Investigation of the Catalytic Activity of a 2-Phenylidenepyridine Palladium(II) Complex Bearing 4,5-Dicyano-1,3-bis(mesityl)imidazol-2-ylidene in the Mizoroki-Heck Reaction

Article abstract of DOI:10.1002/zaac.201500625

The phenylidenepyridine (ppy) palladacycles [PdCl(ppy)(IMes)] (4) [IMes = 1,3-bis(mesityl)imidazol-2-ylidene] and [PdCl(ppy){(CN)₂IMes}] (6) [(CN)₂IMes = 4,5-dicyano-1,3-bis(mesityl)imidazol-2-ylidene] were prepared by facile two ste

Full text of DOI:10.1002/zaac.201500625

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DOI: 10.1002/zaac.201500625
Investigation of the Catalytic Activity of a 2-Phenylidenepyridine
Palladium(II) Complex Bearing 4,5-Dicyano-1,3-bis(mesityl)imidazol-2-
ylidene in the Mizoroki-Heck Reaction
Heiko Baier,[a] Alexandra Kelling,[a] Uwe Schilde,[a] and Hans-Jürgen Holdt*[a]
Keywords: Carbene ligands; Heck reaction; Palladium; Selenium; C–C coupling
Abstract.
The
phenylidenepyridine
(ppy)
palladacycles atom better than IMes. As a measure for the π-acceptor strength of
(CN)2IMes compared to IMes, the selone (CN)2IMes·Se (7) was pre-
pared and characterized by 77Se-NMR spectroscopy. The π-acceptor
strength of 7 was illuminated by the shift of its 77Se-NMR signal. The
77Se-NMR signal of 7 was shifted to much higher frequencies than the
77Se-NMR signal of IMes·Se. Catalytic experiments using the Mizo-
roki-Heck reaction of aryl chlorides with n-butyl acrylate showed that
6 is the superior performer in comparison to 4. Using complex 6, an
extensive substrate screening of 26 different aryl bromides with n-
butyl acrylate was performed. Complex 6 is a suitable precatalyst for
para-substituted aryl bromides. The catalytically active species was
identified by mercury poisoning experiments to be palladium nanopar-
ticles.
[PdCl(ppy)(IMes)] (4) [IMes = 1,3-bis(mesityl)imidazol-2-ylidene]
and [PdCl(ppy){(CN)2IMes}] (6) [(CN)2IMes = 4,5-dicyano-1,3-
bis(mesityl)imidazol-2-ylidene] were prepared by facile two step syn-
theses, starting with the reaction of palladium(II) chloride with 2-phen-
ylpyridine followed by subsequent addition of the NHC ligand to the
precatalyst precursor [PdCl(ppy)]2. Suitable crystals for the X-ray
analysis of the complexes 4 and 6 were obtained. It was shown that 6
has a shorter NHC-palladium bond than the IMes complex 4. The
difference of the palladium carbene bond lengths based on the higher
π-acceptor strength of (CN)2IMes in comparison to IMes. Thus,
(CN)2IMes should stabilize the catalytically active central palladium
sterically as well as electronically, by variation of the nitrogen
substituents or the backbone substituents, respectively.[4] Thus,
ligands for every special purpose can be generated.
Introduction
Since the first mention of the arylation of olefins by R. F.
Heck[1a] and the benzylation of olefins by T. Mizoroki[1a] in the
early 1970s, the so called Mizoroki-Heck reaction became one
of the most important and most intensively discussed catalytic
reactions so far. It is used for the synthesis of pharmaceuticals
and natural products.[1c–j] A great advantage of the Mizoroki-
Heck reaction is that no organometallic substrate is required
for the cross coupling reaction.
One of the greatest challenges for synthetic chemists is the
development of new precatalysts. Tertiary phosphines have
been the ligands of choice for palladium catalyzed reactions
until the middle 1990s. A change of course concerning the
development of palladium(II) precatalysts was initiated by the
presentation of the first palladium precatalysts bearing N-het-
erocyclic carbenes (NHCs) by W. A. Herrmann.[2] In the last
two decades, various NHCs for the application in palladium
catalyzed reactions were presented. In combination with suit-
able coligands, a broad scope of effective NHC-palladium(II)
precatalysts was prepared.[3] NHCs can easily be modified,
One of the most renowned precatalyst families are the
PEPPSI complexes presented by M. Organ (PEPPSI: Pyridine
Enhanced Precatalyst Preparation, Stabilization and Initia-
tion).[5] PEPPSI complexes are palladium(II) complexes with
a pyridine ligand in trans position and two halido ligands in
cis position to the NHC. In a contribution by M. Organ in
2010, the pyridine and one halido ligand were substituted
by 2-phenylidenepyridine (ppy) to obtain precatalyst
[PdCl(ppy)(IPr)] (1) [IP = 1,3-bis(2,6-diisopropylphenyl)imid-
azol-2-ylidene] (Scheme 1).[6] With this complex, the Kumada-
Tamao-Currio (KTC) reaction of phenylmagnesium chloride
with 4-chloroanisole was performed efficiently.
