Degradation of the active species in the catalytic system Pd(OAc)2/NEt3

Article abstract of DOI:10.1039/c6ra20886j

The degradation under ambient humidity and room temperature of Pd(OAc)₂(NEt₃), which is an efficient catalyst for the aerobic oxidation of alcohols, to diethylamine and acetaldehyde derivatives is disclosed. Evolved diethylamine reacted with Pd(OAc)₂ to give Pd(OAc)₂(HNEt₂), which is in dynamic equilibrium with Pd(OAc)₂(HNEt₂)₂. The evolved acetaldehyde generated during degradation process was trapped with a nucleophile to form 2-methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline. NMR spectroscopy and single crystal X-ray diffraction studies have been used to characterize the reaction products of the reaction system.

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ARTICLE
Degradation of the active species in the catalytic system Pd(OAc)2/NEt3
Jesús Sanmartín-Matalobos,*a Concepcion González-Bello,b Lucía Briones-Miguéns,a Matilde Fondoa and
Ana M. García-Deibea
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
and room/reflux temperature. We plan to use NMR
spectroscopy to study the composition of the reaction system.
The degradation under ambient humidity and room temperature
of Pd(OAc)2(NEt3), which is an efficient catalyst for the aerobic
oxidation of alcohols, to diethylamine and acetaldehyde
derivatives is disclosed. Evolved diethylamine reacted with
10 Pd(OAc)2 to give Pd(OAc)2(HNEt2), which is in dynamic
equilibrium with Pd(OAc)2(HNEt2)2. The evolved acetaldehyde
generated during degradation process was trapped with a
nucleophile
to
form
2-methyl-3-tosyl-1,2,3,4-
tetrahydroquinazoline. NMR spectroscopy and single crystal X-
15 ray diffraction studies have been used to characterize the
reaction products of the reaction system.
Introduction
The use of the catalytic system Pd(OAc)2/NEt3 has proven to be a
20 convenient synthetic strategy for the aerobic oxidation of
alcohols to carbonyl compounds, at both high and room
temperatures.1,2 The role of NEt3 is crucial in the ligand-
accelerated catalysis due to the reduction of the activation
energy barrier in the rate-determining β-hydride elimination
25 step (scheme 1).3 Using a combination of experimental and
theoretical studies, it was found that at room temperature the
active species is Pd(OAc)2(NEt3), which is in dynamic equilibrium
with Pd(OAc)2(NEt3)2.3 As the concentration of NEt3 is increased,
the equilibrium favours Pd(OAc)2(NEt3)2 and an inhibitory effect
30 on the oxidation rate is observed.
50 Scheme 1. Proposed mechanism for the aerobic oxidation of a benzyl
alcohol to the corresponding aldehyde catalysed by Pd(OAc)2/NEt3 at
room temperature
Results and discussion
55 We have spectroscopically investigated the composition of a
solution of the catalytic system Pd(OAc)2/NEt3 without added
substrates, and also in the presence of methanol and ethanol.
