Palladium catalyzed Suzuki C-C couplings in an ionic liquid: Nanoparticles responsible for the catalytic activity

Article abstract of DOI:10.1039/b713449e

A new family of functionalized ligands derived from norborn-5-ene-2,3- dicarboxylic anhydride has been used in Suzuki C-C cross-couplings between aryl boronic acids and aryl bromide derivatives in [BMI][PF₆] (BMI = 1-n-butyl-3-methyl-imidazolium), using palladium acetate as catalytic precursor. High conversions and yields are obtained when amine ligands containing hydroxy groups are involved. TEM analyses after catalysis show the formation of small nanoparticles, in contrast to the agglomerates observed when nanoparticles are intentionally preformed, with a consequent decrease in the catalytic activity in the latter case. Some tests, including the correlation effect between solvent and ligand, are carried out to try to identify the true nature of the catalyst. All the results obtained suggest that formation of nanoparticles is required to lead to a catalytically active system. The Royal Society of Chemistry.

Full text of DOI:10.1039/b713449e

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Palladium catalyzed Suzuki C–C couplings in an ionic liquid: nanoparticles responsible
for the catalytic activity
Fernando Fernández, Beatriz Cordero, Jérôme Durand, Guillermo Muller, François Malbosc,
Yolande Kihn, Emmanuelle Teuma and Montserrat Gómez, Dalton Trans., 2007, DOI:
10.1039/b713449e
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PAPER
www.rsc.org/dalton | Dalton Transactions
Palladium catalyzed Suzuki C–C couplings in an ionic liquid: nanoparticles
responsible for the catalytic activity
Fernando Ferna´ndez,a,b Beatriz Cordero,a,b Je´roˆme Durand,a Guillermo Muller,b Franc¸ois Malbosc,c
Yolande Kihn,d Emmanuelle Teumaa and Montserrat Go´mez*a
Received 3rd September 2007, Accepted 12th September 2007
First published as an Advance Article on the web 5th October 2007
DOI: 10.1039/b713449e
A new family of functionalized ligands derived from norborn-5-ene-2,3-dicarboxylic anhydride has
been used in Suzuki C–C cross-couplings between aryl boronic acids and aryl bromide derivatives in
[BMI][PF6] (BMI = 1-n-butyl-3-methyl-imidazolium), using palladium acetate as catalytic precursor.
High conversions and yields are obtained when amine ligands containing hydroxy groups are involved.
TEM analyses after catalysis show the formation of small nanoparticles, in contrast to the agglomerates
observed when nanoparticles are intentionally preformed, with a consequent decrease in the catalytic
activity in the latter case. Some tests, including the correlation effect between solvent and ligand, are
carried out to try to identify the true nature of the catalyst. All the results obtained suggest that
formation of nanoparticles is required to lead to a catalytically active system.
nature of the catalytically active species. In these cases, an unam-
biguous distinction between colloidal and molecular catalysis is
Introduction
however often very difficult.12 Concerning the nature of the active
palladium species involved in Heck and Suzuki couplings, Jones
and co-workers have recently published an extensive review.13 In
contrast to the widespread work carried out for Heck couplings,14
less attention has been paid to identifying the nature of the
catalyst for Suzuki cross-coupling reactions. Hu and Liu, based
on catalyst recycling and TEM analysis, have recently proposed
that for Suzuki couplings using Pd nanoparticles, leaching of
discrete Pd(II) species occurs during the process, regenerating
Pd(0) nanoparticles after the reductive elimination,15 similarly to
that suggested by Dupont et al.14a (in ionic liquid) and de Vries14b
(in organic solvent) for Heck reactions, where nanoparticles are
considered as catalyst reservoirs.
In the last years, we have been interested in the synthesis of
metallic nanoparticles stabilized by ligands16 and functionalized
polymers17 in organic solvents, in order to find pattern reactions18
or specific catalytic inductions19 helping us to discriminate between
colloidal and homogeneous catalysts. In the studied systems, the
presenceofarylgroups becamecrucialinstabilizingtheinteraction
between the metal and the ligand or substrate, probably due to p-
coordination between the metallic surface and aromatic moieties.19
More recently, we have prepared palladium nanoparticles in ILs
from organometallic precursors to be applied in catalytic C–C
couplings.20
With this analysis in mind, we looked for functionalized ligands
with aromatic-free backbones in order to mainly favour the
electrostatic stabilization of the palladium nanoparticles by the
IL, to be subsequently used as catalysts in C–C couplings of aryl
substrates; for this purpose, we chose norbornene derived ligands.
endo-Norbornene monomers have largely been used as substrates
for ring-opening metathesis polymerization, in particular using
Grubbs ruthenium catalysts.21 This kind of monomer, in particular
the imide derivatives, can be readily prepared by Diels–Alder cy-
cloadditions from maleimides22 or norborn-5-ene-2,3-dicarboxylic
anhydride.23 To the best of our knowledge, these compounds have
Since the 1990’s, Pd-catalyzed carbon–carbon couplings (Heck,
Suzuki, Sonogashira and Stille reactions as the most common
couplings) have developed into an important tool in organic
synthesis, predominantly for pharmaceutical and agrochemical
purposes.1 Among them, Heck2 and Suzuki3 couplings have
specially attracted the attention of many researchers, in essence
due to the small loading of metal required to afford high turnover
frequencies,4 so low that the term “homeopathic palladium” is
currently employed.2d,5
Ligand-free palladium catalysts such as palladium acetate
have been largely studied, in particular in ionic liquids (ILs)
containing imidazolium cations,6,7 due to the stabilization of metal
clusters avoiding the formation of catalytic inactive bulk metal.8
The use of ILs as (co)solvents overcomes the main drawbacks
of homogeneous catalysis, i.e. product separation and catalyst
recovery, by immobilization of the catalyst in the ionic liquid
phase.9,10
In ILs, the addition of Lewis bases as catalytic auxiliaries is
not necessary to stabilize metallic nanoparticles (in fact, they
are considered as ligand-free metallic systems if anions coming
from the metallic salts are not considered), but their presence
may enhance the stability of the nanoparticles, as observed when
functionalized ionic liquids are employed,11 besides their probable
role in selective catalytic processes.
From a mechanistic point of view, the presence of metal
nanoparticles in the catalytic reaction lead us to consider the
aLaboratoire He´te´rochimie Fondamentale et Applique´e UMR CNRS 5069,
Univesite´ Paul Sabatier, 118 route de Narbonne, 31062, Toulouse cedex 9,
France. E-mail: gomez@chimie.ups-tlse.fr.; Fax: +33 561558204; Tel: +33
561557738
bDepartament de Qu´ımica Inorga`nica, Universitat de Barcelona, Mart´ı i
Franque`s, 1-11, 08028, Barcelona, Spain
cSOLVIONIC, Parc technologique Delta Sud 09340, Verniolle, France
dCEMES, UPR 8011 CNRS, 29 rue Jeanne Marvig, 31055, Toulouse cedex
4, France
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©

not been previously reported as ligands in metal-catalyzed organic
processes.
