Hybrid organic-inorganic silica materials containing di(2-pyridyl)methylamine-palladium dichloride complex as recyclable catalysts for Suzuki cross-coupling reactions

Article abstract of DOI:10.1016/j.tetlet.2006.01.150

High surface hybrid silica materials containing di(2-pyridyl)methylamine-palladium dichloride complex covalently bonded to the silica matrix were prepared by sol-gel process and successfully tested as reusable catalysts for Suzuki cross-coupling reactions.

Full text of DOI:10.1016/j.tetlet.2006.01.150

Tetrahedron Letters 47 (2006) 2399–2403
Hybrid organic–inorganic silica materials containing
di(2-pyridyl)methylamine–palladium dichloride complex
as recyclable catalysts for Suzuki cross-coupling reactions
a
a,
b
b
*
Montserrat Trilla, Roser Pleixats, Michel Wong Chi Man, Catherine Bied
b
and J o¨ el J. E. Moreau
a
Department of Chemistry, Universitat Aut o` noma de Barcelona, 08193-Cerdanyola del Vall e` s, Barcelona, Spain
b
H e´ t e´ rochimie Mol e´ culaire et Macromol e´ culaire (UMR-CNRS 5076), Ecole Nationale Sup e´ rieure de Chimie de Montpellier,
rue de l’ e´ cole normale, 34296 Montpellier C e´ dex 5, France
8
Received 23 December 2005; revised 27 January 2006; accepted 30 January 2006
Available online 17 February 2006
Abstract—High surface hybrid silica materials containing di(2-pyridyl)methylamine–palladium dichloride complex covalently
bonded to the silica matrix were prepared by sol-gel process and successfully tested as reusable catalysts for Suzuki cross-coupling
reactions.
Ó 2006 Elsevier Ltd. All rights reserved.
Palladium-catalyzed Suzuki cross-coupling1 reactions
have become a powerful and general methodology for
C–C bond formation. On the other hand, the hetero-
genization of homogeneous catalysts by their immobiliza-
tion on polymeric organic or inorganic supports is an
expanding research area offering the advantage of easy
product separation and catalyst recovery. Phosphines
are common ligands used in palladium catalyzed reac-
tions, but they are readily oxidized to their correspond-
ing phosphine oxides, which can prevent the easy
recovery and recycling of the catalyst. Thus, phos-
phine-free palladium catalysts offer the advantage of
superior stability.
substrates for coupling reactions being aryl chlorides,
cheaper and more widely available than their iodide
counterparts. Several phosphine-free palladium systems
7
have been developed in the literature as robust and effi-
cient catalysts (high TON and TOF) for the challenge to
use aryl chlorides in coupling reactions (palladacycles,
N-heterocyclic carbene ligands and bipyridine based sys-
tems). First, we turned our attention to bipyridine-type
ligands to obtain immobilized palladium catalysts onto
a silica matrix. Palladium(II) complexes of bipyridyl
2
3
8
ligands 1 (Fig. 1) have been described by Buchmeiser
as efficient catalysts for C–C and C–N bond formation
and they have been covalently anchored to a polymeric
9
matrix resulting from a ROMP polymerization. N a´ jera
4
Some of us discovered air and moisture stable phos-
developed related palladium(II) complexes 2 (Fig. 1)
phine-free macrocyclic triolefinic palladium(0) com-
plexes. We have reported their immobilization onto
5
6
cross-linked polystyrene, and onto a silica matrix,
COR
N
NHCOR
and the activity of these heterogeneous versions as
recoverable catalysts in Suzuki and telomerization reac-
tions. However, the immobilized versions of macrocyclic
palladium(0) complexes were only found to be efficient
with activated and deactivated aryl iodides, the ideal
N
N
N
N
Pd
Pd
Cl
Cl
Cl
Cl
1
2
Keywords: Supported catalyst; Recoverable palladium catalyst; Sol-gel;
Hybrid organic–inorganic material; Suzuki cross-coupling.
2a R = NH-(CH ) -Si(OEt)
2 3 3
*
Corresponding author. Tel.: +34 93 581 2067; fax: +34 93 581
265; e-mail: roser.pleixats@uab.es
1
Figure 1. Palladium dichloride complexes of bipyridine ligands.
