Some aspects of the structural and coordination chemistry of the 2,2'- biphosphole

Article abstract of DOI:10.1016/S0040-4020(99)00776-0

The 2,2'-biphosphole which presents axial chirality generated by the biphosphole framework and central chiralities due to the phosphorus atoms leads to the existence of six stereoisomers corresponding to three pairs of enantiomers which have been fully ch

Full text of DOI:10.1016/S0040-4020(99)00776-0

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 85–93
Some Aspects of the Structural and Coordination Chemistry of
the 2,20-Biphosphole
a
a
a,
b
a
*
´ ˆ
´
Olivier Tissot, Jerome Hydrio, Maryse Gouygou, Frederic Dallemer, Jean-Claude Daran
and Gilbert G. A. Balavoinea
aLaboratoire de Chimie de Coordination du CNRS, 205, Route de Narbonne, 31077 Toulouse Cedex, France
b
ˆ
Catalysis and Catalytic Processes, Rhone-Poulenc, 85, Avenue des Freres Perret, BP 62, 69192 Saint-Fons Cedex, France
Received 18 March 1999; accepted 25 June 1999
Abstract—The 2,20-biphosphole which presents axial chirality generated by the biphosphole framework and central chiralities due to the
phosphorus atoms leads to the existence of six stereoisomers corresponding to three pairs of enantiomers which have been fully characterised
by X-ray diffraction studies. Among these three diastereoisomers, one has a favourable configuration for chelating metals. The synthesis and
structure of numerous transition metal complexes are reported. Their X-ray analysis proved that in each complex the 2,20-biphosphole
ligands have the expected configuration. ᭧ 1999 Elsevier Science Ltd. All rights reserved.
Introduction
presented in Fig. 2 displays a dihedral angle between the
two phosphole rings (86Њ) which generated an axial chirality
C2. This occurrence of C2-symmetry in the 1,10-diphenyl-
3,30,4,40-tetramethyl-2,20-biphosphole (BIPHOS) in a com-
plex led to a renewed interest in the chemistry of this
bidentate ligand.
The coordination chemistry of monophospholes has been
extensively studied,1 and the evaluation of their potential
in homogenous catalysis has been investigated.2 In particu-
lar, it was proved that phospholes are efficient ligands for
hydrogenation and hydroformylation of various unsaturated
substrates in conjunction with rhodium.2c–f On the other
hand, chiral diphosphole ligands associated to rhodium
have proved to be moderate asymmetric inductors for
these catalytic processes.3 High enantiomeric excesses
(Ͼ96%) and high branched to normal (b/n) ratios (77/23)
have been obtained in the asymmetric hydroformylation of
styrene by the use of platinum complexes in the presence of
SnCl2.4
In this paper we will overview our recent work concerning
the structure and stereochemistry of 2,20-biphosphole com-
pounds as well as their coordination chemistry.
In the field of 2,20-biphosphole chemistry, little work has
been done. Indeed, only a few 2,20-biphosphole compounds,
the 1,10-diphenyl-3,30,4,40-tetramethyl-2,20-biphosphole5
and its derivatives,6 and two 2,20-biphosphole complexes
[Mo(2,20-biphosphole)(CO)4]5 and [Mn2(2,20-biphosphole)-
(CO)8]5 (Fig. 1) have been reported in the literature by
Mathey et al., but no structural information was given.
In 1997, we obtained the X-ray structure of the dinuclear
complex [Fe(h5-C5H5)(C4HMe2PhP)(CO)]2.7 It was the first
structural report of a complex containing the 2,20-biphos-
phole ligand. The molecular structure of this complex
Keywords: stereoisomers; diastereoisomers; 2,20-biphosphole complexes;
transition metal complexes; enantiomers.
* Corresponding author. Tel.: ϩ33-0561-333-174; fax: ϩ33-0561-553-
003; e-mail: gouygou@lcc-toulouse.fr
Figure 1.
