Efficient palladium catalysts containing original imidazolium-tagged chiral diamidophosphite ligands for asymmetric allylic substitutions in neat ionic liquid

Article abstract of DOI:10.1021/om4011577

New imidazolium-tagged chiral diamidophosphite ligands, (S,S)-a and (R)-b, derived from (S,S)-N,N′-dibenzyl-1,2-cyclohexanediamine and (R)-N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine, respectively, and the corresponding palladium allylic complexes of general formula [PdCl(η³-2-Me-C₃H₄)(κ¹P-L) ]BF₄ (1a,b) and [Pd(η³-2-Me-C₃H ₄)(κ¹P-L)₂](BF₄)₃ (2a,b) were synthesized and fully characterized, including the X-ray crystal structure for 1b. These original Pd/L catalytic systems were applied in asymmetric allylic alkylation, amination, and sulfonylation using rac-3-acetoxy-1,3-diphenyl-1-propene as a substrate in neat ionic liquids, [bmim][PF₆] and [Pyr][NTf₂]. The best results in terms of enantioselectivity were obtained with the catalytic precursor 1b in [Pyr][NTf₂]. The catalytic phase containing 1b for the allylic amination could be recycled up to six times without significant loss of asymmetric induction.

Full text of DOI:10.1021/om4011577

Article
pubs.acs.org/Organometallics
Efficient Palladium Catalysts Containing Original Imidazolium-
Tagged Chiral Diamidophosphite Ligands for Asymmetric Allylic
Substitutions in Neat Ionic Liquid
Maritza J. Bravo,† Isabelle Favier,‡,§ Nathalie Saffon,∥ Rosa M. Ceder,† Guillermo Muller,†
Montserrat Gomez,*,‡,§ and Merce Rocamora*,†
́
̀
†
́
́
̀ ̀
ica, Universitat de Barcelona, Martı i Franques 1-11, 08028 Barcelona, Spain
de Toulouse, 118 route de Narbonne, 31062 Toulouse Cedex 9, France
Departament de Quımica Inorgan
‡UPS, LHFA, Universite
́
§LHFA UMR 5069, CNRS, 31062 Toulouse Cedex 9, France
∥Institut de Chimie de Toulouse, FR 2599, Universite
́
Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France
S
* Supporting Information
ABSTRACT: New imidazolium-tagged chiral diamidophosphite
ligands, (S,S)-a and (R)-b, derived from (S,S)-N,N′-dibenzyl-1,2-
cyclohexanediamine and (R)-N,N′-dimethyl-1,1′-binaphthyl-2,2′-
diamine, respectively, and the corresponding palladium allylic
complexes of general formula [PdCl(η3-2-Me-C3H4)(κ1P-L)]BF4
(1a,b) and [Pd(η3-2-Me-C3H4)(κ1P-L)2](BF4)3 (2a,b) were
synthesized and fully characterized, including the X-ray crystal
structure for 1b. These original Pd/L catalytic systems were
applied in asymmetric allylic alkylation, amination, and
sulfonylation using rac-3-acetoxy-1,3-diphenyl-1-propene as a
substrate in neat ionic liquids, [bmim][PF6] and [Pyr][NTf2].
The best results in terms of enantioselectivity were obtained with
the catalytic precursor 1b in [Pyr][NTf2]. The catalytic phase containing 1b for the allylic amination could be recycled up to six
times without significant loss of asymmetric induction.
an appropriate approach. Actually, chiral P-based ligands
containing a phosphate,7 ammonium,8 or imidazolium9 frag-
ment have been conceived, but surprisingly just few of them
have been used in asymmetric catalytic processes in IL medium
such as in hydrogenation8a,9a,b and allylic substitution.7,8b,9c
The experience of some of us in the synthesis of original
chiral diamidophosphite ligands leads us to the design of
imidazolium-tagged derivatives with the aim of their application
in asymmetric allylic substitutions in ionic liquids.10 Diamido-
phosphite ligands present the advantage of being modular in
nature and readily accessible via simple condensation reactions.
Moreover, their cyclic structure in which the phosphorus atom
is a component of the heterocyclic ring contributes to their
stability.
Herein we describe the synthesis of two chiral ionic
imidazolium-tagged diamidophosphite ligands, their palladium
coordination chemistry, and their application in asymmetric
allylic substitutions, such as alkylation, amination, and
sulfonylation processes, in neat ionic liquid medium. A
comparison with the catalytic behavior of these Pd systems in
dichloromethane was also performed.
INTRODUCTION
■
Asymmetric allylic substitutions mediated by palladium systems
using soft nucleophiles represent one of the most studied
enantioselective processes to create carbon−carbon and
carbon−heteroatom bonds.1 Concerning the chiral inductors,
phosphorus-based ligands have been largely applied since the
first work published by Trost et al.,2 leading to excellent
enantioselectivity.3 In most cases, homogeneous catalysts in
organic solvents are involved, but also palladium colloidal based
systems modified by chiral diphosphites have proven to induce
a differentiated reactivity due to the surfacelike catalytic
behavior.4 An important remaining challenge in this asymmetric
reaction is the use of solvents other than the commonly used
volatile organic solvents. For Pd-catalyzed allylic substitutions,
ionic liquids (ILs; mainly imidazolium derivatives) have been
scarcely used, often applied in nonenantioselective reactions.5
To the best of our knowledge, previous work reported by some
of us constituted by palladium complexes containing chiral
diphosphites in imidazolium- and pyrrolidinium-based ionic
liquids is the only efficient catalytic system for allylic alkylation
and amination, allowing the recycling of the catalytic phase and
preserving a high enantioselectivity (more than 95% ee).6 With
the aim to better adapt the catalytic system to an ionic liquid
medium, P-donor ligands with ionic moieties seem to stand for
Received: November 28, 2013
© XXXX American Chemical Society
A
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(S,S)-a and (R)-b were characterized by mass spectrometry
and multinuclear (31P, 1H, and 13C) NMR spectroscopy.
Selected NMR data are shown in Table 1. 31P chemical shifts
are in the same range as those reported for analogous
monodentate diamidophosphites.10a,13 1H NMR spectra for
both ligands show two signals corresponding to each of the
diastereotopic POCH2 methylene protons, coupled to the
geminal proton, the phosphorus atom and the vicinal proton.
Moreover, two doublets are found for the methyl binaphthyl-
amine substituents of (R)-b, suggesting that the local C2
symmetry of the free diamine is lost.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Imidazolium-
Tagged Chiral Diamidophosphite Ligands, (S,S)-a and
(R)-b. The new homochiral diamidophosphite ligands (S,S)-a
and (R)-b were prepared through a two-step sequence using
enantiomerically pure diamines and the corresponding alcohol
hanging from an imidazolium moiety, on the basis of previously
reported methodologies (Scheme 1).9a,10,11 The first step of the
Scheme 1. Synthesis of Imidazolium-Tagged Chiral
Diamidophosphite Ligands (S,S)-a and (R)-b
The corresponding diamidophosphite selenides (S,S)-Se-a
and (R)-Se-b (Figure 1) were prepared in order to evaluate the
Figure 1. Structures of the diamidophosphite selenides (S,S)-Se-a and
(R)-Se-b.
electron-donating ability of the ligands toward metal acceptors,
on the basis of the magnitude of the coupling contant
1J(77Se−31P). These coupling constant values for (S,S)-Se-a
and (R)-Se-b were found to be 882.9 and 885.3 Hz,
respectively, close to those reported for similar diamidophos-
phite ligands.10 These data point to the fact that the new
ligands (S,S)-a and (R)-b exhibit a σ-donor character in the
range between that corresponding to phosphines and
synthesis consists of the formation of chlorodiaza derivatives
(S,S)-Cl-a and (R)-Cl-b, by the reaction of the corresponding
diamine with PCl3 in the presence of an excess of a base
(monitoring by 31P NMR). While the intermediate (S,S)-Cl-a
was quantitatively formed after 2 h of stirring at room
temperature, (R)-Cl-b required a longer time (20 h). Both
intermediates were not isolated and were used immediately
because of their sensitivity to oxygen and moisture.
