Chiral phosphine-phosphite ligands with a substituted ethane backbone. influence of conformational effects in rhodium-catalyzed asymmetric olefin hydrogenation and hydroformylation reactions

Article abstract of DOI:10.1021/om1003545

A family of chiral (3,3′-di-tert-butyl-5,5′,6,6′- tetramethyl-2,2′-biphenol-derived) phosphine-phosphite ligands (P-OP) with a substituted ethane backbone has been synthesized and the performance of these ligands in the Rh-catalyzed enantioselective hydrogenation and hydroformylation of several representative olefins analyzed. Corresponding cationic rhodium complexes provide highly enantioselective catalysts for the hydrogenation of methyl (Z)-α-acetamidocinnamate (MAC) and dimethyl itaconate. The catalyst comparison indicates that, for the two substrates, product configuration is determined by the configuration of the phosphite. Regarding matching and mismatching effects in these hydrogenations, small effects were observed in the reduction of MAC, while for the itaconate the bigger difference between the matched and mismatched cases was of 21% ee. On the other hand, Rh catalysts based on P-OP ligands showed good levels of activity and regioselectivity in the hydroformylation of styrene and allyl cyanide, while moderate enantioselectivities were obtained. Participation of the two stereogenic elements has been observed in these reactions, and their mismatched combination leads to cancellation of enantioselectivity. To further investigate the influence of the ligand backbone in the course of these reactions, structures of rhodium model complexes Rh(Cl)(CO)(P-OP) were analyzed by DFT methods. The results obtained indicate the existence of two types of preferred conformations, whose relative stability depend on the backbone nature. Comparison of structures of the more stable conformers for each ligand indicates that the orientation of the biaryl phosphite group with respect to the coordination plane does not vary substantially along the series. Differently, the position of the phenyl phosphine substituents greatly depends on the backbone. On the basis of these observations it has been concluded that chiral induction in the hydrogenation is very predominantly due to the phosphite part of the ligand. Alternatively, conformation of the phosphine group has a great influence on enantioselectivity in the hydroformylation reactions, and even reversal of product configuration was observed between catalysts with an opposite axial equatorial arrangement of Ph phosphine substituents.

Full text of DOI:10.1021/om1003545

Organometallics 2010, 29, 5791–5804 5791
DOI: 10.1021/om1003545
Chiral Phosphine-Phosphite Ligands with a Substituted Ethane
Backbone. Influence of Conformational Effects in Rhodium-Catalyzed
Asymmetric Olefin Hydrogenation and Hydroformylation Reactions
Inmaculada Arribas,† Sergio Vargas,† Miguel Rubio,†
†
Andres Suarez, Carmen Domene, Eleuterio Alvarez, and Antonio Pizzano*
‡
†
,†
ꢀ
ꢀ
ꢀ
†
´
´
Instituto de Investigaciones Quımicas, Consejo Superior de Investigaciones Cientıficas and Universidad de
ꢀ
Sevilla, Avenida Americo Vespucio no. 49, Isla de la Cartuja. 41092 Sevilla, Spain, and
‡Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford,
South Parks Road, Oxford OX1 3QZ, United Kingdom
Received April 27, 2010
A family of chiral (3,30-di-tert-butyl-5,50,6,60-tetramethyl-2,20-biphenol-derived) phosphine-
phosphite ligands (P-OP) with a substituted ethane backbone has been synthesized and the performance
of these ligands in the Rh-catalyzed enantioselective hydrogenation and hydroformylation of several
representative olefins analyzed. Corresponding cationic rhodium complexes provide highly enantiose-
lective catalysts for the hydrogenation of methyl (Z)-R-acetamidocinnamate (MAC) and dimethyl
itaconate. The catalyst comparison indicates that, for the two substrates, product configuration
is determined by the configuration of the phosphite. Regarding matching and mismatching effects
in these hydrogenations, small effects were observed in the reduction of MAC, while for the itaconate the
bigger difference between the matched and mismatched cases was of 21% ee. On the other hand, Rh
catalysts based on P-OP ligands showed good levels of activity and regioselectivity in the hydroformyla-
tion of styrene and allyl cyanide, while moderate enantioselectivities were obtained. Participation of the
two stereogenic elements has been observed in these reactions, and their mismatched combination leads to
cancellation of enantioselectivity. To further investigate the influence of the ligand backbone in the course
of these reactions, structures of rhodium model complexes Rh(Cl)(CO)(P-OP) were analyzed by DFT
methods. The results obtained indicate the existence of two types of preferred conformations, whose
relative stability depend on the backbone nature. Comparison of structures of the more stable conformers
for each ligand indicates that the orientation of the biaryl phosphite group with respect to the co-
ordination plane does not vary substantially along the series. Differently, the position of the phenyl
phosphine substituents greatly depends on the backbone. On the basis of these observations it has been
concluded that chiral induction in the hydrogenation is very predominantly due to the phosphite part of
the ligand. Alternatively, conformation of the phosphine group has a great influence on enantioselectivity
in the hydroformylation reactions, and even reversal of product configuration was observed between
catalysts with an opposite axial equatorial arrangement of Ph phosphine substituents.
Introduction
the complexity of the catalytic system.2 However, they can be
reduced by an effective differentiation between coordinating
functionalities by steric3 or electronic effects,4 or both.5
Considering the simplification of an asymmetric catalytic
system by electronic factors, phosphine-phosphites (P-OP)
are particularly interesting ligands. These compounds possess
two coordinating fragments with dissimilar donor abilities, as
the phosphine is a good σdonor, while the phosphite is a poorer
σ donor and a stronger π acceptor.6a This class of ligands was
Chiral heterobifunctional ligands constitute an important
class of ligands for asymmetric catalysis, and they have
provided a vast range of applications in reactions such as
hydrogenation, hydroformylation, and allyl substitution.1 In
comparison with C2-symmetric ligands, heterobifunctional
ligands double the number of reaction intermediates, increasing
*Corresponding author. E-mail: pizzano@iiq.csic.es.
(1) (a) Bell, S.; Wustenberg, B.; Kaiser, S.; Menges, F.; Netscher, T.;
Pfaltz, A. Science 2006, 311, 642. (b) Cabrera, S.; Arrayas, R. G.; Alonso, I.;
Carretero, J. C. J. Am. Chem. Soc. 2005, 127, 17938. (c) Cui, X. H.; Ogle,
(3) Hoge, G.; Wu, H.-P.; Kissel, W. S.; Pflum, D. A.; Greene, D. J.;
Bao, J. J. Am. Chem. Soc. 2004, 126, 5966.
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J. Am. Chem. Soc. 2000, 122, 7905. (b) Evans, D. A.; Campos, K. R.; Tedrow,
J. S.; Michael, F. E.; Cagne, M. R. J. Am. Chem. Soc. 2003, 125, 3534.
(c) RajanBabu, T. V.; Radetich, B.; You, K. K.; Ayers, T. A.; Casalnuovo, A. L.;
Calabrese, J. C. J. Org. Chem. 1999, 64, 3429.
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r
2010 American Chemical Society
Published on Web 10/20/2010
pubs.acs.org/Organometallics

5792 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
Scheme 1
Scheme 2
Figure 1
Chart 1
the reactivity of an enantioselective catalyst. Important
parameters such as bite angle or ligand flexibility depend
on the precise structure of the backbone and have a profound
influence on catalyst performance.11,12 In addition, if stereo-
genic elements are present in the ligand backbone, their
position and configuration strongly affect the structure of
the metal environment. For instance, diarylphosphino ligands
such as BDPP13 and CHIRAPHOS (Figure 1)14 display an
asymmetric edge/face arrangement of the P-Ph groups, and
this feature is widely recognized as a powerful element for
asymmetric induction.15 From these considerations we ratio-
nalized that a systematic tuning of the orientation of the Ph
substituents of a PPh2 group can be done with an appropriate
substitution in the backbone, while the influence on an
atropisomeric phosphite group should be small.16 This ap-
proach is complementary to that shown previously in ligands
with P-stereogenic phosphine fragments and conformation-
ally flexible phosphite groups.8a
For the synthesis of the desired backbone-substituted
ligands, a set of chiral hydroxyphosphines have been pre-
pared according to literature procedures. First, (R)-2-diphe-
nylphosphinopropanol ((R)-3) was synthesized by a reaction
between an appropriate tosylate and diphenylphosphine
borane,17 followed by deprotection of the hydroxyl and
phosphino groups (Scheme 1). Second, 2-diphenylphosphi-
no ethanols substituted at position 1 (4-6, Scheme 2) were
prepared by opening the corresponding epoxides with
lithium diphenylphosphide followed by protonation with
NH4Cl.8,9a
introduced by Takaya and Nozaki and applied with outstanding
results in enantioselective olefin hydroformylation reactions.7
Later, Claver and van Leeuwen demonstrated the suitability of
P-OP ligands for rhodium catalyzed olefin hydrogenations.8
Since then, the number of phosphine-phosphite ligands de-
scribed in the literature9 as well as the range of their applications
in catalytic hydrogenation reactions have grown considerably.10
In previous contributions, we have focused on P-OP
ligands with simple benzene and ethane backbones (1, 2).6
Due to the importance of backbone nature in catalyst per-
formance, we have reported here the preparation of a family
of chiral P-OP derivatives with a complete range of ethane-
substituted backbones. These ligands have been examined in
representative asymmetric hydrogenation and hydroformy-
lation reactions to analyze the influence of the backbone
nature in these transformations. In addition, detailed com-
putational studies by DFT methods of suitable models,
complemented with structural investigations by NMR and
X-ray crystallography, have been performed to investigate
the conformational preferences for each ligand.
Results and Discussion
Design and Synthesis of Ligands. The structure of the
backbone of a chiral chelating ligand is a crucial aspect in
ꢀ
ꢀ
(6) (a) Suarez, A.; Mendez-Rojas, M. A.; Pizzano, A. Organometal-
ꢀ
lics 2002, 21, 4611. (b) Suarez, A.; Pizzano, A. Tetrahedron: Asymmetry
2001, 12, 2501. (c) Vargas, S.; Rubio, M.; Suarez, A.; del Río, D.; Alvarez, E.;
Pizzano, A. Organometallics 2006, 25, 961.
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(7) (a) Sakai, N.; Mano, S.; Nozaki, K.; Takaya, H. J. Am. Chem.
Soc. 1993, 115, 7033. (b) Nozaki, K.; Sakai, N.; Nanno, T.; Higashijima, T.;
Mano, S.; Horiuchi, T.; Takaya, H. J. Am. Chem. Soc. 1997, 119, 4413.
(11) (a) van Leeuwen, P. W. N. M; Kamer, P. C. J.; Reek, J. N. H.;
Dierkes, P. Chem. Rev. 2000, 100, 2741. (b) Freixa, Z.; van Leeuwen, P. W.
N. M. Dalton Trans. 2003, 1890. (c) Cobley, C. J.; Froese, R. D. J.; Klosin, J.;
Qin, C.; Whiteker, G. T.; Abboud, K. A. Organometallics 2007, 26, 2986.
ꢁ
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(8) (a) Pamies, O.; van Strijdonck, G. P. F.; Dieguez, M.; Deerenberg,
S.; Net, G.; Ruiz, A.; Claver, C.; Kamer, P. C. J.; van Leeuwen, P. W. N.
ꢁ
ꢀ
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M. J. Org. Chem. 2001, 66, 8867. (b) Pamies, O.; Dieguez, M.; Net, G.;
Ruiz, A.; Claver, C. J. Org. Chem. 2001, 66, 8364–8369.
(12) Burk, M. J.; Pizzano, A.; Martın, J. A.; Liable-Sands, L. M.;
Rheingold, A. L. Organometallics 2000, 19, 250.
(9) (a) Blume, F.; Zemolka, S.; Fey, T.; Kranich, R.; Schmalz, H.-G.
Adv. Synth. Catal. 2002, 344, 868. (b) Kranich, R.; Eis, K.; Geis, O.; M€uhle,
S.; Bats, J. W.; Schmalz, H.-G. Chem.;Eur. J. 2000, 6, 2874. (c) Yan, Y. J.;
Chi, Y. X.; Zhang, X. Tetrahedron: Asymmetry 2004, 15, 2173. (d) Jia, M.;
Li, X. S.; Lam, W. S.; Kok, S. H. L.; Xu, L. J.; Lu, G.; Yeung, C.-H.; Chan,
A. S. C. Tetrahedron: Asymmetry 2004, 15, 2273. (e) Velder, J.; Robert, T.;
(13) BDPP/SKEWPHOS: MacNeil, P. A.; Roberts, N. K.; Bosnich,
B. J. Am. Chem. Soc. 1981, 103, 2273.
(14) CHIRAPHOS: Fryzuk, M. D.; Bosnich, B. J. Am. Chem. Soc.
1977, 99, 6263.
(15) Gridnev, I. D.; Imamoto, T. Acc. Chem. Res. 2004, 37, 633.
(16) We have previously observed that conformational mobility of
coordinated 2a (Ar = Ph) did not affect the phosphite orientation, as
two preferred conformers of [Ir(Cl)(CO)(2a)] showed superimposable
phosphite groups, while the orientation of the Ph substituents of the
phosphino group differs considerably among the two conformers.
(17) (a) McKinstry, L.; Livinghouse, T. Tetrahedron Lett. 1994, 35,
9319. (b) McKinstry, L.; Livinghouse, T. Tetrahedron 1995, 51, 7655.
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Weidner, I.; Neudorfl, J.-M.; Lex, J.; Schmalz, H.-G. Adv. Synth. Catal.
2008, 350, 1309.
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(10) (a) Fernandez-Perez, H.; Pericas, M. A.; Vidal-Ferran, A. Adv.
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Synth. Catal. 2008, 350, 1984. (b) Rubio, M.; Vargas, S.; Suarez, A.;
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Alvarez, E.; Pizzano, A. Chem.;Eur. J. 2007, 13, 1821. (c) Vargas, S.;
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Suarez, A.; Alvarez, E.; Pizzano, A. Chem.;Eur. J. 2008, 14, 9856.