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.01.150

2400
M. Trilla et al. / Tetrahedron Letters 47 (2006) 2399–2403
derived from di(2-pyridyl)methylamine as efficient catal-
ysts for Heck (aryl iodides, bromides and chlorides),
Suzuki (aryl bromides and chlorides) and Sonogashira
monomer 2a with different amounts of TEOS (1:10,
1:20, 1:40) was performed in dimethylformamide under
standard sol-gel conditions with the stoichiometric
amount of water and ammonium fluoride as catalyst,
(
aryl iodides and bromides) reactions in organic and
1
7
aqueous solvents under homogeneous conditions. Very
recently, this complex has been covalently anchored to
a styrene–maleic anhydride co-polymer affording a
recoverable catalyst active in the above-mentioned
leading to palladium-containing materials 5a–c. These
were characterized by surface area BET measurements,
2
9
13
solid state Si NMR and C NMR, IR and elemental
analysis, the amount of palladium being obtained by
ICP (inductively coupled plasma) (Table 1). Hetero-
geneous catalysts are more efficient when the specific
surface area is high. Great amounts of TEOS (10, 20 and
40 molar equivalents with respect to 2a) were used in
1
0
reactions.
Inorganic solids such as silica, particularly known for
their mechanical and thermal stability and also for their
chemical inertia, represent interesting supports for hetero-
order to favour solid formation with high surface areas
1
1
2 À1
genizing catalysts. In this context, the formation of
and indeed these vary from 337 m g
(for 5a) to
1
2
2 À1
organic–inorganic hybrids by the Sol-Gel Chemistry
is a convenient route to solid materials with catalytic
504 m g (for 5c) accordingly to the BET adsorption–
desorption measurements. The solid state NMR spectra
3
,13
29
13
properties.
We want to present here our work on
( Si and C) provide evidence for the presence of the
2
9
the preparation of hybrid organic–inorganic materials
from the co-gelification of the silylated monomer 2a
organic ligand in the hybrid solids. The Si spectra of
5a–c show two groups of chemical shifts: T units at
around À55 to À68 ppm and Q units ranging from
À100 to À120 ppm. T units result from the hydrolysis-
condensation of 2a whereas Q units formed from TEOS.
(
(
Fig. 1) with different amounts of tetraethoxysilane
TEOS) and the preliminary results of the activity and
recyclability of these materials in the Suzuki cross-cou-
pling of p-bromoacetophenone and m-chlorobenzo-
nitrile with phenylboronic acid.
1
3
Only the solid state C NMR of 5a was performed, the
organics in 5b and 5c being in too little amount in the
corresponding hybrids to be measured in reasonable
time. The spectrum of 5a exhibits signals at 8.7 (CH2–
Si), 16.6 (CH3 from residual ethoxy groups), 23.0
(CH –CH Si), 42.6 (CH –N), 58.1 (CH from residual
Our approach is summarized in Scheme 1.
Di(2-pyridyl)methylamine 3 was prepared as recently
2
2
2
2
1
4
described by zinc reduction of the oxime derived from
commercial di(2-pyridyl)methanone. It was immediately
reacted overnight under stirring with freshly distilled 3-
ethoxy groups), 74.3 (CH–N), 126.8, 141.7, 154.5 (3C
from pyridine rings) and 158 (C@O) ppm attributable
to the chemical shifts of the organic part of 5. The signal
(
triethoxysilyl)propyl isocyanate in anhydrous dichloro-
at 8.7 ppm (CH –Si) confirms the covalently bonded
2
methane at room temperature. The resulting urea deriv-
ligand to silica.
1
5
ative 4 was treated with PdCl (CH CN) in anhydrous
2
3
2
toluene at 80–90 °C overnight to afford the palla-
The activity of catalysts 5a–c was tested in the Suzuki
cross-coupling of phenylboronic acid 7 with an aryl
1
6
dium(II) complex 2a. Co-gelification of the silylated
O
NH2
HN
N
H
Si(OEt)3
OCN(CH ) Si(OEt)
2
3
3
N
N
anh CH Cl rt, Ar
2
2,
N
N
4
3
85%
O
PdCl (CH CN)
2
3
2
HN
Pd
N
H
Si(OEt)3
o
anh toluene, 80-90 C, 14 h, Ar
82%
N
N
2a
Cl
Cl
O
HN
N
H
SiO1.5 . n SiO2
n TEOS, anh DMF
H O, NH F
2
4
N
N
5a n = 10
Pd
5
5
b n = 20
c n = 40
Cl
Cl
Scheme 1. Preparation of hybrid silica materials 5a–c.

