Stereochemically dynamic 2,2′-biphosphole ligands for asymmetric catalysis

Article abstract of DOI:10.1021/om0503646

The stereochemically dynamic 2,2′-biphospholes 8, 9, and 10 have been synthesized by asymmetric alkylation of 2,2′-biphospholyl anion with enantiomerically pure diol ditosylates. A good carbon-to-phosphorus induction has been obtained in particular in the case of compound 8. The introduction of a chiral linker between the two phosphorus atoms resulted in partial chirality control of the central and axial chiralities of the 2,2′-biphosphole framework, as three diastereoisomers a, b, and c are obtained among the six expected. In solution at room temperature a, b, and c diastereoisomers exist as an equilibrium mixture; the interconversion occurred by phosphorus-inversion inducing atropoinversion. Reaction of the equilibrium mixture of 2,2′-biphosphole with [MCl₂(CH₃CN)₂] resulted in dynamic resolution leading to diastereo- and enantiopure Pd- and Pt-complexes. Palladium.-catalyzed asymmetric allylic substitution can be achieved with the ligands 8 and 10 with high activities but still moderate enantioselectivities.

Full text of DOI:10.1021/om0503646

Organometallics 2005, 24, 5549-5559
5549
Stereochemically Dynamic 2,2′-Biphosphole Ligands for
Asymmetric Catalysis
Emmanuel Robe´,† Carmen Ortega,†,§ Maciek Mikina,‡ Marian Mikolajczyk,‡
Jean-Claude Daran,*,† and Maryse Gouygou*,†
Laboratoire de Chimie de Coordination, CNRS, 205 Route de Narbonne,
F-31077 Toulouse Cedex, France, and Centre of Molecular and Macromolecular Studies,
Polish Academy of Sciences, 90-363 Lodz, Sienkiewicza 112, Poland
Received May 9, 2005
The stereochemically dynamic 2,2′-biphospholes 8, 9, and 10 have been synthesized by
asymmetric alkylation of 2,2′-biphospholyl anion with enantiomerically pure diol ditosylates.
A good carbon-to-phosphorus induction has been obtained in particular in the case of
compound 8. The introduction of a chiral linker between the two phosphorus atoms resulted
in partial chirality control of the central and axial chiralities of the 2,2′-biphosphole
framework, as three diastereoisomers a, b, and c are obtained among the six expected. In
solution at room temperature a, b, and c diastereoisomers exist as an equilibrium mixture;
the interconversion occurred by phosphorus-inversion inducing atropoinversion. Reaction
of the equilibrium mixture of 2,2′-biphosphole with [MCl2(CH3CN)2] resulted in dynamic
resolution leading to diastereo- and enantiopure Pd- and Pt-complexes. Palladium-catalyzed
asymmetric allylic substitution can be achieved with the ligands 8 and 10 with high activities
but still moderate enantioselectivities.
Introduction
by direct use of this type of ligands without asymmetric
synthesis or resolution clearly presents economical and
environmental advantages.
Advances in the area of transition metal-catalyzed
asymmetric synthesis1 have been traditionally guided
by the concept that stereochemically rigid enantiopure
ligands are required to achieve high enantioselectivities.
Among these chiral ligands, diphosphanes played a
dominant role, although their syntheses and resolution
are difficult because of racemization at higher temper-
ature.2
A conceptually new strategy for asymmetric catalysis
consists in the use of stereochemically dynamic ligands
rather than the use of classical stereochemically rigid
enantiopure ligands.3 In this approach an enantiopure
ligand (L*), sometimes referred to as a chiral activator,
interacts with an achiral or meso ligand (L) and causes
the latter to preferentially adopt one of its chiral
conformations which is ultimately responsible for the
transmission of asymmetry in enantioselective trans-
formation. Successful results have been obtained with
chirally flexible diphosphanes such as BIPHEP,4 DPPF,5
or NUPHOS.6 This approach to asymmetric catalysis
In 1994, we began to focus our attention on a
C2-symmetric diphosphane combining central and axial
chiralities: the 1,1′-diphenyl-3,3′,4,4′-tetramethyl-2,2′-
biphosphole (BIPHOS). This diphosphane is a chirally
flexible ligand because of the configurational instability
of the axial chirality generated by the 2,2′-biphosphole
framework and of the central chiralities at the phos-
phorus atoms.7 The use of the stereochemically dynamic
2,2′-biphosphole (BIPHOS), after spontaneous resolu-
tion by crystallization and complexation on the Pd
center, proved to be as effective as well-known chirally
rigid diphosphines in asymmetric allylic substitution.8
As part of our continuing interest in chiral 2,2′-
biphosphole ligands, we have explored a new approach
to enantiopure 2,2′-biphosphole compounds as asym-
metric ligands and catalysts. This approach is based on
the facile isomerization of 2,2′-biphosphole to accomplish
a dynamic resolution. Recently, we have reported pre-
liminary results on metal dynamic resolution leading
* Corresponding authors. Tel: (33) 5 61 33 31 74. Fax: (33) 5 61 55
30 03. E-mail: daran@lcc-toulouse.fr; gouygou@lcc-toulouse.fr.
† Laboratoire de Chimie de Coordination.
(4) (a) Mikami, K.; Kataoka, S.; Yusa, Y.; Aikawa, K. Org. Lett. 2004,
6, 3699-3701. (b) Mikami, K.; Aikawa, K.; Yusa, Y.; Hatano, M. Org.
Lett. 2002, 4, 91-94. (c) Becker, J. J.; White, P. S.; Gagne´ M. R. J.
Am. Chem. Soc. 2001, 123, 9478-9479. (d) Mikami, K.; Korenaga, T.;
Terada, M.; Ohkuma, T.; Pham, T.; Noyori, R. Angew. Chem., Int. Ed.
Engl. 1999, 38, 495-497.
(5) Mikami, K.; Aikawa, K. Org. Lett. 2002, 4, 99-101.
(6) (a) Doherty, S.; Knight, J. G.; Hardacre, C.; Luo, H.; Newman,
C. R.; Rath, R. K.; Campbell, S.; Nieuwenhuyzen, M. Organometallics
2004, 23, 6127-6133. (b) Doherty, S.; Newman, C. R.; Rath, R. K.;
Luo, H.; Nieuwenhuyzen, M.; Knight, J. G. Org. Lett. 2003, 5, 3863-
3866.
‡ Centre of Molecular and Macromolecular Studies.
§ Present address: Dpto. de Qu´ımica Orga´nica, Facultad de Qu´ım-
ica, Circuito exterior s/n, Ciudad Universitaria, Coyoaca´n 04510,
Me´xico.
(1) Ojima, I. Catalytic Asymmetric Synthesis, 2nd ed.; Wiley-VCH:
New York, 2000. (b) Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H.
Comprehensive Asymmetric Catalysis; Springer-Verlag: Berlin, 1999.
(c) Noyori, R. Asymmetic Catalysis in Organic Synthesis; Wiley: New
York, 1994.
(2) (a) Pietrusiewicz, K. M.; Zablocka, M. Chem. Rev. 1994, 94,
1375-1411. (b) Valentine, D., Jr. Asymmetric Synthesis; Academic
Press Inc.: New York, 1984; Vol. 4, pp 227-312.
(3) (a) Walsh, P. J.; Lurain, A. E.; Basells, J. Chem. Rev. 2003, 103,
3297-3344. (b) Mikami, K.; Aikawa, K.; Yusa, Y.; Jodry, J. J.;
Yamanaka, M. Synlett. 2002, 10, 1561-1578, and references therein.
(7) Tissot, O.; Gouygou, M.; Daran, J.-C.; Balavoine, G. G. A. Chem.
Commun. 1996, 2287-2288.
(8) Tissot, O.; Gouygou, M.; Dallemer, F.; Daran, J.-C.; Balavoine,
G. G. A. Angew. Chem., Int. Ed. 2001, 40, 1076-1078.
10.1021/om0503646 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/01/2005

5550 Organometallics, Vol. 24, No. 23, 2005
Scheme 1. Synthesis of the 2,2′-Biphosphole Derivatives
Robe´ et al.
to diastereo- and enantiopure 2,2′-biphosphole Pd-
complexes.9
Synthesis of 2,2′-Biphosphole Ligands. The strat-
egy used to access resolved 2,2′-biphosphole compounds
is based on a two-step chirality control process: (1)
partial chirality control in order to keep some degree of
freedom; (2) total chirality control by enantioselective
coordination on a metal center.
The axial and central chiralities of the 2,2′-biphosp-
hole framework can be controlled by introducing a chiral
linker, such as a chiral carbon chain, between the two
phosphorus atoms. We have investigated the asym-
metric alkylation of the 2,2-biphosphole dianion with
enantiomerically pure diol ditosylates. The synthetic
pathway involved three steps starting from 1-phenyl-
2,3-dimethylphosphole 1.10 In the first step, pyrolysis
of phosphole 1 using the procedure previously described
by Mathey and et al.11 gave the tetraphosphole 2
(Scheme 1). In the next step, cleavage of the two
phosphorus-phosphorus bonds in 2 using sodium naph-
Here, we report a convenient procedure for the
preparation of various stereochemically dynamic 2,2′-
biphospholes by asymmetric alkylation of 2,2′-biphos-
pholyl anion with enantiomerically pure ditosylates.
