Synthesis and Catalytic Applications of Palladium(II) Complexes Supported by Hydroxyl-Functionalized Triazolylidenes

Article abstract of DOI:10.1002/ejic.201900918

A series of allyl (1–3) and cinnamyl (4–6) palladium(II) complexes supported by hydroxyl functionalized triazolylidenes have been prepared. All new compounds were fully characterized by means of ¹H and ¹³C NMR spectroscopy, FT-IR and elemental analyses. The new triazolylidene palladium complexes were tested as precatalysts in the coupling of aryl chlorides with boronic acids and the coupling of esters with amines to produce biphenyls and amides, respectively. According to the overall results, complexes 4 and 5 displayed the highest catalytic activity in both coupling processes, providing good to excellent yields under mild reaction conditions and using a wide range of substrates.

Full text of DOI:10.1002/ejic.201900918

A Journal of
Accepted Article
Title: Synthesis and catalytic applications of palladium(II) complexes
supported by hydroxyl-functionalized triazolylidenes
Authors: Agustin Armando De la Fuente-Olvera, Oscar Rodolfo
Suarez-Castillo, and Daniel Mendoza-Espinosa
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201900918
Link to VoR: http://dx.doi.org/10.1002/ejic.201900918

10.1002/ejic.201900918
European Journal of Inorganic Chemistry
FULL PAPER
Synthesis and catalytic applications of palladium(II) complexes
supported by hydroxyl-functionalized triazolylidenes
Agustín A. De la Fuente-Olvera, Oscar R. Suárez-Castillo and Daniel Mendoza-Espinosa*
Dedication ((optional))
Abstract: A series of allyl (1-3) and cinnamyl (4-6) palladium(II)
complexes supported by hydroxyl functionalized triazolylidenes have
been prepared. All new compounds were fully characterized by
means of 1H and 13C NMR spectroscopy, FT-IR and elemental
analyses. The new triazolylidene palladium complexes were tested
as precatalysts in the coupling of aryl chlorides with boronic acids
and the coupling of esters with amines to produce biphenyls and
amides, respectively. According to the overall results, complexes 4
and 5 displayed the highest catalytic activity in both coupling
processes, providing good to excellent yields under mild reaction
conditions and using a wide range of substrates.
the triazolylidene ligand offers the possibility of anchoring the
catalyst into a solid support.8 As a result, a huge library of early
and late transition metal complexes containing mono- and poly-
ligating triazolylidenes, pincer platforms, and mixed donor
systems, has been generated and extensively used in
homogeneous catalysis.9
Given the increasing popularity of palladium catalysts in both
industry and academia, considerable efforts targeting the
understanding of the electronics and steric properties of ligands
in catalyst design are constantly ongoing. For several years, our
group has been interested in the design and preparation of
palladium(II) triazolylidene-based complexes for catalyzed cross
coupling reactions.7g,10 In particular, we have been interested on
the synthesis of hydroxyl-functionalized triazolylidene ligands as
they have demonstrated enhanced catalytic performances in C-
C and C-N bond forming reactions compared to alkyl or aryl
substituted NHC ligands.10,11 Additionally, it has been
demonstrated that triazolylidene-based palladium complexes
display enhanced thermal stabilities (above 100 °C) compared to
NHC-based complexes, and they are also air and moisture
stable.7,12
In line with our research devoted to metal-triazolylidenes, we
report herein the preparation and full characterization of a series
of hydroxyl functionalized triazolylidene-based allyl (1-3) and
cinnamyl (4-6) palladium(II) complexes. Their application in the
catalysed preparation of biphenyls via the coupling of aryl
chlorides and boronic acids and the synthesis of amides through
the treatment of esters with amines will be discussed. The
catalytic conversion percentages in both coupling processes
demonstrate that the cinnamyl substituted palladium complexes
4 and 5 display the best activity of the series under mild reaction
conditions. Catalysts comparison, optimized conditions, and
substrate scope in the cross-coupling transformations will be
discussed.
