Structural diversity of phenoxy functionalized triazol-5-ylidene palladium(II) complexes and their application in C-N bond formation

Article abstract of DOI:10.1016/j.jorganchem.2015.12.021

The preparation and isolation of a variety of mono-, bis-, and heteroleptic mesoionic triazol-5-ylidene palladium(II) complexes is reported. Treatment of phenoxy functionalized triazolium salts [Bn-MIC(H)]⁺I^- (1) and [Mes-MIC(H)]⁺I^- (2) with half equivalent of palladium acetate, produced complexes 3 and 4 with a general structure of [(MIC)₂Pd(I)₂] as isomeric cis/trans mixtures. When the reaction of palladium acetate and the cationic precursors was carried out with equimolar amounts in presence of sodium iodide, the μ₂-I₂ bridged complexes 5 and 6 of the type [(MIC)PdI₂]₂ were obtained as unique products. Additionally, the preparation of the heteroleptic PEPPSI-type complexes ([Py(PdI₂)MIC]) 7 and 8 was readily achieved by the thermal treatment of the triazolium precursors with PdCl₂, K₂CO₃, and sodium iodide in pyridine. All complexes have been fully characterized by ¹H and ¹³C NMR, FT-IR, elemental analysis, and in the case of 2, 3_trans, 6, and 7 single crystal X-ray diffraction. Preliminary catalytic results with the palladium series established the enhanced performance of PEPPSI complexes 7 and 8 in the Buchwald-Hartwing catalyzed formation of C-N bonds between aryl halides and primary/secondary amines under mild reaction conditions.

Full text of DOI:10.1016/j.jorganchem.2015.12.021

Journal of Organometallic Chemistry 803 (2016) 142e149
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structural diversity of phenoxy functionalized triazol-5-ylidene
palladium(II) complexes and their application in CeN bond formation
Daniel Mendoza-Espinosa a, , Rodrigo Gonz aꢀ lez-Olvera , Cecilia Osornio ,
**
a
a
a,
*
ꢀ
b
Guillermo E. Negr oꢀ n-Silva , Alejandro Alvarez-Hern aꢀ ndez ,
b
b
Claudia I. Bautista-Hern aꢀ ndez , Oscar R. Su aꢀ rez-Castillo
a
Departamento de Ciencias B aꢀ sicas, Universidad Aut oꢀ noma Metropolitana-Azcapotzalco, Avenida San Pablo No. 180, M ꢀe xico D.F., 02200, Mexico
Area Acad ꢀe mica de Química, Universidad Aut oꢀ noma del Estado de Hidalgo, Carretera Pachuca-Tulancingo Km. 4.5, Mineral de la Reforma, Hidalgo, 42090,
b
ꢀ
Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 October 2015
Received in revised form
The preparation and isolation of a variety of mono-, bis-, and heteroleptic mesoionic triazol-5-ylidene
palladium(II) complexes is reported. Treatment of phenoxy functionalized triazolium salts [Bn-
þ ꢀ
þ ꢀ
MIC(H)] I (1) and [Mes-MIC(H)] I (2) with half equivalent of palladium acetate, produced complexes 3
and 4 with a general structure of [(MIC) Pd(I) ] as isomeric cis/trans mixtures. When the reaction of
palladium acetate and the cationic precursors was carried out with equimolar amounts in presence of
sodium iodide, the -I bridged complexes 5 and 6 of the type [(MIC)PdI were obtained as unique
products. Additionally, the preparation of the heteroleptic PEPPSI-type complexes ([Py(PdI )MIC]) 7 and
was readily achieved by the thermal treatment of the triazolium precursors with PdCl , K CO , and
3
December 2015
2
2
Accepted 11 December 2015
Available online 15 December 2015
m
2
2
2 2
]
2
Keywords:
Triazol-5-ylidenes
Palladium
Catalysis
Structures
8
2
2
3
1
13
sodium iodide in pyridine. All complexes have been fully characterized by H and C NMR, FT-IR,
elemental analysis, and in the case of 2, 3trans, 6, and 7 single crystal X-ray diffraction. Preliminary
catalytic results with the palladium series established the enhanced performance of PEPPSI complexes 7
and 8 in the Buchwald-Hartwing catalyzed formation of CeN bonds between aryl halides and primary/
secondary amines under mild reaction conditions.
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
this description due to the fact that their structures can only be
represented as zwitter ions and not in the neutral canonical form
[4]. Despite that a handful of abnormal/mesoionic carbene com-
plexes supported by pyrazol-4-ylidenes (A) [5], imidazol-5-
ylidenes (B) [6], thiazol-5-ylidenes (C) [7], oxazol-4-ylidene (D)
are available [8](Scheme 1), the easy access to 1,2,3-triazoles by the
copper catalysed cycloaddition of azides and alkynes (CuAAC) and
their readily N3-quaternarization has resulted in the exponential
growth of the 1,2,3-triazol-5-ylidenes (E) efficient in several cata-
lytic processes [9]. Particularly, palladium based MIC complexes are
of great interest due to their potential as homogeneous catalysts in
processes such as carbon-carbon cross coupling or carbon-
heteroatom bond formation; however their structural diversity is
noticeably less developed when compared to classical NHC ana-
logues [10].
The enormous impact of N-heterocyclic carbenes (NHCs) as
spectator ligands for transition metal complexes has stimulated the
research for the directed tuning of their structural and electronic
properties [1]. The design and preparation of improved homoge-
neous catalyst based in NHCs is now envisaged as a useful alter-
native to facilitate synthetic procedures not accessible by classical
methods [2]. In recent years, NHCs were the carbene center is not
flanked by heteroatoms (nitrogen, sulphur, oxygen) in both sides of
their structures, have attracted a big deal of attention as they have
shown stronger
s-donation capacity towards the metal center
when compared to classical analogues [3]. These ligands often
referred as abnormal (aNHCs) or mesoionic carbenes (MICs) owe
Our group is interested in the design and preparation of
palladium-MIC complexes for synthetic applications, in particular
the efficient catalysed formation of carbon-heteroatom bonds. We
have foreseen that the 1,2,3-triazol-5-ylidenes enhanced electron
*
Corresponding author.
** Corresponding author.
E-mail addresses: danielme1982@gmail.com (D. Mendoza-Espinosa), gns@
correo.azc.uam.mx (G.E. Negr oꢀ n-Silva).
http://dx.doi.org/10.1016/j.jorganchem.2015.12.021
0
022-328X/© 2015 Elsevier B.V. All rights reserved.

