An atropo-stereogenic diphosphane ligand with a proximal cationic charge: Specific catalytic properties of a palladium complex thereof

Article abstract of DOI:10.1002/ejic.200800157

A class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N-methyl,N- naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the

Full text of DOI:10.1002/ejic.200800157

FULL PAPER
DOI: 10.1002/ejic.200800157
An Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge:
Specific Catalytic Properties of a Palladium Complex Thereof
Nathalie Debono,[a] Yves Canac,*[a] Carine Duhayon,[a] and Remi Chauvin*[a]
Keywords: Cations / Donor character / Phosphane ligands / Homogeneous catalysis / Palladium
A class of cationic diphosphane ligands combining phos-
phane and amidiniophosphane moieties is illustrated on the
N-methyl,N-naphthylbenzimidazolium framework. The pal-
ladium(II) complex thereof is described and compared to the
corresponding complex of the analogous neutral diphos-
phane. Contrary to first-level expectations, the N2C–P and
N2CP–Pd bonds in the cationic diphosphane complex are not
longer than those occurring in its neutral counterpart. In the
cationic ligand, the proximal positive charge is indeed conju-
gated to one phosphanyl group, and the coordination scheme
is tentatively interpreted by resonance of the phos-
phaneǞmetal dative bond (+N2C–P:Ǟ[Pd]) with a carbeneǞ
liar structural feature, the electronic σ donation (vs. π accep-
tation) towards the palladium centre remains lowered in the
cationic ligand. This specific property can be a priori valu-
able in a catalytic process where oxidative addition is not the
limiting step. It is indeed shown that although the neutral
complex is more active in Suzuki coupling reactions, the cat-
ionic complex is more active in Sonogashira-type coupling
reactions involving predissociated halide substrates, namely
an acyl chloride. These likely atropo-chiral ligands deserve
to be resolved for application in asymmetric catalysis.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
phosphenium dative bond (N2C:Ǟ[+P:ǞPd]). Despite this pecu- Germany, 2008)
C2 symmetry in their optimal form. Given a symmetric di-
Introduction
phosphane R2P–PR2, a subtle Ϫ but sufficient Ϫ electronic
desymmetrization could be achieved by inserting/substitut-
ing a P-bonded moiety on one side of the bridge by a “per-
turbing linkage” X: pseudosymmetric heterobiaryl scaffolds
R2P–X-PR2 are thus a priori attractive. With respect to the
underlying X–R2PǞM dative bond, electron-withdrawing
effects are classically exerted by π retrodonation and σ (–I)
induction due to the oxygen linkages of phosph(in)ites (X =
O, e.g. the binaphos ligand, which is efficient in asymmetric
hydroformylation and hydrogenation catalysis).[6] A short-
coming is, however, the hydrolytic sensitivity of the P–O
bonds, and phosphanes may be naturally preferred. In this
case, however, the remote desired effects must be amplified
Since Noyori’s initial report of binap (A) based on the
chiral 1,1Ј-binaphthyl scaffold,[1] a wide variety of alterna-
tive C2-symmetric biaryl-bridged diphosphanes have been
devised.[2] Among them, the C2-axially chiral heterobiaryl
ligands,[3] first exemplified by Sannicolò on the N,NЈ-
bisbenzimidazolyl scaffold with bimip (B; Scheme 1),[4] pro-
vides additional electron-withdrawing properties that may
be valuable for specific purposes. Indeed, diphosphane li-
gands primarily act as Lewis bases, but the exact nature
and extent of the electron transfer determine the catalytic
properties of the metallic centre. Adjustment of the elec-
tronic properties inside the coordination sphere (where ca-
talysis takes place) may be achieved in two ways: (i) by a
C2-symmetric overall electron transfer from equivalent
phosphorus atoms or (ii) by a C1-dissymmetric balance of
the transfer between phosphorus atoms of different σ-do-
nating and π-accepting characters. Although many disym-
metric (C1) diphosphanes proved to be efficient in various
catalytic applications, a rationale for their design is a priori
tricky. However, because sterically optimized ligands for
asymmetric catalysis should be C2 symmetric according to
the “quadrant” rule,[5] such ligands must not be far from
[a] Laboratoire de Chimie de Coordination (LCC) of CNRS,
205 route de Narbonne, 31077 Toulouse Cedex 4, France
Fax: +33-5-61553003
Scheme 1. Hybridization of the C2-symmetric binap (A) and bimip
(B) ligands into the C1-symmetric biminap ligand (C) and its
bimionap iminium salt (D).
E-mail: chauvin@lcc-toulouse.fr
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Scheme 2. Analogy between amidiniophosphane ligands (of the C+P kind) and phosphonium ylide ligands (of the P+C kind).
by conjugation and/or by doubling the number of electro- active complexes,[14] their reverted phosphane–amidini-
negative atoms in β positions from the coordinating PIII ophosphane Ph2P–[N2C+PPh2] version is hereafter studied
atom, such as the nitrogen atoms in the C2-symmetric bimip with bimionap (D) as an example.
ligand, which was indeed claimed to be a very electron-poor
The first target is thus biminap (C), which will serve to
ligand.[4] The pseudo-C2/C1-symmetric heterobiaryl ver- bring out the effect of the cationic charge in a comparative
sion, the naphthylbenzimidazolyl “biminap” ligand (C) de- study with its N-alkylated product bimionap (D). Both
rived from the hybridization of binap (A) and bimip (B), is ligands are expected to possess an atropo-stereogenic
a natural candidate (Scheme 1).
