Recoverable palladium catalysts for Suzuki-Miyaura cross-coupling reactions based on organic-inorganic hybrid silica materials containing imidazolium and dihydroimidazolium salts

Article abstract of DOI:10.1002/adsc.200800455

The systems formed by palladium acetate [Pd(OAc)₂] and hybrid silica materials prepared by sol-gel from monosilylated imidazolium and disilylated dihydroimidazolium salts show catalytic activity in Suzuki-Miyaura cross-couplings with challenging aryl bromides and chlorides. They are very efficient as recoverable catalysts with aryl bromides. Recycling is also possible with aryl chlorides, although with lower conversions. In situ formation of palladium nanoparticles has been observed in recycling experiments.

Full text of DOI:10.1002/adsc.200800455

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DOI: 10.1002/adsc.200800455
Recoverable Palladium Catalysts for Suzuki–Miyaura Cross-
Coupling Reactions Based on Organic-Inorganic Hybrid Silica
Materials Containing Imidazolium and Dihydroimidazolium Salts
Montserrat Trilla,a Guadalupe Borja,a Roser Pleixats,a,* Michel Wong Chi Man,b
Catherine Bied,b and Joꢀl J. E. Moreaub
a
Department of Chemistry, Universitat Autꢁnoma de Barcelona, 08193 Cerdanyola del Vallꢂs, Barcelona, Spain
Fax : (+34)-93-581-1265; e-mail: roser.pleixats@uab.cat
Institut Charles Gerhardt Montpellier, (UMR 5253 CNRS-UM2-ENSCM-UM1), Architectures Molꢃculaires et Matꢃriaux
b
Nanostructurꢃs, Ecole Nationale Supꢃrieure de Chimie de Montpellier, 8 rue de l’ꢃcole normale, 34296 Montpellier cꢃdex
5, France
Received: July 22, 2008; Revised: October 20, 2008; Published online: November 4, 2008
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200800455.
Abstract: The systems formed by palladium acetate with lower conversions. In situ formation of palladi-
[PdACHTUNGTRENNUNG(OAc)2] and hybrid silica materials prepared by um nanoparticles has been observed in recycling ex-
sol-gel from monosilylated imidazolium and disilylat- periments.
ed dihydroimidazolium salts show catalytic activity
in Suzuki–Miyaura cross-couplings with challenging
aryl bromides and chlorides. They are very efficient Keywords: catalyst recycling; nanoparticles; organic-
as recoverable catalysts with aryl bromides. Recy- inorganic hybrid composites; palladium; sol-gel pro-
cling is also possible with aryl chlorides, although cesses; Suzuki–Miyaura reaction
Introduction
di(2-pyridyl)methylamine-palladium dichloride com-
plex are efficient recyclable catalysts for Heck and
The palladium-catalyzed Suzuki–Miyaura cross-cou- Sonogashira reactions with aryl bromides and for
pling[1] reaction constitutes a powerful methodology Suzuki–Miyaura couplings with aryl bromides and
for C C bond formation that is widely used in syn- chlorides.[6] N-heterocyclic carbenes (NHC) derived
À
thetic organic chemistry. On the other hand, the effi- from imidazolium and dihydroimidazolium salts are
cient recovery and recycling of homogeneous transi- another class of ancillary ligands that allow the forma-
tion metal catalysts remains a scientific challenge of tion of versatile, stable and efficient Pd catalytic sys-
[7]
À
economic and environmental relevance. One of the tems for C C bond forming reactions. Although
most useful strategies for this purpose involves the several Pd-NHC complexes are described in the liter-
immobilization of homogeneous catalysts on polymer- ature, in some cases they are formed in situ from the
ic organic[2] or inorganic[3] supports. Some of us have corresponding salt and a palladium source.[8] There
described the heterogenization of air- and moisture- are few precedents of immobilization of Pd-NHC
stable phosphane-free macrocyclic triolefinic Pd(0) complexes in a silica matrix[7e,f,9] for Suzuki, Heck and
complexes by covalent anchoring to a cross-linked Sonogashira reactions. We describe here the prepara-
polystyrene[4] or silica matrix.[5] We have tested the ac- tion of organic-inorganic hybrid silica materials con-
tivity of these supported versions as recyclable cata- taining imidazolium and dihydroimidazolium salts
lysts in Suzuki–Miyaura coupling and telomerization from mono- and disilylated monomers and the activi-
reactions. These heterogenized macrocyclic complexes ty and recyclability in Suzuki–Miyaura cross-coupling
were only active with aryl iodides and we then turned of catalytic systems formed by a Pd(II) salt and these
to other phosphane-free palladium systems based on hybrid silicas.
