Highly active [Pd(μ-Cl)Cl(NHC)]2 complexes in the Mizoroki-Heck reaction

Article abstract of DOI:10.1002/ejic.201300169

A series of Pd dimers bearing an N-heterocyclic carbene ligand was studied in the Mizoroki-Heck reaction. [Pd(μ-Cl)Cl(SIPr)]₂ (SIPr = {N,N′-bis[2,6-(diisopropyl)phenyl]imidazolidin-2-ylidene}) was shown to be highly efficient in this cross-coup

Full text of DOI:10.1002/ejic.201300169

SHORT COMMUNICATION
DOI:10.1002/ejic.201300169
Highly Active [Pd(μ-Cl)Cl(NHC)]2 Complexes in the
Mizoroki–Heck Reaction
Ulrike I. Tessin,[a] Xavier Bantreil,[a] Olivier Songis,[a] and
Catherine S. J. Cazin*[a]
Keywords: Mizoroki–Heck reaction / Cross-coupling / Carbene ligands / Palladium
A series of Pd dimers bearing an N-heterocyclic carbene li-
gand was studied in the Mizoroki–Heck reaction. [Pd(μ-Cl)-
azolidin-2-ylidene}) was shown to be highly efficient in this
cross-coupling for a range of aryl and heterocyclic bromides,
with low palladium loading (20–200 ppm).
Cl(SIPr)]2 (SIPr
= {N,NЈ-bis[2,6-(diisopropyl)phenyl]imid-
amination,[7a] in the Suzuki–Miyaura reaction at room tem-
perature involving aryl chlorides,[7b] as well as in cross-cou-
pling of Grignard reagents at low catalyst loadings
(Scheme 1).[7c] In order to bring them a step closer to the
category of “universal cross-coupling catalysts”, we investi-
gated their catalytic behaviour in the Mizoroki–Heck cou-
pling.
Introduction
Since Mizoroki and Heck independently reported the re-
action of aryl halides with alkenes in the early 1970s,[1] the
Mizoroki–Heck coupling has been employed in numerous
applications, ranging from the synthesis of pharmaceuticals
to that of fluorescent materials.[2] Although various metals
are reported to catalyse the Mizoroki–Heck coupling,[3] Pd-
based systems are the most commonly used because of their
superior efficiency and selectivity.[4] Complexes based on N-
heterocyclic carbene (NHC)[5] ligands have been extensively
studied, leading to highly active catalysts.[6] Among them,
complexes of the type [Pd(μ-Cl)Cl(NHC)]2 are particularly
attractive, as they are highly active, air- and moisture-stable
and now commercially available.[7,8] Such systems have dis-
played outstanding performance in the Buchwald–Hartwig
Results and Discussion
The coupling of 4-bromotoluene and styrene was first
studied at 120 °C using 200 ppm Pd in the form of complex
[Pd(μ-Cl)Cl(SIPr)]2 (1) (Figure 1). Numerous bases and
high-boiling-point solvents were tested. Whereas toluene
and N-methylpyrrolidinone (NMP) gave poor conversions
with K2CO3 as base (Table 1, entries 1 and 2), dimethylacet-
amide (DMA) and N,N-dimethylformamide (DMF) rapidly
emerged as the solvents of choice, affording the coupling
product in quantitative conversions (Table 1, entries 3 and
4).
Scheme 1. Dimeric palladium complexes in coupling reactions.
[a] EaStCHEM School of Chemistry, University of St Andrews,
St Andrews, KY16 9ST, UK
Fax: +44-1334-463808
E-mail: cc111@st-andrews.ac.uk
Homepage: http://chemistry.st-andrews.ac.uk/staff/cc/group/
CSJ_Cazin/CSJC.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300169.
Figure 1. Dimeric complexes used in this study.
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SHORT COMMUNICATION
Table 1. Optimisation of the Mizoroki–Heck reaction conditions.[a] (Table 2). The conversions obtained range from modest
(59%) to good (83%), and the system based on SIPr shows
a slightly higher activity (Table 2, entries 1–4). The satu-
rated NHC ligands SIMes and SIPr were found to exhibit
better activity than those of their unsaturated counterparts
IMes and IPr (Table 2, entries 1,3 and 2,4).