D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
2
Cu(OAc) -H O
143
donor capacities together with the presence of hemilabile donor
atoms at the 4-position could lead to increased reactivity and sta-
bility versus previously reported NHC systems. With this purpose,
we report herein the directed synthesis of a series of mono-, bis-,
and heteroleptic phenoxy functionalized mesoionic triazol-5-
ylidene palladium(II) complexes. The treatment of triazolium salts
2
N
N
O
1,10-Phenanthroline
Na(asc), R-N3
O
N
R
H
MeI
ACN
(1): R =
(2): R =
Cl
1
and 2 with equimolar amounts of palladium acetate in presence
of sodium iodide generates selectively the dimeric carbenes of the
type [(MIC)PdI . If the reaction of the cationic precursors is car-
ried out with half equivalent of palladium acetate, biscarbenes of
the type [(MIC) Pd(I) ] are obtained as cis/trans mixtures in good
yields. Additionally, the preparation of the heteroleptic PEPPSI
Pyridine Enhanced Precatalyst Preparation and Initiation) type
complexes [Py(PdI )MIC] 7 and 8 was readily achieved by the
thermal treatment of the triazolium precursors with PdCl , and
N
N
I
O
2 2
]
N
R
H
2
2
þ ꢀ
þ ꢀ
Scheme 2. Synthesis of [Bn-MIC(H)] I (1) and [Mes-MIC(H)] I (2) salts.
(
2
2
sodium iodide in pyridine. The full series of palladium(II) com-
plexes have been synthesized under aerobic atmosphere and fully
characterized in solution and solid state. Preliminary catalytic trials
established the enhanced performance of 7 and 8 in the catalyzed
coupling between aryl bromides and amines.
2
. Results and discussion
Fig. 1. Molecular structure of triazolium salt 2. Iodine counterion has been omitted for
clarity. Ellipsoids are shown at 30% probability.
2.1. Synthesis and characterization
þ ꢀ
The 1,2,3-triazolium precursors [Bn-MIC(H)] I (1) and [Mes-
þ ꢀ
MIC(H)] I (2) are readily prepared following the route displayed
in Scheme 2. The initial triazoles are obtained in a one-pot reaction
from the treatment of the corresponding alkyne with the organic
azide (in situ generated in case of the p-chlorbenzyl derivative) [11]
through click process (75e90% yields). N-alkylation with methyl
iodide affords the corresponding cationic precursors in good yields
coworkers demonstrated that treatment of triazolium salts with
ꢁ
Pd(OAc)
2
in chloroform at 30 C provided selectively mononuclear
trans biscarbene palladium complexes; however long reaction
times were required for optimal conversions (36e72 h) [17].
With the cationic precursors 1 and 2 in hand, we decided to
proceed to the palladation process following the thermal method
ꢁ
(
81e86%) after recrystallization from acetonitrile/diethyl ether. The
developed by Albrecht (120 C in DMSO). Under those conditions, a
1
formation of the triazolium salts was confirmed in H NMR spec-
troscopy by the characteristic chemical shift values of the triazolyl
hydrogens (singlets) between 9.02 and 9.11 ppm, and the N-bound
methyl groups displayed as single peaks in the range of
mixture of at least three compounds was observed in the reaction
crude reflecting the poor selectivity of the process. Further at-
tempts to improve the synthesis were carried out by treatment of 1
ꢁ
and 2 with Pd(OAc)
2
in DCM at 30 C for three days. Despite that a
4
.38e4.64 ppm. Unambiguous characterization of 2 was performed
single metal complex was observed, a large amount of unreacted
triazolium salt (~65%) was present in the mixture. As no efficient
conversions were achieved, we tested several reaction conditions
by an X-ray diffraction study [12] and the molecular structure is
depicted in Fig. 1. Triazolium 2 crystallized in the triclinic system
with the P-1 space group. The asymmetric unit contains two tri-
azolium iodide entities with CeC and CeN bond distances, and CCN
angles, similar to other cationic analogues.
According to literature reports, the most common pathways for
the preparation of [MIC]-Pd complexes includes a) the trans-
metallation of MIC-silver(I) precursors [13], b) the generation of
free MICs followed by metallation [6a-b,14], and c) the thermal
and found that the treatment of 1 and 2 with 0.48 equivalents of
ꢁ
Pd(OAc)
2
in acetonitrile at 80 C was successful in the selective
generation of complexes 3 and 4 (Scheme 3) with a general struc-
ture of [(MIC) Pd(I) ] as isomeric cis/trans mixtures. The products
2
2
are easily purified by column chromatography in good yields
(77e81%) and according to the crude reaction mixture analysis no
2
palladation with Pd(OAc) [15]. Drawbacks of the silver carbene
metallation method and the use of strong bases (for preparing free
MICs) include low yields and the use of strictly anhydrous condi-
tions. Concerning thermal methods, it was previously reported by
I
N
N
N
N
I
0
.48 Pd(OAc)
2
O
N
N
3
cis: R = (4-Cl)Bn
R
o
Pd
Acetonitrile, 80 C
Albrecht and coworkers that the palladation of triazolium pre-
4cis: R = mesityl
H
I
ꢁ
N
cursors with Pd(OAc)
2
in DMSO at 120 C was not selective,
N
N
generating invariably a mixture of mono- and dinuclear complexes
in 1:1 ratio [16]. Further investigations by Sankararaman and
1.1 Pd(OAc)
1.5 NaI
2
Acetonitrile
110
o
C
+
N
N
N
N
N
O
N
R
S
N
N
O
N
N
N
I
Pd
I
I
5: R = (4-Cl)Bn
: R = mesityl
3
trans: R = (4-Cl)Bn
N
I
Pd
I
6
4trans: R = mesityl
N
N
N
I
Pd
N
R
N
N
N
O
N
N
A
B
C
D
E
Scheme 1. Examples of aNHC/MIC ligands reported in the literature.
Scheme 3. Synthesis of mono- and bis-MIC palladium complexes 3e6.

144
D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
presence of dimeric carbene complexes was noticed.
aromatic groups, as it was expected for the symmetric dimers. 13
C
NMR spectroscopy displays single palladium-carbene peaks for 5
and 6 located at 129.6 and 129.8 ppm respectively, which is sub-
stantially in higher field when compared with biscarbenes 3 and 4
In solution, the 13C NMR spectra for the cis/trans mixtures
display the Pd¼C peaks at 157.48 and 157.56 ppm for complex 3,
and at 157.5 and 158.7 ppm for complex 4. These chemical shifts are
similar to previously reported complexes with the general structure
(~157 ppm), but relatively close to analogous dimeric [MIC-PdI
2 2
]
2 2
[(MIC) Pd(I) ] [16,17]. Interestingly, the bulkiness of the substituent
complexes [17,18].
at the 4-position in complexes 3 and 4 affects the ratio of the cis/
trans mixtures. For instance, the presence of a flexible benzylic
moiety in 3 allows for the mixture to be present in 1:1 ratio whilst,
the bulkier mesityl group in complex 4 forces the steric congestion
around the metal center to be lessened, increasing the presence of
the trans isomer in a 4:1 ratio. Single crystals of complex 3trans were
obtained by hexanes diffusion into a concentrated acetonitrile
sample of 3 and the molecular structure is depicted in Fig. 2.