bipyridin-2-ylmethane-type ligands for the more chal-
lenging bromides and chlorides. We have found that
À
hybrid silica materials covalently Si C bonded to
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Results and Discussion
TEOS shows a very low surface area (2 m2 gÀ1) result-
ing from the voluminous organic fragment in the ma-
The synthesis of the monomers 2 and 5 and hybrid terial as already observed before.[14] M1 and M3 pres-
materials M1, and M2 and M3 derived thereof are ent higher values (506 and 266 m2 gÀ1, respectively).
summarized in Scheme 1. 1-Mesitylimidazole,[10,11] 1, M1 and M3 have pore diameters of 3.1–2.7 and 4.3–
was reacted with (3-iodopropyl)triethoxysilane[12] in 4.2 nm and pore volumes of 0.307–0.364 and 0.262–
refluxing anhydrous acetonitrile under argon for 24 h 0.253 cm3 gÀ1, respectively. M1 presents a nitrogen
to afford the hygroscopic silylated imidazolium salt 2 sorption isotherm of type IV according to IUPAC, su-
in 99% yield. The co-gelification of 2 with tetraethyl perimposed with the isotherm of smaller mesopores
orthosilicate (TEOS) (1:40) in ethanolic hydrochloric (Figure 1b). Accordingly, the BJH calculation for the
acid solution at 408C with sodium tetrafluoroborate[13] pore-size distribution of M1 from the desorption data
as a promoter for hydrolytic condensation of alkoxysi- reveals a bimodal distribution centered at 2.0 and
lanes and 1-cetyl-3-methylimidazolium chloride 3.1 nm whereas M3 presents a pore-size distribution
(CMICl) as cationic surfactant[13] ([CMICl]0/ centered at 2.1 nm. In both cases the desorption
A
E
N
U
G
branches of the isotherm are sharp indicating periodic
0.5:3.8:0.09:643:32:21) afforded material M1. The re- pore structure. Powder X-ray diffraction (p-XRD) of
action of commercial bis(chloromethyl)mesitylene 3, M1 exhibits a 2D hexagonal p6mm mesopore struc-
with commercial 1-(3-triethoxysilyl)propyl-4,5-dihy- ture (MCM-41 type) as expected[13] (Figure 1a) with
dro-1H-imidazole, 4, in anhydrous acetonitrile at three diffraction peaks attributable to the d100, d110
808C under argon for 24 h gave the salt 5 in 99% and d200 planes (4.1, 2.5 and 2.1 nm, respectively).
yield as an hygroscopic white solid. This disilylated This indexation clearly shows the existence of a hex-
monomer 5 was hydrolyzed at 408C in the absence of agonal mesoporous phase. Contrarily, M3 exhibits a
TEOS under acidic conditions in presence of the worm-like mesoporous organization while M2 is even
same cationic surfactant[13] ([CMICl] /
[H2O]0/A[HCl]0/A[EtOH]0 =1.0:0.5:0.8:630:31:20) but as porting Information). This is mainly due to the in-
0 ACHTUNGTRENN[NUG NaBF4]0/[5]0/ less organized with no mesoporosity at all (see Sup-
C
CHTUNGTRENNUNG
no gel or precipitate was formed in acidic medium, creasing ratio of the organic moiety to silica which
aqueous 6.5M NaOH solution was added until pH 7 may interact with the surfactant disfavouring the for-
to promote polycondensation and to afford material mation of periodic mesoporous structures. Moreover
M2. The co-gelification of 5 with TEOS (1:80) in the case of M2 NaOH was added to favour the
under analogous acidic conditions[13] ([CMICl]0/ solid formation of the material. The basic catalyst
A
E
N
U
G
may alter and disrupt the supramolecules of the sur-
The materials were characterized by solid state materials M1, M2, and M3 contain 0.585, 7.432 and
29Si NMR, 13C NMR for M2, surface area BET meas- 0.828 mmol N/g, respectively. The solid state
urements, IR and elemental analysis (see Supporting 29Si NMR spectra of M1 and M3 show two groups of
Information). M2 prepared from disilylated 5 without chemical shifts: T units at around À55 to À68 ppm, re-
Scheme 1. Synthesis of hybrid silica materials M1–M3.