Entry Solvent
Base
Pd loading Conv.[b] TON[c]
[ppm]
[%]
1
2
3
4
5
6
7
8
Toluene
NMP
DMA
DMF
DMF/H2O
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMA
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KHCO3
K3PO4
KOMe
Cs2CO3
KOtBu
CsF
Cy2NMe
NaOAc
KHCO3
K2CO3
K2CO3
KHCO3
KHCO3
200
200
200
200
200
200
200
200
200
200
200
200
200
200
20
6
8
98
99
76
300
400
Table 2. Catalyst screening.[a]
4900
4950
3800
4950
4400
Ͻ50
200
Ͻ50
2900
500
1050
3450
12500
9000
41500
49500
99
88
Entry Catalyst
Conversion[b] [%] TON[c]
Ͻ1[d]
4
9
1
2
3
4
[Pd(μ-Cl)Cl(SIPr)]2 (1)
[Pd(μ-Cl)Cl(IPr)]2 (2)
[Pd(μ-Cl)Cl(SIMes)]2 (3) 73
[Pd(μ-Cl)Cl(IMes)]2 (4) 59
83
75
41500
37500
36500
29500
10
11
12
13
14
15
16
17
18
Ͻ1[d]
58
10
21
69[e]
25
[a] Reaction conditions: 4-bromotoluene (0.5 mmol), styrene
(0.75 mmol), KHCO3 (1 mmol), DMF (2 mL), catalyst (20 ppm
Pd), 120 °C, 20 h. [b] Conversion to coupling product, based on 4-
bromotoluene, determined by GC, minimum average of two runs.
[c] Mol product/mol Pd.
20
20
20
18
83
DMF
99[f]
[a] Reaction conditions: 4-bromotoluene (0.5 mmol), styrene
(0.75 mmol), base (1 mmol), solvent (2 mL), 120 °C, 20 h. [b] Con-
version to coupling product, based on 4-bromotoluene, determined
by GC, minimum average of two runs. [c] Mol product/mol Pd.
[d] Unidentified side-products were observed in GC. [e] 100 °C. [f]
140 °C.
Table 3. Coupling of styrene with aryl and heterocyclic bromides.[a]
The use of a mixture of DMF and H2O (DMF/H2O 1:1)
induced a slight decrease in the conversion, indicating that
the presence of water is slightly detrimental to the reaction
(Table 1, entry 5). A screening of bases was next carried
out in DMF. Whereas KHCO3 also led to the quantitative
formation of the desired product (Table 1, entry 6), K3PO4,
Cs2CO3, CsF, alkoxide bases and dicyclohexylmethylamine
only led to poor/moderate conversions (Table 1, entries 7–
13). In the case of alkoxide bases, some unidentified side-
products were observed (Table 1, entries 8 and 10). The op-
timisation of the base was also performed in all solvents
previously tested, but no further improvement of the opti-
mal combination solvent/base was found (see Table S1).
Lowering the temperature to 100 °C with KHCO3 in DMF
proved to be detrimental to catalyst efficiency (Table 1, en-
try 14). At a catalyst loading of 20 ppm of Pd, the combina-
tion of DMF and KHCO3 was found to be optimal, leading
to an 83% conversion of 4-bromotoluene (Table 1, entry
17). Increasing the temperature to 140 °C allowed full con-
version with a turnover number (TON) of nearly 50000,
thus competing with highly active systems reported in the
literature (Table 1, entry 18; see Table S2 for an extensive
low-catalyst-loading study).[4a,4b]
A comparative study of NHC-based dimer precatalysts
was then carried out {Figure 1; IMes = N,NЈ-bis[2,4,6-(tri-
methyl)phenyl]imidazol-2-ylidene, SIMes = N,NЈ-bis[2,4,6-
(trimethyl)phenyl]imidazolidin-2-ylidene and IPr = N,NЈ-
bis[2,6-(di-isopropyl)phenyl]imidazol-2-ylidene}.
[a] Reaction conditions: Ar-Br or Het-Br (0.5 mmol), styrene
(0.75 mmol), KHCO3 (1 mmol), DMF (2 mL), [Pd(μ-Cl)Cl(SIPr)]2
(1), 120–140 °C, 20 h. [b] Isolated yield, minimum average of two
The catalytic activity of the four congeners was investi-
gated at 120 °C with a catalyst loading of 20 ppm Pd reactions. [c] Mol product/mol Pd.
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SHORT COMMUNICATION
(30 m, 320 μm, film: 0.25 μm). Palladium complexes 1–4[7,9]
(Table 2) were prepared according to published procedures.