Complex 3trans crystallized in the monoclinic system with the
C2/c space group. The molecular structure of 3trans confirms the
biscarbenic nature of the palladium center which is located in a
distorted square planar environment completed by the coordina-
tion of two iodine atoms. The Pd(1)-C(5)/C(10) (2.036(4)/2.038(4)
Å) and Pd(1)-I(1)/I(2) (2.6051(4)/2.6198(4) Å) bond distances are in
the typical range of such bonds in analogue trans complexes [16,17].
Interestingly, the phenoxy and benzylic moieties are located in the
Unambiguous evidence for the formation of the dimeric com-
plexes was provided by an X-Ray diffraction analysis of complex 6.
The molecular structure displayed in Fig. 3 comprises a set of two
palladium centers, two bridging iodine atoms, and the square
planar coordination sphere around the metal center is completed
by a MIC ligand and a second iodine atom. Due to the formation of a
2 2
central Pd I square, the mesityl and phenoxy moieties in 6 adopt a
mutual anti conformation, while the triazolylidene ring is oriented
perpendicular to the palladium square plane. The palladium-
carbene (1.989(9) Å) and palladium-iodine (~2.59(7) Å) bond dis-
tances in 6 are similar to previously reported dimeric palladium
complexes [17,18] and as expected, the bond distance of the palla-
dium centers with the bridging iodine are elongated to 2.665(8) Å.
The benefits of catalysts that consist on one NHC-ligand and a
second more labile moiety have been previously demonstrated by
experimental and computational data [19]. In this subclass of het-
eroleptic metal complexes, the tightly bonded NHC ligand stabilizes
the metal center while the more labile counterpart favour the
presence of vacant coordination sites necessary for catalytic pro-
cesses. With this background, we turned our attention to PEPPSI
(Pyridine Enhanced Precatalyst Preparation Stabilization and Initi-
ation) palladium catalysts as they can accelerate various amination
and cross-coupling reactions [20]. This type of palladium com-
plexes offers among other advantages, a facile synthesis and air and
moisture stability when compared to traditional palladium cata-
lysts. The preparation of PEPPSI complexes 7 and 8 was carried out
2
same side of the structure allowing for a C axis to be drawn along
the I(1)-Pd(1)-I(2) atoms.
With the successful preparation of mononuclear biscarbene
complexes 3 and 4, we then moved to the quest for the selective
synthesis of dinuclear [(MIC)PdX
starting point, it was clear that the reaction of the triazolium salts
and Pd(OAc) required of stoichiometric amounts to favour the
2 2
] palladium complexes. As
2
MIC/Pd 1:1 ratio. Indeed, the treatment of salts 1 and 2 with
ꢁ
equimolar amounts of Pd(OAc)
2
in acetonitrile (110 C) provided
the expected dinuclear complexes 5 and 6 as major products but
regrettably in mixture with mononuclear complexes 3 and 4,
respectively. Attempts to improve the selectivity towards the
by the one-pot reaction of the triazolium precursors 1 and 2 with
ꢁ
K
2
CO
3
and PdCl
2
in pyridine at 100 C. Despite that the PEPPSI
complexes 5 and 6 by increasing the amount of Pd(OAc)
2
to 1.5 or
complexes were obtained using this initial methodology, the yields
were lower than 40% after purification by column chromatography.
Intrigued by the poor conversions, we performed various structural
analyses of the heteroleptic complexes and observed that the data
was not consistent with palladium centers containing chlorine
atoms. Further product analysis revealed that a Cl/I halogen ex-
change took place likely favoured by the presence of in situ
generated potassium iodide salt and the heating process. With this
information, we modified the reaction conditions by adding an
excess of NaI (2 equiv) to the mixture and prolonged the stirring for
24 h (Scheme 4). The optimized conditions allowed for the isolation
of 7 and 8 in high yields (79e89%) as microcrystalline yellow solids.
2
.0 equivalents proved unsuccessful as the mono- and biscarbenic
mixtures were observed in all cases. Rationalizing that each palla-
dium center in complexes 5 and 6 required of two iodine atoms,
and that each triazolium cation could only provide one, we were
prompted to seek for an external iodine source. We found that upon
the addition of excess of sodium iodide (1.5 eq) to the equimolar
reaction of salts 1 and 2 and Pd(OAc)
and 6 was achieved with the presence of only traces of 3 and 4
Scheme 2). The products were easily isolated as orange solids in
2
, the selective preparation of 5
(
high yields (83e89%) by column chromatography using DCM/
1
acetone (95:5) as eluent. In solution, the H NMR spectra for 5 and 6
display only one set of resonances for the N-methyl, methylene, and
Fig. 2. Molecular structure of 3trans. Hydrogen atoms have been omitted for clarity.
Fig. 3. Molecular structure of 6. Hydrogen atoms have been omitted for clarity. El-
Ellipsoids are shown at 30% probability.
lipsoids are shown at 30% probability.

D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
145
much promise [10]. Initially accessed by the in situ generation of the
N
N
O
II
0
N
free carbene in presence of Pd or Pd sources, NHC-based protocols
for Buchwald-Hartwig amination processes now rely on the prep-
aration of well-defined NHC-palladium precatalysts. With scarce
reports on the use of MIC-Pd based catalysts for aryl amination, we
decided to preliminary test the efficiencies of our newly synthe-
sized palladium triazol-5-yilidenes in the Buchwald-Hartwig pro-
cess. We began our investigation by testing precatalysts 3e8 in the
N-aryl amination of morpholine with bromobenzene. Initial reac-
tion conditions included loading 3 mol% of the appropriate catalyst,
I
R
N
N
2
PdCl , 2NaI
7: R = (4-Cl)Bn
8: R = mesityl
O
N
I
Pd
N
I
R
o
2 3
K CO , Py, 100 C
H
Scheme 4. Synthesis of PEPPSI complexes 7 and 8.