0040–4020/00/$ - see front matter ᭧ 1999 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(99)00776-0

86
O. Tissot et al. / Tetrahedron 56 (2000) 85–93
This stereochemical analysis shows the occurrence of six
stereoisomers corresponding to three pairs of enantiomers.
Only two isomers were observed in solution for the 2,20-
biphosphole compounds. Using the procedure previously
described by F. Mathey and coworkers,8 we synthesised
the 1,10-diphenyl-3,30,4,40-tetramethyl-2,20-biphosphole 18
which we identified as a mixture of two isomers 1a, 1b in
the ratio 88/12 as evidenced by 1H-, 31P- and 13C-NMR data
analysis.9 The existence of two isomers was also observed
for the 1,10-dicyano-3,30,4,40-tetramethyl-2,20-biphosphole
2, obtained from compound 1 (Scheme 1). However, in
the solid state, we were able to characterise the three pairs
of enantiomers by X-ray diffraction analysis. The diastereo-
isomer ([a]SSSϩ[a]RRR) was identified for the dioxide 3a and
disulfide 4a9 obtained by oxidation of the corresponding
2,20-biphosphole 1 (Scheme 1). The molecular structure of
dioxide 3a is presented in Fig. 4. The diastereoisomer
([b]RSSϩ[b]SRR) was characterised for the disulfide derivative
4b9 of 2,20-biphosphole 1b. Fig. 5 shows the molecular
structure of disulfide 4b in the crystal. The structure of the
third isomer ([a]RSRϩ[a]SRS) was obtained for free 2,20-
biphosphole 1 and 2. The molecular structure obtained for
compound 2 is shown in Fig. 6.
Figure 2. The molecular structure of the dinuclear complex [Fe(h5-C5H5)-
(C4HMe2PhP)(CO)]2.
Results
Structure and stereochemistry of the 2,20-biphosphole
The 2,20-biphosphole is a particular diphosphine which
presents axial chirality generated by the biphosphole frame-
work and central chirality due to phosphorus atoms. The
different possibilities of combining axial and central chiral-
ities in 2,20-biphosphole are depicted in Fig. 3 using a
Newman projection along the C–C axis of the bond linking
the phosphole rings.
From these results, we were able to propose a structure for
the two isomers of the 2,20-biphosphole observed in solu-
tion. Since the mixture of 2,20-biphosphole, 1a and 1b in the
ratio 88/12, leads to the dioxide 3a and 3b or to the disulfide
4a and 4b in the same ratio 88/12, the major products arise
from the major isomer 1a and the minor product from the
minor isomer 1b. The minor 2,20-biphosphole stereoisomer
Figure 3. The 23 stereoisomers of 2,20-biphosphole which possess two chiral centres and one chiral axis. Subscript refers to central chirality and superscript to
axial chirality. Among these eight stereoisomers, six are really inequivalents.

O. Tissot et al. / Tetrahedron 56 (2000) 85–93
87
Scheme 1.
1b or 2b corresponds to the pair of enantiomers [b]RSSϩ
[b]SRR and presents opposite absolute configuration for the
two phosphorus atoms. Thus for the major stereoisomer 1a
or 2a, both phosphorus atoms have the same absolute
configuration. We assume that this isomer exists in solution
either in the [a]RSRϩ[a]SRS form or in the [a]RRRϩ[a]SSS form or
as a mixture of these two pairs of enantiomers inter-
converting rapidly on the NMR time scale even at low
temperature (Ϫ70ЊC) by rotation around the C–C bond
bridge and giving only one sharp 31P resonance (dˆ15:7).
The two isomers a and b could not be separated by usual
methods because 2,20-biphosphole exists in solution as an
equilibrium mixture of two diastereoisomers a and b, the
energetically preferred isomer being a. The kinetics studies
of the 1b!1a isomerisation,9 by 31P NMR at low tempera-
ture, shows that the free enthalpy of activation which corre-
sponds to the inversion barrier for the pyramidal phosphorus
centre is DG2#18ˆ16.5 kcal/mol. This low barrier due to
extensive electronic delocalization within the planar transi-
tion state is comparable to those observed for the mono-
phosphole series.10
However, if we consider the [a]RSR and [a]SRS configurations,
the 2,20-biphosphole presents the phosphorus lone pairs in
the right direction to chelate a metal centre. We have
explored the coordination behaviour of the 1,10-diphenyl-
3,30,4,40-tetramethyl-2,20-biphosphole ligand (BIPHOS), 1.