The scope of the reaction with the optimised reaction
conditions and amounts of reactants was next evaluated in
the coupling of a range of aryl bromides and heterocyclic
bromides with styrene, with [Pd(μ-Cl)Cl(SIPr)]2 (1) as pre-
catalyst (Table 3).
General Procedure for the Mizoroki–Heck Reaction: In a glovebox,
a vial was charged with the base (1 mmol), the required amount of
catalyst (stock solution), the aryl bromide (if solid, 0.5 mmol) and
the solvent (2 mL). Outside the glovebox, the aryl bromide (if li-
quid, 0.5 mmol) and styrene (0.75 mmol) were injected through the
septum. The mixture was then stirred at the indicated temperature
for 20 h. The reaction mixture was allowed to cool to room tem-
perature and diluted with CH2Cl2 (7 mL). A saturated aqueous
solution of NH4Cl (20 mL) was added. The aqueous phase was
extracted with CH2Cl2 (3ϫ 10 mL), and the combined organic lay-
ers were dried with MgSO4. After filtration through cotton wool,
the solvent was evaporated. The crude product was purified by
flash column (pentane/diethyl ether) chromatography.
Complex 1 was found to be highly efficient for reactions
involving electronically activated and deactivated as well as
sterically hindered aryl bromides. Quantitative conversions
of coupling products were reached with a Pd loading of
only 100 ppm (Table 3, entries 1–6). Indeed, p-bromotolu-
ene and activated p-bromobenzaldehyde were coupled with
styrene in high isolated yields of 94% and 99%, respectively
(Table 3, entries 1 and 2). Reaction of deactivated substrates
4-bromoanisole and 4-bromoacetophenone required 140 °C
in order to efficiently proceed to completion (Table 3, en-
tries 3 and 4). The catalyst system is also efficient with or-
tho-substituted aryl bromides. Indeed, 2-bromotoluene and
1-bromonaphthalene reacted with styrene to furnish the de-
sired products in 93 and 96% yields, respectively (Table 3,
entries 5 and 6). Heteroaromatic moieties are fragments of
interest to the pharmaceutical industry. Hence, heteroarom-
atic bromides, which are known to be difficult coupling
partners, were next evaluated. In order to reach good con-
Preparation of the Catalysts Stock Solutions: The palladium com-
plex (5 μmol) was weighed into a vial, dissolved with DMF (1 mL).
Aliquots (100 μL) of this solution were diluted to 1 mL to decrease
the catalyst concentration ten times (Pd concentration 0.5–
1 μmolmL–1).
4-Methylstilbene (Table 3, entry 1):[10] Eluent: C5H12/Et2O 99:1.
Colourless solid, yield 94%. 1H NMR (300 MHz, CDCl3): δ = 7.44
(d, J = 7.3 Hz, 2 H), 7.35 (d, J = 8.2 Hz, 2 H), 7.29 (t, J = 7.3 Hz,
2 H), 7.19 (m, 1 H), 7.11 (d, J = 8.2 Hz, 2 H), 7.05 (d, J = 16.4 Hz,
version, the catalyst loading was increased to 200 ppm. 1 H), 7.00 (d, J = 16.4 Hz, 1 H), 2.30 (s, 3 H, CH3) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 137.7, 134.7, 129.5, 128.8, 127.8,
127.5, 126.57, 126.54, 21.4 ppm.
Thus, precatalyst [Pd(μ-Cl)Cl(SIPr)]2 (1) was able to couple
3-bromopyridine and 3-bromoquinoline in good to excel-
lent yields (Table 3, entries 7 and 8). Finally, 2-bromothio-
phene and 3-bromothiophene were treated with styrene in
modest yields, 66% and 42% (Table 3, entries 9 and 10),
respectively.
4-Styrylbenzaldehyde (Table 3, entry 2):[11] Eluent: C5H12/Et2O 9:1.
Pale yellow solid, yield 99%. 1H NMR (300 MHz, CDCl3): δ =
9.89 (s, 1 H, CHO), 7.77 (d, J = 8.2 Hz, 2 H), 7.55 (d, J = 8.2 Hz,
2 H), 7.44 (d, J = 7.2 Hz, 2 H), 7.29–7.13 (m, 4 H), 7.05 (d, J =
16.3 Hz, 1 H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 191.8,
143.6, 136.7, 135.5, 132.3, 130.4, 129.0, 128.6, 127.5, 127.0 ppm.