M. Trilla et al. / Tetrahedron Letters 47 (2006) 2399–2403
2401
Table 1. Some analytical data of 5a–c
Table 2. Suzuki couplings with catalysts 5a–c giving rise to 8 and 10
a
(
Scheme 2)
Cycle
5
a
5b
5c
b
c
6 to 8 (%)
9 to 10 (%)
%
Pd
6.05
3.88
2.63
Mmol Pd/g
0.569
0.365
0.247
5a
5b
5c
5b
7
h
24 h
1
2
3
4
5
6
7
8
9
100
100
96
97
96
95
97
98
97
94
100
100
99
96
96
94
96
96
97
96
100
99
98
98
97
98
96
97
95
95
61
44
34
31
25
—
—
—
—
—
82
59
38
34
26
—
—
—
—
—
bromide, p-bromoacetophenone 6, and an aryl chloride,
m-chlorobenzonitrile 9 (Scheme 2 and Table 2). After
some experimentation (MeOH/H O 3:1, KOH, rt,
2
2
4 h; MeOH/H O 3:1, KOH, 60 °C, 45 min; toluene,
2
K CO , 110 °C, 3 h) the conditions specified in Table 2
2
3
(DMF/H O 95:5, K CO , 110 °C, 45–60 min) were adopted
2
2
3
for the Suzuki coupling of Eq. 1. Ten consecutive cycles
with the same batch of catalyst were performed, main-
taining the same reaction time in every run. The isolated
yields of 4-phenylacetophenone 8 for every catalytic
1
0
a
Conditions: 0.2% molar of Pd, [ArX] = 0.5 M, PhB(OH)
(1.5 equiv), K CO (2 equiv), DMF/H O (95:5), 110 °C, 45 min for
catalysts 5a–b and 60 min for catalyst 5c for the reaction of 6 to 8,
and 24 h for the reaction of 9 to 10 with catalyst 5b.
Isolated yields.
2
,
1
8
2
3
2
material are given in Table 2. No significant differences
were found within the materials with respect to their
recyclability, but the reaction time required to achieve
complete conversion of the aryl halide is longer with
b
c
Conversion of 9 by GLC (undecane as internal standard).
5
c containing less percentage of Pd. The same reaction
(
Eq. 1 of Scheme 2) was also tested under the same con-
ditions with the material 5bSi obtained by refluxing 5b
with excess hexamethyldisilazane for capping surface
silanol groups, but the reaction was slower, 4 h being
required to achieve a 97% isolated yield of 8. We noticed
that the catalytic pale yellow materials 5a–c became grey
after the first cycle and darkened progressively to black.
This is due to the formation of metal nanoparticles in
the materials, which can be observed by high-resolution
electron transmission microscopy (HRTEM) (both the
inorganic matrix and the organic ligand of the hybrids
the solid mixture obtained in this cycle by evaporation
of the filtrate were found to be 12 and 80 ppm, respec-
1
0
tively. N a´ jera has used water or MeOH/H O as solvent
2
systems in their recycling experiments with the catalyst
anchored to organic polymer. In our case, the use of less
amount of water and potassium carbonate as base instead
of KOH improved the recyclability (the system DMF/
H O 95:5 was better than MeOH/H O 3:1).