* Prof. Dr. H.-J. Holdt
Fax: +49-331-9775055
E-Mail: holdt@uni-potsdam.de
[a] Chair of Inorganic Chemistry
Universität Potsdam
Scheme 1. Precatalyst 1 for the Kumada-Tamao-Currio reaction pre-
sented by M. Organ.[6]
Karl-Liebknecht-Straße 24–25
14476 Golm, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201500625 or from the au-
thor.
Another modification of the PEPPSI motif was designed by
Navarro et al., who used diethylamine and triethylamine as so
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called “throw away ligands” in trans position to the NHC-
Results and Discussion
ligand.[6b–f] In combination with sterically demanding NHC li-
gands, they prepared extremely reactive precatalysts for cross-
coupling reactions.[6e]
Syntheses
The formation of the palladium(II) precatalysts 4 and 6 was
achieved in a straight forward two step synthesis. Stirring pal-
ladium(II) chloride and 2-phenylpyridine in methanol for 16 h
at room temperature resulted in the already known dinuclear
complex [PdCl(ppy)]2 (2). Complex 2 was refluxed in aceto-
nitrile in the presence of one equivalent 1,3-bis(mesityl)imid-
azolium chloride (3) and four equivalents potassium carbonate
to yield 4 in 50% overall yield after 4 h. Complex 6 was
formed in 50% overall yield by refluxing 2 and two equiva-
In the recent years, our group presented a series of
palladium(II) precatalysts for the Mizoroki-Heck as well as the
Suzuki-Miyaura reaction.[7,8] The precatalysts in these studies
were bearing the strong acceptor carbene 4,5-dicyano-1,3-
bis(mesityl)imidazol-2-ylidene [(CN)2IMes]. In comparison to
analogous complexes bearing the well-known donor NHC 1,3-
bis(mesityl)imidazol-2-ylidene (IMes), the precatalysts bearing
(CN)2IMes were superior performers in the catalytic reactions
used for these studies (Scheme 2).
lents
4,5-dicyano-1,3-dimesityl-2-(pentafluorophenyl)imid-
azoline (5) in toluene for 16 h. The complexes were purified
by liquid chromatography on silica (Scheme 3).
Scheme 2. NHCs IMes (left) and (CN)2IMes (right) in this study.
As it was shown by M. Organ that ppy palladium(II) com-
plexes could be used as an efficient precatalysts in cross cou-
pling reactions, we wanted to take a more general look at NHC
ppy palladium(II) complexes. For this purpose, the NHC moi-
ety of ppy palladium(II) complexes should be varied concern-
ing the π-accepting abilities of the NHC ligand and the cata-
lytic activity of the resulting precatalysts should be monitored
in reference to the acceptor strength of the used NHC ligand.
In this contribution, we present the synthesis, the characteri-
zation, and the application of the two NHC-phenylidenepyrid-
ine palladium(II) complexes [PdCl(ppy)(IMes)] (4) and
[PdCl(ppy){(CN)2IMes}] (6) in a Mizoroki-Heck reaction of
aryl halides and n-butyl acrylate. It was evident after the initial
catalytic experiments, that 6 performs the Mizoroki-Heck reac-
tion more efficient than 4. Thus, further experiments were per-
Scheme 3. Synthetic route to the [PdCl(ppy)(NHC)] complexes 4 and
6.
The synthesis of 4,5-dicyano-1,3-bis(mesityl)imidazol-2-se-
lone (7) was performed in one step by refluxing 5 for 16 h in
formed exclusively with precatalyst 6. Poisoning experiments toluene in the presence of four equivalents of grey selenium.