The formation of the PEPPSI complexes was evident by the loss
of the CeH peak of the cationic precursors (around 9.1 ppm) and
the presence of new aromatic peaks belonging to the pyridine
ligand. The 13C NMR spectra show the MIC-Pd signals at 135.9 and
t
KO Bu as the base, and 1,4-dioxane as solvent (entries 1e6). As
observed in Table 1, the process performed at room temperature for
6h, revealed that PEPPSI-type complexes 7 and 8 are the most
active precatalysts for the amination process. Interestingly, despite
the larger amount of metal available in the dimeric palladium
complexes 5 and 6, they displayed the lowest conversions of the
series. Optimization of the reaction conditions for our system
shown that the use of DME as solvent and raising the temperature
1
35.4 ppm for 7 and 8 respectively, which are at much lower field
compared to the mono- and dinuclear complexes 3e6. This
behaviour has been previously observed in analogue PEPPSI com-
plexes and is related to the weak Pd-MIC bonding which may have
important contribution to catalytic applications. Single crystals of
complex 7 were obtained by slow diffusion of hexanes into a
concentrated THF solution and the molecular structure is displayed
in Fig. 4.
Complex 7 displays a slightly distorted square planar palladium
center with the pyridine and MIC ligands located trans to each
other. The C(5)-Pd(1)-N(4) and I(1)-Pd(1)-I(2) angles of 175.8(4)
and 177.37(3) are close to the expected 180 for a square plane. The
Pd(1)-C(5) bond distance of 1.955(6) Å is slightly shorter than in
complexes 3e6, and the Pd(1)-N(4) bond distance of 2.093(5) Å is
similar to analogous PEPPSI complexes reported in the literature
13c,21]. The triazolylidene ring in 7 is planar with negligible de-
viations denoted by the C(5)N(1)N(2)N(3) (1.52 ) and C(4)N(3)N(2)
ꢁ
to 50 C provided the highest conversions, reaching up to 94% of
isolated yield when employing catalyst 8. Encouragingly, no
ꢁ
observation of palladium black was observed at 50 C in contrast to
the performance of analogue PEPPSI catalysts in processes per-
formed at similar temperatures [13c,20c].
With the presence of a phenoxy moiety in complexes 7 and 8, it
was pertinent to argue that the latent coordination of the oxygen
atom to the metal center could stabilize low valent catalytic species.
As a proof of concept, we decided to compare the catalytic perfor-
mance of 7 and 8 with complex 9 which represents the non-
phenoxy PEPPSI version [15]. As observed in Table 2, the coupling
of bromobenzene with morpholine under various reaction condi-
tions unveils that complexes 7 and 8 are better precatalysts for the
amination process than complex 9. This could be related within
some other aspects, to the availability of a hemilabile phenoxy
moiety for coordination to palladium.
ꢁ
ꢁ
[
ꢁ
ꢁ
N(1) (0.50 ) torsion angles. Interestingly, to diminish the steric
constrains, the phenoxy and benzylic moieties adopt a mutual anti
conformation with respect to the triazol-5-ylidene plane.
With optimized reaction conditions, we then proceeded to
investigate the scope of the reaction using complexes 7 and 8 as
precatalysts. Results of the coupling reaction of several amines with
aryl halides are summarized in Table 3.
Overall, the catalytic performance of 7 and 8 displayed good
efficiency toward cyclic dialkylamines with activated (entries 1, 4),
neutral (entry 2), and unactivated aryl bromides (entry 3).
2
.2. Catalysis
Since the seminal work by Buchwald and Hartwig [22], palla-
dium catalysed N-aryl amination has attracted increased attention
due to its significance in natural product synthesis. Currently, a vast
amount of synthetic routes leading to biologically valued com-
pounds now employ these methods in both academia and industry
[
23]. Initially limited to aryl bromides and iodides, the use of bulky,
Table 1
electron-rich ancillary ligands such as trialkylphosphines, biar-
ylphosphines, proazaphosphathrane, have enlarged the scope of
these reactions [24]. More recently, the use of N-heterocyclic car-
benes (NHCs) as ligands in Pd-catalyzed aminations has shown
Optimization results in the N-Aryl amination of morpholine with bromobenzene.
[
Cat] 3 mol%
Br
+
H
N
O
N
O
t
KO Bu, solvent
ꢁ
Conv(%)a
Entry
Cat
Temp ( C)
Solvent
1
2
3
4
5
6
7
8
9
3
4
5
6
7
8
3
4
7
8
7
8
7
8
25
25
25
25
25
25
25
25
25
25
35
35
50
50
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
DME
DME
DME
DME
DME
46
42
27
23
60
67
44
49
77
79
83
85
86
94
10
11
12
13
14
DME
DME
DME
Reaction conditions: 3 mol% catalyst loading, 1 mmol of bromobenzene, 1.1 mmol of
t
Fig. 4. Molecular structure of 7. Hydrogen atoms have been omitted for clarity. Ellip-
soids are shown at 30% probability.
morpholine, 1.5 mmol KO Bu, 2 mL solvent, 6h.
a
Isolated yields, average of two runs.

146
D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
Table 2
N-Aryl amination of morpholine with bromobenzene using complexes 7e9.
Table 3
N-Aryl amination of aryl/heterocyclic halides.
[
Cat] 3 mol%
[Cat] 3 mol%
R
R
1
N
R2
R
R
1
N
R2
Br
+
H
N
O
N
O
Br
+
H
t
t
X
KO Bu, solvent
X
KO Bu, DME
X = C, N
ꢁ
Yield(%)a
80
Entry
1
Catalyst
Temp( C)
Solvent
25
25
Dioxane
Entry Aryl halide
Amine
Product
Cat: Yield(%)a
N
N
O
N
Bn(4Cl)
1
7:90
I
Pd
I
NC
Br
H
H
H
H
N
N
N
N
O
O
O
NC
N
O
8
:94
N
(
7)
2
7:89
8:91
Br
N
O
2
3
Dioxane
Dioxane
81
57
N
N
O
N
Mes
3
7:83
I
Pd
N
I
MeO
Br
MeO
N
O
8
:89
(8)
4
7:93
8:96
NC
Br
NC
N
25
N
N
N
Mes
5
7:87
I
Pd
N
I
Br
8
:88
(
9)
H
N
H N
2
4
5
6
7
8
9
50
50
50
DME
DME
DME
89
91
71
6
7:91
8:95
Br
H
N
Reaction conditions: 3 mol% catalyst loading, 1 mmol of bromobenzene, 1.1 mmol of
H N
2
t
morpholine, 1.5 mmol KO Bu, 2 mL solvent, 6h.
a
Isolated yields, average of two runs.
7
7:94
Br
N
H
N
8
:93
Challenging the tolerance of 7 and 8 to sterically encumbered
substrates was explored by the reactions of bromobenzene with N-
methylaniline, 2,6-diisopropilaniline, and 2,4,6-trimethylaniline.