Since the use of these chirally flexible diphosphanes in
asymmetric catalysis relies on the slow interconversion
of chiral configurations, the isomerization process was
studied. These diphosphanes became stereorigid as
disulfide derivatives, allowing structural and stereo-
chemistry studies by X-ray diffraction analysis and
molecular modeling. We have also examined the dy-
namic resolution of these stereochemically dynamic 2,2′-
biphospholes by coordination to transition metals such
as palladium(II) and platinum(II). Their use in pal-
ladium-catalyzed asymmetric allylic substitution is also
reported.
Table 1. Selected Geometrical Parameters within the Biphosphole Framework
P-C-C-P torsion
angle (deg)
dihedral angle between
phosphole rings (deg)
compound code
R[Sp,Sp,Rc,Rc]-12a
R[Rp,Sp,Rc,Rc]-12b
S[Rp,Rp,Rc,Rc]-12c
S[Rp,Sp,Rc,Rc]-13a
R[Sp,Sp,Rc,Rc]-13c
S[Rp,Rp,Rc,Rc]-13b
R[Sp,Sp,Sc,Sc]-11a
S[Rp,Rp,Sc,Sc]-11c
R[Sp,Rp,Sc,Sc]-11b
R[Rp,Sp,Sc,Sc]-15
S[Rp,Sp,Rc,Rc]-17
-79.7(3)
71.50(6)
-52.1(3)
51.92(8)
89.2(9)
79.6(2)
50.4(2)
52.75(6)
-81.9(3)
81.3(1)
81.7(3)
81.1(1)
-55.4(2)
59.8(6)
84.4(3) [mean value]
-23(2) [mean value]
-8.4(3)
87.9(1) [mean value]
33(1) [mean value]
20.2(2)
5.9(2)
29.8(9)
Table 2. Torsion Angles (deg) within the Chiral Chain for Compounds 11a, 11b, and 11c
torsion angle
11a
11c
11b
C(111)-C(1)-C(2)-C(3)
C(1)-C(2)-C(3)-C(311)
169.2(2)
168.5(2)
-163.3(4) [-160.6(4)]
-172(2)[-165(2)]
28.7(5) [28.4(6)]
53(3)[62(3)]

Stereochemically Dynamic 2,2′-Biphosphole Ligands
Organometallics, Vol. 24, No. 23, 2005 5551
Figure 1. Molecular view of R[Sp,Sp,Rc,Rc]-12a with
atom labeling. Ellipsoids represent 30% probability [sym-
metry code: (i) -y, -x, -z + 1/2]. Selected bond distances
(Å): P(1)-S(1) 1.9597(6); P(1)-C(1) 1.840(2); P(1)-C(11)
1.801(2); P(1)-C(14) 1.818(2).
Figure 3. Molecular view of S[Rp,Rp,Rc,Rc]-12c with
atom labeling. Ellipsoids represent 30% probability. Se-
lected bond distances (Å): P(1)-S(1) 1.946(2); P(1)-C(1)
1.846(6); P(1)-C(11) 1.784(6); P(1)-C(14) 1.799(5).
Figure 4. View of the seven-membered rings for com-
pounds R[Sp,Sp,Sc,Sc]-11a and S[Rp,Rp,Sc,Sc]-11c em-
phasizing the difference of conformation for the chiral
chain.
rus12 (Scheme 1). The three diastereoisomers a, b, and
c of each disulfide compound could be isolated by column
Figure 2. Molecular view of R[Rp,Sp,Rc,Rc]-12b with
atom labeling. Ellipsoids represent 30% probability. Se-
lected bond distances (Å): P(1)-S(1) 1.9553(7); P(1)-C(1)
1.846(2); P(1)-C(11) 1.825(2); P(1)-C(14) 1.818(2); P(2)-
S(2) 1.9405(8); P(2)-C(2) 1.827(2); P(2)-C(21) 1.815(2);
P(2)-C(24) 1.809(2).
1
chromatography and characterized by H, 13C, and 31P
NMR spectroscopy, mass spectroscopy, and X-ray dif-
fraction studies.
Structural and Stereochemical Studies. The
ORTEP views of the S-protected ligands 12a-c empha-
sizing the axial chirality of the biphosphole framework
are represented in Figures 1 to 3. The other structures
related to ligands 11a-c and 13a-c are deposited in
the Supporting Information. For all structures, the
distances and angles within the phosphole rings are
identical within experimental error and in good agree-
ment with reported structures.7,13 As shown in Table
1, the P-C-C-P torsion angle and the dihedral angle
between the two phosphole rings are strongly dependent
on the relative chirality of the phosphorus atoms.
Indeed, the absolute value of this torsion angle varies
from 79.7° to 89.2° in the case of the two phosphorus
having the same chirality, whereas this value varies
from 50.4 to 52.1 when the two phosphorus have
thalene led to the 2,2′-biphospholyl anion 3. Then, we
have investigated the asymmetric alkylation of 3 in high
dilution conditions using various enantiomerically pure
diol ditosylates 4-7. (2R,3R)-2,3-Butaneditosylate 4
could not react with 3 possibly because of the too short
C2-chain to bridge the two phosphorus atoms. In con-
trast, ditosylates 5-7 reacted with 3 to afford 2,2′-
biphospholes 8-10, respectively, as a mixture of three
diastereoisomers in each case (Scheme 1).
To facilitate the separation and characterization of
these diastereoisomers, 2,2′-biphospholes 8-10 were
converted into more air-stable disulfide derivatives. 2,2′-
Biphosphole disulfides 11-13 were quantitatively ob-
tained by sulfuration of 8-10, respectively, a process
that occurs with retention of configuration at phospho-
(12) (a) McEven, W. E. Top. Phosphorus Chem. 1965, 2, 1. (b)
Gallaher, M. J.; Jenkins, J. D. Top. Stereochem. 1969, 3, 1.
(13) Tissot, O.; Hydrio, J.; Gouygou, M.; Dallemer, F.; Daran, J.-C.;
Balavoine, G. G. A. Tetrahedron 2000, 56, 85-93. Hydrio, J.; Gouygou,
M.; Dallemer, F.; Balavoine, G. G. A.; Daran, J.-C. Eur. J. Org. Chem.
2002, 675-685.
(9) Ortega, C.; Gouygou, M.; Daran, J.-C. Chem. Commun. 2003,
1154-1155.
(10) Breque, A.; Mathey, F.; Savignac, P. Synthesis 1981, 983-985.
(11) Laporte, F.; Mercier, F.; Ricard, L.; Mathey, F. J. Am. Chem.
Soc. 1994, 116, 3306-3311.

5552 Organometallics, Vol. 24, No. 23, 2005
Robe´ et al.
Figure 5. Different stereoisomers of 2,2′-biphosphole that possess two chiral centers and one chiral axis; each stereoisomer
is also represented in a Newman projection along the axis of the C-C linking the phosphole rings.
chain, but here the low value of the P-C-C-P torsion
angle is related to the opposite configuration of the
phosphorus atoms.
These structural determinations unambiguously es-
tablished the relative configuration of both the central
and the axial elements of chirality of the 2,2′-biphosp-
hole framework. The different possibilities of combining
axial and central chiralities in 2,2′-biphosphole are
depicted in Figure 5. This stereochemical analysis shows
the occurrence of six diastereoisomers.
Only three diastereoisomers are obtained by introduc-
tion of a chiral bridge between the two phosphorus
atoms of the 2,2′-biphosphole framework. The stereo-
isomer C is obtained for compounds 11c, 12c, and 13b,
D for compounds 11a, 12a, and 13c, E for compound
13a, and F for compound 11b and 12b. These results
clearly indicate that the introduction of a short chiral
linker, such as a C3- or C4-chain, between the two
phosphorus atoms prevents the formation of A and B
forms to favor the C and D and E or F configurations
(Figure 5). C and D stereoisomers are always isolated,
whereas either the E or F isomer is obtained.
The E and F stereoisomers could be considered as two
atropoisomers, as illustrated in Figure 6. Conforma-
tional analysis of the rotation process around the C-C
Figure 6. Different atropoisomers of 2,2′-biphosphole 13b.
bond linking the two phosphole rings was performed on
2,2′-biphospholes 13 by molecular mechanics calcula-
tions. According to these calculations, the S[Rp,Sp,Rc,-
opposite configuration. There is however one exception
for compound 11a, for which the torsion angle is -55.4-
Rc]-13b isomer (E form) is energetically more favored
than the R[Rp,Sp,Rc,Rc]-13b′ isomer (F form); the
difference in energy between these two atropoisomers
is 23 kcal‚mol-1. Moreover, these calculations agree with
experimental observations since the three isolated
isomers 13a, 13b, and 13c are located approximatively
at the same energy level (differences in energy are
within the range 5 to 8 kcal‚mol-1).
Since the sulfur addition to trivalent phosphorus
compounds proceeds with retention of configuration,12
these results suggest that the configurations determined
for the 2,2′-biphosphole disulfide would be identical for
the corresponding free 2,2′-biphosphole ligand.