After subsequent purification of the crude product by liquid
chromatography, the pure selenourea derivative 7 was obtained
in a yield of 80% (Scheme 4).
with elemental mercury showed, that the reactions were cata-
lyzed by palladium nanoparticles in the case of 4 as well as of
6. The results of the poisoning experiments match with the
results of our observations in former catalytic studies.[7,8]
The major method for the determination of the acceptor
strength of NHC ligands is the determination of Tolman elec-
tronic parameters (TEP).[9] But when only information about
the π-acceptor strength are needed, other methods are prefera-
ble. C. Ganter presented a series of NHC selenium adducts,
which were characterized by means of 77Se-NMR spec-
troscopy.[10] The 77Se-NMR signals of the investigated selones
are shifted to higher frequencies as the π-acceptor strength of
the NHC moieties increase. Thus, the 4,5-dicyano-1,3-bis(mes-
ityl)imidazol-2-selone (7) was prepared to take a closer look
at the π-acceptor strength of (CN)2IMes. It could be shown
that the 77Se-NMR signal of 7 was shifted to much higher
frequencies than the signal for the literature known 1,3-bis(me-
sityl)imidazol-2-selone.[11]
Scheme 4. Synthesis of the selone (CN)2IMes·Se (7).
The compounds 4, 6 and 7 were characterized by means of
1H- and 13C-NMR spectroscopy, FT-IR spectroscopy, elemen-
tal analysis (H, C, N) as well as by means of high resolution
mass spectroscopy. The selone 7 was additionally charac-
terized by means of 77Se-NMR spectroscopy.
With the 77Se-NMR spectroscopic data of 7, the π-acceptor
strength was measured. The 77Se-NMR signal of 7 was found
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at δ = 167 ppm chemical shift relative to dimethylselenide in
chloroform. S. P. Nolan reported the 77Se-NMR signal for the
analogous 1,3-bis(mesityl)imidazol-2-selone to be found at δ
= 27 ppm.[11] As 77Se-NMR signals of selones shift to higher
frequencies with increasing π-acceptor strength of the substitu-
ents, it is clear that (CN)2IMes has to be a much stronger π-
acceptor than IMes.
X-ray Diffraction
Single crystals suitable for the X-ray analysis were obtained
for the palladium(II) complexes 4 and 6 as well as for the
selone 7. Complex 4 and selone 7 crystallize by slow diffusion
of pentane steam into a concentrated dichloromethane solution
containing 4 and 7, respectively. Complex 6 crystallizes by
slow solvent evaporation of a saturated acetonitrile solution
containing 6.
Figure 1. Molecular structure of [PdCl(ppy)(IMes)] (4). Thermal ellip-
soids are drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity.
The asymmetric unit of 4 contains two independent complex
molecules. In the asymmetric unit of 6, one complex molecule
and 1.25 acetonitrile solvent molecules from the crystallization
were found. Selected bond lengths, angles, and torsion angles
are given in Table 1.
Table 1. Selected bond lengths /Å, angles /°, and torsion angles /° of
the [PdCl(ppy)(NHC)] complexes 4 and 6.
4a)
6
C1–Pd1
C1–N1
C1–N2
Pd1–C24
Pd1–N5
Pd1–Cl1
N1–C1–N2
C4–C2–C3–C5
C1–N1–C15–C16
C1–N2–C6–C7
1.992(5)/1.988(5)
1.373(6)/1.375(6)
1.353(6)/1.350(7)
1.956(6)/1.974(5)
2.092(4)/2.093(4)
2.4096(15)/2.4061(15)
104.0(4)/103.7(4)
–
1.976(4)
1.372(4)
1.359(4)
1.994(4)
2.089(3)
2.3954(9)
104.9(3)
2.2(7)
66.0(7)/105.5(6)
–102.3(6)/–66.1(7)
73.4(5)
–95.1(4)
a) Data for the second molecule in the asymmetric unit are given in
italic letters.
Figure 2. Molecular structure of [PdCl(ppy){(CN)2IMes}] (6). Ther-
mal ellipsoids are drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity.
The molecular structures of 4 and 6 have slightly distorted
square-planar coordination arrangements (Figure 1 and Fig-
ure 2). In analogous manner to the literature known palladi-
um(II) complex [PdCl(ppy)(IPr)] (1) (Scheme 1), the N-donor
of the ppy ligand stands in trans position and the phenylidene
moiety of the ppy ligand is coordinated in cis position to the nitrile groups of (CN)2IMes hinder the rotation of the mesityl
NHC ligand. Because (CN)2IMes is a stronger π-acceptor than groups sterically and thus lead to torsion angles, which con-
IMes, the C1–Pd1 bond in complex 6 is shorter than the C1– verge more towards perpendicularity than the mesityl groups
Pd1 bond in 4. The bond length difference is about 0.015 Å.
Different torsions for the two mesityl substituents in IMes
in IMes.