Diethylamine derivatives. NMR monitoring of the reaction
progress shown that, a THF solution of Pd(OAc)2/NEt3 after 30
60 minutes in absence of air gave rise to Pd(OAc)2(NEt3) with traces
of Pd(OAc)2(NEt3)2 (Fig. 1). After 5h exposure to air (room
temperature and ambient humidity) the presence of
Pd(OAc)2(HNEt2) can be clearly observed. As time passes
concentration of Pd(OAc)2(HNEt2), Pd(OAc)2(HNEt2)2 and HNEt2
65 increases, while concentration of Pd(OAc)2(NEt3) decreases. The
formation of these diethylamine derivatives suggests that an
acid-catalyzed hydrolysis is involved in the process of
degradation of Pd(OAc)2(NEt3). Since HNEt2 was not found when
the reaction takes place in the absence of Pd(OAc)2, the
70 formation of Pd(OAc)2(HNEt2)2 is an evidence of the palladium-
mediated hydrolysis of triethylamine. We have performed an
experiment in the presence of O2 and absence of humidity, but
Besides the displacement of the chemical equilibrium towards
Pd(OAc)2(NEt3)2, other processes could contribute to the
degradation of Pd(OAc)2(NEt3). In this way, Taqui Khan4,5 and
Abbas6 have reported that NEt3 can be transformed into HNEt2
35 and acetaldehyde, under mild conditions, mediated by Ru3+ and
Fe3+, respectively. These findings led us to think that Pd2+ could
give similar results. In fact, although under severe conditions (at
200°C for 40h) and using palladium(0), the metal-catalysed
oxidative hydrolysis of some tertiary amines to secondary
40 amines and carbonyl compounds has been achieved.7
Since Pd(OAc)2(NEt3) is an efficient catalyst for aerobic
oxidation of alcohols to carbonyl compounds, it is expected that
its degradation into diethylamine and acetaldehyde derivatives
could lead to an inhibitory effect on the oxidation rate.
45 Therefore, we have undertaken studies towards the Pd-
mediated hydrolysis of triethylamine under ambient humidity
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The 1D-spectrum of Pd(OAc)2(HNEt2) shows only five proton
signals at about 1.6, 1.7, 2.1, 2.4 and 5.5 ppm corresponding to
25 HNEt2-methyl, acetate-methyl, HNEt2-methylene (two signals),
and amino groups, respectively. The diasterotopic nature of the
geminal protons explains the observation of two signals as
multiplets for methylene groups (1 and 1´).
we have not observed the formation of diethylamine derivatives.
Besides, hydrolysis reaction rate is increased when, in the
presence of water, air is replaced by oxygen, but not
significantly. We have observed that when water in 50:1 molar
ratio (NEt3:H2O) is added the time required to obtain the same
rate of hydrolysis is shortened in several hours, but the effect is
much more marked when the reaction takes place at 60°C
instead of at room temperature. Besides, we have observed that
as the concentration of NEt3 is increased, the equilibrium favours
5
Fig.
2 shows the H–H NMR correlation spectrum of
30 Pd(OAc)2(HNEt2), which is very similar to the spectra of
Pd(OAc)2(HNEt2)2 and HNEt2 (see ESI†). H-H couplings between
amino and methylene groups as well as between methyl and
methylene groups are nicely observed in these 2D-spectra. The
most characteristic feature in these spectra is a broad triplet
35 signal, which corresponds to the amino proton, at about 6.1, 5.5
and 5.2 ppm in Pd(OAc)2(HNEt2), Pd(OAc)2(HNEt2)2 and HNEt2,
respectively. These chemical shifts are coherent with the
palladium complexation by acetate in Pd(OAc)2(HNEt2) and
Pd(OAc)2(HNEt2)2, since it causes a decrease of the electron
40 density around the amino proton. This decrease in shielding (i.e.
deshielding) displaces the NMR signal toward a lower field in
Pd(OAc)2(HNEt2), which shows a more significant decrease of the
electron density around the amino proton. Likewise, exhaustive
NMR studies (see ESI†) demonstrate that Pd(OAc)2(HNEt2)2 in
45 solution has virtually the same structure as that observed in the
solid state by X-ray diffraction.8,9
10 Pd(OAc)2(HNEt2)2, leading to the maximum yield (85%) the 1:8
molar ratio at 60°C. After 63h of exposure to air at room
temperature and ambient humidity, the constituents of the
mixture were separated and spectroscopically characterized.
Acetaldehyde derivatives. We have used the formation10 of 2-
methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline
from
the
nucleophile 2-tosylaminomethylaniline11 (scheme 2) as a tool to
1
50 make acetaldehyde easier to monitor by H NMR spectroscopy,
since it is a volatile compound (bp 21 °C). We have chosen 2-
tosylaminomethylaniline (HATS) because it has already been used
successfully for verifying the Pd-mediated aerobic oxidation of
methanol to formaldehyde.12
15 Fig. 1. 1H NMR spectra in dmso-d6 showing the evolution of system
Pd(OAc)2/NEt3 (1:8 molar ratio) at room temperature and ambient
humidity. A colour code was used for characteristic resonances of each
species.