The second step of the synthesis corresponds to the
condensation of the chlorodiaza derivatives and the alcohol
tagged with the imidazolium group in the presence of
triethylamine. After 12 h of stirring at room temperature, the
diamidophosphite ligands (S,S)-a and (R)-b were obtained in
global yields of 41% and 87%, respectively. In the case of the
synthesis of (R)-b, the addition of DMAP as a catalyst and
excess Et3N as an HCl scavenger was necessary, reducing the
amount of byproducts.10b,12 Despite the ionic nature of the
ligands (S,S)-a and (R)-b, they are soluble in commonly used
organic solvents, such as CH2Cl2, CHCl3, THF, and toluene,
and also in ionic liquids (ILs), such as [bmim][PF6] and
[Pyr][NTf2]. Because of their high tendency to hydrolyze,
these new ligands were used without further purification in the
formation of the corresponding palladium allylic complexes.
1
phosphites (reported values for PPh3 and P(OPh)3 are JPSe
= 745 and 1039 Hz, respectively14).
Synthesis and Characterization of Palladium Allylic
Complexes Containing the Ligands (S,S)-a and (R)-b:
1a,b and 2a,b. Allyl complexes 1a,b of general formula
[PdCl(η3-2-Me-C3H4)(κ1P-L)]BF4 (L = (S,S)-a, (R)-b) were
obtained as a mixture of two diastereomers by reaction of the
organometallic precursor [Pd(η3-2-Me-C3H4)(μ-Cl)]2 with the
appropriate diamidophosphite ligand (Scheme 2).10a The allyl
complexes 2a,b containing 2 equiv of ligand, [Pd(η3-2-Me-
C3H4)(κ1P-L)2](BF4)3 (L = (S,S)-a, (R)-b), were obtained in
the same way but in the presence of AgBF4 to remove the
chloride ligand (Scheme 2). Complex 2b was not soluble in
nonpolar organic solvents and was scarcely soluble in
acetonitrile and acetone but was soluble in the ionic liquids
tested ([bmim][PF6] and [Pyr][NTf2]).
a
1
Table 1. Selected 31P{1H} and H NMR Data for Free and Coordinated Diamidophosphite Ligands
compound
δ(31P{1H})
δ(1H) NCHN
8.88 (s)
δ(1H) NimiCH3
3.87 (s)
δ(1H) POCH2
b
(S,S)-a
(R)-b
133.0 (s)
3.90 (m, 1H), 3.48 (m, 1H)
4.32 (dt, 2JHH = 16.0, 3JHH ≈ 3JHP = 4.0), 4.23 (dt, 2JHH = 16.0,
b
168.9 (s)
8.74 (s)
3.80 (s)
3
3JHH ≈ JHP = 4.0)
c
1a
127.7 (s, maj), 125.9 (s, min)
149.9 (s, min), 148.5 (s, maj)
9.30 (s)
3.85 (s)
4.15 (ov) and 3.40 (m, 1H)
c
1b
9.35 (br s, maj), 9.31 (br 3.93 (s, maj), 3.92 (s, 4.20 (m, 1H) and 3.98 (m, 1H)
s, min)
min)
d
2a
123.0 (d, JPP = 87.4), 121.5 (d,
JPP = 87.4)
8.80 (s), 8.75 (s)
3.92 (s)
4.29 and 3.80 (m, ov), 4.48 and 3.93 (m, ov)
a
Chemical shifts are given in ppm. 31P{1H} (121.44 MHz, 298 K) and 1H (400 MHz, 298 K) were recorded in CDCl3. Coupling constants are given
in Hz. Overlapped signals were assigned from gHSQC spectra. Abbreviations: s, singlet; d, doublet; t, triplet; br, broad; m, multiplet; ov, overlapped.
In toluene. Abbreviations: maj, major isomer; min, minor isomer; assigned when isomers are distinguishable. Recorded in acetone-d6.
b
c
d
B
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153.0 and 147.1 ppm appeared. The phosphorus chemical shifts
of these complexes were upfield in comparison to those of the
free ligand, as reported for similar compounds.10a,16
Scheme 2. Synthesis of Allyl Complexes 1a,b and 2a,b (L =
(S,S)-a, (R)-b)
1
In relation to H NMR spectra, two-dimensional HSQC
experiments permitted us to assign unequivocally all the signals.
Complexes 1a,b exhibited two sets of signals for each syn and
anti proton of the allyl group, confirming the presence of the
two diastereoisomers (Scheme 2), making it possible to
correlate the signals for the allylic fragment with the
diamidophosphite ligand of each isomer, as shown in Tables
1 and 2. For complex 2a the presence of only one isomer was
confirmed by the existence of one signal for each of the four
allylic terminal hydrogen atoms, establishing the nonequiva-
lence of the two coordinated phosphorus atoms. For complex
2b only broad signals were observed, ruling out a complete
attribution.
To elucidate the solution structure and the dynamic behavior
of complexes 1a,b, 2D (NOESY for 1b and ROESY for 1a)
NMR experiments were carried out. NOE contacts between
allylic protons and the diamidophosphite ligand were not
observed, but interestingly exchange signals between allylic
protons were detected. For both complexes, exchanges between
syn/anti allylic protons in positions cis to the phosphorus atom
were observed. However, for protons in trans positions only
syn/syn and anti/anti proton exchanges were detected, in
accordance with a selective opening of the palladium carbon
trans to the phosphorus atom. These exchanges point to the
well-known η3−η1−η3 isomerization process in palladium allylic
complexes.10a,15 Cross peaks assigned to the apparent allyl−
palladium rotation were also observed for both complexes.
Crystals of 1b suitable for an X-ray diffraction study were
obtained from a solution of the complex in a mixture of
dichloromethane and hexane. Figure 2 shows the molecular
view and a selection of bond lengths and angles. The palladium
atom exhibits a distorted-square-planar coordination, bonded to
one phosphorus, one chlorine, and the allylic carbon atoms.
The distances and angles were in the expected range for this
These new organometallic compounds, isolated as brown
solids, are moderately air stable; they were fully characterized
both in the solid state and in solution. A multinuclear (31P, 1H,
and 13C) NMR study permitted us to characterize these
complexes in solution. Relevant NMR data are summarized in
Tables 1 and 2. 31P{1H} NMR spectra showed two sharp
Table 2. Selected 1H and 13C NMR Data of the Allyl Moiety
a
of Complexes 1a,b and 2a
b
b
cd
,
1a
1b
2a
4.67*, 4.50**
Hsyn,trans
4.49 (br s)
4.55 (dd, JHP = 9.6, 3.2,
min), 4.51 (dd, JHP
=
10.0, 3.2, maj)
Hsyn,cis
3.44 (ov), 3.42
(ov)
2.88 (br s, min), 2.82 (br s,
maj)
Hanti,trans 3.43 (ov, maj),
3.26 (s, min)
3.57 (d, JHP = 14.0, maj), 3.42** (d, JHP = 7),
3.54 (d, JHP = 14.0, min) 3.35* (d, JHP = 7)
Hanti,cis
2.38 (s, min), 2.32 2.35 (br s, maj), 2.17 (br s,
(s, maj)
min)
2-CH3
Ctrans
1.92 (s)
1.99 (s, min), 1.80 (s, maj) 2.04 (s)
79.7 (d, JCP
57.3), 78.6 (d,
JCP = 56.3)
=
81.5 (d, JCP = 44.0), 80.7 72.6* (d, JCP =
(d, JCP = 44.0)
33.0), 71.4** (d,
JCP = 42.0)
Ccis
55.4 (s), 55.0 (s) 53.3 (br s), 52.1 (br s)
Ccentral
133.8 (s), 133.5
(s)
133.4 (s), 133.3 (s)
137.8 (s)
24.3 (s)
C2‑CH3
23.37 (s)
23.11 (s)
a
Chemical shifts are given in ppm. 1H (400 MHz, CDCl3, 298 K) and
13C (100.6 MHz, 298 K) were recorded in CDCl3. Coupling constants
are given in Hz. Trans is with respect to the diamidophosphite ligand.