The asymmetric unit of C2 symmetric selone 7 contains half
as well as in (CN)2IMes was observed for complexes 4 and 6, a molecule of the selone. The other half of the molecule was
respectively. In both NHC ligands, one mesityl group is generated corresponding to the C2 symmetry of the molecule
twisted to an almost rectangular position relative to the plane (Figure 3). In analogous manner to the comparison of the C1–
of the carbene ring. The second mesityl group diverged further Pd1 bond lengths of the palladium(II) complexes 4 and 6, the
from perpendicularity. A difference in the twist of the mesityl C1–Se1 bond of 7 was compared to the C1–Se1 bond of 1,3-
groups was detected between IMes in 4 and (CN)2IMes in 6. bis(mesityl)imidazol-2-selone.[12] The C1–Se1 bond in 7
The two mesityl groups in complex 4 are twisted further away [1.794(5) Å] is 0.04 Å shorter than the C1–Se1 bond in the
from orthogonality than the corresponding mesityl substituents selone from IMes. This difference in the C1–Se1 bond lengths
in complex 6 [torsions in 4: 66.0(7)/105.5(6)° and –102.3(6)/ confirms, in agreement to the 77Se-NMR experiments, that
–66.1(7)°; torsions in 6: 73.4(5)° and –95.1(4)°]. Probably, the (CN)2IMes is a strong π-acceptor in comparison to IMes.
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Table 2. Yields of the Mizoroki-Heck reaction of aryl chlorides with
n-butyl acrylate using the [PdCl(ppy)(NHC)] complexes 4 and 6.a)
Entry
GC yieldb) /%
Aryl chloride
4
6
1
2
3
Chlorobenzene
4-Chloroanisole
4-Chloroacetophenone
0
0
10
0
0
31
a) Reaction conditions: T = 140 °C (oil bath), t = 16 h, aryl chloride
(1.0 equiv.), n-butyl acrylate (2.0 equiv.), Na2CO3 (1.4 equiv.), TBAB
(0.1 equiv.), precatalyst (0.1 mol%) in DMF (0.5 mL). b) Yields were
determined from two independent runs by GC-FID using 1,3,5-tri-
methoxybenzene as internal standard.
Due to the inferior catalytic activity of IMes complex 4,
further catalytic reactions of aryl bromides with n-butyl acry-
late were performed exclusively with (CN)2IMes complex 6
(Scheme 6). The substrate screening of aryl bromides was con-
ducted for 26 aryl bromides with differing electronic and steric
properties.
Figure 3. Molecular structure of 4,5-dicyano-1,3-bis(mesityl)imidazol-
2-selone (7). Thermal ellipsoids are drawn at the 50% probability
level. Selected bond lengths /Å, angles /° and torsion angles /°: C1–
Se1 1.798(5); C1–N1 1.376(5); C1–N1i 1.376(5); N1–C2 1.381(5);
N1i–C2i 1.381(5); N1–C1–Ni1 104.8(4); C1–N1–C2 110.6(3); C1–
N1i–C2i 110.6(3); C3–C2–C2i–C3i 0.4(7). Hydrogen atoms are omit-
ted for clarity.
Catalytic Studies
Recently, our group used the Mizoroki-Heck reaction as test
system for the proof of the catalytic activity of palladium(II)
complexes bearing (CN)2IMes.[7] The tested precatalysts un-
fortunately decomposed in the reaction mixture under the harsh
Mizoroki-Heck conditions and formed palladium nanopar-
ticles. Thus, complexes 4 and 6 with the robust ppy moiety
should be tested in the Mizoroki-Heck reaction with the goal
of avoiding the nanoparticle formation.
The catalytic screening was performed, according to our for-
mer Mizoroki-Heck study, in N,N-dimethylformamide (DMF)
using one equivalent aryl halide, two equivalents n-butyl acry-
late, 0.1 mol% precatalyst, 1.4 equivalents sodium carbonate,
and 0.1 equivalents tetra-(n-butyl)ammonium bromide
(TBAB) (Scheme 5). The reaction time was set to 16 h and the
reaction temperature to 140 °C (oil bath). Product yields were
determined by gas chromatography, using 1,3,5-trimethoxy-
benzene as the internal standard.[7]
Scheme 6. General reaction conditions for the Mizoroki-Heck reaction
of aryl bromides with n-butyl acrylate using the precatalyst 6.
In general, complex 6 is a suitable precatalyst for aryl brom-
ides. Good to excellent product yields were obtained with
para-substituted aryl bromides. No general trend between the
yields of aryl bromides bearing electron donating para substit-
uents or electron withdrawing para substituents was identified.
