A convenient and efficient procedure for the palladium-catalyzed cyanation of aryl halides using trimethylsilylcyanide

Article abstract of DOI:10.1016/S0022-328X(03)00503-5

Benzonitriles are easily accessible from the corresponding aryl bromides catalyzed by a palladium-complex using trimethylsilylcyanide (TMSCN) as cyanating agent under mild conditions. The key of success for the cyanation protocol is the slow dosage of the TMSCN to the reaction mixture. This new method is applicable on both activated and deactivated aryl and heteroaryl bromides giving the corresponding benzonitriles in good to excellent yield.

Full text of DOI:10.1016/S0022-328X(03)00503-5

Journal of Organometallic Chemistry 684 (2003) 50ꢀ55
/
www.elsevier.com/locate/jorganchem
A convenient and efficient procedure for the palladium-catalyzed
cyanation of aryl halides using trimethylsilylcyanide
Mark Sundermeier, Sateesh Mutyala, Alexander Zapf, Anke Spannenberg,
Matthias Beller *
Leibniz-Institut fur Organische Katalyse an der Universitat Rostock e.V., Buchbinderstr. 5-6, 18055 Rostock, Germany
¨ ¨
Received 11 February 2003; received in revised form 4 April 2003; accepted 24 May 2003
Dedicated to Professor Ernst Otto Fischer on the occasion of his 85th birthday
Abstract
Benzonitriles are easily accessible from the corresponding aryl bromides in a palladium-catalyzed reaction using trimethylsi-
lylcyanide (TMSCN) as cyanating agent under mild conditions. The key of success for the cyanation protocol is the slow dosage of
the TMSCN to the reaction mixture. This new method is applicable to both activated and deactivated aryl and heteroaryl bromides
giving the corresponding benzonitriles in good to excellent yields.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Aryl halides; Benzonitriles; Cyanation; Homogeneous catalysis; Palladium; Trimethylsilylcyanide
1. Introduction
tuted benzonitriles, and the resulting products are of
considerable importance as integral part of dyes, natural
products, herbicides, agrochemicals, pharmaceuticals,
and new active agents [4].
Palladium-catalyzed coupling processes of aryl ha-
lides are well established methods for carbonꢀcarbon
/
On an industrial scale aryl cyanides are produced
mainly via ammoxidation of the corresponding toluenes
bond formation in organic synthesis on laboratory and
industrial scale for fine chemical synthesis [1]. Their
generality and broad tolerance of functional groups
make these methods especially attractive for the use in
natural product synthesis. In addition, a number of
currently used industrial fine chemicals might be
synthesized by shorter and more selective routes com-
pared to classic stoichiometric organic transformations.
Hence, we are interested for some time in the develop-
ment of palladium-catalyzed coupling reactions of aryl
bromides and chlorides to a practical level [2].
[5]. In addition, still the classic Rosenmundꢀvon Braun
/
reaction, whereby aryl halides react with stoichiometric
amounts of copper(I) cyanide, and the reaction of
diazonium salts with copper(I) cyanide (Sandmeyer
reaction) are used to a considerable extent. Compared
to the latter two methods the transition metal-catalyzed
cyanation of aryl halides is an environmentally more
friendly procedure and does not lead to the formation of
stoichiometric amounts of copper waste. So far, both
nickel [6] and palladium complexes [7] have been used as
catalyst. Mechanistic studies of the palladium-catalyzed
cyanation revealed that cyanide ions deactivate both
palladium(II) and palladium(0) species in the catalytic
cycle (Scheme 2) [8]. Hence, catalyst productivity is
comparably low in cyanation reactions (TON typically
Among the different palladium-catalyzed arylꢀX
/
refinement reactions the catalytic cyanation of aryl
halides (Scheme 1) is somewhat underdeveloped [3].
That is in part surprising because this transformation
offers a simple and elegant approach towards substi-
10ꢀ/50) compared to other palladium-catalyzed coupling
reactions (TON 10 000ꢀ/100 000) [9].