Synthesis and characterisation of 2,20-biphosphole
complexes
The reaction of 2,20-biphosphole 1 (1aϩ1b) with appropri-
ate nickel, palladium and platine precursors produces
[MCl2(BIPHOS)]11 in dichloromethane at room temperature
in excellent yield (Scheme 2). The 31P{1H} NMR spectra of
the reaction mixture exhibit in each case a single resonance
showing that the conversion of (1aϩ1b) into the corre-
sponding complexes 5 is quantitative and that 5 are obtained
in a pure diastereoisomer form. Owing to the low pyramidal
inversion barrier of the phosphorus atom,9,10 it is clear that
1b is quantitatively transformed into 1a in order to favour
coordination onto the metal. These complexes were charac-
terised by elemental analysis, multinuclear NMR spectro-
scopy, mass spectroscopy and X-ray diffraction studies.
Figure 4. The molecular structure of the dioxide 3a.
The molecular view of complex 5b is presented in Fig. 7.
In this complex, the P(1), P(10) and Pd atoms have a
square planar environment with slight distortion from
Figure 5. The molecular structure of the disulfide 4b.
Figure 6. The molecular structure of the 2,20-biphosphole 2a.

88
O. Tissot et al. / Tetrahedron 56 (2000) 85–93
Scheme 2.
forms of the ligand as expected from the stereochemical
analysis (c.f. Fig. 2).
For [NiCl2(BIPHOS)]11 5a and [PtCl2(BIPHOS)]11 5c com-
plexes, X-ray diffraction analysis shows the same stereo-
chemistry of the 2,20-biphosphole ligand, [a]RSR, [a]SRS, in
each complex. This stereochemistry appears to be stable
once coordinated to the metal.
The 2,20-biphosphole ligand 1 can also chelate ruthenium
metal. The h3-allyl-complex, [Ru(h3-allyl)2(BIPHOS)] 6,
was obtained by reaction of 1 with [Ru(h3-allyl)2(COD)].12
In contrast to the formation of nickel, palladium and
platinum complexes which are immediate at room tempera-
ture, the formation of ruthenium complex is very slow,
complete in 8 d at room temperature. Moreover, complex
6 is extremely air and moisture sensitive and has only been
characterised by 1H, 31P-NMR and mass spectroscopy.
The NMR spectra indicated the formation of only one
diastereoisomer from the two expected if we consider the
stereochemistry of the 2,20-biphosphole ligand, [a]RSR and
[a]SRS, and the stereochemistry of a tris-chelate ruthenium
complex, D and L. This reaction proceeds diastereoselec-
tively but we have not been able to determine on the basis of
a single NMR analysis which diastereoisomer has been
obtained.
Figure 7. The molecular structure of the palladium complex 5b.
the idealised situation. The phosphole rings are all planar
within experimental error, but they are twisted with
respect to each other along the C(1)–C(10) bond making
dihedral angles of 46.8Њ. This value compares well with
the 46.6Њ observed for the free ligand 1.6 As the structure
possesses a C2-symmetry axis passing through the metal
atom and crossing the middle of the C(1)–C(10) bond, the
complex 5b is chiral. The structure determination reveals
unambiguously the relative configuration of both central
and axial elements of chirality. However, the solid state
structure corresponds to a racemic mixture since complex
5b crystallises in a centrosymmetric space group. This
racemic complex corresponds to the two [a]RSR and [a]SRS
2,20-biphosphole 1 is a rather good ligand for transition
metals as evidenced by the formation of bis-biphosphole
complexes. The reaction of 1 with [Pd(CH3CN)4](BF4)2
affords a bis-2,20-biphosphole–palladium-complex, [Pd(BI-
PHOS)2](BF4)2,11 7 (Scheme 3) as indicated by elemental
analysis, mass spectroscopy and X-ray analysis.