The yields for the Mizoroki-Heck reaction of bromoanisoles
and bromophenoles decreased with increasing steric stress of
the aryl bromides from the para to the meta and subsequently
to the ortho derivative (Table 3, entries 3–5 and 16–18). Using
sterically stressed and additionally donor substituted aryl
bromides lead to yields of 4% for bromomesitylene (Table 3,
entry 19) or no yield at all for bromo-2,4,6-triisopropylbenzene
(Table 3, entry 23). The reaction of bases like 4-bromoaniline
and 3-bromopyridine lead to the desired products in moderate
to good yields (Table 3, entries 15 and 22). Also, good yields
were achieved for enhanced aromatic systems (Table 3, entries
25 and 26). Even the electronically deactivated 1-bromo-3,4,5-
trimethoxybenzene could be converted into the desired cinna-
mate in good 60% yield (Table 3, entry 24).
It is known from former studies for complexes bearing IMes
or (CN)2IMes to form palladium nanoparticles.[7,8] These
nanoparticles were the catalytically active species for catalytic
processes. Being aware of this fact, poisoning experiments
Scheme 5. General reaction conditions for the Mizoroki-Heck reaction
of aryl chlorides with n-butyl acrylate using the precatalysts 4 and 6.
The catalytic activity of precatalysts 4 and 6 was initially using elemental mercury were performed for the Mizoroki-
determined by the Mizoroki-Heck reaction of aryl chlorides Heck reaction of bromobenzene with n-butyl acrylate and pre-
with n-butyl acrylate (Table 2). No conversion at all was deter- catalysts 4 and 6. No product yield was obtained after 8 h
mined for the reaction of chlorobenzene and 4-chloroanisole when mercury was deployed to the reaction mixture at the start
using the precatalysts 4 and 6. For the reaction of 4-chloroace- of a reaction. When mercury was added to separate reaction
tophenone, the (CN)2IMes complex 6 yielded the desired cou- mixtures after 4 h, no further product formation was observed
pling product in a yield of 31%. A yield of only 10% was upon the addition of mercury (Figure 4). Crudden et al.
obtained using IMes complex 4 (Table 2, entry 3).
showed, that palladium black formation is a common problem,
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Table 3. Yields of the Mizoroki-Heck reaction of aryl bromides with the chelating coligand. Probably, a longer time is required for
n-butyl acrylate using [PdCl(ppy){(CN)2IMes}] (6).a)
the phenylidenepyridine moiety to dissociate than for the dmba
moiety in [PdCl(dmba){(CN)2IMes}].[7] The curve for the poi-
soning experiment of complex 4 is not depicted in Figure 4 as
the data points for the first, most important checkpoints match
the data determined for 6.
As the catalytically active species formed from precatalysts
4 and 6 are palladium nanoparticles, differences in the catalytic
activity should be caused by differences in the nanoparticle
size. Unfortunately, TEM measurements did not provide
images fit for the determination of particle size distributions
due to massive impurities of the organic bulk. No representa-
tive TEM images were found in the data set.
Entry
Aryl bromide
GC-yieldb) /%
1
2
3
4
5
6
7
8
Bromobenzene
4-Bromoacetophenone
4-Bromoanisole
3-Bromoanisole
2-Bromoanisole
73
60
73
66
53
77
54
88
85
50
85
46
90
90
74
84
72
48
4
4-Bromobenzaldehyde
4-Bromotoluene
4-Bromofluorobenzene
2-Bromofluorobenzene
4-Bromo-N,N-diethylaniline
4-Bromonitrobenzene
2-Bromo-5-nitroanisole
4-Bromo(methylbenzoate)
4-Bromobenzonitrile
4-Bromoaniline
4-Bromophenol
3-Bromophenol
2-Bromophenol
Bromomesitylene
1,4-Dibromobenzene
2-Bromobiphenyl
3-Bromopyridine
1-Bromo-2,4,6-triisopropylbenzene
1-Bromo-3,4,5-trimethoxybenzene 60
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Conclusions
Two palladium(II) complexes, 4 bearing the well known
IMes and 6 bearing the maleonitrile based (CN)2IMes, were
prepared. X-ray structures of complexes 4 and 6 were obtained
and the higher acceptor strength of (CN)2IMes in comparison
to IMes, was observed by the shorter palladium-carbene bond
in 6, compared to the palladium-carbene bond in 4. The π-
accepting ability of (CN)2IMes was also shown by 77Se-NMR
spectroscopy of the selone 7 derived from (CN)2IMes. The
77Se-NMR signal of 7 was found at δ = 167 ppm and is shifted
to much higher frequencies than the signal of the selone de-
rived from IMes. The two complexes 4 and 6 were used as
precatalysts in the Mizoroki-Heck reaction of aryl chlorides
with n-butyl acrylate. Because 6 proved the more effective pre-
catalyst, it was used for a substrate screening in the Mizoroki-
Heck reaction using various aryl bromides and n-butyl acry-
late. It could be shown that sterically unhindered aryl bromides
were effectively converted into the desired cinnamates under
the use of precatalyst 6. The product yields massively de-
creased, when the steric stress of the aryl bromides was in-
creased. Palladium nanoparticles were identified to be the cata-
lytically active species when 4 and 6 are used as precatalysts.