(2)°, although the two phosphorus have the same
chirality. In that case, the influence of the conformation
of the chiral chain overcomes the chirality on phospho-
rus. Indeed, if we consider the conformation of the chain
in compounds 11a and 11c as shown in Table 2, the
torsion angles clearly indicate that the position of the
methyl groups with respect to the C(1)‚‚‚C(3) direction
is cis in the case of 11a and trans for 11c. The cis
conformation results in the P atoms being on the
opposite side to the plane containing the chiral chain
(Figure 4), thus restraining the dihedral angle between
the phosphole rings. In compound 11b, a similar cal-
culation reveals a trans conformation for the chiral
Scheme 2. Stereoselective Desulfuration of
[Sp,Sp,Sc,Sc]-(+)-3,3′,4,4′-Tetramethyl-5,5′-diphenyl-1,1′-(pentane-2,4-diyl)-2,2′-biphospholyl 1,1′-disulfide,
11a

Stereochemically Dynamic 2,2′-Biphosphole Ligands
Organometallics, Vol. 24, No. 23, 2005 5553
Finally, as three diastereoisomers are obtained among
the six expected, the chiral controllers have induced
partial chirality control of the 2,2′-biphosphole frame-
work.
In addition a good carbon-to-phosphorus induction has
been observed in particular in the case of compound 8
(11), in which the original R,R chirality of the enantio-
merically pure diol ditosylate induces the preferred S,S
stereochemistry of the phosphorus atoms.14 The de-
crease in induction observed from 8 (11) to 9 (12) is
probably due to an increase of the carbon chain length.
In the case of compound 10 (13), the moderate carbon-
to-phosphorus induction could be assigned to a longer
carbon linker associated with stereogenic centers farther
away from the phosphorus atoms.
Isomerization Process. To study the isomerization
process in these stereochemically dynamic 2,2′-biphos-
pholes, we have investigated the desulfurization of
compounds 11a, 11b, and 11c by using a fully stereo-
selective method15 that affords at low temperature
chiral phosphines with retention of configuration. R[Sp,-
Sp,Sc,Sc]-11a reacted with methyltrifluoromethane sul-
fonate to give compound 14a (δ31P ) 60.5) in quanti-
tative yield (Scheme 2). Then, the reaction with tert-
butyllithium sulfide at -60 °C led to the formation of
R[Sp,Sp,Sc,Sc]-8a as major product along with R[Sp,-
Rp,Sc,Sc]-8b and S[Rp,Rp,Sc,Sc]-8c as minors products,
as indicated by 31P NMR. This is indicative of an
isomerization process taking place at -60 °C. The ratio
8a:8b:8c of 80/15/5 was then obtained at 25 °C.
On the other hand, S[Rp,Rp,Sc,Sc]-11c was quanti-
tatively transformed into 14c (δ31P ) 65.35). Treatment
of 14c with t-BuSLi at -70 °C afforded a mixture of 8c,
8b, and 8a, as evidenced by 31P NMR analysis (Figure
7). The isomerization process was monitored by 31P
NMR from -70 to 25 °C (Figure 7). These data are
consistent with an interconversion of 8c to 8a via 8b.
Since the chiral bridge in 2,2-biphosphole compounds
prevents the formation of A and B forms (Figure 5), the
only possible pathway for this isomerization requires a
phosphorus inversion16 inducing an atropoinversion as
illustrated in Figure 8.17
Palladium and Platinum Complexes. Before en-
gaging in asymmetric catalysis, the coordination chem-
istry of these new ligands was studied. Initial complex-
ing experiments were performed with palladium(II) and
platinum(II) precursors.
The reaction of 8a-c in CH2Cl2 at room temperature
with 1 equiv of [PdCl2(CH3CN)2] led to complete con-
sumption of the ligand in 1 h at room temperature to
afford [PdCl2(2,2′-biphosphole)] 15 (90%) and an uni-
dentified product (10%)18 (Scheme 3). Complex R[Rp,-
Sp,Sc,Sc]-15 could be isolated in a pure form and
(14) Nucleophilic subtitution on carbon resulted in inversion of
configuration in the case of compounds 8 (11) and 9 (12).
(15) (a) Omelanczuk, J.; Mikolajczyk, M. J. Am. Chem. Soc. 1979,
101, 7292. (b) Omelanczuk, J.; Perlikowska, W.; Mikolajczyk, M. J.
Chem. Soc., Chem. Commun. 1980, 24.
(16) In 2,2′-biphosphole, the inversion barrier for the pyramidal
phosphorus is reduced, relative to that in phosphines, as a result of
the increase in aromatic character of the phosphorus in the transition
state; see ref 7.
(17) The driving force of this isomerization process should be the
phosphorus inversion. No interconversion between a, b, and c occurred
even at +90 °C in toluene according to NMR studies. In 2,2-biphosphole
disulfides the pyramidal inversion at phosphorus is suppressed, as the
lone pairs are masked by sulfur.
Figure 7. Variable-temperature 31P{1H} NMR spectra of
desulfurization of 11c.
1
characterized by H, 13C, and 31P NMR spectroscopy,
mass spectroscopy, and X-ray diffraction studies. Two
palladium complexes were also obtained in the same

5554 Organometallics, Vol. 24, No. 23, 2005
Robe´ et al.
Figure 8. Isomerization process in the stereochemically dynamic 2,2-biphospholes.
Scheme 3. Synthesis of 2,2′-Biphosphole Metal
Complexes
conditions with the ligands 9a-c, but they could not
be separated and identified.
With the [PtCl2(CH3CN)2] precursor, the reaction of
the ligands 8a-c, 9a-c, and 10a-c was complete in 3
days at room temperature in dichloromethane and only
Figure 10. Molecular view of S[Rp,Sp,Rc,Rc]-17 with
atom-labeling scheme. Ellipsoids represent 30% prob-
ability. Selected bond distances (Å): Pt(1)-P(1) 2.239(4);
Pt(1)-P(2) 2.247(4); Pt(1)-Cl(1) 2.348(4); Pt(1)-Cl(2) 2.350-
(4); P(1)-C(1) 1.80(2); P(1)-C(11) 1.82(2); P(1)-C(14) 1.78-
(2); P(2)-C(2) 1.87(2); P(2)-C(21) 1.82(2); P(2)-C(24)
1.77(2).
affords [PtCl2(2,2′-biphosphole)] 16, 17, and 18, respec-
1
tively, as indicated by H, 13C, and 31P NMR spectros-
copy and mass spectroscopy. The structure of the
S[Rp,Sp,Rc,Rc]-17 complex was determined by X-ray
diffraction analysis. All these complexes could be quan-
titatively obtained in 3 h by refluxing in dichlo-
romethane the ligands 8a-c, 9a-c, and 10a-c and the
[PtCl2(CH3CN)2] precursor.
Molecular views of complexes R[Rp,Sp,Sc,Sc]-15 and
S[Rp,Sp,Rc,Rc]-17 are shown in Figures 9 and 10. In
both compounds, the coordination around the metal is
square planar. The X-ray structure of 159 and 17
indicates that only the [Rp,Sp] configuration of 2,2-
biphosphole is complexed to the metal center. The axial
chirality of the 2,2-biphosphole framework is reduced
upon complexing. Indeed, owing to the strain induced
by chelating on the metal, the P(1)-C(11)-C(21)-P(2)
torsion angle, (15: -8.4(3)°, 17: 5.9 (2)°) is drastically
reduced from the values observed in free ligands (Table
1). The strain induced by the coordination is also
reflected by the larger difference observed between
torsion and dihedral angles. The phosphole rings are
not only twisted along the C-C bond linking the rings
but are also bent with respect to each other to help the
phosphorus atoms to accommodate the coordination on
the metal atom. It is interesting to point out that this
deformation is much larger with the platinum complex
17.
These results show that reaction of the diastereoiso-
meric mixture of equilibrating 2,2-biphosphole with
[MCl2(CH3CN)2] resulted in a dynamic resolution mix-
ture to give diastereo- and enantiopure Pd- or Pt-
complexes.
Asymmetric Pd-Allylic Substitution. As a pre-
liminary evaluation of the catalytic properties of the
chiral ligands 8 and 10, we have explored the palladium-
catalyzed asymmetric allylic substitution reaction19
(Scheme 3). Thus, the reaction of 1,3-diphenylprop-2-
enyl acetate 19 with the anion of dimethyl malonate in
the presence of [Pd(C3H5)Cl]2 (1.5 mol %) and the chiral
ligands 8 and 10 (3 mol %) provided the expected allylic
substitution product 20 (Scheme 4) in high yields and
moderate enantioselectivities. The results are sum-
marized in Table 3.
This reaction occurred with 33% and 34% ee for 8 and
10, respectively (entries 1, 3), with high activities in both
Figure 9. Molecular view of R[Rp,Sp,Sc,Sc]-15 with atom-
labeling scheme. Ellipsoids represent 50% probability.
Selected bond distances (Å): Pd(1)-P(1) 2.2735(6); Pd(1)-
P(2) 2.2479(6); Pd(1)-Cl(1) 2.3381(7); Pd(1)-Cl(2) 2.3514-
(6); P(1)-C(1) 1.867(3); P(1)-C(11) 1.820(2); P(1)-C(14)
1.803(3); P(2)-C(3) 1.845(3); P(2)-C(21) 1.803(3); P(2)-
C(24) 1.796(3).
(18) This unidentified product is a palladium complex with four
diastereotopic phosphorus having opposite phosphorus configurations
[Rp,Sp] according to 31P NMR (δp 53.2 (d) , δp 51.2(d), JPP 3.25; δp
52.9(s), δp 50.9(s)).