Introduction
Since the pivotal discovery in 2001 by Crabtree,1 the field of
stable mesoionic carbenes (MICs) has presented an exponential
growth in recent years.2 These type of ligands where the
carbene center is not flanked by heteroatoms in both sides of
their structures, have attracted a great deal of attention as they
display enhanced -donor properties compared to classical N-
heterocyclic carbenes (NHCs).3
Among the several platforms stabilizing MICs, 1,2,3-
triazolylidenes are the most popular species found in the
literature.4 Their 1,2,3-triazolium precursors, can be easily
prepared by means of the copper(I) catalyzed “click”
cycloaddition of alkynes and azides5 (CuAAC) and their
subsequent N-alkylation.6 Because of the ease in structural
modification in the triazolylidene scaffolds, great topological
diversity is achieved by changing the substituent appended at
the N3- and C4- positions of the central triazole core. This
structural diversity significantly affects the electronic and steric
properties of the MICs, which in turn accounts for the variation in
the stability and reactivity of the resulting complexes.7
In the last decade, heteroatom-functionalized triazolylidene
ligands incorporating pendant neutral or anionic functional
groups have received considerable attention owing to their
ability to act as chelating or pincer platforms.3,7 Moreover, the
introduction of pendant functional groups into the side chain of
Results and Discussion
The synthesis of the 1,2,3-triazolium salt precursors A-C was
performed according to the literature procedure by means of a
copper catalyzed cycloaddition (CuAAC) of mesityl azide with
the appropriate propargyl alcohol, followed by N-
quaternarization with methyl iodide.10b The preparation of the
palladium complexes relied in the one pot reaction of the
triazolium precursors A-C with a slight excess of potassium
hexamethyl disilazane and half equivalent of appropriate the
palladium dimer in tetrahydrofurane. This procedure provides
the respective palladium complexes 1-6 in a single step without
the need of free MIC species isolation. (Scheme 1).
[a]
Mr. A. A. De la Fuente-Olvera, Dr. O. R. Suarez-Castillo and Dr. D.
Mendoza-Espinosa*
Área Académica de Química
Universidad Autónoma del Estado de Hidalgo
Carretera Pachuca-Tulancingo Km. 4.5, Mineral de la Reforma,
Hidalgo 42090
E-mail: daniel_mendoza@uaeh.edu.mx
URL: https://www.uaeh.edu.mx/campus/icbi/investigacion/quimica/
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejic.201900918
European Journal of Inorganic Chemistry
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As depicted in Figure 1, the former monomeric allyl palladium
complex 1 decomposes into a new species where the allyl group
is released and the palladium center feature a square planar
geometry by the coordination to two carbenes and two iodine
atoms. Interestingly, as observed in the NMR data for
complexes 1-6, the hydroxyl group is not coordinated to the
metal center in the side product (D). The decomposition of
complex 1 may be related to the low steric protection provided
by the hydroxyl group and the highly nucleophilic character of
the triazolylidene ligand which can trigger the rearrangement
process to form complex D.
Scheme 1. Synthesis of triazolylidene complexes 1-6.
Purification of the new complexes is performed by means of
column chromatography using a mixture of dichloromethane and
Palladium catalyzed Suzuki cross coupling or aryl halides with
boronic acids has stablished itself as the most popular process
acetonitrile rendering air and moisture yellow crystalline powders. for the formation of biaryl derivatives.15. Despite the significant
NMR spectroscopy studies and elemental analyses confirmed
the formation of the desired mononuclear Pd(II)-MIC complexes
1-6. Indeed, the preparation of the new palladium carbenes was
evident by the disappearance of the acidic CH proton of the
triazolium precursors in the 1H NMR (above 9 ppm), and the
observation of a low field 13C NMR signal between 166.5-168.8
ppm for the allyl substituted complexes 1-3 and between 165.5-
167.1 for the cinnamyl complexes 4-6. Both complexes series
display carbene-palladium chemical shifts similar to previously
progress in this cross-coupling reaction during the last decade,
several drawbacks still exist. For instance, the reactions typically
require of inert conditions, whereas the high sensitivity of NHC-
Pd0 species toward oxygen can interrupt the catalytic cycle.
Additionally, the use of aryl chlorides or sterically encumbered
substrates for the coupling process remains as a challenging
task. With the recent reports on the enhanced catalytic activity in
cross-coupling reactions promoted by monodentate ligands
containing additional donor heteroatoms (N, S, O),11,15 we
decided to tests our new palladium complexes in the Suzuki-
Miyaura coupling process of aryl chlorides with boronic acids.
We began our investigation by testing precatalysts 1-6 in the
coupling of phenylboronic acid with p-chloroanisole as model
reaction. Initial reaction conditions included loading of 5 mol% of
the appropriate precatalyst, NaOtBu as the base,
tetrahydrofurane, and 12 h of reaction at 100oC.10a As observed
in Table 1, the cinnamyl palladium complexes 4 and 5 are the
most active of the series with yields over 99%. Complex 6 led to
moderate cross coupling reaction yields (< 72%) and
interestingly, the allyl substituted complexes 1-3 show the lowest
conversions (< 53%). Optimization of the reaction conditions
demonstrate that loading of complexes 4 and 5 can be reduced
to 2 mol% and a temperature of 50oC, without significant loss on
the conversions.
reported
mononuclear
triazolylidene-palladium(II)
complexes.10,13 As expected, the characteristic signals for the
allyl fragment in 1-3 are noticeable in the range of 1.5-5.6 ppm
whilst, the aromatic protons of the cinnamyl group in are located
between 7.06-7.27 ppm. The OH groups in all complexes are
1
observed in solution either as triplet or broad peaks in the H
NMR (in the range of 2.16 to 4.01 ppm), suggesting then a sole
coordination of the carbene center towards palladium atom.