The nanoparticles formed from 4 are bigger than the nanopar-
ticles formed from 6. The size difference illustrates the differ-
ence in the reactivity of 4 and 6, respectively. Also, an initia-
tion phase of approximately ten minutes was determined for 4
and 6.
82
84
41
0
1-Bromonaphtalene
9-Bromoanthracene
72
71
a) Reaction conditions: T = 140 °C (oil bath), t = 16 h, aryl bromide
(1.0 equiv.), n-butyl acrylate (2.0 equiv.), Na2CO3 (1.4 equiv.), TBAB
(0.1 equiv.), 6 (0.1 mol%) in DMF (0.5 mL). b) Yields were deter-
mined from two independent runs by GC-FID using 1,3,5-trimeth-
oxybenzene as internal standard.
when high reaction temperatures are used, even when PEPPSI-
type complexes are deployed as precatalysts.[13]
Experimental Section
General Information: All manipulations were carried out in an argon
atmosphere using standard Schlenk techniques. Dry solvents were used
for all manipulations. Solvents were dried after literature pro-
cedures.[14] All other chemicals were purchased from commercial
sources and used for the reactions as received. Compounds 2,[15] 3,[16]
and 5,[17] were synthesized as described in the literature. Elemental
analyses (C, H, N) were performed with an Elementar Vario EL ele-
mental analyzer. NMR spectra were recorded with a Bruker Avance
Figure 4. Reaction rate in the Mizoroki-Heck reaction of bromobenz-
ene with n-butyl acrylate using 6 as precatalyst and adding mercury
after 4 h.
It was also seen that complexes 4 and 6 did not start the
reaction immediately. Both complexes needed an initiation
phase of approximately ten minutes. No product formation was
observed over this time. Such an initiation phase was not deter-
mined for other complexes bearing (CN)2IMes. The catalyti-
1
300 or Bruker Avance 500 spectrometer. Resonances for H- and 13C-
NMR spectra are reported relative to Me4Si (δ = 0.0 ppm) and cal-
ibrated based on the solvent signal for 1H and 13C.[18] Resonances
for 77Se-NMR spectra are reported relative to the external standard
cally active species has to be built from 6 by dissociation of dimethylselenide (60% in CDCl3). Spectra are reported as follows:
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Table 4. Crystallographic data of 4, 6, and 7.
4
6
7
Formula
C64Cl2H64N6Pd2
1200.91
0.38ϫ0.193ϫ0.09
210(2)
C36.5H33.75ClN6.25Pd
701.80
0.125ϫ0.11ϫ0.07
150(2)
C23H22N4Se
433.40
0.2ϫ0.1ϫ0.09
210(2)
Mr /g·mol–1
Crystal size /mm
T /K
Radiation
Crystal system
Space group
a /Å
b /Å
c /Å
Mo-Kα
Mo-Kα
tetragonal
I41/a
18.3141(5)
18.3141(5)
40.6086(15)
90.00
90.00
90.00
13620.4(9)
16
1.369
Mo-Kα
orthorhombic
Fdd2
10.2554(5)
36.6514(13)
11.3895(4)
90.00
90.00
90.00
4281.0(3)
8
1.345
triclinic
¯
P1
10.3427(5)
15.7477(7)
17.6547(9)
92.394(4)
94.045(4)
106.530(3)
2744.0(2)
2
α /°
β /°
γ /°
V /Å3
Z
ρcalcd. /g·cm–3
1.453
0.800
μ /mm–1
0.658
1.769
Refl. measured
Unique refl.
Rint
16884
8621
0.0403
44174
6003
0.0706
13521
1895
0.0475
2Θ max.
49.106
49.996
49.996
R1; wR2 [IϾ2 σ(I)]
R1; wR2 (all data)
Difference dens. min./max.
