulky substituents on aromatic biphenyl
positions has already shown to have a significant effect
on the catalyst performance.13,14,33-38 Having two dif-
ferent donor atoms, the ligand is anticipated to coordi-
nate as follows: the phosphine, the better σ-donor, will
coordinate in an apical position, and the phosphite, the
better π-acceptor, will coordinate in an equatorial posi-
tion.39 This was confirmed by high-pressure NMR and
IR studies of RhH(CO)2(phosphine-phosphite) com-
plexes under catalytic conditions.40-45
(16) Horiuchi, T.; Ohta, T.; Shirakawa, E.; Nozaki, K.; Takaya, H.
J . Org. Chem. 1997, 62, 4285-4292.
(17) Nozaki, K.; Sakai, N.; Nanno, T.; Higashijima, T.; Mano, S.;
Horiuchi, T.; Takaya, H. J . Am. Chem. Soc. 1997, 119, 4413-4423.
(18) Brunner, H.; Zettlmeier, W. Handbook of Enantioselective
Catalysis; VCH: Weinheim, Germany, 1993.
(19) J uge´, S.; Ste´phan, M.; Laffitte, J . A.; Genet, J . P. Tetrahedron
Lett. 1990, 31, 6357.
(20) Stoop, R. M.; Mezzetti, A.; Spindler, F. Organometallics 1998,
17, 668.
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P. W. N. M. Tetrahedron: Asymmetry 1997, 8, 3185-3188.
(22) Geneˆt, J . P.; Pinel, C.; Ratovelomanana-Vidal, V.; Mallart, S.;
Pfister, X.; Can˜o De Andrada, M. C.; Laffite, J . A. Tetrahedron:
Asymmetry 1994, 5, 665.
Resu lts a n d Discu ssion
Liga n d Syn th esis. Ligands 1a -e were synthesized
in three steps starting from the corresponding mono-
phosphines 2-4 (Scheme 1). Methyldiphenylphosphine
was protected by reaction with BH3‚SMe2 to obtain
(33) Buisman, G. J . H.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.
Tetrahedron: Asymmetry 1993, 4, 1625.
(23) Geneˆt, J . P.; Pinel, C.; Ratovelomanana-Vidal, V.; Mallart, S.;
Pfister, X.; Bischoff, L.; Can˜o De Andrada, M. C.; Darses, S.; Galopin,
C.; Laffite, J . A. Tetrahedron: Asymmetry 1994, 5, 675.
(24) Geneˆt, J . P.; J uge´, S.; Laffite, J . A.; Pinel, C.; Mallart, S. Chem.
Abstr. 1994, 121, P156763d.
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Widhalm, M.; Spek, A. L.; Lutz, M. J . Org. Chem. 1999, 64, 3996-
4004.
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227.
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(28) Ohff, M.; Holz, J .; Quirmbach, M.; Bo¨rner, A. Synthesis 1998,
1391.
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Kamer, P. C. J . Recl. Trav. Chim. Pays-Bas 1994, 113, 61.
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W. N. M. J . Chem. Soc., Dalton Trans. 1995, 409-417.
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Kamer, P. C. J .; van Leeuwen, P. W. N. M. Tetrahedron: Asymmetry
1995, 6, 719-738.
(38) Buisman, G. J . H.; van der Veen, L. A.; Kamer, P. C. J .; van
Leeuwen, P. W. N. M. Organometallics 1997, 16, 5681-5687.
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(40) Elsevier, C. J . J . Mol. Catal. 1994, 92, 285.
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H.; Tsurata, H.; Matsukawa, S.; Yamaguchi, K. J . Am. Chem. Soc.
1998, 120, 1635.
(30) Miura, T.; Imamoto, T. Tetrahedron. Lett. 1999, 40, 4833.
(31) Maienza, F.; Worle, M.; Steffanut, P.; Mezzetti, A.; Spindler,
F. Organometallics 1998, 18, 1041.
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1597.
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P. W. N. M.; de Lange, W. G. J . Organometallics 1998, 17, 2543-2552.
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W. N. M. Recl. Trav. Chim. Pays-Bas 1996, 115, 492-498.
(32) Gleich, D.; Schmid, R.; Herrmann, W. A. Organometallics 1998,
17, 2741.

New Chiral Phosphine-Phosphite Ligands
Organometallics, Vol. 19, No. 11, 2000 2067
Sch em e 1
Sch em e 2
prepared (Scheme 2). The interconversion around the
binaphthyl bond is energetically highly unfavorable, and
stable diastereomeric phosphine-phosphite ligands have
been obtained in diastereomerically pure form. Ligands
1f and 1g were synthesized in a similar way as
described for ligands 1a -e. A literature method was
applied for the synthesis of enantiomerically pure (R)-
and (S)-3,3′-bis(trimethylsilyl)-2,2′-binaphthol phospho-
rochloridites.14 Reaction with phosphino alcohol 5a and
decomplexation of the BH3 group gave phosphine-
phosphites 1f and 1g as white solids.
[Rh H(CO)2(L-L)] Com p lexes. The coordination
mode of the ligand in the active complex has been
studied using IR and NMR under 20 bar of syn
gas.34-37,44,56,57 Hydridorhodium phosphine-phosphite
dicarbonyl complexes [RhH(CO)2(L-L)] were prepared
from Rh(acac)(CO)2 and ligands 1. The spectroscopic
data are shown in Table 1. The IR spectrum of RhH-
(CO)2(1a ) in cyclohexane shows absorptions at 2021
(medium) and 1974 (strong) cm-1 due to a symmetric
and an antisymmetric stretch vibration of two equato-
rially coordinated CO ligands. The Rh-H vibration was
not observed in the spectrum. Upon deuteration, there
is no shift observed in the CO absorptions.44,58,59 This
is characteristic of a coordination fashion in which the
hydride and both CO ligands of RhH(CO)2(L-L) are
orientated cis to one another. Similar data were ob-
served for ligands 1b-g.
monophosphine 2 as a crystalline product.46-49 The
boronato group was used both to avoid oxidation of the
phosphine and to activate the methylphosphine toward
lithiation.50 Stereogenic monophosphines 3 and 4 were
synthesized as enantiomerically pure, crystalline prod-
ucts using the methodology of J uge´19 and Mezzetti,20
respectively. After metalation of these phosphines, 2-4,
using sec-BuLi in THF at -40 °C, they reacted with
enantiomerically pure propene oxide or styrene oxide
to yield phosphino alcohols 5a -e.46-49 Phosphino alco-
hols 5a -e were coupled with bisphenol phosphorochlo-
ridite in the presence of triethylamine.33,51 Filtration
over a short silica column, to remove hydrolyzed phos-
phorochloridite, gave pure phosphine-phosphites 6a -e
as colorless oils. Compounds 2-6 show broad signals
in the 31P NMR indicative of a phosphine-borane
complex.21,52,53 Phosphine-phosphite borane adducts 6
were immediately deprotected overnight at 50 °C using
diethylamine. After filtration, the phosphine-phos-
phites 1 were obtained in moderate to good yields (37-
95%). From 1H NMR and 31P NMR we concluded that
in none of the reactions were the stereocenters in the
ligands affected, since no formation of diastereomers
was observed. The existence of a single peak for each
phosphorus atom of 1a -e in the 31P NMR suggests the
rapid isomerization in the biphenyl moiety, which
results in an averaged configuration on the NMR time
scale.14,17 In none of the preceding reactions is the
configuration at the P atom affected. As borane decom-
plexation reactions are known to occur with retention
of configuration at the phosphorus atom,19,54,55 the
absolute configuration at the phosphorus atom is as-
signed as S.