Despite our several attempts to crystallize complexes 1-6, no
single crystals for X-ray diffraction could be obtained. However,
while attempting the crystallization process, we noticed that after
several hours in solution, the allyl palladium complexes 1-3
started to decompose releasing large amounts of black
palladium. This observation was further confirmed by the crystal
structure analysis of a side product obtained from a mixture of
THF and hexanes of the former complex 1.
Table 1. Cross coupling reaction of phenylboronic acid with p-chloroanisole
using precatalysts 1-6.
Entry
Cat
[cat]
Temp
(0C)
100
100
100
100
100
100
100
100
Yield[%]a
mol%
1
2
3
4
5
6
7
8
1
2
3
4
5
6
4
5
5
5
5
5
5
5
3
3
53
50
47
99
99
73
99
99
Figure 1. Molecular structure of the biscarbenic side product D obtained from
the decomposition of complex 1. Ellipsoids are shown at 50% probability.
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10.1002/ejic.201900918
European Journal of Inorganic Chemistry
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9
4
5
4
5
4
5
4
5
2
2
2
2
2
2
1
1
100
100
80
99
99
97
99
95
97
88
83
10
11
12
13
14
15
16
80
Entry
Aryl halide
Boronic acid
Product
Cat : Yield(%)a
50
50
50
1
4 : 99
5 : 98
50
Reaction conditions: p-chloroanisole (1.0 mmol), phenylboronic acid (1.2
mmol), THF 3 mL, 12h. aIsolated yields as the average of two runs.
4 : 97
4 : 95
5 : 94
5 : 93
2
3
In order to get more insight into the catalytic behavior of
complexes 1-6, the catalytic profiles for coupling of p-
chloroanisole and phenylboronic acid were performed with the
reaction conditions presented in Table 1 (Entries 13-14). As
illustrated in Figure 2, catalysts 4 and 5 reach conversions
higher than 80% after only 4 h of reaction and their maximum
conversions are observed within 8 h. In the case of complex 6,
the maximum conversion is reached after 10 h and remained
unchanged after that time. In the case of allyl palladium
complexes 1-3, the reaction reaches maximum conversions after
8-10 h with no further conversions to the biphenyl after. The
latter results suggest that the rearrangement of complexes 1-3
into biscarbenic species (as previously observed in the
crystallization process of complex 1) may deter the catalytic
performance of this precursors during the coupling process.
4
5
6
4 : 92
4 : 96
4 : 83
5 : 89
5 : 90
5 :78
7
8
4 : 93
4: 90
5 :91
5: 84
Reaction conditions: aryl chloride (1.0 mmol), boronic acid (1.3 mmol),
NaOtBu (1.5 mmol), THF 3 mL, 6h. aIsolated yields as the average of
two runs.
Figure 2. Cross coupling of p-chloroanisole and phenylboronic acid using
precatalysts 1-6. Reactions carried out with THF-d8 at 50oC. Conversions
determined by 1H NMR spectroscopy based on the amount of p-chloroanisole
remaining in solution.
With the increased popularity of procedures aiming to the
formation of new carbon-nitrogen bonds, we were interested on
testing complexes 1-6 in the recently reported use of esters as
coupling partners in the catalytic formation of amides.16 We
found this reaction particularly important as it expands the type
of electrophiles that successfully couple with relatively non
nucleophilic amines to yield diverse substituted amides. Thus,
following similar reaction conditions as those reported by
Newman and coworkers,16a complexes 1-6 were initially tested
as precatalysts for the coupling of phenyl benzoate and aniline
as model reaction. According to Table 3, when using 3 mol% of
catalyst loading, K2CO3, and toluene (at 110oC), complexes 4
and 5 show the best activities of the series, providing 80 and
73% yields, respectively (entries 4 and 5). Complex 6 also
containing the cinnamyl moiety provided a lower yield compared
to 4 and 5 likely due to its lower stability in solution. Although the
reaction under the reported conditions was successful, the
With the optimal catalytic conditions for the model system, we
decided next to investigate the reaction scope using complexes
4 and 5. Initially, we tested the reactivity of phenylboronic acid
with a series of several aryl chlorides (activated and unactivated).