Scheme 3.

O. Tissot et al. / Tetrahedron 56 (2000) 85–93
89
Figure 8. The molecular structure of the meso-palladium complex 7.
The molecular structure of the cation is shown in Fig. 8. As
observed in complex 5b, the phosphole rings are planar
within experimental error and they are twisted along the
C(1)–C(11) bond making a dihedral angle of 53.3Њ.
Complex 7 contains both the [a]RSR and [a]SRS absolute config-
urations of the 2,2-biphosphole and it is thus the meso
diastereoisomer. The same meso-palladium complex was
later described by Matsuda and coworkers.13 In addition,
these authors observed the formation of another complex,
the racemic diastereoisomer. The formation of these two
diastereoisomers seems to be solvent dependant. A mixture
of meso and racemic complexes was obtained in a dichloro-
methane solution whereas the formation of only the meso
complex proceeds in a toluene–dichloromethane mixture.
These diastereoisomers are stereochemically stable in
dichloromethane solution. For example, starting to the
meso-palladium complex in dichloromethane solution, no
interconversion to the racemic complex was observed
proving the stereochemistry of the 2,20-biphosphole ligand
is stable once coordinated to the metal.
Figure 9. The molecular structure of the trans–meso-ruthenium complex
10.
spectroscopy and multinuclear NMR spectroscopy.
Unfortunately, we have not yet been able to obtain a crystal
structure of these complexes so we cannot determine if it is
the meso or the racemate.
Bis-2,20-biphosphole-dicarboxylato–ruthenium complexes,
[Ru(O2CCR3)2(BIPHOS)2] RˆCH3, CF3, have been surpris-
ingly obtained by reaction of 2,20-biphosphole 1 with
normal precursors of diphosphine-dicarboxylato–ruthenium
complexes [Ru(O2CCR3)2(P–P)].14 The reaction of biphos-
phole 1 with these ruthenium complexes in dichloromethane
at 30 ЊC gives, in a moderate yield, bis-biphosphole
ruthenium complexes 9 and 10,15 respectively, (Scheme 4)
as indicated by mass spectroscopy.
X-ray structural analysis15 confirms for complex 10 the
formation of [Ru(O2CCF3)2(BIPHOS)2]. The ORTEP plot
given in Fig. 9 shows a near-octahedral geometry for
ruthenium and mutually trans ligated monodentate trifluoro-
acetate groups. Although unexpected, the monodentate
coordination mode of the trifluoroacetate groups is not
Similar bis-2,20-biphosphole–rhodium complexes, [Rh(BI-
PHOS)2]X,11 were synthesised from [Rh(COD)2]BF4 or
[RhCl(COD)]2 precursors. In these cases, only one
diastereoisomer was obtained and identified by mass
Scheme 4.

90
O. Tissot et al. / Tetrahedron 56 (2000) 85–93
near-octahedral geometry for ruthenium. As in 10, this
complex 12 contains the pair of enantiomers of biphosphole
1 with [a]RSR and [a]SRS absolute configurations but with two
cis monodentate trifluoroacetate groups leading to a chiral
arrangement around the ruthenium atom. However, the solid
state structure corresponds to the racemic mixture,
D(([a]RSRϩ[a]SRS) and L([a]SRSϩ[a]RSR), since complex 12
crystallises in a centrosymmetric space group. The two
Ru–P bond lengths corresponding to the P atoms trans to
˚
each other, 2.358(4) and 2.394(4) A, are similar to those
observed for 10, whereas for the two P atoms trans to the
trifluoroacetate, the Ru–P distances are much shorter,
˚
2.275(3) and 2.296(4) A, as also observed in related
complexes.17
This large difference could be the consequence of a strong
trans influence of the trifluoroacetate ligands. We assume
that the formation of the kinetic product 9 or 10 is probably
controlled by steric factors. Indeed, the molecular structures
reveal that steric constraints between the two enantiomers of
1 seem to be lower in the trans–meso 9 or 10 than in the cis
(^) 11 or 12. On the other hand, we assume that the isomeri-
zation of the trans–meso 9 or 10 into the thermodynamic
product cis (^) 11 or 12 is triggered by the trans influence
of the monodentate trifluoroacetate ligands. We may assume
that this trans influence facilitates a decoordination–recoor-
dination process of one of the trifluoroacetate ligands
eventually assisted by the formation of an intermediate
with a dihapto coordination of the other (Scheme 5).