Ammonium derivatives, 9 and 10, were prepared by classical
amine quaternization from the appropriated amine, 2, 3, with
iodomethane,25 followed by an anion exchange reaction using
lithium bis(trifluoromethanesulfonyl)imide, LiNTf2 (Scheme 3).26
Herein we report the synthesis and characterization of new
ligands coming from endo-norborn-5-ene-2,3-dicarboxylic anhy-
dride (1–10, Fig. 1) and their catalytic effect in palladium-
catalyzed Suzuki C–C coupling reactions using arylbromides and
arylboronic acid derivatives in ionic liquid [BMI][PF6] (BMI =
1-n-butyl-3-methyl-imidazolium). Evaluation of the nature of the
plausible catalyst is also described.
Scheme 3 Synthesis of ammonium derivatives 9 and 10.
The three types of compounds (amines, imides and ammonium
derivatives) were obtained in good yields (in the range 68–95%),
and the overall yield for ammonium ligands was 50–55%.
Catalytic results
Suzuki cross-coupling between bromobenzene and phenylboronic
acid under basic biphasic conditions, [BMI][PF6]–H2O (water was
necessary to favour the solubility of phenyl boronic acid and
sodium carbonate),27 was carried out using palladium catalysts
containing amines (1–4), imides (5–8) or ammonium (9–10)
ligands (Scheme 4). Catalytic precursor was generated in situ from
palladium acetate and the appropriate ligand. The catalytic results
are summarized in Table 1.
Fig. 1 Amines (1–4), imides (5–8) and ammonium (9 and 10) ligands
derived from endo-carbic anhydride.
Results and discussion
Synthesis of ligands
Imides 5–8 (Fig. 1) were prepared by condensation of endo-
norborn-5-ene-2,3-dicarboxylic anhydride with the appropriated
primary amine in toluene at reflux (Scheme 1), based on the
methodology described in the literature.23
Scheme 4 Pd-catalyzed C–C coupling between bromobenzene and
phenylboronic acid (L = 1–10).
The best results (up to 98% isolated yield in biphenyl) were
obtained using amines functionalized by hydroxy groups, ligands
2 and 3 (entries 2 and 3, Table 1). The corresponding amide
systems, 6 and 7, and ammonium derivatives, 9 and 10, were less
efficient (entries 6, 7 and 9, 10 respectively, Table 1), with yields
in the 27–48% range, due to the loss of electron-donor character
Table 1 Suzuki C–C coupling of bromobenzene with phenylboronic acid
catalyzed by palladium acetate containing amines (1–4), imides (5–8) and
ammonium (9–10) derivatives (Scheme 4)a
Entry
Ligand
Yield of isolated product (%)
Scheme 1 Synthesis of imides 5–8.
1
2
3
4
5
6
7
8
9
1
28
83b
98
5
24
34
48
43
27
46
1
The corresponding amines, 1–4, were obtained by standard re-
duction of carbonyl groups with LiAlH4,24 from the corresponding
isolated imides (Scheme 2).
2
3
4
5
6
7
8
9
10
11
10
TMEDA
a Reaction conditions: Pd : L : bromobenzene : phenylboronic acid : sodium
carbonate = 2.5 : 6.25 : 100 : 120 : 250 mmol in 1 cm3 of [BMI][PF6] and
2 cm3 of water at 110 ◦C during 24 h; all reactions in duplicate. b Under
the same conditions but not using deoxygenated water, the yield was 60%.
Scheme 2 Synthesis of amines 1–4.
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Table 3 Effect of the solvent in Suzuki C–C coupling of bromobenzene
with phenylboronic acid catalyzed by palladium acetate containing ligands
3 and 4a
of the heterocyclic nitrogen atom. But for mono- or bis-amine
systems, ligands 1 and 4 respectively, the yields were very low, in
particular for 4 (entries 1 and 4, Table 1); for this latter system,
the yellow colour of the ionic liquid phase remained after the
reaction time, in contrast to the black colour observed for the
other systems. In order to confirm this behaviour, the symmetrical
bis(amine) N,N,NꢀNꢀ-tetramethylethane-1,2-diamine (TMEDA)
was also tested, leading to an inactive catalytic system (entry 11,
Table 1), analogous to that observed for 4 (entry 4, Table 1).
This lack of activity could be due to the formation of stable
palladium(II) complexes containing bidentate coordinated ligands,
which do not evolve towards Pd(0) active species.
Yield of isolated
Entry
Ligand Solvent
t/h T/◦C product (%)
1
2
3
4
5
6b
3
3
3
4
4
3
[BMI][PF6]–H2O
1
1
6
6
6
60
60
100
100
100
60
93
0
36
57
4
Toluene–H2O
Toluene–H2O
Toluene–H2O
[BMI][PF6]–H2O
Neat H2O
24
50
a Reaction conditions: Pd : L : bromobenzene : phenylboronic acid : sodium
carbonate = 1 : 1.2 : 100 : 120 : 250 mmol in 1 cm3 of [BMI][PF6] or toluene
and 2 cm3 of water; all reactions in duplicate. b Catalytic reaction in 3 cm3
of water.
From these preliminary results, we can prove the crucial role of
hydroxy groups together with a heterocyclic amine moiety, to give
active palladium catalysts in ionic liquid.28
It is also important to underline the inhibitor effect of oxygen.
The product yield diminishes when water is not deoxygenated, as
indicated for the Pd/2 system (entry 2, Table 1).
With the best catalytic system, Pd/3, temperature, palladium
content, palladium : ligand ratio and reaction time, were optimized
for the model coupling reaction (Scheme 4). The results are shown
in Table 2.
phase to the organic phase at low substrate conversions (63 ppm,
entry 8 in Table 2), but less than 10 ppm for quantitative yields
(entry 8, Table 4). A similar trend was observed for Heck reactions
using both palladium heterogeneous catalyst precursors29 and
preformed nanoparticles;14a in the latter case, it was proposed that
palladium nanoparticles act as a reservoir of catalytically active
molecular species.
Although the system was even active at room temperature
(entry 3, Table 2), the reaction rate decreased notably below 60 ◦C
(entries 1–3, Table 2). The kinetics is probably due to the required
time to form the catalytic active species. Palladium loading (entries
1, 4 and 5, Table 2) and Pd : ligand ratio (entries 4 and 6, Table 2)
adjusments led to an excellent catalytic system working at 1 mol%
of palladium with a 1 : 1.2 Pd : 3 ratio (entry 6, Table 2).
Remarkably high rates were observed at short reaction times
(entry 8 vs. 6 and 7, Table 2). The ligand-free system (if acetate is
not considered) gave a low yield in biphenyl (entry 9, Table 2).
Under the optimized conditions (entry 6, Table 2) and after
1 h of reaction, 1 mmol of substrate was added to the catalytic
mixture, obtaining in this second run 70% yield in biphenyl. This
fact shows that the catalytic system is still active after the first run.