2
2
Then, we tested the material 5b in a more challenging
substrate, the m-chlorobenzonitrile, 9, which was
reacted with phenylboronic acid 7 to afford 3-cyanobiphe-
nyl, 10 (Eq. 2 of Scheme 2) under the conditions of
Table 2 (0.2% molar of Pd, DMF/H O 95:5, K CO ,
1
9
can contribute to their stabilization). Electron diffrac-
tion (ED) of the sample showed the pattern characteris-
tic of face-centred cube (fcc) palladium(0). In Figure 2,
we show an example of HRTEM micrographs of one
of the samples (material 5c after the fourth cycle,
DMF/H O, K CO , 110 °C, 60 min), the size distribution
2
2
3
110 °C). As expected, the reaction was much slower than
with the aryl bromide, and even after being left for 24 h,
a total conversion could not be achieved. Conversions of
9 were determined by GLC at two reaction times (7 h
and 24 h) for each of the five consecutive cycles (Table
2). In this case, a significant decrease of conversion upon
recycling was found, prolonged reaction times being not
useful. More research is necessary to improve the results
with aryl chlorides.
2
2
3
of nanoparticles and the ED image (d-spacings = 0.239,
.207, 0.147, 0.124 nm). The nanoparticles were not
0
observed by TEM in the materials before being tested
as catalysts, but darkening of the recovered materials
after the first run was observed under any condition
used (see Supplementary data). Palladium nanoparticles
observed by TEM have been also recently described by
1
0
N a´ jera. The amount of Pd determined by ICP-MS in
the product 8 isolated from the first cycle performed
with catalyst 5a under the conditions of Table 2 and in
In summary, high surface hybrid silica materials with
covalently attached di(2-pyridyl)methylamine–palladium
0
.2 % Pd
CH CO
Br
+
(HO)2B
CH CO
eq.1
3
3
base, solvent
temp., time
6
7
8
0
.2 % Pd
Cl
+
(HO) B
eq.2
2
base, solvent
temp., time
NC
NC
7
10
9
Scheme 2. Suzuki cross-couplings tested with catalysts 5a–c.

2402
M. Trilla et al. / Tetrahedron Letters 47 (2006) 2399–2403
Figure 2. (a) and (b) HRTEM micrographs of Pd nanoparticles; (c) ED image; (d) Particle size distribution (104 particles; mean particle size:
.1 ± 0.9 nm).
5
dichloride complex were prepared and found to be very
active and recoverable catalysts for Suzuki cross-coupling
of activated aryl bromides. They are also active for aryl
chlorides, although further investigation is needed in
order to improve the yield and the recyclability. Forma-
tion of fcc Pd(0) nanoparticles has been shown by
HRTEM and ED.
References and notes
1. (a) Suzuki, A. J. Organomet. Chem. 1999, 576, 147–168;
(
b) Suzuki, A. J. Organomet. Chem. 2002, 653, 83–90; (c)
Suzuki, A. Chem. Commun. 2005, 4759–4763.
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Rev. 2002, 102, 3275–3299; (b) Leadbeater, N. E.; Marco,
M. Chem. Rev. 2002, 102, 3217–3274.
2
3
. (a) Ying, J. Y.; Mehnert, C. P.; Wong, M. S. Angew.
Chem., Int. Ed. 1999, 38, 56–77; (b) Lindner, E.; Schneller,
T.; Auer, F.; Mayer, H. A. Angew. Chem., Int. Ed. 1999,
Acknowledgements
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8, 2154–2174; (c) Wight, A. P.; Davis, M. E. Chem. Rev.
002, 102, 3589–3613; (d) Lu, Z.; Lindner, E.; Mayer, H.
Financial support from the Ministry of Science and
Technology of Spain (Project BQU2002-04002-C02)
Generalitat de Catalunya (Project SGR2001-00181),
and Universitat Aut o` noma de Barcelona (Project
PNL2005-10) is gratefully acknowledged. M.T. thanks
Generalitat de Catalunya for a predoctoral scholarship.
The CNRS and the French Ministry of Research and
Technology are also acknowledged for fundings.
A. Chem. Rev. 2002, 102, 3543–3578; (e) De Vos, D. E.;
Dams, M.; Sels, B. F.; Jacobs, P. A. Chem. Rev. 2002, 102,
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615–3640.
4
. Cerezo, S.; Cort e´ s, J.; L o´ pez-Romero, J. M.; Moreno-
Ma n˜ as, M.; Parella, T.; Pleixats, R.; Roglans, A. Tetra-
hedron 1998, 54, 14885–14904.
5. Cort e´ s, J.; Moreno-Ma n˜ as, M.; Pleixats, R. Eur. J. Org.
Chem. 2000, 239–243.