Article
Organometallics, Vol. 29, No. 22, 2010 5793
Scheme 3
Table 1. MAC Hydrogenationa
entry
precatalyst
P-OP
% ee (conf)
1
2
3
4
5
6
7
8
[Rh(COD)2]BF4 + P-OP
(S)-2a
99 (R)
95 (R)
97 (S)
93 (R)
99 (S)
95 (R)
99 (R)
95 (R)
(R,S)-7
(R,R)-7
(R,S)-8
(R,R)-8
(R,S)-9
(S,S)-9
(S)-10
a All hydrogenations were completed under the conditions specified.
Reactions were carried out at room temperature with an initial hydrogen
pressure of 4 bar, in methylene chloride at a S/C = 100, with a Rh/P-OP
1:1.1 ratio. Reaction time was 24 h. Conversion and configuration were
determined as previously.6a
Table 2. Hydrogenation of Dimethyl Itaconatea
entry
precatalyst
P-OP
% ee (conf)
1
2
3
4
5
6
7
8
[Rh(COD)(P-OP)]BF4
[Rh(COD)2]BF4 + P-OP
(S)-2
(S)-2
99 (S)
99 (S)
99 (S)
80 (R)
95 (S)
74 (R)
99 (S)
93 (S)
89 (S)
99 (S)
(R,S)-7
(R,R)-7
(R,S)-8
(R,R)-8
(R,S)-9
(S,S)-9
(S)-10
(S)-2
9
10b
a All hydrogenations were completed under conditions specified.
Reactions were carried out at room temperature with an initial hydrogen
pressure of 4 bar, in methylene chloride at a S/C = 100 unless otherwise
noted. Reaction time was 24 h. Conversion and configuration were
determined as previously.6b b S/C = 5000, reaction time 12 h.
Scheme 4
adduct, while further condensation followed by deboronation
led to the desired compounds 7.
Asymmetric Hydrogenation Reactions. We have next stud-
ied the influence of backbone substitution in several cata-
lytic hydrogenations. First, a series of hydrogenation re-
actions of methyl (Z)-R-acetamidocinnamate (MAC) 13
have been performed (Scheme 4, Table 1). For these reac-
tions, catalyst precursors prepared in situ from [Rh(COD)2]
BF4 and a stoichiometric amount of the P-OP ligand were
used. All catalysts completed the reactions under the condi-
tions specified, and as observed before for MAC hydrogena-
tion with [Rh(COD)(1a)]BF4,6a an S phosphite fragment
gives an R product (and conversely an S product for an R
phosphite). Interestingly, high enantioselectivities, between
93 and 99% ee, were obtained with all catalysts. Therefore, a
low dependence of catalyst performance on backbone struc-
ture has been observed.
Scheme 5
Dimethyl itaconate hydrogenation was next examined
(Table 2). As a first observation, phosphite configuration
again determines product configuration. Here, an S phos-
phite gives an S product. These results indicate an analogous
stereochemical hydrogen addition for both substrates.
Analysis of the results obtained indicates the existence of
matching and mismatching effects for several couples of
diastereomeric catalysts. For instance, in the case of catalysts
based on ligands 7, a very high ee was observed for the R,S
diastereomer (entry 3), whereas the R,R derivative contains
the mismatched combination of stereogenic elements and
produced a lower ee (entry 4). The substitution of the Ph
group by a Me one provides a less marked effect (entries 7
and 8). By comparison, if the Me group is in the R position to
From the hydroxyphosphines, phosphine-phosphites can
be prepared by a simple condensation with a chlorophos-
phite in the presence of a base (Scheme 3). In the case of deri-
vatives of compound (R)-6, due to the presence of impurities,
the phosphine was first protected as the corresponding borane

5794 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
Table 3. Hydroformylation of Styrenea
standard conditions (Table 3). Only the catalyst based on the
more encumbered ligand 10 gave a lower conversion (entry 9).
In addition, the regioselectivity was high and nearly con-
stant along the series. Regarding the configuration of the
product, an S phosphite fragment seems to favor aldehyde
(R)-18, as this is the preferred enantiomer formed in the
reactions prepared with ligands (S)-2, (S,S)-9, (R,S)-9, and
(S)-10. Conversely (S)-18 should analogously be expected
from an R phosphite, and this is shown in the reactions per-
formed with (R,R)-7 and (R,R)-8. Among the ligands tested,
(R,R)-8 provided the more enantioselective catalyst of the
series, with a moderate 54% ee (entry 6). Comparison with
absence of enantioselectivity obtained with (R,S)-8 indicates
the existence of a strong mismatching interaction between
the stereogenic elements of the latter ligand. Similar effects
have been observed with β-substituted ligands 7 and 9. Thus,
ligands (S,S)-9 and (R,R)-7 (which possess the same relative
stereochemistry) contain the matched combination of stereo-
genic elements, while for their diastereomeric counterparts
cancellation and severe decrease of enantioselectivity were
observed (Δee = 39% and 37%, respectively). These values
are lower, however, than those obtained with catalysts based
on BINAPHOS- (95% ee)7 or TADDOL-based phosphine-
phosphites (85% ee).19a
On the other hand, all catalysts based on ligands 7-10
were highly active in the hydroformylation of allyl cyanide
and completed the reactions at S/C = 1000 under our stan-
dard reaction conditions. In addition, good regioselectivities
toward the desired branched 21 were obtained. As observed
for styrene, product configuration is ultimately determined
by the influence of backbone and phosphite stereogenic ele-
ments. In general, an R phosphite configuration favors an S
product. However, the phosphine group can exert an effect
on induction comparable to or even higher than that of the
phosphite. For instance, (R,R)-7 gives predominantly the S
product (45% ee, entry 4), while for (R,S)-7 the S product is
slightly preferred (7% ee, entry 3). Similar results are ob-
served with Me-substituted ligands 9, although the enantios-
electivities are lower. Finally, diastereomeric ligands 8 also
displayed important matching-mismatching effects. Thus
(R,R)-8 is the matched ligand and provided the higher
enantioselectivity of the series, with a moderate value of
52% ee (entry 6). For diastereomer (R,S)-8, the two stereo-
genic elements severely interfere and the corresponding
catalyst was unselective (entry 5).
Computational and Structural Studies. With the aim to get
more insight on the ligand influence in the catalytic reactions,
we have investigated the conformational preferences of
ligands 7-10. In a previous study analyzing the structure
of Ir(Cl)(CO)(P-OP) complexes, two preferred conforma-
tions, a twisted-boat structure (A) and a chair-like confor-
mation (B),6c were detected for derivatives of ethane-bridged
ligands 2. Interestingly, the phosphorus fragments do not
suffer from significant steric hindrance from Cl and CO co-
ligands in these complexes. Then, the conformational pre-
ferences in these square-planar compounds can reasonably
be considered as their inherent preferences for a 90° bite
angle. For the present study, we have employed a set of
analogous rhodium chlorocarbonyls Rh(Cl)(CO)(P-OP).
As a starting point, derivative Rh(Cl)(CO)[(S)-2a0]20 was
optimized from the two mentioned conformations, leading
to structures Rh-(S)-2a0-A and Rh-(S)-2a0-B (Figure 2). As
observed before for the iridium derivatives, there is a
negligible difference of energy between these two structures
entry
precatalyst
P-OP conv i:n % ee (conf)
1b
2b
3
4
5
6
7
8
9
Rh(acac)(CO)2 + P-OP (S)-1a
(S)-2a
(R,S)-7
93 98:2
100 96:4
96 96:4
43 (S)
25 (R)
rac
37 (S)
rac
54 (S)
6 (R)
45 (R)
32 (R)
(R,R)-7 100 97:3
(R,S)-8 97 97:3
(R,R)-8 98 97:3
(R,S)-9 100 96:4
(S,S)-9
(S)-10
100 97:3
70 97:3
a Reactions were carried out at 50 °C with an initial gas pressure of 20
bar (CO/H2=1), in toluene at a S/C = 1000 in a 750 mL reaction vessel.
Conversion was determined by 1H NMR and enantiomeric excess (ee) by
chiral GC. Configuration was determined by comparison of optical
rotation to the literature value. b Reference 18
.
Table 4. Hydroformylation of Allyl Cyanidea
entry
precatalyst
P-OP conv i:n % ee (conf)
1b
2
3
4
5
6
7
8
9
Rh(acac)(CO)2 + P-OP (S)-1a
(S)-2a
70 94:6
100 94:6
23 (S)
35 (R)
7 (S)
45 (S)
rac
52 (S)
rac
29 (R)
17 (R)
(R,S)-7 100 94:6
(R,R)-7 100 95:5
(R,S)-8 100 93:7
(R,R)-8 100 96:4
(R,S)-9 100 94:6
(S,S)-9
(S)-10
100 96:4
100 96:4
a Reactions were carried out at 50 °C with an initial gas pressure of 20
bar (CO/H2=1), in toluene at a S/C = 1000 in a 750 mL reaction vessel.
Conversion was determined by 1H NMR and enantiomeric excess (ee) by
chiral GC. Configuration was determined by comparison of optical
rotation to the literature value. b Reference 18
.
the phosphine, an appreciable difference between diastereo-
mers is again observed. Thus ligand (R,S)-8 provided a 95%
ee (entry 5), while the mismatched (R,R)-8 yielded a 74% ee
(entry 6). Finally, for ligands without stereogenic centers at
the backbone, the dimethyl-substituted ligand (S)-10 af-
forded an 89% ee, while the unsubstituted ligand (S)-2
provided a very high enantioselectivity (99% ee, entry 1).
Interestingly, this catalyst showed a good reactivity and was
able to complete a reaction at S/C = 5000 in 12 h without
detriment to the ee value (entry 10).
Hydroformylation Reactions. In a previous study we have
detected a switch in product configuration in the asymmetric
hydroformylation of styrene performed with Rh catalysts
based on ligands 1a and 2a (R = R0 = Ph). This observation
was attributed to a different conformation of the apical PPh2
group in the corresponding Rh(H)(P-OP)(CO)(olefin) species.18
From these results and from the expected backbone influ-
ence in phosphine orientation in compounds 7-10, it seems
interesting examining the performance of these ligands in
some model hydroformylation reactions.19 In particular, the
reactions of styrene and allyl cyanide have been examined.
In the hydroformylation of styrene, all catalysts showed a
good activity and gave conversions over 95% under our
ꢀ
(18) Rubio, M.; Suarez, A.; Alvarez, E.; Bianchini, C.; Oberhauser,
ꢀ
W.; Peruzzini, M.; Pizzano, A. Organometallics 2007, 26, 6428.
(19) For other asymmetric hydroformylations using phosphine-
phosphite ligans see: (a) Robert, T.; Abiri, Z.; Wassenaar, J.; Sandee,
A. J.; Romanski, S.; Neudorfl, J. -M.; Schmalz, H. -G.; Reek, J. N. H.
Organometallics 2010, 29, 478. (b) Deerenberg, S.; Kamer, P. C. J.; van
ꢁ
Leeuwen, P. W. N. M. Organometallics 2000, 19, 2065. (c) Pamies, O.; Net,
G.; Ruiz, A.; Claver, C. Tetrahedron: Asymmetry 2002, 12, 3441.
(d) Kless, A.; Holz, J.; Heller, D.; Kadyrov, R.; Selke, R.; Fischer, C.; Borner,
A. Tetrahedron: Asymmetry 1996, 7, 33.
€