(19) Trost, B. M.; Van Vranken, D. L. Chem. Rev. 1996, 96, 395-
422.

Stereochemically Dynamic 2,2′-Biphosphole Ligands
Organometallics, Vol. 24, No. 23, 2005 5555
an excess of sodium (∼0.5 g) in dry THF (6 mL) until the
solution became green. Solid tetramer 1 (400 mg, 0.54 mmol)
was then added slowly in portions. The reaction mixture
turned red and was stirred until it became green again (∼2
h). This solution of dianion 2 and a THF solution (6 mL) of
ditosylate (1.08 mmol) were transferred dropwise by cannula
at the same time into an other Schlenk containing 200 mL of
dry THF, and the reaction mixture was stirred for 16 h at room
temperature. After evaporation to dryness, the resulting
residue was extracted with small portions of pentane. The
combined pentane extracts were filtered through Celite, and
the solvents were evaporated to give crude compound. This
compound was purified by filtration on alumina under argon
using a mixture of 95/5 pentane/dichloromethane as solvent.
8. 31P NMR (CDCl3): δ 16 (8c), 18 (8a), 27(d, P1), 31(d, P2),
JP1,P2 ) 42 Hz (8b).
Scheme 4. Allylic Substitution Reaction
Table 3. Results of Asymmetric Allylic
Substitution Reaction of 1,3-Diphenylprop-2-enyl
Acetate with the Anion of Dimethyl Malonate
reaction
time
ee% of 18c
entry ligand
base
solvent
yieldb (confign)d
1
2
3
8 (3%) BSA/AcOK CH2Cl2 30 min 96%
33 (S)
15 (S)
34 (S)
8 (3%) BSA/AcOK THF
5 h
66%
93%
10 (3%) BSA/AcOK CH2Cl2 1 h
a Reaction conditions: 1 mmol of (E)-1,3-diphenylprop-2-enyl
9. 31P NMR (CDCl3): δ 21.49 (s, P1), 22.7 (s, P2) (9b), 22.25
(9a), 33.66 (9c).
acetate, 3 mmol of dimethylmalonate with 3% palladium as
1
[PdCl(allyl]2 at RT. The complete conversion was observed by H
NMR expect for the entries 1 and 3. b Isolated yield. c Determined
by 1H NMR using the chiral shift reagent Eu(hfc)3. d Determined
on the basis of the sign of the specific rotation of the product.
10. 31P NMR (CDCl3): δ 0.48 (d, P1), 9.06 (d, P2), JP1,P2 )
8.0 Hz (10a), 6.13 (10c), 8.31 (10b).
General Procedure for Compounds 11, 12, and 13.
Sulfur (2 equiv) was added to a solution of crude 2,2′-
biphosphole compound in dichloromethane (30 mL), and the
reaction mixture was stirred overnight at room temperature.
After evaporation to dryness, the mixture was chromato-
graphed on silica gel.
R[Sp,Sp,Sc,Sc]-(+)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(pentane-2,4-diyl)-2,2′-biphospho-lyl 1,1′-Disulfide,
11a. Eluent: pentane/dichloromethane, 40/60. Yellow solid
(yield ) 53%). Mp ) 298-301 °C. 1H NMR (CDCl3): δ 0.77
(dd, JH,P ) 17.8 Hz, JH,H ) 6.9 Hz, 6H, CH3-CH), 1.78 (m,
1H, CH2), 1.85 (m, 1H, CH2), 2.07 (dd, JH,P ) 2.5 Hz, JH,P
) 2.3 Hz, 6H, CH3-C-C), 2.10 (d, JH,P ) 2.6 Hz, 6H, CH3-C-
CPh), 3.13 (m, 2H, CH-P), 7.36 (m, 6H, Ph), 7.68 (m, 4H, Ph).
13C NMR (CDCl3): δ 15.73 (d, JC,P ) 12.9 Hz, CH3-C-CPh),
16.07 (dd, JC,P ) 12.5 Hz, JC,P ) 2.2 Hz, CH3-C-C), 17.55 (t,
JC,P ) 1.73 Hz, CH3-CH), 32.30 (dd, JC,P ) 45.6 Hz, JC,P )
2.6 Hz, CH), 39.09 (t, JC,P ) 2.94 Hz, CH2), 128.37 (s, Ph)
128.88 (s, Ph) 129.42 (t, JC,P ) 2.54 Hz, Cortho), 130.95 (dd,
JC,P ) 76.9 Hz, JC,P ) 12.4 Hz, Ph-C-P), 133.50 (dd, JC,P )
73.4 Hz, JC,P ) 2.0 Hz, C-Ph), 135.34 (d, JC,P ) 10.4 Hz,
cases with complete conversion after 30-60 min at room
temperature using CH2Cl2 as solvent and N,O-bis-
(trimethylsilyl)acetamide (BSA)/AcOK as base. The use
of THF as solvent decreased the rate of the reaction
(entry 2), as the complete conversion was not observed
after 5 h, and affected the enantioselectivity (15%).
These results show that palladium-catalyzed allylic
substitution of 1,3-diphenylprop-2-enyl acetate with the
anion of dimethyl malonate can be achieved with ligands
8 and 10 with high activities but still moderate enan-
tioselectivities (up to 34% ee) in comparison with the
best values obtained with the well-known chirally rigid
diphosphines.19
Conclusions
A new and convenient preparation of stereodynamic
2,2′-biphosphole ligands and a highly and practical
transformation to diastereo- and enantiopure complexes
have been achieved. Furthermore, the direct use of these
stereodynamic ligands in palladium-catalyzed asym-
metric allylic substitution has been demonstrated.
Catalyst optimization through the modification of the
chiral linker represents a viable approach currently
being developed.
C
ipso), 148.69 (dd, JC,P ) 23.9 Hz, JC,P ) 2.2 Hz, CH3-C-C),
148.79 (dd, JC,P ) 22.9 Hz, JC,P ) 2.2 Hz, CH3-C-C-Ph). 31
P
NMR (CDCl3): δ 61.03. [R]D +155.6 (CH2Cl2, c 0.5). MS (DCI,
NH3) m/z: (%) 507 (100%) [M + H]+. Anal. Calcd for C29H32P2S2
(507.15): C 68.78, H 6.36, S 12.64. Found: C 68.05, H 6.24, S
13.28. Crystals suitable for X-ray analysis were obtained by
slow evaporation of a dichloromethane solution.
R[Sp,Rp,Sc,Sc]-(+)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(pentane-2,4-diyl)-2,2′-biphospho-lyl 1,1′-Disulfide,
11b. Eluent: diethyl ether. Yellow solid. Yield ) 10%. 1H NMR
(CDCl3): δ 0.96 (d, JH,H ) 10 Hz, 3H, CH3-CHP(1)), 1.00 (d,
JH,H ) 5 Hz, 3H, CH3-CHP(2)), 1.71 (m, 2H, CH-P), 2.04
(d, JH,P ) 10 Hz, 6H, CH3-C-C), 2.08 (d, JH,P ) 2.5 Hz, 6H,
CH3-C-CPh), 2.12 (m, 2H, CH2), 7.35 (m, 2H, Ph), 7.40 (m,
4H, Ph) 7.64 (m, 4H, Ph). 13C NMR (CDCl3): δ 15.11(d, JC,P
) 12.5 Hz, CH3-C-CPh), 17.41 (s, CH3-CH), 18.65 (d, JC,P
) 11.2 Hz, CH3-C-C), 22.64 (s, CH2), 29.66 (s, CH), 127.95 (d,
JC,P ) 7.5 Hz, C-P), 128.47 (s, Cpara), 128.89 (s, Cmeta), 129.10
(s, Cortho), 134.24 (d, JC,P ) 11.2 Hz, Ph-C-P), 136.66 (s, Cipso),
146.50 (s, CH3-C-C), 148.20 (s, CH3-C-C-Ph). 31P NMR
(CDCl3): δ 63.3 P(1), 67.3 P(2). [R]D +417.1 (CH2Cl2, c 0.14).
MS (DCI, NH3) m/z: (%) 507 (100%) [M + H]+. Crystals
suitable for X-ray analysis were obtained by slow evaporation
of a diethyl ether solution.
Experimental Section
General Procedures. All reactions were carried out under
dry argon by using Schlenk glassware and vacuum line
techniques. Solvents were freshly distilled from standard
drying agents. 1H, 13C{1H, 31P}, and 31P{1H} 195Pt NMR spectra
were recorded on Bruker WMX 400 and AV 500 instruments.
Mass spectra were obtained on a Nermag R10-10 instrument.
Elemental analyses were performed by the “Service d’Analyse
du Laboratoire de Chimie de Coordination” at Toulouse.
Optical rotations were measured with a Perkin-Elmer 241
polarimeter.
1-Phenyl-3,4-dimethylphosphole 1,10 tetraphosphole 2,11 di-
anion 3,11 and enantiomerically pure diol ditosylates (R,R)-4,
(R,R)-5, (S,S)-6, and (R,R)-720 were prepared as described in
the literature.