The palladium content in biphenyl was determined by ICP-MS
for the isolated product obtained under optimized conditions at
different reaction times (60, 30 and 10 minutes; see entries 6–8 in
Table 2). The palladium content diminution with the conversion
increase shows a notary metal leaching from the ionic liquid
The requirement to employ well-adapted ligands to the medium
could be demonstrated by the cross-coupling reactions in toluene
and [BMI][PF6], with Pd(OAc)2/3 and Pd(OAc)2/4 as catalytic
systems (Table 3). While Pd/3 behaved as an outstanding system
in ionic liquid (entry 1, Table 3), no activity was observed under
the same conditions in toluene (entry 2, Table 3); the expected
product was only obtained at harsh conditions but in low yield
(entry 3, Table 3). On the contrary, Pd/4 was actually active in
toluene (entries 4 vs. 5, Table 3). In addition, when neat water
was used as solvent, the Pd/3 catalytic system was less efficient
(entry 1 vs. 6, Table 3) due to the less effective catalyst stabilization
than that observed under biphasic conditions, [BMI][PF6]–water.
These results together with that observed for TMEDA (entry 11,
Table 1) show that palladium(II) precursors containing a N,N-
bidentate ligand are more robust towards reduction to Pd(0) in
the ionic liquid than in toluene, avoiding the formation of active
Pd(0) species in [BMI][PF6].
Arylbromide and arylboronic acid derivatives bearing func-
tional groups in ortho or para position to bromide and/or
boronic acid moieties, were tested using our best catalytic system
(Pd(OAc)2/3) under the optimized conditions (Scheme 5), to
give mono- or di-substituted biaryl products. The results are
summarized in Table 4.
Table 2 Suzuki C–C coupling of bromobenzene with phenylboronic acid
catalyzed by palladium acetate containing ligand 3a
Yield of isolated
product (%)
Entry Pd/mol% L/mol% T/◦C t/min
1
2
3
4
5
6
7
8
9
2.5
2.5
2.5
1
0.25
1
1
1
1
6.25
6.25
6.25
2.5
0.625
1.2
1.2
1.2
0
60
50
rt
60
60
60
60
60
60
60
60
98
29
5760 (4 d) 87
60
60
60
30
10
60
88
24
93 (27.5)b
84 (40.0)b
56 (63.0)b
46
Scheme 5 Formation of substituted biaryl compounds from mono-sub-
stituted bromobenzene and arylboronic acid derivatives by Pd-catalyzed
cross-coupling.
a Reaction conditions: bromobenzene : phenylboronic acid : sodium
carbonate = 1 : 1.2 : 2.5 mmol in 1 cm3 of [BMI][PF6] and 2 cm3 of water;
all reactions in duplicate. b In brackets, palladium content determined by
ICP-MS (in ppm).
Mono-substituted biaryl compounds. When either methoxy
or trifluoromethyl groups were introduced in the para position
of the bromide substrate, the corresponding mono-substituted
5574 | Dalton Trans., 2007, 5572–5581
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Table 4 Suzuki C–C coupling of substituted-bromobenzene and substituted-phenylboronic acid derivatives catalyzed by palladium acetate containing
ligand 3 (Scheme 5)a
Entry
R1
R2
R3
R4
Conversionb (%)
Yield of cross-coupling product (%)
Products ratioc (cc/by-products)
1
2
3
4
5
6
7
8
9
10
11
12
13
H
H
H
H
CH3
H
H
H
H
CF3
OCH3
H
H
H
H
H
CF3
OCH3
H
H
H
H
H
H
CF3
OCH3
H
H
H
OCH3
CF3
H
100
87
100
100
41
74
69
100
71
99
70
97
>99
87
71
66
41
71
13
100/0
15/1 (cc/hcb)
4/1 (cc/hcb)
7/1 (cc/hcb)
4/1 (cc/hcb)
100/0
1/3 (cc/db)
100/0
15/5/1/2 (cc/hcb/hch/dh)
55/1/1.5 (cc/hcb/hch)
3/1 (cc/hcb)
—
H
CH3
OCH3
H
H
CH3
H
99 (9.5)d
53
95
70
—
—
H
CF3
e
e
H
—
H
H
—
H
—
—
H
100
—
a Reaction conditions: Pd : 3 : arylbromide : arylboronic acid derivative : sodium carbonate = 1 : 1.2 : 100 : 120 : 250 mmol in 1 cm3 of [BMI][PF6] and
2 cm3 of water at 60 ◦C during 1 h; all reactions in duplicate. b Based on arylbromide consumption. c Determined by 1H NMR. Products obtained are
shown in brackets (cc: cross-coupling product; hcb: homocoupling product from arylboronic acid; hch: homocoupling product from arylbromide; db:
deboronation product; dh: dehalogenation product). d In brackets, palladium content determined by ICP-MS (in ppm). e 1-Bromo-2-methylnaphthalene
used as substrate; reaction time: 24 h.
biphenyl compound was obtained in high yield (entries 1 and
2, Table 4), especially for the trifluoromethyl derivative. Attempts
to obtain the same products but starting from the appropriate
boronic acid, led to lower yields in the cross-coupling product.
Formation of the boronic acid homocoupling by-product (entries
3 and 4, Table 4), was particularly significant in the case of 4-
trifluoromethylphenylboronic acid (entry 3, Table 4). In all these
cases, no significant differences due to the electronic character of
the substituents could be observed either in the substrate or in the
boronic acid derivative (entries 1 vs. 2 and 3 vs. 4, Table 4).
When the functionalization was introduced in the ortho posi-
tion, from 2-methylbromobenzene or 2-methylphenylboronic acid
(entries 5 and 6 respectively, Table 4), a significant steric influence
for the substrate (41% yield) but less important for the boronic
acid (71% yield) was observed. In addition, the introduction
of a methoxy group in the ortho position of the boronic acid
caused a dramatic decrease of the yield in cross-coupling product
with important formation of deboronation product (entry 7,
Table 4). Cross-coupling between 1-bromo-2-methylnaphthalene
and phenylboronic acid gave the desired product in 70% yield, with
38% yield of boronic acid homocoupling after 24 h of reaction
(entry 11, Table 4), an analogous trend to that observed for 2-
methylbromobenzene (entry 5, Table 4).
trifluoromethylbromobenzene (entries 1, 8 and 10, Table 4) allows
an activity increase compared with the formation of biphenyl
(entry 6, Table 2). However, the substituents in the ortho position
lead to an activity decrease (entries 5, 6 and 7 Table 4 vs. entry 6
Table 2) due to steric hindrance, except when the activated 4-
trifluoromethylbromobenzene was used as substrate (entry 10,
Table 4); this effect is dramatic when 2-methoxyphenylboronic
acid is used, giving the lowest yield in the cross-coupling product
(entry 7, Table 4).
Concerning chemoselectivity, 4-trifluoromethylbromobenzene
directs the reaction towards the formation of cross-coupling
product (entries 1, 8 and 10, Table 4). However in the other
cases, except for the reaction between bromobenzene and 2-
methylphenylboronic acid (entry 6, Table 4), formation of by-
products (homocoupling, deboronation and dehalogenation prod-
ucts) was observed. Among them, homocoupling from arylboronic
acids was the most important side-reaction, being remarkable
when electron-deactivated boronic acid and/or substrate (entries
2, 3 and 9, Table 4) were involved or sterically hindered substrates
were used (entries 5 and 11, Table 4), most probably due to
its activation towards oxidative addition, in competition with
that of arylbromide substrate. It is important to mention the
coupling between bromobenzene and 2-methoxyphenylboronic
acid, giving as major product the corresponding deboronation
product (entry 7, Table 4). Dehalogenation (entry 9, Table 4) and
homocoupling from substrate were occasionally obtained in low
yield (less than 7%, entries 9 and 10, Table 4).