Article
Organometallics, Vol. 29, No. 22, 2010 5795
Figure 2. Rh-POP fragments of optimized structures of chlorocarbonyl models Rh(Cl)(CO(P-OP0).
Table 5. Relative Energy and Torsion Angles of Rh(Cl)(CO)
(P-OP) Complexes
ΔEa
j1
j3
j4
b
b
j2
b
b
entry
ligand-conf
1
2
3
4
5
6
7
8
(S)-2a0-A
(S)-2a0-B
(R,S)-70-A
(R,S)-70-B
(S,S)-70-A
(S,S)-70-B
(R,S)-80-A
(R,S)-80-B
(S,S)-80-A
(S,S)-80-B
(R,S)-90-A
(R,S)-90-B
(S,S)-90-A
(S,S)-90-B
(S)-100-A
(S)-100-B
(S)-1a
0.00
-0.10
0.00
-4.78
0.00
8.55
0.00
3.18
0.00
0.59
140.6
136.0
145.5
135.9
145.8
123.6
129.0
131.2
145.5
137.6
151.5
135.4
146.2
128.3
155.5
127.0
129.4
-99.8
-102.4
-88.3
-102.7
-93.9
-116.5
-111.9
-106.7
-93.7
-100.8
-82.1
-103.1
-94.1
-112.2
-82.2
-113.6
-107.3
121.4
104.8
137.3
106.3
114.5
121.3
132.7
114.1
110.7
101.7
127.8
105.6
114.4
109.3
115.2
111.1
151.2
-116.3
-132.6
-101.5
-131.0
-122.0
-119.1
-106.6
-125.6
-128.7
-138.2
-109.4
-131.8
-121.8
-127.7
-122.8
-126.1
-89.2
Figure 3. Torsion angle (j1-j4) definition.
and Rh-(S,S)-90-A being preferred by 3.92 and 3.82 kcal mol-1
,
3
9
respectively. If the methyl group is replaced by a phenyl frag-
ment, the conformational preference is maintained, although
the energy differences increase. Thus, Rh-(R,S)-70-B and Rh-
10
11
12
13
14
15
16
17c
0.00
-3.92
0.00
3.82
0.00
-0.04
(S,S)-70-A are stabilized by 4.78 and 8.55 kcal mol-1, re-
3
spectively, with respect to the axial conformers. Differently,
in the disubstituted ligand 100 one of the Me groups cannot
avoid the axial position, and the preference shown above is
disrupted, resulting in two conformers with very similar
energy. For ligands 80 an opposite behavior is observed,
and structure Rh-(R,S)-80-A, which possesses an axial Me
a Conformer energy with respect to the A conformer. b Torsion angles
(deg) as defined in Figure 4. c Torsion values taken from the X-ray
structure of Rh(Cl)(CO)(1a).6a
substituent, is 3.18 kcal mol-1 more stable than equatorially
(0.10 kcal mol-1, Table 5). Next, a set of starting chloro-
3
3
substituted conformation B. In contrast to that, for diaste-
reoisomer (S,S)-80, the preference is not as marked and
carbonyl models bearing ligands 70-100 were generated from
the structures Rh-(S)-2a0-A and Rh-(S)-2a0-B, introducing
the appropriate substitution in the backbone, and subse-
quently geometry optimized. Interestingly, for complexes Rh
(Cl)(CO)(90) the more stable structure possesses the methyl
backbone in an equatorial position, structures Rh-(R,S)-90-B
structure A is more stable by only 0.59 kcal mol-1
.
3
Further interesting observations can be made upon com-
parison of torsion angles j1-j4 (Figure 3, Table 5). At first
glance, there are bigger differences in magnitude between the
torsion phosphite angles j1 and j2 than between those of the
phosphine. In addition, for conformation type A the differ-
ence between j1 and j2 is generally greater than in con-
former B. It can also be observed that j1 is kept uniformly
high along the series ranging from 129.0° to 155.5° in con-
formers A and from 123.6° to 137.6° in structures B. Accord-
ingly, j2 show lower values in conformers A (82.1-111.9°)
(20) In model complexes Me groups in 3,30 positions of the biaryl
moieties have been suppressed to quicken calculations. Then, the model
ligand generated by suppression of Me groups in 1 is notated as 10.
Model ligands 70-100 are notated analogously. In the discussion, to
avoid redundancy, only the notation of the ligand and conformation will
be mentioned; therefore Rh-(S)-20-A refers to the structure of Rh(Cl)-
(CO)[(S)-20-A].

5796 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
than in B (100.8-116.5°). Most interestingly, the relative
values of j1 and j2 give an indication of the steric hindrance
offered by the phosphite in quadrants Q1 and Q2. For
instance, a superposition of the two conformers of Rh(Cl)
(CO)(100) (Figure 4) indicates that structure B, with values
j1 = 127.0° and j2 = -113.6°, shows a markedly higher
steric encumbrance in Q2 than in Q1. By comparison,
In order to have complementary experimental informa-
tion, we have performed studies by NMR and X-ray on
selected examples. Initially, cationic complexes [Rh(COD)
(P-OP)]BF4 (P-OP = (R,S)-8, 11a; (R,R)-8, 11b) were pre-
pared by a stoichiometric reaction between the free ligand
and [Rh(COD)2]BF4. These two compounds have been fully
characterized and examined in detail by a 2D-NOESY ex-
periment, in order to detect their conformational prefer-
ences. For complex 11a, meaningful NOE contacts between
H(2) and both H(3) and H(4) are in accord with conforma-
tion A (Figure 5). However, in comparison to the calculated
structure for the chlorocarbonyl, the conformation of 11a
should possess the Me group of the backbone in a less axial
position. Thus, NOE contacts of H(1) with H(6) have been
observed, but not with H(5) or H(8). On the other hand,
complex 11b shows in solution a structure of type A, which is
in good agreement with the more stable structure calculated
for Rh-(S,S)-80. Thus, signals in the NOESY experiments
were observed for contacts between H(1) and H(3), H(4), and
ortho-aryl protons of the two Ph-P, H(5) and H(6). These
aromatic protons show contacts with their corresponding
But groups of the phosphite, H(7) and H(8), respectively. In
addition, H(2) shows contacts with H(3) but not with H(4),
and a signal was also observed between H(2) and both H(5)
and H(7). Therefore, the low difference in energy between
conformer A, which displays torsion angle values j1
=
155.5° and j2 = -82.2°, has a smaller difference in steric
impediment between Q2 and Q1.
For the phosphine group, the difference between torsion
angles j3 and j4 is not as marked as in the phosphite
fragment. Considering more stable conformers, j4 has a
generally higher magnitude than j3, although the order is
reversed in Rh-(S)-2a0-A and Rh-(R,S)-80-A. Therefore a
strong variation of the positions of the phosphine substitu-
ents is observed along the series. Depending on the structure,
a Ph axial can be located on Q3 or Q4, and consequently an
equatorial Ph in Q4 or Q3, respectively. In addition, there are
structures where both Ph groups have intermediate positions
between the axial and equatorial types. Therefore, consider-
ing that for a PPh2 group the edge axial Ph originates a higher
steric impediment,15 different arrangements of sterically encum-
bered quadrants21 are obtained depending on the ligand
conformation and the backbone structure.
Figure 4. Superposition between structures of Rh(Cl)(CO)[(S)-
100-A] (orange) and Rh(Cl)(CO)[(S)-100-B] (gray).
Figure 6. ORTEP view of complex 12.
Figure 5. Selected NOE observed in the Rh-P-OP fragment of compounds 11. 11a: H(1)-H(6); H(2)-H(3); H(2)-H(4); H(2)-H(5);
H(4)-H(7); H(6)-H(8). 11b: H(1)-H(3); H(1)-H(4); H(1)-H(6); H(2)-H(3); H(2)-H(5); H(2)-H(7); H(4)-H(8); H(4)-H(6).

Article
Organometallics, Vol. 29, No. 22, 2010 5797
Figure 7. A and B structures for hydrogen oxidative addition transition states (OATS) in MAC hydrogenation.
chlorocarbonyl conformers of (S,S)-80 should be higher in
11b due to the bigger size of the COD ligand, as conformer A
is clearly preferred in solution.
Attempts to obtain suitable crystals for X-ray crystal-
lography of cationic rhodium derivatives were unsuccessful,
but alternatively we could obtain them for complex PdCl2-
((R,S)-7) (12). Interestingly, complex 12 displays in the solid
state a chair conformation B (Figure 6), in contrast with the
twisted-boat conformation observed before for an unsubsti-
tuted ethane derivative.10b Interestingly, the phenyl group
Figure 8
occupies an equatorial position in the present structure,
Rh-P bond, and the backbone flexibility. From this model it
which is in good accord with the structure calculated for
the more stable conformer of Rh(Cl)(CO)((R,S)-70). In addi-
tion, j1-j4 torsion angles compare well between the two
structures. Thus, in the X-ray structure they amount to
124.6°, -111.1°, 108.7°, and -124.1°, while calculated values
are 135.9°, -102.7°, 106.3°, and -131.0°, respectively.
Considerations about Catalyst Enantioselectivity. In the
hydrogenations of the MAC enamide, a low influence of
the backbone nature on catalyst enantioselectivity has been
observed. This observation can be explained by a recent
computational work by Vidal and Maseras22 on related
systems, which proposes that enantioselectivity is regulated
in the hydrogen oxidative addition step. Then, the corre-
sponding transition states (OATS) have a trigonal-bipyra-
midal structure with the phosphite group electronically
favored in an apical position, olefin, dihydrogen, and phos-
phine in the equatorial plane, and the carbonyl oxygen in
the remaining axial position. Moreover the calculations have
detected an elongation of the Rh-P(phosphine) bond in the
transition state. Application of this model to an S-phosphite
ligand led to two structures, A and B, which differ in the
olefin coordinated face (Figure 7). Of them, A has a lower
steric hindrance between the phosphite and chelated
substrate;23 therefore the R enantiomer should be preferred,
in good accord with the experimental observations. More-
over, the low influence of the orientation of the phosphine
substituents can be ascribed to the higher angle between the
phosphine and olefin coordination positions, the elongated
can be expected that even a P-stereogenic phosphine group
can have a low impact on enantioselectivity. To provide
support for this assumption, we have performed MAC
hydrogenation with ethane-bridged P-stereogenic ligands
2b (Figure 8). Accordingly, the phosphine group configura-
tion showed a minimal influence on the enantioselectivity.
Then, a catalyst based on (S,S)-2b gave the R product with a
99% ee, while a diastereomeric catalyst bearing (S,R)-2b
produced the S enantiomer with a 97% ee.
In contrast to MAC hydrogenation results, appreciable
mismatching effects were observed in the reduction of di-
methyl itaconate. To further analyze the difference between
the two substrates,24,25 we have first investigated by DFT
methods (B3LYP, 6-31G*/TZVP basis set) the structure of
Rh(I) itaconate adducts bearing a simplified phosphine-
phosphite. Thus, biphenyl and backbone substituents have
been removed to lower the influence of steric effects, while
reflecting the electronic properties of the ligands 7-10. Then,
structures cis-pro-(R) and cis-pro-(S) contain the olefin co-
ordinated byits pro-R and pro-S faces (Figure9), respectively,
in the cis position to the phosphite fragment. Following this
notation, structures named trans-pro-(R) and trans-pro-(S)
correspond to adducts with olefin and phosphite in mutually
trans positions. Interestingly, the results show that the two
cis structures have practically the same energy. These are, in
(24) Catalysts bearing π-accepting ligands have shown either lock and
key or anti-lock and key mechanisms for these substrates. (a) Reetz,
M. T.; Meiswinkel, A.; Mehler, G.; Angermund, K.; Graf, M.; Thiel, W.;
Mynott, R.; Blackmond, D. G. J. Am. Chem. Soc. 2005, 127, 10305.
(b) Wassenaar, J.; Kuil, M.; Lutz, M.; Spek, A. L.; Reek, J. N. H. Chem.;
Eur. J. 2010, 16, 6509. (c) Evans, D. A.; Michael, F. E.; Tedrow, J. S.;
(21) Knowles, W. S. Acc. Chem. Res. 1983, 16, 106.
ꢀ
ꢀ
(22) Fernandez-Perez, H.; Donald, S. M. A.; Munslow, I. J.; Benet-
Buchholz, J.; Maseras, F.; Vidal-Ferran, A. Chem.;Eur. J. 2010, 16,
6495.
Campos, K. R. J. Am. Chem. Soc. 2003, 125, 3534. (d) Ref 22
.
(23) (a) Gridnev, I. D.; Higashi, N.; Asakura, K.; Imamoto, T. J. Am.
Chem. Soc. 2000, 122, 7183. (b) Gridnev, I. D.; Imamoto, T.; Hoge, G.;
Kouchi, M.; Takahashi, H. J. Am. Chem. Soc. 2008, 130, 2560.
(25) For comparison of relative stability of Rh(I) adducts of MAC
and itaconate, see: Schmidt, T.; Dai, Z.; Drexler, H.-J.; Baumann, W.;
€
Jager, C.; Pfeifer, D.; Heller, D. Chem.;Eur. J. 2008, 14, 4469.