. (a) Blanco, B.; Mehdi, A.; Moreno-Ma n˜ as, M.; Pleixats,
R.; Rey e´ , C. Tetrahedron Lett. 2004, 45, 8789–8791; (b)
Blanco, B.; Brissart, M.; Moreno-Ma n˜ as, M.; Pleixats, R.;
Mehdi, A.; Rey e´ , C.; Bouquillon, S.; H e´ nin, F.; Muzart, J.
Appl. Cat. A: General 2006, 297, 117–124.
. Reviews: (a) Littke, A. F.; Fu, G. C. Angew. Chem., Int.
Ed. 2002, 41, 4176–4211; (b) Bedford, R. B.; Cazin, C. S.
J.; Holder, D. Coord. Chem. Rev. 2004, 248, 2283–2321.
6
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
7
2
006.01.150.

M. Trilla et al. / Tetrahedron Letters 47 (2006) 2399–2403
2403
8
9
. (a) Buchmeiser, M. R.; Wurst, K. J. Am. Chem. Soc. 1999,
21, 11101–11107; (b) Silberg, J.; Schareina, T.; Kempe,
R.; Wurst, K.; Buchmeiser, M. R. J. Organomet. Chem.
001, 622, 6–18.
. (a) N a´ jera, C.; Gil-Molt o´ , J.; Karlstr o¨ m, S.; Falvello, L.
R. Org. Lett. 2003, 5, 1451–1454; (b) N a´ jera, C.; Gil-
Molt o´ , J.; Karlstr o¨ m, S. Adv. Synth. Catal. 2004, 346,
2 4
Cl O Pd: C, 41.35; H, 5.29; N, 9.19; Si, 4.60; Pd, 17.45.
Found: C, 41.25; H, 5.43; N, 9.10; Si 4.46; Pd(ICP),
16.52.
1
2
4
17. Typical procedure: A solution of NH F (168 lL of a 1 M
solution, 0.168 mmol of fluoride, 9.33 mmol of water),
anhydrous DMF (6.8 mL) and distilled and deionized
water (1035 lL, 57.5 mmol) was added to a solution of 2a
(0.252 g, 0.413 mmol) and TEOS (3.489 g, 16.4 mmol) in
anhydrous DMF (10 mL). The mixture was stirred man-
ually for a minute to get an homogeneous solution and
was left at room temperature without stirring. Gelation
occurred after 2 h and the gel was allowed to age for
3 days, after which it was powdered and washed succes-
sively twice with water and three times with ethanol. The
solid was dried under vacuum overnight (2 mmHg, 60 °C),
yielding 5c as a yellow powder (1.274 g). IR (KBr): 3447,
1
798–1811; (c) Gil-Molt o´ , J.; N a´ jera, C. Eur. J. Org.
Chem. 2005, 4073–4081.
0. Gil-Molt o´ , J.; Karlstr o¨ m, S.; N a´ jera, C. Tetrahedron 2005,
1, 12168–12176.
1. Gladysz, J. A. Chem. Rev. 2002, 102, 3215–3216.
2. (a) Brinker, C. J.; Scherer, G. W. Sol-Gel Science;
Academic Press: London, 1990; (b) Sanchez, C.; Robot,
F. New J. Chem. 1994, 18, 1007–1047; (c) Shea, K. J.;
Moreau, J. J. E.; Loy, D. A.; Corriu, R. J. P.; Boury, B. In
Functional Hybrid Materials; Gomez-Romero, P., San-
chez, C., Eds.; Wiley-VCH: Weinheim, 2004; p 50.
1
6
1
1
À1
1655, 1564, 1079, 959, 799, 459 cm . Anal. (%) found: C,
8.38; H, 1.24; N, 1.86; Si, 35.00; Pd(ICP), 2.63. Materials
5a–b were obtained in a similar manner except the molar
ratio 2a:TEOS. Material 5a: Anal. (%) found: C, 11.77; H,
1.90; N, 4.43; Si, 26.82; Pd(ICP), 6.05. Material 5b: Anal.
(%) found: C, 10.32; H, 1.24; N, 2.66; Si, 29.51; Pd(ICP),
3.88.
