Palladium(II) complexes of aminothiazole-based phosphines: Synthesis, structural characterization, density functional theory calculations and catalytic application in heck reaction

Article abstract of DOI:10.1002/aoc.3793

Three Pd(II) complexes of some hemilabile ligands, aminothiazole-based phosphines, were synthesized to investigate the catalytic activity of them in Heck cross-coupling reactions. The crystal structures of complexes PdCl₂[(Ph₂P)HN(C₃H₂NS)] (C₁) and PdCl₂[(Ph₂P)HN(C₇H₄NS)] (C₃) were determined using X-ray crystallography, which reveals that the ligand coordinates in a chelating mode through P and N (endocyclic) atoms in square planar geometry. Experimental and theoretical studies (atoms in molecules and natural bond orbital analyses) show that the Pd(II) interacts more strongly with the P atom than the N atom in the chelated ligand, N^P. This trait can promote catalytic activity of the complexes in comparison with our previous work in which chelated ligands with two phosphorus atoms, P^P, were used. The influence of non-covalent intermolecular interactions on the assembly of the solid-state structures is also discussed in terms of geometrical analysis. The prepared complexes turn out to be useful pre-catalysts in Heck cross-coupling reactions owing to the coordinative flexibility of the hemilabile ligands. The protocol affords the corresponding products in greater yield than the same reactions with bis(phosphino)amine Pd(II) complexes, as the catalysts in our previous work.

Full text of DOI:10.1002/aoc.3793

Received: 22 December 2016
DOI: 10.1002/aoc.3793
Revised: 6 February 2017
Accepted: 12 February 2017
F U L L PA P E R
Palladium(II) complexes of aminothiazole‐based phosphines:
Synthesis, structural characterization, density functional theory
calculations and catalytic application in heck reaction
Khodayar Gholivand1
Farzaneh T. Fadaei1
| Mohammad Kahnouji1 | S. Mark Roe2 | Akram Gholami1 |
1 Department of Chemistry, Faculty of
Science, Tarbiat Modares University, Tehran,
Iran
Three Pd(II) complexes of some hemilabile ligands, aminothiazole‐based phos-
phines, were synthesized to investigate the catalytic activity of them in Heck
cross‐coupling reactions. The crystal structures of complexes PdCl2[(Ph2P)
HN(C3H2NS)] (C1) and PdCl2[(Ph2P)HN(C7H4NS)] (C3) were determined using
X‐ray crystallography, which reveals that the ligand coordinates in a chelating mode
through P and N (endocyclic) atoms in square planar geometry. Experimental and
theoretical studies (atoms in molecules and natural bond orbital analyses) show that
the Pd(II) interacts more strongly with the P atom than the N atom in the chelated
ligand, N^P. This trait can promote catalytic activity of the complexes in comparison
with our previous work in which chelated ligands with two phosphorus atoms, P^P,
were used. The influence of non‐covalent intermolecular interactions on the assem-
bly of the solid‐state structures is also discussed in terms of geometrical analysis.
The prepared complexes turn out to be useful pre‐catalysts in Heck cross‐coupling
reactions owing to the coordinative flexibility of the hemilabile ligands. The proto-
col affords the corresponding products in greater yield than the same reactions with
bis(phosphino)amine Pd(II) complexes, as the catalysts in our previous work.
2 Department of Chemistry, School of Life
Sciences, University of Sussex, Brighton
BN1 9QJ, UK
Correspondence
Khodayar Gholivand, Department of
Chemistry, Faculty of Science, Tarbiat
Modares University, Tehran, Iran.
Email: gholi_kh@modares.ac.ir
KEYWORDS
aminothiazole‐based phosphines, crystal structure, heck coupling reaction, hemilabile ligands, palladium
complexes
1 | INTRODUCTION
Recent studies of platinum complexes with
aminothiazole‐based phosphines have revealed structural
Tuning of the stereoelectronic properties of ligands, effective
on structure and reactivity of the complexes of those ligands,
is an important object of research concerning metal‐catalysed
carbon–carbon bond formation reactions.[1–5] In this regard,
hemilabile phosphines are of interest due to the variety of
ways for coordination[6–11] and also their potential in cataly-
sis.[12–17] Indeed, these ligand systems, with P,N‐donors,
are able to coordinate reversibly to a metal centre providing
or protecting temporarily a vacant coordination site, a feature
that is very desirable for catalysts.[18]
diversity including monodentate P and bidentate PN or PS
bound in versatile compositions, whereas we have not found
any report of analogous palladium complexes in the litera-
ture.[19–23] The substituents at the aminothiazole backbone
can play an important role in determining the structure of
products.[24,25] Besides, the presence of large groups attached
to the phosphorus centre also causes the aminophosphine to
be more stable against hydrolysis.[26–31]
To improve and extend this area, we selected three new
complexes of palladium with hemilabile N^P ligands,
Appl Organometal Chem. 2017;e3793.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3793