* Corresponding author. Tel.: ꢁ
/
49-381-466-930; fax: ꢁ49-381-466-
/
Recently, we have been able to show, that an efficient
control of the concentration of dissolved cyanide ions in
9324.
E-mail address: matthias.beller@ifok.uni-rostock.de (M. Beller).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00503-5

M. Sundermeier et al. / Journal of Organometallic Chemistry 684 (2003) 50ꢀ
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51
Scheme 1. Palladium- or nickel-catalyzed cyanation of arylꢀX.
/
Fig. 1. Crystal structure of 1 [12]. The thermal ellipsoids correspond to
30% probability. Hydrogen atoms have been omitted for clarity. For
the disordered CF3 group the fluorine atoms with highest probability
˚
of occupation are shown. Selected bond lengths (A) and angles (8):
Scheme 2. Proposed mechanism of the palladium-catalyzed cyanation
of bromobenzene using TMSCN as cyanating agent.
PdÃ
P1Ã
P1 87.01(13).
/
P1 2.331(2), PdÃ
/
P2 2.346(2), PdÃ
PdÃP2 94.63(5), P2Ã
/
Br 2.5244(9), PdÃ
/
C 2.012(4);
/
PdÃBr 88.98(5), BrÃ
/
/
/
/
PdÃC 89.32(13), CÃ
/
/
PdÃ
/
solution is required in order to improve catalytic
efficiency [8a]. This is difficult to achieve applying solid
KCN or NaCN as cyanation agent due to the nature of
the reaction mixture (suspension). However, slow addi-
tion of acetone cyanohydrin gives improved results [10].
Another interesting ‘liquid cyanation reagent’ would
be trimethylsilylcyanide (TMSCN). TMSCN can easily
be handled on laboratory scale and has safety advan-
tages compared to other cyanide sources. To the best of
our knowledge there has been no palladium- or nickel-
catalyzed cyanation of aryl bromides or aryl chlorides
reported in the literature [11].
Scheme 3. Stoichiometric reaction of 1 with TMSCN.
dium(II) (1), which is supposed to form an active
intermediate of the catalytic cycle (Scheme 2) by ligand
exchange, was used. Compared to other palladium
sources this complex does not require a pre-formation
to form an active catalyst species. In all catalytic
experiments TMSCN is continuously dosed to the
reaction mixture using a syringe pump. In agreement
with literature there is no reaction observed using
TMSCN under the previously optimized reaction con-
ditions without dosage [14].
2. Results and discussion
During attempts to prepare arylpalladium(II) cyano
complexes we discovered that trans-bromo[4-(trifluor-
omethyl)phenyl]bis(triphenylphosphine)palladium(II)
(1) [12] (Fig. 1) reacts readily and highly selectively with
TMSCN. The corresponding benzonitrile was obtained
in 95% yield even below 0 8C (Scheme 3). Hence, we
thought that TMSCN should be an efficient and mild
cyanation reagent for a palladium-catalyzed coupling
reaction.
Catalytic studies with TMSCN were performed in-
itially using the cyanation of 4-bromobenzotrifluoride
(Table 1). Based on our previous investigations [8a,13]
we applied catalyst systems based on palladium in the
presence of 1,5-bis(diphenylphosphino)pentane (dpppe)
and N,N,N?,N?-tetramethylethylenediamine as ligands
in toluene. As the palladium catalyst trans-bromo[4-
(trifluoromethyl)phenyl]bis(triphenylphosphine)palla-
However, slow dosage of TMSCN to 4-bromobenzo-
trifluoride and 2 mol.% of 1 resulted in smooth
formation of 4-(trifluoromethyl)benzonitrile. The de-
sired nitrile is obtained in quantitative yield (]99%)
/
without any by-product being observed (Table 1, entry
1). This is the first example of a palladium-catalyzed
cyanation of aryl bromides using TMSCN as the
cyanide source. Excellent conversion and selectivity
was also observed at more convenient reaction condi-
tions (80 8C) and in the presence of 1 mol.% of catalyst
(Table 1, entries 2 and 4). However, at 60 8C no
full conversion took place (Table 1, entry 3). The use
of
trans-bromo(3-tolyl)bis(triphenylphosphine)palla-
dium(II) (2) instead of 1 gave similarly good results.
