Enantiopure platinum(II) complexes with chiral diphosphine and diphosphinite ligands derived from 2,2-biphosphole: Synthesis, crystal structure and catalysis

Article abstract of DOI:10.1016/j.ica.2007.09.043

Enantiopure platinum(II) complexes have been synthetized with chiral stereodynamic diphosphine and diphosphinite ligands derived from 2,2-biphosphole through a dynamic chirality control upon coordination. Catalytic performances of these platinum complexes have been explored in asymmetric hydroformylation. All complexes proved to be effective catalysts with respect to chemoselectivity and regioselectivity but induced only low enantioselectivities.

Full text of DOI:10.1016/j.ica.2007.09.043

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 1861–1867
www.elsevier.com/locate/ica
Enantiopure platinum(II) complexes with chiral diphosphine
and diphosphinite ligands derived from 2,2-biphosphole: Synthesis,
crystal structure and catalysis
a
b
b
a
´
´
Emmanuel Robe , Csaba Hegedus , Jozsef Bakos , Yannick Coppel ,
¨
a
a,
*
Jean-Claude Daran , Maryse Gouygou
a
Laboratoire de Chimie de Coordination, CNRS, 205 Route de Narbonne, F-31007 Toulouse Cedex, France
b
Institute of Chemistry, University of Pannonia, H-8201 Veszpre´m, P.O. Box 158, Hungary
Received 5 July 2007; accepted 29 September 2007
Available online 12 October 2007
Abstract
Enantiopure platinum(II) complexes have been synthetized with chiral stereodynamic diphosphine and diphosphinite ligands derived
from 2,2-biphosphole through a dynamic chirality control upon coordination. Catalytic performances of these platinum complexes have
been explored in asymmetric hydroformylation. All complexes proved to be effective catalysts with respect to chemoselectivity and reg-
ioselectivity but induced only low enantioselectivities.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: 2,20-Biphospholes; Diphosphines; Diphosphinites; Stereodynamic ligands; Enantiopure platinum complexes; Hydroformylation
1. Introduction
sis using flexible diphosphine ligands such as BIPHEP [3],
DPPF [4] or NUPHOS [5].
The development of asymmetric catalysts is of impor-
tance in synthetic organic reactions [1]. Asymmetric cata-
lysts are generally metal complexes with stereochemically
rigid enantiopure ligands. However, stereochemically
dynamic ligands could be controlled into a single enantio-
meric conformation on a metal center and hence this meth-
odology opens a new synthetic approach for the obtention
of enantiopure complexes [2]. The advantage of this
approach over the traditional one is that catalysts can be
optimized by the synthesis of achiral and meso ligands
instead of the synthesis of enantiopure ligands which
require elaborated and expensive methods (e.g. asymmetric
synthesis or resolution). Successful results have been
obtained in transition metal-catalyzed asymmetric synthe-
In 2001, we had reported the first application of the chi-
ral stereochemically dynamic 2,20-biphosphole (BIPHOS)
to asymmetric allylic substitution [6] involving crystalliza-
tion-induced spontaneous resolution and kinetic stabiliza-
tion by coordination to Pd center. The flexibility of the
2,20-biphosphole ligands relied on the configurational
instability of the axial chirality generated by the 2,20-
biphosphole framework and on the central chiralities at
the phosphorus atoms [7]. In a more convenient procedure,
we have discovered that a dual chirality control can be
achieved by introducing a chiral carbon linker between
the two phosphorus atoms that favors a single enantio-
meric form on metal center [8]. Enantiomeric Pd-complexes
have then been obtained and the use of these stereodynam-
ic ligands in Pd-catalyzed asymmetric allylic substitution
has been demonstrated [9]. Generalization of the use of
these chiral stereodynamic ligands in asymmetric catalysis
requires to change the metal center and/or to modify the
*
Corresponding author. Tel.: +33 (0)5 61 33 31 74; fax: +33 (0)5 61 55
30 00.