Pd(OAc)2
N
+
r.t.
air
THF
or
ꢀ
H
+
HN(Et)2
O
O
Pd(OAc)2
S
O
N
H
NH2
O
HN
O
O
Pd
O
S
HN
N
O
HN
O
55
Scheme 2. Pd-mediated hydrolysis of triethylamine in the presence of 2-
tosylaminomethylaniline (HATs) to yield 2-methyl-3-tosyl-1,2,3,4-
tetrahydroquinazoline and di(acetato)bis(diethylamine) palladium(II)
.
We have investigated the evolution of the chemical
60 composition of solution of Pd(OAc)2/NEt3 to which 2-
a
tosylaminomethylaniline has been added. After heating at about
60°C for 5h, NMR spectroscopy revealed the presence of
20 Fig. 2. Two-dimensional proton-proton NMR correlation spectrum of
Pd(OAc)2(HNEt2). A colour code was used to highlight the observed H-H
couplings.
Pd(OAc)2(HNEt2)2
and
2-methyl-3-tosyl-1,2,3,4-
2
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tetrahydroquinazoline (Fig. 3). Since Pd(OAc)2(HNEt2) results 35 methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline obtained from a
from Pd(OAc)2(NEt3), which is the catalytic species on the
oxidation of alcohols, it is expected an inhibitory effect on the
oxidation rate of alcohols. In fact we have not detected
oxidation of methanol to formaldehyde, even though we have
reaction mixture containing Pd(OAc)2/NEt3-d15 and 2-
tosylaminomethylaniline evidenced total deuteration at 2-
position, leading to CD3 and CD groups (Fig. 4). As a consequence
of the replacement of the CH by the CD group the original
5
found possible oxidation of methanol under not very different 40 multiplicity of the NH proton changed from a doublet to a
reaction conditions.12 In view that 2-substituted-1,2,3,4-
tetrahydroquinazolines10 are accessible in almost quantitative
yield via nucleophilic addition of 2-aminobenzylamine
singlet.
10 derivatives to aldehydes, the presence of 2-methyl-3-tosyl-
1,2,3,4-tetrahydroquinazoline in the mixture is a sign of the
formation of acetaldehyde. Besides diethylamine and
acetaldehyde derivatives, there are other by-products in the
reaction mixture, such as Pd(OAc)(ATs)(NEt3) and Pd(ATs)2 (see
15 ESI†). As time passes, concentration of Pd(OAc)2(HNEt2)2 and 2-
methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline increases, while
concentration of Pd(OAc)(ATs)(NEt3) and Pd(ATs)2 decreases. After
8h, the main constituents of the mixture were separated and
spectroscopically characterized.
Fig. 4. Two-dimensional proton-proton NMR correlation spectrum of 2-
methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline in acetone-d6.
A colour
45 code was used to highlight the observed H-H couplings.
2-tosylaminomethylaniline derivatives. Although we have
used 2-tosylaminomethylaniline (HATs) to trap the acetaldehyde
generated during degradation of NEt3, the mentioned
nucleophile interacts with Pd(OAc)2 resulting in Pd(ATs)2. We
50 have observed that in the absence of Pd(OAc)2, Pd(ATs)2 acts as a
source of Pd+2 and ATs- allowing the hydrolysis of NEt3 and the
formation of 2-methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline.
Therefore Pd(ATs)2 plays a role in the degradation of NEt3. A two-
dimensional carbon-proton NMR correlation spectrum (HMBC)
1
55 of Pd(ATs)2 with fully assigned H and 13C spectra is shown in Fig.