C(aryl)-N(amine) bond. It is worth noting that related non-
The electron-withdrawing effect of X (an imidazolyl ring classical stereogenic elements have been exemplified by
in the case of biminap), is of the second order only, but it C(aryl)–C(amide)[15] and C(aryl)–N(non-amine) bonds in
should culminate in α,β-cationic phosphanes. Cationic chiral phosphane ligands based on quinazolinone-contain-
phosphanes, the counterparts of the more widely exem- ing N-anilide[16] and N-arylimide[17] moieties. Although
plified anionic phosphanes such as tris(3-sulfonatophenyl)- atropo-stereogenic C(aryl)–N(indoline) bonds were recently
phosphane trisodium salt (tppts),[7] have been used for per- described,[18] only few examples of such C(aryl)–N(amine)
forming catalysis in aqueous or polar media,[8] or for the bonds have been reported.[19]
design of “true” zwitterionic organometallates.[9] For such
purposes, the cationic charge is conjugatively isolated and/
Results and Discussion
or in remote position in order to avoid perturbation of the
metal centre. In an opposite purpose, we may wonder about
the possible active role of a cationic charge on the catalysis
itself. Beyond the through-bond (inductive/mesomeric) ef-
Synthesis of Ligands and Complexes
The synthesis of biminap (C) starts from readily available
fect, the through-space electrostatic (field) effect is also to 1-(1-naphthyl)-1H-benzimidazole (1), which was prepared
be considered. In a rigid framework, the resulting steady as reported in the literature by a coupling reaction between
electrostatic field embedding the metal centre should influ- benzimidazole and 1-iodonaphthalene in the presence of
ence the approach of polar substrates and the selectivity of copper iodide.[20]
charge-controlled processes. The biaryl framework of bimi-
Because the most acidic proton of 1 is located at the C-
nap (C) could bring the required rigidity and its nitrogen 2 position of the benzimidazolyl ring, the addition of one
atoms in the ideal sites for cationization: the N-methyl-N,1Ј- equivalent of BuLi in thf followed by chlorodiphenylphos-
benzimidazolionaphthyl diphosphane “bimionap” (D) is phane allowed the isolation of monophosphane 2 in 76%
therefore a challenging target (Scheme 1).
yield, which was fully characterized, including by X-ray dif-
Several cationic binap derivatives bearing ammonium or fraction analysis.[21] Interestingly, and as described re-
phosphonium charges at the periphery have been pro- cently,[22] the use of two equivalents of Buli and one equiva-
posed,[10] and in particular, binapium,[11] which is a mono- lent of chlorodiphenylphosphane in Et2O resulted in the
phosphane that could not enter the coordination sphere of isolation of isomeric monophosphane 3 in 34% yield. In
cationic metals,[12] but which was made P,C-chelating by this case, selective monophosphanylation occurs mainly at
passing to the corresponding ylide.[13] Phosphonium ylides the most nucleophilic position, namely, the lithiated ortho
are actually phosphoniocarbyl ligands that can be regarded carbon atom of the naphthyl group. Finally, double depro-
as reversed amidiniophosphane ligands. The analogy is not tonation of 1 with two equivalents of BuLi in Et2O and
only geometric, but also electronic (Scheme 2): although the the addition of the corresponding stoichiometric amount of
σ-donating character is particularly strong for the former chorodiphenylphosphane afforded targeted diphosphane 4
“P+C” ligands (of X-type), it should be particularly weak in 39% yield.
for the latter “C+P” ligands (of L-type).
Despite the presence of different nucleophilic centres
Whereas aryl-bridged phosphane–phosphonium ylide (nitrogen and phosphorus atoms), a single equivalent of
Ph2P–[Ph2P+C] ligands afforded stable and catalytically methyl triflate (MeOTf, a hard methylating reagent) selec-
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An Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge
tively reacted with 4 in CH2Cl2 to give desired N-methyl-
ated monocation 5 in 96% yield. The ionic nature of 5 is
primarily indicated by its very-low solubility in nonpolar
solvents and by the appearance of a 1H NMR signal at δ =
3.81 ppm corresponding to the N-methyl substituent. This
Table 1. Selected bond lengths [Å] from X-ray diffraction studies
in the biminap series (4 and 6) and bimionap series (5 and 7).
4
6
5
7
C1–P1
C1–N1
C1–N2
P1–Pd
P2–Pd
N2–C9
C10–P2
1.808(5)
1.333(6)
1.399(6)
–
1.824(5)
1.310(8)
1.384(7)
2.2467(13)
2.2555(13)
1.409(9)
1.847(3)
1.330(3)
1.349(3)
–
1.810(16)
1.353(18)
1.346(18)
2.249(4)
2.268(5)
1.450(18)
1.845(15)
–
–
1.434(6)
1.828(5)
1.432(3)
1.833(3)
Scheme 3. Selective phosphanylation and methylation of the N-
naphthylbenzimidazole core.
1.838(8)
Figure 1. ORTEP views of the X-ray crystal structures of diphosphanes 4 (top left) and 5 (top right) and complexes 6 (bottom left) and
7 (bottom right) [with 30% probability for thermal ellipsoids of all non-hydrogen atoms in 5 and 6. A common atom numbering scheme
(centre) is adopted. All atoms were isotropically refined in 4, and only Pd and P atoms were anisotropically refined in 7]. For representative
bond lengths, see Table 1.
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is confirmed in the 31P NMR spectrum by the deshielding biminap 4 by the PdCl2 unit results in a shortening of the
of the phosphorus atom connected to the benzimidazolyl C1–N1 bond from 1.333(6) Å in 4 to 1.310(8) Å in 6 and
from δ = –26.7 ppm in 4 to δ = –18.6 ppm in 5. In a consis- a lengthening of the C1–P1 bond from 1.808(5) Å in 4 to
tent manner, the second phosphorus atom bonded to the 1.824(5) Å in 6. This could be interpreted by some contri-
naphthyl moiety is much less but still slightly deshielded (4: bution of the zwitterionic imidophosphonium form 4b in
δ = –18.1 ppm; 5: δ = –16.3 ppm) (Scheme 3). The structure the description of free biminap 4 beside the iminophos-
of diphosphanes 4 and 5 were finally confirmed by X-ray phane form 4a (Scheme 5a): the phosphorus lone pair of
diffraction analysis (Table 1, Figure 1).[21]
electrons is no longer available in complex 6, and the loss
Diphosphanes 4 and 5 possessing imidazolyl[23] and of the possible double bond character of the N2C–P bond
imidazolium[24] substituents, respectively, were then envi- of 4 should indeed result in the observed lengthening upon
sioned as rigidly chelating ligands. They were thus treated complexation.
with a stoichiometric amount of (CH3CN)2PdCl2 in thf.