Figure 10. The molecular structure of the cis-(^)-ruthenium complex 12.
unprecedented and there are many examples of such a
bonding mode for the trifluoroacetate.16 The four Ru–P
˚
bond distances lie in the range 2.32–2.42 A found for
related ruthenium(II) bisphosphine trans disubstituted
complexes.17 This complex contains both the [a]RSR and
[a]SRS absolute configurations of the biphosphole 1 (c.f.
Fig. 2) and it is then the meso diastereoisomer as already
observed in the [Pd(BIPHOS)2](BF4)2 complex.11
We are presently investigating the mechanism of this
isomerization reaction.
However, these meso-ruthenium complexes 9 and 10 are
stereochemically less stable in dichloromethane solution
than the meso-palladium complex. Transformation of
complexes 9 and 10 proceeded in solution leading to the
formation of new complexes 11 and 12,15 respectively,
(Scheme 4). Remarkable difference was observed for the
stability of complexes 9 and 10: conversion of 9 is complete
in 6 h whereas 8 d are necessary for 10. This conversion,
followed using 31P-NMR spectroscopy, displays the disap-
pearance of the singlet (9: dˆ54:5, 10: dˆ54:5), correspond-
ing to four equivalent phosphorus nuclei in complexes 9
and 10 concomitant with the appearance of an ABCD
system corresponding to four non-equivalent phosphorus
nuclei in complexes 11 and 12. Elemental analysis and
mass spectroscopy also confirmed the formation of bis-
biphosphole–ruthenium complexes for compounds 11 and
12. The molecular structure of complex 12,15 determined by
X-ray analysis and represented in Fig. 10, shows a chiral
Conclusion
The 2,20-biphospholes are peculiar diphosphines presenting
axial chirality generated by the biphosphole framework and
central chiralities due to the phosphorus atoms. The differ-
ent possibilities of combining axial and central chiralities
imply the existence of three pairs of enantiomers which
have been fully characterised by diffraction studies of the
2,20-biphosphole derivatives. The existence of only two
diastereoisomers in solution, as an equilibrium mixture,
was explained by the low inversion barrier for the pyramidal
phosphorus centre and the free rotation around the C–C
bond linking the phosphole rings.
However, the stereochemical and structural analyses reveal
that only one configuration, [a]RSR and [a]SRS, is favourable for
chelating transition metals atoms. Numerous complexes of
Scheme 5.

O. Tissot et al. / Tetrahedron 56 (2000) 85–93
91
Ni, Pd, Pt, Rh and Ru with this specific configuration have
been obtained with the 1,10-diphenyl-3,30,4,40-tetramethyl-
2,20-biphosphole ligand (BIPHOS) and fully characterised
by NMR and X-ray diffraction. Moreover, this stereochem-
istry of the 2,20-biphosphole ligand appears to be stable
once coordinated to the metal.
1,10-Dicyano-3,30,4,40-tetramethyl-2,20-biphosphole (2).
solution of 1,10-diphenyl-3,30,4,40-tetramethyl-2,20-
A
biphosphole 1 (0.160 g, 0.43 mmol) in 5 ml of THF was
added to a suspension of lithium (10-fold excess) in THF.
After 3 h, the excess lithium was removed from the crude
mixture. This solution was then added to a solution of
cyanogen bromide (0.405 g, 3.85 mmol) in 5 ml of THF
and 10 ml of toluene at Ϫ60 ЊC. The mixture was then
allowed to warm at room temperature for 1 h. The mixture
was concentrated under vacuum and filtrated over silica gel
to give 0.083 g of a yellow solid (71%). 31P-NMR (CDCl3):
d Ϫ37.34 (83%, 2a) and Ϫ41.88 (17%, 2b).