Goodness of fit
0.0435/0.1152
0.0634/0.1225
–0.804 / 0.696
1.072
0.0379/0.0858
0.0640/0.0956
–0.470 / 0.478
1.011
0.0261/0.0663
0.0289/0.0678
–0.322 / 0.321
1.052
chemical shift (δ ppm), multiplicity, integration and coupling constant
(Hz). Mass spectra were recorded with a Micromass Q-TOFmicro (ESI)
or with a Thermo Quest SSQ 710 (70eV) (EI). IR Spectra were re-
romethane as eluent. Complex 4 was obtained in 55% yield as a color-
less solid. EA: C 63.90, H 5.53, N 6.99%; found: C 63.89, H 5.68, N
7.12%. HR-MS (EI) m/z: calcd. for C32H33ClN3Pd: 600.1398 [M]+;
1
corded with a Thermo Nicolet NEXUS FTIR in a KBr disk between found: 600.1404 [M]+. H NMR (300 MHz, CDCl3): δ = 9.29 (d, J =
400 and 4000 cm–1 and with a resolution of 4 cm–1. Background mea-
surements were performed before the measuring the samples using a 1 H), 7.54 (d, J = 7.8 Hz, 1 H), 7.23 (s, 2 H), 7.09–6.85 (m, 8 H),
5.7 Hz, 1 H), 7.67 (dt, J = 7.5, 1.8 Hz, 1 H), 6.82 (dd, J = 7.3, 1.5 Hz,
KBr disc or dichloromethane between KBr plates respectively. Single
6.79 (dd, J = 7.5, 1.2 Hz, 1 H), 2.45 (s, 6 H), 2.29 (s, 6 H), 2.28 (s, 6
crystal intensity data were collected with a STOE IPDS-2 at 210 K H). 13C NMR (75 MHz, CDCl3): δ = 164.8, 154.8, 150.1, 146.6, 140.3,
(for 4 and 7) or 150 K (for 6) using graphite-monochromated Mo-Kα 139.0, 138.7, 138.0, 136.6, 134.5, 129.8, 129.3, 128.3, 124.3, 124.1,
radiation (λ = 0.71073 Å). Crystal structures were solved by direct
123.4, 122.0, 118.1, 21.1, 20.3, 20.0. FT-IR (KBr): ν˜ = 3448, 3156,
methods using SHELXS-2013/1.[19a] Refinements were performed by 3117, 3089, 3004, 2960, 2919, 2857, 2728, 1603, 1581, 1484, 1436,
full-matrix least square methods on F2 using SHELXS-2014/7.[19b]
Non-hydrogen atoms were refined with anisotropic temperature fac-
tors. The deposited atom data (CIF) as well as the data in Table 4
reflect only the known cell content.
1401, 1376, 1354, 1327, 1268, 1222, 1165, 1156, 1104, 1065, 1023,
924, 850, 756, 735, 706, 663, 645, 631, 593, 579, 420 cm–1.
[PdCl(ppy){(CN)2IMes}] (6): In a 50 mL round-bottomed flask
equipped with a magnetic stirrer and a reflux condenser, compounds
2 (85.0 mg, 0.14 mmol) and 5 (150 mg, 0.28 mmol) were suspended
in toluene (20 mL). The reaction mixture was heated to reflux for 16 h.
After cooling to room temperature, the solvent was evaporated. The
residue was dissolved in dichloromethane (2 mL) and pure 6 was ob-
tained in 55% yield by liquid chromatography on silica (height: 30 cm;
diameter: 2 cm) with dichloromethane as eluent in form of a colorless
solid. EA: C 62.68, H 4.80, N 10.75%; found: C 62.83, H 4.72, N
10.92%. HR-MS (EI) m/z: calcd. for C34H31ClN5Pd: 650.1303 [M]+;
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ,
UK. Copies of the data can be obtained free of charge on quoting the
depository numbers CCDC-1416827 (4), CCDC-1416828 (6),
and CCDC-1416829 (7) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
1
found: 650.1299 [M]+. H NMR (300 MHz, CDCl3): δ = 9.23 (d, J =
5.7 Hz, 1 H), 7.73 (dt, J = 7.7, 1.7 Hz, 1 H), 7.57 (d, J = 8.1 Hz, 1
H), 7.43 (dd, J = 7.7, 1.4 Hz, 1 H), 7.13–6.93 (m, 7 H), 6.96 (dd, J =
7.7, 0.9 Hz, 1 H), 2.46 (s, 6 H), 2.33 (s, 6 H), 2.31 (s, 6 H). 13C NMR
(75 MHz, CDCl3): δ = 190.5, 154.0, 150,1, 146.6, 141.6, 139.7, 137.7,
134.6, 132.7, 130.6, 130.0, 128.7, 124.9, 123.9, 122.3, 118.4, 117.8,
106.8, 21.2, 20.2, 20.1. FT-IR (KBr): ν˜ = 3433, 3045, 3026, 2961,
2921, 2859, 2242, 1605, 1581, 1485, 1457, 1437, 1371, 1325, 1298,
1157, 1067, 1023, 852, 757, 735, 714, 647, 631, 498 cm–1.