Next we were interested in the scope and limitation of
the new protocol. Table 2 shows some different aryl

52
M. Sundermeier et al. / Journal of Organometallic Chemistry 684 (2003) 50ꢀ55
/
Table 1
Use of TMSCN in the palladium-catalyzed cyanation of 4-bromobenzotrifluoride
Entry
Catalyst (mol.%)
Dpppe [mol.%]
Temperature [8C]
Conversion a [%]
Yield a [%]
1
2
3
4
1 (2)
1 (2)
1 (2)
1 (1)
2
2
2
1
120
80
100
100
17
]
]/
/
99
99
15
99
60
120
100
]/
General conditions: 4-bromobenzotrifluoride (2 mmol), 1, dpppe and TMEDA (0.4 mmol) were dissolved in toluene (2 ml) under argon. The
mixture was heated under stirring, and 1 M TMSCN solution (2.1 ml) was added via syringe pump to the solution (dosage rate: 0.1 ml hꢂ1). After
cooling to room temperature 400 ml of diethyleneglycol di-n-butylether were added for GC-analysis.
a
Conversions and yields were determined by GC.
halides, tested in the palladium-catalyzed cyanation
using TMSCN in the presence of 1 or 2 as catalyst.
In general, a wide variety of aryl bromides can easily
be transformed into the corresponding substituted
benzonitriles. Activated aryl bromides, e.g. 4-bromo-
benzotrifluoride, methyl 4-bromobenzoate, 4?-bromo-
acetophenone, 4-bromofluorobenzene, 4-bromonitro-
prevent catalyst deactivation by excess cyanide ions in
solution. The generality of the described procedure has
been shown by conversion of a variety of activated, non-
activated, and deactivated aryl or heteroaryl bromides
into the corresponding benzonitriles.
benzene, and 4-bromobenzonitrile (Table 2, entries 1ꢀ
7) gave the desired products in good to very good yield
(53ꢀ99%). Somewhat surprising, there is no significant
/
3. Experimental
/
3.1. General
difference in reactivity observed when applying non-
activated and deactivated aryl bromides. Bromoben-
zene, 3-bromotoluene, 4-bromotoluene, 3-bromoani-
sole, and 4-bromoanisole react with TMSCN in good
All chemicals are commercially available and were
used without further purification. Toluene was stored
˚
over molecular sieve 4 A. TMSCN was used as a 1 M
to excellent yield (62ꢀ
nitriles (Table 2, entries 8ꢀ
/
99% yield) to the corresponding
solution in toluene. All products were fully character-
ized after isolation (1H-NMR, 13C-NMR, MS, IR, and
elemental analysis) or in the case of commercially
/13). In case of the reaction of
3-bromotoluene with TMSCN the effect of the P/Pd-
ratio was studied. 3-Methylbenzonitrile was obtained in
84% yield in the presence of 2 mol.% Pd and 2 mol.%
dpppe (Table 2, entry 9). When the metal content was
reduced to 1 mol.% (1 mol.% dpppe) the yield decreased
to 65%. However, by decreasing the palladium/phos-
phine ratio to 1:6 the product was observed in 92%
(Table 2, entry 10). Hence, we conclude that it should be
possible to even improve the shown product yields by
variation of the Pd/P ratio. Apart from aryl bromides we
also tested one heteroaryl bromide (3-bromopyridine)
and an activated aryl chloride (4-chlorobenzotrifluoride)
(Table 2, entries 14, 15). The products were obtained in
68 and 39% yield, respectively. Improved results for the
cyanation of aryl chlorides are expected at higher
reaction temperature. Unfortunately, the relatively low
available products by comparison of GCꢀ
/
MS data.