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Figure 1. a) p-XRD of M1; b) N2 sorption isotherm of M1 and plot of the pore size distribution.
sulting from the hydrolysis-condensation of the corre- small amount of biphenyl (8% GC yield) by homo-
sponding monomers 2 and 5, and Q units ranging coupling of phenylboronic acid 6 was observed. The
from À96 to À110 ppm formed from TEOS. As ex- use of degassed solvents and a nitrogen atmosphere
pected, M2 spectrum shows only T2 and T3 units at improved the conversion to 88% (entry 5). A similar
À
À57.3 and À65.6 ppm showing that no Si C bond result (90% conversion at 24 h) was obtained when
cleavage occurred during the hydrolysis process. the base was changed to Cs2CO3 and the solvent was
Mixtures of Pd(OAc)2 (0.2% mol) and these mate- anhydrous and degassed dioxane at the same temper-
ACHTUNGTRENNUNG
rials (0.2–0.4% mol) were tested as catalytic systems ature (1108C) (conditions B, entry 6), although bi-
in the Suzuki cross-couplings of phenylboronic acid 6 phenyl formation could not be completely avoided.
(1.5 equiv.) with p-bromoacetophenone 7, p-bromo- Contrarily, the reaction performed in degassed THF-
ACHTUNGTRENNUNG
The three materials M1–M3 gave efficient and fast entry 7). The 33% conversion achieved after 3 h was
reactions with the activated aryl bromide 7 giving not increased after prolonged heating. Material M3
almost quantitative isolated yields of 8 in 0.5–1 h gave superior performance for the same reaction and
under the conditions indicated in Table 1 (A: K2CO3, a quantitative yield of the coupling product 10 was
DMF-H2O 95:5, 1108C) (entries 1–3). The same con- achieved after 5 h (conditions A: K2CO3, DMF-H2O
ditions were assayed for the deactivated aryl bromide 95:5, 1108C) (entry 8). Material M1 was also tested
9 and material M2 (entry 4), incomplete conversion of under two sets of conditions A and B (entries 9 and
9 being obtained (74%) after 24 h. The formation of a 10). The use of potassium carbonate in DMF-H2O
Scheme 2. Suzuki cross-couplings catalyzed by PdX2/M systems.
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Table 1. Suzuki cross-couplings between phenylboronic acid 6 and aryl halides 7, 9 and 11 with Pd/M systems[a] (Scheme 3).
Entry
ArX
M (% mol)
Conditions[b]
t [h]
Ph-Ar (%)
Ph-Ph (%)
1
2
3
4
5
6
7
8
7
7
7
9
9
9
9
9
9
9
11
11
11
M1 (0.4)
M2 (0.2)
M3 (0.2)
M2 (0.2)
M2 (0.2)
M2 (0.2)
M2 (0.2)
M3 (0.2)
M1 (0.4)
M1 (0.4)
M3 (0.2)
M3 (0.2)
M3 (0.2)
A
A
A
A
1
0.5
1
24
24
24
3
5
5
5
8 (99)[c]
–
–
–
8
–
3
–
–
–
–
11
8
8
8 (96)[c]
8 (100)[c]
10 (74)[d]
10 (88)[d]
10 (90)[d]
10 (33)[d,g]
10 (100)[c]
10 (94)[d]
10 (63)[d]
8 (34)[h]
A[e]
B[f]
C[e]
A
9
A[e]
B[f]
D
10
11
12
13[i]
24
24
24
E
D
8 (46)[h]
8 (37)[h]
[a]
PdACHTUNGTRENNUNG(OAc)2 (0.2% mol) was used, except for entry 13.