E-mail address: gouygou@lcc-toulouse.fr (M. Gouygou).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.09.043

1862
E. Robe´ et al. / Inorganica Chimica Acta 361 (2008) 1861–1867
steric and electronic properties of the ligand. We have
reported preliminary results on the obtention of platinum
complexes [9]. On the other hand, we have recently
extended the family of chiral stereodynamic 2,20-biphosp-
hole ligands by introducing a chiral alkoxy linker [10]. In
this paper, we report our recent work concerning the prep-
aration and characterization of diastereo- and enantiopure
platinum complexes with chiral stereodynamic diphos-
phines and diphosphinites derived from 2,20-biphosphole.
The first evaluation of these new complexes in the hydro-
formylation reaction is also described.
2.2.3. Synthesis of (+)-dichloro-1,10-(2,3-O-isopropylidene-
2,3-dihydroxybutane-1,4-dioxy)-3,30,4,40-tetramethyl-5,50-
diphenyl-2,20-biphosphole platinum (IV.3)
Yellow solid. Yield 0.127 g (84%). 31P NMR d = 109.89
(s, JPt,P = 2909.4 Hz). [a]D = +311.9 (CH2Cl2, c = 0.2). MS
(FAB, MNBA matrix) m/z = 763 [MꢀCl]+.
2.2.4. Synthesis of (+)-dichloro-1,10-(1,3-diphenylpropane-
1,3-dioxy)-3,30,4,40-tetramethyl-5,50-diphenyl-2,20-
biphosphole platinum (IV.4)
Yellow solid. Yield 0.148 g (90%). 31P NMR d = 107.78
(s, JPt,P1 = 2921 Hz), 108.18 (s, JPt,P2 = 2848 Hz).
[a]D = +91.8 (CH2Cl2, c = 0.3). MS (FAB, MNBA matrix)
m/z = 860 [MꢀCl]+.
2. Experimental
2.1. Materials and methods
2.2.5. Synthesis of S[Rp,Sp,Sc,Sc]-(+)-dichloro-1,10-
(2,7-dimethyloctane-3,6-dioxy)-3,30,4,40-tetramethyl-5,50-
diphenyl-2,20-biphosphole platinum (IV.5)
Yellow solid. Yield 0.128 g (83%). 31P NMR d = 106.71
(d, JP1,P2 = 6.06 Hz, JPt,P1 = 4112.7 Hz), 109,77 (d,
JP1,P2 = 6.06 Hz, JPt,P1 = 3787.3 Hz). 195Pt NMR (CDCl3)
d = ꢀ3812.1 (s, JPt–P1 = 4112 Hz, JPt–P2 = 3787 Hz).
[a]D = +193.7 (CH2Cl2, c = 0.2). Crystals suitable for
X-ray analysis were obtained by slow evaporation of a
dichloromethane solution.
All reactions were carried out under an atmosphere of
dry argon using conventional Schlenk glassware and vac-
uum line techniques. Solvents were dried using established
procedures and distilled under dinitrogen immediately
prior to use. The experiments requiring H2/CO pressure
were carried out in a stainless-steel high pressure reactor.
31P{1H} and 195Pt NMR spectra were recorded on the
Bruker AMX 400 and AV 500 instruments. Mass spectra
were obtained on a Nermag R10-10 instrument. Optical
rotations were measured with a Perkin Elmer 241 polar-
imeter. Diphosphines I [9], platinum complexes II [9]
and diphosphinites III [10] were prepared as described
in the literature.
2.3. General procedure for the hydroformylation reaction
In a typical experiment, a solution of 0.313 mmol of
platinum complex IV, anhydrous SnCl2 (1 equiv.) and sty-
rene (200 equiv) in 2 mL of dichloromethane were placed in
a Schlenk-tube under argon and this mixture was stirred
for 10 min. The stainless-steel autoclave was filled with this
solution and then purged with syn gas [CO/H2 (1:1] and
then pressurized to the required pressure with this gas mix-
ture and stirred for the desired time. At the end of the reac-
tion the autoclave was depressurized and the conversion
and composition of the reaction mixture were determined
by GC (SPB-1). The reaction mixture was vacuum distilled
to remove the catalyst and the distilled product was ana-
lyzed to determine the enantiomeric excess of the aldehyde
by chiral GC on a Hewlette–Packard HP 4890 gas chro-
matograph equipped with a split/spiltless injector and a
b-DEX 225 column (30 m, internal diameter 0.25 mm, film
thickness 0.25 lm, carrier gas: 100 kPa nitrogen, F.I.D.
detector). The retention times of the enantiomers are
30.4 min (R), and 31.4 min (S). The configuration of the
prevailing enantiomer in the product was determined by
the sign of the optical rotation of the corresponding
aldehyde.