General Procedure for Compounds 8, 9, and 10. In a
Schlenk tube, naphthalene (0.02 g, 1.88 mmol) was stirred with
S[Rp,Rp,Sc,Sc]-(+)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(pentane-2,4-diyl)-2,2′-biphospho-lyl 1,1′-Disulfide,
11c. Eluent: pentane/dichloromethane, 45/55. Yellow solid
(yield ) 4%). Mp ) 178-180 °C. 1H NMR (CDCl3): δ 1.00 (dd,
JH,P ) 18.5 Hz, JH,H ) 7.4 Hz, 6H, CH3-CH), 2.15 (dd, JH,P
) 2.2 Hz, JH,P ) 0.9 Hz, 6H, CH3-C-C), 2.18 (m, 2H, CH2),
(20) Bakos, J.; To´th, I.; Heil, B.; Marko´, L. J. Organomet. Chem.
1985, 279, 23-29.

5556 Organometallics, Vol. 24, No. 23, 2005
Robe´ et al.
2.26 (dd, JH,P ) 3.2 Hz, JH,P ) 1.9 Hz, 6H,CH3-C-CPh), 2.37
(m, 2H, CH-P), 7.34 (m, 2H, Ph), 7.42 (m, 4H, Ph) 7.70 (m,
4H, Ph). 13C NMR (CDCl3): δ 15.70 (dd, JC,P ) 14.0 Hz, JC,P
) 1.0 Hz, CH3-C-CPh), 16.48 (s, CH3-CH), 16.82 (dd, JC,P )
13.2 Hz, JC,P ) 3.6 Hz, CH3-C-C), 32.01 (t, JC,P ) 1.8 Hz,
CH2), 38.16 (d, JC,P ) 44.2 Hz, CH), 125.75 (dd, JC,P ) 74.3
Hz, JC,P ) 9.6 Hz,C-P), 128.37 (s, Cpara), 128.99 (s, Cmeta),
129.30 (t, JC,P ) 2.8 Hz, Cortho), 133.63 (dd, JC,P ) 76.9 Hz,
JC,P ) 12.4 Hz, Ph-C-P), 134.98 (dd, JC,P ) 12.4 Hz, JC,P )
2.7 Hz, Cipso), 149.50 (dd, JC,P ) 23.2 Hz, JC,P ) 4.1 Hz, CH3-
C-C), 153.00 (dd, JC,P ) 24.2 Hz, JC,P ) 6.4 Hz, CH3-C-C-
Ph). 31P NMR (CDCl3): δ 67.34. [R]D +356.6 (CH2Cl2, c 0.5).
MS (DCI, NH3) m/z: (%) 507 (100%) [M + H]+. Anal. Calcd
for C29H32P2S2 (507.15): C 68.78, H 6.36, S 12.64. Found: C
68.69, H 6.89, S 11.70. Crystals suitable for X-ray analysis
were obtained by slow evaporation of a dichloromethane
solution.
Hz, JC,P(2) ) 10.0 Hz, CH3-C-C-P(2)). 31P NMR (CDCl3): δ
55.36 P(2), 51.05 P(1). [R]D -127.6 (CH2Cl2, c 0.5). MS (DCI,
NH3) m/z: (%) 565 (100%) [M + H]+. Anal. Calcd for
C31H34O2P2S2 (564.15): C 65.96, H 6.03, S 11.34. Found: C
66.20, H 6.41, S 9.06. Crystals suitable for X-ray analysis were
obtained by slow evaporation of a dichloromethane solution.
S[Rp,Rp,Rc,Rc]-(+)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(2,3-O-isopropylidene-2,3-dihydroxybutane-1,4-diyl)-
2,2′-biphospholyl 1,1′-Disulfide, 13b. Eluent: pentane/
dichloromethane, 35/75. Yellow solid (yield ) 20%). Mp ) 244-
1
245 °C. H NMR (CDCl3): δ 1.31 (s, 6H, CH3-CO), 2.09 (dd,
JH,P ) 3.1 Hz, JH,P ) 2.3 Hz, 6H, CH3), 2.13 (m, 2H, CH2-
P), 2.17 (dd, JH,P ) 2.5 Hz, JH,P ) 0.7 Hz, 6H, CH3), 2.35
(dd, JH,P ) 15.3 Hz, JH,H ) 14.9 Hz, 2H, CH2-P), 4.40 (m,
2H, CH-CH2-P), 7.41 (m, 6H, Ph), 7.61 (m, 4H, Ph). 13C NMR
(CDCl3): δ 15.60 (d, JC,P ) 6.7 Hz, CH3-C-CPh), 15.95 (dd,
JC,P ) 12.7 Hz, JC,P ) 2.8 Hz, CH3-C-C), 27.23 (s, (CH3)2C),
31.51 (d, JC,P ) 46.5 Hz, CH2-P), 76.8 (dd, JC,P ) 5.3 Hz,
JC,P ) 1.2 Hz CH-CH2-P), 107.59 (s, (CH3)2C), 127.54 (dd,
JC,P ) 79.9 Hz, JC,P ) 11.9 Hz, C-P), 129.06 (d, JC,P ) 1.6
Hz, Cmeta), 129.25 (d, JC,P ) 0.7 Hz Cpara), 129.50 (dd, JC,P )
4.6 Hz, JC,P ) 0.8 Hz Cortho), 132.62 (dd, JC,P ) 11.1 Hz, JC,P
) 1.5 Hz, Cipso), 135.49 (dd, JC,P ) 79.2 Hz, JC,P ) 2.9 Hz,
C-Ph), 147.23 (dd, JC,P ) 23.9 Hz, JC,P ) 2.5 Hz, CH3-C-C-
Ph), 152.36 (dd, JC,P ) 25.8 Hz, JC,P ) 7.7 Hz, CH3-C-C-P).
31P NMR (CDCl3): δ 54.93. [R]D +43.9 (CH2Cl2, c 0.5). MS (DCI,
NH3) m/z: (%) 565 (100%) [M + H]+. Anal. Calcd for
C31H34O2P2S2 (564.15): C 65.96, H 6.03, S 11.34. Found: C
65.56, H 6.56, S 9.12. Crystals suitable for X-ray analysis were
obtained by slow evaporation of a dichloromethane solution.
R[Sp,Sp,Rc,Rc]-(+)-(-)-3,3′,4,4′-Tetramethyl-5,5′diphen-
yl-1,1′-(2,3-O-isopropylidene-2,3-dihydroxybutane-1,4-
diyl)-2,2′-biphospholyl 1,1′-Disulfide, 13c. Eluent: pentane/
dichloromethane, 30/70. Yellow solid (yield ) 14%). Mp ) 252-
12a, 12b, and 12c, which could not be isolated in a pure
form, have been partly characterized.
R[Sp,Sp,Rc,Rc]-3,3′,4,4′-Tetramethyl-5,5′diphenyl-1,1′-
(hexane-2,5-diyl)-2,2′-biphospholyl 1,1′-Disulfide, 12a.
Pentane/dichloromethane: 30/70. Yellow solid. 1H NMR
(CDCl3): δ 0.86 (m, 6H, CH3-CH), 2.06 (d, JH,P ) 2.3 Hz,
6H, CH3-C-C), 2.13 (d, JH,P ) 2.2 Hz, 6H, CH3-C-CPh), 7.36
(m, 6H, Ph), 7.65 (m, 4H, Ph). 31P NMR (CDCl3): δ 70.9.
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a dichloromethane solution.
R[Rp,Sp,Rc,Rc]-3,3′,4,4′-Tetramethyl-5,5′diphenyl-1,1′-
(hexane-2,5-diyl)-2,2′-biphospholyl 1,1′-Disulfide, 12b.
Eluent: ether. Yellow solid. 1H NMR (CDCl3): δ 0.85 (m, 6H,
CH3-CH), 1.83 (m, 2H, CH2), 1.97 (d, JH,P ) 2.3 Hz, 6H, CH3-
C-C), 2.07 (d, JH,P ) 2.4 Hz, 6H, CH3-C-CPh), 7.30 (m, 6H,
Ph), 7.66 (m, 4H, Ph). 31P NMR (CDCl3): δ 64.67 P(1), 64.73
P(2). MS (DCI, NH3) m/z: (%) 521 (100%) [M + H]+. Crystals
suitable for X-ray analysis were obtained by slow evaporation
of a dichloromethane solution.
S[Rp,Rp,Rc,Rc]-3,3′,4,4′-Tetramethyl-5,5′diphenyl-1,1′-
(hexane-2,5-diyl)-2,2′-biphospholyl 1,1′-Disulfide, 12c. Pen-
tane/dichloromethane: 50/50. Yellow solid. 1H NMR (CDCl3):
δ 0.81 (m, 6H, CH3-CH), 2.07 (d, JH,P ) 2.2 Hz, 6H, CH3-C-
C), 2.17 (d, JH,P ) 2.4 Hz, 6H, CH3-C-CPh), 7.34 (m, 6H, Ph),
7.60 (m, 4H, Ph). 31P NMR (CDCl3): δ 70.1. MS (DCI, NH3)
m/z: (%) 521 (100%) [M + H]+. Crystals suitable for X-ray
analysis were obtained by slow evaporation of a dichlo-
romethane solution.