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GHOLIVAND ET AL.
aminothiazole derivatives, to compare with our previous
work in which palladium complexes with P^P donor ligand
were used (Scheme 1).[32] According to the literature, cata-
lytic activity of complexes in coupling reactions may be
related to the metal–ligand interactions and lability of Pd–
ligand bond and facile breaking of it during the Heck
reaction.[18] New ligands were selected with P^N donor
instead of P^P donor. The new products were characterized
using infrared (IR) and NMR spectroscopies. The crystal
structures of PdCl2[(Ph2P)HN(C3H2NS)] (C1) and
PdCl2[(Ph2P)HN(C7H4NS)] (C3) were determined using
X‐ray crystallography which reveals a shortening of P─Pd
bond distances of about 0.02 Å in C1 and C3 in comparison
with our previous work on palladium complexes of P^P
ligands. The Heck coupling reaction yields for the com-
pounds used in this study are more than those for analogous
complexes which were investigated in our previous work.
The nature and strength of Pd─P and Pd─N interactions in
the three palladium complexes were investigated using
quantum theory of atoms in molecules (AIM) and natural bond
orbital (NBO) analyses.
SCHEME 2 Synthesis of ligands L1, L2 and L3 and their complexes
C1, C2 and C3
ligands with [PdCl2(COD)] afforded chelate complexes
[PdCl2L].
Aminothiazole‐based phosphines can exist in solution in
two tautomeric forms, in which the N─H proton involves
the endo‐cyclic or exo‐cyclic nitrogen atom.[18,19,22] The 31P
chemical shifts of the ligands at 41.1 to 42.2 ppm are in
agreement with the reported values for aminophosphines
with the exocyclic N─H group.[19,22] Upon coordination of
the ligand, the 31P resonance shifts to 77.5–85.2 ppm. The
1H NMR spectrum of C1 shows thiazolyl ring protons at
6.84 ppm, which are only slightly downfield shifted from
the value observed for the free ligand. The CH3 group signal
in the spectrum of C2 (at 2.37 ppm) shows downfield shift
relative to that of ligand L2. The (NHamine) signal of the
complexes appears at about 10 ppm, as a broad peak, indica-
tive of extensive hydrogen bonding. IR spectra of ligands L1–
L3 show that the ν(N─H), ν(C─N) and ν(P─N) frequencies
2 | RESULTS AND DISCUSSION
2.1 | Synthesis and characterization
In this work, three aminophosphine ligands based
on aminothiazole were prepared via phosphination
of 2‐aminothiazole, 2‐amino‐4‐methylthiazole or 2‐
aminobenzothiazole, with one equivalent of Ph2PCl in
the presence of triethylamine in dichloromethane solution
at 0 °C (Scheme 2). Compounds L1, L2 and L3 were iso-
lated as white and air‐stable solids in high yields (71, 82
and 80%, respectively). Although these ligands have
already been synthesized using a different method,[18,19]
the present synthesis pathway is simpler because of the
use of a more appropriate temperature. Reaction of the
are in the ranges 3430–3444, 1523–1592 and 870–925 cm−1
,
respectively. Vibrations of (C─N) and (P─N) bonds in
the IR spectra of the palladium complexes, in the range
1552–1642 and 932–986 cm−1, show an increase in
comparison to those of the corresponding ligands which
can be related to chelating of ligands in the complexes.
2.2 | Structural study
Single crystals of C1 and C3, suitable for X‐ray analysis, were
obtained from solutions of dichloromethane by slow evapora-
tion at room temperature. But attempts to obtain qualified
crystals of C2 were not successful. The crystallographic data
and the most relevant geometric parameters are summarized
in Tables 1 and 2, respectively.
The title compounds crystallize in the space group P21/n
with Z = 4. In each complex, the ligand binds in a chelating
mode through P1 and N1 (endo‐cyclic). The other coordina-
tion sites of the square planar Pd(II) centres are occupied by
chlorine atoms (Figure 1). The angles around the Pd atoms
SCHEME 1 General structures of (a) currently synthesized
[PdCl2(P^N)] complexes and (b) previously reported[32] [PdCl2(P^P)]
complexes