We were pleased to find that the respective hindered diarylamines
8
7:79
:83
Br
H
H
N
O
N
N
O
8
N
9
7:85
:87
(
entries 5e7) were obtained in good yields after column chroma-
Br
N
N
N
8
tography purification.
N
With the premise that heterocyclic moieties are widely repre-
sented in biologically active molecules, the coupling of heterocyclic
halides with amines are of great interest. With this in mind, we
carried out the treatment 2-bromopyridine with morpholine,
piperidine, and N-methylaniline (entries 8e10). To our delight, the
coupling of these substrates proceeds smoothly under our catalytic
protocol providing the expected heterocyclic substrates in good
conversions. Finally, to test the catalysts performance with cheaper
chloride substrates, we carried out the coupling of benzylchloride,
p-cyano benzylchloride and 2-chloropyridine with morpholine. As
observed in Table 1 (entries 11e13), the conversion to products is
successful but the yields are lower when compared to the analogue
bromide couplings.
1
0
7:76
8:81
Br
Cl
N
H
N
N
N
1
1
1
2
7:75
H
H
H
N
N
N
O
O
O
N
O
8
:78
7:80
NC
Cl
NC
N
O
8
:82
13
7:70
Cl
N
N
O
8
:67
N
Reaction conditions: 3 mol% catalyst loading, 1 mmol arylhalide, 1.2 mmol amine,
t
ꢁ
1
.5 mmol KO Bu, 1 mL of DME, 50 C, 6h.
a
Isolated yields, average of two runs.
To further investigate the performance of 7 and 8, a direct
comparison between these precatalysts was performed by GC
analysis in the process of N-Aryl amination of morpholine with
bromobenzene. As expected from the comparable product yields
and according to Fig. 5, both complexes display similar catalytic
behaviour. A short induction period was present for 8 relative to 7
which may be related to the steric effect of the mesityl moiety
which may facilitate the reductive elimination step in the catalytic
cycle of the amination process.
3
. Conclusions
In conclusion we have described the selective preparation and
isolation a variety of mono-, bis-, and heteroleptic mesoionic tri-
azol-5-ylidene palladium(II) complexes. The selective preparation
of mono- and biscarbene complexes relies in the stoichiometry of
palladium acetate used in the reaction. Heteroleptic PEPPSI type
complexes are obtained as single products and the yields can be
Fig. 5. Comparison of catalytic activity of 7 and 8 in the N-aryl amination of mor-
pholine with bromobenzene.

D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
147
improved after the addition of an external iodine source. All com-
plexes have been synthesized under aerobic conditions and fully
molecules were treated with the program SQUEEZE [27]. Correc-
tions of the X-ray data for 3trans by SQUEEZE (47 electron cell) were
close to the required values (44 electron cell). The programs ORTEP
[28] and POV-Ray [29] were used to generate the X-ray structural
diagrams pictured in this article.
1
13
characterized by H and C NMR, FT-IR, elemental analysis, and in
the case of 2, 3trans, 6, and 7 by single crystal X-ray diffraction. All
crystal structures contain square planar palladium centers and no
coordination through the phenoxy moiety is observed. Preliminary
catalytic trials established the enhanced performance of PEPPSI
complexes 7 and 8 in the Buckwald-Hartwig amination under low
catalyst loadings and mild reaction conditions using aryl bromides/
chlorides as substrates. Further study of the catalytic applications of
these triazol-5-ylidene palladium complexes is subject of investi-
gation in our research group.
4.1.1. Synthesis of 1-mesytil-4-(phenoxymethyl)-1H-1,2,3-triazole
To a 20 mL round-bottomed flask equipped with a magnetic
stirrer, were charged 7 mg (0.035 mmol, 5 mol%) of Cu(OAc)
7 mg (0.035 mmol, 5 mol%) of 1,10-phenanthroline monohydrate,
and 139 mg (0.70 mmol) of sodium -ascorbate. After addition of
5 mL of a mixture EtOH-H O (4:1 v/v), the resulting suspension was
stirred for five minutes at room temperature. Subsequently, 93 mg
0.70 mmol) of 1-(ethynyloxy)benzene and 124 mg (0.77 mmol) of
2 2
ꢂH O,
L
2
(
4
. Material and methods
mesityl azide, were added to the reaction mixture, which was
stirred during 16 h at room temperature. The resulting suspension
was extracted with dichloromethane (2 ꢃ 20 mL), washed with
brine, and dried over magnesium sulphate. After solvent removal
under vacuum, the crude product was purified by column chro-
4.1. General methods
Commercially available reagents and solvents were used as
received. 1-(ethynyloxy)benzene [11], 1(4-chlorobenzyl)-4-(phe-
noxymethyl)-1H-1,2,3-triazole [11], triazolium 1 [9i], and mesityl
azide [25], were synthesized as reported in the literature. All ma-
nipulations related to the synthesis of triazolium salts and metal
complexes were performed under air. Melting points were deter-
mined on a Fisher-Johns apparatus and are uncorrected. IR spectra
were recorded on a Bruker Alpha FT-IR/ATR spectrometer. NMR
spectra were obtained with a Bruker Ascend (400 MHz) spec-
trometer. GC-MS analyses were performed in an Agilent GC model
HP 5890 coupled with a mass detector model 5973. Elemental
analyses were obtained with a Perkin Elmer Series II CHNS/O 2400
instruments. X-Ray diffraction analyses were collected in an Agilent
matography (CH
2
Cl
2
-MeOH 99:1 v/v) providing the title product as
ꢁ
a white solid in 90% yield (0.63 mmol, 185 mg). m.p. ¼ 108e110 C.
1
H NMR (CDCl
.35 (s, 2H, ArOCH
CHar), 7.28e7.34 (m, 2H, CHar), 7.66 (s, 1H, CHtriazole). C NMR
3
, 400 MHz):
d
¼ 1.97 (s, 6H, CH
3 3
), 2.37 (s, 3H, CH ),
5
2
), 6.98e7.02 (m, 3H, CHar), 7.04 (d, J ¼ 7.7 Hz, 2H,
13
(
CDCl
3
, 100.6 MHz):
d
¼ 17.3, 21.1, 62.3, 115.0, 121.3, 124.6, 129.1,
ꢀ1
129.5, 133.4, 135.1, 140.1, 144.2, 158.2. FT-IR/ATR
n
max cm : 3121,
3
094, 3040, 3016, 2937, 2876, 1602, 1585, 1496, 1483, 1469. Found:
O C, 73.69; H, 6.53; N,
C, 73.81; H, 6.24; N, 14.00; Calc for: C18
4.32.