1
255 °C. H NMR (CDCl3): δ 1.37 (s, 6H, CH3-CO), 2.13 (m,
12H, CH3), 2.34 (ABX, JH,P ) 15.0 Hz, JH,H ) 15.0 Hz, JH,H
) 7.0 Hz, 2H,CH2-P), 2.70 (ABX, JH,P ) 15.0 Hz, JH,H )
15.0 Hz, JH,H ) 4.5 Hz, 2H, CH2-P), 4.75 (m, 2H, CH-CH2-
P), 7.40 (m, 6H, Ph), 7.60 (m, 4H, Ph). 13C NMR (CDCl3): δ
15.44 (d, JC,P ) 13.0 Hz, CH3-C-CPh), 16.59 (dd, JC,P ) 12.4
Hz, JC,P ) 2.0 Hz, CH3-C-C), 27.87 (s, (CH3)2C), 34.25 (d, JC,P
) 45.3 Hz, CH2-P), 76.65 (d, JC,P ) 4.3 Hz, CH-CH2-P), 109.19
(s, (CH3)2C), 127.35 (dd, JC,P ) 77.9 Hz, JC,P ) 11.9 Hz, C-P),
128.94 (d, JC,P ) 1.5 Hz, Cmeta), 129.22 (s, Cpara), 129.70 (d,
JC,P ) 5.0 Hz, Cortho), 132.70 (dd, JC,P ) 11.3 Hz, JC,P ) 0.9
Hz, Cipso), 136.94 (dd, JC,P ) 77.0 Hz, JC,P ) 2.9 Hz, C-Ph),
146.17 (dd, JC,P ) 23.3 Hz, JC,P ) 2.3 Hz, CH3-C-C-Ph),
S[Rp,Sp,Rc,Rc]-(-)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(2,3-O-isopropylidene-2,3-dihydroxybutane-1,4-diyl)-
2,2′-biphospholyl 1,1′-Disulfide, 13a. Eluent: pentane/
dichloromethane, 40/60 (yellow solid). Yield ) 32%. Mp ) 215-
153.55 (dd, JC,P ) 25.65 Hz, JC,P ) 7.5 Hz, CH3-C-C-P). 31
P
NMR (CDCl3): δ 53.37. [R]D -8.4 (CH2Cl2, c 0.5). MS (DCI,
NH3) m/z: (%) 565 (100%) [M + H]+. Anal. Calcd for
C31H34O2P2S2 (564.15): C 65.96, H 6.03, S 11.34. Found: C
65.74, H 6.00, S 10.20. Crystals suitable for X-ray analysis
were obtained by slow evaporation of a dichloromethane
solution.
General Procedure for the Desulfurization. To a solu-
tion of 2,2′-biphosphole (0.26 mmol) in dichloromethane (5 mL)
was added dropwise CF3SO3Me (0.058 mL, 0.52 mmol). After
1 h of stirring, the resulting suspension was evaporated to
dryness and the 2,2′-biphosphonium salt was washed with
small portions of pentane. A solution of this salt in dichlo-
romethane (5 mL) was added dropwise to a solution of t-BuSLi,
resulting from treatment at -40 °C of 2-methyl-2-propane thiol
(0.645 mL, 0.57 mmol) in ether (4 mL) with n-buthyllithium
(0.208 mL, 0.52 mmol, 2.5 M in hexane). The resulting mixture
was stirred for 15 min at -78 °C and for 2 h at RT and then
evaporated to dryness. The resulting residue was extracted
with small portions of pentane. The combined pentane phases
were washed with water, dried over MgSO4, and evaporated
to give crude compound in 95% yield.
1
220 °C. H NMR (CDCl3): δ 1.30 (s, 6H, CH3-CO), 1.63 (m,
1H, CH2-P(1)), 2.00 (s, 3H, CH3-C-C), 2.03 (s, 3H, CH3-C-
CPh), 2.07 (s, 3H, CH3-C-C), 2.08 (s, 3H, CH3-C-CPh), 2.58
(m, 1H, CH2-P(2)), 2.68 (m, 1H, CH2-P(1)), 3.05 (m, 1H, CH-
CH2-P(2)), 3.67 (m, 1H, CH2-P2), 4.41 (m, 1H, CH-CH2-P(1)),
7.33-7.53 (m, 10H, Ph). 13C NMR (CDCl3): δ 15.51 (d, JC,P-
(1) ) 13.3 Hz, CH3-C-CPh), 15.57 (d, JC,P(2) ) 12.2 Hz, CH3-
C-CPh), 17.31 (dd, JC,P(2) ) 12.1 Hz, JC,P(1) ) 1.5 Hz, CH3-
C-C), 17.97 (d, JC,P(2) ) 12.67 Hz, CH3-C-C), 27.15 (s,
(CH3)2C), 27.24 (s, (CH3)2C), 28.45 (d, JC,P(1) ) 47.3 Hz, CH2-
P(1)), 34.31 (d, JC,P(2) ) 45.5 Hz, CH2-P(2)), 76.67 (d, JC,P-
(2) ) 2.3 Hz, CH-CH2-P(2)), 78.06 (dd, JC,P(1) ) 5.3 Hz,
JC,P(2) ) 2.9 Hz, CH-CH2-P(1)), 107.82 (s, (CH3)2C), 127.59
(dd, JC,P(2) ) 76.7 Hz, JC,P(1) ) 12.6 Hz, C-P(2)), 128.82 (s,
Cpara), 128.87 (s, Cpara), 129.12 (s, Cmeta), 129.15 (s, Cortho), 129.29
(s, Cmeta), 130.00 (s, Cortho), 130.92 (dd, JC,P(1) ) 79.0 Hz, JC,P-
(2) ) 13.5 Hz, C-P(1)), 132.41 (d, JC,P(2) ) 12.0 Hz, Cipso-P(2)),
132.68 (d, JC,P(1) ) 12.0 Hz, Cipso-P(1)), 135.93 (d, JC,P(1) )
78.5 Hz, Ph-C-P(1)), 136.93 (d, JC,P(2) ) 77.5 Hz, Ph-C-P(2)),
146.88 (d, JC,P(2) ) 22.1 Hz, CH3-C-C-Ph), 148.14 (d, JC,P-
(1) ) 24.1 Hz, CH3-C-C-Ph), 150.23 (dd, JC,P(1) ) 24.7 Hz,
JC,P(2) ) 9.5 Hz, CH3-C-C-P(1)), 151.27 (dd, JC,P(2) ) 23.1
R[Rp,Sp,Sc,Sc]-(+)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(pentane-2,4-diyl)-2,2′-biphospholyl-P,P′-dichloro-

Stereochemically Dynamic 2,2′-Biphosphole Ligands
Organometallics, Vol. 24, No. 23, 2005 5557
palladium(II), 15. To a solution of compound 8 (40 mg, 0.09
mmol) in CH2Cl2 (10 mL) was added [PdCl2(CH3CN)2] (27.46
mg, 0.10 mmol) in CH2Cl2 (10 mL). The resulting solution was
stirred 16 h at room temperature, filtered through a 0.45 µm
PTFE filter, and then concentrated under reduced pressure
to give a solid residue. This resulting solid was dissolved in a
small amount of CH2Cl2 and precipitated with a large excess
of pentane. After filtration, the red solid obtained was dried
under vacuum (50 mg, 90%). 1H NMR (CDCl3): δ 0.75 (dd,
JH,P2 ) 14.2 Hz, JH,H ) 7.0 Hz, 3H, CH3-CH), 0.93 (dd, JH,-
P1 ) 16.4 Hz, JH,H ) 7.2 Hz, 3H, CH3-CH), 2.22 (d, JH,P1 )
2.4 Hz, 3H, CH3-C-C), 2.26 (d, JH,P2 ) 2.4 Hz, 3H, CH3-C-
C), 2.44 (s, 3H, CH3-C-CPh), 2.47 (s, 3H, CH3-C-CPh), 7.32-
7.49 (m, 6H, Hmeta,para), 7.90 (m, 4H, Hortho). 13C NMR (CDCl3):
δ 12.68 (d, JC,P ) 6.2 Hz, CH3-CHP(1)), 17.73 (dd, JC,P )
10.3 Hz, JC,P ) 18.6 Hz, CH3-C-C), 19.05 (s, CH3-CHP(2)),
19.56 (dd, JC,P ) 10.3 Hz, JC,P ) 41.1 Hz, CH3-C-C), 29.72
(dd, JC,P ) 4.5 Hz, JC,P ) 20.7 Hz, CHP(1)), 34.18 (dd, JC,P
) 7.0 Hz, JC,P ) 19.3 Hz, CH P(2)), 43.79 (t, JC,P ) 7.5 Hz,
CH2), 128.74 (d, JC,P ) 14.7 Hz, CHp), 129.66 (d, JC,P ) 24.4
Hz, CHm), 131.4 (d, JC,P ) 5.2 Hz, CHo), 133.19 (d, JC,P )
12.6 Hz, Cipso), 132.36 (d, JC,P ) 4.7 Hz,CHo), 135.26 (m, C-P),
141.96 (d, JC,P ) 51.8 Hz, Ph-C), 143.59 (dd, JC,P ) 11.35
Hz, JC,P ) 46 Hz, CH3-C-), 155.06 (dd, JC,P ) 16.62 Hz,
JC,P ) 16.58 Hz, CH3-C). 31P NMR (CDCl3): δ 76.4 (s, P1),
84.5 (s, P2). [R]D +144 (CH2Cl2, c 0.15). MS (FAB, MNBA
matrix) m/z: 583[M - Cl]+ (100%), 547[M+ - 2Cl]+ (60%).