As observed in Table 2, the conversion to the desired biphenyls
is successful providing good to excellent yields (entries 1-4).
Additionally, complexes 4 and 5 demonstrated good catalytic
performance in the preparation of a series ortho-substituted
biaryls (entries 5-8). As it was expected, the less hindered
coupling partners render the best yields (93-96%) while the
more challenging tri-ortho-substituted product reached
maximum conversion of 84%.
a
Table 2. Scope of the cross coupling of aryl chlorides and boronic acids
catalyzed by complexes 4 and 5.
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10.1002/ejic.201900918
European Journal of Inorganic Chemistry
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conversion values obtained with complexes 4 and 5 were
actually lower when compared to the PdIPr(allyl)Cl complex
reported in the literature (91%).16a Further optimization of the
reaction conditions employing complexes 4 and 5 revealed that
increasing the catalyst loading to 5 mol% after 16 h of reaction
allows for the preparation of the desired amide with yields over
93%. Attempts to optimize the reaction temperature after raising
the catalyst loading proved unsuccessful.
4:91
5:89
2
3
4:95
5:94
Table 3. Cross coupling reaction of phenyl benzoate with aniline using
precatalysts 1-6.
4:70
5:66
4
5
6
4:97
5:95
Entry
Cat
[cat]
Temp
(0C)
110
110
110
110
110
110
110
110
110
110
80
Yield[%]a
mol%
1
1
2
3
4
5
6
4
5
4
5
4
5
---
3
3
3
3
3
3
4
4
5
5
5
5
---
53
50
47
80
73
64
85
79
93
90
88
83
27
4:94
5:85
2
3
4
Reaction conditions: Ester (1.0 mmol), phenylboronic acid (1.2 mmol), toluene
3 mL, 16h. aIsolated yields as the average of two runs.
5
6
7
With the similar catalytic activities for observed for complexes 4
and 5 and the temperature used in the procedure, the possibility
of formation of heterogeneous palladium as the active catalyst
prompted us to perform mercury poisoning tests17 in the
formation of benzanilide (Table 4, entry 1). Thus, the formation
of benzanilide in presence of 4 was disturbed by the addition of
excess of Hg(0) at different reaction times (t = 0-16 h). The
conversion percentages for complex 4 when mercury is added at
0 and 2 h decreased to 80 and 84%, respectively (Figure 3).
These results indicate that after addition of the metal poison, the
catalyst is still highly active. Additionally, if the poisoning process
is delayed form times between 6 and 8 h, no significant changes
in the conversions were noticed (89-91%).
8
9
10
11
12
13
80
110
Reaction conditions: p-chloroanisole (1.0 mmol), phenylboronic acid (1.2
mmol), THF 2 mL, 12h. aIsolated yields as the average of two runs.
With the optimal reaction conditions and best precatalysts
stablished, we then explored the reaction scope. As observed in
Table 4, the ester and substituted anilines scope is broad and
tolerates sterically hindered, electron rich, and electron-
withdrawing substituents. The overall conversion results indicate
that complex 4 display better catalytic performance compared to
complex 5, particularly observed in the yield of the more
substituted amide (entry 6).
Table 4. Cross coupling reaction of esters with substituted anilines using
precatalysts 4 and 5.
Figure 3. Mercury poisoning tests at different reaction times for the formation
of benzanilide catalyzed for complex 4.
Cat :
Entry
Ester
Amine
Product
Yield(%)a
In order to investigate the effect of the hydroxyl pendant arm
featured in complexes 4 and 5, their catalytic efficiencies in the
coupling of chloranisole with phenylboronic acid were compared
with a phenoxy-functionalized complex containing an allyl group
(7),10a and a non-oxygen functionalized version with a cinnamyl
moiety (8)18 (Figure 4).
4:93
5:90
1
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10.1002/ejic.201900918
European Journal of Inorganic Chemistry
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The beneficial catalytic effect of the cinnamyl group in NHC-
palladium complexes in cross coupling processes has been
previously reported.18 In general, the superior efficiency of NHC-
(cinnamyl)Pd complexes as active catalysts is related to the
easier elimination of the cinnamyl group (compared to the
simpler allyl group) by tBuONa leading to the formation of active
Pd0 species. In this regard and with our reaction conditions, the
activation process for the Pd0 complexes may be similar to
Nolan’s activation pathway for the (allyl)(IPr)Pd complex.19 In this
activation mechanism, the tert-butoxy anion attacks the cinnamyl
moiety, and then the cinnamyl tert-butyl ether is eliminated from
the palladium complex leading to the formation of the Pd0
species which could be stabilized by the hydroxyl moiety
(Scheme 2). To get more insight into this possibility, we carried
out a trapping experiment, reacting complex 1 with equimolar
amounts of NaOtBu in presence of PPh3. The expected
Figure 4. Triazolylidene complexes 7 and 8.