The 31P NMR spectrum of RhH(CO)2(1a ) shows
signals at 6.91 and 163.89 ppm attributed to the
phosphine and the phosphite, respectively. For the
Rh-H coupling constant a value of 9 Hz is found,
whereas J {P1-H} and J {P2-H} are found to be 102 and
<2 Hz, respectively. The coupling constant of P1-Rh is
101 Hz and P2-Rh is 237 Hz. The coupling constant
J {P1-P2} is 24.3 Hz. From these results and from
literature it is expected that the structure of the HRh-
(CO)2(P1-P2) is a trigonal bipyramid (Chart 1).7-11
The value found for the P1-H coupling of 102 Hz is
typical of a complex containing an apical hydride and
an apical phosphine. The magnitude of the coupling
constant of P2-H of 2 Hz is similar to that reported for
an apical hydride with an equatorial phosphite.34-36
A
To study the influence of the biaryl moiety on the
catalyst, bulky binaphthol-based ligands 1f,g were
coupling constant of 106 Hz in trigonal bipyramidal
HRh(CO)2(DPEphos) has been found for an apical
phosphine,58,59 whereas for apical phosphite complexes
of trigonal bipyramidal HRh(CO)2(diphosphite), cou-
pling constants of 160 Hz have been reported.15,60,61
(46) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K.
J . Am. Chem. Soc. 1990, 112, 5244.
(47) Imamoto, T. Pure Appl. Chem. 1993, 65, 655.
(48) Pellon, P. Tetrahedron Lett. 1992, 33, 4451.
(49) Imamoto, T.; Kusumoto, T.; Suzuki, N.; Sato, K. J . Am. Chem.
Soc. 1985, 107, 5301.
(50) Schmidbauer, H. J . J . Organomet. Chem. 1980, 200, 287.
(51) J ongsma, T. Thesis, Polymer-bound rhodium hydroformylation
catalysts, University of Groningen, 1992.
(52) Wolfe, B.; Livinghouse, T. J . Am. Chem. Soc. 1998, 120, 5116.
(53) Uziel, J .; Ste´phan, M.; Kaloen, E.-B.; Geneˆt, J .-P.; J uge´, S. Bull.
Soc. Chim. Fr. 1997, 134, 379.
(56) Moasser, B.; Gladfelter, W. L.; Roe, D. C. Organometallics 1995,
14, 3832-3838.
(57) Moasser, B.; Gladfelter, W. L. Inorg. Chim. Acta 1996, 242,
125-136.
(58) DPEphos stands for 2,2′-bis(diphenylphosphino)diphenyl ether.
(59) van der Veen, L. A.; Boele, M. D. K.; Bregman, F. R.; Kamer,
P. C. J .; van Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J .; Schenk,
H. J . Am. Chem. Soc. 1998, 120, 11616.
(54) J uge´, S.; Merde`s, R.; Ste´phan, M.; Genet, J . P. Phosphorus,
Sulfur Silicon Relat. Elem. 1993, 77, 199.
(55) J uge´, S.; Ste´phan, M.; Merde`s, R.; Genet, J . P.; Halut-Desportes,
D. J . Chem. Soc., Chem. Commun. 1993, 531.
(60) Meakin, P.; J esson, J . P.; Tebbe, F. N.; Muetterties, E. L. J .
Am. Chem. Soc. 1971, 93, 1797.

2068 Organometallics, Vol. 19, No. 11, 2000
Deerenberg et al.
Ta ble 1. Sp ectr a l Da ta of th e Com p lexes Rh H(CO)2(p h osp h in e-p h osp h ite) u n d er 20 ba r Syn Ga s
NMRa,b
P1 ) phosphine
P2 ) phosphite
hydride
J {H-Rh}
IRc,d
ligand
δ(P1)
J {P1-H}
J {P1-Rh}
δ(P2)
J {P2-H}
J {P2-Rh}
J {P1-P2}
δ(H)
ν(CO)
ν(CO)
Binaphos
1a (S,S)
1b (S,S)
1c (S,R)
1d (-,S)
1e (-,S)
1f (S,S,R)
1g (S,S,S)
26.92
6.91
23.2
102
114
102
90
96
105
94
119
101
97
184.86
163.89
162.71
159.89
162.59
163.37
171.70
171.36
159.9
<2
181.6
237
239
237
229
231
236
238
39.7
24.3
40.7
34.0
20.8
31.4
41.6
11.9
-8.85
-9.58
-9.40
-9.47
-9.45
-9.02
-9.75
-9.90
9.8
9.0
9.2
9.0
9.1
9.1
e
1974
1974
1972
1974
1973
1975
1979
1973
2018
2021
2016
2018
2019
2020
2020
2021
10.56
22.20
18.14
16.60
3.75
<3.5
<2
99
104
103
100
103
15.5
15.7
e
7.07
<2
8.2
a
1
HRh(P-P)(CO)2 complexes prepared in benzene-d6 at 50 °C. 31P and H spectra recorded in benzene-d6 at room temperature. b Chemical
shifts (δ) in ppm; coupling constants (J ) in hertz. c HRh(P-P)(CO)2 complexes prepared in cyclohexane at 50 °C, and IR spectra recorded
at 50 °C. Absorptions (ν) in cm-1
.
e Broadened multiplet.
d
Ch a r t 1. Str u ctu r e of HRh (L-L)(CO)2
steric factors. The CO absorption bands of rhodium
dicarbonyl complexes of BINAPHOS at 2018 (medium)
and 1974 (strong) that previously were assigned to
Rh-H and Rh-CO absorptions, respectively, are similar
to the analogous complexes of ligand 1 and containing
BINAPHOS in an apical-equatorial position. As ex-
pected, deuteration of the complex did not shift or
decrease the CO absorptions. A small absorption at 2058
did disappear, which was assigned to the Rh-H vibra-
tion. Interestingly, the complexes derived from ligands
1a -c exist as single species, as shown by HP NMR.
Variable-temperature (295-163 K) 31P and 1H NMR
experiments did not demonstrate fluxional processes.
The spectra were recorded under 15 bar of syngas in
acetone-d6/THF-d8 ) 1:1. At very low temperature (163
Upon selective decoupling of the phosphine and the
phosphite in the 1H NMR, the coupling constants of 102
and 2 Hz disappeared, respectively. From these NMR
data we conclude that the hydride orientation is trans
to the phosphine (P1) and cis to the phosphite (P2). The
magnitude of J {Rh-H}, 9 Hz, confirms the equatorial
apical coordination; that is, a coupling constant between
a rhodium and an apical hydride having a phosphine
or a phosphite trans is around 9 Hz, whereas a coupling
constant between rhodium and an apical hydride having
a CO ligand trans is less than 4 Hz. The obtained
coupling constants are indicative of a structure close to
an ideal trigonal bipyramid. For ligands 1d and 1e
J {P1-H} of 15 Hz is larger than expected for perfect
equatorial coordination. This can be due to distortion
of the trigonal bipyramidal structure or due to an equi-
librium of the complex between P1-equatorial-P2-apical
coordination and P1-apical-P2-equatorial coordination.
The HP-IR spectrum shows only two vibrations in the
Rh-CO region, indicative of a single species, unless the
absorptions coincide. From molecular modeling calcula-
tions it is expected that Rh-CO absorptions of com-
plexes with P1-equatorial-P2-apical coordination or P1-
apical-P2-equatorial will coincide.62 We assume that the
large magnitude of J {P1-H} for ligands 1d and 1e is
caused by distortion of the trigonal bipyramidal struc-
ture. From NMR spectroscopy it is concluded that in
the RhH(CO)2(L-L) complexes, prepared from phos-
phine-phosphite ligands 1a -g, the phosphine, the best
σ-donor, occupies an apical position and the phosphite,
the best π-acceptor, occupies an equatorial position.39
This is in contrast with the coordination mode found
for the [RhH(CO)2(L-L) complex of BINAPHOS, in
which the phosphine occupies an equatorial position and
the phosphite an apical position. Despite the structural
similarity of our ligands 1 and BINAPHOS, the coor-
dination fashion is different. Apparently, this is due to
1
K) 31P and H NMR spectra showed the same coupling
constants as at room temperature, except for a small
increase of the phosphite-hydride coupling from 2 to 8
Hz. This small change in J {P2-H} is attributed to small
conformational changes in the backbone of the ligand
on cooling. Upon selective decoupling of the phosphine
1
signal the H NMR spectrum showed total disappear-
ance of the large phosphine-hydride coupling of 102 Hz.
This confirms the formation of only one complex with
the phosphine at axial position trans to the hydride.
Although rapid atropisomerization of the biphenyl
moiety might still be possible, we assume that the
biphenyl moiety is fixed in the most stable conformation,
as already suggested by us before.14 The interconversion
of the biphenyl moiety from R to S seems to be inhibited
by the coordination to the Rh(I) center or by the ligand
backbone. Ligands 1f and 1g each give rise to a single
Rh complex, as can be concluded from HP NMR and HP-
IR.
Asym m etr ic Hyd r ofor m yla tion of Styr en e. Com-
plexes RhH(CO)2(ligand 1) have been used as catalysts
in the asymmetric hydroformylation of styrene. The
results are given in Table 2. 2-Phenylpropanal 8
(branched aldehyde) was obtained with moderate enan-
tioselectivity (Scheme 3). Regioisomer 9 (linear alde-
hyde) was formed in relatively small amounts. Styrene
as a substrate has a preference for the formation of the
branched aldehyde due to the stability of the intermedi-
ate benzylic rhodium species, induced by the formation
of a stable η3-complex.2 Other products, resulting from
hydrogenation or polymerization of styrene, were not
observed.
(61) Hyde, E. M.; Swain, J . R.; Verkade, J . G.; Meakin, P. J . Chem.
Soc., Dalton Trans. 1976, 1196.
(62) Bo, C. Unpublished result and results in ref 59.
The effect of the temperature and the ligand-to-
rhodium ratio on the enantioselectivity was investigated

New Chiral Phosphine-Phosphite Ligands
Organometallics, Vol. 19, No. 11, 2000 2069
Ta ble 2. Asym m etr ic Hyd r ofor m yla tion of Styr en e
Ca ta lyzed by HRh (CO)2(1) a t 50 °C u n d er 20 ba r of
Syn Ga sa
The ligands were compared under “standard” condi-
tions, i.e., a temperature of 50 °C and a ligand-to-
rhodium ratio of 4. The fastest ligand, 1a , also gives the
highest ee of 63%. Use of ligands 1b and 1c resulted in
lower initial turnover frequencies, whereas ligands 1d
and 1e showed almost equal activity as 1a , but did not
yield high enantioselectivities (9% and 18%, respec-
tively). Ligand 1f consisting of a stereogenic binaphthol
with bulky trimethylsilyl substituents at the ortho-
positions results in a high reaction rate and moderate
enantioselectivity (run 17). Due to the conformation of
the binaphthol group, ligand 1f probably causes less
steric hindrance at the rhodium complex compared to
RhH(CO)2(ligand 1a ), and therefore, it is more reactive.
Inversion of the stereocenter of the binaphthol moiety
in ligand 1g resulted in a lower reaction rate and low
enantioselectivity (run 18).
The results of ligands 1 in the hydroformylation of
styrene can be summarized as follows:
(1) A large group attached to the backbone is impor-
tant to obtain a high ee. The phenyl group of ligand 1e
has a larger influence than the methyl group of ligand
1d .
(2) Introduction of a phosphine with a stereogenic
phosphorus atom (1a and 1b) enhances the ee remark-
ably. The naphthyl group of ligand 1a and the o-anisyl
group of ligand 1b have a large effect on the enantiose-
lectivity. Apparently, the combination of the substituent
at the stereogenic phosphine and the stereocenter in the
backbone creates a complex that induces enantioselec-
tivity. The stereogenic phosphine is important, since the
corresponding achiral ligand 1e does not yield a high
enantioselectivity.
entry
no.
T, time,
conv,
%
ee,
%
c
d
e
f
g
ligand
°C
h
L/Rh
b/l TOF
1
2
3
4
5
6
7
8
9
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
(SP,SC)-1a
50
40
25 237
24
24
4
4
4
4
1
2
5
10
2
4
5
4
5
10
4
4
4
4
55
13
29
41
50
16
12
14
5
24
2
20
7
11
15
15
8
10
16
18
h
h
20
h
25
h
h
45 63 (S)
10 60 (S)
2
59 (S)
153 46 (S)
88 6 (S)
60
50
50
50
50
50b
50
50b
50
50
50
50b
50
5
4
6
6
6
5
25
3
15
6
6
95 34 (S)
39 59 (S)
42 41 (S)
17 51 (S)
18 57 (S)
12 48 (S)
28 22 (R)
24 33 (R)
24 28 (R)
10 (SP,SC)-1b
11 (SP,SC)-1b
12 (SP,RC)-1c
13 (SP,RC)-1c
14 (SP,RC)-1c
15 (SC)-1d
16 (SC)-1e
17 (SP,SC,Rax)-1f 50
18 (SP,SC,Sax)-1g 50
7
17
25
18
19
41
69
95
26
18
2
9
49
9 (R)
56 18 (S)
111 40 (S)
8
25
4 (S)
a
b
Styrene to catalyst molar ratio is 2000. Catalyst formation
period 1-3 h. c Ligand-to-rhodium ratio. Percent conversion of
d
styrene. e Branched to linear aldehydes ratio. f TOF in mol styrene
(mol Rh)-1 h-1 determined at the end of the reaction time by GC.
g
Enantiomeric excess. Absolute configurations are drawn in
parentheses. Could not be determined, because peak was too
small compared to styrene peak.
h
Sch em e 3
using ligands 1a , 1b, and 1c (runs 1-15). The ratio of
H2 and CO was kept constant.17 Rh(acac)(CO)2 was the
catalyst precursor of choice, since other precursors were
reported to give lower enantioselectivities.17 A satisfac-
tory branched over linear ratio (>92%) and a moderate
ee (63%, 55% conversion) were achieved in toluene,
under H2/CO ) 10 bar/10 bar at 50 °C for 24 h (run 1).
Variation of the temperature showed that at 50 °C
the highest enantioselectivity was found. The ee of the
product decreases with increasing temperature (run 4).
At lower temperature the ee does not change signifi-
cantly (runs 2 and 3). The enantioselectivity of the
reaction is constant in time; even after a very long
reaction period of almost 10 days (run 3) the ee remains
constant. At higher temperature the activity increases,
as can be seen from the increase of the initial turnover
frequencies from 2 to 45 mol mol-1 h-1 (runs 1-3). All
the other reactions were performed at 50 °C, because
at this temperature the optimum rate and enantiose-
lectivity were found.
(3) The absolute configuration of the major enanti-
omer of the product aldehyde is always S when the
configuration of the stereocenter in the backbone is S.
Inversion of the configuration of this carbon atom
results in an inversion of the product aldehyde from S
to R. Ligand 1d is an exception to this rule. Although
the absolute configuration at the stereocenters of ligands
1d and 1c is different, the methyl substituent at the
stereocenter holds the same position as the phenyl
substituent, resulting in the same enantiomer.63 Thus,
the sense of enantiofacial selection is predominantly
controlled by the configuration of the stereocenter in the
bridge. Ligand 1c gives a lower ee due to a mismatched
combination of the stereocenters at the phosphine
moiety and the backbone.
(4) The use of ligand 1f having a (R)-binaphthyl
moiety results in an ee of 40% (S), whereas the use of
diastereomer 1g having a (S)-binaphthyl moiety results
in an ee of 4% (S). In the HP NMR spectra of [HRh-
(ligand 1a )(CO)2], the formation of only one diastereo-
mer was observed. Therefore, comparing the results
obtained with ligands 1a , 1f, and 1g, we assume that
the fast interchanging atropisomers of ligand 1a adopt
predominantly the same conformation as ligand 1f.
Thus, the conformation of the biphenyl moiety at the
phosphite is controlled by the substituent at the ster-
eocenter in the backbone.
Variation of the ligand-to-rhodium ratio shows that
for ligand 1a the optimum ee is reached at a ligand-to-
rhodium ratio of 4-5 (runs 5-8). At lower ligand-to-
rhodium ratios there may still be unmodified rhodium
species present at the concentrations used (runs 5 and
6). At higher ligand-to-rhodium ratios the ee decreases
probably due to monodentate coordination of more than
one ligand to the rhodium center. This trend was also
found for ligands 1b (runs 9-11) and 1c (runs 12-15).39
Therefore, all other ligands are tested with a ligand-to-
rhodium ratio of 4 (runs 15-18).
(5) The stereogenic group at the backbone controls not
only the configuration of the biaryl moiety at the
(63) Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem., Int. Ed.
Engl. 1966, 5, 385.

2070 Organometallics, Vol. 19, No. 11, 2000
Deerenberg et al.
Hewlett-Packard data system (Chrom-Card). FAB exact mass
spectra were recorded by the Institute of Mass Spectroscopy
of the University of Amsterdam on a J EOL J MS-SX/SX102A
spectrometer. Elemental analyses were carried out on an
Elementar Vario EL apparatus.
phosphite but also the configuration of the product.
Since the phosphite is coordinated in an equatorial
position, the equatorially coordinated group is important
for obtaining high enantioselectivities. This is in ac-
cordance with the results of Takaya et al., who also
found that for BINAPHOS the equatorially coordinating
moiety, the phosphine in this instance, has the largest
influence.17
Hyd r ofor m yla tion Exp er im en ts. Hydroformylation reac-
tions were carried out in an autoclave, equipped with glass
inner beaker, a substrate inlet vessel, a liquid sampling valve,
and a magnetic stirring rod. The temperature was controlled
by a thermocouple. In a typical experiment, the autoclave was
filled with the phosphine-phosphite ligand (0.040 mmol, P/Rh
ratio of 8). Subsequently, the autoclave was purged two times
with 20 bar of syn gas (CO:H2 ) 1:1), and Rh(acac)(CO)2 (0.010
mmol, 5.0 mL of a 2.0 mM stock solution in toluene) and
toluene (5.0 mL) were added. The autoclave was purged again
with syn gas and pressurized to the appropriate initial
pressure. After heating the autoclave to the reaction temper-
ature, the reaction mixture was stirred for 18 h to form the
active catalyst. Styrene (2.29 mL, 20.0 mmol, filtered over
neutral, activated aluminum oxide), the internal standard
decane (5.0 mmol, 0.98 mL), and toluene (6.73 mL, total
solvent volume 20.0 mL) were purged with syn gas and
brought into the autoclave. During the reaction several
samples were taken from the reaction vessel. After the desired
reaction time the autoclave was cooled and depressurized. The
toluene was evaporated, and the residue was distilled under
vacuum to remove the catalyst. A sample of the reaction
mixture was dissolved in ethanol. Sodium borohydride was
added, and the reaction mixture was stirred for 2 h at room
temperature. After quenching the reaction mixture with water,
the mixture was extracted two times with ethyl acetate/
petroleum ether 60-80 °C (1:1). The combined organic layers
were dried over magnesium sulfate and concentrated in vacuo.
About 40 µL of reduced reaction mixture was dissolved in
ethanol (10 mL) and analyzed by GC for determination of the
enantiomeric excess.
Con clu sion s
A series of novel ligands containing a stereogenic
phosphine moiety and a phosphite moiety with axial
chirality controlled by a stereocenter in the backbone
have been prepared and used as ligands in the rhodium-
catalyzed hydroformylation reaction. The ligands were
synthesized conveniently in eight steps and derivatized
systematically. In the [HRh(ligand 1)(CO)2] complexes
the ligands coordinate in an equatorial-apical coordina-
tion fashion with the phosphine moiety in the apical
position. We have shown that the equatorially coordi-
nated group, i.e., the phosphite moiety, is important for
obtaining high enantioselectivity. This is in accordance
with the results of Takaya et al., who found that also
for BINAPHOS the equatorially coordinating group has
the largest influence. Good enantioselectivities were
obtained in the asymmetric hydroformylation of styrene.
To obtain high ee’s, however, it is necessary to have two
stereocenters in the ligand. The experiments done using
the ligands containing stereogenic binaphthol groups
show a cooperative effect of the binaphthol moiety and
the group attached to the stereocenter in the backbone.
HP NMR Exp er im en ts. In a typical experiment the NMR
tube was filled with a solution of Rh(CO)2(acac) (5.0 mg, 0.019
mmol), ligand (0.019 mmol), and benzene-d6 (1.5 mL). The tube
was purged two times with 15 bar of H2/CO (1:1), pressurized
with 20 bar of H2/CO (1:1), and left overnight at 50 °C. After
cooling to room temperature the NMR spectra were recorded.
Va r ia ble Tem p er a tu r e HP NMR Exp er im en ts. For
variable-temperature high-pressure NMR experiments (295-
163 K) the HRh(L-L)(CO)2 complex was prepared in a mixture
of acetone-d6/THF-d8 ) 1:1.
HP -F T-IR Exp er im en ts. In a typical experiment the HP-
IR autoclave was filled with a solution of Rh(CO)2(acac) (3.87
mg, 0.015 mmol), ligand (0.015 mmol), and cyclohexane (15
mL). The autoclave was purged two times with 15 bar of H2/
CO (1:1), pressurized with 20 bar of H2/CO (1:1), and heated
to 50 °C. Catalyst formation was followed in time by FT-IR
and was usually complete within 1 h.
Exp er im en ta l Section
Gen er a l Meth od s. Chemicals were obtained from Acros
Chimica and Aldrich Chemical Co. All reactions were carried
out in flame-dried glasswork using standard Schlenk tech-
niques under an atmosphere of argon. Toluene was distilled
from sodium. THF and Et2O were distilled from sodium/
benzophenone. Triethylamine and diethylamine were distilled
from CaH2. PCl3 was distilled before use. For column chro-
matography silica gel 60 (230-400 mesh) purchased from
Merck was used. Compounds 3 and 4 were synthesized
following the procedures of Mezzetti20 and J uge´,19 respectively.
Melting points were determined on a Gallenkamp MFB-595
melting point apparatus in open capillaries and are uncor-
rected. NMR spectra were obtained on Bruker AMX 300 and
DRX 300 spectrometers. 31P and 13C spectra were measured
1H-decoupled unless stated otherwise. TMS was used as a
reference for 1H and 13C NMR and H3PO4 for 31P NMR.
Infrared spectra were recorded on a Nicolet 510 FT-IR spec-
trophotometer. HP-IR spectra were measured using a 20 mL
homemade stainless steel autoclave equipped with mechanical
stirring and ZnS windows. Hydroformylation reactions were
carried out in a homemade 200 mL stainless steel autoclave.
Syn gas (CO/H2, 1:1, 99.9%) was purchased from Air Liquide.
D2 was purchased from Hoekloos. Optical rotations were
measured on a Perkin-Elmer 241 polarimeter.
Com p ou n d 5a . Phosphine-borane 4 (0.599 g, 2.27 mmol),
azeotropically dried with toluene (2 × 5 mL), was dissolved in
THF (5 mL), and the solution was cooled to -25 °C. sec-BuLi
(1.68 mL of a 1.35 M/L cyclohexane solution) was added to
this solution, and stirring was continued for 10 min. The
cooling bath was removed, and the solution was stirred at room
temperature for 1 h. This solution was added dropwise to a
solution of (R)-phenyl oxirane (0.26 mL, 2.27 mmol) in THF
(5 mL) at -60 °C. The reaction mixture was allowed to warm
to room temperature overnight. The reaction mixture was
quenched with water and extracted with Et2O (2 × 30 mL).
The combined extracts were dried over MgSO4 and concen-
trated in vacuo. The residue was purified by column chroma-
tography (eluent: 1: toluene, 2: 10% EtOAc in toluene), giving
5a (0.635 g, 1.65 mmol, 73%) as a white solid. Anal. Calcd for
Gas chromatographic analyses were run on an Interscience
HR GC Mega 2 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). Enantiomeric excesses
were measured after reduction with NaBH4 to the correspond-
ing alcohols on a Carlo Erba Vega 6000 gas chromatograph,
J &W Scientific, CycloSil-B(J W) column, film thickness 0.25
µm, carrier gas 80 kPa He, FID detector equipped with a
C
25H26BOP: C, 78.14; H, 6.82. Found: C, 78.10; H, 6.91. 1H
NMR (CDCl3): δ 8.07-8.00 (m, 2H, Ar-H), 7.91-7.88 (m, 2H,
Ar-H), 7.59-7.20 (m, 13H, Ar-H), 4.69 (dd, 1H, J ) 5.4 and

New Chiral Phosphine-Phosphite Ligands
Organometallics, Vol. 19, No. 11, 2000 2071
1
7.1 Hz, CHOH), 2.52 (m, 2H, PCH2CH2), 1.94 (m, 2H, PCH2-
CH2), 1.90-0.50 (m, 3H, BH3). 31P NMR (CDCl3): δ 17.20 (br
d). 13C NMR (CDCl3): δ 143.15 (q), 133.96 (d, J CP ) 10.6 Hz),
133.77 (d, J CP ) 6.8 Hz, q), 132.89 (d, J CP ) 6.0 Hz, q), 132.70,
131.48 (d, J CP ) 9.1 Hz), 130.71, 130.49 (q), 129.08, 128.70 (d,
J CP ) 10.5 Hz), 128.38, 127.64, 126.57, 126.19 (d, J CP ) 6.0
Hz), 126.06, 125.62, 124.67, 124.14 (q), 74.13 (d, J CP ) 14.2
Hz, CH), 31.76 (CH2), 21.65 (d, J CP ) 38.2 Hz, CH2). Mp: 113-
Found: C, 75.38; H, 7.32. H NMR (CDCl3): δ 7.67-7.61 (m,
4H, Ar-H), 7.50-7.40 (m, 6H, Ar-H), 7.34-7.28 (m, 5H, Ar-
H), 4.75 (dd, 1H, J ) 6.1 and 6.4 Hz, CHOP), 2.42 (m, 1H,
PCHCH), 2.24 (m, 1H, PCHCH), 1.97 (m, 2H, PCH2), 1.60-
0.40 (m, 3H, BH3). 31P NMR (CDCl3): δ 16.80 (br d, J PB ) 58
Hz). 13C NMR (CDCl3): δ 143.30 (q), 131.98 (d, J CP ) 9.1 Hz),
131.91 (d, J CP ) 9.1 Hz), 131.01 (2 × s), 129.47 (d, J ) 24.2
Hz, q), 128.90 (d, q), 128.71, 128.58, 128.40, 127.63, 125.64,
73.99 (d, J CP ) 14.0 Hz), 31.89, 21.31 (d, J CP ) 38.3 Hz). Mp:
25
114 °C. [R]D ) -25.8 (c 1.11, CHCl3). MS HR-FAB [found
25
383.1743; C25H25B1O1P1 (M•+ - H) requires 383.1736].
Com p ou n d 5b. This compound was prepared as described
for 5a . Phosphine-borane 3 and (R)-phenyl oxirane have been
used for the synthesis of 5b. The product was purified by
column chromatography (eluent: 1: toluene, 2: 10% EtOAc
in toluene), giving 5b (0.560 g, 1.54 mmol, 96%) as a white
solid. Anal. Calcd for C22H26BO2P: C, 72.55; H, 7.20. Found:
92-93 °C; [R]D ) -36.6 (c 0.98, CHCl3). MS HR-FAB [found
334.1658; C21H24B1O1P1 (M•+) requires 335.1658].
Com p ou n d 6a . Alcohol 5a (0.605 g, 1.58 mmol) was
azeotropically dried with toluene (2 × 5 mL) and dissolved in
toluene (20 mL) and NEt3 (0.46 mL, 3.3 mmol), and the
solution was cooled to -20 °C. A solution of 3,3′,5,5′-tetra(tert-
butyl)-2,2′-bisphenol phosphorochloridite (0.787 g, 1.66 mmol)
in toluene (5 mL) was added dropwise, and the reaction
mixture was allowed to warm to room temperature overnight.
The reaction mixture was filtered over Celite and concentrated
in vacuo. Filtration over a short column of silica (eluent:
toluene) afforded 6a (1.22 g, 1.48 mmol, 94%) as a foam. 31P
NMR (CDCl3): 143.60 (s), 17.29 (br s). MS HR-FAB [found
823.4614; C53H66B1O3P2 (M•+ + H) requires 823.4580]. Com-
pound 6a was used immediately without further purification.
Com p ou n d 6b. This compound was prepared as described
for 6a . Phosphino alcohol 5b and 3,3′,5,5′-tetra(tert-butyl)-2,2′-
bisphenol phosphorochloridite have been used for the synthesis
of 6b. Filtration over a short column of silica (eluent: toluene)
afforded 6b (1.10 g, 1.37 mmol, 100%) quantitatively as a foam.
31P NMR (CDCl3): δ 144.11 (s) and 16.98 (br s). MS HR-FAB
[found 803.4467; C50H66B1O4P2 (M•+ + H) requires 803.4529].
Compound 6b was used immediately without further purifica-
tion.
Com p ou n d 6c. This compound was prepared as described
for 6a . Phosphino alcohol 5c and 3,3′,5,5′-tetra(tert-butyl)-2,2′-
bisphenol phosphorochloridite have been used for the synthesis
of 6c. Filtration over a short column of silica (eluent: toluene)
afforded 6c (1.86 g, 2.27 mmol, 100%) quantitatively as a foam.
31P NMR (CDCl3): δ 143.65 (s), 17.29 (br s). MS HR-FAB
[found 823.4627; C53H66B1O3P2 (M•+ + H) requires 823.4580].
Compound 6c was used immediately without further purifica-
tion.
1
C, 72.28; H, 7.29. H NMR (CDCl3): δ 7.96 (ddd, 1H, J ) 1.5,
7.5 and 13.5 Hz, Ar-H), 7.64 (m, 2H, Ar-H), 7.49 (m, 1H,
Ar-H), 7.44-7.24 (m, 8H, Ar-H), 7.05 (dt, 1H, J ) 1.4 and
7.4 Hz, Ar-H), 6.85 (dd, 1H, J ) 3.3 and 8.4 Hz, Ar-H), 4.66
(t, 1H, J ) 6.4 Hz, CHOH), 3.52 (s, 3H, OCH3), 2.48 (m, 2H,
PCH2CH2), 2.12 (m, 1H, PCH2CH2), 1.82 (m, 1H, PCH2CH2),
1.90-0.50 (m, 3H, BH3). 31P NMR (CDCl3): δ 16.58 (br s). 13
C
NMR (CDCl3): δ 161.12 (CH3OCq), 143.47 (q), 136.29 (d, J CP
) 14.1 Hz), 133.53, 131.35 (d, J CP ) 9.3 Hz), 130.18, 130.06
(d, J CP ) 57.7 Hz, q), 128.30, 128.07 (d, J CP ) 10.1 Hz), 127.53,
125.76, 120.98 (d, J CP ) 12.2 Hz), 115.65 (d, J CP ) 52.1 Hz, q),
110.80, 74.43 (d, J CP ) 15.0 Hz), 54.98, 32.19, 19.82 (d, J CP
)
40.1 Hz). Mp: 102-103 °C. [R]D25 ) -15.1 (c 1.25, CHCl3). MS
HR-FAB [found 363.1660; C22H25B1O2P1 (M•+ - H) requires
363.1685].
Com p ou n d 5c. This compound was prepared as described
for 5a . Phosphine-borane 4 and (S)-phenyl oxirane have been
used for the synthesis of 5c. The product was purified by
column chromatography (eluent: 1: toluene, 2: 10% EtOAc
in toluene), giving 5c (0.873 g, 2.27 mmol, 100%) quantitatively
as a white solid. Anal. Calcd for C25H26BOP: C, 78.14; H, 6.82.
Found: C, 77.90; H, 7.04. 1H NMR (CDCl3): δ 8.03 (m, 2H,
Ar-H), 7.90 (m, 2H, Ar-H), 7.59-7.20 (m, 13H, Ar-H), 4.69
(dd, 1H, J ) 5.4 and 7.1 Hz, CHOH), 2.52 (m, 2H, PCH2CH2),
1.94 (m, 2H, PCH2CH2), 1.90-0.50 (m, 3H, BH3). 13C NMR
(CDCl3): δ 143.14 (q), 134.03 (d, J CP ) 11.1 Hz), 133.75 (d,
J CP ) 6.9 Hz, q), 132.90 (d, J CP ) 5.5 Hz, q), 132.73, 131.04 (d,
J CP ) 9.0 Hz), 130.69, 130.00 (q), 129.08, 128.68 (d, J CP ) 9.8
Hz), 128.37, 127.61, 126.62, 126.20, 126.07, 125.58, 124.74 (d,
J CP ) 12.2 Hz), 123.86 (q), 74.04 (d, J CP ) 14.1 Hz), 31.82,
21.65 (d, J CP ) 38.40 Hz). 31P NMR (CDCl3): δ 17.10 (br d,
J PB ) 48 Hz). Mp: 121-122 °C. [R]D25 ) +23.9 (c 1.01, CHCl3).
Com p ou n d 6d . This compound was prepared as described
for 6a . Phosphino alcohol 5d and 3,3′,5,5′-tetra(tert-butyl)-2,2′-
bisphenol phosphorochloridite have been used for the synthesis
of 6d . Filtration over a short column of silica (eluent: toluene)
afforded 6d (0.550 g, 0.77 mmol, 65%) as a foam. 31P NMR
(CDCl3): δ 145.43 (s), 16.66 (br s). Compound 6d was used
immediately without further purification.
MS HR-EI [found 384.1786;
384.1814].
C ) requires
49H60O3P2 (M•+
Com p ou n d 6e. This compound was prepared as described
for 6a . Phosphino alcohol 5e and 3,3′,5,5′-tetra(tert-butyl)-2,2′-
bisphenol phosphorochloridite have been used for the synthesis
of 6e. Filtration over a short column of silica (eluent: toluene)
afforded 6e (1.64 g, 2.13 mmol, 97%) as a foam. 31P NMR
(CDCl3): δ 143.46, 17.10 (br s). MS HR-FAB [found 773.4435;
Com p ou n d 5d . This compound was prepared as described
for 5a . Phosphine-borane 2 and (S)-propene oxide have been
used for the synthesis of 5d . The product was purified by
column chromatography (eluent: 1: toluene, 2: 10% EtOAc
in toluene), giving 5d (0.362 g, 1.33 mmol, 57%) as a colorless
oil. 1H NMR (CDCl3): δ 7.68 (m, 4H, Ar-H), 7.42 (m, 6H, Ar-
H), 3.79 (m, 1H, CHOH), 2.47 (m, 1H, PCHCH), 2.22 (m, 1H,
PCHCH), 1.64 (m, 2H, PCH2), 0.98 (d, 3H, J ) 6.3 Hz, CH3),
1.90-0.50 (m, 3H, BH3). 31P NMR (CDCl3): δ 16.6 (br d, J )
67 Hz). 13C NMR (CDCl3): δ 131.98 (d, J CP ) 8.7 Hz), 131.88
(d, J ) 7.6 Hz), 131.03, 129.55 (d, J ) 24.9 Hz, q), 128.98 (q),
128.55 (d, J CP ) 8.4 Hz, 2C), 67.74 (d, J CP ) 14.3 Hz), 31.91,
23.12, 21.49 (d, J CP ) 38.7 Hz). [R]D25 ) -15.1 (c 1.25, CHCl3).
MS HR-FAB [found 258.1179; C16H19OP (M•+ - BH3) requires
258.1174].
C
49H64B1O3P2 (M•+ + H) requires 773.4424]. Compound 6e was
used immediately without further purification.
Com p ou n d 1a . Phosphine-borane 6a (1.15 g, 1.40 mmol)
was dissolved in diethylamine (20 mL) and stirred overnight
at 50 °C. The reaction mixture was concentrated in vacuo.
Filtration over silica (eluent: toluene) gave 1a (1.02 g, 1.26
mmol, 90%) as a white solid. Anal. Calcd for C54H62O3P2: C,
1
78.68; H, 7.73. Found: C, 78.75; H, 7.65. H NMR (CDCl3): δ
8.41 (dd, 1H, J ) 4.4 and 8.0 Hz, Ar-H), 7.82 (dd, 2H, J ) 6.8
and 7.5 Hz, Ar-H), 7.43-7.11 (m, 18H, Ar-H), 5.18 (m, 1H,
CHOP), 2.06 (m, 2H, PCH2 CHH′), 1.88 (m, 2H, PCH2 CHH′),
1.38 (s, 9H, tert-butyl), 1.34 (s, 9H, tert-butyl), 1.28 (s, 9H, tert-
butyl), 1.24 (s, 9H, tert-butyl). 31P NMR (CDCl3): δ 143.75 (s)
and -26.75 (s). 13C NMR (CDCl3): δ 146.10 (q), 145.84 (q),
140.65 (q), 139.95 (q), 139.68 (q), 135.43 (d, J ) 20.4 Hz, q),
134.40 (q), 133.33, 132.57 (2 × d, J CP ) 26.4 Hz, q), 132.36 (d,
Com p ou n d 5e. This compound was prepared as described
for 5a . Phosphine-borane 2 and (R)-phenyl oxirane have been
used for the synthesis of 5e. The product was purified by
column chromatography (eluent: 1: toluene, 2: 10% EtOAc
in toluene), giving 5e (1.56 g, 4.67 mmol, 100%) quantitatively
as a white solid. Anal. Calcd for C21H24BOP: C, 75.47; H, 7.24.

2072 Organometallics, Vol. 19, No. 11, 2000
Deerenberg et al.
J CP ) 18.9 Hz, q), 129.59-123.83 (CH-arom.), 78.59 (dd, J CP
) 8.7 and 15.2 Hz), 34.97 (q), 34.42 (q), 34.23 (d, CH2), 31.33,
30.72 (d, J ) 7.7 Hz), 22.18 (d, J CP ) 12.2 Hz, CH2). Mp: 91.5-
of 1e. Filtration over silica (eluent: toluene) gave 1e (1.35 g,
1.78 mmol, 86%) as a white solid. Anal. Calcd for C49H60O3P2:
1
C, 77.54; H, 7.97. Found: C, 77.36; H, 8.06. H NMR (CDCl3):
25
92.5 °C. [R]D ) +63.1 (c 1.0, CHCl3). MS HR-FAB [found
δ 7.39 (dd, 2H, J ) 2.4 and 4.6 Hz, Ar-H), 7.27-7.24 (m, 13H,
Ar-H), 7.19 (d, 1H, J ) 2.3 Hz, Ar-H), 7.16 (d, 1H, J ) 2.4
Hz, Ar-H), 7.12 (m, 2H, Ar-H), 5.17 (m, 1H, CHOP), 2.01
(m, 2H, PCH2CH2), 1.77 (m, 2H, PCH2CH2), 1.38 (s, 9H, tert-
butyl), 1.35 (s, 9H, tert-butyl), 1.29 (s, 9H, tert-butyl), 1.27 (s,
9H, tert-butyl). 31P NMR (CDCl3): δ 143.88 (s) and -15.29 (s).
13C NMR (CDCl3): δ 146.10 (q), 145.84 (q), 140.59 (q), 139.97
(d, q), 139.66 (q), 138.19 (q), 137.91 (d, q), 132.74 (q), 132.51
(d, J CP ) 18.9 Hz, Ar-C), 132.32 (d, J CP ) 18.9 Hz, Ar-C),
132.32 (q), 128.30, 128.17, 128.08, 127.99, 127.64, 126.98,
126.24 (d, J CP ) 9.1 Hz), 123.96 (d, J CP ) 17.4 Hz), 78.61 (dd,
J CP ) 8.5 and 14.8 Hz), 34.99 (q), 34.42 (q), 34.03 (CH2), 31.36,
31.33, 30.80 (d, J ) 3.2 Hz), 30.70, 22.72 (d, J ) 12.2 Hz, CH2),
31.32, 30.76 (d, J CP ) 10.7 Hz), 29.49, 20.60 (d, J CP ) 37.9
Hz). Mp: 178-179 °C. [R]D25 ) +40.0 (c 1.01, CHCl3). MS HR-
FAB [found 759.4080; C49H61O3P2 (M•+ + H) requires 759.4096].
809.4196; C54H63O3P2 (M•+ + H) requires 809.4252].
Com p ou n d 1b. This compound was prepared as described
for 1a . Phosphine-borane 6b has been used for the synthesis
of 1b. Filtration over silica (eluent: toluene) gave 1b (0.99 g,
1.25 mmol, 96%) as a white solid. Anal. Calcd for C50H62O4P:
1
C, 76.11; H, 7.93. Found: C, 76.07; H, 8.06. H NMR (CDCl3):
δ 7.52 (d, 1H, J ) 2.2 Hz, Ar-H), 7.41-7.12 (m, 14H, Ar-H),
6.92-6.76 (m, 3H, Ar-H), 5.16 (m, 1H, CHOH), 3.69 (s, 3H,
OCH3), 1.99 (m, 2H, PCH2 CHH′), 1.79 (m, 2H, PCH2 CHH′),
1.37 (s, 9H, tert-butyl), 1.34 (s, 9H, tert-butyl), 1.28 (s, 9H, tert-
butyl), 1.25 (s, 9H, tert-butyl). 31P NMR (CDCl3): δ 144.13 (s)
and -24.81 (s). 13C NMR (CDCl3): δ 160.99 (q), 146.05 (q),
145.80 (q), 140.80 (q), 139.96 (q), 139.68 (q), 137.12 (q), 132.75
(d, J ) 19.6 Hz), 132.52 (d, J ) 19.6 Hz), 131.94-110.04 (CH-
arom.), 78.80 (dd, J CP ) 8.8 and 15.7 Hz), 55.13, 34.98, 34.68
(d), 34.41, 31.32, 30.81, 30.69, 21.01 (d, J CP ) 11.6 Hz). Mp:
Com p ou n d 1f. Alcohol 5a (0.220 g, 0.573 mmol) was
azeotropically dried with toluene (2 × 2 mL) and dissolved in
toluene (10 mL) and NEt3 (0.160 mL, 1.16 mmol), and the
solution was cooled to -20 °C. A solution of freshly prepared
(R)-3,3′-bis(trimethylsilyl)-2,2′-binaphthol phosphorochloridite
(0.573 mmol) in toluene (5 mL) was added dropwise, and the
reaction mixture was allowed to warm to room temperature
overnight. The reaction mixture was filtered over Celite and
concentrated in vacuo. Filtration over a short column of silica
(eluent: toluene) afforded 6f as a foam. 31P NMR (CDCl3):
143.67 (s), 18.20 (br s). Phosphine-borane 1f was subsequently
prepared as described for 1a . The product was purified by
column chromatography (toluene) giving 1f (0.200 g, 0.242
mmol, 42%) as a foam. Anal. Calcd for C51H50O3P2Si2: C, 73.88;
H, 6.08. Found: C, 73.47; H, 6.39. 1H NMR (CDCl3): δ 8.35
(dd, 1H, J ) 4.5 and 7.6 Hz, Ar-H), 8.00-7.75 (m, 6H, Ar-
H), 7.46-7.04 (m, 20H, Ar-H), 4.72 (m, 1H, CHOP), 1.80 (m,
2H, PCH2CH2), 1.52 (m, 2H, PCH2CH2), 0.35 (s, 9H, Si(CH3)3),
0.20 (s, 9H, Si(CH3)3). 31P NMR (CDCl3): δ 145.20 (s) and
25
79.0-80.5 °C. [R]D ) +41.8 (c 1.11, CHCl3). MS HR-FAB
[found 788.4174; C50H63O4P2 (M•+ + H) requires 759.4202].
Com p ou n d 1c. This compound was prepared as described
for 1a . Phosphine-borane 6c has been used for the synthesis
of 1c. Filtration over silica (eluent: toluene) gave 1c (1.83 g,
2.26 mmol, 100%) as a white solid. Anal. Calcd for C54
H
-
62O3P2: C, 78.68; H, 7.73. Found: C, 78.32; H, 7.90. 1H NMR
(CDCl3): δ 8.43 (m, 1H, Ar-H), 7.82 (dd, 2H, J ) 8.0 and 10.6
Hz, Ar-H), 7.49-7.38 (m, 4H, Ar-H), 7.30-7.15 (m, 14H, Ar-
H), 5.24 (m, 1H, CHOP), 2.16-1.83 (m, 4H, PCH2CH2), 1.40
(s, 9H, tert-butyl), 1.36 (s, 9H, tert-butyl), 1.31 (s, 9H, tert-
butyl), 1.27 (s, 9H, tert-butyl). 31P NMR (CDCl3): δ 143.81 (s),
-27.26 (s). 13C NMR (CDCl3): δ 149.62 (q), 146.16 (q), 145.91
(q), 145.22 (q), 142.82 (q), 140.59 (q), 140.01 (q), 139.72 (q),
137.51 (d, J CP ) 12.8 Hz, q), 135.38 (d, J CP ) 21.1 Hz, q), 134.89
(d, J CP ) 16.6 Hz, q), 133.33 (d, J CP ) 4.5 Hz, q), 132.81 (q),
132.60 (d, J CP ) 18.9 Hz, CH), 132.39 (q), 132.30 (q), 129.47-
123.70 (CH-arom.), 78.60 (dd, J CP ) 8.4 and 15.3 Hz), 35.02
(q), 34.46 (q), 34.24 (d, J ) 8.7 Hz, CH2), 31.42, 30.80 (d, J )
25
25
11.8 Hz), 22.32 (d, J CP ) 12.2 Hz, CH2). Mp: 91-91.5 °C. [R]D
-26.48 (s). Mp: 101-102 °C. [R]D ) -350 (c 1.01, CHCl3).
MS HR-FAB [found 829.2876; C51H51O3P2Si2 (M•+ + H) re-
) -25.8 (c 0.96, CHCl3). MS HR-FAB [found 809.4210;
C
53H63O3P2 (M•+ + H) requires 809.4252].
quires 829.2852].
Com p ou n d 1d . This compound was prepared as described
Com p ou n d 1g. This compound was prepared as described
for 1f. Phosphino alcohol 5e and (S)-3,3′-bis(trimethylsilyl)-
2,2′-binaphthol phosphorochloridite (0.573 mmol) have been
used for the synthesis of 6e. Filtration over a short column of
silica (eluent: toluene) afforded 6g as a foam. 31P NMR
(CDCl3): 143.67 (s), 18.23 (br s). Phosphine-borane 1g was
subsequently prepared as described for 1a . The product was
purified by column chromatography (toluene) giving 1g (0.245
g, 0.296 mmol, 52%) as a foam. Anal. Calcd for C51H50O3P2Si2:
for 1a . Phosphine-borane 6d has been used for the synthesis
of 1d . Filtration over silica (eluent: toluene) gave 1d (1.83 g,
2.26 mmol, 100%) as a white solid. Anal. Calcd for C44
H
-
58O3P2: C, 75.83; H, 8.39. Found: C, 75.80; H, 8.49. 1H NMR
(CDCl3): δ 7.45 (dd, 2H, J ) 2.4 and 4.1 Hz, Ar-H), 7.42-
7.37 (m, 10H, Ar-H), 7.32-7.29 (dd, 2H, J ) 2.4 and 4.1 Hz,
Ar-H), 4.53 (ddq, 1H, J ) 6.1, 6.1 and 14.5, CHOP), 2.18 (ddd,
1H, J ) 5.7, 11.5 and 13.2 Hz, PCH2CHH′), 2.04 (ddd, 1H, J
) 5.7, 10.8 and 13.8 Hz, PCH2CHH′), 1.74 (m, 2H, PCH2), 1.49
(s, 9H, tert-butyl), 1.46 (s, 9H, tert-butyl), 1.37 (s, 9H, tert-
butyl), 1.37 (s, 9H, tert-butyl), 1.25 (d, 3H, J ) 6.1 Hz, CH3).
31P NMR (CDCl3): δ 145.68 (s), -15.19 (s). 13C NMR (CDCl3):
δ 160.98 155.31 (d, J CP ) 8.3 Hz), 142.37 (d, J CP ) 13.6 Hz),
141.71, 141.62, 141.56, 141.49, 140.52, 136.46 (d, J CP ) 14.3
Hz), 133.55, 131.19 (d, J CP ) 9.8 Hz), 130.45, 130.07, 129.68,
128.82, 128.11, 128.07, 128.02, 127.93, 127.76, 126.88, 125.09,
120.91 (d, J CP ) 9.8 Hz), 114.76, 113.96 (d, J CP ) 14.3 Hz),
112.65 (d, J CP ) 13.6 Hz), 110.57, 78.28 (dd, J CP ) 10.8 and
17.7 Hz), 55.39, 54.69, 35.03, 31.63, 30.60, 29.49, 21.24, 19.32
1
C, 73.88; H, 6.08. Found: C, 71.76; H, 6.71. H NMR (CDCl3):
δ 8.37 (dd, 1H, J ) 4.5 and 8.1 Hz, Ar-H), 8.08-7.78 (m, 6H,
Ar-H), 7.47-7.03 (m, 18H, Ar-H), 6.82 (m, 2H, Ar-H), 4.95
(m, 1H, CHOP), 2.10 (m, 2H, PCH2CH2), 1.77 (m, 2H, PCH2-
CH2), 0.30 (s, 9H, Si(CH3)3), 0.17 (s, 9H, Si(CH3)3). 31P NMR
25
(CDCl3): 143.88 (s) and -27.09 (s). Mp: 97.5-98.5 °C. [R]D
) +353 (c 1.01, CHCl3). MS HR-FAB [found 829.2870;
C
51H51O3P2Si2 (M•+ + H) requires 829.2852].
Ack n ow led gm en t. Financial support from CW/
25
(d, J CP ) 39.9 Hz). Mp: 64-65 °C. [R]D ) -10.6 (c 1.01,
STW is gratefully acknowledged. Dr. K. Nozaki is
gratefully acknowledged for supplying BINAPHOS. Dr.
C. Bo is gratefully acknowledged for the calculations.
CHCl3). MS HR-FAB [found 697.3957; C44H59O3P2 (M•+ + H)
requires 697.3939].
Com p ou n d 1e. This compound was prepared as described
for 1a . Phosphine-borane 6e has been used for the synthesis
OM990760M