19 3
H N
1
4
.1.2. Synthesis of 1,2,3-triazolium 2
Methyl iodide (2.26 g, 15.9 mmol) was added to a 6 mL aceto-
nitrile solution of 1-mesytil-4-(phenoxymethyl)-1H-1,2,3-triazole
467 mg, 1.59 mmol) and the resulting clear solution was refluxed
Gemini Diffractometer using Mo K
were integrated, scaled, sorted, and averaged using the CrysAlisPro
software package. The structures we solved using direct methods,
a
radiation (l ¼ 0.71073 Å). Data
(
2
using SHELX 97 and refined by full matrix least squares against F
for 16 h. After reaching room temperature, the solvent was reduced
to 2/3 of the original volume and diethyl ether was added until a
precipitate is formed. The residue was washed thoroughly with
cold diethyl ether (3 ꢃ 20 mL) and dried under vacuum. Pure
product as colourless crystals in 86% yield (595 mg, 1.37 mmol) was
obtained after recrystallization with acetonitrile/diethyl ether (1:3).
[26]. All non hydrogen atoms were refined anisotropically. The
position of the hydrogen atoms were kept fixed with common
isotropic display parameters. The crystallographic data and some
details of the data collection and refinement are given in Table 4. In
the crystal structure of 3trans two highly disordered acetonitrile
ꢁ
1
m.p. ¼ 145e147 C. H NMR (CDCl
3
, 400 MHz):
), 5.90 (s, 2H, ArCH
d
¼ 2.11 (s, 6H, CH
3
),
2
.38 (s, 3H, CH ), 4.64 (s, 3H, NCH
3
3
2
O), 7.02e7.06
Table 4
Crystallographic Data and Summary of data Collection and Structure Refinement.
(m, 3H, CHar), 7.13 (d, J ¼ 7.8 Hz, 2H, CHar), 7.29e7.34 (m, 2H, CHar),
13
9
4
.11 (s, 1H, CHtriazolium). C NMR (CDCl
3
, 100 MHz):
d
¼ 18.0, 21.2,
3
trans∙2MeCN
38Cl
6
C
7
C
0.9, 59.7, 115.3, 122.7, 129.93, 129.94, 131.0, 132.7, 134.4, 141.2,
Formula
Fw
C
38
H
2
I
2
N
8
O
2
Pd
19
H
21
I N
2 3
OPd
22
H
21ClI
2
N
4
OPd
ꢀ1
142.7, 156.7. FT-IR/ATR
n
max cm : 3069, 3012, 2986, 2954, 2920,
1069.89
667.59
753.08
1
5
769, 1599, 1586, 1487, 1470, 1302, 1172, 868, 838, 762. Found: C,
4.47.; H, 4.95; N, 9.42; Calc for: C19 OI C, 54.42; H, 5.09; N,
9.65.
cryst syst
Space group
T, K
a, Å
b, Å
Monoclinic
C2/c
293(2)
29.5993(8)
9.6929(3)
29.2241(11)
90
108.263(4)
90
7963.4 (4)
8
1.648
2.187
Triclinic
P-1
293(2)
Orthorhombic
P212121
293(2)
10.5447(7)
13.1626(9)
18.3505(10)
90
90
90
2547.0(3)
4
1.964
22 3
H N
9.7170(5)
10.1580(4)
11.9574(4)
87.444(3)
70.382(4)
81.858(4)
1100.54(8)
2
4.1.3. Synthesis of complexes 3 and 4
c, Å
Complex 3. The triazolium salt 1 (88.3 mg, 0.20 mmol) and
a
, deg
, deg
b
palladium acetate (22.0 mg, 0.098 mmol) were charged in a 20 mL
pressure tube. Dry acetonitrile was added (5 mL) and the reaction
g
, deg
3
V, Å
ꢁ
mixture was heated at 80 C for 16 h. After reaching room tem-
Z
d
m
ꢀ
3
perature, the solvent was removed under reduced pressure and the
residue was extracted with 15 mL of DCM. After filtration over celite
and vacuum drying the crude product was purified by column
chromatography using a mixture of DCM/acetone (99:1) giving 3
calc g.cm
, mm
2.015
3.661
ꢀ
1
3.278
refl collected
51563
0.822
5900
0.0309
0.0358
0.0446
0.0788
0.0821
1.115
13642
0.887
3868
0.0311
0.0469
0.0754
0.1479
0.1667
1.075
29675
0.867
4483
0.0546
0.0328
0.0441
0.0709
0.0788
1.034
T
N
min/Tmax
measd
int
(
80 mg, 81% yield) as an analytical pure cis/trans mixture (1:1 ratio).
[
R
]
1
Cis isomer: H NMR (CDCl
5.44 (s, 4H, ArCH N), 5.81 (s, 4H, ArCH
CHar), 7.14e7.15 (m, 4H, CHar), 7.23e7.29 (m, 8H, CHar), 7.42 (d,
3
, 400 MHz):
d
¼ 4.05 (s, 6H, NCH
3
),
R [I> 2sigma(I)]
R (all data)
2
2
O), 6.97 (t, J ¼ 7.7 Hz, 2H,
R
R
w
[I> 2sigma(I)]
(all data)
13
w
J ¼ 7.8 Hz, 4H, CHar). C NMR (CDCl
3
, 100 MHz): ¼ 37.3, 58.2, 61.9,
d
GOF
1
15.2, 121.7, 128.86, 129.81, 130.4, 132.7, 134.37, 140.9, 157.36, 157.48

148
D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
(
C¼Pd).
Trans isomer: H NMR (CDCl
.55 (s, 4H, ArCH N), 5.95 (s, 4H, ArCH
CH
3 3 3 2
), 2.48 (s, 6H, CH ), 4.16 (s, 6H, NCH ), 5.68 (s, 4H, ArCH O), 6.92
1
3
, 400 MHz):
d
¼ 4.07 (s, 6H, NCH
3
),
(s, 4H, CHar), 7.23 (t, J ¼ 7.7 Hz, 2H, CHar), 7.25e7.26 (m, 2H, CHar),
13
5
2
2
O), 7.01 (t, J ¼ 7.7 Hz, 2H,
7.28e7.32 (m, 6H, CHar). C NMR (CDCl
3
, 100 MHz):
d
¼ 20.5, 21.3,
CHar), 7.16e7.17 (m, 4H, CHar), 7.25e7.33 (m, 8H, CHar), 7.50 (d,
37.5, 63.2, 115.3, 121.5, 129.1, 129.8 (CHar þ C¼Pd), 135.5, 139.1,
13
ꢀ1
J ¼ 7.8 Hz, 4H, CHar). C NMR (CDCl
15.2, 121.9, 128.89, 129.83, 130.6, 132.8, 134.41, 141.0, 157.39, 157.56
C¼Pd).