Overlapped signals were assigned from gHSQC spectra. Abbreviations:
s, singlet; d, doublet; t, triplet; br, broad; m, multiplet; ov, overlapped.
b
Abbreviations: maj, major isomer; min, minor isomer; assigned when
c
isomers are distinguishable. */** denotes the two nonequivalent allyl
CH2. Recorded in acetone-d6.
d
signals for 1a,b, with a 1.2/1 ratio arising from the two
disatereoisomers formed, due to the different relative spatial
arrangements of the chiral ligand and the allylic group around
the metal center.10a,15
Both complexes with two diamidophosphite ligands, 2a,b,
exhibited nonequivalence of the two phosphorus atoms in the
corresponding 31P{1H} NMR spectra. For 2a, two doublets
corresponding to an AA′ spin system at 121.5 and 123.0 ppm
appeared with coupling constants (2JPP′ = 87.4 Hz) similar to
those reported for related cis-L,L complexes.9a Complex 2b
showed one broad signal at 146.9 ppm when the spectrum was
recorded in CD3COCD3. However, when the spectrum was
recorded in the ionic liquid [Pyr][NTf2], two broad signals at
Figure 2. Molecular view of the cation corresponding to complex 1b
(ellipsoids drawn at 50% probability). Hydrogen atoms and the BF4
anion are omitted for clarity. Selected distances (Å) and angles (deg):
Pd(1)−C(31) 2.104(4), Pd(1)−C(29) 2.188(5), Pd(1)−P(1)
2.2626(12), Pd(1)−Cl(1) 2.3784(10), P(1)−O(33) 1.619(3),
P(1)−N(2) 1.661(4), P(1)−N(1) 1.687(4), C(29)−C(30)
1.390(6), C(30)−C(31) 1.422(7); P(1)−Pd(1)−Cl(1) 94.79(4),
C(29)−C(30)−C(31) 115.4(4).
C
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type of complex10a and were similar to those of analogous
complexes stabilized with phosphoramidites containing a
binaphthol moiety.15,17 The longer Pd−C length placed at a
position trans to the phosphorus atom is in agreement with the
greater trans influence of the diamidophosphite ligand relative
to the chloro ligand. The P−N distances are both shorter than
those expected for a single bond, pointing to some extent of a
P−N double bond.18 The values of the angles around the
nitrogen atoms are consistent with a significant sp2 character, in
agreement with the partial double-bond character of the P−N
bond (∑(N1) = 342.8° and ∑(N2) = 357.5°). Bond distance
values for the planar imidazolium ring evidence electronic
delocalization.
Pd-Catalyzed Asymmetric Allylic Substitutions. The
amination (using benzylamine as nucleophile, A), alkylation
(dimethyl malonate, B), and sulfonylation (sodium p-
toluenesulfinate, C) of rac-3-acetoxy-1,3-diphenyl-1-propene
(rac-I) were evaluated in neat imidazolium (IL1)- and
pyrrolidinium-based (IL2) ionic liquids using Pd catalytic
systems containing the corresponding chiral imidazolium-
tagged diamidophosphite ligands (S,S)-a and (R)-b (Scheme
3).
Table 3. Allylic Amination of rac-I using Benzylamine as
Nucleophile in Neat IL Catalyzed by Pd/L Systems
a
e
f
entry
PdL
L/Pd
IL
conversn (%)
ee of II (%)
b
1
Pd/a
1.25
1.25
1.25
1.25
2.25
2.25
2.25
2.25
1
IL1
IL2
IL1
IL2
IL1
IL2
IL1
IL2
IL2
IL2
IL2
IL2
IL2
IL2
IL2
IL2
52
59
40
43
86
81
93
96
66
100
66
62
23
0
33 (S)
30 (S)
43 (S)
57 (S)
<5
b
b
2
Pd/a
3
Pd/b
Pd/b
b
4
b
b
b
5
Pd/a
Pd/a
6
<5
7
Pd/b
Pd/b
50 (S)
73 (S)
46 (S)
74 (S)
26 (S)
76 (S)
34 (S)
b
8
c
9
1a
c
10
11
12
1b
1
d
1a + a
1.25
1.25
2
d
1b + b
g
c
13
2a
g
c
14
2b
2
g
d
15
2a + a
2b + b
2.25
2.25
50
22
25 (S)
50 (S)
g
d
16
a
Reaction conditions: rac-I/Bn-NH2/Pd/L = 100/100/1/1.25, 1 mL
b
of IL, 35 °C, 6 h. L = (S,S)-a, (R)-b. Catalyst generated under in situ
conditions by mixing [Pd(μ-Cl)(η3-C3H5)]2 and the appropriate
c
amount of the corresponding ligand. Preformed catalyst used as
d
Scheme 3. Asymmetric Allylic Substitutions in Neat Ionic
Liquid Medium Catalyzed by Palladium Systems Containing
Imidazolium-Tagged Diamidophosphite Ligands (S,S)-a and
(R)-b
catalytic precursor. Preformed catalyst in the presence of 0.25% of
e
free ligand used as catalytic precursor. Determined by 1H NMR.
f
g
Determined by HPLC. Catalytic data for 24 h.
1a,b. The activity for both catalysts was better than that
observed using the corresponding catalysts generated under in
situ conditions (entries 2 and 4 vs 9 and 10); in addition, the
asymmetric induction was improved, in particular for 1b, giving
74% enantiomeric excess (entry 10), analogous to that obtained
using a large excess of ligand (entry 8). We added some free
ligand in the catalytic mixture (giving a total (R)-b/Pd ratio of
1.25) with the aim of improving the selectivity. Despite that,
only a slight enhancement was observed (76% ee), together
with an important decrease in activity (entry 10 vs 12). For 1a
in the presence of added free ligand, the activity was maintained
but the selectivity dropped (entry 9 vs 11).
The preformed complexes 2a,b showed low activity (entries
13 and 14). The addition of free ligand improved their activity,
leading to low enantiomeric excesses (entries 15 and 16). It is
important to note that for b the in situ generated catalyst gives
a better activity and selectivity than those for the analogous
system using the preformed complex 2b (entry 8 vs 16).
For comparative purposes, we carried out the allylic
amination reaction in dichloromethane (Table S1 in the
Supporting Information). Using preformed complexes as
catalytic precursors, we observed very low activities for 1a,b
and 2b even after 24 h at 40 °C (conversions lower than 12%),
except for 2a, for which high conversion was achieved (up to
72%), but giving the racemic amine II.