5. From the NMR study it has been deduced that Pd(ATs)2 adopts
a square-planar geometry.
The electronic spectra of HAT and Pd(ATs)2 have been recorded
in acetonitrile as solvent. Three absorptions, in the ultraviolet
60 region, at about 205, 230 and 293 nm, are assignable to intra-
ligand orbital transitions in the mentioned compounds. In the
visible region of square-planar palladium complexes, three spin-
allowed d-d transitions and three spin forbidden singlet-triplet
d-d transitions from the three lower lying d levels to the empty
20
1
Fig. 3. H NMR spectra in dmso-d6 showing the evolution of the reaction
system Pd(OAc)2/NEt3 in the presence of HATs at about 60ºC. A colour
code was used for the characteristic resonances of each species.
2
2
65 dx -y orbitals are predicted.14 Spin-allowed d-d transitions were
1
1
expected to correspond to the transitions A1g→1A2g, A1g→1B1g
and A1g→1Eg. However, strong charge transfer transition for
Two-dimensional correlation NMR spectroscopy in
1
Pd(ATs)2 interfere and prevent the observation of all the
expected bands in the visible region.
25 combination with a selective NOE provides insight into the
molecular
structure
of
2-methyl-3-tosyl-1,2,3,4-
70
The molecular structure of Pd(ATs)2, which is represented as
an ORTEP diagram in Fig. 6, was determined using single crystal
X-ray diffraction techniques.15-18 The asymmetric unit only
contains half molecule of the neutral complex, and the complete
molecule is generated by a symmetry operation based on an
tetrahydroquinazoline. The deduced spatial arrangement of this
molecule in solution is in good agreement with that displayed by
the calculated most stable conformer of 2-methyl-3-tosyl-
30 1,2,3,4-tetrahydroquinazoline,13 which displays an anti-
disposition of methyl and tosyl groups (see ESI).
75 inversion centre located at the centre of the metal ion (#1 -x+1, -
y, -z). This inversion implies both a trans-disposition of the donor
atoms, and an anti-conformation of the tosyl groups respect to
An isotope labelling experiment using NEt3-d15 as starting
material has demonstrated that acetaldehyde derived from
triethylamine. Thus, a 1H NMR spectrum of tetradeuterated 2-
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the chromophore, which is absolutely plane. Thus, the four
donor N-atoms and the palladium ion are exactly in the same
plane, so the four N-Pd-N angles sum 360 °. The main angles and
bond distances are collected in Table 1.
molecules that are connected through intermolecular H bonds
between parallel single chains. By contrast, the monoclinic
polymorph only displays single chains, without connecting to
20 neighboring chains (Fig. 7 bottom). Mutual intermolecular
N-H···O interactions between coordinated amino groups and
tosyl groups of contiguous molecules lead to the formation of a
ring of 12 elements based on two donors and two acceptors
R2,2(12) according to graph sets.20 As Figure
7 shows,
25 intramolecular π-stacking takes place between the relatively
electron deficient tosyl group and the electron rich aminomethyl
aniline moiety. As a consequence, the centroids of these two
aromatic rings are at ca. 3.64 Å, while they are forming an angle
of only 10.8°.
30 Table 1. Main bond lengths, bond and torsion angles, and H bonding
scheme for Pd(ATs
)
2
Atoms[a]
Distances[b]
Atoms
Angles[c]
Pd1-N2
Pd1-N2#1
Pd1-N1
Pd1-N1#1
N1-C1
2.029(6)
2.029(6)
2.044(6)
2.043(6)
1.460(10)
1.482(9)
1.598(7)
N2-Pd1-N2#1
N2-Pd1-N1
N2#1-Pd1-N1
N1-Pd1-N1#1
C7-N3-S1
180.0
92.1(2)
87.9(2)
180.0
117.4(5)
109.7(4)
N2-C7
N2-S1
N2-S1-C8
N1-C1-C6-C7
C1-C6-C7-N2
C7-N2-S1-C8
6.3(11)
50.5(10)
-80.5(6)
5
D—H···A[a]
D—H[b]
H···A[b]
2.21
D···A[b]
2.909 (8)
D—H···A[c]
124
Fig 5. Correlation spectrum (HMBC) of Pd(ATs)2 (in dmso-d6). The most
important C-H couplings were highlighted.