5798 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
Figure 9. Structures of itaconate adducts and relative energies of compound cis-pro-(S) at the B3LYP, 6-31G*/TZVP, and 6-31G*/
LANL2DZ (in parentheses) levels of theory.
addition, more stable than the corresponding trans adducts
by ca. 4 and 7 kcal mol-1. Calculations using the LANL2DZ
3
basis set24b render similar values. These data clearly account
for an electronic preference of the olefin for the cis coordi-
nation position to the phosphite. These differences are
similar to those observed for methyl N-acetylamino acrylate
adducts of phosphine-phosphite complexes (2-4 kcal mol-1 22
)
3
and lower than values obtained by Reek et al with Rh(I)
adducts based on a rigid phosphine-phosphoramidite ligand.24b
Regarding olefin coordination, the cis-pro-(R) compound
shows the expected bonding mode with the olefinic carbon
bearing the electron-withdrawing CO2Me (CR) closer to the
coordination plane.26 On the contrary, the olefin centroid is
roughly in the coordination plane in cis-pro-(S) without an
appreciable destabilization. Finally, the trans adducts exhi-
bit the CR closer to the olefinic plane, although the trans-pro-
(R) structure shows the olefin slightly above the coordination
Figure 10. Pictures of the transition states for dimethylitaco-
nate reflecting the phosphite steric effects.
differences observed in the chlorocarbonyls, although it
should be taken with caution due to the dynamic nature of
these complexes. An examination of the values of the differ-
ence j1 - |j2| (which indicates the relative occupation of
the phosphite side quadrants; see above) seems to draw a
correlation between its magnitude and catalyst enantioselec-
tivity. For instance, for structures of (S)-2a0, (R,S)-70-B, and
(R,S)-80-A j1 - |j2| ranges between 17° and 41°, and the
corresponding catalysts give enantioselectivities between
95% and 99% ee. In contrast, ligand (S,S)-70-A, which
gives a higher value (52°), provided a lower enantioselec-
tivity. More complex situations arise when two confor-
mations with disparate values of j1 - |j2| have compar-
able energy, as in the case of (S,S)-80 and (S)-100. In these
cases enantioselectivities of 74% and 89% were obtained;
therefore participation of both conformations should take
place.
plane, which may be responsible for its higher energy (3.3 kcal
3
mol-1) over the trans-pro-(S) structure. From the electron-
ically preferred cis adducts, trigonal-bipyramidal A0 and B0
can be expected after hydrogen addition (Figure 10). Of them
B0 is less sterically hindered; therefore preference for the S
product enantiomer can be expected, in accord with experi-
mental results. Moreover, the results of the catalytic hydro-
genations indicate that the reduction of this substrate is
rather sensitive to small variations of the chiral pocket
generated by the P-OP ligand. A qualitative picture of this
influence can tentatively be proposed upon the structural
(26) (a) Price, D. W.; Drew, M. G. B.; Hii., K. K.; Brown, J. M.
Chem.;Eur. J. 2000, 6, 4587. (b) Feldgus, S.; Landis, C. R. Organome-
tallics 2001, 20, 2374.

Article
Organometallics, Vol. 29, No. 22, 2010 5799
Figure 11. Proposed transition states for olefin insertion in hydroformylation (L = CO, olefin).
On the other hand, the influence of the phosphine group in
the hydroformylation reactions can be enlightened with the help
of the backbone structure has been examined in rhodium
catalytic asymmetric hydrogenation and hydroformylation
reactions. In the hydrogenation of MAC a relatively minor
influence of the backbone was observed and generally high
enantioselectivities were obtained (93-99% ee). Otherwise,
for dimethyl itaconate some moderate matching and mis-
matching effects, Δee up to 21%, were observed depending
on the relative configuration of the ligand stereogenic ele-
ments. In contrast, asymmetric hydroformylations showed a
very different behavior, and cooperation of stereogenic
elements in both the phosphite and the backbone is needed
for the attainment of moderate enantioselectivities. In addi-
tion, important differences in enantioselectivity were ob-
served between diastereomeric pairs of ligands (Δee up to
54%). DFT calculations performed on model chlorocarbonyls
Rh(Cl)(CO(P-OP) indicate the presence of two preferred
conformations: a twisted boat and a chair-like structure.
Along the series of ligands, the variation of the phosphite
group orientation with respect to the coordination plane is
small, although some variation in steric effects on phosphite
side quadrants is observed along the series. In contrast, the
position of the phosphine substituents is very variable. Thus,
considering typical quadrant diagrams, Ph orientation and
position on Q3 and Q4 depend on the backbone structure,
the conformer type, and the phosphite configuration. These
structural features have disparate influences in the two types
of catalytic reactions, due to the different stereochemical
relations between the coordinated substrate and the two
phosphorus functionalities in the relevant trigonal-bipyra-
midal transition states proposed for these transformations.
ꢀ
of a computational study by Bo and Carbo for catalysts based
on heterobifunctional aminophosphine-phosphoramidite li-
gands with an equatorial-apical coordination mode.27 This
contribution proposes that enantiodifferentiation in styrene
hydroformylation occurs in the olefin insertion step, being
enantioselectivity governed by a π-π aryl interaction between
styrene and a subtituent of the coordinated apical group.
Previously, we have observed that this interaction operates in
the hydroformylation of vinyl arenes with benzene-bridged
ligands.18 Application of this model to the present system leads
to transition states in which the phosphite, olefin, and CO
occupy the equatorial plane, while hydride and phosphine
stand in axial positions, which interestingly differs in the
orientation of the phenyl phosphine substituents. Thus, in the
series Rh-(S)-1a0, Rh-(R,S)-80-A, Rh-(S,S)-80, there is a gradual
change of the Ph group in Q4 from an axial position to an
equatorial one, while the Ph group in Q3 shows an opposite
change (Figure 11).28 Interestingly, the enantioselectivity in
styrene hydroformylation changes along the series as fol-
lows: 43% (S), rac, 54% (R).29 An analogous trend was ob-
served in the hydroformylation of allyl cyanide with 23% (S),
rac, and 52% ee (R), respectively.29 These data are in line
with the critical importance of the structure of the apical
group in enantioselectivity in hydroformylation reactions
reported in the literature27,30 and, in addition, illustrate the
importance of conformational effects on the spatial orienta-
tion of the apical group and hence on enantioselectivity.
Conclusions
Experimental Section
A set of chiral phosphine-phosphites with substituted
ethane backbones have been synthesized, and the influence
General Procedures. All reactions and manipulations were
performed under nitrogen or argon, either in a Braun Labmaster
100 glovebox or using standard Schlenk-type techniques. All
solvents were distilled under nitrogen with the following desic-
cants: sodium benzophenone ketyl for diethyl ether (Et2O) and
tetrahydrofuran (THF); sodium for hexanes and toluene; CaH2
for dichloromethane (CH2Cl2); and NaOMe for methanol
(MeOH). Enantiomers of 3,30-di-tert-butyl-5,50,6,60-tetramethyl-
2,20-bisphenoxyphosphorus chloride31 and ligands (S)-1a and
(S)-2a were prepared as described previously.6a,c All other
ꢀ
ꢀ
(27) Carbo, J. J.; Lledos, A.; Vogt, D.; Bo, C. Chem.;Eur. J. 2006,
12, 1457.
(28) For these considerations it has been assumed that P-OP ligands
have the same conformational preferences in square-planar chlorocar-
bonyls and in the planar bypiramidal hydridodicarbonyls. This is
however reasonable, as P-OP have the same bite angle in both struc-
tures and conformational preferences observed in chlorocarbonyls
should not be obscured by steric effects provided by CO and Cl co-
ligands.
(29) Values for ligand (S,S)-8 extrapolated from experimental ones
obtained with (R,R)-8.
(30) (a) Yan, Y.; Zhang, X. J. Am. Chem. Soc. 2006, 108, 7198.
(b) Ref 7.
(31) Alexander, J.; Schrock, R. R.; Davis, W. M.; Hultzsch, K. C.;
Hoveyda, A. H.; Houser, J. H. Organometallics 2000, 19, 3700.