We also tested the catalytic behavior of the preformed
complexes 1a,b in the allylic alkylation of rac-I using sodium
dimethylmalonate as nucleophile (Table 4). Analogously to the
allylic amination, complex 1b induced higher enantioselectiviy
than 1a (entries 1−4), giving up 45% of ee (entry 2). We also
observed that the addition of free ligand at the catalytic medium
produced a decrease of the asymmetric induction, but in this
case the conversion was practically complete after 6h of
reaction (entries 3−4). When the nucleophile was generated
under the largely employed conditions,20 it means generating
the nucleophile by addition of dimethylmalonate and (N,O)-
We chose the allylic amination as a benchmark reaction in
order to study the effect of the solvent in the examined
substitutions (Table 3). The named in situ catalytic reactions
(generation of the catalytic precursor by mixing [Pd(μ-Cl)(η3-
C3H5)]2 and the appropriate ligand in the IL for 30 min at 35
°C) revealed that the nature of the ionic liquid did not trigger
important differences in the activity (entries 1 vs 2, 3 vs 4, 5 vs
6, 7 vs 8). Concerning the enantioselectivity, Pd/b catalytic
systems led to better asymmetric inductions in the pyrrolidium
ionic liquid IL2 than in IL1 (entries 3 vs 4, 7 vs 8), but no
important differences were observed when the corresponding
Pd/a system was involved (entries 1 and 2). Surprisingly, the
catalytic effect of the ligand/metal ratio was dependent on the
ligand nature. While the high ligand/Pd ratio (L/Pd = 2.25)
triggered a negative effect in the asymmetric induction for the
Pd/a system in relation to that constituted by L/Pd = 1.25
(entries 1 and 2 vs 5 and 6), for the system Pd/b, a significant
increase of the enantiomeric excess (up to 73%) was observed
using a L/Pd ratio of 2.25, mainly in IL2 (entries 3 and 4 vs 7
and 8). In any case, the activity increased when an excess of
ligand was present (entries 1−4 vs 5−8).
These results obtained under in situ conditions led us to
choose IL2 for further catalytic study.19
With the aim of checking the effect of the catalytic precursor,
we also examined the behavior of the preformed complexes
D
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rendering this reaction particularly appropriate to be carried out
in ionic liquid medium.24 Actually, complexes 1a,b were both
highly active, 1b being the catalyst inducing a higher
asymmetric induction (up to 72% (S), entries 8 and 9),
analogously to that observed for the alkylation and amination
reactions (see above).
An accurate literature search showed us that the attribution
of absolute configuration to both enantiomers for the allylic
sulfonylation product IV was not described.25 For this reason,
we separated the two isomers from a racemic mixture of IV by
SFC techniques on a semipreparative scale. Both isomers were
fully characterized and identified by NMR, polarimetry, and X-
ray diffraction on monocrystal (Figure 3), leading us to an
unequivocal assignment.
Table 4. Allylic Alkylation and Sulfonylation of rac-I using
Sodium Dimethylmalonate (B) and Sodium p-
Toluenesulfinate (C) as Nucleophiles, Respectively, in Neat
a
IL2 Catalyzed by Pd/L Systems
d
e
entry
NuH
PdL
L/Pd
conversn (%)
ee of II (%)
b
1
2
B
B
B
B
B
B
B
C
C
1a
1
11
64
13 (R)
45 (R)
12 (R)
25 (R)
0
b
1b
1a + a
1
f
c
3
1.25
1.25
1
87
f
c
4
g
1b + b
100
81
b
5
1b
b
6
7
8
9
2b
2
38
37 (R)
18 (R)
19 (S)
72 (S)
b
2a
2
23
b
1a
1
85
b
1b
1
70
a
Reaction conditions: rac-I/NuH/Pd/L = 100/150/1/1.25, 1 mL of
b
IL2, 35 °C; 3 h for B and 24 h for C. L = (S,S)-a, (R)-b. Preformed
c
catalyst used as catalytic precursor. Preformed catalyst in the presence
d
of 0.25% of free ligand used as catalytic precursor. Determined by 1H
e
NMR. Determined by HPLC for allylic alkylations and by SFC for
f
g
allylic sulfonylations. Catalytic data for 6 h. Nucleophile generated
under in situ conditions by reaction of BSA and dimethyl malonate in
the presence of a pinch of potassium acetate.
bis(trimethylsilyl)acetamide (BSA) in the catalytic medium, the
racemic alkylated compound III was obtained (entry 5), due to
the instability of the ligand under these conditions.21 In
contrast to that observed in the allylic amination, complex 2b
was slightly active, but inducing a low asymmetric induction
(37% vs 45%, entry 6 vs 2). No significant differences between
both processes, amination and alkylation, were observed when
2a was involved (both low activity and selectivity).
In neat dichloromethane, a similar trend was observed in
comparison with that for the allylic amination (Table S2 in the
Supporting Information). Conversions were low (up 28% after
24 h) for catalysts 1a,b and 2b; complex 2a gave total
conversion but induced a moderately high enantioselectivity
(65% of ee), in contrast to the lack of asymmetric induction in
the case of the allylic amination (Table S1, Supporting
Information). This difference could be due to the higher
Lewis base behavior of benzylamine in comparison to that of
the dimethylmalonate anion, most likely inducing some extent
of chiral ligand decoordination. However, in IL, probably due
to the ionic interactions between the catalytic species and the
solvent, the palladium center is less accessible and consequently
the coordination of benzylamine to the metal center is less
favored, leading to a significant asymmetric induction (up to
76% ee) in contrast to the racemic mixtures obtained in
dichloromethane.
Figure 3. Molecular views of (S)-IV (left) and (R)-IV (right)
(ellipsoids drawn at shown at 50% probability). For the two
compounds, only one of the two independent molecules of the
asymmetric unit is shown and H atoms are omitted (except those on
the asymmetric carbons).
One of the main interests in using ionic liquids as solvents in
catalysis is the feasible immobilization of the metallic catalyst in
the IL phase and consequently the catalyst recycling. To the
best of our knowledge, only one efficient recyclable system has
been reported by some of us, in the case of Pd-catalyzed
asymmetric allylic substitutions.6 We then decided to study the
recyclability of the best of our catalytic systems here described,
1b, applied in the allylic amination for which the highest
enantioselectivity was obtained (Table 1). As shown in Figure
4, the activity decreased somewhat after the first run (from 75%
to 67%) but was nearly preserved up to the sixth run. The
enantioselectivity was almost constant up to the sixth run (for
run 1, 88 (S)/12 (R); for run 6, 83 (S)/17 (R)). Even when the
activity clearly decreased (for run 10, conversion 25%), the
selectivity was still quite high (79 (S)/21 (R)), which points to
The important differences observed in terms of enantiose-
lectivity could be due to plausible pathways without asymmetric
induction, involving palladium nanoparticles, taking into
account the trend of ionic liquids to stabilize metallic
nanoclusters.22 For all of the systems studied, the catalytic
solutions remained yellow even after 24 h of reaction, without
formation of palladium black. The absence of metallic
nanoparticles for catalytic solutions, showing asymmetric
induction, and also those leading to racemic mixtures was
confirmed by transmission electronic microscopy.
These encouraging results prompted us to test a more
challenging allylic substitution, such as the sulfonylation
reaction (Table 4). The model nucleophile used for this
reaction is sodium p-toluenesulfinate,23 exhibiting a very low
solubility in the usual organic solvents and consequently
Figure 4. Allylic amination recycling in IL2 catalyzed by 1b.
Conversion and ee values are represented by black and gray bars,
respectively.
E
dx.doi.org/10.1021/om4011577 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
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(S,S)-a. (S,S)-N,N′-Dibenzyl-1,2-diaminecyclohexane (0.41 g, 1.40
mmol) and NEt3 (0.60 mL, 4.30 mmol) were dissolved in 10 mL of
toluene. PCl3 (0.16 mL, 1.80 mmol) dissolved in 5 mL of toluene was
added dropwise at 0 °C, and the mixture was stirred for 2 h at room
temperature. After evaporation to dryness the oil was dissolved in 10
mL of toluene and NEt3 (0,6 mL, 4.3 mmol) and a solution of 1-(2-
hydroxyethyl)-3-methylimidazolium tetrafluoroborate (0.30 g, 1.4
mmol) in acetonitrile (2 mL) and THF (4 mL) was added dropwise.