1-(4-styrylphenyl)ethanone (Table 3, entry 3):[10] Eluent: C5H12/
Et2O 4:1. Colourless solid, yield 96%. 1H NMR (300 MHz,
CDCl3): δ = 7.95 (d, J = 8.3 Hz, 2 H), 7.60–7.53 (m, 4 H), 7.39 (t,
J = 7.3 Hz, 2 H), 7.30–7.16 (m, 3 H), 2.61 (s, 3 H, CH3) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 197.7, 142.2, 136.8, 136.1,
131.6, 129.02, 128.94, 128.5, 127.6, 127.0, 126.6, 26.7 ppm.
Conclusions
[Pd(μ-Cl)Cl(SIPr)]2 (1) has been shown to be an excellent
precatalyst for the Mizoroki–Heck reaction involving aryl
and heterocyclic bromides at catalyst loadings in the ppm
range. The catalytic behaviour of this commercially avail-
able complex adds one more important cross-coupling reac-
tion to the arsenal of this family of complexes. Ongoing
work in our laboratory aims to further extend the reaction
chemistry of this very useful catalyst family not only to
other cross-coupling reactions but also to other bond-form-
ing transformations.
4-Methoxystilbene (Table 3, entry 4):[10] Eluent: C5H12/Et2O 4:1.
Colourless solid, yield 91%. 1H NMR (300 MHz, CDCl3): δ =
7.43–7.38 (m, 4 H), 7.28 (t, J = 7.6 Hz, 2 H), 7.18 (m, 1 H), 7.01
(d, J = 16.3 Hz, 1 H), 6.90 (d, J = 16.3 Hz, 1 H), 6.84 (d, J =
8.6 Hz, 2 H), 3.76 (s, 3 H, CH3) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 159.4, 137.8, 130.3, 128.8, 128.3, 127.9, 127.4, 126.8,
126.4, 114.3, 55.5 ppm.
2-Methylstilbene (Table 3, entry 5):[10] Eluent: C5H12/Et2O 99:1.
Colourless liquid, yield 93%. 1H NMR (300 MHz, CDCl3): δ =
7.67 (d, J = 6.7 Hz, 1 H), 7.60 (d, J = 7.6 Hz, 2 H), 7.36–7.25 (m,
7 H), 7.07 (d, J = 16.2 Hz, 1 H), 2.51 (s, 3 H, CH3) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 137.8, 136.5, 135.9, 130.5, 130.1,
128.8, 127.69, 127.67, 126.7, 126.3, 125.5, 20.0 ppm.
Experimental Section
General Remarks: All reactions were performed under an inert at-
mosphere of argon or nitrogen using standard Schlenk line and
glovebox techniques. Solvents were dispensed from a solvent purifi-
cation system from Innovative Technology. Flash column
chromatography was performed on silica gel 60 (230–400 mesh). 1H
1-Styrylnaphthalene (Table 3, entry 6):[10] Eluent: C5H12/Et2O 90:5.
and 13C{1H} NMR spectra were recorded, at 300 and 75 MHz, Pale yellow liquid, yield 96%. 1H NMR (300 MHz, CDCl3): δ =
respectively, with a Bruker Spectrospin 300 MHz spectrometer op-
erating at 298 K. Proton and carbon chemical shifts were internally
referenced to the residual proton resonance in CDCl3 [δ = 7.26 and
77.16 ppm, respectively]. Gas chromatography (GC) analyses were
performed with an Agilent 7890A apparatus equipped with a flame
ionisation detector and a (5%-phenyl)methylpolysiloxane column
8.24 (d, J = 7.4 Hz, 1 H), 7.93–7.86 (m, 2 H), 7.81 (d, J = 8.2 Hz,
1 H), 7.76 (d, J = 7.2 Hz, 1 H), 7.62 (d, J = 8.5 Hz, 2 H), 7.56–
7.47 (m, 3 H), 7.44–7.39 (m, 2 H), 7.34–7.31 (m, 1 H), 7.16 (d, J
= 16.3 Hz, 1 H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 137.8,
135.2, 133.9, 131.9, 131.5, 128.9, 128.8, 128.2, 127.9, 126.8, 126.2,
126.0, 125.8, 123.9, 123.8 ppm.
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SHORT COMMUNICATION
3-Styrylpyridine (Table 3, entry 7):[12] Eluent: C5H12/Et2O 70:30.