2.2. General procedure for platinum complexes IV
To a solution of diphosphinite III (0.19 mmol) in
CH2Cl2 (10 mL) was added [PtCl2(PhCN)2] (0.09 g,
0.19 mmol). The resulting solution was stirred 3 h at room
temperature, filtered through a 0.45 lm PTFE filter and
then concentrated under reduced pressure to give a solid
residue. This resulting solid was dissolved in small amount
of CH2Cl2 and precipitate with a large excess of pentane.
After filtration, the yellow solid obtained was dried under
vacuum.
2.2.1. Synthesis of (ꢀ)-dichloro-1,10-(pentane-2,4-dioxy)-
3,30,4,40-tetramethyl-5,50-diphenyl-2,20-biphosphole
platinum (IV.1)
Yellow solid. Yield 0.127 g (90%). 31P NMR
(81.015 MHz, CDCl3): d = 105.30 (s, JPt,P = 2878.5 Hz).
[a]D = ꢀ315 (CH2Cl2, c = 0.2). MS (FAB, MNBA matrix)
m/z = 706 [MꢀCl]+.
2.2.2. Synthesis of (+)-dichloro-1,10-(hexane-2,5-dioxy)-
3,30,4,40-tetramethyl-5,50-diphenyl-2,20-biphosphole
platinum (IV.2)
Yellow solid. Yield 0.125 g (87%). 31P NMR d = 105.02
(s, JPt,P = 2891.4 Hz). [a]D = +313.2 (CH2Cl2, c = 0.2). MS
(FAB, MNBA matrix) m/z = 720 [MꢀCl]+.
2.4. X-ray crystallographic study
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 a Stoe IPDS diffractom-
eter for II.1 or an Oxford-Diffraction XCALIBUR CCD

E. Robe´ et al. / Inorganica Chimica Acta 361 (2008) 1861–1867
1863
Table 1
Crystal data and structural refinement parameters
3. Results and discussion
Identification code
II.1
IV.5
3.1. Platinum containing diphosphines
Empirical formula
Formula weight
Temperature, K
Crystal system
Space group
C30H34Cl4P2Pt
793.40
180(2)
Monoclinic
P21
9.1258(9)
12.1613(8)
14.1511(14)
90.0
104.253(11)
90.0
1522.2(2)
2
1.731
5.085
C34 H42Cl2O2P2Pt
810.61
180(2)
Monoclinic
P21
9.7857(12)
11.7618(9)
14.2326(11)
90.0
91.404(8)
90.0
1637.6(3)
2
1.644
4.575
Chiral stereochemically dynamic diphosphines I derived
from 2,20-biphospholes were prepared in three steps from
1-phenyl-3,4-dimethylphosphole according to the method
we have recently reported (Scheme 1) [9].
The introduction of a chiral carbon linker between the
two phosphorus atoms resulted in a partial chirality con-
trol of the central and axial chiralities of the 2,20-biphosp-
hole framework as only three diastereoisomers are
obtained among the six expected (Fig. 1).
These three diastereoisomers isomerize at room temper-
ature in solution through a phosphorus inversion inducing
atropo inversion leading to an equilibrium mixture [14], the
driving force being the pyramidal inversion barrier [15] of
the phosphorus atom.
˚
A, A
˚
B, A
˚
C, A
a, ꢁ
b, ꢁ
c, ꢁ
3
˚
Volume, A
Z
Density (calcd), Mg/m3
Abs. coef., mmꢀ1
F(000)
780
808
Crystal size, mm3
h range, ꢁ
Reflct collected
0.28 · 0.12 · 0.04
2.24 to 26.00
15083
5731 (0.0561)
Multi-scan
0.5698 and 0.4818
0.947
0.0281, 0.0575
0.0360, 0.0591
0.022(7)
0.45 · 0.19 · 0.185
3.34–28.28
14561
8013 (0.0662)
Multi-scan
1.0 and 0.1472
0.984
0.0473, 0.0937
0.0617, 0.0992
0.013(8)
ꢀ2.233 / 1.887
Complexation of the diastereoisomeric mixture of equil-
ibrating diphosphines I with 1 equiv. of [PtCl2(CH3CN)2]
or [PtCl2(PhCN)2] was complete in 3 h by refluxing in tol-
uene and quantitatively afforded a mononuclear cis-dic-
horoplatinum complex II, [PtCl2(L*)] (L* = I), as
Ind. reflct (Rint
)
Abs. cor.
Transmission coef.
GOF on F2
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
Flack’s parameter
Largest diff. peak and hole
1
evidenced by H, 13C, 31P NMR spectroscopy and mass
spectroscopy. Mass spectroscopy analysis allowed to iden-
tify the formation of a mononuclear complex. The 31P
NMR spectra indicate the presence of a single complex
with two diastereotopic phosphorus with for each an over-
lapping doublet due to the 33.8% of the phosphorus nuclei
0.983 / 1.246
1
coupled to 195Pt. The values of the JPꢀPt coupling con-
diffractometer for IV.5. Data were collected using mono-
chromatic Mo Ka radiation (k = 0.71073).
stants (II-1: 3193 Hz, II-2: 3265 Hz, II-3: 3232 Hz) are typ-
ical of cis-dichloro mononuclear platinum complexes [16].
These coupling constants as well as the 195Pt chemical shifts
were comparable to the values found for similar 2,2-
biphosphole complex [Pt(BIPHOS)Cl2] (d = ꢀ4357.3 ppm,
1JPꢀPt = 3409 Hz) [17]. The two diastereotopic phosphorus
are consistent with the opposite configuration of the phos-
phorus atoms in complex II. In addition, the NMR spectra
The structures were solved by direct methods (SIR97
[11]) and refined by least-squares procedures on F2 using
SHELXL-97 [12]. All H atoms were introduced in calculation
in idealized positions and treated as riding on their parent
C atoms. The drawing of the molecules was realised with
the help of ORTEP32 [13]. Crystal data and refinement
parameters are shown in Table 1.
Me
Ph
Me
Ph
Me Me
OTs
*
Me
Ph
Me
Ph
MeMe
Me
Ph
Me
Ph
MeMe
Me
Me
Na-naphthalene
P
P
P
P
OTs
THF, 25˚C
Δ
P
P
P
P
THF, 25°C
P
*
*
Ph
Me
Ph
Me
Ph
I
(S,S)-1
(R,R)-2
Me
Me
I-1a-c (80/15/5), 70%
I-2a-c (38/50/12), 77%
I-3a-c (55/30/15), 78%
Me
Me
Me
Me
Me
Me
Me
(R,R)-3
Me
Ph
H
H
[PtCl (CH CN) ]
O
O
2
3
2
Ph
P
I
P
Me
Me
Pt
*
Toluène, Δ
Cl
Cl
II
II-1: 92%
II-2: 91%
II-3: 94%
Scheme 1.

1864
E. Robe´ et al. / Inorganica Chimica Acta 361 (2008) 1861–1867
a
b
c
d
e
f
R' R'
R' R'
R' R'
R' R'
R'
R' R'
R' R'
R'
R'
R
R'
R'
R'
R
R'
R'
R
R'
R'
R'
R'
R
P
P
P
P
P
P
P
P
P
P
P
P
P
P
R
R
R
R
R
R
R
R
*
*
*
*
*
*
•
•
•
•
•
P
P
P
P
P
P
P
P
P
P
*
*
*
*
*
*
Fig. 1. The six stereoisomers of 2,20-biphosphole framework 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. Only c, d and e (f) forms have been obtained.
of these complexes show the presence of a single compound
in solution even within the temperature range ꢀ60 to
+85 ꢁC. These results indicate no dynamic configuration
change of the 2,20-biphosphole chelated to the platinum.
Obviously, complete stabilization of the 2,20-biphosphole
framework chiralities has occurred by complexation as
the result of the hindered inversion of the phosphorus con-
figurations as well as atropoinversion of 2,20-biphosphole
on metal center.
The molecular structures of II.1 and II.2 [9] have been
established by X-ray diffraction studies (Figs. 2 and 3). In
both complexes, the coordination around the metal is
square planar with a cis arrangement of the ligands. Com-
pound II.1 crystallizes in a non centrosymmetric space
group (P21). The refinement of the Flack’s parameter [18]
(0.04(2)) clearly indicates that II.1 is enantiomerically pure
in solid state and the absolute configuration is
S[Rp,Sp,Sc,Sc] (axial chirality [phosphorus chirality, car-
bon chirality]).
two phosphorus atoms have oppositive configuration
[Rp,Sp] that confirms the 31P NMR analysis. Axial and
central chiralities of 2,20-biphosphole, fixed by Pt-coordi-
nation, led to a drastically reduced torsion angle in com-
plexes II as evidenced by the P(1)–C(11)–C(21)–P2
torsion angles (+7.76ꢁ for II.I and +5.35ꢁ for II.2.
According to these results, the reaction of the diastereo-
isomeric mixture of equilibrating diphosphines derived
from 2,2-biphospholes with Pt(II) precursor resulted in a
dynamic chirality control of the axial and P-central chiral-
ities to give diastereo- and enantiopure Pt-complexes.
3.2. Platinum containing diphosphinites
Chiral stereochemically dynamic diphosphinite ligands
III derived from 2,20-biphosphole have been synthetized
by introducing a chiral alkoxy linker between the two phos-
phorus atoms [10] of the 2,20-biphosphole framework
(Scheme 2) according to a similar strategy as described
for diphosphines I. Diphosphinites III were isolated in high
yields as air-stable solids. These diphosphinites have been
observed as a single compound by NMR in solution even
within the temperature range ꢀ60 ꢁC to +85 ꢁC. The indi-
vidual diastereoisomers could not be detected in solution
by NMR probably because these diastereoisomers are
interconverting rapidly on the NMR time scale. Indeed
On the other hand, II.2 is also enantiomericaly pure in
solid state [space group P212121, Flack’s parameter
0.022(7)]. Its chirality is described as S[Rp,Sp,Rc,Rc].
It is interesting to note that the ligand adopts a single
configuration in these platinum complexes in which the
Fig. 2. Molecular view of S[Rp,Sp,Sc,Sc]-II.1 with atom labelling
Fig. 3. Molecular view of S[Rp,Sp,RC,RC]-II.2 with atom labelling
scheme. Ellipsoids represent 30% probability. P(1)–C(11)–C(21)–P(2)
torsion angle: +7.8(6)ꢁ Selected bond distances (A): Pt(1)–P(1) 2.230(2);
Pt(1)–P(2) 2.251(1); Pt(1)–Cl(1) 2.352(2); Pt(1)–Cl(2) 2.343(1); P(1)–C(1)
1.834(7); P(1)–C(11) 1.795(7); P(1)–C(14) 1.796(6); P(2)–C(2) 1.867(7);
P(2)–C(21) 1.817(6); P(2)–C(24) 1.817(6).
scheme. Ellipsoids represent 30% probability. P(1)–C(11)–C(21)–P(2)
˚
˚
torsion angle: +5.4(2)ꢁ Selected bond distances (A): 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).

E. Robe´ et al. / Inorganica Chimica Acta 361 (2008) 1861–1867
1865
Me
Ph
Me
Ph
Me
Me
Me
Me
Me
Ph
Me
Ph
MeMe
Na-naphthalene
Me
Ph
Me
Ph
MeMe
P
P
P
P
BrCN
Δ
THF, -78 à 25˚C
THF, 25°C
P
P
P
P
P
Ph
Me
Ph
Me
Ph
CN
CN
Me Me
Me
Me
Me
H
H
Ph
OLi
O
O
Me
Me
=
*
*
THF, 25˚C
Ph
Me
(R,R)-1
OLi
(S,S)-2 (R,R)-3
(S,S)-5
(S,S)-4
Me
Ph
Me
Ph
Me Me
P
P
Me
Ph
Me
Me
O
O
Me
*
[PtCl (PhCN) ]
2
2
Ph
III
P
III
III.1: 82%
P
III.2: 85%
III.3: 81%
III.4: 85%
III.5: 83%
CH Cl
2
Pt
Cl Cl
*
2
O
O
IV.1: 90 %
IV
IV.2: 87 %
IV.3: 84 %
IV.4: 90 %
IV.5: 83 %
Scheme 2.
the reduced phosphorus-inversion barrier is not affected by
p-donor substituents on the phosphorus [19] so a same
isomerization process for diphosphinites III for observed
to diphosphines I may be considered.
configuration change of the 2,20-biphosphole chelated to
1
the platinum has been observed by 31P and H NMR in
the temperature range ꢀ70 to +85 ꢁC.
The molecular structure of IV.5, established by X-ray
diffraction studies, shows a square planar complex for plat-
inum and a cis arrangement of the ligands (Fig. 4).
X-ray structural determinations of IV.5 revealed the for-
mation of an enantiopure complex [P21, Flack’s parame-
ter = 0.013(8)]. The chirality of the 2,20-biphosphole
framework in IV.5 is described as S[Sp,Rp,Sc,Sc]
(Fig. 4) thus indicating that the ligand adopts a single con-
figuration in the complex in which, as expected, the two
phosphorus atoms have opposite configuration [Sp, Rp].
As observed in the cases of diphosphine complexes II,
the coordination to platinum locked up both axial and cen-
tral chiralities of 2,20-biphosphole leading to a drastically
reduced torsion angle in complex IV.5 (9.9ꢁ).
The reaction of diphosphinites III with 1 equiv. of
[PtCl2(PhCN)2] led to complete consumption of the ligand
in 3 h at room temperature in dichloromethane to quanti-
tatively afford a mononuclear dichoroplatinum complex
IV, [PtCl2(L*)] (L* = III), (Scheme 2) as supported by mass
spectroscopy. Contrary to complexes II, these platinum
1
complexes give broad signals in 31P and H NMR, except
for complexes IV.4 and IV.5, even within the temperature
range ꢀ70 to +85 ꢁC. This broadness can be explained
by an aggregation phenomena in solution.1 Furthermore,
1
the values of the JP–Pt coupling constants span in a large
range (2848–3788 Hz) relative to that observed in platinum
complexes including diphosphinites ligands. The well-
resolved 31P NMR spectra of complexes IV.4 and IV.5
exhibit two diastereotopic phosphorus having opposite
phosphorus configurations flanked by platinum satellites
According to these structural results, the chiral stereody-
namic diphosphinites III derived from 2,20-biphosphole
afford diastereo- and enantiopure complexes through a
dual chirality control locked by platinum coordination as
observed in the case of the chiral stereodynamic diphos-
phines I.
(IV.4: dP1 = 107.78 ppm, dP2 = 108.18 ppm, JPt–P1
=
2848 Hz, JPt–P2 = 2921 Hz; IV.5: dP1 = 106.71 ppm,
dP2 = 109.77 ppm, JP1–P2 = 6.1 Hz, JPtꢀP1 = 4112 Hz,
JPt–P2 = 3787 Hz; dPt = ꢀ3812.1 ppm). These results
clearly indicate the formation of a pure diastereoisomer
as in the case of diphosphines complexes II. In addition,
complete stabilization of 2,20-biphosphole framework
chiralities has occurred by complexation as no dynamic
3.3. Hydroformylation reactions
As a preliminary work, the catalytic properties of these
platinum complexes have been explored in the hydrofor-
mylation of styrene (Scheme 3) [20].
Initial experiments were performed at room temperature
in dichloromethane under 100 atm of CO:H2 (1:1)
using [PtCl2(L*)], L* = I or II, with anhydrous SnCl2 as
1
The broadness of the line can be explain by a short T2 relaxation
associate to an aggregation phenomena in solution as no dynamic effect
have been observed by variable temperature experiment.

1866
E. Robe´ et al. / Inorganica Chimica Acta 361 (2008) 1861–1867
co-catalyst (Table 2). Excellent chemoselectivities were
observed with diphosphine and diphosphinite complexes
and as a result hydrogenated products (alkane, alcohol)
were not detected. (Scheme 3). In addition, high regioselec-
tivities were recorded in each case giving predominantly the
branched aldehydes (76–91%). However, low activities and
enantioselectivities were obtained with both diphosphine
and diphosphinite complexes at room temperature. It is
interesting to note that the steric properties of the chiral
linker could affect the activity of the catalyst. The best
activities were performed with the diphosphine complex
II.3 and the diphosphinite complex IV.3, including the
same chiral linker 3. The steric properties of the linker seem
to be more important than the electronic properties of the
ligand since the activities, regioselectivities and enantiose-
lectivities of complexes II.3 and IV.3 are almost the same.
The results obtained with these platinum complexes
containing 2,2-biphosphole-based ligands can be com-
pared to those obtained with the rhodium complex
[Rh(BPHOS)(COD)]BF4 in terms of chemoselectivities
(100%) and regioselectivities (b/l = 98/2) [21].
Fig. 4. Molecular view of complex S[Sp,Rp,Sc,Sc]-IV.5 with atom
labelling scheme. Ellipsoids drawn at the 50% probability level. P(1)–
˚
C(11)–C(21)–P(2) torsion angle: 9.9(8)ꢁ Selected bond lengths (A) and
bond angles(ꢁ): Pt(1)–Cl(1) 2.340(2); Pt(1)–Cl(2) 2.343(2); Pt(1)–P(1)
2.234(2); Pt(1)–P(2) 2.216(2); Cl(1)–Pt(1)–Cl(2) 88.85(8); Cl(1)–Pt(1)–
P(1) 175.75(9); Cl(1)–Pt(1)–P(2) 93.55(8); Cl(2)–Pt(1)–P(1) 95.07(8);
Cl(2)–Pt(1)–P(2) 177.56(8); P(1)–Pt(1)–P(2) 82.55(7).
CHO
OH
Activities of all complexes increase at higher tempera-
ture (Table 3). At 60 ꢁC, the complete conversion of styrene
over 5 h was obtained with complex II.3 and IV.3 but both
chemioselectivity and regioselectivity were affected.
According to these results, diphosphine and diphosphi-
nite platinum complexes proved to be regioselective cata-
lyst in the hydroformylation of styrene but induced only
low enantioselectivities.
CO/H2
OH
CHO
[Rh]
*
*
Scheme 3.
Table 2
Hydroformylation of styrene at 20 ꢁC with [PtCl2(L*)]/SnCl2
a
)
Entry
Complexes
Temps (h)
Conversionb (%)
Aldehyde contentb (%)
b/lb (%)
Eeb (%) (configuration)
1
2
3
4
5
6
7
a
II.1
II.2
II.3
IV.2
IV.3
IV.4
IV.5
72
72
94
72
72
14
4
64
5
81
4
2
100
100
97
100
100
100
100
83/17
83/17
91/9
87/13
81/19
87/13
76/24
18 (R)
–
12 (R)
–
2c
–
500
72
–
Reaction conditions: T = 20 ꢁC; p(CO/H2 = 1/1) = 100 atm. [substrate]/cat= 200.
Determined by chiral GC b-DEX 225.
The configuration of the major product is not determined for ee lower than 5%.
b
c
Table 3
a
Hydroformylation of styrene at 60 ꢁC with [PtCl2(L*)]/SnCl2
Entry
Complexes
Temps (h)
Conversionb (%)
Aldehyde contentb (%)
b/lb (%)
Eeb (%) (configuration)
1
2
3
4
5
6
7
8
a
II.1
II.2
II.3
IV.1
IV.2
IV.3
IV.4
IV.5
23
24
5
23
24
24
100
24
12
10
99
12
14
68
24
58
100
100
88
100
100
100
96
76/24
76/24
82/18
81/19
81/19
86/14
72/28
68/32
–
–
2c
–
3c
3c
4c
92
15 (S)
Reaction conditions: T = 20 ꢁC; p(CO/H2 = 1/1) = 100 atm. [substrate]/cat = 200.
Determined by chiral GC b-DEX 225.
The configuration of the major product is not determined for ee lower than 5%.
b
c

E. Robe´ et al. / Inorganica Chimica Acta 361 (2008) 1861–1867
1867
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Noyori, Angew. Chem., Int. Ed. Engl. 38 (1999) 495.
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4. Conclusions
Chiral stereodynamic diphosphine and diphosphinite
ligands derived from 2,2-biphospholes were used to form
diastereo- and enantiopure platinum complexes through a
dual chirality control of the axial chirality and central chi-
ralities of the 2,20-biphosphole framework by Pt-coordina-
tion. These complexes, evaluated in asymmetric
hydroformylation, proved to be very effective catalysts with
respect to regioselectivities (up to 91%) to branched alde-
hyde, but their behavior in terms of enantioselectivities
was not satisfactory. Use of these new stereodynamic diph-
osphinite ligands derived from 2,20-biphosphole in other
asymmetric catalytic reactions as well as optimizations
through the modifications of the chiral backbone is cur-
rently in progress.
[7] O. Tissot, M. Gouygou, J.-C. Daran, G.G.A. Balavoine, Chem.
Commun. (1996) 2287.
´
[8] C. Ortega, M. Gouygou, J.-C. Daran, Chem. Commun. (2003) 1154.
´
´
[9] E. Robe, C. Ortega, M. Mikina, M. Mikolajczyk, J.C. Daran, M.
Gouygou, Organometallics 24 (2005) 5549.
´
[10] E. Robe, C. Hegedus, J. Bakos, J.-C. Daran, M. Gouygou, submitted
¨
for publication.
[11] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
vazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagn, J.
Appl. Crystallogr. 32 (1999) 115.
Acknowledgments
[12] G.M. Sheldrick, SHELXL97. Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Germany, 1997.
Research supported by the CNRS, the MENRT (E.R.
[13] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[14] For 2,2-biphosphole bearing a short chiral linker like a C3 or a C4
carbon chain, an isomerization process between three diastereoiso-
mers occurring at temperature below ꢀ60ꢁC has been observed by
NMR. See Ref. [9].
´
grant), the Universite Paul Sabatier (E.R.), the Hungarian
National Science Foundation (OTKA Grants No.
T046825) and through a European Community Marie Cur-
ie Action (contrat no. HPMT-CT-2001-00398).
[15] In phospholes, 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 phosphole in the transition state. The
activation barrier to phosphorus inversion in 2,20-biphosphole is
measured to be only 16.5 kcal/mol leading to phosphorus inversion at
ꢀ60ꢁC, see Ref. [7,9].
Appendix A. Supplementary material
CCDC 613284 and 634479 contain the supplementary
crystallographic data for IV.5 and II.1. These data can be
obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.ica.2007.09.043.
[16] P.S. Pregosin, in: Verkade, D.L. Quin (Eds.), Phosphorus-31 NMR
Spectroscopy, VCH Publishers, 1987, p. 465.
[17] M. Gouygou, O. Tissot, J.-C. Daran, G.G.A. Balavoine, Organome-
tallics 16 (1997) 1008.
[18] H.D. Flack, Acta Cryst. A 39 (1983) 876.
[19] (a) p-Donor substituents on the phosphorus of phospholes do not
affect the activation barrier according to experimental measurements
´
and calculations: J. Hydrio, PhD thesis (2000) Universite Paul
Sabatier, Toulouse, France;
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