According to Table 5 and following our optimized reaction
conditions (from Table 2), complexes 4, 5, 7 and 8 are the best
of the series with yields over 95%. The phenoxy functionalized
complex 7 reaches only 67% after 6h or reaction. Decreasing
the catalyst loading to 1% mol diminishes the conversions of
complexes 4, 5, and 8 to approximately 90%.
triazolylidene-Pd0 species containing PPh3 were observed by 31
P
NMR spectroscopy, with the phosphane signal of the Pd
complex located at δ = 25.2 ppm.
Table 5. Cross coupling reaction of phenylboronic acid with p-chloroanisole
using precatalysts 4, 5, 7 and 8.
Conclusions
In summary, we have reported the convenient synthesis of a
series of allyl (1-3) and cinnamyl (4-6) palladium complexes
bearing hydroxyl-functionalized triazolylidenes. All new
compounds have been properly characterized by NMR
spectroscopy, FT-IR and elemental analysis. The new air and
moisture stable triazolylidene complexes (1-6) were tested as
precatalysts in the synthesis of biphenyls via the coupling of aryl
chlorides and boronic acids and the preparation of amides
through the treatment of esters with amines. In general, the
catalytic trials established the enhanced catalytic performance of
the cinnamyl substituted palladium complexes (4-6) compared
with the allyl palladium analogues (1-3), with complexes 4 and 5
as the best of the series. The increased efficiency of complexes
4-6 may be related to a higher thermal stability of the cinnamyl
palladium complexes in solution. The reaction scope described
in the present study demonstrate the broad applicability of the
new cinnamyl complexes in the catalyzed synthesis of a variety
of biaryls and amides providing of a new alternative for these
important organic transformations. Further exploration of the
catalytic potential of complexes 4-6 is currently being explored in
our laboratory.
Entry
Cat
[cat]
Temp
(0C)
50
Yield[%]a
mol%
1
2
3
4
5
6
7
4
5
7
8
4
5
8
2
2
2
2
1
1
1
99
98
67
95
88
90
86
50
50
50
50
50
50
Reaction conditions: chloroanisole (1.0 mmol), phenylboronic acid (1.3
mmol), NaOtBu (1.5 mmol), THF 3 mL, 6h. aIsolated yields as the
average of two runs.
With the results retrieved from Table 4, we can notice that the
hydroxyl group in complex 4 and 5 does not have and important
effect in the catalytic performance as complex 8 display similar
conversions. However, the effect of the allyl and cinnamyl
moiety is more noticeable as complex 7 displayed the lower
efficiency.
Experimental Section
Commercially available reagents and solvents were used as received.
Triazolium salts A-C were synthesized as reported in the literature.10b
Synthesis of all metal complexes was performed under an atmosphere of
dry nitrogen using standard Schlenk techniques. Solvents were dried by
standard methods and distilled under nitrogen. IR spectra were recorded
on
a Bruker Alpha FT-IR/ATR spectrometer. Melting points were
determined on a Fisher-Johns apparatus and are uncorrected. NMR
spectra were obtained with a Bruker Ascend (400 MHz) spectrometer.
Elemental analyses were obtained with a Thermo Finnegan CHNSO-
1112 apparatus and a Perkin Elmer Series II CHNS/O 2400 instruments.
Scheme 2. Proposed mechanism for the preparation of triazolylidene-Pd0
active species.
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10.1002/ejic.201900918
European Journal of Inorganic Chemistry
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X-Ray diffraction analyses were collected in an Agilent Gemini
Diffractometer using Mo K radiation (l = 0.71073 Å). Data were
integrated, scaled, sorted, and averaged using the CrysAlisPro software
package. The structures we solved using direct methods, using SHELX
2014 and refined by full matrix least squares against F2.20 All non
hydrogen atoms were refined anisotropically. The position of the
hydrogen atoms was kept fixed with common isotropic display
parameters. CCDC 1949460 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
CH2), 2.08 (s, 3H, CH3), 2.25 (s, 4H, CH3 and OH, overlapped), 2.70 (d, J
= 13.4 Hz, CH2CH, 1H), 3.11 (m, 2H, CH2), 3.46 (d, J = 6.20 Hz, CH2CH,
1H), 3.60 (m, 2H, CH2OH), 4.04 (bs, 1H, CH2CH), 4.07 (s, 3H, NCH3),
4.81 (m, 1H, CH2CHCH2), 6.86 (d, J = 7.88 Hz, MesH, 2H). 13C-RMN
(CDCl3, 100 MHz): δ = 18.1, 18.6, 21.2, 22.2, 31.4, 36.2, 56.0, 60.7, 68.7,
113.1, 128.8, 129.1, 134.5, 134.9,136.7, 139.8, 146.8, 166.5 (C=Pd). FT-
IR/ATR vmax cm-1: 3442, 3041, 2998, 2960, 2923, 2737, 1756, 1608,
1445, 1377, 1319, 1015, 920, 854, 799, 737, 682. Found: C, 40.67; H,
4.56; N, 7.39; Calc for: C18H26IN3OPd C, 40.51; H, 4.91; N, 7.87.