Colourless solid, yield 78%. 1H NMR (300 MHz, CDCl3): δ = 8.73
(d, J = 2.2 Hz, 1 H), 8.48 (dd, J = 3.2, 1.6 Hz, 1 H), 7.84 (dt, J =
8, 2.2 Hz, 1 H), 7.53 (d, J = 7.3 Hz, 2 H), 7.39 (t, J = 7.3 Hz, 2
H), 7.33–7.26 (m, 2 H), 7.18 (d, J = 16.5 Hz, 1 H), 7.5 (d, J =
16.5 Hz, 1 H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 148.7,
136.7, 133.1, 132.7, 130.9, 128.9, 128.3, 126.8, 125.0, 123.6 ppm.
3-Styrylquinoline (Table 3, entry 8):[12] Eluent: C5H12/Et2O 85:15.
Pale yellow solid, yield 99%. 1H NMR (300 MHz, CDCl3): δ =
9.10 (d, J = 2.1 Hz, 1 H), 8.13 (d, J = 2 Hz, 1 H), 8.07 (d, J =
8.5 Hz, 1 H), 7.79 (dd, J = 8.1, 1.2 Hz, 1 H), 7.67–7.62 (m, 1 H),
7.56–7.48 (m, 3 H), 7.40–7.25 (m, 4 H), 7.20 (d, J = 16.6 Hz, 1 H)
ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 149.6, 147.6, 136.9,
132.4, 131.1, 130.4, 129.4, 129.3, 129.0, 128.4, 128.2, 128.0, 127.1,
126.8, 125.3 ppm.
2-Styrylthiophene (Table 3, entry 9):[12] Eluent: C5H12/Et2O 85:15.
Pale yellow solid, yield 66%. 1H NMR (300 MHz, CDCl3): δ =
7.49–7.46 (m, 2 H), 7.38–7.33 (m, 2 H), 7.28–7.19 (m, 3 H), 7.08
(m, 1 H), 7.03–7.00 (m, 1 H), 6.94 (d, J = 16.1 Hz, 1 H) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 143.0, 137.1, 131.0, 128.8,
128.5, 127.7, 126.4, 126.2, 124.5, 121.9 ppm.
3-Styrylthiophene (Table 3, entry 10):[10] Eluent: C5H12/Et2O 85:15.
Pale yellow solid, yield 42%. 1H NMR (300 MHz, CDCl3): δ =
7.49–7.46 (m, 2 H), 7.36–7.30 (m, 4 H), 7.26–7.21 (m, 2 H), 7.12
(d, J = 16.3 Hz, 1 H), 6.95 (d, J = 16.3 Hz, 1 H) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 140.3, 137.5, 128.8, 127.6, 126.4,
126.3, 125.1, 123.0, 122.5 ppm.
S. Hsu, J. Polym. Sci., Part A 2009, 47, 2713; d) X. Huang, Y.
Xu, Q. Miao, L. Zong, H. Hu, Y. Cheng, Polymer 2009, 50,
2793; e) J. A. Mikroyannidis, M. M. Stylianakis, K. Y. Cheung,
M. K. Fung, A. B. Djurisˇic´, Synth. Met. 2009, 159, 142.
[3] a) R. Loska, C. M. Rao Volla, P. Vogel, Adv. Synth. Catal.
2008, 350, 2859; b) K. Mitsudo, T. Imura, T. Yamaguchi, H.
Tanaka, Tetrahedron Lett. 2008, 49, 7287.
[4] a) M. Oberholzer, R. Gerber, C. M. Frech, Adv. Synth. Catal.
2012, 354, 627; b) P. Srinivas, K. Srinivas, P. R. Likhar, B. Srid-
har, K. V. Mohan, S. Bhargava, M. L. Kantam, J. Organomet.
Chem. 2011, 696, 795; c) I. P. Beletskaya, A. V. Cheprakov,
Chem. Rev. 2000, 100, 3009; d) R. B. Bedford, C. S. J. Cazin,
D. Holder, Coord. Chem. Rev. 2004, 248, 2283; e) N. T. S. Phan,
M. Van der Sluys, C. W. Jones, Adv. Synth. Catal. 2006, 348,
609; f) V. T. Trepohl, M. Oestreich in Modern Arylation Meth-
ods (Ed.: L. Ackermann), Wiley-VCH, Weinheim, 2009, p. 221.