Di-substituted biaryl compounds. Suzuki C–C cross-coupling
reactions between both substituted-arylbromide and substituted-
arylboronic acid derivatives were also studied. Quantitative
yield was obtained from 4-trifluoromethylbromobenzene and 4-
methoxyphenylboronic acid (entry 8, Table 4). With the same
substrate, the ortho-methyl-substituted boronic acid led to 95%
yield in the cross-coupling product (entry 10, Table 4). In contrast,
the introduction of an electron donating group in the arylbromide
and an electron withdrawing one in the boronic acid led to a
moderate yield in the desired biaryl compound, together with
several by-products (entry 9, Table 4).
Taking into account that 2-methylbromobenzene and 1-bromo-
2-methylnaphthalene with phenylboronic acid (entries 5 and 11
respectively, Table 4), and also 2-methylphenylboronic acid with
bromobenzene (entry 6, Table 4) gave mainly the ortho-substituted
cross-coupling product in moderated yield, we planned to evaluate
the asymmetric induction in Suzuki C–C coupling (Scheme 6). Un-
fortunately, no cross-coupling product was obtained in any case.
Under harsh conditions, only dehalogenation and deboronation
products were obtained in agreement with the reactivity involving
heterogeneous catalysts (see below).
These data clearly show that only the substrate containing the
electron withdrawing trifluoromethyl group in the para position, 4-
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efficient in the presence of oxidants, in particular dioxygen,35 due to
the formation of peroxo-palladium complexes, key intermediates
for this reaction.36
TEM analysis. TEM micrographs of the post-catalysis ionic
liquid phase was carried out for the coupling of bromobenzene
with phenylboronic acid (entry 8, Table 2). In fact, small nanopar-
ticles were observed (ca. mean diameter 8 nm) showing a pile
organization in the ionic liquid (Fig. 2a).
Scheme 6 Asymmetric Suzuki C–C coupling reactions using Pd(OAc)2/3
as catalyst in [BMI][PF6] (Pd : 3 ratio = 1 : 1.2).
Catalyst nature
The remarkable effect observed in terms of catalytic activity
depending on the ligand nature and the solvent involved (see
above) led us to study more carefully the catalyst nature of the
species generated from palladium acetate in [BMI][PF6].
Poison tests. Mercury is a classical test to identify heteroge-
neous catalysts,30 but also other metal(0) species, such as molecular
complexes and colloids, can be identified.31 On the other hand,
Lewis bases represent a tool to identify homogeneous catalysts.32
In our case, addition of mercury (for a typical procedure,
see Experimental section), after 10 min of reaction between
bromobenzene and phenylboronic acid (at this time, conversion
is ca. 60%), quenched the reaction; only 68% yield was obtained
after 1 h in contrast to that obtained without mercury (93%, entry 6
in Table 2). This result reveals that Pd(0) species (molecular or
heterogeneous) are involved in the catalytic process.
On the other hand, triphenylphosphine was added to the
catalytic reaction in two different Pd : PPh3 ratios, 1 : 0.3 and
1 : 4 (for a typical procedure, see Experimental section). In both
cases, the reaction was inhibited (after 1 h, 75% and 55% yield
were respectively obtained for 1 : 0.3 and 1 : 4 Pd : PPh3 ratio),
the reaction being completely stopped for Pd : PPh3 = 1 : 4. It is
important to mention that using Pd(OAc)2 : PPh3 (1 : 2) as catalytic
precursor gave 65% yield, under our optimized conditions. This
behaviour is in agreement with that observed for molecular
palladium/mono(phosphine) systems in organic solvents, the
optimum Pd : P ratio being 1 : 1; higher phosphine contents
lead to less active systems for the most cases.33 But it also agrees
with the reported induction period observed for Heck couplings
using triphenylphosphine and palladium acetate as precursors of
nanoparticles in ionic liquids.34 Therefore, these results point to
the presence of catalytically active molecular species.
Fig. 2 TEM micrographs of: a) post-catalytic solution using Pd(OAc)2/3
as catalyst (see entry 7 in Table 2) and b) the corresponding size histogram
(90 nanoparticles measured); c) preformed Pd3 nanoparticles dispersed in
[BMI][PF6].
In order to compare the catalytic behaviour of the particles
generated under catalytic conditions with that observed using pre-
formed material, palladium nanoparticles were prepared following
the methodology previously described.20,37 Pd3 nanoparticles were
synthesised from palladium acetate in the presence of ligand
3 under a hydrogen atmosphere in [BMI][PF6] (Scheme 7).
TEM images essentially revealed the formation of agglomerates
(Fig. 2c).
It is also important to underline the inhibitor effect of oxygen.
As described above, the product yield diminishes when solvents
are not deoxygenated. This trend cannot be justified in terms of
homogeneous palladium catalysts. Homocoupling of arylboronic
acids (in our case, this would increase the yield in biphenyl) is more
Pd3 was used as catalytic precursor in the cross-coupling
catalytic reaction between bromobenzene and phenylboronic acid
(110 ◦C, 24 h, 2.5 mol% Pd). The low yield obtained (52%) is
in agreement with the agglomerated material used in comparison
with that formed during the catalytic reaction (Fig. 2a), as found
5576 | Dalton Trans., 2007, 5572–5581
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©

Conclusions
The most important conclusion of this work concerns the effect of
the solvent together with the ligand nature in the catalytic activity
for Suzuki C–C coupling. While in organic solvents, homogeneous
catalytic species are stable enough in the presence of good donor
ligands, as for bidentate nitrogen donor ligands (otherwise inactive
agglomerates are formed), in ionic liquids, palladium systems
are only active when nanoparticles are formed in situ. In this
latter case, the presence of ligands containing hydroxy groups
enhances the stability of the metallic nanoparticles. The formation
of palladium(II) molecular precursors in [BMI][PF6] prevents the
formation of Pd(0) species and consequently the catalytic system
becomes inactive.
Concerning the nature of the catalyst in [BMI][PF6] from palla-
dium acetate, poison tests reveal that Pd(0) species are involved in
the catalytic process. Formation of PdNPs in [BMI][PF6] (exhib-
ited by TEM analysis) is required to give an active catalytic system.
These particles are catalytically active towards dehalogenation
and deboronation of the corresponding aryl compounds and we
cannot exclude their role in the C–C coupling processes, in view
of the homocoupling observed in many cases.
Scheme 7 Synthesis of palladium nanoparticles containing ligand 3.
by Narayanan and El-Sayed for Suzuki reactions using palladium
nanoparticles stabilized by polyvinylpyrrolidone.38 However the
system was more active when 4-methoxybromobenzene was
used as substrate, giving 70% yield of cross-coupling product
(Scheme 8), the opposite trend to that found for the catalyst using
palladium acetate as precursor (93%, entry 6 in Table 2, vs. 87%,
entry 2 in Table 4), indicating, in the latter case, the presence of
molecular species.
Therefore, the mechanism proposed for Pd-catalyzed Heck C–
C coupling where palladium nanoparticles act as a reservoir of
active molecular species,13 seems to be also reasonable for Suzuki
coupling, although the catalytic activity of nanoparticles cannot
be excluded at this time.