FT-IR/ATR
862, 2851, 1631, 1603, 1493, 1455, 1404, 1023, 1003, 895, 756.
Found: C, 41.53.; H, 3.75; N, 8.02; Calc for: C34 Pd C,
1.34; H, 3.27; N, 8.51.
Complex 4. The triazolium salt 2 (87.0 mg, 0.20 mmol) and
3
, 100 MHz):
d
¼ 37.4, 58.4, 62.1,
141.3, 145.0, 157.5. FT-IR/ATR
n
max cm : 3106, 3096, 3031, 2978,
1
(
2912, 2880,1700,1692,1675,1582,1482,1441,1301, 1144,1075, 853,
774, 657. Found: C, 34.03.; H, 3.51; N, 6.57; Calc for:
C H N O I Pd C, 34.18; H, 3.17; N, 6.29.
38 42 6 2 4 2
ꢀ
n
max cm 1: 3109, 3105, 3061, 3032, 2991, 2961, 2874,
2
H32Cl
2
N
6
O
2
I
2
4.1.5. Synthesis of complexes 7 and 8
4
Complex 7. The triazolium salt 1 (88.3 mg, 0.20 mmol), sodium
iodide (60 mg, 0.40 mmol), anhydrous potassium carbonate
(138 mg, 1 mmol), and palladium chloride (36.0 mg, 0.20 mmol)
were charged in a 20 mL pressure tube. Dry pyridine was added
palladium acetate (22.0 mg, 0.098 mmol) were charged in a 20 mL
pressure tube. Dry acetonitrile was added (5 mL) and the reaction
mixture was heated at 80 C for 16 h. After reaching room tem-
ꢁ
ꢁ
(5 mL) and the reaction mixture was heated at 100 C for 24 h. After
perature, the solvent was removed under reduced pressure and the
residue was extracted with 15 mL of DCM. After filtration over celite
and vacuum drying the crude product was purified by column
chromatography using DCM as eluent giving 4 (75 mg, 77% yield) as
reaching room temperature, the solvent was removed under
reduced pressure and the residue was extracted with 15 mL of DCM.
After filtration over celite and vacuum drying the crude product
was purified by column chromatography using a mixture of DCM/
acetone (98:2) giving 7 (119 mg, 79% yield) as crystalline yellow
an analytical pure cis/trans mixture (1:4 ratio).
1
ꢁ
1
Cis isomer: H NMR (CDCl
3
, 400 MHz):
), 5.48 (s, 4H, ArCH
CHar), 6.96e6.99 (m, 4H, CHar), 7.21e7.24 (m, 2H, CHar), 7.31e7.33
d
¼ 1.98 (s,12H, CH
3
), 2.26
O), 6.84 (s, 4H,
solid. m.p. ¼187e189 C. H NMR (CDCl
3
, 400 MHz):
d
¼ 4.07 (s, 3H,
(
s, 6H, CH
3
), 4.20 (s, 6H, NCH
3
2
NCH ), 5.54 (s, 2H, ArCH N), 5.98 (s, 2H, ArCH
3
2
2
O), 7.06 (t, J ¼ 7.4 Hz,
1H, CHar), 7.19 (d, J ¼ 8.7 Hz, 2H, CHar), 7.32e7.38 (m, 4H, CHar), 7.41
(d, J ¼ 7.4 Hz, 2H, CHar), 7.63 (d, J ¼ 8.7 Hz, 2H, CHar), 7.74 (t,
1
3
(
1
m, 4H, CHar). C NMR (CDCl
3
, 100 MHz):
d
¼ 20.8, 21.1, 37.2, 62.7,
13
15.3, 122.1, 129.09, 129.83, 135.6, 136.1, 139.6, 141.3, 157.1 (C¼Pd),
J ¼ 7.7 Hz, 1H, CHar), 8.99 (d, J ¼ 6.5 Hz, 2H, CHar). C NMR (CDCl
3
,
1
57.5.
100 MHz):
d
¼ 38.0, 59.0, 61.8, 115.2, 122.0, 124.5, 129.0,129.9, 131.5,
1
Trans isomer: H NMR (CDCl
3
, 400 MHz):
d
¼ 2.01 (s, 12H, CH
3
),
131.9, 135.0, 135.9 (C¼Pd), 137.6, 139.8, 153.9, 157.3. FT-IR/ATR
n
max
ꢀ1
2
.49 (s, 6H, CH ), 4.15 (s, 6H, NCH
3
3
), 5.69 (s, 4H, ArCH
2
O), 6.93 (s, 4H,
cm : 3059, 3035, 3022, 2945, 2918, 2849, 1585, 1484, 1445, 1406,
1313, 1291, 1221, 1166, 1008, 848, 745, 693. Found: C, 35.21; H, 2.69;
CHar), 6.99e7.04 (m, 4H, CHar), 7.12e7.14 (m, 2H, CHar), 7.39e7.43
1
3
(
1
1
m, 4H, CHar). C NMR (CDCl
15.5, 121.6, 129.13, 129.81, 135.5, 135.7, 139.1, 141.4, 157.5 (C¼Pd),
58.7.
FT-IR/ATR
3
, 100 MHz):
d
¼ 20.5, 21.3, 37.5, 63.2,
4 2
N, 7.08; Calc for: C22H21ClN OI Pd C, 35.09; H, 2.81; N, 7.44.
Complex 8. The triazolium salt 2 (87.0 mg, 0.20 mmol), sodium
iodide (60 mg, 0.40 mmol), anhydrous potassium carbonate
(138 mg, 1 mmol), and palladium chloride (36.0 mg, 0.20 mmol)
were charged in a 20 mL pressure tube. Dry pyridine was added
n
max cm 1: 3056, 3029, 3010, 2951, 2922, 2854, 1596,
ꢀ
1493, 1454, 1398, 1374, 1246, 1033, 848, 752. Found: C, 47.15.; H,
ꢁ
3
.99; N, 8.45; Calc for: C38
H
42
N
6
O
2
I
2
Pd C, 46.81; H, 4.34; N, 8.62.
(5 mL) and the reaction mixture was heated at 100 C for 24 h. After
reaching room temperature, the solvent was removed under
reduced pressure and the residue was extracted with 15 mL of DCM.
After filtration over celite and vacuum drying the crude product
was purified by column chromatography using DCM giving 8
4
.1.4. Synthesis of complexes 5 and 6
Complex 5. The triazolium salt 1 (88.3 mg, 0.20 mmol), sodium
iodide (45 mg, 0.30 mmol), and palladium acetate (47.0 mg,
ꢁ
0
.21 mmol) were charged in a 20 mL pressure tube. Dry acetonitrile
(133 mg, 89% yield) as crystalline yellow solid m.p. ¼ 201e203 C.