A: K2CO3, DMF-H2O 95:5, 1108C; B: Cs2CO3, dioxane, 1108C; C: K2CO3, THF-H2O 80:20, 908C; D: K2CO3, DMF-H2O
[b]
95:5, 1508C; E: Cs2CO3, DMF-H2O 95:5, 1508C.
Isolated yields.
Conversion of 9 (GC, undecane).
Degassed.
[c]
[d]
[e]
[f]
[g]
[i]
Anhydrous and degassed.
The conversion was not improved after prolonged heating (24 h).[h] GC yield of 8 (undecane).
PdCl2 (0.2% mol) was used.
Table 2. Recyclability of Pd/M systems for the reaction of
Table 3. Recyclability of Pd/M systems for the reaction of
phenylboronic acid 6 with p-bromoanisole 9 to give 10 (see
Scheme 2).[a]
phenylboronic acid 6 with p-bromoacetophenone 7 to give 8
(see Scheme 2).[a]
Cycle
M1
M2
M3
Cycle
M2
M3
[b]
[b]
[b]
t [h]
%
t [h]
%
t [h]
%
Conditions A[b]
Conditions B[b]
Conditions A
[c]
[c]
[d]
t [h]
%
t [h]
%
t [h]
%
1
2
3
4
5
1
1
1
1
1
99
83
87
91
87
0.5
4.5
4.5
4.5
4.5
96
94
95
97
99
1
1
1
1
1
100
99
98
99
97
1
2
3
4
5
24
24
88
67
24
24
90
31
5
5
5
5
100
65
68
54
85
24
[a]
Conditions: PdACHTUNGTRENNUNG(OAc)2 (0.2%), M (0.2 or 0.4%), K2CO3,
[a]
DMF-H2O 95:5, 1108C.
Isolated yields.
Conditions A: PdACHTUNGTERNNU(G OAc)2 (0.2%), M (0.2%), K2CO3,
[b]
DMF-H2O 95:5, 1108C. Conditions B: Pd
M (0.2%), Cs2CO3, dioxane, 1108C.
Degassed solvents.
Conversion of 9 (GC).
Isolated yields of 10.
ACHTUNGRTENUN(NG OAc)2 (0.2%),
[b]
[c]
[d]
95:5 gave higher conversions than cesium carbonate
in dioxane for the same temperature (1108C) and the
same reaction time (5 h).
The reaction of 6 with the more challenging aryl
chloride 11 was undertaken under three different con-
The systems PdACHTNUTRGNEUNG(OAc)2/M were found to be excel-
ditions (entries 11–13). The system PdACTHUNTRGNE(UNG OAc)2/M3 with lent recyclable catalysts for the Suzuki reaction of
two different bases (potassium and cesium carbonate) phenylboronic acid 6 with p-bromoacetophenone 7.
in DMF-H2O 95:5 at 1508C (conditions D and E) The dihydroimidazolium salt-based materials M2 and
gave moderate yields of 8 after 24 h, formation of bi- M3 gave slightly better performance than the imida-
phenyl being a competitive process for the consump- zolium based material M1, as no decrease in activity
tion of phenylboronic acid. The use of palladium chlo- was observed after five cycles and almost quantitative
ride instead of palladium acetate under conditions D yields of the coupling product 8 were isolated
gave similar results (entry 11 vs entry 13).
(Table 2).
The reusability of the catalytic systems Pd/M for
For the Suzuki coupling of phenylboronic acid 6
aryl bromides and chlorides (Scheme 2) is shown in with deactivated aryl bromide 9 Pd/M3 remains supe-
Table 2, Table 3 and Table 4.
rior to Pd/M2 system (Table 3), the former giving
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