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a CH2Cl2 solution.
2H, H′ortho). 13C NMR (CDCl3): δ 12.53 (d, JC,P1 ) 2.86 Hz,
CH3-CHP(1)), 15.88 (d, JC,P2 ) 2.51 Hz, CH3-CHP(2)), 16.31
(d, JC,P1 ) 10.1 Hz, CH3-C-C), 16.42 (d, JC,P1 ) 10.1 Hz,
CH3-C-C), 19.45 (d, JC,P ) 11.3 Hz, CH3-C-C), 20.05 (dd, JC,P
) 10.1 Hz, CH3-C-C), 27.33 (d, JC,P ) 2.5 Hz, JC,P ) 26.7
Hz, CHP(1)), 29.84 (s, CHP(2)), 33.63 (d, JC,P ) 26.4 Hz, CH2),
37.08 (d, JC,P ) 33.96 Hz, CH2), 128.21 (m, CHp), 128.39 (m,
CHm), 131.06 (d, JC,P ) 2.5 Hz,CHo), 131.65 (d, JC,P ) 2.5
Hz,CHo), 133.54 (d, JC,P ) 11.3 Hz Cipso), 134.02 (d, JC,P )
11.3 Hz, C-P), 143.65 (m, Ph-C), 145.98 (m, CH3-C-), 153.65
(d, JC,P ) 17.5 Hz, CH3-C). 31P NMR (CDCl3): δ 50.24 (dt,
JP1,P2 ) 6.1 Hz, JP1,Pt ) 3265.0 Hz, P1), 62.00 (t, JP2,Pt )
3265.0 Hz, P2). 195Pt NMR (CDCl3): δ -4209.73 (t, JPt,P )
3270.0 Hz). [R]D -124.6 (CH2Cl2, c 0.15). MS (FAB, MNBA
matrix) m/z: 687[M - Cl]+. Crystals suitable for X-ray analysis
were obtained by slow evaporation of a dichloromethane
solution.
(+)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-1,1′-(2,3-O-iso-
propylidene-2,3-dihydroxybutane-1,4-diyl)-2,2′-biphos-
pholyl-P,P′-dichloroplatinum(II), 18. Yellow solid (yield )
94%). 1H NMR (CDCl3): δ 1.34 (m, 6H, CH3-CO), 1.76 (m, 1H,
CH2-P(1)), 2.09 (d, 3H, CH3-C-C), 2.10 (d, 3H, CH3-C-C), 2.34
(s, 3H, CH3-C-CPh), 2.45 (s, 3H, CH3-C-CPh), 2.65 (m, 2H,
CH2-P(2)), 3.06 (m, 1H, CH2-P(1)), 3.75 (m, 1H, CH-CH2-P(2)),
5.03 (m, 1H, CH-CH2-P(1)), 7.37-7.65 (m, 10H, Ph). 13C NMR
(CDCl3): δ 16.54 (d, JC,P(1) ) 15.0 Hz, CH3-C-CPh), 16.59
(d, JC,P(2) ) 16.2 Hz, CH3-C-CPh), 19.35 (d, JC,P(1) ) 11.2
Hz, CH3-C-C), 20.15 (d, JC,P(2) ) 11.2 Hz, CH3-C-C), 26.77
(s, (CH3)2C), 26.94 (s, (CH3)2C), 33.09 (d, JC,P(2) ) 27.5 Hz,
CH2-P(2)), 36.23 (d, JC,P(1) ) 30.0 Hz, CH2-P(1)), 78.04 (d,
JC,P(1) ) 10 Hz, CH-CH2-P(1)), 78.68 (d, JC,P(2) ) 3.7 Hz,
CH-CH2-P(2)), 109.27 (s, (CH3)2C), 128.56 (s, Cpara), 128.63 (s,
General Procedure for Platinum Complexes 16, 17,
and 18. To a solution of ligand 8, 9, or 10 (0.19 mmol) in CH2-
Cl2 (20 mL) was added slowly [PtCl2(CH3CN)2] (69 mg, 0.19
mmol). The resulting solution was refluxed 3 h, then allowed
to warm to room temperature and concentrated under reduced
pressure to give a solid residue. This yellow solid was dissolved
in a small amount of CH2Cl2 and precipitated with a large
excess of pentane. After filtration, the solid was washed with
small portions of pentane and dried under vacuum.
Cpara), 130.56 (d, JC,P ) 3.7 Hz, Cmeta), 130.85 (s, C-P(2)),
131.61 (d, Cortho), 131.73 (d, JC,P(1) ) 3.7 Hz, C-P(1)), 132.10
(d, JC,P(2) ) 11.2 Hz, Cipso-P(2)), 133.08 (s, Cipso-P(1)), 135.20
(s, Ph-C-P(1)), 136.75 (s, Ph-C-P(2)), 144.69 (m, CH3-C-C-Ph),
145.38 (s, CH3-C-C-Ph), 153.11 (s, CH3-C-C-P(1)), 153.22 (s,
CH3-C-C-P(2)). 31P NMR (CDCl3): δ 34.55 (dt, JP1,P2 ) 4.05
Hz, JP1,Pt ) 3231.9 Hz, P1), 37.36 (t, JP2,Pt ) 3231.9 Hz,
P2). 195Pt NMR (CDCl3): δ -4144.98 (t, JPt,P ) 3238.9 Hz).
[R]D +227.7 (CH2Cl2, c 0.18). MS (FAB, MNBA matrix) m/z:
731[M - Cl]+.
(-)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-1,1′-(pentane-2,4-
diyl)-2,2′-biphospholyl-P,P′-dichloroplatinum(II), 16. Yel-
1
low solid (yield ) 92%). H NMR (CDCl3): δ 0.79 (dd, JH,P2
) 25.0 Hz, JH,H ) 5.0 Hz, 3H, CH3-CHP2), 0.96 (dd, JH,P1
) 25.0 Hz, JH,H ) 5.0 Hz, 3H, CH3-CHP1), 1.50 (m, 2H, CH-
P), 2.20 (d, JH,P1 ) 5.0 Hz, 3H, CH3-C-C), 2.29 (d, JH,P2 )
5.0 Hz, 3H, CH3-C-C), 2.42 (s, 3H, CH3-C-CPh), 2.47 (s, 3H,
CH3-C-CPh), 2.53 (m, 2H, -CH2-CHP), 7.33-7.37 (m, 2H,
General Procedure for Palladium-Catalyzed Allylic
Substitution. A mixture of ligand 8 or 10, 1,3-diphenylprop-
2-enyl acetate (0.413 g, 1.63 mmol), and [(Pd(C3H5)Cl)]2 (3 mg,
0.03 mmol) in dry solvent (20 mL) was stirred at room
temperature for 2 h. To the resulting solution were added
dimethyl malonate (0.374 mL, 3.25 mmol), a small amount of
potassium acetate, and BSA (0.300 mL, 3.25 mmol). The
reaction was carried out at room temperature and monitored
by TLC for disappearance of acetate. After complete reaction,
the resulting mixture was diluted with diethyl ether (5 mL)
and quenched with a saturated aqueous solution of ammonium
chloride (5 mL). The aqueous phase was extracted with Et2O,
and the combined organic layers were dried over sodium
sulfate, filtered, and evaporated. The conversion was calcu-
H
H
para), 7.44-7.48 (m, 4H, Hmeta), 7.85 (d, JH,H ) 5.0 Hz, 2H,
ortho), 7.98 (d, JH,H ) 5.0 Hz,2H, H′ortho). 13C NMR (CDCl3):
δ 13.55 (d, JC,P1 ) 3.7 Hz, CH3-CHP(1)), 17.14 (d, JC,P1 )
11.2 Hz, CH3-C-C), 17.23 (d, JC,P1 ) 11.2 Hz, CH3-C-C),
18.33 (s, CH3-CHP(2)), 18.75 (d, JC,P ) 10.0 Hz, CH3-C-C),
19.15 (d, JC,P ) 11.2 Hz, CH3-C-C), 27.98 (dd, JC,P ) 2.5
Hz, JC,P ) 26.2 Hz, CHP(1)), 32.89 (dd, JC,P ) 3.7 Hz, JC,P
) 28.7 Hz, CHP(2)), 43.53 (s, CH2), 128.24 (d, JC,P ) 6.25
Hz, CHp), 128.68 (s, CHm), 128.89 (s, CHm), 130.73 (d, JC,P )
3.7 Hz,CHo), 131.79 (d, JC,P ) 3.7 Hz,CHo), 133.16 (d, JC,P
) 12.5 Hz, Cipso), 133.94 (d, JC,P ) 11.2 Hz, C-P), 141.58 (m,
Ph-C), 143.21 (m, CH3-C-), 154.69 (m, CH3-C). 31P NMR
(CDCl3): δ 53.86 (dt, JP1,P2 ) 12.1 Hz, JP1,Pt ) 3193.6 Hz,
P1), 58.41 (t, JP2,Pt ) 3193.6 Hz, P2). 195Pt NMR (CDCl3): δ
-4232.24 (t, JPt,P ) 3167.7 Hz). [R]D -96.1 (CH2Cl2, c 0.23).
MS (FAB, MNBA matrix) m/z: 673[M - Cl]+.