Synthesis of cinnamyl palladium complexes 4-6
Synthesis of allyl palladium complexes 1-3
Complex 4. Palladium cinnamyl chloride dimer (36 mg, 0.070 mmol),
potassium hexamethyl disylazide (37 mg, 0.181 mmol) and the triazolium
salt A (50 mg, 0.139 mmol) were combined in a Schlenk flask and
dissolved in THF (10 mL) at -78°C. The resulting mixture was stirred for 2
h. The final clear suspension was dried under vacuum and the residue
was extracted with benzene (5 ml). After evaporation of the solvent, the
product was obtained as yellow solid in 74% yield (59 mg, 0.103 mmol)
Complex 1. Palladium allyl chloride dimer (26 mg, 0.070 mmol),
potassium hexamethyl disylazide (37 mg, 0.181 mmol) and triazolium salt
A (50 mg, 0.139 mmol) were combined in a Schlenk flask and dissolved
in THF (10 mL) at -78°C. The resulting mixture was stirred for 1 h. The
final clear suspension was dried under vacuum and the residue was
extracted with benzene (5 ml). After evaporation of the solvent, the
product was obtained as yellow solid in 72% yield (66 mg, 0.121 mmol)
after purification by column chromatography using
a mixture of
after purification by column chromatography using
a mixture of
dichloromethane/acetonitrile (90:10). M.p. = 114-116 °C. 1H-RMN (CDCl3,
400 MHz): δ = 1.95 (s, 3H, CH3), 2.10 (s, 3H, CH3), 2.30 (s, 3H, CH3),
3.28 (d, J = 6.44 Hz, CH2CH), 3.48 (bs, 1H, OH), 4.06 (d, J = 1.72 Hz,
CH2CH), 4.15 (s, 3H, NCH3), 4.44 (d, J = 12.8 Hz, CH2CH), 4.74 (dd, J =
13.94 Hz, CH2OH, 1H), 6.92 (d, J = 6.4 Hz, MesH, 2H), 7.12 (d, J = 7.16
Hz, ArH, 1H), 7.22 (t, J = 7.62 Hz, ArH, 2H), 7.27 (d, J = 7.48 Hz, ArH,
2H). 13C-RMN (CDCl3 100 MHz): 18.02, 18.75, 21.34, 36.46, 51.79,
60.50, 88.52, 109.02, 126.98, 127.59, 128.47, 128.82, 129.34, 136.73,
138.75, 140.26, 146.86, 167.10 (C=Pd). FT-IR/ATR vmax cm-1: 3412,
3030, 2924, 2853, 2335, 1942, 1852, 1734, 1605, 1440, 1370, 1212,
1208, 1151, 1073, 1030, 1006, 853, 756, 693. Found: C, 44.01; H, 4.82;
N, 7.70; Calc for: C21H26IN3OPd C, 44.27; H, 4.60; N, 7.37.
dichloromethane/acetonitrile (90:10). M.p. = 72-74 °C. 1H-RMN (CDCl3,
400 MHz): δ = 1.80 (d, J = 12.2 Hz, CH2CH, 1H), 1.93 (s, 3H, CH3), 2.07
(s, 3H, CH3), 2.26 (s, 3H, CH3), 2.72 (d, J = 13.4 Hz, CH2CH, 1H), 3.38 (d,
J = 6.48 Hz, CH2CH, 1H), 3.46 (t, J = 14.5, OH, 1H), 4.08 (bs, 1H,
CH2CH), 4.18 (s, 3H, NCH3), 4.76 (m, 4H, CH2CHCH2 y CH2OH), 6.88 (d,
J = 5.52 Hz, MesH, 2H). 13C-RMN (CDCl3, 100MHz): δ = 18.0, 18.5,
21.3, 36.5, 55.0, 56.7, 68.7, 113.5, 128.8, 129.2, 134.7, 135.2, 136.7,
140.1, 146.8, 168.8 (C=Pd). FT-IR/ATR vmax cm-1: 3399, 3072, 3035,
2962, 2923, 2856, 1869, 1741, 1607, 1488, 1442, 1382, 1379, 1328,
1261, 1216, 1150, 1024, 937, 853, 800, 738, 704, 657. Found: C, 37.76;
H, 4.23; N, 8.28; Calc for: C16H22IN3OPd C, 38.00; H, 4.39; N, 8.31.