The corresponding palladium dichloride adducts 6 and 7
were isolated in 94 and 97% yield, respectively (Scheme 4).
Scheme 5. (a) Resonance description of the imidazolylphosphane
end of biminap in the free state (4) and the complexed state (6); (b)
resonance description of the imidazoliophosphane end of bimionap
Scheme 4. Synthesis of isostructural PdCl2 complexes of biminap 4
and bimionap 5.
in the free state (5) and the complexed state (7).
Comparative Analysis of the Structure of Neutral and
As in the neutral series, the same trend is observed for
Cationic Systems
the values of the C10–C9–N2–C1 torsion angles in cationic
Complexes 6 and 7 were fully characterized by multinu- bimionap 5 (73.93°) and its PdCl2 complex 7 (59.76°). In
clear NMR spectroscopy and by X-ray diffraction analysis cationic diphosphane 5, the C1 and N1 atoms exhibit pure
(Table 1, Figure 1).[21] The 31P NMR resonances for 6 and sp2 character (sum of the angles: 359.8 and 360°, respec-
7 occur at δ = 13.6, 25.4 ppm and δ = 18.8, 24.0 ppm, tively), whereas the P1 atom is strongly pyramidalized (sum
respectively, which are in the typical range for Pd–diphos- of the angles: 309.5°). Moreover, the C1–N1 [1.330(3) Å]
phane derivatives. In contrast to 6, which is air-stable and and C1–P1 [1.847(3) Å] distances correspond to a C=N
can be purified by chromatography on silica gel, cationic bond and a C–P bond, respectively. To explain these data,
complex 7 is more sensitive and has to be handled under 5 has to be regarded as C-phosphanyl-substituted amidin-
an inert atmosphere.
ium salt 5a (or its carbene–phosphenium adduct form 5aЈ)
In neutral complex 6, the seven-membered palladacycle rather than as (C-diamino)phosphonium salt 5b. This re-
is symmetrically twisted (λ/δ configuration with respect to veals the superior p-donor ability of the nitrogen atoms rel-
the P1–Pd–P2 unit). This reflects the local C2 symmetry ative to that of the phosphorus atom. Complexation of cat-
nearby the two pseudoequivalent phosphorus atoms P1 and ionic diphosphane ligand 5 results in a slight lengthening
P2: as expected, the dissymmetrical backbone exerts a sec- of the C–N bond length [from 1.330(3) Å in 5 to
ond-order influence. In contrast, in cationic complex 7, be- 1.353(18) Å in 7], which is thus indicative of a decrease in
yond the steric effect of the added N-methyl substituent, an their double bond character and corresponds to some elec-
internal electronic/electrostatic distortion may help to dif- tron withdrawal from the PPd fragment. The simultaneous
ferentiate the two phosphorus atoms while pushing the important shortening of the C1–P1 bond by ca. ∆ =
whole bridge on the same side of the square planar P2PdCl2 –0.037 Å [from 1.847(3) Å in 5 to 1.810(16) Å in 7] was
moiety (Figure 1).
however intriguing, because double N2C=P bond character
Selected geometrical parameters of diphosphanes 4 and should involve the P1 lone pair that is simultaneously in-
5 and complexes 6 and 7 are listed in Table 1. In the neutral volved in the PǞPd bond [P1–Pd 2.249(4) Å]. The P1–Pd
series, coordination induces a decrease in the C10–C9–N2– bond length is in the classical range for similar phosphorus–
C1 dihedral angle (4: 75.66°; 6: 64.52°). Complexation of palladium bonds [e.g., in the (bimip)PdCl2 complex: P–Pd
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An Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge
≈2.267 Å].[4a] This value is more reliable (esd = 0.004 Å)
than the C1–P1 bond length (esd = 0.016 Å), and the rele-
vance of the latter could be questioned with respect to the
Scheme 6. A Suzuki–Miyaura coupling reaction catalyzed by
biminap (6) and cationic bimionap (7) complexes.
analytical uncertainty. Another explanation would be that
the short +N2C–P bond provided by the X-ray diffraction
analysis could reveal the dative nature of the CǞP bond,
which results in an electron “shift effect”. According to a
similar effect previously discussed,[25] the distance between
the centroids of the electron clouds of C1 and P1 would be
shorter than the internuclear distance. The carbeneǞphos-
phenium character is indeed expected to be enhanced by
complexation of the lone pair of the phosphorus atom of 5
to the palladium atom of 7.
reaction in the presence of copper iodide (1%) and triethyl-
amine (1.0 equiv.) over a 5-h period to afford diphenyl-
propynone in 5 and 73% yield, respectively.
The two-electron interaction between P1 and Pd can thus
be summarized by describing complex 7 as the contribution
of two kinds of limiting forms: (i) a diaminocarbene–phos-
phenium form 7a or 7aЈ and (ii) the amidiniophosphane
forms 7b and 7c (Scheme 5b). The relevance of the “diami-
nocarbeneǞphospheniumǞmetal” coordination scheme is
also supported by independent reports. The Lewis ampho-
teric behaviour of a phosphenium moiety was indeed pre-
viously invoked in a dinuclear phosphanylidene complex.[26]
More generally, in the strongly σ-donating N-heterocy-
clic carbenes (NHCs), the cyclic C–N bonds are slightly
longer and the carbenic angle is significantly reduced with
respect to the corresponding imidazolium salt.[27] Within
the limits of crystallographic errors, the same tendency is
observed in the bimionap ligand for the C1–N1 bond
(1.330 Å in 5, 1.353 Å in 7) and the N1–C1–N2 angle
(108.6° in 5, 107.2° in 7).
Scheme 7. A Sonogashira-type coupling reaction catalyzed by
biminap (6) and cationic bimionap (7) complexes.
This marked difference in catalytic efficiency was studied
in more detail by monitoring the yield and conversion by
GC analysis (Figure 2). The initial slopes of yield and con-
version curves are higher with bimionap complex 7 than
those obtained with biminap complex 6. Although the
curves level off after 1 h with biminap complex 6, the reac-
tion proceeds smoothly over 5 h with bimionap complex 7.