GHOLIVAND ET AL.
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TABLE 1 Crystal data and structure refinement for C1 and C3
C1
C3
Empirical formula
C15H13Cl2N2PPdS
461.60
C19H15Cl2N2PPdS
511.66
Formula weight
Wavelength, cu Kα (Å)
1.54184
1.54184
T (K)
173
173
Crystal system
Space group
a (Å)
Monoclinic
P21/n (no. 14)
10.0789(2)
14.6339(2)
11.7561(2)
90
Monoclinic
P21/c (no. 14)
12.7157(6)
12.2188(5)
13.1840(6)
90
b (Å)
c (Å)
α (°)
β (°)
106.018(2)
90
97.696(4)
90
γ (°)
V (Å3)
1666.63(5)
4
2029.96(16)
4
Z
Density (g cm−3
)
1.840
1.674
μ (mm−1
)
13.976 mu(cu Ka)
912.0
11.546
F(000)
1016
θ min, max (°)
4.9, 71.2
0.05 × 0.05 × 0.20
3.5, 71.2
0.15 × 0.15 × 0.50
Crystal size (mm)
Index ranges
−12 ≤ h ≤ 11; −13 ≤ k ≤ 17; −14 ≤ l ≤ 13
−15 ≤ h ≤ 15; −14 ≤ k ≤ 14; −9 ≤ l ≤ 15
Reflections collected
Rint (%)
17 181
6214
0.0414
0.0417
Data/restraints/parameters
Goodness‐of‐fit on F2
R1 [I > 2σ(I)]
3207/0/199
1.024
3781/0/235
1.045
0.0457
0.0201
WR2 [I > 2σ(I)]
0.0481
0.1096
Largest diff. Peak/hole (e Å−3
)
0.325 and −0.595
2917
1.093 and −1.555
3270
Observed data [I > 2.0σ(I)]
present a distortion from the values for a regular square
planar coordination mode. P1–Pd1–N1 angles are acute
(83.73(5)° and 84.07(11)° for C1 and C3, respectively), while
Cl1–Pd1–Cl2, N1–Pd1–Cl1 and P1–Pd1–Cl2 ones deviate
by about 1–10° from 90° (Table 2).
The Pd─P, Pd─N and Pd─Cl bond lengths are nearly
equal in these compounds. Notably, the Pd─Cl distances
are in the reverse correlation with the binding strength of
the corresponding trans donors. The longer Pd1─Cl2 bond
than the Pd1─Cl1 one in both complexes indicates a higher
donating ability of P with respect to Nendo (trans influence).
Similarly, a comparison between the structure of C1 and C3
reveals that the shortening of Pd─N or Pd─P bond (in C1
or C3, respectively) is also accompanied by an increase in
the opposite Pd─Cl bond length. For instance, the shorter
Pd1─P1 distance (2.184 Å in C3 versus 2.205 Å in C1)
corresponds to the longer Pd1─Cl2 bond (2.400 Å in C3 ver-
sus 2.388 Å in C1).
We also noticed that on coordination of the ligand to
Pd(II), the P─C and P─Namine bond lengths reduce (about
0.022 and 0.015 Å, respectively), while the C─Nendo
distances are longer than those found in the free ligands.[19,20]
The electronic redistribution of the ligand upon complexa-
tion, moreover, causes some geometrical changes in the
thiazole rings. The other bond distances and angles within
the ligand do not vary significantly in the coordinated
structures.
In the structure of L1 and L3, the P and Nendo atoms adopt
anti‐configuration as a result of the formation of pairwise
intermolecular Namine─H⋅⋅⋅Nendo hydrogen bonds, creating
dimeric aggregates.[19,20] The P,N‐coordination mode leads
to the syn‐configuration for these atoms in the complexes.