After it was stirred overnight at room temperature 1 mL of hexane was
added. The mixture was cooled to 4 °C and the white precipitate of
amine hydrochloride was filtered off. The solvent was removed under
vacuum, and a waxy brown oil was obtained and used without further
purification. Yield: 0.37 g (41%). HRMS (ESI; m/z): C26H34BF4N4OP
the stability of the ligand under catalytic conditions. The
activity clearly decreases after the sixth run due to catalyst
deactivation; actually, ICP-MS analyses of the organic products
after the first, fifth, and ninth runs showed the absence of
palladium, proving that no metal leaching is produced after
extraction from the ionic liquid catalytic phase.
CONCLUDING REMARKS
■
Imidazolium-tagged chiral diamidophosphite ligands L coming
from optically pure cyclohexyl and binaphthyl diamines, (S,S)-a
and (R)-b, respectively, have been successfully prepared by a
two-step synthetic route. These monodentate phosphanes
could stabilize palladium allyl complexes containing one and
two ligands per metal, corresponding to complexes of the
general formula [PdCl(η3-2-Me-C3H4)(κ1P-L)]BF4 (1a,b) and
[Pd(η3-2-Me-C3H4)(κ1P-L)2](BF4)3 (2a,b). Both types of
complexes, less sensitive than the related free ligands, were
fully characterized in the solid state (including the X-ray crystal
structure of 1b) and in solution by NMR analyses, showing the
formation of the expected allylic diastereomers for 1a,b
complexes and also the characteristic palladium allyl dynamic
behavior. The ionic character of these palladium systems favors
their solubility in ionic liquids, such as those based on
imidazolium and pyrrolidinium cations. 1a,b and 2a,b
complexes have been used as catalytic precursors for
asymmetric allylic substitutions of rac-3-acetoxy-1,3-diphenyl-
1-propene (amination, alkylation, and sulfonylation) in neat
ionic liquid, giving better enantioselectivity in [Pyr][NTf2].
The best asymmetric induction was achieved using the
preformed complex 1b as catalyst, leading to 76% ee for the
amination and 72% ee for the sulfonylation with conversions
higher than 60%, in contrast to the lack of activity observed in
dichloromethane. The amination reaction was particularly
sensitive to the metal/ligand ratio when ligand (S,S)-a was
involved, probably due to the higher lability of (S,S)-a in
comparison to (R)-b in the presence of nucleophile species.
The stability of the Pd/b catalytic system was proved by its
ability to be recycled.
25
449.2445 [M − BF4]+. [α]D = +98.4° (c 1.0, CH2Cl2). 31P NMR
1
(toluene, 121.44 MHz; δ (ppm)): 133.0 (s). H NMR (CDCl3, 300
MHz; δ (ppm), J (Hz)): 8.88 (s, 1H, NCHN), 7.46−7.10 (12H,
10CH(Ar) + 2NCH), 4.37−3.88 (7H, 4CH2(Bn) + 1OCH2
+
2NCH2), 3.87 (s, 3H, CHNCH3), 3.48 (m, 1H, 1OCH2), 2.95 (m, 1H,
CH(Cy)), 2.52 (m, 1H, CH(Cy)), 1.97−0.95 (8H, CH2(Cy)). 13C
NMR (CDCl3, 100 MHz; δ (ppm), J (Hz)): 140.2 (d, 2JCP = 7.0, 1C,
2
C(Ar)), 139.9 (d, JCP = 3.0, 1C, C(Ar)), 136.7 (s, 1C, NCHN),
129.0−126.9 (10C, CH(Ar)), 123.0 (s, 2C, NCH), 67.9 (d, 2JCP = 7.0,
2
2
1C, CH(Cy)), 66.1 (d, JCP = 9.0, 1C, CH(Cy)), 61.3 (d, JCP = 5.0,
3
2
1C, OCH2), 51.0 (d, JCP = 3.0, 1C, NCH2), 50.2 (d, JCP = 32.0, 1C,
2
CH2(Bn)), 47.7 (d, JCP = 15.0, 1C, CH2(Bn)), 36.2 (s, 1C, NCH3),
30.0 (d, 3JCP = 2.0, 1C, CH2(Cy)), 29.6 (d, 3JCP = 3.0, 1C, CH2(Cy)),
24.1 (s, 1C, CH2(Cy)), 24.0 (s, 1C, CH2(Cy)).
(R)-b. (R)-N,N′-Dimethyl-1,1′-binaphthyl-2,2′-diamine (0.5 g, 1.6
mmol) and freshly dried and distilled i-Pr2EtN were dissolved in 10
mL of toluene. PCl3 (0.30 mL, 3.50 mmol) dissolved in 5 mL of
toluene was added dropwise at 0 °C. After it was stirred for 20 h at
room temperature, the mixture was evaporated to dryness. To the
solid obtained dissolved in toluene (10 mL) and NEt3 (0.60 mL, 4.3
mmol) was added a catalytic amount of DMAP (2.6 mg, 0.021 mmol).
Then a solution of 1-(2-hydroxyethyl)-3-methylimidazolium tetra-
fluoroborate (0.30 g, 1.4 mmol) in acetonitrile (2 mL) and THF (4
mL) was added dropwise over 6 h. After the mixture was stirred
overnight at room temperature, 1 mL of hexane was added. The
mixture was cooled to 4 °C, and the amine hydrochloride was filtered
off. The solvent was removed under vacuum, and a yellow solid was
obtained and used without further purification. Yield: 0.77 g (87%).
HR-MS (ESI; m/z): C28H28BF4N4OP 485.2111 [M − BF4 + H2O]+.
[α]D25 = −394.96° (c 1.0, CH2Cl2). 31P NMR (toluene, 121.44 MHz;
δ (ppm)): 168.9 (s). 1H NMR (CDCl3, 400 MHz; δ (ppm), J (Hz)):
8.74 (s, 1H, NCHN), 7.92−6.95 (14H, 12CH(Ar) + 2NCH), 4.32 (dt,
2JHH = 16.0, 3JHH = 3JHP = 4.0, 1H, OCH2), 4.23 (dt, 2JHH = 16.0, 3JHH
Further studies will seek to exploit the modularity of these
ligands to improve their catalytic activity and selectivity.
EXPERIMENTAL SECTION
■
=
3JHP = 4.0, 1H, OCH2), 3.95 (m, 2H, NCH2), 3.80 (s, 3H,
CHNCH3), 3.01 (d, 3JHP = 12.0, 3H, CH3(NMe)), 2.83 (d, 3JHP = 8.0,
General Information. All manipulations were performed under a
dry nitrogen atmosphere using standard vacuum-line Schlenk
techniques. Solvents were purified by standard procedures and
distilled under nitrogen; Et3N and i-Pr2EtN were distilled from
CaH2 and collected over 4 Å molecular sieves before use. 1-(2-
Hydroxyethyl)-3-methylimidazolium tetrafluoroborate,26 (S,S)-N,N′-
dibenzyl-1,2-cyclohexanediamine,27 and the dimeric palladium com-
3H, CH3(NMe)). 13C NMR (CDCl3, 100 MHz; δ (ppm), J (Hz)):
2
2
144.3 (d, JCP = 8.0, 1C, C(Ar)), 142.1 (d, JCP = 7.0, 1C, C(Ar)),
136.9 (s, 1C, NCHN), 132.9−121.0 (20C, 6C(Ar) + 12CH(Ar) +
2
3
2NCH), 61.1 (d, JCP = 9.0, 1C, OCH2), 51.0 (d, JCP = 6.0, 1C,
NCH2), 37.9 (d, JCP = 44.0, 1C, CH3(NMe)), 36.2 (s, 1C,
NCHCH3), 35.1 (d, JCP = 26.0, 1C, CH3NMe).