The difference in lifetime of the two catalysts derived from
6 and 7 can be tentatively attributed to some side reaction
of the basic/nucleophilic imidazole nitrogen atoms of 6 with
the acylium moiety of benzoyl chloride. With either com-
plex, the gap observed between the conversion of phenyl-
acetylene and the yield of diphenylpropynone is due to the
formation of unidentified side products.
Comparative Analysis of Catalytic Properties of Neutral
and Cationic Systems
The catalytic properties of biminap and bimionap com-
plexes 6 and 7 were first tested in a classical Suzuki coup-
ling reaction between phenylboronic acid and 4-bromo-
anisole. In the presence of neutral complex 6 (0.5 mol-%)
and in thf as the solvent, the desired biaryl was produced
in 73% yield after 12 h at 60 °C. By using cationic catalyst
7 under the same conditions, the coupling product was ob-
tained in 37% yield only. This result is not surprising, be-
cause the Suzuki reaction is known to be accelerated by the
use of strongly σ-donating diaminocarbene or alkylphos-
phane ligands facilitating the oxidative addition of the aryl
halide, which is the limiting step of the catalytic cycle
(Scheme 6).[28] Concerning the challenging aryl chloride
Figure 2. Kinetic curves of the Sonogashira-type coupling reaction
depicted in Scheme 7 catalyzed by biminap and cationic bimionap
complexes 6 and 7, respectively; dodecane was used as an internal
substrates, for example, binap was indeed shown to be tot- standard.
ally ineffective,[29] and the related and even less-donating
biminap (and of course bimionap) ligand was not studied
It was previously suggested that the mechanism of Sono-
further in this reaction. Moreover, although the biminap gashira-type reactions with acyl chlorides obey the same
ligand could be envisioned for its own, it is here first consid- mechanism as the “true” Sonogashira reactions with aryl
ered as a neutral reference with respect to bimionap.
halides: the acyl chloride oxidatively adds to a Pd0 species
A Sonogashira-type coupling reaction was also investi- thus to form an acyl PdII intermediate, which then reacts
gated with the benzoyl chloride and phenylacetylene sub- with the in situ generated copper acetylide.[30] In fact, the
strates in a stoichiometric ratio (Scheme 7). Both neutral dramatic differences displayed in Figure 2, could be simply
and cationic catalysts 6 and 7 were found to catalyze the explained by the difference in electrophilicity of the neutral
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was then dried with MgSO4 and concentrated under vacuum. Puri-
fication by chromatography on silica gel (pentane/ethyl acetate, 8:1)
gave a solid residue (yield: 0.57 g, 76%). Recrystallization at room
temperature from pentane/ethyl acetate afforded white crystals
(m.p. 217–220 °C). 1H NMR (500 MHz, CDCl3): δ = 6.78 (d, JH,H
= 6.0 Hz, 1 H, CH), 6.92 (d, JH,H = 9.0 Hz, 1 H, CH), 7.06–7.32
(m, 12 H, CH), 7.36–7.46 (m, 4 H, CH), 7.82–7.91 (m, 3 H, CH)
ppm. 13C NMR (500 MHz, CDCl3): δ = 110.7 (CH), 120.5 (CH),
122.6 (CH), 122.9 (d, JC,P = 1.0 Hz, CH), 123.7 (CH), 125.2 (CH),
and cationic catalytic intermediates resulting from precur-
sors 6 and 7, respectively. The scope of this catalytic system
with other terminal alkynes is under current investigation.
Conclusions
We developed an efficient short synthesis of a class of
atropo-stereogenic neutral monophosphanes 2 and 3 and
neutral 4 or cationic 5 diphosphanes. Biminap 4 and
bimionap 5 were shown to act as chelating ligands of palla-
dium in neutral and cationic complexes 6 and 7, respec-
tively. In the cationic ligand, the proximal positive charge is
conjugated to one phosphanyl group, and the coordination
scheme is tentatively interpreted by resonance of the phos-
126.8 (CH), 127.2 (CH), 127.3 (CH), 128.3 (CH), 128.3 (d, JC,P
=
7.6 Hz, CH) 128.6 (d, JC,P = 7.8 Hz, CH), 129.2 (CH), 129.4 (CH),
130.0 (CH), 130.5 (d, JC,P = 1.0 Hz, 1 C), 132.5 (d, JC,P = 2.0 Hz,
1 C), 133.9 (d, JC,P = 5.5 Hz, 1 C), 134.2 (d, JC,P = 20.8 Hz, CH),
134.3 (C), 134.3 (d, JC,P = 21.1 Hz, CH), 134.6 (d, JC,P = 6.1 Hz,
1 C), 138.4 (d, JC,P = 1.3 Hz, 1 C), 144.2 (d, JC,P = 2.3 Hz, 1 C),
156.1 (d, JC,P = 11.2 Hz, NCN) ppm. 31P NMR (500 MHz,
phaneǞmetal dative bond (+N2C–P:Ǟ[Pd]) with a car- CDCl3): δ = –24.71 ppm. MS (DCI/NH3): m/z = 429 [M + H]+.
beneǞphosphenium dative bond (N2C:Ǟ[+P:ǞPd]).
C29H21N2P (428.47): calcd. C 81.29, H 4.94, N 6.54; found C 81.10,
H 4.36, N 6.35.
Through the study of a Sonogashira-type reaction, we
showed that the presence of a proximal cationic charge was
able to significantly modify the electronic availability of the solution of 1 (1.0 g, 4.12 mmol) in Et2O (110 mL) cooled to –78 °C
N-(2Ј-Diphenylphosphanyl-1Ј-naphthyl)-1H-benzimidazole (3): To a
was added tmeda (0.98 g, 8.68 mmol) and then BuLi (1.9  in hex-
ane, 4.60 mL, 8.68 mmol). The suspension was warmed to room
temperature and stirred for 4 h. Then after addition of chlorodi-
phenylphosphane (0.68 mL, 3.68 mmol) at –78 °C, the solution was
slowly warmed to room temperature and stirred for 2 h. After the
addition of methanol (0.20 mL, 4.94 mmol), the organic layer was
washed with a saturated aqueous solution of NH4Cl (3ϫ20 mL).