These results have highlighted the potential of this ligand
in coordination chemistry. More work is currently being
done in order to define the evaluation of BIPHOS in
catalysis.
1
2a: H NMR (CDCl3): d 1.99 (s, 6H, Me31, 310), 2.18 (s,
Experimental
6H, Me21, 210), 6.32 (m, 2H, vCH–P); 13C NMR (CDCl3):
d 157.9 (t, JCP 7 Hz, C2), 151.0 (t, JCP 20 Hz, C3), 131.5 (t,
JCP 25 Hz, C1), 119.5 (s, CH, C4), 115.9 (d, JCP 82 Hz, CN),
18.8 (t, JCP 2.2 Hz, C31,131), 15.7 (s, C21,121). MS (DCI,
CH4), m/z: 290 (Mϩϩ18, 100%), 272 (Mϩ, 2%). Anal.
Found (Calcd.) for C14H14N2P2: C, 61.59 (61.76); H, 5.20
(5.15); N, 10.15 (10.29). Single crystals of 2a were isolated
by slow evaporation in dichloromethane.
All reactions were conducted under an inert atmosphere of
dry argon using Schlenk glassware and vacuum line tech-
niques. Solvents were freshly distilled from standard drying
agents. Preparative column chromatography was performed
on Merck silica gel (70–20 mm).
1H, 13C{1H, 31P} and 31P{1H} NMR spectra were recorded
on a Bruker WMX 400 instrument operating at 400, 162 and
100 MHz, respectively. Chemical shifts are reported in parts
per million (ppm) relative to Me4Si (1H and 13C) or 85%
1,10-Diphenyl-3,30,4,40-tetramethyl-2,20-biphosphole
dioxide (3). To a solution of biphosphole 1 (310 mg,
0.082 mmol) in dichloromethane (6 ml) cooled at Ϫ15ЊC,
was slowly added a solution of 3-chloroperoxybenzoic acid
(290 mg, 1.67 mmol, 2.02 equiv.) in dichloromethane
(2.5 ml). During the addition the temperature was kept
between Ϫ15ЊC and Ϫ10ЊC. After stirring for 3.5 h at
Ϫ10ЊC, the mixture was washed at room temperature
twice with a saturated solution of NaHCO3. The two
phases were separated on a phase separator filter and the
organic phase was evaporated to give 310 mg (92%) of
compound 3 (3aϩ3b) as a pale yellow powder. The
major product 3a was obtained in a pure form as colourless
crystals from a dichloromethane solution by slow diffusion
with pentane.
H3PO4 (31P). For H and 13C data, biphosphole ligands and
1
biphospholes complexes have the same numbering as in the
X-ray structures. The following abbreviations are used: s,
singlet; d, doublet; t, triplet; m, multiplet. Elemental
analyses were performed by the ‘Service d’Analyse du
Laboratoire de Chimie de Coordination’ at Toulouse,
France. Mass spectra were obtained on a Mermag R10-10
instrument.