2
2
28
plex [Pd(η3-2-Me-C3H4)(μ-Cl]2 were prepared as previously
General Procedure for the Synthesis of Selenide Derivatives
(S,S)-Se-a and (R)-Se-b. The selenide derivatives were prepared
following the method described in the literature.10b A 0.15 mmol
amount of the corresponding diamidophosphite dissolved in 2 mL of
toluene in the presence of 2.4 mmol of selenium powder was stirred
under N2 for 24 h at room temperature. The reaction mixture was
filtered through Celite. The compounds were characterized by 31P
NMR (101 MHz) in toluene.
described. Ionic liquids IL1 (1-butyl-3-methylimidazolium hexafluor-
ophosphate) and IL2 (N-butyl-N-methylpyrrolidinium bis-
((trifluoromethyl)sulfonyl)amide) were treated under vacuum at 60
°C overnight prior to use. Other chemicals were used as purchased. 1H
and 13C (standard SiMe4) and 31P (standard H3PO4) NMR spectra
were recorded on 300 and 400 MHz spectrometers. High-resolution
mass spectra were obtained on a time-of-flight instrument using
electrospray ionization. Enantiomeric excesses for II and III were
determined by HPLC at 25 °C with a UV PDA detector; enantiomeric
excesses for IV were determined by SFC with a UV PDA detector at
35 °C.
(S,S)-Se-a. 31P NMR (CDCl3, 121.44 MHz; δ (ppm), J (Hz)): 87.6
(d, JPSe = 882.9).
(R)-Se-b. 31P NMR (toluene, 121.44 MHz; δ (ppm), J (Hz)): 90.3
(d, JPSe = 885.3).
General Procedure for the Synthesis of [PdCl(η3-2-Me-
C3H4)(κ1P-L)]BF4 (1a,b). For 1a,b, 0.17 g (0.44 mmol) of [Pd(η3-2-
Me-C3H4)(μ-Cl)]2 was dissolved in 5 mL of CH2Cl2 and 0.88 mmol
of the corresponding diamidophosphite in toluene (10 mL) was added
Synthesis of Diamidophosphites (S,S)-a and (R)-b. The
diamidophosphites (S,S)-a and (R)-b were prepared by following
the method described in the literature for similar ligands with some
modifications.10
F
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Organometallics
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at 0 °C. The mixture was stirred at room temperature overnight and
the solvent removed under reduced pressure. After washing with ether
a brownish solid was obtained in both cases.
153.0 (bs), 147.1 (bs). 31P NMR (acetone-d6, 121.44 MHz; δ (ppm)):
146.9 (bs). H NMR (acetone-d6, 300 MHz; δ (ppm), J (Hz)): 8.89
(bs, 2H, NCHN), 8.43−6.94 (28H, 24CH(Ar) + 4NCHN), 4.78−2.70
(30H, 6CHNCH3 + 4OCH2 + 4NCH2 + 2Hsyn + 2Hanti +
12CH3(NMe)), 2.88 (bs, 3H, 3CH3 (allyl)). Anal. Calcd for
C60H63B3F12N8O2P2Pd: C, 53.11; H, 4.68; N, 8.26. Found: C, 47.77;
H, 4.68; N, 7.59.
Although elemental analysis results for 2a,b complexes are outside
the range viewed as establishing analytical purity, they are provided to
illustrate the best values obtained to date.
1
1a. Yield: 0.11 g (22%). Mp: 154−158 °C dec. 31P NMR (CDCl3,
121.44 MHz; δ (ppm)): 127.7 (s, major isomer); 125.9 (s, minor
1
isomer). H NMR (CDCl3, 400 MHz; δ (ppm), J (Hz), mixture of
two isomers): 9.30 (s, 1H, NCHN), 7.65 (s, 1H, NCH), 7.50−7.00
(11H, 10CH(Ar) + 1NCH), 4.70−3.70 (10H, 3CH2(Bn) +
3CHNCH3 + 1OCH2 + 2NCH2 + 1Hsyn,trans), 3.68−3.20 (3H,
1OCH2 + 1Hanti,trans + 1Hsyn,cis), 3.11 (m, 2H, 1CH2(Bn) + 1CH(Cy)),
2.80 (m, 1H, CH(Cy)), 2.40−2.30 (1H, Hanti,cis), 2.13−1.47 (7H,
4CH2(Cy) + 3CH3(allyl)), 1.47−0.96 (4H, CH2 (Cy)). 13C NMR
(CDCl3, 100 MHz; δ (ppm), J (Hz), mixture of two isomers): 138.8
(s, 1C, C(Ar)), 137.6 (s, 1C, C(Ar)), 133.8; 133.5 (1C, C(allyl)),
129.5−126.5 (11C, 10CH(Ar) + 1NCHN), 124.1 (s, 1C, NCH),
General Procedure for Pd-Catalyzed Allylic Substitutions of
rac-I in IL. Allylic Amination. Reactions were carried out into an
Schlenk tube under Ar at 35 °C. A 0.01 mmol amount of the palladium
catalytic precursor (preformed complex1a, 1b, 2a, or 2bor
generated under in situ conditions by stirring [PdCl(η3-C3H5)]2 and
the appropriate amount of the corresponding ligand for 30 min) was
dissolved in 1 mL of IL. Then, 1 mmol of rac-3-acetoxy-1,3-diphenyl-
1-propene and 1 mmol of benzylamine were added to the solution.
The mixture was stirred at room temperature for the desired time. At
the end of the reaction, the products were extracted with cyclohexane
and filtered over Celite. The solvent was then removed under reduced
2
2
122.5 (s, 1C, NCH), 79.7; 78,6 (d, JCP,trans= 57.3; JCP,trans= 56.3, 1C,
CH2(allyl)), 68.0; 67.7 (s, 1C, CH(Cy)), 65.6 (s, 1C, CH(Cy)), 63.1;
2
2
63.0 (d, JCP = 13.0, JCP = 12.0, 1C, OCH2), 55.4; 55.0 (s, 1C,
CH2(allyl)), 50.0−46.4 (3C, 2CH2(Bn) + 1NCH2), 36.2 (s, 1C,
CHNCH3), 30.0−23.5 (4C, CH2(Cy)), 23.4 (s, 1C, CH3(allyl)). Anal.
Calcd for C30H41BClF4N4OPPd: C, 49.14; H, 5.64; N, 7.64. Found: C,
49.83; H, 5.99; N, 7.98.
1
pressure. Conversions were determined by H NMR. Enantiomeric
1b. Yield: 0.29 g (43%). Mp: 180−184 °C dec. 31P NMR (CDCl3,
121.44 MHz; δ (ppm)): 149.9 (s, minor isomer); 148.5 (s, major
excesses were determined by HPLC on a Chiralcel-OJ-H chiral
column, using heptane/isopropyl alcohol 90/10 as eluent and a flow of
1 mL/min.
1
isomer). H NMR (CDCl3, 400 MHz; δ (ppm), J (Hz), mixture of
Allylic Alkylation. The procedure was analogous to that described
for allylic amination, using 1.5 mmol of Na(CH(COOMe)2).