The organic layer was then extracted with additional Et2O (60 mL),
dried with MgSO4 and concentrated under vacuum. Purification
by chromatography on silica gel (pentane/ethyl acetate, 8:1) gave 3
neighbouring phosphorus atom, and consequently to tune
finely the electronics of the corresponding catalyst. It is im-
portant to note that recently, electron-rich ligands have
been extensively studied, particularly with the tremendous
development of NHCs, but surprisingly, the chemistry of
electron-poor ligands remained less explored.
Owing to the known restricted rotation about naphthyl–
naphthyl and benzimidazolyl–benzimidazolyl bonds, both
the neutral and cationic ligands should be atropo-chiral,
and their resolution and applications in asymmetric cataly- as a white solid (yield: 0.55 g, 34%; m.p. 147–151 °C). 1H NMR
(500 MHz, CDCl3): δ = 6.82 (d, JH,H = 8.1 Hz, 1 H, CH), 7.08 (d,
JH,H = 8.5 Hz, 1 H, CH), 7.14 (m, 1 H, CH), 7.20 (m, 2 H, CH),
7.23–7.29 (m, 3 H, CH), 7.30–7.41 (m, 8 H, CH), 7.56 (m, 1 H,
CH), 7.76 (d, JP,H = 1.8 Hz, 1 H, NCHN), 7.93–7.98 (m, 3 H, CH)
ppm. 13C NMR (500 MHz, CDCl3): δ = 111.0 (CH), 120.3 (CH),
122.5 (CH), 122.9 (d, JC,P = 2.5 Hz, CH), 123.5 (CH), 127.7 (CH),
128.0 (CH), 128.2 (CH), 128.5 (d, JC,P = 6.3 Hz, 2 CH), 128.9 (d,
JC,P = 7.5 Hz, 2 CH), 129.0 (CH), 129.3 (CH), 129.5 (CH), 129.7
(CH), 131.1 (d, JC,P = 2.5 Hz, 1 C), 133.8 (d, JC,P = 20.1 Hz, 2
CH), 133.9 (d, JC,P = 20.1 Hz, 2 CH), 134.4 (C), 135.6 (C), 135.9
(d, JC,P = 12.6 Hz, 1 C), 136.2 (d, JC,P = 12.6 Hz, 1 C), 136.5 (d,
JC,P = 18.9 Hz, 1 C), 136.6 (d, JC,P = 25.2 Hz, 1 C), 143.0 (C), 144.3
(d, JC,P = 2.5 Hz, NCHN) ppm. 31P NMR (500 MHz, CDCl3): δ
= –16.56 ppm. MS (DCI/NH3): m/z = 429 [M + H]+. HRMS
(ESI+): calcd. for C29H22N2P 429.1521; found 429.1516.
sis can be henceforth envisioned. Efforts in this sense are
currently in progress.
Experimental Section
General Remarks: Tetrahydrofuran and diethyl ether were dried
and distilled from sodium/benzophenone, and pentane, dichloro-
methane and acetonitrile were dried and distilled from P2O5. All
other reagents were used as commercially available. All reactions
were carried out under an argon atmosphere by using Schlenk and
vacuum-line techniques. Column chromatography was carried out
on silica gel (60 Å, C.C 70–200 µm). The following analytical in-
struments were used. 1H, 13C and 31P NMR: Bruker ARX 250,
DPX 300, Avance 400 and 500. Mass spectrometry: Quadrupolar
Nermag R10–10H. Elemental analyses: Perkin–Elmer 2400 CHN
(flash combustion and detection by catharometry). NMR chemical
shifts δ are in ppm, with positive values to high frequency relative
to the tetramethylsilane reference; coupling constants J are in Hz.
NMR assignment: (b) benzimidazole; (n) naphthalene. Gas chro-
matographic analyses were performed with a HP-4890 GC. Com-
pound 1 was synthesized according to the reported procedure.[20]
2-(Diphenylphosphanyl)-N-(2Ј-diphenylphosphanyl-1Ј-naphthyl)-1H-
benzimidazole (4): To a solution of 1 (1.0 g, 4.11 mmol) in Et2O
(110 mL) cooled to –78 °C was added tmeda (0.98 g, 8.64 mmol)
and then BuLi (2.2  in hexane, 3.95 mL, 8.64 mmol). The suspen-
sion was warmed to room temperature and stirred for 4 h. After
the addition of chlorodiphenylphosphane (1.6 mL, 8.64 mmol) at
–78 °C, the solution was slowly warmed to room temperature and
stirred for 2 h. After the addition of MeOH (0.20 mL, 4.94 mmol),
the organic layer was washed with a saturated aqueous solution
of NH4Cl (3ϫ20 mL). The organic layer was then extracted with
additional Et2O (60 mL), dried with MgSO4 and concentrated un-
der vacuum. Purification by chromatography on silica gel (pentane/
ethyl acetate, 8:1) gave 4 as a solid residue (yield: 0.97 g, 39%).
Recrystallization at –20 °C from CH2Cl2/pentane gave white crys-
2-(Diphenylphosphanyl)-N-(1Ј-naphthyl)-1H-benzimidazole (2): To a
solution of 1 (0.42 g, 1.75 mmol) in thf (40 mL) cooled to –78 °C
was added tmeda (0.26 mL, 1.75 mmol) and then BuLi (2.5  in
hexane, 0.70 mL, 1.75 mmol). The suspension was slowly warmed
to –40 °C and stirred for 1 h. Then, after the addition of chlorodi-
phenylphosphane (0.32 mL, 1.75 mmol) at –78 °C, the solution was
warmed to room temperature and stirred for 2 h. The reaction mix-
ture was washed with a saturated aqueous solution of NH4Cl
(20 mL). After extraction with Et2O (2ϫ20 mL), the organic layer
1
tals (m.p. 238–241 °C). H NMR (500 MHz, CDCl3): δ = 6.47 (d,
JH,H = 8.1 Hz, 1 H, CH), 6.71 (d, JH,H = 8.4 Hz, 1 H, CH), 6.93
2996
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2991–2999

An Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge
(td, JH,H = 7.2 Hz, JH,H = 0.9 Hz, 1 H, CH), 7.04 (td, JH,H
7.2 Hz, JH,H = 1.2 Hz, 1 H, CH), 7.15–7.31 (m, 9 H, CH), 7.33– NMR (500 MHz, CDCl3): δ = 121.0 (CH) 121.2 (d, JC,P(b)
7.36 (m, 8 H, CH), 7.39–7.48 (m, 3 H, CH), 7.51 (dd, JPH = 2.5 Hz, 56.4 Hz, 1 C), 123.2 (d, JC,P(n) = 54.8 Hz, 1 C), 123.7 (CH), 124.2
=
(d, JH,H = 8.3 Hz, 1 H, CH), 7.78–7.86 (m, 6 H, CH) ppm. 13C
=
JH,H = 8.5 Hz, 1 H), 7.59–7.63 (m, 2 H), 7.91 (d, JH,H = 8.0 Hz, 1 (CH), 124.8 (CH), 126.8 (d, JC,P(b) = 69.9 Hz, 1 C), 127.5 (d, JC,P(b)
H), 8.03 (t, JH,H = 8.0 Hz, 2 H, CH) ppm. 13C NMR (500 MHz, = 12.9 Hz, 2 CH), 128.0 (CH), 128.1 (d, JC,P(n) = 11.7 Hz, 2CH),
CDCl3): δ = 110.9 (CH), 120.4 (CH), 122.3 (CH), 123.3 (d, JC,P
2.0 Hz, CH), 123.4 (CH), 127.3 (CH), 127.4 (CH), 127.9 (CH),
128.3–128.6 (m, 10 CH), 129.0 (CH), 129.4 (CH), 129.9 (CH),
130.2 (d, JC,P = 2.0 Hz, CH), 131.3 (dd, JC,P = 4.0 Hz, JC,P
=
128.2 (CH), 128.3 (d, JC,P(b) = 11.7 Hz, 2 CH), 128.4 (CH), 128.4
(d, JC,P(n) = 5.6 Hz, CH), 128.5 (d, JC,P(n) = 11.9 Hz, 2 CH), 128.7
(CH), 129.3 (d, JC,P(n) = 6.0 Hz, 1 C), 129.5 (dd, JC,P(b) = 4.6 Hz,
JC,P(n) = 46.2 Hz, 1 C), 129.9 (d, JC,P(n) = 9.1 Hz, CH), 131.3 (d,
JC,P(b) = 3.1 Hz, CH), 131.4 (d, JC,P(n) = 2.8 Hz, CH), 131.5 (d,
JC,P(b) = 2.5 Hz, CH), 131.6 (d, JC,P(n) = 2.6 Hz, CH), 134.1 (d,
JC,P(n) = 4.2 Hz, 1 C), 134.7 (CH), 134.8 (d, JC,P(n) = 10.6 Hz, 2
CH), 134.9 (d, JC,P(b) = 10.4 Hz, 2 CH), 135.2 (d, JC,P(n) = 1.8 Hz,
1 C), 135.5 (d, JC,P(b) = 13.1 Hz, 2 CH), 135.8 (C), 143.1 (d, JC,P(b)
= 13.6 Hz, 1 C), 144.8 (dd, JC,P(b) = 78.8 Hz, JC,P(n) = 6.3 Hz, 1 C)
ppm. 31P NMR (500 MHz, CDCl3): δ = +13.60 (Pb), +25.40 (Pn)
ppm. MS (ESI+): m/z = 753 [M – Cl]+. HRMS (ESI+): calcd. for
C41H30N2P2ClPd 753.0608; found 753.0610.
=
2.0 Hz, 1 C), 133.2 (dd, JC,P = 18.1 Hz, JC,P = 2.0 Hz, 2 CH), 133.3
(dd, JC,P = 19.1 Hz, JC,P = 2.0 Hz, 2 CH), 134.2 (d, JC,P = 1.0 Hz,
1 C), 134.3 (C), 134.3 (d, JC,P = 22.1 Hz, 2 CH), 135.0 (d, JC,P
22.1 Hz, 2 CH), 135.1 (d, JC,P = 5.0 Hz, 1 C), 136.2 (d, JC,P
13.1 Hz, 1 C), 136.7 (d, JC,P = 12.1 Hz, 1 C), 137.0 (dd, JC,P
15.6 Hz, JC,P = 1.5 Hz, 1 C), 137.9 (dd, JC,P = 26.2 Hz, JC,P
2.0 Hz, 1 C), 138.3 (C), 144.3 (d, JC,P = 1.0 Hz, 1 C), 156.3 (d, JC,P
= 9.1 Hz, 1 C) ppm. 31P NMR (500 MHz, CDCl3): δ = –18.10 (d,
5JP,P = 32.8 Hz, Pn), –26.69 (d, 5JP,P = 32.8 Hz, Pb) ppm. MS (DCI/
NH3): m/z = 613 [M + H]+. C41H30N2P2·0.08CH2Cl2 (619.44):
calcd. C 79.67, H 4.87, N, 4.53; found C 79.65, H 4.63, N 4.52.
=
=
=
=
Palladium Complex 7: A mixture of complex PdCl2(CH3CN)2
(0.31 g, 1.18 mmol) and 5 (0.92 g, 1.18 mmol) was dissolved in thf
(50 mL) at –20 °C and stirred for 2 h. After concentration under
vacuum, the residue was washed with Et2O (50 mL) to afford an
orange solid (yield: 1.1 g, 97%). Recrystallization at –20 °C from
2-(Diphenylphosphanyl)-N-(2Ј-diphenylphosphanyl-1Ј-naphthyl)-NЈ-
methyl-1H-benzimidazolium Trifluoromethanesulfonate (5): To a
solution of 4 (0.49 g, 0.80 mmol) in CH2Cl2 (20 mL) cooled to
–78 °C was added methyl trifluoromethanesulfonate (0.09 mL,
0.80 mmol). The solution was then warmed to room temperature
and stirred for 12 h. After concentration under vacuum, the residue
was washed with Et2O (40 mL) to afford a white solid (yield: 0.59 g,
96%). Recrystallization at –20 °C from CH3CN/Et2O gave white
crystals (m.p. 217–220 °C). 1H NMR (500 MHz, CD3CN): δ = 3.81
1
CH2Cl2/pentane gave yellow crystals (m.p. 206–210 °C). H NMR
(500 MHz, CD2Cl2): δ = 3.98 (s, 3 H, CH3), 6.56 (d, JH,H = 8.5 Hz,
1 H, CH), 6.91 (m, 1 H, CH), 7.03 (pseudo-td, JH,P(n) = 2.9 Hz,
JH,H = 7.8 Hz, 2 H, CH), 7.14 (m, 1 H, CH), 7.19 (dd, JH,P(n)
9.9 Hz, JH,H = 8.9 Hz, 1 H, CH), 7.38 (ddd, JH,H = 8.3 Hz, JH,H
=
=
7.0 Hz, JH,H = 1.3 Hz, 1 H, CH), 7.61–7.76 (m, 16 H, CH), 7.78–
7.84 (m, 5 H, CH), 8.43 (ddd, JH,P(b) = 13.4 Hz, JH,H = 7.9 Hz,
JH,H = 1.7 Hz, 2 H, CH) ppm. 13C NMR (500 MHz, CD2Cl2): δ =
(s, 3 H, CH3), 6.55 (d, JH,H = 8.5 Hz, 1 H, CH), 6.97 (dd, JH,H
=
8.5 Hz, JH,H = 0.7 Hz, 1 H, CH), 7.09 (td, JH,H = JH,P = 8.4 Hz,
JH,H = 1.3 Hz, 1 H, CH), 7.15–7.33 (m, 11 H, CH), 7.36–7.47 (m,
7 H, CH), 7.49–7.56 (m, 3 H, CH), 7.58–7.66 (m, 2 H, CH), 7.95
(d, JH,H = 8.6 Hz, 1 H, CH), 8.04 (d, JH,H = 8.3 Hz, 1 H, CH), 8.16
(d, JH,H = 8.5 Hz, 1 H, CH) ppm. 13C NMR (500 MHz, CD3CN): δ
= 34.7 (CH3), 113.3 (CH), 113.6 (CH), 121.2 (q, JC,F = 320.8 Hz,
36.8 (CH3), 113.7 (CH), 114.3 (CH), 120.7 (q, JC,F = 323.3 Hz,
–
CF3SO3 ), 122.0 (d, JC,P(b) = 22.0 Hz, 1 C), 123.3 (d, JC,P(n)
=
56.6 Hz, 1 C), 123.4 (d, JC,P(b) = 61.5 Hz, 1 C), 124.9 (CH), 126.3
(d, JC,P(n) = 64.1 Hz, 1 C), 128.0 (CH), 128.3 (d, JC,P(n) = 6.7 Hz,
CH), 128.6 (CH), 128.7 (CH), 128.8 (d, JC,P(b) = 17.8 Hz, CH),
128.8 (d, JC,P(b) = 12.1 Hz, 1 C), 128.9 (d, JC,P(n) = 15.5 Hz, 2 CH),
129.4 (CH), 129.5 (d, JC,P(b) = 12.9 Hz, 2 CH), 130.3 (CH), 130.4
(CH), 131.9 (d, JC,P(n) = 3.8 Hz, 1 C), 132.1 (CH), 132.2 (CH),
132.3 (CH), 132.9 (C), 133.1 (d, JC,P = 2.6 Hz, CH), 133.5 (d, JC,P
= 2.7 Hz, CH), 134.3 (d, JC,P(n) = 10.8 Hz, 2 CH), 134.5 (d, JC,P(b)
= 14.6 Hz, 1 C), 135.1 (C), 135.2 (2 CH), 135.3 (C), 135.4 (CH),
146.1 (d, JC,P(b) = 29.4 Hz, 1 C) ppm. 31P NMR (500 MHz,
CD2Cl2): δ = +18.80 (Pb), +24.05 (Pn) ppm. HRMS (ESI+): calcd.
for C42H33N2P2Cl2Pd 803.0531; found 803.0424.
–
CF3SO3 ), 121.6 (d, JC,P = 2.1 Hz, CH), 126.6 (dd, JC,P = 1.7, JC,P
= 7.5 Hz, 1 C), 127.6 (CH), 127.8 (CH), 128.0 (d, JC,P = 7.8 Hz, 1
C), 128.4 (CH), 128.6 (CH), 128.8 (CH), 128.9 (d, JC,P = 8.5 Hz,
CH), 129.0 (d, JC,P = 6.5 Hz, CH), 129.4 (d, JC,P = 7.8 Hz, CH),
129.5 (CH), 129.6 (CH), 129.8 (d, JC,P = 7.2 Hz, CH), 129.9 (CH),
131.0 (CH), 131.3 (CH), 132.0 (CH), 133.0 (d, JC,P = 20.0 Hz, CH),
133.1 (d, JC,P = 20.0 Hz, CH), 133.8 (C), 133.9 (C), 134.2 (d, JC,P
= 22.1 Hz, CH), 134.3 (d, JC,P = 2.4 Hz, 1 C), 134.3 (d, JC,P
8.4 Hz, 1 C), 134.4 (C), 134.5 (C), 134.6 (d, JC,P = 23.1 Hz, CH),
136.3 (dd, JC,P = 17.1 Hz, JC,P = 1.8 Hz, 1 C), 153.6 (d, JC,P
=
=
57.6 Hz, 1 C) ppm. 31P NMR (500 MHz, CD3CN): δ = –16.32 (d,
5JP,P = 35.5 Hz, Pn), –18.63 (d, 5JP,P = 35.5 Hz, Pb) ppm. MS (DCI/
NH3): m/z: 627 [M]+. HRMS (ESI+): calcd. for C42H33N2P2
627.2119; found 627.2128.
General Procedure for Suzuki–Miyaura C–C Coupling: A mixture
of boronic acid (0.18 g, 1.5 mmol), p-bromoanisole (0.12 mL,
1.0 mmol), Cs2CO3 (0.66 g, 2.0 mmol) and 6 or 7 (0.5 mol-%) in
dry thf (3 mL) was stirred at 60 °C for 12 h. The reaction mixture
was quenched with H2O (3 mL) and extracted with Et2O
(3ϫ5 mL). The organic layer was then dried with MgSO4 and con-
centrated in vacuo. Purification by chromatography on silica gel
(pentane/CH2Cl2, 5:1), gave a white solid (for 6: 0.34 g, 73%; for
7: 0.07 g, 37%).
Palladium Complex 6: A mixture of complex PdCl2(CH3CN)2
(0.15 g, 0.57 mmol) and 4 (0.35 g, 0.57 mmol) was dissolved in thf
(20 mL) at –20 °C and stirred for 2 h. After concentration under
vacuum, purification by chromatography on silica gel (acetone/
CH2Cl2) gave a yellow solid (yield: 0.42 g, 94%). Recrystallization
at –20 °C from CH3CN afforded yellow crystals (m.p. 260–265 °C). General Procedure for Sonogashira Coupling: A mixture of 6 or 7
1H NMR (500 MHz, CDCl3): δ = 6.46 (d, JH,H = 8.2 Hz, 1 H,
(0.5 mol-%) and CuI (7 mg, 0.036 mmol, 1 mol-%) were dissolved
CH), 6.75–6.79 (m, 3 H, CH), 6.90–6.94 (m, 1 H, CH), 6.95–7.06 in dry thf (15 mL). Then, benzoyl chloride (0.42 mL, 3.64 mmol),
(m, 4 H, CH), 7.17 (ddd, JH,H = 1.1 Hz, JH,H = 7.2 Hz, JH,H
=
phenylacetylene (0.24 mL, 3.64 mmol), dodecane (0.82 mL,
3.64 mmol) and Et3N (0.51 mL, 3.64 mmol) were successively
added. The catalysis was performed at room temperature for the
desired time. Timing was immediately commenced when Et3N was
added. Reaction samples (0.5 mL), obtained at specified time inter-
8.3 Hz, 1 H, CH), 7.21 (dd, JH,H = 8.9 Hz, JH,P(n) = 9.8 Hz, 1 H,
CH), 7.28 (ddd, JH,H = 1.4 Hz, JH,H = 7.0, JH,H = 8.4 Hz, 1 H,
CH), 7.43–7.55 (m, 7 H, CH), 7.59 (br. d, JH,H = 8.3 Hz, 1 H, CH),
7.63 (br. d, JH,H = 8.5 Hz, 1 H, CH), 7.66–7.71 (m, 2 H, CH), 7.72
Eur. J. Inorg. Chem. 2008, 2991–2999
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2997

N. Debono, Y. Canac, C. Duhayon, R. Chauvin
FULL PAPER
Table 2. Crystal structure determination of compounds 2, 4, 5, 6 and 7.
2
4
5
6
7
Empirical formula
Formula mass
Crystal system
Space group
T [K]
a [Å]
b [Å]
C29H21 N2 P
428.47
monoclinic
P21/n
C41H30N2P2
612.65
monoclinic
P21/n
C43H33F3N2O3P2S
776.75
monoclinic
P21/c
C47H39Cl2N5P2Pd
913.11
monoclinic
P21/c
C46H39Cl8F3N2O3P2PdS
1208.86
monoclinic
P21/n
180
150
180
180
160
8.9789(10)
14.7578(17)
17.1572(18)
90
10.2697(9)
16.9795(11)
18.6210(19)
90
13.0218(4)
14.5941(5)
19.5513(6)
90
11.0920(3)
12.6067(3)
30.3522(8)
90
14.3280(10)
21.585(2)
16.0520(10)
90
c [Å]
α [°]
β [°]
98.101(13)
90
2250.8(4)
1.26
104.535(11)
90
3143.1(5)
1.30
97.463(3)
90
3684.1(2)
1.40
96.552(2)
90
4216.53(19)
1.44
94.928(6)
90
4946.0(7)
1.62
γ [°]
V [Å3]
Dcalcd. [gcm–3]
Z
4
4
4
4
4
µ [mm–1]
Refl. measured
Refl. unique/Rint
0.141
22314
4326
0.172
31507
6184
0.234
34589
9861
0.683
39285
11201
0.969
46650
11116
Refl. with I Ͼ nσ(I) 1413 (n = 2.1)
1848 (n = 2)
181
4877 (n = 1.2)
487
5732 (n = 3)
375
2313 (n = 2)
280
Nv
134
R
Rw
0.0515
0.0587
1.14
0.0471
0.0552
1.15
0.0454
0.0459
1.13
0.0546
0.0614
1.10
1.81/1.06
0.0601
0.0695
1.15
1.44/0.78
GooF
∆ρmax/∆ρmin [eÅ–3]
0.40/0.27
0.39/0.25
0.42/0.48
[3]
[4]
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vals, were purified after washing with a saturated aqueous solution
of NH4Cl (0.5 mL) and then filtered through silica gel. Conversion
and yield were only determined by GC. It was checked that the
presence of the internal standard does not affect the results (the
same kinetic curves are obtained in the absence of dodecane).
Crystal Structure Determination of Compounds 2, 4, 5, 6 and 7:
Intensity data were collected with an Xcalibur Oxford Diffraction
diffractometer or with an IPDS Stoe diffractometer by using a
graphite-monochromated Mo-Kα radiation source and equipped
with an Oxford Cryosystems Cryostream Cooler Device. Structures
were solved by direct methods by using SIR92 and refined by full-
matrix least-squares procedures on F by using the PC version of
the CRYSTALS program. Atomic scattering factors were taken
from the International Tables for X-ray Crystallography. In case of
weak diffracting crystals (2, 4 and 7), we were not able to refine all
atoms anisotropically (Table 2). Hydrogen atoms were refined by
using a riding model. Absorption corrections were introduced by
using the MULTISCAN program.
[5]
[6]
[7]
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Beyond the Ministère de l’Enseignement Supérieur de la Recherche
et de la Technologie and the Université Paul Sabatier, the authors
thank the Centre National de la Recherche Scientifique for the
post-doctoral fellowship of N. D. The authors also thank Christine
Lepetit for helpful discussions.
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Eur. J. Inorg. Chem. 2008, 2991–2999

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Received: February 11, 2008
Published Online: May 28, 2008
Eur. J. Inorg. Chem. 2008, 2991–2999
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2999