5800 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
reagents were purchased from commercial suppliers and used as
received. NMR spectra were obtained on a Bruker DPX-300,
DRX-400, or DRX-500 spectrometer. 31P{1H} NMR shifts
were referenced to external 85% H3PO4, while 13C{1H} and 1H
shifts were referenced to the residual signals of deuterated sol-
vents. All data are reported in ppm downfield from Me4Si. All
NMR measurements were carried out at 25 °C, unless otherwise
stated. GC analyses were performed by using a Hewlett-Packard
model HP 6890 chromatograph. HRMS data were obtained on
a JEOL JMS-SX 102A mass spectrometer. Elemental analyses
were run by the Analytical Service of the Instituto de Investiga-
was treated with TBAF (0.665 g, 2.54 mmol) at 0 °C. The
suspension was stirred for 4 h at room temperature. The solvent
was removed, and the residue was chromatographed on silica
(EtOAc/hexane, 1:1) to yield the desired product as a colorless
oil (0.280 g, 87%). [R]20 = -20 (c 1.3, THF). IR (Nujol mull,
D
cm-1): 3444 (br s, ν(OH)). 1H NMR (CDCl3, 300 MHz): δ 1.00 (br
=
q, 1JHB = 79.8 Hz, 3H, BH3), 1.18 (dd, 3JHP = 15.6 Hz, 3JHH
7.2 Hz, 3H, CHMe), 2.27 (s, 1H, OH), 2.82 (m, 1H, CH), 3.70 (m,
2H, CH2), 7.43 (m, 6H, 6 H arom), 7.70 (m, 4H, 4 H arom).
31P{1H} NMR (C6D6, 121 MHz): δ 18.2 (br m).11B{1H} NMR
(C6D6, 96 MHz): δ 0.4 (d, JBP = 52 Hz). 13C{1H} NMR (CDCl3,
75 MHz): δ 12.1 (CHMe), 31.8 (d, JCP = 35 Hz, CH), 63.5 (d, JCP
=6Hz, CH2), 127.8 (d, JCP =37Hz, Cq arom), 128.5 (d, JCP =37
Hz, Cq arom), 129.0 (d, JCP = 9 Hz, 2 CH arom), 129.2 (d, JCP = 9
Hz, 2 CH arom), 131.6 (2 CH arom), 132.6 (d, JCP = 9 Hz, 2 CH
arom), 132.9 (d, JCP = 9 Hz, 2 CH arom). HRMS (FAB): m/z
281.1251, [M þ Na]þ (exact mass calculated for C15H20BONaP:
281.1243).
ciones Quımicas in a Leco CHNS-932 elemental analyzer.
´
Optical rotations were measured on a Perkin-Elmer model 341
polarimeter. IR spectra were acquired on a Bruker Vector 22
instrument.
(S)-1-(tert-Butyldimethylsiloxy)propan-2-yl 4-Methylbenzenesul-
fonate. A solution of tert-butyldimethylchlorosilane (1.03 g,
6.83 mmol) in CH2Cl2 (10 mL) was added to (S)-propane-1,2-
diol (0.5 mL, 6.83 mmol), NEt3 (0.9 mL, 6.8 mmol), and DMAP
(0.167 g, 1.37 mmol) dissolved in CH2Cl2 (20 mL). The solution
was stirred for 3 days. The resulting mixture was quenched with
water (10 mL), and the organic layer was separated and treated
with a saturated aqueous solution of NH4Cl (10 mL). Phases
were separated, and the organic phase was dried with Na2SO4,
filtered, and evaporated. The resulting residue was used in the
next reaction without further purification. The residue was
dissolved in CH2Cl2 (20 mL) and treated with tosyl chloride
(0.981 g, 5.14 mmol) and pyridine (2.1 mL, 26.0 mmol). The
mixture was stirred for 2 days. The solvent was removed, and the
residue was chromatographed on silica (CH2Cl2/hexane, 1:1)
((R)-1-Methyl-2-hydroxyethyl)diphenylphosphine ((R)-3). To
a solution of (R)-3 BH3 (0.280 g, 1.08 mmol) in toluene (5 mL)
3
was added DABCO (0.365 g, 3.25 mmol). The mixture was
stirred for 3 days. The solvent was removed, and the residue was
redissolved in Et2O and filtered through a short pad of silica.
The product was obtained as a white oil after evaporation of the
solvent (0.237 g, 90%). [R]20 = -13 (c 1.0, THF). IR (Nujol
D
mull, cm-1): 3354 (br w, ν(OH)). 1H NMR (CDCl3, 300 MHz):
1.09 (dd, 3JHP = 13.8 Hz, 3JHH = 6.9 Hz, CHMe), 1.55 (s, 1H,
OH), 2.58 (m, 1H, CH), 3.54 (br m, 1H, CHH), 3.7 (br m, 1H,
CHH), 7.32 (m, 6H, 6 H arom), 7.48 (m, 4H, 4 H arom). 31P{1H}
NMR (CDCl3, 121 MHz): δ -10.6 (s). 13C{1H} NMR (CDCl3,
75 MHz): δ 14.5 (d, JCP = 14 Hz, CHMe), 34.1 (d, JCP = 11 Hz,
CH), 65.9 (d, JCP = 23 Hz, CH2), 128.7 (d, JCP = 14 Hz, 2 CH
arom), 128.8 (2 CH arom), 129.2 (d, JCP = 6 Hz, 2 CH arom),
133.3 (d, JCP = 19 Hz, 2 CH arom), 134.0 (d, JCP = 20 Hz, 2 CH
arom), 136.1 (d, JCP = 13 Hz, Cq arom), 136.8 (d, JCP = 13 Hz,
Cq arom). HRMS (CI): m/z 245.1093, [M þ H]þ(exact mass
calculated for C15H18OP: 245.1095).
to yield the desired product as a colorless oil (1.10 g, 62%).
[R]20 = -14 (c 1.1, THF). H NMR (CDCl3, 300 MHz): δ
1
D
-0.04 (s, 3H, SiCH3), -0.03 (s, 3H, SiCH3), 0.81 (s, 9H, CMe3),
1.22 (d, 3JHH = 6.3 Hz, 3H, CHMe), 2.42 (s, 3H, Me-Ph), 3.53
(m, 2H, CH2), 4.50 (qdd, JHH = 5.4 Hz, JHH = 5.4 Hz,
3
3
3
3JHH = 5.4 Hz, 1H, CH), 7.37 (d, JHH = 8.4 Hz, 2H, 2 H
arom), 7.74 (d, 3JHH = 8.4 Hz, 2H, 2 H arom). 13C{1H} NMR
(CDCl3, 75 MHz): δ -5.3 (SiMe), -5.2 (SiMe), 17.6 (CHMe),
18.5 (CMe3), 21.9 (Me-Ph), 26.0 (CMe3), 65.8 (CH2), 79.9 (CH),
128.0 (2 CH arom), 129.9 (2 CH arom), 130.2 (Cq arom), 144.7
(Cq arom).
(S)-(2-Methyl-2-hydroxyethyl)diphenylphosphine ((S)-4). This
compound was prepared from (S)-2-methyloxirane, as de-
scribed for 5. Colorless oil (1.38 g, 94%). [R]20D = -14 (c 1.0,
THF). IR (film, cm-1): 3280 (s, ν(OH)). 1H NMR (CDCl3, 300
3
(R)-(1-(tert-Butyldimethylsiloxy)propan-2-yl)diphenylphosphine-
borane. Over a solution of diphenylphosphine-borane (0.972 g,
4.86 mmol) in THF (10 mL), cooled to -78 °C, was added LiBun
(3.0 mL, 1.6 M solution in hexanes). The mixture was stirred for 1 h
at room temperature and then cooled to -50 °C and treated with a
solution of (S)-1-(tert-butyldimethylsiloxy)propan-2-yl 4-methyl-
benzenesulfonate (0.837 g, 2.43 mmol) in DMF (10 mL). The
resulting mixture was stirred overnight at room temperature, and
volatiles were removed under vacuum. The resulting residue was
dissolved in Et2O and treated with an aqueous solution of HCl
(1.0 M, 10 mL). The organic layer was separated and dried with
Na2SO4. The solvent was removed, and the residue was chroma-
tographed on silica (5% AcOEt/hexane) to yield the desired
MHz): δ 1.31 (d, JHH = 6.0 Hz, 3H, CHMe), 2.27 (m, 2H,
PCH2), 2.42 (m, 1H, OH), 3.91 (m, 1H, CH), 7.32 (m, 6H, 6 H
arom), 7.45 (m, 4H, 4 H arom). 31P{1H} NMR (CDCl3, 121
MHz): δ -24.0 (s). 13C{1H} NMR (CDCl3, 75 MHz): δ 24.9 (d,
J
CP = 8 Hz, CHMe), 39.8 (d, JCP = 13 Hz, PCH2), 66.2(d, JCP
17 Hz, CH), 128.9 (m, 5 CH arom), 129.1 (CH arom), 132.0 (d,
CP = 19 Hz, 2 CH arom), 133.2 (d, JCP = 19 Hz, 2 CH arom),
=
J
138.4 (d, JCP = 11 Hz, Cq arom), 138.5 (d, JCP = 11 Hz, Cq
arom). HRMS (CI): m/z 245.1093, [M þ H]þ (exact mass
calculated for C15H18OP: 245.1095).
(R)-(2-Methyl-2-hydroxyethyl)diphenylphosphine ((R)-4). This
compound was prepared from (R)-2-methyloxirane, as described
for 5. Colorless oil (1.39 g, 95%). [R]20D = þ14 (c 1.0, THF). IR
product as a colorless oil (0.580 g, 64%). [R]20 = -30 (c 1.0,
(film, cm-1): 3288 (s, ν(OH)). H NMR (CDCl3, 300 MHz): δ
1
D
1
THF). H NMR (CDCl3, 300 MHz): δ -0.05 (s, 3H, SiCH3),
1.30 (dd, 3JHH = 6.0 Hz, 4JHH = 0.9 Hz, 3H, CHMe), 2.20 (m,
1H, OH), 2.29 (m, 2H, PCH2), 3.90(m, 1H, CH), 7.32 (m, 6H, 6 H
arom), 7.42 (m, 4H, 4 H arom). 31P{1H} NMR (CDCl3, 121
MHz): δ -24.1 (s). 13C{1H} NMR (CDCl3, 75 MHz): δ 24.9 (d,
-0.02 (s, 3H, SiCH3), 0.83 (s, 9H, CMe3), 0.90 (br m, 3H, BH3),
1.18 (dd, 3JHP = 15.9 Hz, 3JHH = 6.9 Hz, 3H, CHMe), 2.82 (m,
1H, CH), 3.73 (m, 2H, CH2), 7.45 (m, 6H, 6 H arom), 7.78 (m, 4H,
4 H arom). 31P{1H} NMR (C6D6, 121 MHz): δ 16.8 (br m).
11B{1H} NMR (C6D6, 96MHz):δ-2.0 (d, JPB =41Hz). 13C{1H}
NMR (CDCl3, 75 MHz): δ -5.4 (2 SiCH3), 12.1 (CHMe), 18.3
(CMe3), 25.9 (CMe3), 32.1 (d, JCP = 34 Hz, CH), 63.8 (d, JCP = 9
Hz, CH2), 128.6 (d, JCP = 54 Hz, 2 Cq arom), 128.8 (d, JCP = 10
J
CP = 8 Hz, CHMe), 39.7 (d, JCP = 13 Hz, PCH2), 66.2(d, JCP
17 Hz, CH), 128.9 (m, 5 CH arom), 129.1 (CH arom), 132.0 (d,
CP = 19 Hz, 2 CH arom), 133.2 (d, JCP = 19 Hz, 2 CH arom),
=
J
138.3 (d, JCP = 12 Hz, Cq arom), 138.5 (d, JCP = 12 Hz, Cq
arom). HRMS (CI): m/z 245.1093, [M þ H]þ (exact mass cal-
culated for C15H18OP: 245.1095).
Hz, 4 CH arom), 131.1 (d, JCP = 3 Hz, CH arom), 131.2 (d, JCP
=
3 Hz, CH arom), 132.5 (d, JCP = 9 Hz, 2 CH arom), 132.6 (d,
JCP = 9 Hz, 2 CH arom).
((R)-1-Methyl-2-hydroxyethyl)diphenylphosphine-borane ((R)-
(2,2-Dimethyl-2-hydroxyethyl)diphenylphosphine (5). Over a
solution of Ph2PH (1.00 g, 5.37 mmol) and 1,2-epoxy-2-methyl-
propane (0.462 g, 6.43 mmol) in THF (20 mL), cooled to 0 °C,
was added LiBun (1.8 mL, 1.6 M solution in hexanes) dropwise.
The mixture was stirred for 2 h, and the solvent was removed
3 BH3). A solution of (R)-(1-(tert-butyldimethylsiloxy)propan-2-
3
yl)diphenylphosphine-borane (0.465 g, 1.25 mmol) in THF (20 mL)