3.2. General procedure
A two necked round bottom reaction flask (25 ml)
with condenser was charged with palladium catalyst
(0.04 mmol) and dpppe (17.6 mg, 0.04 mmol) and
purged with argon. The aryl halide (2 mmol),
N,N,N?,N?-tetramethylethylenediamine (60 ml; 0.4
mmol), and toluene (2 ml) were added. The reaction
mixture was heated to 120 8C and while magnetically
stirring a 1 M TMSCN solution (2.1 ml; 2.1 mmol) was
dosed via a syringe pump with a dosage rate of 0.1 ml
hꢂ1 (0.1 mmol hꢂ1). After 21 h the reaction was cooled
to room temperature (r.t.), internal standard (diethyle-
neglycol di-n-butylether; 400 ml) was added and the
reaction mixture was diluted with dichloromethane.
Conversion and yield were determined by GC analysis.
boiling point of the TMSCN (114ꢀ117 8C) prevents the
realization of such reactions in standard glassware
equipment.
/
In summary, we have shown that TMSCN reacts
readily and selectively with arylpalladium(II) halide
complexes to give the corresponding benzonitriles.
TMSCN is a mild and easy cyanating agent for the
palladium-catalyzed cyanation of aryl halides. Key to
success of the catalytic reactions is the dosage of the
cyanide via syringe pump to the reaction mixture to
3.3. Oxidative addition products
In a three necked round bottom reaction flask (50 ml)
with condenser 5.78 g (5.0 mmol) tetrakis(triphenylphos-
phine)palladium(0) were placed and purged with argon.
The aryl bromide (20 mmol) and toluene (20 ml) were

M. Sundermeier et al. / Journal of Organometallic Chemistry 684 (2003) 50ꢀ
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53
Table 2
Scope and limitation of the palladium-catalyzed cyanation of aryl halides with TMSCN
General conditions: aryl and heteroaryl halide (2 mmol), palladium complex (0.04 mmol), dpppe (0.04 mmol; Pd:Pꢃ
/
1:4) and TMEDA (0.4 mmol)
were dissolved in toluene (2 ml) under argon. The mixture was refluxed under stirring, and 1 M TMSCN solution (2.1 ml) was added via syringe
pump to the solution (dosage rate: 0.1 ml hꢂ1). After cooling to room temperature 400 ml of diethyleneglycol di-n-butylether were added for GC-
analysis.
[a] Conversions and yields were determined by GC.
[b] 0.02 mmol palladium complex; 0.04 mmol dpppe (Pd:Pꢃ
/1:6).
[c] Solvent:xylene; 140 8C.
added and the reaction mixture was stirred at 80 8C for
4 h. After cooling to r.t. the solvent and excess aryl
bromide were distilled off the mixture under reduced
pressure. The solid residue was washed three times with
diethyl ether and the remaining crude product was
dissolved in dichloromethane. After addition of pentane
3.4. Analytical data
3.4.1. trans-Bromo[4-(trifluoromethyl)phenyl]bis-
(triphenylphosphine)palladium(II)
1H-NMR (400 MHz, CD2Cl2, 297 K): d 7.52 (m,
3
12H), 7.38 (m, 6H), 7.29 (m, 12H), 6.76 (d, J(H,H)ꢃ
/
3
the oxidative addition product was obtained in 80ꢀ
/
95%
8.1 Hz, 2H), 6.41 (d, J(H,H)ꢃ
/
8.1 Hz, 2H); 13C{1H}-
NMR (101 MHz, CD2Cl2, 297 K) [15]: d 136.3 (q,
yield as colorless crystals.

54
M. Sundermeier et al. / Journal of Organometallic Chemistry 684 (2003) 50ꢀ
/55
1
3J(C,F)ꢃ
2J(C,P)ꢃ
Hz), 123.6 (s); 31P-NMR (162 MHz, CD2Cl2, 297 K): d
1], 775, 630,
/
5.3 Hz), 135.0 (t, J(C,P)ꢃ
/
6.2 Hz), 131.4 (t,
(o) M. Beller, A.F. Indolese, Chimia 55 (2001) 684;
22.9 Hz), 130.4 (s), 128.3 (t, 3J(C,P)ꢃ
/5.2
(p) W. Magerlein, A.F. Indolese, M. Beller, J. Organomet. Chem.