ꢁ
1
was added (5 mL) and the reaction mixture was heated at 110 C for
2
H NMR (CDCl
3
, 400 MHz):
d
¼ 2.34 (s, 6H, CH
3 3
), 2.41 (s, 3H, CH ),
4 h. After reaching room temperature, the solvent was removed
4.22 (s, 3H, NCH
3 2
), 5.76 (s, 2H, ArCH O), 7.06 (s, 2H, CHar), 7.24e7.29
under reduced pressure and the residue was extracted with 15 mL
of DCM. After filtration over celite and vacuum drying the crude
product was purified by column chromatography using a mixture of
DCM/acetone (99:1) giving 5 (112 mg, 83% yield) as crystalline or-
(m, 3H, CHar), 7.39e7.43 (m, 4H, CHar), 7.65 (t, J ¼ 7.7 Hz, 1H, CHar),
13
8.84 (d, J ¼ 6.5 Hz, 2H, CHar). C NMR (CDCl
3
, 100 MHz):
d
¼ 21.2,
21.3, 38.1, 63.0, 115.3, 122.0, 124.2, 129.5, 129.9, 135.4 (C¼Pd), 135.6,
ꢀ1
137.2, 138.5, 140.6, 140.7, 153.8, 157.3. FT-IR/ATR nmax cm : 3067,
ꢁ
1
ange solid. m.p. ¼ 248e250 C. H NMR (CDCl
s, 6H, NCH ), 5.49 (s, 4H, ArCH N), 5.93 (s, 4H, ArCH
J ¼ 7.7 Hz, 2H, CHar), 7.14 (d, J ¼ 7.8 Hz, 4H, CHar), 7.34e7.40 (m, 8H,
3
, 400 MHz):
d
¼ 4.08
3041, 3012, 2945, 2918, 2856, 1604, 1591, 1484, 1445, 1406, 1327,
1243, 1192, 1023, 843, 756, 691. Found: C, 36.53.; H, 3.73; N, 7.84;
Calc for: C24H N OI Pd C, 36.80; H, 3.51; N, 7.50.
26 4 2
(
3
2
2
O), 7.04 (t,
1
3
CHar), 7.62 (d, J ¼ 7.8 Hz, 4H, CHar). C NMR (CDCl
3
, 100 MHz):
d
¼ 38.2, 58.9, 61.0, 115.1, 122.2, 129.2, 129.6 (C¼Pd), 129.9, 131.5,
4.1.5.1. General procedure for the Buchwald-Hartwig amination or
aryl bromides (Table 2). Potassium tert-butoxide (1.5 mmol), and
the precatalyst (3 mol%), were charged into a 5 mL screw-cap vial
that was sealed with a septum and purged with argon. The amine
(1.2 mmol) was added via syringe, and the reaction was allowed to
stir for 5 min at room temperature. DME (1 mL) was the injected via
syringe followed by the aryl bromide (1.0 mmol). The reaction
ꢀ
1
135.2, 139.9, 144.6, 157.0. FT-IR/ATR
n
max cm : 3100, 3082, 3053,
2
953, 2921, 2853, 1723, 1694, 1649, 1600, 1482, 1446, 1266, 1144,
1
069, 848, 760, 690. Found: C, 30.70; H, 2.65; N, 6.32; Calc for:
Pd C, 30.29; H, 2.39; N, 6.23.
Complex 6. The triazolium salt 2 (87.0 mg, 0.20 mmol), sodium
iodide (45 mg, 0.30 mmol), and palladium acetate (47.0 mg,
C
34
H
32Cl
2
N
6
O
I
2 4
2
ꢁ
0
.21 mmol) were charged in a 20 mL pressure tube. Dry acetonitrile
mixture was stirred at 50 C for 6 h, filtered through a bed of celite
ꢁ
was added (5 mL) and the reaction mixture was heated at 110 C for
and washed with ethyl acetate (2 ꢃ 3 mL). The filtrate was evap-
2
4 h. After reaching room temperature, the solvent was removed
orated under vacuum and purified by column chromatography on
under reduced pressure and the residue was extracted with 15 mL
of DCM. After filtration over celite and vacuum drying the crude
product was purified by column chromatography using DCM as
eluent giving 6 (119 mg, 89% yield) as a crystalline orange solid.
2
silica gel using appropriate mixtures of hexanes/Et O as eluent.
Acknowledgements
ꢁ
1
m.p. ¼ 227e229 C. H NMR (CDCl
3
, 400 MHz):
d
¼ 1.99 (s, 12H,
We are grateful to Consejo Nacional de Ciencia y Tecnología,

D. Mendoza-Espinosa et al. / Journal of Organometallic Chemistry 803 (2016) 142e149
2768e2813.
149
CONACyT (project 181448). DME, GNS, RGO, AAH, and OSC wish to
[
[
[
11] (a) D. Mendoza-Espinosa, G.E. Negr oꢀ n-Silva, L. Lomas-Romero, A. Guti eꢀ rrez-
Carrillo, D. Soto-Castro, Synthesis 45 (2013) 2431e2437;
acknowledge the SNI for the distinction and the stipend received.
DME acknowledges PROMEP project (UAM-PTC-475) for the
research grant received.
(
b) D. Mendoza-Espinosa, G.E. Negron-Silva, L. Lomas-Romero, A. Gutierrez-
Carrillo, R. Santill aꢀ n, Synth. Commun. 44 (2014) 807e817.
12] Data for triazolium 2: 22IN O; fw 435.30; space group P-1;
a ¼ 10.1419(4), b ¼ 10.4396(3), c ¼ 10.7476(4), ¼ 118.982(3), ¼ 94.364(3),
¼ 94.755(3); V ¼ 983.14(6); Z ¼ 2; d ¼ 1.470; ¼ 1.638; Rint ¼ 0.0336;
[I > 2
ꢀ
ꢀ
C
19
H
3
a
b
Appendix A. Supplementary data
g
m
GOF ¼ 1.208; R [I > 2
s
(I)] ¼ 0.0358; wR
2
s
(I)] ¼ 0.1294.
13] See for example: (a) J.C.Y. Lin, R.T.W. Wang, C.S. Lee, A. Bhattacharyya,
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.12.021.
W.S. Wang, I.J.B. Lin, Chem. Rev. 109 (2009) 3561e3598;
(
(
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4
(
3
56e461;
d) J. Cai, X. Yang, K. Arumugam, C.W. Bielawski, J.L. Sessler, Organometallics
0 (2011) 5033e5037;
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