Conversions were determined by 1H NMR. Enantiomeric excesses
were determined by HPLC on a Chiralcel-OJ-H chiral column, using
heptane/isopropanol 80/20 as eluent and on a Chiralcel-OD chiral
column using heptane/isopropyl alcohol 98/2 as eluent and a flow of 1
mL/min for both columns.
two isomers): 9.35; 9.31 (bs, 1H, NCHN), 8.07−7.04 (14H,
12CH(Ar) + 2NCH), 4.60−4.40 (2H, 1Hsyn,trans + 1NCH2), 4.35−
4.15 (2H, 1NCH2 + 1CH2O), 4.05−3.85 (4H, 1CH2O + 3CHNCH3),
3.57; 3.54 (d, 2JHP = 14.0, 1H, Hanti,trans), 3.28; 3.19 (d, 3JHP = 12.0, 3H,
3
3
CH3(NMe)), 3.07; 2.95 (d, JHP = 12.0, JHP = 8.0, 3H, CH3(NMe)),
2.88; 2.82 (bs, 1H, Hsyn,cis), 2.35; 2.17 (bs, 1H, Hanti,cis), 1.99; 1.80 (s,
3H, CH3(allyl)). 13C NMR (CDCl3, 100 MHz; δ (ppm), J (Hz),
mixture of two isomers): 141.5−121.2 (24C, 8C(Ar) + 1C(allyl) +
Allylic Sulfonylation. The procedure was analogous to that
described for allylic amination, using 1.5 mmol of Na(p-MeC6H4SO2).
Conversions were determined by 1H NMR. Enantiomeric excesses
were determined by SFC on a Chiralpak OJ-H column, with CH3CN
20% as eluent and a flow of 4 mL/min under 100 bar of CO2.
Preparation of rac-IV: Separation of Both Enantiomers.
[Pd(η3-C3H5)(μ-Cl)]2 (0.01 mmol, 2 mg) and triphenylphosphine
(0.05 mmol, 13.12 mg) were dissolved in 4 mL of dichloromethane
and stirred for 30 min. rac-3-Acetoxy-1,3-diphenyl-1-propene (0.5
mmol, 126 mg) dissolved in 0.2 mL of CH2Cl2 was added, followed by
p-toluenesulfonic acid sodium salt (0.7 mmol, 136 mg), and the
mixture was stirred at 100 °C for 24 h. The reaction mixture was
extracted with pentane (10 × 1 mL), the sample was filtered through
SiO2, and the solvent was evaporated under reduced pressure. Yield:
2
12CH(Ar) + 1NCHN + 2NCH), 81.5; 80.7 (d, JCP,trans= 44.0, 1C,
2
CH2(allyl)), 62.9 (d, JCP = 8.0 1C, OCH2), 53.3; 52.1 (bs, 1C,
2
2
CH2(allyl)), 50.3; 50.2 (s, 1C, NCH2), 39.3; 39.0 (d, JCP = 19.0, JCP
= 18.0 1C, CH3(NMe)), 36.3 (s, 1C, CHNCH3), 35.7; 35.5 (d, 2JCP
4.0, JCP = 3.0, 1C, NCH3), 23.2 (s, 1C, CH3 (allyl)). Anal. Calcd for
C32H35BClF4N4OPPd: C, 51.16; H, 4.70; N, 7.46. Found: C, 49.81; H,
4.83; N, 7.20.
=
2
General Procedure for the Synthesis of [Pd(η3-2-Me-C3H4)-
(κ1P-L)2](BF4)3 (2a,b). To a solution of the appropiate ligand (1.6
mmol) in toluene (7 mL) was added a solution of [Pd(η3-2-Me-
C3H4)(μ-Cl)]2 (0.16 g, 0.41 mmol) in CH2Cl2 (10 mL) dropwise. The
mixture was cooled to 0 °C, and a solution of AgBF4 (0.16 g, 0.82
mmol) in THF (10 mL) was added. The mixture was stirred for 1 h at
room temperature (protected from the light). The AgCl that formed
was filtered and the solvent was removed. The pasty solid that was
obtained was washed and stirred several times with ether until a
brownish solid was obtained.
1
113 mg (65%). H NMR (CDCl3, 300 MHz; δ (ppm), J (Hz)): 2.44
(s, 3H), 4.85 (dd, J = 0.6, J = 7.5, 1H), 6.60 (d, J = 7.5, 1H), 6.64 (dd, J
= 15.6, J = 7.5, 1H) 7.25 (d, J = 8.3, 2H), 7.3−7.5 (m, 10H), 7.57 (d, J
= 8.3, 2H). 13C NMR (CDCl3, 75.5 MHz; δ (ppm)): 21.6 (CH3), 75.4
(CH), 120.3 (CH), 126.8 (2 CH), 128.6 (2 CH), 128.7 (2 CH), 129.3
(2 CH), 129.4 (2 CH), 129.7 (CH), 132.5 (C), 134.5 (C), 136.0(C),
138.0 (CH), 144.6 (C).
2a. Yield: 0.24 g (22%). Mp: 99−108 °C dec. HR-MS (ESI; m/z):
353.1512 [M]3+. 31P NMR (CH2Cl2/toluene, 121.44 MHz; δ (ppm), J
(Hz)): 123.0 (d, 2JPP= 87.4), 121.5 (d, 2JPP= 87.4). 1H NMR (acetone-
d6, 400 MHz; δ (ppm), J (Hz)): 8.80 (s, 1H, NCHN), 8.75 (s, 1H,
NCHN), 7.73−7.15 (24H, 20CH(Ar) + 4NCH), 4.68−3.75 (24H,
8CH2(Bn) + 6CHNCH3 + 4OCH2 + 2Hsyn + 4NCH2)), 3.45−2.94
(6H, 4CH(Cy) + 2Hanti), 2.10−1.09 (19H, 16CH2(Cy) + 3CH3
(allyl)). 13C NMR (acetone-d6, 100 MHz; δ (ppm), J (Hz)):
140.1−139.6 (2C, C(Ar)), 138.0−137.5 (3C, 2C(Ar) + 1C(allyl)),
130.0−128.1 (22C, 20CH(Ar) + 2NCHN)), 124.7 (s, 2C, NCH),
123.5 (s, 2C, NCH), 72.6 (d, 2JCP,trans = 33.0, 1C, CH2(allyl)), 71.4 (d,
Both enantiomers were separated by semipreparative SFC analysis
and crystallized from diethyl ether/pentane solution. For (S)-IV,
25
25
[α]D = +22.4° (c 0.33 g/100 mL, CH3CN); for (R)-IV, [α]D
=
−22.4° (c 0.33 g/100 mL, CH3CN).
General Procedure for the Recycling of the Pd-Catalyzed
Allylic Amination. After each run, the reaction mixture was cooled to
room temperature and extractions were carried out using cyclohexane
(3 × 5 mL) from the ionic liquid phase. Under these conditions,
neither the ionic liquid nor catalyst (palladium species and ligand) was
extracted (checked by NMR and ICP-MS analyses). Upon extractions,
the catalytic ionic liquid phase was then treated under vacuum in order
to remove the volatiles. The corresponding amounts of substrate (rac-
I) and nucleophile (BnNH2) were then added for starting a new run.
Crystallographic Data. Data for 1b. A prismlike specimen of
C33H38BCl3F4N4OPPd, approximate dimensions 0.190 × 0.210 ×
0.340 mm, was used for the X-ray crystallographic analysis. The X-ray
intensity data were measured on a D8 Venture system equipped with a
2
2JCP,trans = 42.0, 1C, CH2(allyl)), 68.1 (d, JCP = 29.0, 2C, CH(Cy)),
2
2
67.3 (d, JCP = 24.0, 2C, CH(Cy)), 63.5 (pt, JCP = 17.0 2C, OCH2),
50.5−49.6 (2C, CH2(Bn)), 49.0 (s, 2C, NCH2), 47.6−47.0 (2C,
CH2(Bn)), 36.6 (s, 2C, NCH3), 29.9−28.8 (4C, CH2(Cy)), 25.0−24.0
(5C, 4CH2 (Cy))
+ 1CH3 (allyl)). Anal. Calcd for
C56H75B3F12N8O2P2Pd: C, 50.91; H, 5.72; N, 8.48. Found: C, 48.85;
H, 5.89; N, 7.85.