1
3. (a) Schubert, U. New J. Chem. 1994, 18, 1048–1058;
(
b) Adima, A.; Moreau, J. J. E.; Wong Chi Man, M. J.
Mater. Chem. 1997, 7, 2331–2333; (c) Abu-Reziq, R.;
Avnir, D.; Blue, J. Angew. Chem., Int. Ed. 2002, 41, 4132–
4
134.
1
4. Chang, J.; Plummer, S.; Berman, E. S. F.; Striplin, D.;
Blauch, D. Inorg. Chem. 2004, 43, 1735–1742.
2 3
18. Typical procedure: K CO (1.935 g, 14 mmol) was added
to a stirred mixture of 5b (0.0384 g, 0.014 mmol of Pd), 6
(1.422 g, 7 mmol), and 7 (1.306 g, 10.5 mmol) in DMF/
H O (95:5) (14 mL) and it was heated at 110 °C for 45 min
2
(GLC monitoring). Product 8 precipitated by the addition
of water to the crude mixture. The filtered solid was
washed with water and then it was taken in ethyl acetate.
Insoluble 5b was filtered. The filtrate was dried with
anhydrous sodium sulfate and the solvent was evaporated
to give pure 8 (1.374 g, 100% yield). The catalyst 5b was
washed successively with water, ethanol and diethyl ether,
it was dried and reused in the next run.
1
5. Compound 4: mp 113–114 °C; IR (ATR): 3353, 3281,
À1
1
2
973, 2875, 1626, 1561, 1076, 950, 758 cm
;
H NMR
(
(
(
(
CDCl
3
,
250 MHz):
d
0.52–0.59 (m, 2H), 1.18
t, J = 7.0 Hz, 9H), 1.54 (m, 2H), 3.14 (m, 2H), 3.76
q, J = 7.0 Hz, 6H), 5.11 (br t, J = 5.6 Hz, 1H), 6.07
d, J = 6.6 Hz, 1H), 6.91 (d, J = 6.6 Hz, 1H), 7.10 (ddd,
J = 7.5, 4.9 and 1.1 Hz, 2H), 7.40 (d, J = 7.9 Hz, 2H), 7.58
1
3
(
td, J = 7.7 and 1.8 Hz, 2H), 8.46 (d, J = 4.9 Hz, 2H);
C
3
NMR (CDCl , 62.5 MHz): d 7.9, 18.6, 23.8, 43.3, 58.6,
6
0.4, 122.5, 122.6, 137.1, 149.2, 157.9, 160.2. Anal. Calcd
(
6
%) for C H N SiO : C, 58.31; H, 7.46; N, 12.95; Si,
.49. Found: C, 57.43; H, 8.52; N, 12.93; Si, 6.43.
19. For the formation of C–C bonds under catalysis by
transition-metal nanoparticles: (a) Moreno-Ma n˜ as, M.;
Pleixats, R. Acc. Chem. Res. 2003, 36, 638–643; For
adsorption of metal nanoparticles on supports see, for
instance: (b) Roucoux, A.; Schulz, J.; Patin, H. Chem. Rev.
2002, 102, 3757–3778; For the stabilizing interaction of
bipyridyl ligands with Pd(0) nanoparticles, see: (c) Naka,
K.; Yaguchi, M.; Chujo, Y. Chem. Mater. 1999, 11, 849–
851.
2
1
32
4
4
1
6. Compound 2a: IR (ATR): 3331, 3109, 2973, 2882, 1630,
À1
1
1
2
9
563, 1471, 1070, 953, 764 cm ; H NMR (CD SOCD ,
3 3
50 MHz, 329 K): d 0.52–0.70 (m, 2H), 1.17 (t, J = 7.0 Hz,
H), 1.43–1.67 (m, 2H), 3.12–3.24 (m, 2H), 3.77 (q,
J = 7.0 Hz, 6H), 6.30–6.52 (m, 1H), 7.09–7.28 (m, 1H),
7
2
.55 (t, J = 6.5 Hz, 2H), 7.66–7.96 (m, 3H), 8.03–8.24 (m,
H), 8.83–9.00 (m, 2H). Anal. Calcd (%) for C H N Si-
2
1
32
4