Article
Organometallics, Vol. 29, No. 22, 2010 5801
under vacuum. The resulting residue was extracted with CH2Cl2
(3 ꢀ 10 mL) and treated with an excess of NH4Cl. The mixture
was filtered, evaporated, and extracted with Et2O (2 ꢀ 15 mL).
Evaporation of the solvent yields the desired product as a
colorless oil (1.03 g, 75%). IR (film, cm-1): 3396 (s, ν(OH)).
1H NMR (CDCl3, 300 MHz): δ 1.30 (s, 6H, 2 Me), 1.85 (br s, 1H,
(Cq arom), 136.7 (Cq arom), 137.8 (Cq arom), 139.6 (Cq arom),
144.7 (d, JCP = 4 Hz, Cq arom), 145.5 (Cq arom). HRMS (CI):
m/z 702.3558, [M]þ (exact mass calculated for C44H53BO3P2:
702.3563).
(R)-1-Phenyl-2-(diphenylphosphino)ethyl (S)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,S)-7).
A solution of (R,S)-7 BH3 (0.380 g, 0.54 mmol) in toluene
2
OH), 2.42 (d, JHP = 3.3 Hz, 2H, PCH2), 7.30 (m, 6H, 6 H
arom), 7.44 (m, 4H, 4 H arom). 31P{1H} NMR (CDCl3, 121
3
(20 mL) was treated with DABCO (0.306 g, 2.72 mmol). The
suspension was stirred for 3 days. The solvent was evaporated,
and the resulting residue was dissolved in Et2O and filtered
through a short pad of neutral alumina. The product was
obtained as a white solid after solvent evaporation (0.270 g,
75%). [R]20D =þ225 (c1.0, THF). 1HNMR(CDCl3,300MHz):δ
1.11 (s, 9H, CMe3), 1.27 (s, 9H, CMe3), 1.73 (s, 3H, Ar-Me), 1.77
(s, 3H, Ar-Me), 2.22 (s, 3H, Ar-Me), 2.23 (s, 3H, Ar-Me), 2.58
(m, 1H, PCHH), 2.94 (m, 1H, PCHH), 4.92 (m, 1H, CH), 6.98
(m, 3H, 3 H arom), 7.10 (s, 1H, H arom), 7.14-7.27 (m, 11H, 11
H arom), 7.35 (m, 2H, 2 H arom). 31P{1H} NMR (CDCl3, 121
MHz): δ -25.8 (d, JPP = 5 Hz, PC), 135.4 (d, P-O). 13C{1H}
NMR (CDCl3, 75 MHz): δ 16.8 (Ar-Me), 17.2 (Ar-Me), 20.7
(Ar-Me), 20.8 (Ar-Me), 31.4 (2 CMe3), 34.7 (CMe3), 34.8
(CMe3), 39.5 (d, JCP = 13 Hz, PCH2), 77.1 (m, CH), 127.9 (2
CH arom), 128.6 (m, 9 CH arom), 128.9 (d, JCP = 13 Hz, 2 CH
arom), 130.8 (Cq arom), 131.5 (Cq arom), 132.2 (Cq arom), 132.6
MHz): δ -25.8 (s). 13C{1H} NMR (CDCl3, 75 MHz): δ 31.2 (d,
JCP = 7 Hz, 2 Me), 45.0 (d, JCP = 15 Hz, PCH2), 71.3 (d, JCP =
15 Hz, OCq), 128.7 (m, 6 CH arom), 133.2 (d, JCP = 19 Hz, 4 CH
arom), 139.3 (d, JCP = 10 Hz, 2 Cq arom). HRMS (CI): m/z
258.1164, [M]þ (exact mass calculated for C16H19OP: 258.1173).
(R)-(2-Phenyl-2-hydroxyethyl)diphenylphosphine-borane ((R)-
6 BH3). LiBun (1.8 mL, 1.6 M solution in hexanes) was added
3
dropwise to a solution of Ph2PH (1.12 g, 6.01 mmol) and (R)-2-
phenyloxirane (0.828 g, 6.89 mmol) in THF (20 mL) cooled to
-60 °C. The mixture was stirred for 2 h at room temperature,
and the solvent was removed under reduced pressure. The
resulting residue was redissolved in CH2Cl2 (30 mL), and
BH3 SMe2 (0.65 mL, 6.89 mmol) was slowly added at 0 °C.
3
The reaction was stirred for 2 h and quenched with an aqueous
solution of HCl (1.0 M, 2.0 mL). The organic layer was sepa-
rated, and the aqueous phase was extracted with CH2Cl2 (2 ꢀ
10 mL). Organic phases were combined, dried over MgSO4, and
filtered, and the solvent was removed. The residue was chroma-
tographed on silica (Et2O/hexane, 1:1), yielding the desired
(Cq arom), 132.7 (d, JCP = 19 Hz, 2 CH arom), 133.2 (d, JCP
=
19 Hz, 2 CH arom), 134.5 (Cq arom), 135.3 (Cq arom), 137.4 (Cq
arom), 137.9 (d, JCP = 14 Hz, Cq arom), 138.3 (Cq arom), 138.8
(d, JCP = 12 Hz, Cq arom), 141.1 (Cq arom), 145.2 (Cq arom),
145.7 (Cq arom). HRMS (CI): m/z 689.3271, [M þ H]þ (exact
mass calculated for C44H51O3P2: 689.3313).
product as a white solid (1.10 g, 52%). [R]20 = -25 (c 1.0,
D
THF). IR (Nujol mull, cm-1): 3419 (s, ν(OH)). 1H NMR
(CDCl3, 300 MHz): δ 1.05 (br m, 3H, BH3), 2.67 (m, 2H, PCH2),
3
3
(R)-1-Phenyl-2-(diphenylphosphinoborane)ethyl (R)-3,30-Di-
tert-butyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,
R)-7 BH3). This compound was prepared by following the pro-
3.15 (m, 1H, OH), 5.08 (ddd, JHP = 9.6 Hz, JHH = 9.6 Hz,
3JHH = 2.4 Hz, 1H, CH), 7.28 (m, 5H, 5 H arom), 7.45 (m, 6H, 6
H arom), 7.71 (m, 4H, 4 H arom). 31P{1H} NMR (CDCl3, 121
MHz): δ 11.1 (q, JPB = 63 Hz). 11B{1H} NMR (CDCl3, 96
MHz): δ 2.5 (d, JBP = 50 Hz). 13C{1H} NMR (CDCl3, 75 MHz):
δ 37.3 (d, JCP = 34 Hz, PCH2), 69.9 (CH), 125.8 (2 CH arom),
128.2 (CH arom), 128.6 (Cq arom), 128.9 (2 CH arom), 129.2 (d,
JCP = 11 Hz, 2 CH arom), 129.3 (d, JCP = 10 Hz, 2 CH arom),
130.1 (Cq arom), 131.6 (CH arom), 131.9 (CH arom), 132.3 (d,
3
cedure described for (R,S)-7 BH3. White foamy solid (0.270 g,
3
75%). [R]20D = -235 (c 1.0, THF). 1H NMR (CDCl3, 500 MHz):
δ 0.90 (br m, 3H, BH3), 1.30 (s, 9H, CMe3), 1.38 (s, 9H, CMe3),
1.78 (s, 3H, Ar-Me), 1.92 (s, 3H, Ar-Me), 2.16 (s, 3H, Ar-Me),
2.23 (s, 3H, Ar-Me), 2.45 (m, 1H, PCHH), 2.95 (m, 1H, PCHH),
5.58 (m, 1H, CH), 6.93 (m, 3H, 3 H arom), 7.05-7.48 (m, 14H,
14 H arom). 31P{1H} NMR (CDCl3, 202 MHz): δ 10.0 (br s,
P-C), 134.0 (s, P-O). 13C{1H} NMR (CDCl3, 126 MHz): δ 16.5
(Ar-Me), 16.8 (Ar-Me), 20.4 (2 Ar-Me), 31.2 (d, JCP = 5 Hz,
JCP = 9 Hz, 2 CH arom), 132.6 (d, JCP = 9 Hz, 2 CH arom),
144.1 (d, JCP = 12 Hz, Cq arom). HRMS (CI): m/z 319.1435,
[M - H]þ (exact mass calculated for C20H21BOP: 319.1423).
(R)-1-Phenyl-2-(diphenylphosphinoborane)ethyl (S)-3,30-Di-
tert-butyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,
CMe3), 31.5 (CMe3), 34.4 (CMe3), 34.5 (CMe3), 34.7 (d, JCP
=
26 Hz, PCH2), 72.6 (d, JCP = 8 Hz, CH), 127.5 (2 CH arom),
127.7 (CH arom), 127.8 (2 CH arom), 128.1 (m, 4 CH arom),
129.0 (d, JCP = 9 Hz, 2 CH arom), 129.1 (Cq arom), 130.5 (CH
arom), 130.6 (Cq arom), 130.7 (CH arom), 131.6 (d, JCP = 9 Hz,
2 CH arom), 131.8 (d, JCP = 5 Hz, Cq arom), 131.9 (Cq arom),
132.1 (d, JCP = 9 Hz, 2 CH arom), 132.2 (Cq arom), 134.9 (Cq
arom), 135.0 (Cq arom), 136.9 (Cq arom), 138.0 (2 Cq arom),
139.5 (Cq arom), 144.9 (d, JCP = 5 Hz, Cq arom), 145.3 (Cq
arom). HRMS (CI): m/z 702.3557, [M]þ (exact mass calculated
for C44H53BO3P2: 702.3563).
S)-7 BH3). To a solution of (S)-3,30-di-tert-butyl-5,50,6,60-tetra-
3
methyl-2,20-bisphenoxyphosphorus chloride (0.400 g, 0.96 mmol),
NEt3 (1.41 mL, 9.75 mmol), and DMAP (0.006 g, 0.048 mmol)
in toluene (30 mL) was added (R)-6 (0.300 g, 0.96 mmol) in
toluene (20 mL). The mixture was stirred overnight and filtered,
and the solvent was evaporated. The resulting residue was
dissolved in Et2O (20 mL), and the solution was filtered through
a short pad of neutral alumina. The solvent was evaporated,
yielding the desired product as a white foamy solid (0.501 g,
75%). [R]20 = þ216 (c 1.0, THF). 1H NMR (CDCl3, 500
(R)-1-Phenyl-2-(diphenylphosphino)ethyl (R)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,R)-7).
This compound was prepared by following the procedure
D
MHz): δ 0.88 (br m, 3H, BH3), 1.11 (s, 9H, CMe3), 1.31 (s, 9H,
CMe3), 1.75 (s, 3H, Ar-Me), 1.95 (s, 3H, Ar-Me), 2.23 (s, 3H, Ar-
Me), 2.34 (s, 3H, Ar-Me), 2.97 (m, 2H, PCH2), 5.31 (m, 1H,
CH), 6.88 (m, 3H, 3 H arom), 6.93 (m, 1H, H arom), 7.05 (m, 3H,
3 H arom), 7.10 (s, 1H, H arom), 7.17 (m, 4H, 4 H arom), 7.38 (t,
3JHH = 7.0 Hz, 2H, 2 H arom), 7.44 (m, 1H, H arom), 7.46 (dd,
3JHH = 8.5 Hz, 3JHP = 8.5 Hz, 2H, 2 H arom). 31P{1H} NMR
(CDCl3, 202 MHz): δ 10.0 (br s, P-C), 133.0 (s, P-O). 13C{1H}
NMR (CDCl3, 126 MHz): δ 16.4 (Ar-Me), 16.8 (Ar-Me), 20.3 (2
Ar-Me), 30.9 (CMe3), 31.2 (d, JCP = 5 Hz, CMe3), 34.4 (2
CMe3), 35.9 (d, JCP = 35 Hz, PCH2), 74.5 (d, JCP = 9 Hz, CH),
127.4 (m, 5 CH arom), 127.6 (2 CH arom), 127.9 (2 CH arom),
128.6 (d, JCP = 14 Hz, 2 CH arom), 130.5 (CH arom), 130.6 (Cq
arom), 130.8 (CH arom), 130.9 (Cq arom), 131.5 (d, JCP = 9 Hz,
2 CH arom), 131.7 (Cq arom), 131.9 (d, JCP = 4 Hz, Cq arom),
132.3 (m, 2 CH arom þ2 Cq arom), 135.0 (Cq arom), 135.1
described for (R,S)-7. White foamy solid (0.120 g, 60%).
1
[R]20 = -238 (c 1.0, THF). H NMR (CDCl3, 300 MHz): δ
D
1.26 (s, 9H, CMe3), 1.29 (s, 9H, CMe3), 1.76 (s, 3H, Ar-Me), 1.87
(s, 3H, Ar-Me), 2.14 (s, 3H, Ar-Me), 2.25 (s, 3H, Ar-Me), 2.49
(m, 2H, PCH2), 5.01 (m, 1H, CH), 7.05 (m, 3H, 3 H arom),
7.10-7.22 (m, 9H, 9 H arom), 7.27 (m, 5H, 5 H arom). 31P{1H}
NMR (CDCl3, 121 MHz): δ -25.8 (s, P-C), 134.9 (s, P-O).
13C{1H} NMR (CDCl3, 75 MHz): δ 16.8 (Ar-Me), 17.2 (Ar-
Me), 20.7 (2 Ar-Me), 31.4 (d, JCP = 5 Hz, CMe3), 31.7 (CMe3),
34.8 (CMe3), 34.9 (CMe3), 38.8 (d, JCP = 14 Hz, PCH2), 77.2 (m,
CH), 127.4 (2 CH arom), 127.9 (CH arom), 128.4 (m, 7 CH
arom), 129.0 (d, JCP = 7 Hz, 2 CH arom), 129.4 (CH arom),
131.0 (Cq arom), 131.8 (Cq arom), 132.0 (d, JCP = 5 Hz, Cq
arom), 132.5 (d, JCP = 19 Hz, 2 CH arom), 132.6 (Cq arom),

5802 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
133.5 (d, JCP = 20 Hz, 2 CH arom), 134.5 (Cq arom), 135.3 (Cq
arom), 137.5 (Cq arom), 137.8 (d, JCP = 13 Hz, Cq arom), 138.2
(Cq arom), 138.8 (d, JCP = 13 Hz, Cq arom), 141.3 (Cq arom),
145.5 (m, 2 Cq arom). HRMS (CI): m/z 689.3292, [M þ H]þ
(exact mass calculated for C44H51O3P2: 689.3313).
31P{1H} NMR (CDCl3, 121 MHz): δ-23.1 (s, P-C), 138.5 (s, P-O).
13C{1H} NMR (CDCl3, 75 MHz): δ 16.9 (Ar-Me), 17.2 (Ar-Me),
20.7 (2 Ar-Me), 23.2 (dd, JCP = 14 Hz, JCP = 6 Hz, Me), 31.6 (d,
JCP = 5 Hz, CMe3), 31.9 (CMe3), 34.9 (CMe3), 35.0 (CMe3), 38.5
(d, JCP = 16Hz, PCH2), 71.9 (dd, JCP =25 Hz, JCP = 13Hz, CH),
127.9 (CH arom), 128.3 (CH arom), 128.5 (CH arom), 128.6 (d,
(R)-2-Methyl-2-(diphenylphosphino)ethyl (R)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,R)-8).
Over a solution of (R)-3,30-di-tert-butyl-5,50,6,60-tetramethyl-
2,20-bisphenoxyphosphorus chloride (0.172 g, 0.41 mmol) and
NEt3 (0.07 mL, 0.50 mmol) in toluene (10 mL) was added (R)-3
(0.100 g, 0.41 mmol) in toluene (10 mL). The mixture was stirred
overnight and filtered, and the solvent was evaporated. The
resulting residue was dissolved in Et2O (20 mL) and the solution
filtered through a short pad of neutral alumina. The solvent was
evaporated, yielding (R,R)-8 as a white foamy solid (0.175 g,
JCP = 7 Hz, 2 CH arom), 128.8 (d, JCP = 7 Hz, 2 CH arom), 129.3
(CH arom), 131.0 (Cq arom), 131.8 (Cq arom), 132.3 (d, JCP
=
5 Hz, Cq arom), 132.6 (Cq arom), 132.7 (d, JCP = 19 Hz, 2 CH
arom), 133.2 (d, JCP = 20 Hz, 2 CH arom), 134.5 (Cq arom), 135.4
(Cq arom), 137.5 (Cq arom), 137.7 (d, JCP =12Hz, Cq arom), 138.1
(Cq arom), 138.8 (d, JCP = 12 Hz, Cq arom), 145.2 (d, JCP = 6 Hz,
Cq arom), 145.6 (Cq arom). HRMS(CI):m/z 626.3062, [M]þ (exact
mass calculated C39H48O3P2: 626.3078).
(R)-1-Methyl-2-(diphenylphosphino)ethyl (S)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,S)-9).
This compound was prepared by following the procedure
68%). [R]20 = -271 (c 1.0, THF). 1H NMR (CDCl3, 300
D
MHz): δ 1.04 (dd, 3JHP = 15.0 Hz, 3JHH = 7.0 Hz, CHMe), 1.26
(s, 9H, CMe3), 1.41 (s, 9H, CMe3), 1.74 (s, 3H, Ar-Me), 1.85 (s,
3H, Ar-Me), 2.21 (s, 3H, Ar-Me), 2.22 (s, 3H, Ar-Me), 2.51 (m,
1H, CH), 3.10 (m, 1H, CHH), 3.75 (m, 1H, CHH), 6.87 (s, 1H, H
arom), 7.12 (s, 1H, H arom), 7.30 (m, 8H, 8 H arom), 7.41(m,
2H, 2 H arom). 31P{1H} NMR (CDCl3, 121 MHz): δ -10.1 (s,
P-C), 126.4 (s, P-O). 13C{1H} NMR (CDCl3, 75 MHz): δ 14.5 (d,
JCP = 15 Hz, CHMe), 16.7 (Ar-Me), 17.0 (Ar-Me), 20.7 (2 Ar-
described for (S,S)-9, starting from the phosphine (R)-4. White
foamy solid (0.350 g, 69%). [R]20 = þ204 (c 1.0, THF). H
1
D
4
NMR (CDCl3, 300 MHz): δ 1.30 (d, JHP = 6.0 Hz, 3H,
CHMe), 1.42 (s, 9H, CMe3), 1.43 (s, 9H, CMe3), 1.79 (s, 3H,
Ar-Me), 1.81 (s, 3H, Ar-Me), 2.23 (s, 3H, Ar-Me), 2.26 (s, 3H,
Ar-Me), 2.31 (m, 1H, PCHH), 2.68 (m, 1H, PCHH), 4.43 (m,
1H, CH), 7.12 (s, 1H, H arom), 7.16 (s, 1H, H arom), 7.31 (m,
6H, 6 H arom), 7.40 (m, 4H, 4 H arom). 31P{1H} NMR (CDCl3,
121 MHz): δ -23.1 (d, JPP = 7 Hz, P-C), 137.4 (d, P-O).
13C{1H} NMR (CDCl3, 75 MHz): δ 16.8 (Ar-Me), 17.1 (Ar-
Me), 20.7 (Ar-Me), 20.8 (Ar-Me), 23.7 (dd, JCP = 8 Hz, JCP = 4
Hz, CHMe), 31.5 (d, JCP = 5 Hz, CMe3), 31.9 (CMe3), 34.8
(CMe3), 35.0 (CMe3), 38.5 (dd, JCP = 15 Hz, JCP = 4 Hz,
PCH2), 71.7 (dd, JCP = 24 Hz, JCP = 11 Hz, CH), 127.9 (CH
arom), 128.1 (CH arom), 128.7 (d, JCP = 4 Hz, 2 CH arom),
128.8 (d, JCP = 5 Hz, 2 CH arom), 128.9 (CH arom), 129.0 (CH
arom), 130.9 (Cq arom), 131.7 (Cq arom), 132.3 (d, JCP = 5 Hz,
Cq arom), 132.6 (Cq arom), 132.9 (d, JCP = 19 Hz, 4 CH arom),
134.5 (Cq arom), 135.4 (Cq arom), 137.5 (Cq arom), 138.0 (d,
JCP = 12 Hz, Cq arom), 138.2 (Cq arom), 138.7 (d, JCP = 12 Hz,
Cq arom), 145.2 (d, JCP = 6 Hz, Cq arom), 145.7 (Cq arom).
HRMS (CI): m/z 626.3060, [M]þ (exact mass calculated for
C39H48O3P2: 626.3078).
1,1-Dimethyl-2-(diphenylphosphino)ethyl (S)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((S)-10).
This compound was prepared by following the procedure
described for (R,S)-8, using phosphine 5. White foamy solid
(0.352 g, 65%). [R]20D = þ190 (c 1.0, THF). 1H NMR (CDCl3,
400 MHz): δ 1.41 (s, 9H, CMe3), 1.42 (s, 9H, CMe3), 1.45 (s, 3H,
CMe2), 1.52 (s, 3H, CMe2), 1.77 (s, 3H, Ar-Me), 1.78 (s, 3H, Ar-
Me), 2.19 (s, 3H, Ar-Me), 2.22 (s, 3H, Ar-Me), 2.72 (m, 2H,
PCH2), 7.08 (s, 1H, H arom), 7.11 (s, 1H, H arom), 7.28 (m, 6H,
6 H arom), 7.39 (m, 4H, 4 H arom). 31P{1H} NMR (CDCl3, 162
MHz): δ -21.7 (d, JPP = 7 Hz, P-C), 139.9 (d, P-O). 13C{1H}
NMR (CDCl3, 101 MHz): δ 16.5 (Ar-Me), 16.7 (Ar-Me), 20.4 (2
Ar-Me), 30.2 (m, CMe2), 31.1 (d, JCP = 5 Hz, CMe3), 31.9
(CMe3), 34.5 (CMe3), 34.8 (CMe3), 44.7 (dd, JCP = 18 Hz,
Me), 31.0 (CMe3), 31.5 (d, JCP = 5 Hz, CMe3), 32.5 (dd, JCP
=
14 Hz, JCP = 3 Hz, CH), 34.7 (CMe3), 34.8 (CMe3), 66.5 (d,
JCP = 31 Hz, CH2), 127.9 (CH arom), 128.4 (CH arom), 128.6
(2 CH arom), 128.7 (2 CH arom), 129.1 (CH arom), 129.2 (CH
arom), 130.9 (Cq arom), 131.5 (Cq arom), 131.7 (d, JCP = 5 Hz,
Cq arom), 131.8 (Cq arom), 133.6 (d, JCP = 17 Hz, 2 CH arom),
133.9 (d, JCP = 17 Hz, 2 CH arom), 134.5 (Cq arom), 135.1 (Cq
arom), 135.9 (d, JCP = 12 Hz, Cq arom), 136.0 (d, JCP = 12 Hz,
Cq arom), 136.7 (Cq arom), 138.2 (Cq arom), 145.8 (m, 2 Cq
arom). HRMS (CI): m/z 626.3064, [M]þ (exact mass calculated
for C39H48O3P2: 626.3078).
(R)-2-Methyl-2-(diphenylphosphino)ethyl (S)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((R,S)-8).
This compound was prepared by following the procedure
described for (R,R)-8. White foamy solid (0.100 g, 39%).
1
[R]20 = þ272 (c 1.0, THF). H NMR (CDCl3, 300 MHz): δ
D
1.05 (dd, 3JHP = 15.0 Hz, 3JHH = 7.0 Hz, CHMe), 1.30 (s, 9H,
CMe3), 1.48 (s, 9H, CMe3), 1.58 (s, 3H, Ar-Me), 1.72 (s, 3H, Ar-
Me), 2.13 (s, 3H, Ar-Me), 2.23 (s, 3H, Ar-Me), 2.49 (m, 1H, CH),
2.95 (m, 1H, CHH), 3.93 (m, 1H, CHH), 7.04 (s, 1H, H arom),
7.15 (s, 1H, H arom), 7.18-7.26 (m, 8H, 8 H arom), 7.32 (m, 2H,
2 H arom). 31P{1H} NMR (CDCl3, 202 MHz): δ -7.9 (s, P-C),
126.5 (s, P-O). 13C{1H} NMR (CDCl3, 75 MHz): δ 14.6 (d,
J
CP = 17 Hz, CHMe), 16.7(Ar-Me), 16.9 (Ar-Me), 20.6 (Ar-Me),
20.7 (Ar-Me), 31.2 (CMe3), 31.5 (d, JCP = 5 Hz, CMe3), 32.0 (d,
CP = 13 Hz, CH), 34.8 (CMe3), 34.9 (CMe3), 67.3 (d, JCP = 23
J
Hz, CH2), 127.9 (CH arom), 128.3 (CH arom), 128.5 (d, JCP = 4
Hz, 2 CH arom), 128.6 (d, JCP = 3 Hz, 2 CH arom), 128.7 (CH
arom), 129.1 (CH arom), 130.8 (Cq arom), 131.5 (Cq arom),
131.9 (d, JCP = 5 Hz, Cq arom), 132.5 (Cq arom), 133.3 (d, JCP
=
19 Hz, 2 CH arom), 133.8 (d, JCP = 18 Hz, 2 CH arom), 134.6
(Cq arom), 135.2 (Cq arom), 135.6 (d, JCP = 14 Hz, Cq arom),
136.4 (d, JCP = 21 Hz, Cq arom), 136.8 (Cq arom), 138.2 (Cq
arom), 145.6 (d, JCP = 4 Hz, Cq arom), 145.8 (Cq arom). HRMS
(CI): m/z 626.3055, [M]þ (exact mass calculated for C39H48O3P2:
626.3078).
(S)-1-Methyl-2-(diphenylphosphino)ethyl (S)-3,30-Di-tert-bu-
tyl-5,50,6,60-tetramethylbiphenyl-2,20-diyl Phosphite ((S,S)-9). The
synthesis of this compound was effected as described for (R,R)-8,
using the phosphine (S)-4 and (S)-3,30-di-tert-butyl-5,50,6,60-tetra-
methyl-2,20-bisphenoxyphosphorus chloride. White foamy solid
(0.310 g, 60%). [R]20D = þ224 (c 1.0, THF). 1H NMR (CDCl3,
300 MHz): δ 1.42 (s, 21H, 2CMe3 þ Me), 1.81 (s, 3H, Ar-Me), 1.84
(s, 3H, Ar-Me), 2.17 (s, 3H, Ar-Me), 2.23 (m, 1H, PCHH), 2.26 (s,
3H, Ar-Me), 2.43(m, 1H, PCHH), 4.49(m, 1H, CH), 7.09(s, 1H, H
arom), 7.16 (s, 1H, H arom), 7.26-7.44 (m, 10H, 10 H arom).
JCP = 7 Hz, PCH2), 82.0 (dd, JCP = 22 Hz, JCP = 9 Hz, CMe2),
127.6 (CH arom), 127.9 (CH arom), 128.5 (d, JCP = 6 Hz, 4 CH
arom), 128.7 (CH arom), 128.7 (CH arom), 130.7 (Cq arom),
131.3 (Cq arom), 132.2 (Cq arom), 132.4 (d, JCP = 5 Hz, Cq
arom), 132.9 (d, JCP = 3 Hz, 2 CH arom), 133.1 (d, JCP = 3 Hz,
2 CH arom), 134.0 (Cq arom), 135.1 (Cq arom), 137.4 (Cq arom),
137.8 (Cq arom), 138.8 (d, JCP = 12 Hz, Cq arom), 139.0 (d,
J
CP = 12 Hz, Cq arom), 144.9 (d, JCP = 7 Hz, Cq arom), 145.6
(Cq arom). HRMS (CI): m/z 640.3214, [M]þ (exact mass calcu-
lated C40H50O3P2: 640.3235).
[Rh(COD)((R,S)-8)]BF4 (11a). Phosphine-phosphite (R,S)-8
(0.018 g, 0.029 mmol) dissolved in CH2Cl2 (5 mL) was added
dropwise to a solution of [Rh(COD)2]BF4 (0.008 g, 0.029 mmol)
in CH2Cl2 (5 mL). The resulting orange solution was stirred for
1 h, concentrated up to one-fourth of its initial volume, and
filtered. Et2O (20 mL) was added to the above solution to