Scheme 8 Suzuki cross-coupling catalyzed by preformed palladium
nanoparticles containing ligand 3.
More detailed studies are currently in progress in order to shed
light on the interactions between ligand and metallic surface.
In order to check whether nanoparticles are formed from N-
heterocyclic palladium complexes,31a,39 Pd(OAc)2 and [BMI][PF6]
were mixed at room temperature and at 110 ◦C for 24 h. In any case,
1
a N-heterocyclic carbene palladium complex was formed as H
Experimental
and 13C NMR monitoring revealed, in contrast to what was found
by Xiao and co-workers using [BMI][Br],40 probably due to the
poor coordinating ability of the hexafluorophosphate anion. This
experiment rules out the formation of palladium nanoparticles
from carbene intermediates, but it does not exclude the formation
of carbenes at the metallic surface when nanoparticles are
present.41
General
All compounds were prepared under a purified nitrogen or argon
atmosphere using standard Schlenk and vacuum-line techniques.
The organic solvents were purified by standard procedures and
distilled under nitrogen. ILs were supplied by Solvionic (99.5+%;
chloride contents certified to <1 ppm). ILs were treated under
◦
Catalytic selectivity. Reactivity patterns, mainly concerning
hydrogenation, have been used to distinguish between homoge-
neous and heterogeneous catalysts, although it is really difficult to
find reactions that solely work with homogeneous and not hetero-
geneous catalysts, and vice versa.32 But not only the (in)activity
may suggest the identity of the catalyst. Recent reported cases
point to a distinction taking into account the selectivity trend, in
particular concerning the asymmetric induction.19,42
Chemoselectivity for Heck and Suzuki couplings could also
be a useful tool in discussing the nature of the catalyst, taking
into account the fact that homocoupling, dehalogenation and de-
boronation reactions of aryl derivatives are typically catalyzed by
heterogeneous palladium species.43,44 In our case, homocoupling
side products were obtained in many cross-coupling reactions
(see Table 4); in addition, bromobenzene in the absence of
phenylboronic acid and phenylboronic acid in the absence of
bromobenzene gave quantitative debromination and deborona-
tion products respectively, without formation of homo-coupling
product (entries 12 and 13, Table 4). These facts suggest that in situ
generated PdNPs are responsible for this reactivity.
reduced pressure at 70 C overnight prior to use. NMR spectra
were recorded on Varian Bruker DRX 500 (1H, standard SiMe4),
Varian Gemini (13C, 50 MHz, standard SiMe4) and Bruker DRX
250 (31P, 101.2 MHz, standard H3PO4) spectrometers in CDCl3
unless otherwise cited. Chemical shifts were reported downfield
from standards. IR spectra were recorded on a FTIR Nicolet
Impact 400 spectrometer. Mass chromatograms were carried out
by the “Servei dꢀEspectrometria de Masses” of the Universitat
de Barcelona (Chemical ionization on a ThermoFinnigan Trace
DSQ instrument using methane or ammonia as reactant gas;
electronic impact on a Hewlett Packard 5989A apparatus and
electrospray on a ZQ (Micromass, UK) instrument). Optical
rotations were measured in a Perkin Elmer 241MC polarimeter.
Elemental analyses were carried out by the “Serveis Cientifico-
Te`cnics” of the Universitat Rovira i Virgili (Tarragona) on an
Eager 1108 microanalyzer. The elemental analysis of palladium
was determined by ICP-MS and carried out by Antellis. The
images of particles dispersed in [BMI][PF6] were obtained from
a transmission electron microscope running at 120 kV. A drop of
solution was deposited on a holey carbon grid and the excess
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 5572–5581 | 5577
©

of [BMI][PF6] was removed in order to obtain a film as thin
as possible. Images were recorded on the film of IL lying on
the holes of the grid. The size of the nanoparticles was directly
determined from TEM images recorded with a high magnification
(>500 000). Due to the overlapping of nanoparticles, the diameter
was individually measured on particles at the boundary of
agglomerates.
mmax(KBr pellet)/cm−1 3447 (OH), 2994, 2975, 1676 (CO), 1394,
1368, 1294, 1262, 1184, 1085, 1057, 1019, 1007, 803, 764, 698, 663
and 620; dH(400 MHz; CDCl3; Me4Si) 1.45 (1 H, d, J 8.8, CHHꢀ
bridge), 1.63 (1 H, d, J 8.8, CHHꢀ bridge), 3.16–3.20 (2 H, m, 2 ×
CHolefinCHCH2 bridge), 3.25–3.27 (2 H, m, 2 × CHCON), 3.80
(1 H, dd, J 6.8 and 12.0, CHHꢀCHCHPh), 3.87 (1 H, dd, J 5.2
and 12.0, CHHꢀCHCHPh), 4.59 (1 H, q, J 6.0, CHHꢀCHCHPh),
ꢀ
ꢀ
=
5.20 (1 H, d, J 6.0, CHH CHCHPh), 5.58 (1 H, br s, CH CH ),
ꢀ
=
5.67 (1 H, br s, CH CH ) and 7.23–7.36 (5 H, m, Ph); dC(100 MHz;
Synthesis of ligands
CDCl3; Me4Si) 43.1 (CH), 43.2 (CH), 43.9 (CH), 44.2 (CH), 50.5
(CH2), 56.8 (CH2), 59.5 (CH), 69.8 (CH) 123.7 (2 × CH), 125.9
(CH), 126.7 (2 × CH), 132.4 (CH), 132.5 (CH), 138.9 (C), 179.0
General procedure for the synthesis of endo-bicyclo[2.2.1]hept-
5-en-2,3-dicarboximides (5–8). endo-Norborn-5-ene-2,3-dicar-
boxylic anhydride (1.64 g, 10.0 mmol) was dissolved in distilled
toluene (50 cm3) and the resulting suspension was vigorously
stirred until total dissolution. The appropriate primary amine
(15.0 mmol) was added dropwise and a yellowish suspension
was immediately formed. The mixture was heated at 80 ◦C and
allowed to stir for 24 or 48 h. The cooled colourless solution was
concentrated under vacuum, giving a white oil which was then
dissolved in dichloromethane (20 cm3) and consecutively washed
with 1 M H2SO4 (3 × 20 cm3) and water (3 × 20 cm3). The
aqueous phases were washed with 20 cm3 of dichloromethane.
The combined organic phases were dried with anhydrous Na2SO4,
filtered and the solvent evaporated under reduced pressure,
yielding the corresponding imide.
(CO) and 179.4 (CO); m/z (EI) 314 (M+. C18H19NO4 requires
+
313.4).