[5] a) S. Díez-González, N. Marion, S. P. Nolan, Chem. Rev. 2009,
109, 3612; b) C. S. J. Cazin (Ed.), N-Heterocyclic Carbenes in
Transition Metal Catalysis and Organocatalysis, Springer, New
York, 2011.
[6]
a) N. Marion, O. Navarro, J. Mei, E. D. Stevens, N. M. Scott,
S. P. Nolan, J. Am. Chem. Soc. 2006, 128, 4101; b) A. Char-
toire, M. Lesieur, L. Falivene, A. M. Z. Slawin, L. Cavallo,
C. S. J. Cazin, S. P. Nolan, Chem. Eur. J. 2012, 18, 4517; c) A.
Chartoire, X. Frogneux, S. P. Nolan, Adv. Synth. Catal. 2012,
354, 1897; d) A. R. Martin, A. Chartoire, A. M. Z. Slawin, S. P.
Nolan, Beilstein J. Org. Chem. 2012, 8, 1637; e) V. Jurcˇík, S. P.
Nolan, C. S. J. Cazin, Chem. Eur. J. 2009, 15, 2509; f) S. Fanta-
sia, J. D. Egbert, V. Jurcˇík, C. S. J. Cazin, H. Jacobsen, L. Cav-
allo, D. M. Heinekey, S. P. Nolan, Angew. Chem. 2009, 121,
5284; Angew. Chem. Int. Ed. 2009, 48, 5182; g) C. E. Hart-
mann, V. Jurcˇík, O. Songis, C. S. J. Cazin, Chem. Commun.
2013, 49, 1005; h) J. Broggi, V. Jurcˇík, O. Songis, A. Poater, L.
Cavallo, A. M. Z. Slawin, C. S. J. Cazin, J. Am. Chem. Soc.
2013, DOI: 10.1021/ja311087c; i) T. E. Schmid, D. C. Jones, O.
Songis, O. Diebolt, M. R. Furst, A. M. Z. Slawin, C. S. J. Ca-
zin, Dalton Trans. 2013, DOI: 10.1039/c2dt32858e.
Supporting Information (see footnote on the first page of this arti-
cle): Solvent and base screening, experiments with low catalyst
1
loading, H and 13C{1H} NMR spectra of all biaryl products.
Acknowledgments
[7]
a) M. S. Viciu, R. M. Kissling, E. D. Stevens, S. P. Nolan, Org.
Lett. 2002, 4, 2229; b) O. Diebolt, P. Braunstein, S. P. Nolan,
C. S. J. Cazin, Chem. Commun. 2008, 3190; c) C. E. Hartmann,
S. P. Nolan, C. S. J. Cazin, Organometallics 2009, 28, 2915; d)
S. Akzinnay, F. Bisaro, C. S. J. Cazin, Chem. Commun. 2009,
5752.
The authors are grateful to the Royal Society (University Research
Fellowship to C. S. J. C), the Engineering and Physical Sciences Re-
search Council (EPSRC) and the EaStCHEM School of Chemistry
for funding and to Umicore for the loan of palladium salts.
[8] [Pd(μ-Cl)Cl(SIPr)]2 (1) and [Pd(μ-Cl)Cl(IPr)]2 (2) are commer-
cially available.
[1] a) T. Mizoroki, K. Mori, A. Ozaki, Bull. Chem. Soc. Jpn. 1971,
44, 581; b) R. F. Heck, J. P. Nolley Jr., J. Org. Chem. 1972, 37,
2320.
[2] For examples, see: a) C. Torborg, M. Beller, Adv. Synth. Catal.
2009, 351, 3027; b) D. Schils, F. Stappers, G. Solberghe, R.
van Heck, M. Coppens, D. Van den Heuvel, P. Van der Donck,
T. Callewaert, F. Meeussen, E. De Bie, K. Eersels, E. Schout-
eden, Org. Process Res. Dev. 2008, 12, 530; c) S.-H. Yang, C.-
[9] D. R. Jensen, M. S. Sigman, Org. Lett. 2003, 5, 63.
[10] B. Mu, T. Li, W. Xu, G. Zeng, P. Liu, Y. Wu, Tetrahedron 2007,
63, 11475.
[11] J. Bietz, H. Ritter, Macromol. Chem. Phys. 2009, 210, 1114.
[12] K. M. Dawood, W. Solodenko, A. Kirsching, ARKIVOC 2007,
104.
Received: February 3, 2013
Published Online: March 18, 2013
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