1
lated from the crude reaction mixture by H NMR spectros-
copy. Subsequent purification by chromatography on silica
eluting with ethyl acetate/pentane (15/85) afforded the product
as a white solid. The enantiomeric excess was determined by
1H NMR using the chiral shift reagent Eu(hfc)3.
X-ray Structure Determination. A single crystal of each
compound was mounted under inert perfluoropolyether at the
tip of a glass fiber and cooled in the cryostream of either an
Oxford-Diffraction XCALIBUR CCD diffractometer for 12b or
a Stoe IPDS diffractometer for 12a, 12c, 13a, 13b, and 16.
Data were collected using monochromatic Mo KR radiation (λ
) 0.71073).
S[Rp,Sp,Rc,Rc]-(-)-3,3′,4,4′-Tetramethyl-5,5′diphenyl-
1,1′-(hexane-2,5-diyl)-2,2′-biphospholyl-P,P′-dichloroplat-
inum(II), 17. Yellow solid (yield ) 91%). 1H NMR (CDCl3): δ
0.91 (dd, JH,P2 ) 15.0 Hz, JH,H ) 15.0 Hz, 3H, CH3-CH),
1.07 (dd, JH,P1 ) 20.0 Hz, JH,H ) 15.0 Hz, 3H, CH3-CH),
1.74 (m, 4H, -CH2-CHP), 1.96 (d, JH,P1 ) 1.92 Hz, 3H, CH3-
C-C), 2.12 (d, JH,P2 ) 1.92 Hz, 3H, CH3-C-C), 2.34 (s, 3H,
CH3-C-CPh), 2.37 (s, 3H, CH3-C-CPh), 7.29-7.37 (m, 2H,
Hpara), 7.39-7.43 (m, 4H, Hmeta), 7.65 (m, 2H, Hortho), 7.71 (m,

5558 Organometallics, Vol. 24, No. 23, 2005
Table 4. Crystal Data and Structure Refinement
Robe´ et al.
12b
12a
12c
11b
C29H27P2S3
empirical formula
fw
temp, K
wavelength, Å
cryst syst
space group
a, Å
C
30H34P2S2
C
30H34P2S2
C
30H34P2S2
520.63
180(2)
520.63
520.63
506.61
180(2)
0.71073
triclinic
P1h
180(2)
180(2)
0.71073
0.71073
triclinic
P1h
0.71073
tetragonal
P41212
8.2848(7)
8.2848(7)
39.289(3)
90.0
tetragonal
P43212
9.3019(6)
9.3019(6)
31.650(3)
90.0
7.5069(7)
8.4348(8)
8.937(2)
b, Å
c, Å
10.911(2)
15.546(4)
82.55(3)
73.47(3)
67.38(3)
1341.1(6)
2
11.3734(10)
78.136(7)
83.429(7)
82.062(8)
695.26(11)
1
R, deg
â, deg
90.0
90.0
90.0
90.0
γ, deg
volume, Å3
2696.8(4)
4
2738.6(4)
4
Z
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
1.243
1.282
1.263
1.255
0.324
0.334
0.329
0.334
276
1104
1104
536
cryst size, mm3
θ range, deg
no. of reflns collected
no. of indep reflns [R(int)]
completeness, %,
abs corr
0.401 × 0.334 × 0.221
3.17 to 28.28
6110
4374 (0.0131)
99.2
multiscan
0.9247, 0.8729
F2
4374/3/313
1.118
0.55 × 0.31 × 0.25
2.51 to 24.21
20 655
2166 (0.0472)
99.3
none
0.36 × 0.28 × 0.008
2.28 to 26.14
24 612
2726 (0.2224)
99.6
analytical
0.9974, 0.9042
F2
2726/0/159
0.905
0.425 × 0.15 × 0.025
2.42 to 23.25
8682
6302 (0.1570)
91.1
empirical (DIFABS)
0.984 and 0.858
F2
6302/543/609
0.906
R1 ) 0.1021,
wR2 ) 0.2666
R1 ) 0.2052,
wR2 ) 0.3242
not reliable
0.417 and -0.396
max., min. transmn
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
F2
2166/0/157
1.067
R1 ) 0.0293,
wR2 ) 0.0792
R1 ) 0.0306,
wR2 ) 0.0804
-0.06(5)
R1 ) 0.0256,
wR2 ) 0.0636
R1 ) 0.0277,
wR2 ) 0.0656
0.00(9)
R1 ) 0.0545,
wR2 ) 0.1012
R1 ) 0.1717,
wR2 ) 0.1445
0.0(3)
R indices (all data)
abs struct param
largest diff peak and
hole, e Å-3
0.326 and -0.237
0.149 and -0.161
0.376 and -0.491
13a
13b(c)
16
empirical formula
fw
C
31H34O2P2S2
C
124H136O8P8S8
C
30H34Cl2P2Pt
564.64
2258.57
722.50
temp, K
180(2)
180(2)
180(2)
0.71073
orthorhombic
P212121
9.1281(9)
12.5047(10)
24.788(2)
90.0
90.0
90.0
wavelength, Å
cryst syst
space group
a, Å
0.71073
monoclinic
P21
0.71073
triclinic
P1h
8.9710(16)
14.164(2) Å
11.563(2) Å
90.0
93.02(2)
90.0
10.9358(9)
12.2064(11)
24.537(2)
93.484(11)
100.258(11)
112.899(9).
2938.2(5)
1
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
1467.3(4)
2
2829.5(4)
4
Z
density(calcd), Mg/m3
abs coeff, mm-1
F(000)
1.278
1.276
1.696
0.317
0.317
5.279
596
1192
1424
cryst size, mm3
θ range, °
0.4 × 0.32 × 0.32
2.27 to 26.14
14704
0.56 × 0.26 × 0.08
2.13 to 26.04.
29430
0.46 × 0.21 × 0.074
2.31 to 26.00
18049
no. of reflns collected
no. of indep reflns [R(int)]
completeness, %,
abs corr
max., min. transmission
refinement method
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)]
5718 (0.0517)
98.1
none
21206 (0.0481)
92.8
multiscan
1.0 and 0.896
F2
21206/1311/1376
0.938
5482 (0.1005)
99.2
multiscan
0.3639 and 0.2947
F2
5482/0/172
1.124
F2
5718/1/340
1.042
R1 ) 0.0264,
wR2 ) 0.0621
R1 ) 0.0298,
wR2 ) 0.0639
0.04(4)
R1 ) 0.0370,
wR2 ) 0.0795
R1 ) 0.0514,
wR2 ) 0.0842
0.04(4)
R1 ) 0.0749,
wR2 ) 0.1786
R1 ) 0.0913,
wR2 ) 0.1851
0.04(2)
R indices (all data)
absolute structure param
largest diff peak and
hole, e Å-3
0.280 and -0.238
0.318 and -0.278
2.955 and -4.389
The structures were solved by direct methods (SIR9721) and
refined by least-squares procedures on F2 using SHELXL-97.22
All H atoms attached to carbon were introduced in the
calculation in idealized positions and treated as riding models.
Absolute configuration was confirmed by the refinement of the
Flack’s enantiopole parameter23 and careful examination of the
sensitive reflections. In compound 13b, which crystallized in
the non-centrosymmetric P1 space group, there are four
molecules in the unit cell. It is interesting to note that these
four molecules correspond to two different diasteroisomers,

Stereochemically Dynamic 2,2′-Biphosphole Ligands
Organometallics, Vol. 24, No. 23, 2005 5559
[Sc,Sc,R,Sp,Sp] and [Sc,Sc,S,Rp,Rp], related two by two. The
data collected for compound 11b were of very low quality owing
to poor crystals. Although the results unambiguously reveal
the opposite configuration of P atoms, the absolute configu-
ration of the molecule could not be reliably determined and
was then established from the known configuration of the
chiral chain as defined in the structures of compounds 11a
and 11b. The drawing of the molecules was realized with the
help of ORTEP32.24 Crystal data and refinement parameters
are shown in Table 4.
Computational Details. The molecular mechanics calcula-
tions were carried out with the CAChe program using the
MM2 force field. Molecular models 13a, 13b, and 13c were
created from the original crystal data. The molecular geom-
etries were fully optimized until the energy change is less than
10-5 kcal/mol or until the molecule has been updated 3000
times. Conformational analysis of the rotation process around
the C-C bond linking the two phospholes rings was carried
out. A total of 721 points have been optimized to generate the
potential energy surface.
Crystallographic data are also given as CIF files. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Acknowledgment. We thank the Centre National
de la Recherche Scientifique, the Ministe`re de l’Education
Nationale, de la Recherche et de la Technologie (E.R.),
UNAM (C.O.), and Demsol Programme of European
Community (M.M.).
(21) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. SIR97 a program for automatic solution of crystal structures by
direct methods. J. Appl. Crystallogr. 1999, 32, 115.
(22) Sheldrick, G. M. SHELXL 97. Programm for crystal structure
refinement; University of Go¨ttingen: Germany, 1997.
(23) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 876. Bernar-
dinelli, G.; Flack, H. D. Acta Crystallogr., Sect. A 1985, 41, 500.
(24) Farrugia, L. J. ORTEP3 for Windows. J. Appl. Crystallogr.
1997, 30, 565.
Supporting Information Available: Crystallographic
data are also given as CIF files. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM0503646