Complex 2. Palladium allyl chloride dimer (26 mg, 0.070 mmol),
potassium hexamethyl disylazide (37 mg, 0.181 mmol) and the triazolium
salt B (54 mg, 0.139 mmol) were combined in a Schlenk flask and
dissolved in THF (10 mL) at -78°C. The resulting mixture was stirred for 1
h. The final clear suspension was dried under vacuum and the residue
was extracted with benzene (5 ml). After evaporation of the solvent, the
product was obtained as yellow solid in 62% yield (45 mg, 0.087 mmol)
Complex 5. Palladium cinnamyl chloride dimer (36 mg, 0.070 mmol),
potassium hexamethyl disylazide (37 mg, 0.181 mmol) and the triazolium
salt B (55 mg, 0.139 mmol) were combined in a Schlenk flask and
dissolved in THF (10 mL) at -78°C. The resulting mixture was stirred for 2
h. The final clear suspension was dried under vacuum and the residue
was extracted with benzene (5 ml). After evaporation of the solvent, the
product was obtained as yellow solid in 58% yield (47 mg, 0.806 mmol)
after purification by column chromatography using
a mixture of
dichloromethane/acetonitrile (90:10). M.p. = 76-78 °C. 1H-RMN (CDCl3,
400 MHz): δ = 1.94 (s, 4H, CH3 and CH2CH, overlapped), 2.09 (s, 3H,
CH3), 2.25 (s, 3H, CH3), 2.56 (bs, 1H, OH), 2.70 (d, J = 13.44 Hz,
CH2CH, 1H), 3.20 (m, 2H, CH2), 3.51 (d, J = 6.48 Hz, CH2CH, 1H), 4.03
(m, 3H, CH2CH and CH2OH, overlapped), 4.10 (s, 3H, NCH3), 4.81 (m,
1H, CH2CHCH2), 6.86 (d, J = 8.88 Hz, MesH, 2H). 13C-RMN (CDCl3, 100
MHz): δ = 18.12, 18.7, 21.2, 29.1, 36.7, 56.1, 60.8, 68.7, 113.1, 128.8,
129.1, 134.6, 135.0, 136.7, 139.8, 144.9, 166.6 (C=Pd). FT-IR/ATR vmax
cm-1: 3423, 3069, 3031, 2957, ,2923, 2868, 2734, 1647, 1608, 1489,
1444, 1378, 1321, 1262, 1245, 1189, 1145, 1050, 922, 853, 803, 738,
682. Found: C, 39.41; H, 4.96; N, 8.34; Calc for: C17H24IN3OPd C, 39.29;
H, 4.65; N, 8.09.
after purification by column chromatography using
a mixture of
dichloromethane/acetonitrile (90:10). M.p. = 98-100 °C 1H-RMN (CDCl3,
400 MHz): δ = 1.96 (s, 3H, CH3), 2.13 (s, 3H, CH3), 2.29 (s, 3H, CH3),
2.43 (bs, 1H, OH), 3.19 (m, 2H, CH2), 3.38 (d, J = 5.68 Hz, CH2CH, 1H),
3.93 (s, 1H, CH2CH), 4.01 (bs, 2H, CH2OH), 4.05 (s, 3H, NCH3), 4.41 (d,
J = 12.72 Hz, CH2CH), 7.37 (m, 1H, CH2CHCH2), 6.91 (d, J = 10.36 Hz,
MesH, 2H), 7.08 (d, J = 2.60 Hz, ArH, 1H), 7.22 (m, ArH, 4H). 13C-RMN
(CDCl3 100 MHz): 18.20, 19.02, 21.31, 29.23, 36.80, 51.20, 60.79, 88.53,
108.78, 126.81, 127.63, 128.37, 128.81, 129.37, 136.78, 138.83, 139.98,
144.90, 165.58 (C=Pd). FT-IR/ATR vmax cm-1: 3414, 3022, 2923, 2854,
2346, 1952, 1852, 1740, 1665, 1599, 1439, 1379, 1320, 1243, 1144,
1050, 854, 757, 694. Found: C, 45.26; H, 4.83; N, 7.20; Calc for:
C22H28IN3OPd C, 45.54; H, 4.78; N, 7.35.