Imide 8. Obtained from N,N-dimethylethylenediamine (1.32 g,
15.0 mmol). Product obtained as a white solid (2.01 g, 86%)
(Found: C, 66.6; H, 7.9; N, 11.7. Calc. for C13H18N2O2: C, 66.6; H,
7.7; N, 12.0%); mmax(KBr pellet)/cm−1 2989, 2946, 2791, 1699 (CO),
1395, 1340, 1227, 1152, 1045, 1000, 914, 842 and 722; dH(400 MHz;
CDCl3; Me4Si) 1.52 (1 H, d, J 8.4, CHHꢀ bridge), 1.71 (1 H,
d, J 8.4, CHHꢀ bridge), 2.22 (6 H, s, 2 × CH3), 2.33 (2 H, t,
J 6.9, CH2CH2NMe2), 3.24–3.26 (2 H, m, 2 × CHolefinCHCH2
bridge), 3.36–3.38 (2 H, m, 2 × CHCON), 3.44 (2 H, t, J 6.9,
=
CH2CH2NMe2) and 6.07 (2 H, br t, J 1.8, CH CH); dC(100 MHz;
CDCl3; Me4Si) 36.2 (CH2), 44.95 (2 × CH), 45.4 (2 × CH3), 45.9
Imide 5. Obtained from (S)-1-phenylethylamine (1.82 g,
15.0 mmol). The crude product was recrystallized in a mixture
of hexane–ethyl acetate (5 : 1), giving a white solid (2.43 g,
(2 × CH), 52.2 (CH2), 56.3 (CH2), 134.5 (2 × CH) and 177.8 (2 ×
CO); m/z (EI) 234 (M+. C13H18N2O2 requires 234.3).
+
91%). [a]D +72.4◦ (c 1.0 in CHCl3); mmax(KBr pellet)/cm−1 3065
25
General procedure for the synthesis of endo-4-aza-tricyclo-
[5.2.1.02.6]dec-8-enes (1–4). The corresponding imide (6.0 mmol)
was dissolved in freshly distilled THF (100 cm3) and stirred until
total dissolution. The solution was cooled at 0 ◦C and LiAlH4
(2.28 g, 60.0 mmol) was slowly added, giving a white suspension.
The mixture was heated at reflux for 48 h, then cooled at 0 ◦C.
20 cm3 of diethyl ether and a saturated aqueous solution of Na2SO4
were added. The addition of the aqueous solution was slowly
performed and was stopped when effervescence was no longer
observed in the reaction mixture. The white gel was then filtered
over Celite and the solution obtained was washed several times
with a mixture of CH2Cl2–MeOH (9 : 1). The organic phase
was washed with water (3 × 20 cm3), dried with anhydrous
Na2SO4, filtered and concentrated at reduced pressure, yielding
the corresponding amine.
=
( CH), 3000, 2943, 2874, 1761 (CO), 1696 (CO), 1387, 1365, 1217,
1196, 1109, 1022, 739, 726 and 700; dH(400 MHz; CDCl3; Me4Si)
1.47 (1 H, d, J 8.4, CHHꢀ bridge), 1.65 (1 H, d, J 8.0, CHHꢀ
bridge), 1.68 (3 H, d, J 7.5, CHCH3Ph), 3.12–3.19 (2 H, m, 2 ×
CHolefinCHCH2bridge), 3.33 (2 H, br d, J 9.3, 2 × CHCON), 5.24
ꢀ
=
(1 H, q, J 7.5, CHMePh), 5.85 (1 H, dd, J 2.9 and 5.6, CH CH ),
ꢀ
=
6.00 (1 H, dd, J 2.9 and 5.6, CH CH ) and 7.22–7.36 (5 H, m,
CHMePh); dC(100 MHz; CDCl3; Me4Si) 16.5 (CH3), 45.2 (CH),
45.3 (CH), 45.35 (CH), 45.4 (CH), 49.8 (CH), 52.1 (CH2), 127.2–
128.2 (5 × CH), 134.4 (CH), 139.7 (C), 177.6 (CO) and 177.6 (CO);
m/z (CI, CH4) 268.3 (M + H+. C17H18NO2 requires 268.3).
+
Imide 6. Obtained from (R)-2-aminobutanol (1.34 g,
15.0 mmol). Product obtained as a colourless oil (2.24 g, 95%).
[a]D +12.2◦ (c 1.0 in CHCl3); mmax(NaCl film)/cm−1 3435 (OH),
25
=
2967 ( CH), 2937, 2874, 1765, 1692 (CO), 1456, 1396, 1373,
1297, 1190, 1131, 1068, 842 and 719; dH(400 MHz; CDCl3; Me4Si)
0.83 (3 H, t, J 7.5, NCHCH2CH3), 1.52 (1 H, d, J 8.7, CHHꢀ
bridge), 1.60–1.72 (2 H, m, NCHCH2CH3), 1.70 (1 H, d, J
8.7, CHHꢀ bridge), 2.77 (1 H, br s, OH), 3.22–3.24 (2 H, m,
2 × CHolefinCHCH2bridge), 3.34 (2 H, br s, 2 × CHCON), 3.60
(1 H, dd, J 3.0 and 11.7, CHCHHꢀOH), 3.79 (1 H, dd, J 7.1
Amine 1. Obtained from 5 (1.60 g, 6.0 mmol). Product obtained
as a yellow oil (1.26 g, 88%). [a]D +68.5◦ (c 1.0 in CHCl3);
25
mmax(NaCl film)/cm−1 3060, 2967, 2864, 2798, 1489, 1453, 1370,
1307, 1137, 958, 762, 735 and 699; dH(400 MHz; CDCl3; Me4Si)
1.28 (3 H, d, J 6.8, CHCH3Ph), 1.50 (1 H, d, J 8.0, CHHꢀ bridge),
1.63 (1 H, dt, J 1.8 and 8.4, CHHꢀ bridge), 1.80 (1 H, dd, J 7.4 and
9.4, CHCHHꢀN), 1.88 (1 H, dd, J 7.0 and 8.6, CHCHHꢀN), 2.51
(1 H, t, J 8.6, CHCHHꢀN), 2.70 (1 H, br s, CHolefinCHCH2 bridge),
2.76–2.84 (1 H, m, CHCHHꢀN), 2.79 (1 H, br s, CHolefinCHCH2
bridge), 2.88–2.95 (1 H, m, CHCHHꢀN), 2.98 (1 H, t, J 8.2,
CHCHHꢀN), 3.12 (1 H, q, J 6.7, CHMePh), 6.09–6.14 (2 H, m,
and 11.6, CHCHHꢀOH), 3.84–3.91 (1 H, m, J 1.2, 3.0 and 7.1,
CHCHH OH) and 6.11 (2 H, br s, CH CH); dC(100 MHz; CDCl3;
Me4Si) 10.5 (CH3), 21.0 (CH2), 45.05 (CH), 45.1 (CH), 45.45 (CH),
45.6 (CH), 52.1 (CH2), 55.8 (CH), 62.4 (CH2), 134.5 (CH), 134.6
(CH), 177.6 (CO) and 178.6 (CO); m/z (CI, CH4) 236.3 (M + H+.
ꢀ
=
+
C13H18NO3 requires 236.3).