2b. Yield: 0.53 g (49%). Mp: 177−180 °C dec. HR-MS (ESI; m/z):
365.1189 [M]3+. 31P NMR ([Pyr][NTf2], 121.44 MHz; δ (ppm)):
G
dx.doi.org/10.1021/om4011577 | Organometallics XXXX, XXX, XXX−XXX

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multilayer monochromator and a Mo high brilliance Incoatec
Microfocus source (λ = 0.71073 Å) at a temperature of 100(2) K.
The frames were integrated with the Bruker SAINT software
package using a Bruker SAINT algorithm.29 Data were corrected for
absorption effects using the multiscan method SADABS.30 The
structure was solved and refined using the Bruker SHELXTL software
package.31
(4) (a) Jansat, S.; Gom
Claver, C.; Castillon
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Claver, C.; Jansat, S.; Chaudret, B.; Philippot, K. Adv. Synth. Catal.
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1999, 1247. (b) Ross, J.; Chen, W.; Xu, L.; Xiao, J. Organometallics
Data for (R)-IV and (S)-IV. Intensity data were collected at a
temperature of 193(2) K on a Bruker-AXS APEX II Quazar
diffractometer ((R)-IV) using a 30 W air-cooled microfocus source
(ImS) with focusing multilayer optics and on a Bruker-AXS SMART
APEX II diffractometer ((S)-IV) with graphite-monochromated Mo
Kα radiation (wavelength 0.71073 Å) by using ϕ and ω scans. The
data were integrated with SAINT, and an empirical absorption
correction with SADABS was applied.29,30 The structures were solved
by direct methods, using SHELXS-9731 and refined using the least-
squares method on F2. All non-H atoms were treated anisotropically.
The hydrogen atoms were fixed geometrically and treated as a riding
model. H atoms on the asymmetric carbons were located in difference
Fourier maps and included in the subsequent refinement without using
restraints.
For crystallographic data, see Table S3 in the Supporting
Information.
CCDC-969637 (1b), CCDC-969512 ((R)-IV), and CCDC-969513
((S)-IV) contain supplementary crystallographic data. These data can
be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
̀
2001, 20, 138. (c) Kmentova, I.; Gotov, B.; Solcaniova, E.; Toma, S.
Green Chem. 2002, 4, 103. (d) Lyubimov, S. E.; Davankov, V. A.;
Gavrilov, K. N. Tetrahedron Lett. 2006, 47, 2721. (e) Leclercq, L.;
Suisse, I.; Nowogrocki, G.; Agbossou-Niedercorn, F. Green Chem.
2007, 9, 1097. (f) Moucel, R.; Perrigaud, K.; Goupil, J.-M.; Madec, P.-
J.; Marinel, S.; Guibal, E.; Gaumont, A.-C.; Dez, I. Adv. Synth. Catal.
2010, 352, 433.
(6) Favier, I.; Balanta Castillo, A.; Godard, C.; Castillon
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, S.; Claver,
C.; Gomez, M.; Teuma, E. Chem. Commun. 2011, 47, 7869.
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(7) Benessere, V.; Lega, M.; Silipo, A.; Ruffo, F. Tetrahedron 2011,
67, 4826.
(8) (a) Berthod, M.; Joerger, J. M.; Mignani, G.; Vaultier, M.;
Lemaire, M. Tetrahedron: Asymmetry 2004, 15, 2219. (b) Lyubimov, S.
E.; Davankov, V. A.; Maksimova, M. G.; Petrovskii, P. V.; Gavrilov, K.
N. J. Mol. Catal. A: Chem. 2006, 259, 183. (c) Vallee, C.; Chauvin, Y.;
́
Basset, J. M.; Santini, C. C.; Galland, J. C. Adv. Synth. Catal. 2005, 347,
1835.
(9) (a) Gavrilov, K. N.; Lyubimov, S. E.; Bondarev, O. G.;
Maksimova, M. G.; Zheglov, S. V.; Petrovskii, P. V.; Davankov, V.
A.; Reetz, M. T. Adv. Synth. Catal. 2007, 349, 609. (b) Lee, S.; Zhang,
Y. J.; Piao, J. Y.; Yoon, H.; Song, C. E.; Choi, J. H.; Hong, J. Chem.
Commun. 2003, 2624. (c) Sebesta, R.; Bilcik, F. Tetrahedron:
Asymmetry 2009, 20, 1892. (d) Hodgson, R.; Douthwaite, R. E. J.
Organomet. Chem. 2005, 690, 5822.
(10) (a) Ayora, I.; Ceder, R. M.; Espinel, M.; Muller, G.; Rocamora,
M.; Serrano, M. Organometallics 2011, 30, 115. (b) Bravo, M. J.;
Ceder, R. M.; Muller, G.; Rocamora, M. Organometallics 2013, 32,
2632.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, tables, figures, and CIF files giving NMR spectra for
ligands (S,S)-a and (R)-b and complexes 1a,b and 2a,b,
catalytic procedures and data for the allylic substitutions in
CH2Cl2, and crystallographic data for 1b, (R)-IV, and (S)-IV.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(11) Trost, B. M.; Lam, T. M. J. Am. Chem. Soc. 2012, 134, 11319.
(12) Schonleber, M.; Hilgraf, R.; Pfaltz, A. Adv. Synth. Catal. 2008,
̈
350, 2033.
AUTHOR INFORMATION
(13) Reetz, M. T.; Oka, H.; Goddard, R. Synthesis 2003, 12, 1809.
(14) Dixon, I. M.; Lebon, E.; Loustau, G.; Sutra, P.; Vendier, L.; Igau,
A.; Juris, A. Dalton Trans. 2008, 562.
(15) Filipuzzi, S.; Pregosin, P. S.; Albinati, A.; Rizzato, S.
Organometallics 2006, 25, 5955.
(16) Tsarev, V. N.; Lyubimov, S. E.; Shiryaev, A. A.; Zheglov, S. V.;
Bondarev, O. G.; Davankov, V. A.; Kabro, A. A.; Moiseev, S. K.;
Kalinin, V. N.; Gavrilov, K. N. Eur. J. Org. Chem. 2004, 2214.
(17) Shintani, R.; Park, S.; Shirozu, F.; Murakami, M.; Hayashi, T. J.
Am. Chem. Soc. 2008, 130, 16174.
■
Corresponding Author
*M.R.: tel, +34 934039135; fax, + 34 934021273; e-mail,
merce.rocamora@qi.ub.es. M.G.: tel, +33 561557738; fax, + 33
561558204; e-mail, gomez@chimie.ups-tlse.fr.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
(18) Ceder, R. M.; Garcıa, C.; Grabulosa, A.; Karipcin, F.; Muller, G.;
Financial support from the Spanish Ministerio de Ciencia y
Tecnologia (CTQ2010-1592/BQU), the Generalitat de Cata-
lunya Departament d’Universitats, Recerca i Societat de la
́
Rocamora, M.; Font-Bardıa, M.; Solans, X. J. Organomet. Chem. 2007,
692, 4005.
(19) [Pd(μ-Cl)(η3-C3H5)]2 in the absence of any ligand is inactive in
IL2 after 24 h at 35 °C.
Informacio
́
(2009SGR1164), the Centre National de la
Paul
(20) Trost, B. M.; Murphy, D. J. Organometallics 1985, 4, 1143.
(21) CH2Cl2 solutions of 1a,b and 2a,b in the presence of BSA and
KOAc were followed by 31P NMR. Full decomposition of the
complexes was observed after 6 h of stirring at room temperature.
(22) For selected contributions, see: (a) Favier, I.; Madec, D.;
Recherche Scientifique (CNRS), and the Universite
́
Sabatier are gratefully acknowledged. M.J.B. thanks the
IFARHU-SENACYT program for a Ph.D. grant.
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I
dx.doi.org/10.1021/om4011577 | Organometallics XXXX, XXX, XXX−XXX