N1—H1B···O1#1 1.02
N1—H1A···O2#2 0.76
2.17
2.929 (8)
173
[a] #1 = -x+1, -y, -z; #2 = -#1 = x+1, y, z. [b] in Å. [c] in degrees.
Fig. 6. Molecular structure of Pd(ATs)2. Ellipsoids have been represented
10 at 50% probability level.
Pd(ATs)2 crystallizes in the monoclinic space group P21/c. A
polymorph of this compound, which crystallized in the triclinic
space group P-1 has been already reported by us.19 Despite of
the subtle differences between the molecules of the two
15 polymorphs (Fig. 7 top), their packing scheme are sensibly
different. Thus, the triclinic crystal displays double chains of
35
Fig. 7. Top: Comparison of monoclinic (yellow) and triclinic (green)
polymorphs of Pd(ATs)2. Bottom: Intermolecular N-H···O bonds that give
rise to a single-chain architecture
.
4
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least squares on F2.18 Thus, non-hydrogen atoms when were
anisotropically refined, but some of them were oblate, and even
40 prolate. Since U restraints were not effective in this case, one of
them, which is sited on an aromatic ring, was isotropically
refined. Hydrogen atoms were included in the structure factor
calculation in geometrically idealized positions, with thermal
parameters depending of the parent atom, by using a riding
45 model. H atoms of the coordinated amine group where localized
in Fourier maps and then refined with a thermal parameter
depending of the parent N atom.
Conclusions
The results reported here showed that in air (and ambient
humidity, at room or reflux temperature), occurs degradation of
Pd(OAc)2(NEt3) into HNEt2 and acetaldehyde. Evolved
diethylamine reacted with Pd(OAc)2 to give Pd(OAc)2(HNEt2),
which is in dynamic equilibrium with Pd(OAc)2(HNEt2)2. The
evolved acetaldehyde generated during degradation process was
trapped with a nucleophile to form 2-methyl-3-tosyl-1,2,3,4-
tetrahydroquinazoline.
5
10 Experimental
CCDC 991659 contains the supplementary crystallographic data
50 for this paper. These data can be obtained free of charge from
Materials and methods
The
Cambridge
Crystallographic
Data
Centre
via
Excluded 2-tosylaminomethylaniline11 all starting materials and
reagents were commercially available and were used without
further purification. 1H NMR spectra (500 MHz) and 13C NMR
15 spectra (125 MHz) were measured in deuterated solvents. J
values are given in Hertz. NMR assignments were carried out by
a combination of COSY, NOESY, HSQC and HMBC experiments.
Infrared spectra were recorded as KBr pellets on a Jasco FT/IR-
410 spectrophotometer in the range 4000-600 cm-1. Elemental
20 analyses were performed on a Carlo Erba EA 1108 analyzer.
Electrospray mass spectra were recorded on a Bruker Microtof
spectrometer. MALDI-TOF mass spectra were recorded on a
Bruker Ultraflex III TOF/TOF using methanol as solvent and DCTB
as matrix.
www.ccdc.cam.ac.uk/data_request/cif
NMR monitoring of the system Pd(OAc)2/NEt3 at r. t.
55 A THF solution (8 mL) of Pd(OAc)2 (40.4 mg, 0.18 mmol) and NEt3 (0.2
mL, 1.44 mmol) was stirred for 30 min under anhydrous conditions. The
filtrate was concentrated to dryness at room temperature under
reduced pressure and a sample of the resulting yellow solid was studied
by 1H NMR spectroscopy. Then, the isolated powdery mixture was
60 dissolved in THF and exposed to air, and after 5h a small amount of
Pd(OAc)2(HNEt2) was formed. After 63h of exposure to air,
Pd(OAc)2(HNEt2)2 (main), PdH(OAc)(NEt3) and HNEt2, were also formed.