Complex 3. Palladium allyl chloride dimer (26 mg, 0.070 mmol),
potassium hexamethyl disylazide (37 mg, 0.181 mmol) and the triazolium
salt B (59 mg, 0.139 mmol) were combined in a Schlenk flask and
dissolved in THF (10 mL) at -78°C. The resulting mixture was stirred for 1
h. The final clear suspension was dried under vacuum and the residue
was extracted with benzene (5 ml). After evaporation of the solvent, the
product was obtained as yellow solid in 80% yield (59 mg, 0.111 mmol)
Complex 6. Palladium cinnamyl chloride dimer (36 mg, 0.070 mmol),
potassium hexamethyl disylazide (37 mg, 0.181 mmol) and the triazolium
salt C (58 mg, 0.139 mmol) were combined in a Schlenk flask and
dissolved in THF (10 mL) at -78°C. The resulting mixture was stirred for 2
h. The final clear suspension was dried under vacuum and the residue
was extracted with benzene (5 ml). After evaporation of the solvent, the
product was obtained as yellow solid in 78% yield (65 mg, 0.108 mmol)
after purification by column chromatography using
a mixture of
dichloromethane/acetonitrile (90:10). M.p. = 68-71 °C. 1H-RMN (CDCl3,
400 MHz): δ = 1.94 (s, 4H, CH2CH and CH3, overlapped), 2.00 (m, 2H,
after purification by column chromatography using
dichloromethane/acetonitrile (90:10). M.p.= 85-87 °C 1H-RMN (CDCl3,
400 MHz): δ = 1.95 (s, 3H, CH3), 1.97 (s, 2H, CH2), 2.12 (s, 3H, CH3),
a mixture of
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10.1002/ejic.201900918
European Journal of Inorganic Chemistry
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2.28 (s, 3H, CH3), 2.30 (s, 1H, OH), 3.11 (m, 2H, CH2), 3.36 (d, J = 6.36
Hz , CH2CH, 1H), 3.60 (m, 2H, CH2OH), 3.91 (s, 1H, CH2CH), 4.01 (s,
3H, NCH3), 4.39 (d, J = 12.76 Hz, CH2CH, 1H), 5.37 (m, 1H, CH2CHCH2),
6.91 (d, J = 10.84 Hz, MesH, 2H), 7.06 (s, 1H, ArH), 7.22 (m, 4H, ArH).
13C-RMN (CDCl3 100 MHz): 18.14, 18.99, 21.30, 22.26, 31.32, 36.17,
36.37, 51.37, 60.72, 88.36, 108.93, 126.77, 127.64, 128.35, 128.79,
129.38, 136.77, 138.91, 139.98, 146.80, 165.51 (C=Pd). FT-IR/ATR vmax
cm-1: 3429, 3022, 2922, 2854, 2336, 1954, 1860, 1733, 1608, 1489,
1433, 1378, 1319, 1245, 1142, 1061, 995, 928, 894, 856, 800, 756, 692.
Found: C, 45.97; H, 4.89; N, 6.77; Calc for: C23H30IN3OPd C, 46.21; H,
5.06; N, 7.03.
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temperature for 2 hours and monitored by 1H NMR spectroscopy. Water
was added to the reaction mixture, the organic layer was extracted with
ethyl acetate, dried with magnesium sulfate, and the solvent was
evaporated under vacuum. When necessary the product was purified by
column chromatography on silica gel using a proper mixture of ethyl
acetate/hexanes as eluent.
General procedure for catalytic preparation of amides
A solvent bomb equipped with a magnetic stir bar, was loaded with
K2CO3 (1.3 equiv), the catalyst (5 mol%), the appropriate ester (0.1
mmol), and amine (0.11 mmol). The solvent bomb was placed under
vacuum and purged with nitrogen for three times. Toluene (3 mL) and
degassed water (20 equiv) were subsequently added to the reaction
mixture and the contents were heated at 100 oC for 24 h. After cooling to
room temperature, the reaction mixture was diluted with ethyl acetate
and the organic phase was washed with water and brine, and further
dried with magnesium sulfate. The crude mixture was concentrated in
vacuo and subjected to purification by column chromatography.
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Acknowledgements
We are grateful to PRODEP (project UAEH-PTC-792) for
financial support.
Keywords: Triazolylidenes • palladium • catalysis• cross
coupling • hydroxyl
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
We report the synthesis and
Mesoionic carbenes*
characterization
palladium(II)
a
series
of
Agustín De la Fuente-Olvera, Oscar R.
Suarez-Castillo and Daniel Mendoza-
Espinosa*
complexes
bearing
hydroxyl-functionalized triazolylidene
ligands. Their catalytic performance in
the synthesis of a series of biaryls and
amides via cross-coupling procedures
is discussed.
Page No. – Page No.
Title
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