X-Ray structure determinations were performed at room
temperature for 3a and at 160 K for 2a on a Stoe IPDS
diffractometer equipped with a graphite oriented monochro-
mator utilising MoKa radiation (lˆ0:71073). Structures
were solved by direct methods (SIR92)18 and refined by
least-squares procedures on Fobs. H atoms could be located
on difference Fourier syntheses, but they were introduced
into the calculation in the idealised position (d(CH)ˆ
1
3a: H NMR: d 2.08 (s, 6H, Me31,131), 2.15 (t,3ϩ4JHP
2
2.2 Hz, 6H, Me21,121), 5.86 (d, JHP 27.8 Hz, 2H, vCH–
P), 6.97–7.02 (m, 4H, Ph), 7.14–7.19 (m, 2H, Ph), 7.29–
7.34 (m, 4H, Ph); 31P{1H} NMR: d 42.20; 13C{1H} NMR: d
2
4
˚
154.14 (dd, JCP 19.9 Hz, JCP 2.8 Hz, C2,12), 153.69 (dd,
0.96 A) and their atomic coordinates were recalculated
2JCP 29.1 Hz, JCP 5.5 Hz, C3,13), 131.46 (s, C114,214),
4
after each cycle. They were given isotropic thermal para-
meters 20% higher than those of the carbon to which they
are attached. Least-squares refinements were carried out by
minimising the function w(FoϪFc)2, where Fo and Fc are the
observed and calculated structure factors. The calculations
were carried out with the CRYSTALS package programs.19
Molecular views were drawn using ORTEP 3.20 Crystal and
data collection parameters, the final residual values, the
relevant structure refinement parameters, the atomic coordi-
nates for the non-hydrogen atoms, the positional and isotro-
pic displacement coefficients for hydrogen atoms, a list of
anisotropic displacement coefficients for the non-hydrogen
atoms and a full list of bond distances and bond angles have
been deposited with the Cambridge Crystallographic Data
Base.
2
130.15 (d, JCP 10.8 Hz, C112,116,212,216), 128.53 (d,
3JCP 12.6 Hz, C113,115,213,215), 128.48 (dd, JCP 99.0 Hz,
1
2JCP 8.8 Hz, C1,11), 126.27 (d, JCP 97.2 Hz, C111,112),
1
1
4
122.43 (dd, JCP 98.3 Hz, JCP 2.2 Hz, C4,14), 17.91 (d,
3JCP 18.6 Hz, C31,131), 15.27 (dd, JCP 15.0 Hz, JCP
2.7 Hz, C21,121). MS (DCI/NH3): 407 (Mϩ1, 100%).
Anal. Found (Calcd.) for C24H24P2O2: C, 70.21 (70.93); H,
5.96 (5.95).
3
4
3b: 1H NMR: d 1.72 (s, 6H, Me31,131), 2.07 (s, 6H,
2
Me21,121), 5.95 (d, JHP 25.0 Hz, 2H, vCH–P), 7.21–
7.71 (m, 10H, Ph); 31P{1H} NMR: d 41.00.
1,10-Diphenyl-3,30,4,40-tetramethyl-2,20-biphosphole
disulfide (4). To a solution of biphosphole 1 (270 mg,
0.72 mmol) in dichloromethane (8 ml) was added 104 mg
(3.24 mmol, 4.5 equiv.) of sulfur. After 2 h of reflux, the
solvent was evaporated to give 299 mg (95%) of compound
The starting materials 2,20-biphosphole compound 18 and
complexes 5,11 7,11 811 and 1015 were prepared as previously
described in the literature.

92
O. Tissot et al. / Tetrahedron 56 (2000) 85–93
4 (4aϩ4b) as yellow powder. 4a and 4b were separated by
chromatography on silica gel with dichloromethane as
eluant.
9: 1H NMR: d 1.67 (s, 6H, CO2CH3), 1.92 (s, 12H, Me121,221,
421,521), 2.04 (d, JH–H 1.0 Hz, 12H, Me131,331,431,531),
6.78 (m, 4H, vCH–P), 6.86 (m, 12H, Ph), 6.96 (m, 8H, Ph);
31P{1H} NMR: d 58.18. MS (FAB, MNBA matrix); m/z:
968 (Mϩ, 45%), 909 ([MϪ(CO2CH3)]ϩ, 100%), 849
([MϪ2(CO2CH3)]ϩ, 66%).
4
1
4
4a: H NMR: d 2.11 (t, JHP 2.63 Hz, 6H, Me21,121), 2.14
(s, 6H, Me31,131), 6.03 (d, 2JHP 31.49 Hz, 2H, vCH–P), 7.03
(m, 4H, Ph), 7.19 (m, 2H, Ph), 7.35 (m, 4H, Ph); 31P{1H}
2
NMR: d 50.75; 13C{1H} NMR: d 153.32 (dd, JCP 25.6 Hz,
The cis-(^)-complex 11 was quantitatively obtained from
the trans–meso 9 in 6 h in a dichloromethane solution.
2
4
3JCP 7.6 Hz, C2,12), 152.32 (dd, JCP 15.0 Hz, JCP 2.1 Hz,
4
C3,13), 131.17 (d, JCP 3.1 Hz, C114,214), 131.10 (dd,
1JCP 82.9 Hz, JCP 11.5 Hz, C1,11), 130.31 (d, JCP
11: 31P{1H} NMR: d 34.17–34.41 (m), 38.65–39.69 (m),
50.17–50.76 (m), 61.20–62.27 (m), 62.75–63.47 (m). MS
(FAB, MNBA matrix); m/z: 909 ([MϪ(CO2CH3)]ϩ, 100%),
849 ([MϪ2(CO2CH3)]ϩ, 42%).
2
2
3
12.0 Hz, C112,116,212,216), 128.42 (d, JCP 12.9 Hz,
1
4
C113,115,213,215), 127.08 (dd, JCP 82.1 Hz, JCP 2.7 Hz,
1
3
C4,14,), 124.02 (d, JCP 76.5 Hz, C111,211), 17.91 (d, JCP
3
4
16.6 Hz, C31,131), 15.42 (dd, JCP 13.3 Hz, JCP 1.9 Hz,
C21,121). MS (DCI/NH3): 439 (Mϩ1, 100%). Anal.
Found (Calcd.) for C24H24P2S2: C, 65.63 (65.73); H, 5.36
(5.51); S, 14.68 (14.62). Single crystals of 4a were obtained
by slow evaporation in dichloromethane.
Acknowledgements
ˆ
We acknowledge the CNRS and Rhone-Poulenc for finan-
cial support; and Professor F. Mathey for advice and fruitful
discussions.
1
4
4b: H NMR: d 1.66 (t, JHP 2.33 Hz, 6H, Me21,121), 2.09
(s, 6H, Me31,131), 6.09 (d, 2JHP 30,9 Hz, 2H, vCH–P), 7.37
(m, 4H, Ph), 7.49 (m, 2H, Ph), 7.62 (m, 4H, Ph); 31P{1H}
NMR: d 51.37; 13C{1H} NMR: d 153.49 (dd, JCP 15.0 Hz,
2
References
4JCP 2.0 Hz, C3,13), 150.56 (dd, JCP 25.8 Hz, JCP 7.7 Hz,
2
3
1
2
C2,12), 133.05 (dd, JCP 81.7 Hz, JCP 11.2 Hz, C1,11),
131.89 (d, JCP 3.0 Hz, C114,214), 131.08 (d, JCP
11.7 Hz, C112,116,212,216), 128.44 (d, JCP 12.8 Hz,
C113,115,213,215), 127.13 (d, JCP 77.8 Hz, C111,211),
1. Mathey, F.; Fisher, J.; Nelson, J. H. Struct. Bonding 1983, 55,
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2. (a) Wilkes, L. M.; Nelson, J. H.; Mac Cusker, L. B.; Seff, K.;
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4
2
3
1
1
4
125.59 (dd, JCP 82.7 Hz, JCP 2.1 Hz, C4,14), 18.03
3
3
4
(d, JCP 16.6 Hz, C31,131), 15.01 (dd, JCP 13.4 Hz, JCP
1.8 Hz, C21,121). MS (DCI/NH3): 439 (Mϩ1, 95%).
Anal. Found (Calcd.) for C24H24P2S2: C, 65.75 (65.73);
H, 5.40 (5.51); S, 14.36 (14.62). Single crystals of
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´
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and light sensitive.
6: 1H NMR: d 1.17 (s, 2H, allyl), 1.36 (s, 2H, allyl), 1.69 (s,
2H, allyl), 1.77 (s, 2H, allyl), 1.92 (s, 6H, Meallyl), 1.95 (s,
4
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2
4
(dd, JH-P 30.4 Hz, JH–H 1.9 Hz, 2H, vCH–P), 7.22 (m,
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