=
CH CH), 7.17–7.23 (1 H, m, Ph) and 7.25–7.27 (4 H, m, Ph);
Imide 7. Obtained from (1S,2S)-2-amino-1-phenyl-1,3-pro-
dC(100 MHz; CDCl3; Me4Si) 23.0 (CH3), 44.9 (CH), 45.0 (CH),
46.3 (CH), 46.4 (CH), 53.7 (CH2), 55.7 (CH2), 56.0 (CH2), 66.0
(CH), 126.9 (CH), 127.3 (2 × CH), 128.3 (2 × CH), 137.1 (CH),
panediol (2.51 g, 15.0 mmol). Product obtained as a white
crystalline solid (2.76 g, 88%). [a]D +10.0◦ (c 1.0 in CHCl3);
25
5578 | Dalton Trans., 2007, 5572–5581
This journal is
The Royal Society of Chemistry 2007
©

137.5 (CH) and 145.7 (C); m/z (ESI(+)) 240 (M + H+. C17H22N+
requires 240.2).
methanesulfonyl)imide (2.47 g, 8.6 mmol) was added to the
solution. The mixture was stirred for 48 h at room temperature and
a white suspension was formed. Salts were removed upon filtration,
and the solution was washed with water (3 × 20 cm3). The organic
phase was dried with anhydrous Na2SO4, filtered and concentrated
under reduced pressure◦to give the product as a colourless oil
(1.27 g, 88%). [a]D25 +0.5 (c 0.95 in CHCl3); mmax(NaCl film)/cm−1
3532, 2977, 2944, 2884, 1473, 1350, 1194, 1134, 1054, 789 and 739;
dH(400 MHz; CDCl3; Me4Si) 1.04 (3 H, t, J 7.4, NCHCHHꢀCH3),
1.68–1.73 (1 H, m, NCHCHHꢀCH3), 1.72 (1 H, d, J 8.8, CHHꢀ
bridge), 1.81–1.87 (1 H, m, NCHCHHꢀCH3), 1.89 (1 H, dt, J 1.6
and 8.8, CHHꢀ bridge), 2.53 (1 H, t, J 10.4, CHCHHꢀN), 2.70 (1 H,
t, J 10.6, CHCHHꢀN), 3.01 (2 H, br s, 2 × CHolefinCHCH2bridge),
3.01–3.06 (1 H, m, CHCHHꢀOH), 3.04 (3 H, s, NCH3), 3.14–
3.27 (2 H, m, 2 × CHCHHꢀN), 3.68 (1 H, dd, J 7.6 and 11.6,
CHCHHꢀN), 3.85 (1 H, dd, J 7.6 and 13.2, CHCHHꢀN), 3.89 (1 H,
d, J 14.0, CHCHHꢀOH), 4.04 (1 H, d, J 14.0, CHCHHꢀOH) and
Amine 2. Obtained from 6 (1.41 g, 6.0 mmol). Product obtained
as a yellow oil (1.02 g, 82%). [a]D −28.8◦ (c 0.93 in CHCl3);
25
mmax(NaCl film)/cm−1 3396 (OH), 3060, 2957, 2874, 2818, 1463,
1346, 1111, 1054 and 729; dH(400 MHz; CDCl3; Me4Si) 0.86 (3 H, t,
J 7.6, NCHCHHꢀCH3), 1.18–1.26 (1 H, m, NCHCHHꢀCH3), 1.42
(1 H, d, J 8.0, CHHꢀ bridge), 1.49–1.56 (1 H, m, NCHCHHꢀCH3),
1.53 (1 H, d, J 8.4, CHHꢀ bridge), 2.29–2.32 (2 H, m, 2 ×
CHCHHꢀN), 2.36–2.42 (1 H, m, CHCHHꢀOH), 2.63 (1 H, t,
J 8.2, CHCHHꢀN), 2.74–2.81 (3 H, m, CHCHHꢀN and 2 ×
CHolefinCHCH2bridge), 2.83 (2 H, br s, 2 × CHCHHꢀN), 3.18
(1 H, dd, J 8.0 and 10.4, CHCHHꢀOH), 3.52 (1 H, dd, J 4.8 and
ꢀ
=
10.4, CHCHH OH) and 6.20 (2 H, br s, CH CH); dC(100 MHz;
CDCl3; Me4Si) 11.3 (CH3), 19.3 (CH2), 45.2 (CH), 45.3 (CH), 45.8
(CH), 45.9 (CH), 50.3 (CH2), 52.3 (CH2), 52.9 (CH2), 60.8 (CH2),
63.3 (CH), 136.3 (CH) and 136.5 (CH); m/z (ESI(+)) 208 (M +
H+. C13H22NO+ requires 208.2).
=
6.33–6.38 (2 H, m, CH CH); dC(100 MHz; CDCl3; Me4Si) 11.0
(CH3), 19.3 (CH2), 44.0 (CH), 44.6 (CH), 44.7 (CH), 46.3 (CH3),
54.2 (CH2), 58.5 (CH2), 67.4 (CH2), 67.6 (CH2), 77.8 (CH), 119.9
(2 × CF3, q, J 319.2), 137.3 (CH) and 137.8 (CH); m/z (ESI(+))
222.3 (M+. C14H24NO+ requires 222.2); m/z (ESI(−)) 280.1 (M−.
Amine 3. Obtained from 7 (1.88 g, 6.0 mmol). Product obtained
as a yellowish solid (1.66 g, 97%). [a]D +58.1◦ (c 1.0 in CHCl3)
25
(Found: C, 75.0; H, 8.3; N, 5.0. Calc. for C18H23NO2: C, 75.7; H,
8.1; N, 4.9%); mmax(NaCl film)/cm−1 3379 (OH), 2957, 1453, 1350,
1130, 1054 and 699; dH(400 MHz; CDCl3; Me4Si) 1.42 (1 H, d,
J 8.0, CHHꢀ bridge), 1.52 (1 H, d, J 8.0, CHHꢀ bridge), 2.53–
2.59 (2 H, m, 2 × CHCHHꢀN), 2.71–2.91 (6 H, m, CHCHHꢀN,
CHHꢀCHCHPh, 2 × CHCHHꢀN and 2 × CHolefinCHCH2 bridge),
2.99 (1 H, t, J 8.0, CHCHHꢀN), 3.42 (1 H, dd, J 4.4 and 11.4,
−
C2F6NO4S2 requires 279.9).
Ionic ligand 10. Amine 3 (700 mg, 2.45 mmol) was dissolved in
10 cm3 of methanol and methyl iodide (1.74 g, 12.3 mmol) was
added to the solution. The mixture was allowed to stir at room
temperature overnight and the solvent was then removed under
reduced pressure. The yellowish solid obta◦ined was recrystallyzed
from a MeOH–Et2O (1 : 2) mixture at 4 C, yielding the iodide
ionic derivative as a white solid (720 mg, 69%).
CHHꢀCHCHPh), 3.52 (1 H, dd, J 7.2 and 11.4, CHHꢀCHCHPh),
ꢀ
=
4.36 (1 H, d, J 9.2, CHH CHCHPh), 6.29 (2 H, s, CH CH) and
7.25–7.35 (5 H, m, Ph); dC(100 MHz; CDCl3; Me4Si) 45.0 (CH),
45.3 (CH), 46.5 (CH), 46.5 (CH), 49.9 (CH2), 52.5 (CH2), 52.7
(CH2), 59.5 (CH2), 66.8 (CH), 72.2 (CH), 127.1 (2 × CH), 128.1
(CH), 128.7 (2 × CH), 136.3 (CH), 136.5 (CH) and 142.5 (C); m/z
The iodide ionic derivative (714 mg, 1.3 mmol) was dissolved
in 1 cm3 of methanol and then 20 cm3 of dichloromethane and
lithium bis(trifluoromethanesulfonyl)imide (1.5 g, 5.15 mmol)
were added to the solution. The mixture was allowed to stir
at room temperature for 24 h and the solvent was evaporated,
obtaining a yellow oil. Salts were precipitated from a MeOH–
Et2O (1 : 2) mixture and then removed by filtration. The solvent
was evaporated under reduced pressure to give the product as
(CI, NH3) 286.6 (M + H+. C18H24NO2 requires 286.4).