¨
641 (2002) 30.
/
[3] G.P. Ellis, T.M. Romney-Alexander, Chem. Rev. 87 (1987)
779.
24.3; MS (FAB, NBA, m/z): 855 [Mꢁꢂ
/
407, 339, 262; IR (Nujol, cmꢂ1): 3054, 1437, 1322, 1111,
1096, 1069, 745, 693, 519; Anal.: Calc. for
C43H34BrF3P2Pd: C, 60.34; H, 4.00; Br, 9.33; P, 7.24;
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¨
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[6] For the nickel-catalyzed cyanation of aryl halides see: (a) L.
Cassar, M. Foa`, F. Montanari, G.P. Marinelli, J. Organomet.
Chem. 173 (1979) 335;
3.4.2. trans-Bromo(3-
tolyl)bis(triphenylphosphine)palladium(II)
1H-NMR (400 MHz, CDCl3, 297 K): d 7.49 (m, 12H),
7.30 (m, 6H), 7.23 (m, 12H), 6.55 (m, 1H), 6.14 (m, 3H),
1.52 (s, 3H); 31P-NMR (162MHz, CD2Cl2, 297 K): d 24.3.
(b) Y. Sakakibara, F. Okuda, A. Shimoyabashi, K. Kirino, M.
Sakai, N. Uchino, K. Takagi, Bull. Chem. Soc. Jpn 61 (1988)
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(d) M.-H. Rock, A. Merhold (Bayer AG), WO 98/37058, 1998.
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Acknowledgements
The authors thank Mrs. H. Baudisch (GCꢀMS,
/
IfOK), and Dr. W. Baumann (NMR, IfOK) for
analytical support. Generous support of this project
from the state Mecklenburg-Western Pomerania, the
‘Fonds der Chemischen Industrie’ and the ‘Bundesmi-
nisterium fur Bildung und Forschung (BMBF)’ are
¨
gratefully acknowledged. OMG is thanked for gifts of
palladium compounds.
(c) J.R. Dalton, S.L. Regen, J. Org. Chem. 44 (1979) 4443;
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¨
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84.78(3), bꢃ80.42(3),
2, lcalc
1.571 g cmꢂ3
5959 reflections measured, 5959 were independent of symmetry
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colourless prism, space group
˚
P/
/
bꢃ
/
11.710(2), cꢃ
/
18.290(4) A, aꢃ
1988.6(7) A , Zꢃ
/
/
3
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/
66.25(3)8, Vꢃ
/
/
ꢃ/
,
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/
(b) M. Sundermeier, A. Zapf, M. Beller, Agnew. Chem. Int. Ed.
42 (2003) 1661.
[11] N. Chatani, T.J. Hanafusa, J. Org. Chem. 51 (1986) 4714.
[12] X-ray data of 1 were collected on a STOE-IPDS diffractometer
Union Road, Cambridge CB2 1EZ, UK (fax: ꢁ
/
44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk).
[13] M. Sundermeier, A. Zapf, M. Beller, J. Sans, Tetrahedron Lett. 42
(2001) 6707.
using graphite monochromated MoꢀKa radiation. The structure
/
was solved by direct methods (SHELXS-86: G.M. Sheldrick, Acta
Crystallogr. Sect. A 1990, 46, 467) and refined by full-matrix least-
squares techniques against F2 (SHELXL-93). Non-hydrogen atoms
(except atoms of disordered groups) were refined anisotropically.
The hydrogen atoms were included at calculated positions and
refined using the riding model. The fluorine atoms of the CF3
group were found to be disordered over three different rotational
[14] 2 mmol aryl halide, 2 mmol cyanide, 0.04 mmol palladium(II)
acetate, 0.08 mmol dpppe, 0.4 mmol TMEDA, 2 ml toluene,
160 8C, 16 h, in a pressure tube.
[15] Signals for PdÃ
/
C, C Ã
/
CF3 and C ÃCF3 were not detectable under
/
routine measurement conditions.