NMR monitoring of the system Pd(OAc)2/NEt3 at 60°C.
65 A THF solution (8 mL) of NEt3 (0.2 mL, 0.8 mmol) was charged with
Pd(OAc)2 (40 mg, 0.2 mmol) and HATs (24 mg, 0.08 mmol) and then was
heated under reflux for 8 h. Samples of the solution were concentrated
to dryness under vacuum and the resulting solids were studied by 1H
25 Crystal structure analysis data
Diffraction data for Pd(ATs)2 were collected from a thin crystal
needle at 100(2) K, using graphite-monochromated Mo-Kα
radiation (λ = 0.71073 Å) from a fine focus sealed tube. Some
significant crystal parameters and refinement data are
30 summarized in Table 2.
NMR spectroscopy.
70
Degradation of Pd(OAc)2(NEt3) into Pd(OAc)2(H2NEt2)2
Without added substrates. A THF solution (2 mL) of Pd(OAc)2 (10.0 mg,
0.045 mmol) and NEt3 in various molar ratios (5.6 ꢁL, 0.040 mmol; 11.1
ꢁL, 0.08 mmol; 16.7 ꢁL, 0.12 mmol; 44.6 ꢁL, 0.32 mmol and 55.7 ꢁL, 0.40
75 mmol) was heated under reflux for 30 min. The resulting black powdery
solid was filtered off. The filtrate was concentrated to dryness under
reduced pressure and the resulting yellow solid was solved in diethyl
ether. After recrystallization (4 h evaporation at room temperature)
yellow prismatic crystals of Pd(OAc)2(HNEt2)2 suitable for X-ray
80 diffraction studies were obtained.
Table 2. Diffraction data for Pd(ATs
)
2
Formula
Mr
Crystal system
Space group
Unit cell
C28H30N4O4PdS2
657.08
Monoclinic
P21/c (No. 14)
a = 6.8995(15) Å
b = 8.5875(19) Å
c = 22.797(4) Å
α
β
γ
= 90 °
= 98.652(7) °
= 90 °
Volume (Å3)
Z
1335.4(5)
2
1.634
Degradation of Pd(OAc)2(NEt3) into 2-methyl-3-tosyl-1,2,3,4-
tetrahydroquinazoline
Dc (g/cm3)
ꢁ
(mm-1)
0.90
Without added substrates. A solution of Pd(OAc)2 (10 mg, 0.045 mmol),
85 HATs (6 mg, 0.02 mmol) and NEt3 (28 ꢁL, 0.20 mmol) in THF (2 mL) was
heated under reflux (about 60 ºC) for 8 h. The resulting black powdery
solid was filtered off. The filtrate was concentrated to dryness under
vacuum at about 45 ºC. The experiment was reproduced by using 5 times
the amount of reagents and the resulting mixture was separated by
90 chromatography with ethyl acetate:hexane (50:50). The eluting solution
was then concentrated to dryness under vacuum resulting in a white
solid.
F(000)
672
θ
range (º)
1.8 to 24.7
9929 / 2264
0.0743
2264 / 0 / 175
R1 = 0.0692, wR2 = 0.1561
R1 = 0.1066, wR2 = 0.1794
1.388, -1.466
Ref. col. / Ref. Ind
Rint
Data / restr./param.
R1, wR2 [I > 2
R1, wR2 (all data)
Residuals (e.Å–3
σ(I)]
)
Data were processed and corrected for Lorentz and polarization
effects. Multi-scan absorption corrections were performed using
35 the SADABS routine.15,16 The structure was solved by standard
direct methods.17 Some problems related to the thin nature of
the crystals were observed during the refinement by full matrix
In the presence of methanol. A tetrahydrofuran solution (2 mL) of NEt3
(14 ꢁl, 0.10 mmol) was charged with Pd(OAc)2 (10 mg, 0.05 mmol, HATs (6
95 mg, 0.02 mmol) and methanol (40 ꢁL). Then, the solution was heated
under reflux for 8h. The resulting black powdery solid was filtered off.
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The filtrate was concentrated to dryness under vacuum to remove
55 Notes and references
tetrahydrofuran as well as excess of methanol and NEt3. Yield = 40%.
a Departamento de Química Inorgánica, Facultad de Química,
Universidad de Santiago de Compostela, Avda. de las ciencias s/n, 15782-
Santiago de Compostela, Spain.
Pd(OAc)2(H2NEt2)2
Fax: +34 981 528073; E-mail: jesus.sanmartin@usc.es
60 b Centro Singular de Investigación en Química Biolóxica e Materiais
Moleculares (CIQUS) and Departamento de Química Orgánica,
Universidade de Santiago de Compostela, calle Jenaro de la Fuente s/n,
15782 Santiago de Compostela, Spain
5
Yields depending on the used molar ratio Pd(OAc)2/NEt3 (in parenthesis):
39% (1:1), 50% (1:2), 64% (1:3), 84% (1:7) and 58% (1:9). 1H NMR (500
MHz, dmso-d6): δ/ppm 5.55 (t, J = 9.5 Hz, 2H, 2xNH), 2.44 (m, 4H, 4xH-1),
2.10 (m, 4H, 4xH-1’), 1.72 (s, 6H, 2xCOCH3) and 1.54 (t, J = 7.1 Hz, 12H,
12xH-2). 13C NMR (125 MHz, dmso-d6): δ/ppm 178.0 (2xCO), 46.5 (4xCH2-
10 1), 24.1 (2xCOCH3) and 14.4 (4xCH3-2). IR (KBr, cm-1): 3206 ν(NH), 1587
νa(COO) and 1404 νs(COO). Elemental analysis (Found): C 38.9, H 7.8, N
7.8%. Calc. for C12H28N2O4Pd: C, 38.7; H, 7.6; N, 7.6%.
65
70
75
80
†Electronic Supplementary Information (ESI) available: spectroscopic
characterization of the compounds. See DOI: 10.1039/b000000x/
1
2
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M. J. Schultz, C. C. Park and M. S. Sigman, Chem. Commun., 2002,
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2-methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline
15 Yield = 12.3 mg (41%). 1H NMR (400 MHz, dmso-d6): δ/ppm 7.56 (d, J =
8.2 Hz, 2H, 2xH-2’), 7.16 (d, J = 8.1 Hz, 2H, 2xH-3’), 6.83 (m, 2H, H-5+H-7),
6.46 (t, J = 7.1, 1H, H-6), 6.25 (d, J = 8.1 Hz, 1H, H-8), 6.09 (d, J = 3.4 Hz,
1H, NH), 5.22 (m, 1H, H-2), 4.54 (d, J = 17.2 Hz, 1H, CHH-4) and 4.36 (d, J
= 17.2 Hz, 1H, CHH-4), 2.25 (s, 3H, CH3-4’) and 1.22 (d, 3H, J = 6.3 Hz, CH3-
20 2). 1H NMR (250 MHz, CDCl3): δ/ppm 7.59 (d, J = 8.3 Hz, 2H, 2xH-2’), 7.06
(d, J = 8.3 Hz, 2H, 2xH-3’), 6.90 (t, 1H, H-7), 6.86 (d, 1H, H-5), 6.67 (dt, J =
7.5 and 1.1 Hz, 1H, H-6), 6.29 (d, J = 8.1 Hz, 1H, H-8), 5.36 (dq, J = 6.4 and
1.0 Hz, 1H, H-2), 4.70 (d, J = 17.4 Hz, 1H, CH2-4), 4.47 (d, J = 17.4 Hz, 1H,
CH2-4), 2.29 (s, 3H, CH3) and 1.40 (d, J = 6.4 Hz, 3H, CH3). 13C NMR (62.5
25 MHz, CDCl3): δ/ppm 143.2 (C4’), 139.7 (C8a), 136.2 (C1’), 129.0 (2× C3’),
127.6 (C5), 127.3 (2× C2’), 126.4 (C7), 118.8 (C6), 116.9 (C4a), 116.4 (C8),
61.4 (CH), 41.8 (CH2), 21.5 (CH3) and 21.4 (CH3). IR (KBr, cm-1): 3387(s)
ν(NH) cm-1, 1326(s) νas(SO2), 1158(vs) νs(SO2). MS (ESI) m/z = 325 (MNa+).
HRMS calcd for C16H18N2NaO2S (MNa+): 325.0981; found, 325.0967.
30 Elemental analysis (Found): C 63.5, H 5.8, N 9.1; S, 10.5%. Calc. for
C16H18N2O2S: C, 63.6; H, 6.0; N, 9.3; S, 10.6%.
M. M. Taqui Khan, S. A. Mirza and H. C. Bajaj, React. Kinet. Catal.
Lett., 1987, 33, 67.
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12 (a) J. Sanmartín-Matalobos, A. M. García-Deibe, L. Briones-Miguéns,
90
95
C. González-Bello, C. Portela-García and M. Fondo, Dalton Trans.,
2014, 43, 722. (b) J. Sanmartín-Matalobos, A. M. García-Deibe, L.
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M. Fondo, New J. Chem., 2013, 37, 3043.
Pd(ATs)2
1H NMR (400 MHz, dmso-d6): δ/ppm 7.55 (d, J = 8.1 Hz, 4H, 4xH-2´), 7.04
35 (t, J = 7.3 Hz, 2H, 2xH-5), 7.03 (d, J = 8.0 Hz, 4H, 4xH-3´), 7.02 (s, 4H,
2xNH2), 6.90 (d, J = 7.9 Hz, 2H, 2xH-3), 6.89 (t, J = 7.9 Hz, 2H, 2xH-4), 6.83
(d, J = 7.7 Hz, 2H, 2xH-6), 4.07 (s, 4H, 2xCH2), 2.27 (s, 6H, 2xCH3). 13C NMR
(100 MHz, dmso-d6): δ/ppm 141.3 (2xC-1´), 140.2 (2xC-4´), 137.4 (2xC-1),
133.9 (2xC-2), 129.1 (2xC-3), 128.4 (4xC-3´), 128.1 (2xC-5), 125.9 (4xC-2´),
40 124.6 (2xC-4), 120.4 (2xC-6), 49.2 (2xCH2) and 20.7 (2xCH3). IR (KBr, cm-1):
3442 ν(OH), 3248 and 3180 ν(N-H), 1272 νas(SO2) and 1127(s) νs(SO2).
MS (MALDI-TOF, DCTB): m/z (%): 655.9 (100) [M+H]+. Elemental analysis
(Found): C, 51.1; H, 4.5; N, 8.3; S, 9.4%. Calc. for C28H30N4O4S2Pd: C, 51.2;
H, 4.6; N, 8.5; S, 9.8%.
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Acknowledgements
Financial support from the Spanish Ministry of Economy
and Competiveness (SAF2013-42899-R), Xunta de Galicia
(GRC2013-041) and the European Regional Development
50 Fund (ERDF) is gratefully acknowledged. We are also
grateful to the Centro de Supercomputación de Galicia
(CESGA) for use of the SVG supercomputer.
17 M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G. L. Cascarano, L.
De Caro, C. Giacovazzo, G. Polidori and R. Spagna, J. Appl. Cryst.
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Deibe and J. Sanmartín-Matalobos, Eur. J. Inorg. Chem., 2015, 2744.
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