Article
Organometallics, Vol. 29, No. 22, 2010 5803
precipitate the complex. The solid was filtered off, washed with
Et2O (3 ꢀ 10 mL), and dried. Yellow solid (0.015 g, 65%). 1H
NMR (CDCl3, 500 MHz): δ 1.37 (s, 9H, CMe3), 1.48 (dd,
one-fourth of its original volume, and hexane (30 mL) was
added to precipitate the product. The resulting solid was filtered
off, washed with hexane (3 ꢀ 20 mL), and dried. Yellow solid
3
1
3JHP = 14.0 Hz, JHH = 7.0 Hz, 3H, CHMe), 1.71 (s, 9H,
(0.025 g, 60%). H NMR (CDCl3, 300 MHz): δ 1.49 (s, 9H,
CMe3), 1.72 (s, 3H, Ar-Me), 1.82 (s, 3H, Ar-Me), 2.03 (m, 1H,
CHH COD), 2.25 (m, 6H, 6 CH2 COD), 2.23 (s, 3H, Ar-Me),
2.29 (s, 3H, Ar-Me), 2.46 (m, 1H, CHH COD), 2.58 (br m, 1H,
CHMe), 3.96 (br m, 1H, dCH COD), 4.19 (m, 2H, CH2), 4.65
(br m, 2H, 2 dCH COD), 6.00 (br m, 1H, dCH COD), 7.15 (s,
1H, H arom), 7.24 (s, 1H, H arom), 7.55 (m, 5H, 5 H arom),
CMe3), 1.52 (s, 9H, CMe3), 1.74 (s, 3H, Ar-Me), 1.77 (s, 3H, Ar-
Me), 2.22 (s, 3H, Ar-Me), 2.24 (s, 3H, Ar-Me), 2.51 (ddd,
2JHH = 14.8 Hz, 3JHH = 11.5 Hz, 2JHP = 3.8 Hz, 1H, CHH),
2.75 (ddd, 2JHH = 14.8 Hz, 3JHH = 14.8 Hz, 2JHP = 3.6 Hz, 1H,
CHH), 5.19 (ddd, 3JHH = 11.2 Hz, 3JHH =11.2 Hz, 3JHP = 8.0
Hz, 1H, CHPh), 6.85 (m, 2H, 2 H arom), 7.17 (m, 5H, 5 H arom),
7.41 (m, 3H, 3 H arom), 7.53-7.70 (m, 5H, 5 H arom), 7.16 (m,
2H, 2 H arom). 31P{1H} NMR (CDCl3, 121 MHz): δ 18.3 (d,
JPP = 6 Hz, P-C), 98.6 (d, P-O). 13C{1H} NMR (CDCl3,
75 MHz): δ 16.6 (Ar-Me), 16.9 (Ar-Me), 20.4 (Ar-Me), 20.5
(Ar-Me), 31.7 (CMe3), 32.6 (CMe3), 35.1 (m, 2 CMe3 þ PCH2),
74.4 (m, CH), 124.7 (2 CH arom), 127.0 (Cq arom), 127.4 (Cq
arom), 127.8 (Cq arom), 128.3 (CH arom), 128.7 (2 CH arom),
128.8 (2 CH arom), 129.1 (CH arom), 129.2 (CH arom), 129.3
(CH arom), 129.4 (Cq arom), 130.0 (Cq arom), 131.4 (CH arom),
132.5 (CH arom), 132.8 (CH arom), 132.9 (CH arom), 133.6 (d,
JCP = 5 Hz, CH arom), 135.0 (CH arom), 135.1 (CH arom),
135.7 (Cq arom), 136.0 (Cq arom), 136.4 (d, JCP = 5 Hz, Cq
arom), 137.1 (d, JCP = 3 Hz, Cq arom), 138.8 (d, JCP = 6 Hz, Cq
arom), 138.9 (d, JCP = 6 Hz, Cq arom), 145.9 (d, JCP = 14 Hz,
Cq arom), 146.1 (d, JCP = 10 Hz, Cq arom). Anal. Calcd for
3
7.64-7.73 (m, 3H, 3 H arom), 8.12 (ddd, JHP = 10.0 Hz,
3JHH = 8.0 Hz, 3JHH = 2.0 Hz, 2H, 2 H arom). 31P{1H} NMR
(CDCl3, 121.5 MHz): δ 20.3 (dd, JPRh = 141 Hz, JPP = 60 Hz,
P-C), 121.2 (dd, JPRh = 243 Hz, P-O). 13C{1H} NMR (CDCl3,
75 MHz): δ 13.9 (CHMe), 16.4 (Ar-Me), 16.6 (Ar-Me), 20.4 (Ar-
Me), 20.4 (Ar-Me), 28.7 (CH2 COD), 29.5 (CH2 COD), 30.3
(CH2 COD), 31.6 (CH2 COD), 31.7 (CMe3), 31.9 (CMe3), 32.2
(d, JCP = 7 Hz, CH), 34.9 (CMe3), 35.0 (CMe3), 70.4 (CH2), 93.8
(dd,JCP =10Hz,JCRh =6Hz,dCH COD), 107.4 (dd, JCP =7Hz,
JCRh = 7 Hz, dCH COD), 110.4 (dd, JCP = 12 Hz, JCRh
=
6 Hz, dCH COD), 112.1 (dd, JCP = 12 Hz, JCRh = 5 Hz, dCH
COD), 124.7 (Cq arom), 126.0 (Cq arom), 126.3 (Cq arom), 126.9
(Cq arom), 128.3 (CH arom), 129.0 (CH arom), 129.2 (CH
arom), 129.4 (CH arom), 129.8 (CH arom), 129.9 (CH arom),
132.0 (CH arom), 132.8 (CH arom), 133.1 (CH arom), 133.2
(CH arom), 133.9 (Cq arom), 134.0 (Cq arom), 134.8 (CH arom),
134.9 (CH arom), 135.5 (Cq arom), 136.2 (Cq arom), 136.7 (d,
JCP = 4 Hz, Cq arom), 136.8 (d, JCP = 2 Hz, Cq arom), 143.9 (d,
JCP = 4 Hz, Cq arom), 145.1 (d, JCP = 7 Hz, Cq arom). HRMS
(FAB): m/z 837.3085, [M - BF4]þ (exact mass calculated
C47H60O3P2Rh: 837.3073).
C44H50Cl2O3P2Pd 1/2CH2Cl2: C 58.82; H 5.66. Found: C
59.15; H 5.82. HRMS (FAB): m/z 829.1968, [M - Cl]þ (exact
mass calculated C44H50O3P2ClPd: 829.1959).
3
Representative Procedure for Catalytic Hydrogenation Reac-
tions. In a glovebox, to a 2 mL glass vial were added the ap-
propriate olefin (0.22 mmol), phosphine-phosphite ligand (0.46
μmol), and [Rh(COD)2]BF4 (0.42 μmol) from freshly prepared
stock solutions in CH2Cl2 (total volume = 0.5 mL). Vials were
placed in a steel reaction vessel model HEL CAT18 that holds up
to 18 reactions. The reactor was purged three times with H2 and
finally pressurized to 4 bar. After the desired reaction time, the
reactor was slowly depressurized, solutions were evaporated,
[Rh(COD)((R,R)-8)]BF4 (11b). This complex was prepared as
described for 11a. Yellow solid (0.017 g, 65%). 1H NMR
3
3
(CDCl3, 300 MHz): δ 0.90 (dd, JHP = 11.8 Hz, JHH = 7.0
Hz, 3H, CHMe), 1.43 (s, 9H, CMe3), 1.60 (s, 9H, CMe3), 1.75 (s,
3H, Ar-Me), 1.82 (s, 3H, Ar-Me), 1.90-2.20 (m, 4H, 2 CH2
COD), 2.24 (s, 3H, Ar-Me), 2.28 (s, 3H, Ar-Me), 2.30 (m, 4H, 2
CH2 COD), 3.09 (m, 1H, CHMe), 3.78 (m, 1H, CHH), 4.02 (br
m, 1H, dCH COD), 4.27 (m, 1H, CHH), 4.30 (br m, 1H, dCH
COD), 5.12 (br m, 1H, dCH COD), 5.82 (br m, 1H, dCH
COD), 7.17 (s, 1H, H arom), 7.22 (s, 1H, H arom), 7.40 (m, 2H, 2
H arom), 7.50-7.80 (m, 5H, 5 H arom), 7.73 (m, 1H, H arom),
1
and conversions were determined by H NMR. The resulting
mixtures were dissolved in EtOAc and filtered through a short
pad of silica to remove the catalyst. Enantiomeric excesses were
analyzed by chiral GC, as follows: Dimethyl methylsuccinate:
Supelco γ-DEX 225; 70 °C (5 min), then 10 °C/min up to 130 °C,
15.0 psi He. t1(S) = 12.56 min, t2(R) = 12.74 min. N-Acetyl
phenylalanine methyl ester: Chrompack Chirasil L-Val; 80 °C
(3 min), then 3 °C/min up to 190 °C, 15.0 psi He. t1(R) = 32.14 min,
t2(S) = 32.76 min.
3
3
8.06 (dd, JHP = 10.0 Hz, JHH = 8.0 Hz, 2H, 2 H arom).
31P{1H} NMR (CDCl3, 121 MHz): δ 16.2 (dd, JPRh = 138 Hz,
JPP = 58 Hz, P-C), 122.6 (dd, JPRh = 246 Hz, P-O). 13C{1H}
NMR (CDCl3, 75 MHz): δ 13.2 (d, JCP = 6 Hz, CHMe), 16.5
(Ar-Me), 16.8 (Ar-Me), 20.5 (Ar-Me), 20.6 (Ar-Me), 28.2 (CH2
COD), 29.0 (dd, JCP = 28 Hz, JCRh = 13 Hz, CH), 30.0 (2 CH2
COD), 30.5 (CH2 COD), 32.0 (CMe3), 32.4 (CMe3), 35.0
(CMe3), 35.1 (CMe3), 69.4 (d, JCP = 4 Hz, CH2), 94.5 (dd,
Procedure for Catalytic Hydroformylation Reactions. A 750 mL
Parr reaction vessel that holds six Kilmax 35 mL tubes in a Teflon
rack was introduced in a glovebox. Each tube was charged with
styrene (0.78 g, 7.5 mmol) or allyl cyanide (0.50 g, 7.5 mmol),
Rh(acac)(CO)2 (2 mg, 0.008 mmol), 4 equiv of the corresponding
phosphine-phosphite dissolved in toluene (7 mL), and a magnetic
stirrer. The reactor was then removed from the glovebox, purged
three times with a 1:1 mixture of H2/CO, followed by pressurizing it
to 20 bar, and heated to 50 °C. The reaction solutions were stirred
for the desired reaction time. Then the reactor was slowly depres-
surized; conversion and iso:n ratio were determined by 1H NMR
from an aliquot of the resulting solution. The mixture of aldehydes
was then obtained by the evaporation of the solvent to dryness.
Styrene hydroformylation: 2-phenylpropanal was oxidized to the
corresponding carboxylic acid and analyzed by GC (Chrompack
β-236M, 170 °C (5 min), then 10 °C/min up to 180 °C (5 min), 28.0
psi He); t1(S) = 3.60 min, t2(R) = 3.68 min. Allyl cyanide hydro-
formylation: the enantiomeric excess was analyzed by GC (Astec
Chiraldex A-TA 30 m, 90 °C, (7 min), 5 °C/min up to 150 °C
(5 min), 24.5 psi He); t1(S) = 13.20 min, t2(R) = 13.60 min.
Computational Details. Calculations were performed within the
density functional theory using the B3LYP exchange-correlation
functional32 as implemented in the Gaussian03 program package.33
Geometry optimizations were performed without any symmetry
J
J
CP = 9 Hz, JCRh = 6 Hz, dCH COD), 106.2 (dd, JCP = 7 Hz,
CRh = 7 Hz, dCH COD), 108.7 (dd, JCP = 13 Hz, JCRh = 5
Hz, dCH COD), 112.0 (dd, JCP = 13 Hz, JCRh = 5 Hz, dCH
COD), 124.7 (Cq arom), 125.3 (Cq arom), 126.2 (Cq arom), 126.7
(Cq arom), 128.5 (CH arom), 129.3 (CH arom), 129.4 (CH
arom), 129.6 (CH arom), 129.8 (d, JCP = 3 Hz, Cq arom),
130.0 (CH arom), 130.1 (CH arom), 131.0 (CH arom), 131.1
(CH arom), 131.9 (d, JCP = 2 Hz, CH arom), 133.6 (d, JCP = 2
Hz, CH arom), 134.2 (Cq arom), 135.5 (Cq arom), 136.3 (Cq
arom), 136.3 (CH arom), 136.5 (CH arom), 137.1 (d, JCP = 4
Hz, Cq arom), 137.2 (d, JCP = 2 Hz, Cq arom), 144.0 (d, JCP
=
13 Hz, Cq arom), 144.8 (d, JCP = 6 Hz, Cq arom). HRMS
(FAB): m/z 837.3085, [M - BF4]þ (exact mass calculated
C47H60O3P2Rh: 837.3073).
PdCl2((R,S)-7) (12). To a solution of PdCl2(MeCN)2 (0.013 g,
0.050 mmol) in toluene (5 mL) was added (R,S)-7 (0.037 g, 0.054
mmol) dissolved in toluene (5 mL). The mixture was stirred for
3 h, and the solvent was removed under vacuum. The resulting
solid was dissolved in CH2Cl2 (10 mL) and filtered through
a short pad of Celite. The solution was concentrated up to

5804 Organometallics, Vol. 29, No. 22, 2010
Arribas et al.
constraints using a TZVP basis set with the exception of Rh,
which was described with the Stuttgart Relativistic Small Core
ECP basis set and polarization functions.34,35 Optimized geo-
metries were characterized as minima by computing the harmonic
vibrational frequencies. Coordinates of all optimized complexes
are available upon request.
X-ray Structure Determinations. Crystallographic data were
collected on a Bruker-Nonius X8Apex-II CCD diffractometer
using graphite-monochrotomated Mo KR1 radiation (λ =
0.71073 A). The data were reduced (SAINT)36 and corrected
for Lorentz polarization and absorption effects by multiscan
method (SADABS).37 Structures were solved by direct methods
(SIR-2002)38 and refined against all F2 data by full-matrix least-
squares techniques (SHELXTL-6.12).39n All the non-hydrogen
atoms were refined with anisotropic displacement param-
eters. The hydrogen atoms were included from calculated posi-
tions and refined riding on their respective carbon atoms with
Table 6. Crystallographic Data and Structure Refinement for 12
chem formula
fw
cryst size, mm
cryst syst
space group
a, A
b, A
C45H51Cl5O3P2Pd
985.45
0.27 ꢀ 0.22 ꢀ 0.21 mm3
monoclinic
P21
11.1836(5)
13.9514(7)
c, A
R, deg
15.4756(7)
90
107.5900(10)
90
2301.71(19)
β, deg
γ, deg
V, A3
Z
2
1.422
0.801
1012
Dcalcd, g cm-3
μ, mm-1
F(000)
θ range
1.38° to 30.52°
51 415
11 673 [R(int) = 0.0292]
0.8448 and 0.8108
full-matrix least-squares on F2
11 673/1/515
no. of measd reflns
no. of unique reflns
min., max. transm factor
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
absolute struct param
(32) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(33) (a) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37,
785. (b) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain,
M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin,
R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.:
Wallingford, CT, 2004.
1.025
R1 = 0.0323, wR2 = 0.0814
R1 = 0.0352, wR2 = 0.0835
-0.011(16)
largest diff peak and hole, e A-3
1.384 and -1.074
3
isotropic displacement parameters. A summary of cell param-
eters, data collection, and structure solution and refinement is
given in Table 6.
Acknowledgment. We gratefully acknowledge MICINN
(CTQ2009-11867 and CONSOLIDER-INGENIO,
CSD2007-00006, FEDER support) and Junta de Andalucıa
´
(34) Dolg, M.; Stoll, H.; Preuss, H.; Pitzer, R. M. J. Phys. Chem.
(2008/FQM-3830). We thank Prof. F. Maseras (ICIQ) for
hepful comments. We also acknowledge Dr. Reddy’s for
a generous gift of enantiomers of 3,30-di-tert-butyl-5,50,6,
60-tetramethyl-2,20-bisphenol. M.R. also thanks CSIC for
an I3P posdoctoral contract. C.D. thanks The Royal Society
for a University Research Fellowship.
1993, 97, 5852.
(35) (a) Feller, D. J. Comput. Chem. 1996, 17, 1571. (b) Schuchardt,
K. L.; Didier, B. T.; Elsethagen, T.; Sun, L.; Gurumoorthi, V.; Chase, J.; Li, J.;
Windus, T. L. J. Chem. Inf. Model. 2007, 47, 1045.
(36) SAINT 6.02; Bruker-AXS, Inc.: Madison, WI, USA, 1997-1999.
(37) Sheldrick, G. SADABS; Bruker-AXS, Inc.: Madison,WI, USA,
1999.
(38) Burla, M. C.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.;
Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2003, 36,
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Supporting Information Available: Selected NMR spectra and
crystallographic details as a CIF file. This material is available
free of charge via the Internet at http://pubs.acs.org.
(39) SHELXTL 6.14; Bruker-AXS, Inc.: Madison, WI, USA, 2000-
2003.