Synthetic Procedures
Synthesis of [PdCl(ppy)(IMes)] (4): In a 50 mL round-bottomed flask
equipped with a magnetic stirrer and a reflux condenser, compounds
2 (86.9 mg, 0.15 mmol), 3 (100 mg, 0.29 mmol), and potassium carb-
onate (162 mg, 1.17 mmol) were suspended in acetonitrile (20 mL).
The mixture was heated to reflux for 4 h. After cooling to room tem-
perature, the excess of potassium carbonate was removed by filtration,
followed by evaporation of the solvent. The residue was dissolved in
dichloromethane (3 mL) and the product was purified by liquid 4,5-Dicyano-1,3-bis(mesityl)imidazol-2-selone (7): In a 50 mL round
chromatography on silica (height: 25 cm; diameter: 3 cm) with dichlo-
bottomed flask equipped with a magnetic stirrer and a reflux con-
Z. Anorg. Allg. Chem. 2016, 140–147
145
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
www.zaac.wiley-vch.de
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Org. Biomol. Chem. 2007, 5, 31–44; g) M. Oestreich, The Mizo-
denser,
5 (100 mg 0.19 mmol) and grey selenium (60.0 mg,
roki-Heck Reaction, Wiley, Chichester, UK, 2009; h) N. Selander,
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0.77 mmol) were suspended in toluene (20 mL). The reaction mixture
was heated to reflux for 16 h. After cooling to room temperature, the
solvent was evaporated and the residue was suspended in dichloro-
methane (20 mL). To remove the excess of selenium, the suspension
was filtered over a pad of celite 500 (height: 1 cm; diameter: 2 cm).
The celite was washed with additional 50 mL dichloromethane and the
dichloromethane phases were united. The solvent was evaporated. The
residue was dissolved in dichloromethane (2 mL). Pure 7 was obtained
in 80% yield by liquid chromatography on silica (height: 25 cm; dia-
meter: 2 cm) with dichloromethane as eluent in form of a shiny yellow
crystalline solid. EA: C 63.74, H 5.12, N 12.93%; found: 63.74 H
5.23 N 12.66%. HR-MS (ESI) m/z: calcd. for C23H22N4Se: 434.1010
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1
[M]+; found: 435.1074 [M + H]+. H NMR (300 MHz, CDCl3): δ =
7.10 (s, 4 H), 2.39 (s, 6 H), 2.17 (s, 12 H). 13C NMR (75 MHz,
CDCl3): δ = 165.3, 141.7, 135.3, 130.6, 130.2, 113.7, 106.3, 21.4, 17.9.
77Se NMR (75 MHz, CDCl3): δ = 166.6. FT-IR (KBr): ν˜ = 3036,
2984, 2944, 2916, 2857, 2235 (CN), 1744, 1606, 1481, 1456, 1376,
1320, 1289, 1210, 1189, 1078, 1034, 1012, 894, 861, 773, 705, 561,
552, 490 cm–1.
Representative Procedure for the Mizoroki-Heck Reaction: In a
2 mL Schlenk tube with a magnetic stirrer, sodium carbonate (18.7 mg;
176 μmol; 1.4 equiv.) and TBAB (4.1 mg; 12.6 μmol; 0.1 equiv.) were
submitted. A solution of the precatalyst (126 nmol; 0.001 equiv.) and
1,3,5-trimethoxybenzene (2.11 mg; 12.6 μmol; 0.1 equiv.) in 0.5 mL
N,N-dimethylformamide was added. The mixture was stirred at room
temperature for 5 min. Afterwards, bromobenzene (19.8 mg; 13.2 μL;
126 μmol) and n-butyl acrylate (32.3 mg; 35.9 μL; 252 μmol;
2.0 equiv.) were added via syringe and the tube was sealed and secured
three times by evacuating and subsequently flushing with argon. The
flask was placed in a preheated oil bath at 140 °C and stirred for 16
h. After finishing the reaction, the flask was cooled to 0 °C in an ice
bath immediately. The cold mixture was hydrolyzed with hydrochloric
acid (2 mL 1 n) and chloroform (2 mL) was added subsequently. The
mixture was poured into 20 mL water and the aqueous phase was ex-
tracted three times with 2 mL chloroform.
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For the substrate screening, the crude product was dissolved in 1.5 mL
chloroform (GC grade from MERCK) and the yield was determined
using a Perkin-Elmer Clarus 580, equipped with a Perkin-Elmer Elite
5 MS column (length: 30 m, diameter: 0.25 mm). Signals were de-
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For the calibration of the GC setup, the coupling products were iso-
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meter: 15 mm) with hexane-ethyl acetate mixtures as eluent and char-
1
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Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
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Received: August 4, 2015
Published Online: December 4, 2015
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© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim