Palladium(ii) complexes with planar chiral ferrocenyl phosphane-(benz) imidazol-2-ylidene ligands

Article abstract of DOI:10.1039/c3nj00863k

We describe here the first examples of planar chiral ferrocenyl phosphane-benzimidazol-2-ylidene ligands and their coordination chemistry with palladium(ii). All ligand precursors, namely enantiopure ferrocenyl phosphane-(benz)imidazolium salts, and all e

Full text of DOI:10.1039/c3nj00863k

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Palladium(II) complexes with planar chiral
ferrocenyl phosphane–(benz)imidazol-2-ylidene
ligands†
Cite this: New J. Chem., 2014,
38, 338
Pauline Loxq,ab Nathalie Debono,ab Suleyman Gulcemal,c Jean-Claude Daran,ab
¨
¨
Eric Manoury,ab Rinaldo Poli,abd Bekir Çetinkayac and Agnes Labande*ab
`
We describe here the first examples of planar chiral ferrocenyl phosphane–benzimidazol-2-ylidene
ligands and their coordination chemistry with palladium(II). All ligand precursors, namely enantiopure
ferrocenyl phosphane–(benz)imidazolium salts, and all enantiopure palladium complexes have been fully
characterised by 1H, 31P and 13C NMR, mass spectrometry and X-ray diffraction methods for seven
examples. The potential of these very bulky bidentate ligands in catalysis was evaluated and compared
to their imidazol-2-ylidene analogues. The influence of sterics was shown to be non-negligible as the
bulkiest ligand gave the lowest activities in the asymmetric Suzuki–Miyaura reaction.
Received (in Victoria, Australia)
30th July 2013,
Accepted 31st October 2013
DOI: 10.1039/c3nj00863k
www.rsc.org/njc
and help stabilise the intermediate species in C–C coupling
reactions such as for instance the Suzuki–Miyaura reaction.9–11
Introduction
The synthesis and coordination chemistry of functionalised Furthermore, we have recently turned our attention to the
N-heterocyclic carbene (NHC) ligands and their applications in asymmetric version of this reaction, obtaining encouraging
catalysis have attracted the attention of several groups,1–3 including results with the use of palladium complexes containing enantio-
ours.4–7 These strong s-donor ligands proved very efficient in merically pure phosphane–imidazol-2-ylidene ligands (Fig. 1).7
catalysis, even surpassing phosphanes in many cases.8 One We therefore turned our efforts towards the synthesis of
advantage of using N-heterocyclic carbenes is the high stability palladium complexes containing novel chiral 1,2-disubstituted
conferred on the metal complexes, thus avoiding the use of ferrocenyl phosphane–(benz)imidazol-2-ylidene ligands in enantio-
excess ligand or catalyst deactivation. Fine tuning the stereo- merically pure form and describe here their synthesis. Their
electronic properties of the N-heterocyclic carbene may allow us catalytic properties in the asymmetric Suzuki–Miyaura reaction11–15
finding useful trends in the search of the best catalyst, particularly have been evaluated and compared to those of the above
in terms of enantioselectivity. Recently, we described the synthesis mentioned phosphane–imidazol-2-ylidene complexes.7 Finally,
of 1,10-disubstituted ferrocenyl phosphane–benzimidazol-2-ylidene the activity of a phosphane–imidazol-2-ylidene ligand in the
ligands for applications in rhodium-catalysed hydrosilylation of asymmetric 1,2-addition of phenylboronic acid to 4-nitrobenz-
carbonyl groups. It was shown in this case that the replacement of aldehyde has been evaluated.16–19
the imidazol-2-ylidene moiety by the more bulky, electron-rich
benzimidazol-2-ylidene bearing two methyl groups on the aromatic
ring enhanced the catalytic activity dramatically.6
It is now commonly admitted that strongly electron-
donating, bulky ligands favour oxidative addition on palladium
Results and discussion
Synthesis of (benz)imidazolium salts
With the intention of varying the stereoelectronic properties of
the ferrocenyl phosphane–NHC ligands in a rational way, we
decided to focus on the NHC moiety without changing the
a CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne,
BP 44099, F-31077 Toulouse Cedex 4, France. E-mail: agnes.labande@lcc-toulouse.fr;
diphenylphosphano group. The s-donating properties of
benzimidazol-2-ylidene ligands are situated between those of
unsaturated imidazol-2-ylidenes and of saturated imidazolin-2-
ylidenes, which has been demonstrated in several examples of
catalytic applications.20,21 Apart from the electronic properties,
their structure should bring more bulkiness to the bifunctional
ligands. In order to probe the effect of bulky substituents on
Fax: +33 561553003; Tel: +33 561333158
b
´
Universite de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France
c Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey
d Institut Universitaire de France, 103 bd Saint-Michel, F-75005 Paris, France
† Electronic supplementary information (ESI) available: ORTEP representations
of compounds 2a and 4a; crystal data and refinement parameters for 2c–d and
4b–d. CCDC 940117–940121. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3nj00863k
338 | New J. Chem., 2014, 38, 338--347
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Scheme 1 Palladium(II) complexes described in our previous work.7
Fig. 1 ORTEP representations of benzimidazolium salts rac-2c (top) and
rac-2d (bottom). Ellipsoids are shown at the 50% level. All hydrogens are
omitted for clarity. Selected bonds (Å), rac-2c: C(23)–C(24) = 1.388(8);
rac-2d: C(23)–C(24) = 1.390(3).
both activity and enantioselectivity, we have also changed the
nature of the N-substituent.
The synthesis of the phosphane–imidazolium salt with R =
Me (3a) has already been described, both in racemic5 and
enantiomerically pure form.7 The synthesis of other racemic
and enantiomerically pure imidazolium and benzimidazolium
salts was carried out following these established protocols.5
Racemic alcohol rac-1 was used mainly to develop and optimise
the synthesis of various salts and palladium complexes, but
only enantiopure (S)-palladium complexes were used in catalytic
reactions since we expected them to exhibit similar levels of
activity compared to the previously described neutral palladium
complex [PdCl2(ImMe)] (Scheme 1).7 Imidazolium salt 2b was
Scheme 2 Synthesis of phosphane-(benz)imidazolium salts.
obtained in moderate yield from ferrocenyl alcohol 1 and salts are applied. Eventually, their purification was successful
N-[(2,4,6-trimethylphenyl)methyl] imidazole (Scheme 2). by eluting the N-substituted benzimidazole excess with pure
The synthesis of benzimidazolium salts 2c,d, however, diethyl ether and then the benzimidazolium salts with a DCM–
proved to be more difficult. Benzimidazoles are poorer nucleo- acetone mixture on a silica gel chromatography column. The
philes compared to imidazoles, thus giving greater amounts of 1H NMR spectra of (benz)imidazolium salts 2b–d show the
side products and lower yields of benzimidazolium salts. Their expected signal above d 8.5, characteristic of the acidic C2
purification was also less straightforward: the excess of proton. AB systems were observed for the diastereotopic pro-
N-substituted benzimidazoles that are not consumed during tons of the methylene bridge situated between the ferrocenyl
the reaction cannot be removed with aqueous acidic washings and (benz)imidazolyl moieties for all salts, as well as for
due to their lower hydrophilicity and have a tendency to trail on protons of the methylene bridge linking the (benz)imidazolyl
silica when the same eluting conditions as for the imidazolium and mesityl groups (salts 2b and 2d), which is consistent with
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the introduction of planar chirality at ferrocene and with the
generation of rather rigid structures due to steric crowding.
The structure of the intermediates 2c and 2d (Fig. 1) was
confirmed by X-ray diffraction methods. The structures of the two
salts as well as that of 2a‡7 are very close: the only notable structural
difference resides in the length of the C–C bond in the imidazolium
motif, which is significantly shorter in the imidazolium salt
(C(7)–C(8) = 1.344(4) Å) than in the benzimidazolium salts. This
has already been observed in similar structures and indicates
delocalisation of the C–C bond p-electron density over the fused
benzene ring.6
The imidazolium and benzimidazolium salts exhibited different
reactivity during the diphenylthiophosphano group deprotec-
tion by RANEYs nickel. Indeed, whereas the desulfurisation of
the thiophosphane–imidazolium salt 2b to give 3b went to
completion at room temperature in 16 h, longer reaction times
and moderate heating (40 1C) were necessary to achieve complete
desulfurization of the thiophosphane–benzimidazolium salts 2c,d
to give 3c,d (31P NMR monitoring). This is a first confirmation that
steric crowding is more important in the benzimidazolium family,
with possible implications in catalysis. As expected, upon
deprotection of the diphenylthiophosphano group, the 31P
NMR signal of (benz)imidazolium salts shifted from d ca. 40.5
for 2 to ca. ꢀ27 for 3.
Scheme 3 Synthesis of neutral NHC–phosphane palladium(II) complexes.
1.992(6) Å, 4d) and Pd–P (2.2444(8) Å, 4a, to 2.2546(19) Å, 4d)
bond lengths compare well with those in other previously
published neutral palladium complexes bearing chelating
NHC–phosphane ligands.21,22 As observed previously for
complex 4a,9 the Pd–Cl bonds trans to the NHC are all slightly
but significantly shorter than the Pd–Cl bonds trans to the
diphenylphosphano groups, which is surprising since the more
donating NHC should exert a greater trans influence than the
phosphane, but this was also observed elsewhere.21,22 Similar to
the (benz)imidazolium salts, the C–C bond of the heteroaromatic
unit is slightly longer in the case of benzimidazol-2-ylidenes
(1.372(5) Å for 4c and 1.391(8) Å for 4d) than in the case of
imidazol-2-ylidenes (1.350(6) Å for 4a and 1.345(4) Å for 4b),
which could denote some delocalisation of the double bond due
to the presence of the fused benzene ring. No other significant
differences in bond lengths are notable between the four struc-
tures. However, the C(NHC)–Pd–P bite angle is significantly
narrower in complex 4a with 84.95(9)1 and increases with the
steric bulkiness of the ligand to reach 91.94(19)1 in complex 4d.
Synthesis of palladium(II) complexes
The synthesis and X-ray structural characterisation of complex 4a,
obtained by deprotonation of 3a both in racemic and enantiopure
forms, have been previously published.‡7 We have now extended
this procedure to the synthesis of the analogous complexes with
the NHC ligands obtained from 3b, 3c and 3d (Scheme 3).
All phosphane–(benz)imidazolium salts were deprotonated
with tBuONa in the presence of the palladium precursor
PdCl2(PhCN)2 to give neutral N-heterocyclic carbene–phosphane
palladium complexes 4b–d in moderate yields. All products are
air-stable and could be purified by column chromatography on
silica gel. The absence of the acidic proton characteristic of
(benz)imidazolium salts in the 1H NMR spectra indicated carbene
formation. The 31P NMR spectra of all complexes showed a major
species with a signal between d 3.86 and 4.56, along with ca. 2% of
a second species at around d 15. This minor species was obtained
whatever the complex and mass spectrometry analysis of the
mixture by electrospray revealed a small amount of palladium
dimer along with the expected monomeric structure. The carbenic
carbon in 13C NMR was found at d 156.0 for complex 4b bearing
an imidazol-2-ylidene moiety and went downfield for complexes
4c,d possessing the benzimidazol-2-ylidene group with, respec-
tively, d 166.70 and 166.74. The same trend has been observed for
other neutral palladium(II) NHC complexes in the literature.21,22
The structures of all new complexes were established by
X-ray crystallography and compared with that of 4a.7 The bond
lengths and angles are all within the expected range for neutral
palladium complexes with a slightly distorted square-planar
geometry (Fig. 2 and 3, Table 1). Pd–C(NHC) (1.973(2) Å, 4b, to
Asymmetric Suzuki–Miyaura reaction
Palladium(II) complexes 4b–d were evaluated in the asymmetric
version of the Suzuki–Miyaura cross-coupling reaction between
Fig. 2 ORTEP representation of complex (S)-4b. Ellipsoids are shown at
the 50% level. All hydrogens are omitted for clarity.
‡ ORTEP representations of compounds 2a and 4a are given in the ESI.†
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Scheme 4 Asymmetric Suzuki–Miyaura reaction between 2-substituted
a-naphthyl bromides and a-naphthylboronic acid.
the coupling of various naphthyl bromides with a catalytic
charge of 0.5 mol% at 40 1C. All reactions were stopped after
24 h to maximise conversions and allow comparison of the
results (Scheme 4).
The first observation to be made is that steric hindrance in
the catalyst indeed plays a role since for each reaction the
product yield decreases as the steric crowding on the complex
increases (Table 2). Whereas 4a gives excellent yields of the
expected coupling product for most substrates, 4b gives the
products in only moderate yields and the unexpectedly low
yield for the ethoxy substrate cannot be rationally explained.
Complexes 4c and 4d bearing the more bulky benzimidazol-
2-ylidene backbone also give moderate yields of the expected
coupling products. Although the yields were low with all com-
plexes except for 4a, it seems that steric bulk could be slightly
beneficial for the asymmetric induction in some cases, since
slightly better e.e.s were obtained with 4b (up to 46%), bearing
Fig. 3 ORTEP representations of complexes (S)-4c (top) and rac-4d
(bottom). Ellipsoids are shown at the 50% level. All hydrogens are omitted
for clarity.
Table 2 Catalytic performances of complexes 4a–d in the reaction of
Scheme 4a
Table 1 Selected distances (Å) and angles (1) for complexes 4b–d and
comparison with those of 4a7
Entry
R
Pd cat.
Conv.b (%)
Yieldc (%)
e.e.d (%)
1
2
3
4
5
6
7
8
Mee
(S)-4a
(R)-4a
(S)-4b
(S)-4c
(S)-4d
(S)-4a
(R)-4a
(S)-4b
(S)-4c
(S)-4d
(S)-4a
(R)-4a
(S)-4b
(S)-4c
(S)-4d
(S)-4d
(S)-4a
(S)-4b
(S)-4c
(S)-4d
n.d.
95
63
60
62
n.d.
n.d.
88
67
67
n.d.
n.d.
22
80
79
75
26
28
35
88
88
58
48
47
95
93
65
54
57
95
92
22
65
62
54
0
40 (S) f
42 (R) f
46 (S)
9 (S)
4a
4b
4c
4d
Distance (Å)
Pd–C(NHC)
Pd–P
Pd–Cl(trans-NHC)
Pd–Cl(trans-P)
CQC (NHC)
1.991(3)
1.973(2)
1.975(4)
2.2475(9)
2.3043(12) 2.3395(16)
2.3347(10) 2.3725(18)
1.372(5)
1.992(6)
2.2546(19)
37 (S)
35 (R) f
33 (S) f
31 (R)
17 (S)
22 (R)
23 (R) f
24 (S) f
26 (R)
13 (S)
23 (R)
28 (R) g
—
2.2444(8) 2.2449(5)
2.3397(8) 2.3414(6)
2.3614(9) 2.3798(5)
OMe
OEt
1.350(6)
1.345(4)
1.391(8)
9
10
11
12
13
14
15
16
17
18
19
20
Angle (1)
N–C(NHC)–N
C(NHC)–Pd–P
N–C(CH2)–C(Cp)
N–C(CH2)–C(Mes)
106.4(3)
84.95(9)
112.2(3)
—
106.1(2)
88.90(6)
109.22(19) 111.1(3)
115.3(2)
106.4(3)
89.94(10)
107.3(5)
91.94(19)
110.7(5)
114.7(5)
—
P(O)(OEt)2
0
0
0
—
—
—
naphthyl bromides and naphthylboronic acid. We previously
demonstrated that complex 4a is active for the coupling of
substituted naphthyl bromides with naphthylboronic acid at
low catalyst loadings and gives, as expected, similar levels of
enantioselectivities with the (R) and (S) enantiomers.7 There-
fore, the other complexes were tested directly under the same
conditions with the enantiomerically pure ligands possessing
8
a
Reagents and conditions: naphthyl bromide (1.0 equiv.), boronic acid
(1.2 equiv.), Pd cat. (0.5 mol%), K2CO3 (2.4 equiv.), toluene, 24 h.
b
Determined by integration of characteristic 1H NMR signals in
c
d
the crude mixture. Isolated yield. Determined by HPLC with a
Chiracel-OJ column. The commercial 1-bromo-2-methylnaphthalene
contains ca. 6% of 2-methylnaphthalene. Ref. 7. 2 mol% of Pd
e
f
g
the (S) configuration. As expected, all complexes are active for catalyst were used.
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Table 3 Catalytic performances of complex (R)-4a in the reaction of
Scheme 5
a CH2Mes substituent in place of a methyl group. Again,
unexpectedly low e.e.s were obtained with complex 4c, which
cannot only be explained in terms of steric congestion since
complex 4d, which possesses the bulkiest ligand, gives better
e.e.s than complex 4c. Increasing the catalytic charge from
Entry
t (h)
Solvent
Base
Yieldc (%)
e.e.d (%)
1a
2b
24
24
4
24
4
THF
KOH
CsF
CsF
K2CO3
K2CO3
22
22
32
69
45
13 (R)
3 (R)
7 (R)
12 (R)
11 (R)
Dioxane
Dioxane
Toluene
Toluene
0.5 mol% to 2 mol% did not improve the level of enantioselectivity 3b
4b
or the yield of coupling product (entry 16). The naphthyl bromide
5b
bearing a phosphonate substituent at the 2-position has been
a
Reagents and conditions: 4-nitroenzaldehyde (1 equiv.), phenylboronic
acid (2 equiv.), KOH (3 equiv.), THF (5 mL), 24 h. b Reagents and conditions:
4-nitroenzaldehyde (1 equiv.), phenylboronic acid (1.5 equiv.), base
(2 equiv.), solvent (1 mL). Isolated yield. Determined by HPLC with
a Chiracel-AD-H column and compared with published results.18,19
widely used in asymmetric Suzuki–Miyaura reactions and usually
gives better e.e.s than other substrates, as it seems that a chelating
functionality on one coupling partner is beneficial to achieve
good enantioselectivities.11,14 However, in our case none of the
expected coupling product was obtained whatever the complex
used, only a mixture of naphthyl bromide and the corresponding
dehalogenated product. Hydrodehalogenation has already been
observed under the conditions of the Suzuki–Miyaura coupling23
and this could indicate that the oxidative addition takes place
but the following step, i.e. the transmetallation of the boronic
acid, does not occur. One of the reasons could be the bulkiness
of our ligands, but chelating diphosphanes have also been
reported not to give conclusive results with this substrate.13
Therefore, the chelating nature of our ligands, which have two
strongly coordinating groups, could be detrimental to the reac-
tion in certain cases.
c
d
solvent–base couple to dioxane–CsF was no better: although the
1H NMR spectrum of the crude mixture showed almost complete
consumption of the starting aldehyde, several unidentified
by-products were also observed (entries 2 and 3). Only the
toluene–K2CO3 couple gave interesting results in terms of selectivity
and yield (entries 4 and 5). Unfortunately, the levels of enantio-
selectivity measured for complex (R)-4a were poor, with up to 13%
e.e. in THF (entry 1), and are comparable to those obtained by
Suzuma et al.18 However, this is a preliminary work and a more
thorough study of the reaction conditions with this and other chiral
palladium complexes will be carried out in order to improve the
efficiency of this challenging reaction.
Asymmetric 1,2-addition of phenylboronic acid to
4-nitrobenzaldehyde
Conclusions
The addition products such as diarylmethanols are very important
intermediates in the synthesis of biologically active compounds.24
This reaction has been well studied with rhodium complexes, with
the first example of enantioselective 1,2-addition of boronic acids
to aldehydes described by Miyaura in 1998.25 Diarylmethanols
have thus been obtained with very good enantioselectivities (up to
94% e.e.),26 but the use of cheaper palladium complexes in the
asymmetric version of this reaction is much less common.17–19
Indeed, only two recent examples show poor to moderate enantio-
selectivities, using a planar chiral ferrocenyl phosphine (up to 11%
e.e.)18 or axially chiral NHC ligands (up to 65% e.e.).19 We thus
turned to the 1,2-addition of PhB(OH)2 to 4-nitrobenzaldehyde,
hoping to improve the previously measured enantioselectivities
(Scheme 5, Table 3). As the synthesis of 4a is more straightforward
than that of 4b–d, we therefore carried out preliminary tests with
enantiopure (R)-4a only. The reaction was first conducted in THF
We have described in this paper the synthesis of a new family of
chiral Pd complexes, containing enantiomerically pure phos-
phane–(benz)imidazol-2-ylidene ligands. A first application of
these complexes to the asymmetric Suzuki–Miyaura reaction has
revealed that the bulkiness of ferrocene conjugated with that of
benzimidazol-2-ylidene seems to be detrimental to the catalytic
activity. The influence of the NHC structure on enantioselectivity
is not entirely predictable and the best e.e. of 46% was obtained
with 4b, only a 4% improvement compared to the previously
investigated complex 4a, and to the detriment of the yield.
Preliminary tests in the catalysed 1,2-addition of phenylboronic
acid to 4-nitrobenzaldehyde with complex 4a showed moderate
activities and low enantioselectivities. Future work will aim at
designing other types of chiral functionalised N-heterocyclic
carbenes in order to find the best compromise between activity
and enantioselectivity.
using KOH as base and 5 mol% of palladium complex (entry 1).
The selectivity with THF/KOH was not satisfactory as a non-
negligible amount of 4-nitrobenzyl alcohol from the Cannizzaro
reaction, as well as other minor by-products were observed in
the 1H NMR spectrum of the crude mixture. Changing the
Experimental
General considerations
All manipulations were performed under an inert atmosphere
of dry argon by using vacuum line and Schlenk tube techniques.
Solvents for syntheses were dried and degassed by standard
methods before use. 1D- and 2D-NMR spectra were recorded on
Bruker AV500 and Bruker AV300 spectrometers. 1H and 13C
chemicals shifts (d) are given in ppm (the residual peak of
deuterated solvent was used as reference). 31P chemical shifts
Scheme 5 1,2-Addition of phenylboronic acid to 4-nitrobenzaldehyde.
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are reported in ppm. Peaks are labelled as singlet (s), doublet (d), immediately followed by N-methyl benzimidazole (466 mg,
triplet (t), multiplet (m) and broad (br). The proton and carbon 2.91 mmol). After 5 minutes, the mixture was washed with
assignments were performed by COSY, NOESY, HSQC, 1H-13C 2 M aq. HCl, water, sat. aq. NaHCO3 and water, dried (MgSO4),
1
HMBC, H-31P HMBC experiments. MS spectra were performed filtered and concentrated in vacuo. The residue was purified by
by the mass spectrometry service of the Paul Sabatier University. precipitation with a mixture of petroleum ether and methyl tert-
Optical rotations were measured in a 1 dm cell using a Perkin- butyl ether (80/20) from a CH2Cl2 solution to give an orange
Elmer 241 photopolarimeter. GC chromatograms were recorded solid (193 mg, 27% yield). X-ray quality crystals of rac-2c were
on a HP 4890A GC equipped with a DB-5 MS UI capillary column obtained by slow diffusion of diethyl ether from a dichloro-
and the products were identified by comparison with authentic methane solution. 1H NMR (300 MHz, CDCl3, 298 K) d 8.79
samples. HPLC chromatograms were recorded on a Shimadzu (1H, s, NCHN), 7.73–7.69 (3H, m, CH PPh2 + BIm), 7.55–7.47
LC-2010A(HT) equipped with Chiralcel OJ or Chiralcel AD-H (4H, m, CH PPh2), 7.21–7.15 (3H, m, CH PPh2), 6.95–6.93
columns. Commercial chemicals were from Acros, Aldrich, Alfa (3H, m, CH PPh2 + BIm), 6.57 (1H, AB syst., JHH = 14 Hz,
Aesar, or Fluka and used as received. 1,2-Ferrocenyl alcohol 1,27 Fc-CH2), 5.23 (1H, br. s, CpA), 5.21 (1H, AB syst., JHH = 14 Hz,
imidazolium salts 2a, 3a5 and palladium complex 4a7 were prepared Fc-CH2), 4.58 (1H, br. s, CpA), 4.48 (5H, s, CpB), 3.78 (1H, br. s,
according to previously reported procedures. Abbreviations: CpA), 3.64 (3H, s, NCH3), 2.37 (3H, s, CH3 BIm), 2.16 (3H, s, CH3
CpA: cyclopentadienyl ring with PPh2 or PPh2(=S) substituents; BIm). 13C{1H} NMR (75.5 MHz, CDCl3, 298 K) d 140.47 (NCHN),
CpB: unsubstituted cyclopentadienyl ring; Fc: ferrocenyl; Im: 136.95 + 136.98 (Cq BIm), 133.08 (d, JCP = 80 Hz, Cq PPh2),
imidazolyl; BIm: benzimidazolyl; Mes: mesityl. Cq: quaternary 131.99 (d, JCP = 86 Hz, Cq PPh2), 131.85 (d, JCP = 2 Hz, CH PPh2),
carbon.
131.77 (d, JCP = 12 Hz, CH PPh2), 131.25 (d, JCP = 11 Hz, CH
PPh2), 130.94 (d, JCP = 2 Hz, CH PPh2), 129.78 + 129.24 (Cq BIm),
128.34 (d, JCP = 13 Hz, CH PPh2), 127.61 (d, JCP = 12 Hz, CH
Syntheses
FcPPh2(=S)CH2Im+CH MesBF4ꢀ 2b. To a solution of ferrocenyl PPh2), 114.22 + 111.58 (CH BIm), 82.37 (d, JCP = 13 Hz, Cq CpA),
alcohol 1 (100 mg, 0.23 mmol) in dry CH2Cl2 (10 mL) was 77.24 (CH CpA), 76.38 (d, JCP = 10 Hz, CH CpA), 75.27 (d, JCP = 91
quickly added HBF4 (54 wt% in Et2O, 50 mL, 0.35 mmol), Hz, Cq CpA), 71.39 (5 CH CpB), 71.18 (d, JCP = 10 Hz, CH CpA),
immediately followed by N-2,4,6 trimethylbenzylimidazole 45.60 (CH2-Fc), 33.37 (NCH3), 20.64 + 20.52 (CH3 BIm). 31P{1H}
(110 mg, 0.55 mmol). After 5 minutes, the mixture was washed NMR (121.5 MHz, CDCl3, 298 K) d 40.34. MS (ESI) m/z 575 [M+]
with 2 M aq. HCl, water, sat. aq. NaHCO3 and water, dried (100), 415 [M+ ꢀ C10H12N2] (18). HRMS (ES+) calcd for
2
(MgSO4), filtered and concentrated in vacuo. The residue was
purified by precipitation with methyl tert-butyl ether from a (c = 0.54, CH2Cl2).
CH2Cl2 solution to give a yellow solid (80 mg, 50% yield).
C
33H32N2PSFe 575.1374; found 575.1367. (S)-2c: [a]2D0 = ꢀ81
FcPPh2(=S)CH2BIm+CH MesBF4 2d. To a solution of ferroce-
ꢀ
2
1H NMR (300 MHz, CDCl3, 298 K) d 8.61 (1H, s, NCHN), nyl alcohol 1 (474 mg, 1.09 mmol) in dry CH2Cl2 (20 mL) was
7.78–7.71 (2H, m, CH PPh2), 7.60–7.47 (4H, m, CH PPh2), 7.40 quickly added HBF4 (54 wt% in Et2O, 380 mL, 2.75 mmol,
(1H, m, CH PPh2), 7.30 (3H, m, CH PPh2), 7.15 (1H, s, CH Mes), 2.5 equiv.), immediately followed by N-2,4,6 trimethylbenzyl
6.88 (2H, s, NCH = CH), 6.51 (1H, s, CH Mes), 6.40 (1H, AB syst., benzimidazole (800 mg, 2.88 mmol, 2.7 equiv.). After 5 minutes,
JHH = 14 Hz, CH2-Fc), 5.22 (1H, AB syst., JHH = 14 Hz, CH2-Fc), the mixture was washed with 2 M aq. HCl, water, sat. aq.
5.21 (1H, br. s, CpA), 5.14 (1H, AB syst., JHH = 14 Hz, CH2-Mes), NaHCO3 and water, dried (MgSO4), filtered and concentrated
4.91 (1H, AB syst., JHH = 14 Hz, CH2-Mes), 4.53 (1H, br. s, CpA), in vacuo. The residue was purified by precipitation with a
4.35 (5H, s, CpB), 3.86 (1H, br. s, CpA), 2.28 (3H, s, p-CH3 Mes), mixture of petroleum ether and methyl tert-butyl ether (80/20)
2.13 (6H, s, o-CH3 Mes). 13C{1H} NMR (75.5 MHz, CDCl3, 298 K) from a CH2Cl2 solution, followed by column chromatography
d 139.88 (Cq Mes, C-CH2), 137.93 (2 Cq Mes, C-o-CH3), 134.91 on silica gel (eluents: diethyl ether, then CH2Cl2, then CH2Cl2–
(NCHN), 134.66 (d, JCP = 86 Hz, Cq PPh2), 132.08 (d, JCP = 56 Hz, Acetone 90/10) to give an orange solid (481 mg, 57% yield).
Cq PPh2), 131.90 (d, JCP = 11 Hz, CH PPh2), 131.70 (d, JCP = 3 Hz, X-ray quality crystals of rac-2d were obtained by slow diffusion
CH PPh2), 131.25 (d, JCP = 10 Hz, CH PPh2), 129.89 (2 CH, of diethyl ether in a dichloromethane solution. 1H NMR
NCH = CH), 128.47 (d, JCP = 11 Hz, CH PPh2), 128.33 (d, JCP
=
(500 MHz, CDCl3, 301 K) d 8.68 (1H, s, NCHN), 7.72–7.68
12 Hz, CH PPh2), 125.35 (Cq Mes, C-p-CH3), 122.04 (CH Mes), (3H, m, CH PPh2 + BIm), 7.58–7.55 (1H, m, CH PPh2),
120.24 (CH Mes), 83.44 (d, JCP = 12 Hz, Cq CpA), 76.76 (d, JCP
10 Hz, CH CpA), 76.00 (d, JCP = 11 Hz, CH CpA), 73.55 (d, JCP
=
=
7.51–7.47 (2H, m, CH PPh2), 7.22–7.18 (1H, m, CH PPh2),
7.07–7.00 (3H, m, CH PPh2 + BIm), 6.94 (2H, s, CH Mes),
93 Hz, Cq CpA), 71.39 (d, JCP = 9 Hz, CH CpA), 71.23 (5 CH CpB), 6.90–6.85 (2H, m, CH PPh2), 6.48 (1H, AB syst., Fc-CH2), 5.51
47.91 (CH2-Fc or CH2-Mes), 47.40 (CH2-Fc or CH2-Mes), 21.04 (1H, AB syst., Fc-CH2), 5.40 (1H, br, CpA), 5.32 (1H, AB syst.,
( p-CH3 Mes), 19.61 (o-CH3 Mes). 31P{1H} NMR (121 MHz, CH2-Mes), 4.98 (1H, AB syst., CH2-Mes), 4.57 (1H, br s, CpA),
CDCl3, 298 K) d 40.65. MS (ESI) m/z 615 [M+] (100), 415 [M+ – 4.42 (5H, s, CpB), 3.81 (1H, s, CpA), 2.34–2.33 (9H, m, CH3 BIm +
C
13H16N2] (8). HRMS (ES+) calcd for C36H36N2PSFe 615.1687; p-CH3Mes), 2.17 (6H, s, o-CH3 Mes). 13C NMR{1H} (125.8 MHz,
found 615.1688. (S)-2b: [a]2D0 = ꢀ11 (c = 0.55, CH2Cl2).
CDCl3, 301K) d 139.97 (Cq p-CH3C Mes), 139.51 (NCHN), 137.94
FcPPh2(=S)CH2BIm+CH BF4 2c. To a solution of ferrocenyl (Cq o-CH3C Mes), 137.23 + 137.20 (Cq CH3C BIm), 134.01
alcohol 1 (418 mg, 0.97 mmol) in dry CH2Cl2 (20 mL) was (d, JCP = 86 Hz, Cq PPh2), 132.00 (d, JCP = 11 Hz, CH PPh2),
quickly added HBF4 (54 wt% in Et2O, 330 mL, 2.42 mmol), 131.99 (d, JCP = 87 Hz, Cq PPh2), 131.92 (d, JCP = 3 Hz, CH PPh2),
ꢀ
3
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131.20 (d, JCP = 3 Hz, CH PPh2), 130.83 (d, JCP = 11 Hz, CH PPh2), 134.62 (d, JCP = 20 Hz, CH PPh2), 131.81 (d, JCP = 19 Hz, CH
130.07 (CH Mes), 129.72 + 129.60 (Cq BIm), 128.66 (d, JCP PPh2), 130.93 (Cq BIm), 129.94 (Cq BIm), 129.55 (CH PPh2),
=
13 Hz, CH PPh2), 127.75 (d, JCP = 12 Hz, CH PPh2), 124.95 128.38 (d, JCP = 8 Hz, CH PPh2), 127.88 (CH PPh2), 127.65
(Cq NCH2C Mes), 114.79 + 112.33 (CH BIm), 83.05 (d, JCP = 12 (d, JCP = 6.5 Hz, CH PPh2), 113.11 (CH BIm), 111.89 (CH BIm),
Hz, Cq CpA), 77.28 (CH CpA, seen by HSQC{31P}), 76.12 (d, JCP
=
83.97 (Cq CpA), 77.21 (Cq CpA), 74.30 (CH CpA), 72.94 (CH CpA),
12 Hz, CH CpA), 73.91 (d, JCP = 94 Hz, Cq CpA), 71.59 (CH CpB), 71.06 (CH CpA), 70.30 (CH CpB), 46.26 (d, JCP = 9 Hz, CH2-Fc),
71.17 (d, JCP = 10 Hz, CH CpA), 46.72 (CH2-Fc), 45.77 (CH2-Mes), 32.93 (CH3-N), 20.61 + 20.47 (CH3 BIm). 31P{1H} NMR (121.5
21.10 (p-CH3 Mes), 20.73 + 20.69 (CH3 BIm), 20.03 (o-CH3 Mes). MHz, CDCl3, 298K) d ꢀ26.43. MS (ESI) m/z 543 [M+] (100), 575
31P{1H} NMR (202.5 MHz, CDCl3, 301 K) d 40.88. MS (ESI) m/z [M+ + S] (70), 383 [M+ ꢀ C10H12N2] (65). HRMS (ES+) calcd
693 [M+] (100). HRMS (ES+) calcd for C42H42N2PSFe 693.2156; for C33H32N2PFe 543.1699; found 543.1662. (S)-3c: [a]2D0 = ꢀ201
found 693.2164. (S)-2d: [a]2D0 = ꢀ158 (c = 0.53, CH2Cl2).
(c = 0.55, CH2Cl2).
FcPPh2CH2BIm+CH MesBF4 3d. Yellow solid (500 mg, 82%
ꢀ
2
General procedure for thꢀe synthesis of (benz)imidazolium salts
1
yield). H NMR (500 MHz, CDCl3, 301 K) d 8.90 (1H, s, NCHN),
FcPPh2CH2Im/BIm+RBF4 3b–d
7.50–7.47 (3H, m, CH BIm + PPh2), 7.44–7.38 (3H, m, CH PPh2),
RANEYs nickel (50 to 100 equivalents) was washed with 6.98 (1H, t, JHH = 7.5 Hz, CH PPh2), 6.94 (2H, s, CH Mes), 6.81
degassed methanol (3 ꢁ 10 mL), degassed diethyl ether (3 ꢁ (2H, t, JHH = 7.5 Hz, CH PPh2), 6.79 (1H, s, CH BIm), 6.63–6.60
10 mL), and finally degassed acetonitrile (3 ꢁ 10 mL). A solution (2H, m, CH PPh2), 5.78 (1H, dd, JHH = 14.9 Hz, JPH = 1.8 Hz,
of (benz)imidazolium salt 2b–d in acetonitrile (20 mL) was added CH2-Fc), 5.57 (1H, AB syst., JHH = 14.9 Hz, CH2-Fc), 5.33 (1H, AB
and the mixture was heated at 40 1C for 20 h. After cooling syst., JHH = 14.7 Hz, CH2-Mes), 5.26 (1H, AB syst., JHH = 14.6 Hz,
to room temperature, the supernatant was filtered through a CH2-Mes), 5.08 (1H, br. s, CH CpA), 4.49 (1H, br. s, CH CpA),
short path of Celites and the RANEYs nickel was rinsed with 4.13 (5H, s, CH CpB), 3.88 (1H, br. s, CH CpA), 2.33 (3H, s, p-CH3
acetonitrile. The filtrate was concentrated and the solid residue Mes), 2.23 (6H, s, CH3 BIm), 2.17 (6H, s, o-CH3 Mes). 13C{1H}
was dried in vacuo.
NMR (125.8 MHz, CDCl3, 301 K) d 139.88 (Cq p-CH3C Mes),
FcPPh2CH2Im+CH MesBF4 3b. Yellow solid (220 mg, 88% 139.83 (d, JCP = 1.8 Hz, NCHN), 139.11 (d, JCP = 8 Hz, Cq PPh2),
ꢀ
2
1
yield). H NMR (300 MHz, CDCl3, 298 K) d 8.73 (1H, s, NCHN), 138.00 (Cq o-CH3C Mes), 136.81 (Cq CH3C BIm), 136.10 (d, JCP
=
7.49 (2H, m, CH PPh2), 7.39 (3H, m, CH PPh2), 7.16 (3H, m, CH 6 Hz, Cq PPh2), 135.02 (d, JCP = 21 Hz, o-CH PPh2), 131.28 (d,
PPh2), 6.97 (2H, m, CH PPh2), 6.87 (2H, br s, CH Mes), 6.82 (1H, JCP = 18 Hz, o-CH PPh2), 130.04 (CH Mes), 129.70 (d, p-CH
br s, NCH = CH), 6.42 (1H, br s, NCH = CH), 5.50 (1H, AB syst., PPh2), 129.68 (Cq BIm), 129.45 (d, p-CH PPh2), 128.34 (d, JCP
=
JHH = 15 Hz, CH2-Fc), 5.37 (1H, AB syst., JHH = 15 Hz, CH2-Fc), 8 Hz, m-CH PPh2), 127.58 (d, JCP = 6 Hz, m-CH PPh2), 127.48 (Cq
5.09 (2H, s, CH2-Mes), 4.93 (1H, br s, CH CpA), 4.48 (1H, br s, BIm), 124.65 (Cq NCH2C Mes), 113.62 (d, JCP = 5 Hz, CH BIm),
CH CpA), 4.11 (5H, s, CH CpB), 3.92 (1H, br s, CH CpA), 2.27 (3H, 112.46 (CH BIm), 85.17 (d, JCP = 28 Hz, Cq CpA), 76.21 (d, JCP
s, p-CH3 Mes), 2.01 (6H, s, o-CH3 Mes). 13C{1H} NMR (75.5 MHz, 9 Hz, Cq CpA), 73.82 (d, JCP = 3.7 Hz, CH CpA), 72.79 (d, JCP
=
=
CDCl3, 298 K) d 139.98 (Cq Mes), 138.94 (d, JCP = 7 Hz, Cq PPh2), 4.5 Hz, CH CpA), 71.39 (CH CpA), 70.35 (CH CpB), 46.53 (dd,
138.00 (Cq Mes), 135.56 (d, JCP = 7 Hz, Cq PPh2), 135.10 (NCHN), JCP = 9.6 Hz, CH2-Fc), 46.28 (d, CH2-Mes), 21.07 (p-CH3 Mes),
134.71 (d, JCP = 21 Hz, CH PPh2), 132.19 (d, JCP = 19 Hz, CH 20.59 + 20.46 (CH3 BIm), 19.75 (o-CH3 Mes). 31P{1H} NMR (202.5
PPh2), 129.89 (CH Mes), 129.68 (CH Mes), 128.43 (d, JCP = 8 Hz, MHz, CDCl3, 301 K) d ꢀ25.68. MS (ESI) m/z 677 [M+ + O] (10),
CH PPh2), 128.32 (d, JCP = 7 Hz, CH PPh2), 124.93 (Cq Mes), 661 [M+] (100), 383 [M+ ꢀ C19H22N2] (10). HRMS (ES+) calcd
121.48 (NCH = CH), 120.06 (NCH = CH), 84.23 (d, JCP = 28 Hz, Cq for C42H42N2PFe 661.2435; found 661.2443. (S)-3d: [a]D20 = ꢀ224
CpA), 76.92 (d, JCP = 9 Hz, Cq CpA), 73.73 (CH CpA), 72.93 (c = 0.55, CH2Cl2).
(d, JCP = 4 Hz, CH CpA), 71.52 (CH CpA), 70.25 (CH CpB), 49.00
General procedure for the synthesis of PdCl2[L] complexes 4b–d
(d, JCP = 11 Hz, CH2-Fc), 47.40 (CH2-Mes), 22.63 (p-CH3 Mes),
21.01 (o-CH3 Mes). 31P{1H} NMR (121.5 MHz, CDCl3, 298 K): A mixture of PdCl2(PhCN)2 (1 equiv.), FcPPh2CH2Im/BIm+RBF4
ꢀ
d ꢀ27.18. MS (ESI) m/z 583 [M+] (85) 383 [M+ ꢀ C13H16N2] (100). 3b–d (50 mg, 1 equiv.) and NaOtBu (1.1 equiv.) in dry CH3CN
HRMS (ES+) calcd for C36H36N2PFe 583.1966; found 583.1962. (50 mL) was heated at 50 1C for 16 h. The solution was allowed
(S)-3b: [a]2D0 = ꢀ161 (c = 0.51, CH2Cl2).
to cool to room temperature, concentrated in vacuo and the
ꢀ
FcPPh2CH2BIm+MeBF4 3c. Orange solid (164 mg, 90% residue was purified by flash chromatography on silica gel
1
yield). H NMR (300 MHz, CDCl3, 298 K) d 8.75 (1H, s, NCHN), (eluent: CH2Cl2/MeOH 9/1).
7.51 (1H, s, CH BIm), 7.46–7.37 (4H, m, CH PPh2), 7.28 (1H, s,
4b: orange solid (35 mg, 61% yield). X-ray quality crystals of
CH PPh2), 7.08 (1H, s, CH BIm), 7.01 (1H, m, CH PPh2), 6.83 (S)-4b were obtained by slow diffusion of petroleum ether in a
(2H, m, CH PPh2), 6.65 (2H, m, CH PPh2), 5.79 (1H, AB syst., solution of dichloromethane. 1H NMR (500 MHz, CDCl3, 298 K)
JHH = 15 Hz, CH2-Fc), 5.34 (1H, AB syst., JHH = 15 Hz, CH2-Fc), d 7.92 (2H, m, CH PPh2), 7.51 (1H, m, CH PPh2), 7.44 (2H, m,
5.06 (1H, br s, CH CpA), 4.50 (1H, br s, CH CpA), 4.22 (5H, s, CH CH PPh2), 7.41 (1H, m, CH PPh2), 7.32 (2H, m, CH PPh2), 7.18
CpB), 3.84 (1H, br s, CpA), 3.67 (3H, s, N-CH3), 2.37 (6H, br s, (2H, m, CH PPh2), 6.79 (1H, s, NCH = CH), 6.78 (2H, s, CH Mes),
CH3 BIm). 13C{1H} NMR (75 MHz, CDCl3, 298 K) d 140.35 6.54 (1H, AB syst., JHH = 15 Hz, CH2-Fc), 5.97 (1H, s, NCH = CH),
(NCHN), 138.10 (d, JCP = 7 Hz, Cq PPh2), 136.92 (Cq CH3C 5.94 (1H, AB syst., JHH = 15 Hz, CH2-Mes), 4.75 (1H, AB syst.,
BIm), 136.82 (Cq CH3C BIm), 135.28 (d, JCP = 7.5 Hz, Cq PPh2), JHH = 15 Hz, CH2-Fc), 4.74 (1H, br s, CH CpA), 4.42 (1H, br s,
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CH CpA), 4.28 (5H, s, CH CpB), 4.00 (1H, AB syst., JHH = 15 Hz, 132.45 (Cq CH3-C BIm), 132.34 (Cq CH3-C BIm), 131.47 (Cq Mes,
CH2-Mes), 3.70 (1H, br s, CH CpA), 2.24 (3H, s, p-CH3 Mes), 1.91 C-p-CH3), 131.18 (Cq Mes, C-o-CH3), 131.02 (d, JCP = 11 Hz, CH
(6H, s, o-CH3 Mes). 13C{1H} NMR (125.8 MHz, CDCl3, 298 K) d PPh2), 129. 89 (Cq Mes, C-o-CH3), 129.10 (CH Mes), 128.79
156 ppm (Cq NCN-Pd, determined by HMBC), 139.03 (2 Cq Mes, (d, JCP = 55 Hz, Cq PPh2), 127.43 (d, JCP = 11 Hz, CH PPh2),
C-o-CH3), 138.72 (Cq Mes, C-p-CH3), 135.75 (d, JCP = 10 Hz, CH 128.49 (d, JCP = 10 Hz, CH PPh2), 126.84 (CH Mes), 112.45
PPh2), 134.46 (d, JCP = 54 Hz, Cq PPh2), 131.33 (d, JCP = 11 Hz, (CH BIm), 109.23 (CH BIm), 86.52 (d, JCP = 14 Hz, Cq CpA), 74.42
CH PPh2), 131.16 (CH PPh2), 130.68 (CH PPh2), 129.18 (CH (CH CpA), 72.05 (Cq, CpA), 72.93 (d, JCP = 1.5 Hz, CH CpA), 71.39
Mes), 128.86 (d, JCP = 54 Hz, Cq PPh2), 128.71 (d, JCP = 11 Hz, CH (5 CH,CpB), 70.16 (d, JCP = 1.5 Hz, CH CpA), 49.00 (CH2-Mes),
PPh2), 127.39 (d, JCP = 11 Hz, CH PPh2), 126.78 (Cq Mes, C-CH2), 46.52 (CH2-Fc), 21.12 (o-CH3 Mes), 20.92 (CH3 BIm), 20.37
121.00 (NCH = CH), 119.00 (NCH = CH), 86.99 (d, JCP = 14 Hz, Cq ( p-CH3 Mes), 20.26 (CH3 BIm). 31P{1H} NMR (202.5 MHz,
CpA), 74.85 (CH CpA), 72.90 (d, JCP = 56 Hz, CH CpA), 71.83 (d, CDCl3, 298 K) d 3.86. MS (DCI-CH4) m/z 801 [M – Cl] (100),
JCP = 58 Hz, Cq CpA), 71.43 (5 CH CpB), 70.13 (CH CpA), 50.08 767 [M – 2Cl] (58). HRMS (Cl+) calcd for C42H41N2PFePdCl
(CH2-Fc), 48.03 (CH2-Mes), 20.92 (p-CH3 Mes), 20.60 (o-CH3 801.1080; found 801.1118. (S)-4d: [a]2D0 = ꢀ32 (c = 0.51, CH2Cl2).
Mes). 31P{1H} NMR (202.5 MHz, CDCl3, 298 K) d 4.56. MS
(ESI) m/z 723 [M – Clꢀ] (100), 242 [PdCl2Im] (80). HRMS (ES+)
General procedure for Suzuki–Miyaura coupling reactions
calcd for C36H35N2PFePdCl 723.0623; found 723.0652. (S)-4b: In a typical run, a mixture of naphthyl bromide (0.29 mmol,
[a]2D0 = ꢀ5 (c = 0.5, CH2Cl2).
1 equiv.), naphthylboronic acid (0.34 mmol, 1.2 equiv.),
4c: orange solid (30 mg, 54% yield). X-ray quality crystals of potassium carbonate (0.69 mmol, 2.4 equiv.) and catalyst
(S)-4c were obtained by slow diffusion of acetone in a solution (0.5 mol%) in 2 mL of toluene (+50 mL of CH2Cl2 for complete
1
of dichloromethane. H NMR (500 MHz, CD2Cl2, 298 K) d 8.08 solubilisation) was stirred for 24 h at 40 1C. The solution was
(2H, m, CH o-PPh2), 7.61 (1H, m, CH p-PPh2), 7.52 (2H, m, CH allowed to cool to room temperature, washed with water and
m-PPh2), 7.28 (1H, m, CH p-PPh2), 7.20 (1H, s, CH BIm), 7.06 the aqueous phase was extracted with diethyl ether. The organic
(2H, m, CH o-PPh2), 6.83 (1H, s, CH BIm), 6.76 (2H, m, CH phase was dried over MgSO4, filtered and concentrated
m-PPh2), 6.64 (1H, AB syst., JHH = 15 Hz, CH2-Fc), 5.21 (1H, AB in vacuo. The residue was purified by flash chromatography
syst., JHH = 15 Hz, CH2-Fc), 4.94 (1H, br s, CH CpA), 4.43 (1H, br on silica gel (hexane or hexane/ethyl acetate 9/1). Enantiomeric
s, CH CpA), 4.42 (1H, br s, CH CpB), 3.62 (3H, s, N-CH3), excesses were determined by HPLC with a Chiralcel OJ column
2.38 (3H, s, CH3-BIm), 2.32 (3H, s, CH3-BIm). 13C{1H} NMR (eluent: Hexane/iPrOH 9/1, rate: 1 mL minꢀ1, T = 30 1C).
(125.8 MHz, CD2Cl2, 298 K) d 166.70 (Cq NCN-Pd), 136.02 Retention time for 2-methylbinaphthyl: 6.42 min (R isomer)–
(d, JCP = 10 Hz, o-CH PPh2), 134.31 (d, JCP = 55 Hz,Cq PPh2), 9.93 min (S isomer). Retention time for 2-methoxybinaphthyl:
133.49 (Cq BIm), 133.10 (2 Cq CH3-C BIm), 131.40 (d, JCP
2.5 Hz, p-CH PPh2), 130.90 (Cq BIm), 130.65 (d, JCP = 11 Hz, 2-ethoxybinaphthyl: 7.66 min (S isomer)–11.90 min (R isomer).
o-CH PPh2), 130.00 (d, JCP = 2.5 Hz, p-CH PPh2), 128.34 (d, JCP
10 Hz, m-CH PPh2), 127.58 (d, JCP = 54 Hz, Cq PPh2), 127.48
=
9.22 min (S isomer)–15.66 min (R isomer). Retention time for
=
General procedure for 1,2-addition reactions
(d, JCP = 11 Hz, m-CH PPh2), 110.45 (CH BIm), 109.71 (CH BIm), A mixture of 4-nitrobenzaldehyde (0.2 mmol, 1 equiv.), phenyl-
86.80 (d, JCP = 14 Hz, Cq CpA), 74.23 (d, JCP = 2.5 Hz, CH CpA), boronic acid (0.4 mmol, 2 equiv. (THF) or 0.3 mmol, 1.5 equiv.
73.51 (d, JCP = 8 Hz, CH CpA), 71.36 (5 CH CpB), 71.00 (d, JCP
=
(other solvents)), base (0.6 mmol, 3 equiv. (THF) or 0.4 mmol,
58 Hz, Cq CpA), 70.39 (d, JCP = 6 Hz, CH CpA), 46.15 (CH2-Fc), 2 equiv. (other solvents)) and catalyst (5 mol%) in a solvent
33.60 (N-CH3), 20.04 (CH3 BIm), 19.95 (CH3 BIm). 31P{1H} NMR (THF: 5 mL, other solvents: 1 mL) was stirred for 24 h at 65 1C.
(202.5 MHz, CD2Cl2, 298 K) d 4.38. MS (ESI) m/z 683 [M – Clꢀ] After cooling to room temperature, water was added and the
(100), 647 [M
33H31N2PFePdCl 683.0309; found 683.0313. (S)-4c: [a]D20
ꢀ59 (c = 0.54, CH2Cl2).
–
2Clꢀ] (33). HRMS (ES+) calcd for aqueous phase was extracted with tBuOMe. The organic phases
C
=
were washed with brine, dried (MgSO4), filtered and concentrated
1
in vacuo. After analysis by H NMR (d6-acetone), the residue was
4d: yellow solid (20 mg, 35% yield). X-ray quality crystals of purified by flash chromatography on silica gel (petroleum ether/
rac-4d were obtained by slow diffusion of diethyl ether in a EtOAc 8/1 then 4/1) to give pure (4-nitrophenyl)(phenyl)methanol as
solution of dichloromethane. 1H NMR (500 MHz, CDCl3, 298 K) a yellow solid. It was analysed by chiral HPLC using a Chiracel
d 8.00 (2H, m, CH PPh2), 7.52–7.46 (2H, m, CH PPh2), 7.31–7.29 AD-H column, (eluent: Hexane/iPrOH 80/20, flow rate =
(2H, m, CH PPh2), 7.12 (1H, m, CH BIm), 6.96–6.94 (2H, m, CH 0.5 mL minꢀ1, wavelength = 214 nm, 13.9 min (R isomer) and
PPh2), 6.77 (2H, s, CH PPh2), 6.78 (2H, 2s, CH Mes), 6.77 (1H, 16.4 min (S isomer)).
AB syst., JHH = 15 Hz, Fc-CH2), 6.28 (1H, AB syst., JHH = 15 Hz,
CH2-Mes), 5.41 (1H, s, CH BIm), 5.14 (1H, AB syst., JHH = 15 Hz,
X-ray structural analyses
Fc-CH2), 4.85 (1H, br. s, CpA), 4.40 (1H, br. s, CpA), 4.32 (5H, s, A single crystal of each compound was mounted under inert
CpB), 4.31 (1H, AB syst., JHH = 15 Hz, CH2-Mes), 3.65 (1H, perfluoropolyether at the tip of a glass fiber and cooled in the
br. s, CpA), 2.29 (6H, s, CH3 BIm), 1.95 (6H, s, o-CH3 Mes), 1.91 cryostream of either an Oxford-Diffraction XCALIBUR CCD
(3H, s, p-CH3 Mes). 13C{1H} NMR (125.8 MHz, CDCl3, 298 K) d diffractometer for rac-2c and (S)-4c, a Bruker APEXII diffractometer
166.74 (Cq NCN-Pd), 138.47 (Cq BIm), 135.93 (d, JCP = 10 Hz, for rac-2d and (S)-4b or an Agilent Technologies GEMINI EOS
o-CH PPh2), 134.19 (d, JCP = 54 Hz, Cq PPh2), 133.49 (Cq BIm), diffractometer for rac-4d.
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The structures were solved by direct methods (SIR9728) and
Paper
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refined by least-squares procedures on F2 using SHELXL-97.29
All H atoms attached to carbon were introduced in calculation
in idealised positions and treated as riding models. In four of
the five compounds, rac-2d, (S)-4b, (S)-4c and rac-4d, it was
difficult to locate some disordered solvents, and the SQUEEZE
option from PLATON30 has been used. The absolute configu-
ration for compounds (S)-4b and (S)-4c has been determined by
refining the Flack’s parameter.31 The drawing of the molecules
was realised with the help of ORTEP32.32
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Acknowledgements
`
´
We thank the CNRS, the Ministere de l’Enseignement Superieur et
de la Recherche (doctoral grant to P.L.), the Institut Universitaire de
France (grant to S.G.) and the Agence Nationale de la Recherche
(ANR-07-JCJC-0041, postdoctoral grant to N.D.) for financial
support of this work.
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