+
Amine 4. Obtained from 8 (1.41 g, 6.0 mmol). Product obtained
as a pale brown oil (1.03 g, 83%). mmax(NaCl film)/cm−1 3402,
2964, 2868, 2818, 1649, 1453, 1340, 1254, 1137, 1041 and 729;
dH(400 MHz; CDCl3; Me4Si) 1.57 (1 H, br d, J 8.0, CHHꢀ bridge),
1.69 (1 H, br dt, J 1.6 and 8.0, CHHꢀ bridge), 1.83 (2 H, br s,
2 × CHCHHꢀN), 2.21 (6 H, s, N(CH3)2), 2.36 (2 H, br t, J 7.0,
CH2CH2NMe2), 2.49 (2 H, br td, J 1.2 and 7.1, CH2CH2NMe2),
2.78 (2 H, br s, 2 × CHolefinCHCH2 bridge), 2.93 (4 H, br s,
2 × CHCHHꢀN and 2 × CHCHHꢀN) and 6.12 (2 H, t, J 1.6,
a yellow oil (909 mg, 93%). [a]D +14.7◦ (c 1.0 in MeOH);
25
mmax(NaCl film)/cm−1 3571 (OH), 1652, 1635, 1349, 1203, 1132,
1058, 798 and 745; dH(400 MHz; CD3OD; Me4Si) 1.80 (1 H, d,
J 8.4, CHHꢀ bridge), 1.90 (1 H, dt, J 2.0 and 8.4, CHHꢀ bridge),
2.80 (1 H, t, J 11.0, CHCHHꢀN), 2.95–3.03 (3 H, m, CHCHHꢀN
and 2 × CHCHHꢀN), 3.24–3.41 (4 H, m, 2 × CHCHHꢀN and
2 × CHolefinCHCH2bridge), 3.45 (3 H, s, NCH3), 3.53 (1 H, dd,
J 7.2 and 12.0, CHHꢀCHCHPh), 3.89 (1 H, dd, J 2.0 and 12.0,
CHHꢀCHCHPh), 4.44 (1 H, dd, J 7.4 and 10.4, CHHꢀCHCHPh),
5.27 (1 H, d, J 10.4, CHHꢀCHCHPh), 6.38 (1 H, dd, J 3.0 and 6.0,
=
CH CH); dC(100 MHz; CDCl3; Me4Si) 44.6 (2 × CH), 46.0 (2 ×
CH3), 46.7 (2 × CH), 53.9 (CH2), 54.4 (CH2), 57.3 (2 × CH2), 58.5
(CH2) and 137.4 (2 × CH); m/z (EI) 206.0 (M. C13H22N2+ requires
206.2).
Synthesis of endo-N-methyl-(4-aza-tricyclo[5.2.1.02.6]dec-8-enyl)
bis(trifluoromethanesulfonyl)imides (9, 10).
ꢀ
ꢀ
=
=
CH CH ), 6.41 (1 H, dd, J 3.0 and 6.0, CH CH ) and 7.25–7.40
(5 H, m, Ph); dC(100 MHz; CD3OD; Me4Si) 43.0 (CH), 44.5 (2 ×
CH), 45.1 (CH), 46.6 (CH3), 53.6 (CH2), 58.6 (CH2), 66.7 (CH2),
70.9 (CH), 71.3 (CH2), 79.0 (CH), 120.0 (2 × CF3, q, J 317.5),
127.4 (2 × CH), 128.65 (3 × CH), 137.1 (CH), 137.3 (CH) and
Ionic ligand 9. Amine 2 (1.00 g, 4.8 mmol) was dissolved
in 50 cm3 of methanol and methyl iodide (3.42 g, 24.1 mmol)
was added to the solution. The mixture was stirred at room
temperature for 48 h and the solvent was then removed under
reduced pressure. The white foam obtained was recrystallyzed
from a MeOH–Et2O (1 : 5) mixture at 4 ◦C, giving the iodide
ionic derivative as a white solid (1.39 g, 82%).
141.6 (C); m/z (ESI(+)) 300.3 (M+. C19H26NO2 requires 300.2);
+
−
m/z (ESI(−)) 280.1 (M−. C2F6NO4S2 requires 279.9).
Synthesis of palladium nanoparticles, Pd3
The iodide ionic derivative (1.00 g, 2.9 mmol) was dis-
solved in 50 cm3 of dichloromethane and lithium bis(trifluoro-
Palladium acetate (22.4 mg, 0.1 mmol) and ligand 3 (5.7 mg,
0.02 mmol) were placed in a Fisher–Porter bottle and dissolved
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 5572–5581 | 5579
©

in 4 cm3 of [BMI][PF6]. The brown mixture was stirred under
vacuum at room temperature for 1 h and the bottle was then
filled with 1 bar pressure of hydrogen. After 20 min of reaction,
the solution blackened and it was stirred for one additional hour
before removing the hydrogen under reduced pressure. The black
suspension was stored under an inert argon atmosphere.
General procedure for poison tests in [BMI][PF6]
The experimental procedure used for the poison tests was anal-
ogous to that described for the standard molecular conditions,
adding the poison (Hg: 200.6 mg, 1 mmol; PPh3: 0.8 mg, 3 ×
10−3 mmol or 10.5 mg, 0.04 mmol depending on the molecular or
colloidal conditions) after 10 min of catalytic reaction at 60 ◦C
and heating at this temperature for 50 additional min after poison
addition.
General procedure for catalytic Suzuki C–C coupling in
[BMI][PF6]
Acknowledgements
Coupling using palladium acetate as catalytic precursor. Note:
for simplicity reasons, only the experimental procedure of the
catalytic Suzuki C–C coupling under the optimized conditions
is described.
The authors wish to thank the Universite´ Paul Sabatier, CNRS
and Ministerio de Educacio´n y Ciencia (CTQ2004–01546/BQU)
for financial support.
Palladium acetate (2.2 mg, 0.01 mmol) and the corresponding
ligand (0.012 mmol) were dissolved in 1 cm3 of [BMI][PF6]
previously deoxygenated and stirred for 1 h under vacuum at
room temperature, giving a brown or yellow solution. After this
time, the substrate (1.0 mmol), the boronic acid (1.2 mmol) and
Na2CO3 (265.0 mg, 2.5 mmol) dissolved in 2 cm3 of deoxygenated
water were consecutively added, forming a biphasic system. The
mixture was then heated at 60 ◦C during 1 h and then cooled
to room temperature. The catalytic mixture was extracted with
hexane (5 × 10 cm3) and the combined organic phases were dried
with anhydrous Na2SO4, filtered and concentrated under reduced
pressure, yielding the product either as a white solid or as a yellow
oil.
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5580 | Dalton Trans., 2007, 5572–5581
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The Royal Society of Chemistry 2007
Dalton Trans., 2007, 5572–5581 | 5581
©