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GHOLIVAND ET AL.
TABLE 2 Selected bond lengths (Å) and bond angles (°) for solid‐
state structures of C1 and C3
dH⋅⋅⋅Cg = 2.87 Å, dC⋅⋅⋅Cg = 3.620(3) Å, θ = 136°: Cg is the
centroid of thiazolyl ring; C2H (2A)⋅⋅⋅Cg, dH⋅⋅⋅Cg = 2.93 Å,
dC⋅⋅⋅Cg = 3.696(3) Å, θ = 138° and C14─H14⋅⋅⋅Cg,
dH⋅⋅⋅Cg = 2.85 Å, dC⋅⋅⋅Cg = 3.523(1) Å, θ = 131°: Cg is the
centroid of Ph ring) and CH⋅⋅⋅S interactions (Table 3)
between these chains arrange the molecules in (101) layers
(Figure 2b). Finally, the combination of all the mentioned
intermolecular interactions completes a three‐dimensional
network in crystal C1. Notably, the Cl1 atom is only
involved in an intramolecular interaction C9H9⋅⋅⋅Cl1
(Table 3) which forms a six‐membered (Cl1–Pd1–P1–C4–
C9–H9) ring.
In the structure of C3, both of the chlorine atoms contrib-
ute in stabilizing the crystal packing. Non‐classic
C10H10⋅⋅⋅Cl1 hydrogen bonds link the neighbouring
N2H2⋅⋅⋅Cl2 chains (mentioned already) thus generating
two‐dimensional arrangements (Figure 3a). Also, CH⋅⋅⋅π
C1
C3
P1–N2
1.690(2)
2.2900(7)
2.3882(6)
2.2047(6)
2.0346(18)
93.49(2)
1.693(5)
2.2871(11)
2.3997(10)
2.1842(11)
2.082(4)
Pd1–Cl1
Pd1–Cl2
Pd1–P1
Pd1–N1
∠Cl1–Pd1–Cl2
∠Cl1–Pd1–P1
∠Cl1–Pd1–N1
∠Cl2–Pd1–P1
∠Cl2–Pd1–N1
∠P1–Pd1–N1
91.03(4)
89.96(2)
100.99(11)
174.59(4)
167.92(11)
83.87(4)
173.68(5)
172.94(2)
92.83(5)
83.73(5)
84.07(11)
interactions (C17─H17⋅⋅⋅Cg, dH⋅⋅⋅Cg = 2.99 Å, dC⋅⋅⋅Cg
=
Herein, the NH group participates in a head‐to‐tail hydrogen
bonding (N2─H2⋅⋅⋅Cl2), giving rise to the formation of [001]
chains of the Pd complexes (Table 3).
In the structure of C1, the Cl2 atom is also involved in
other non‐classic hydrogen bonding (C13─H13⋅⋅⋅Cl2) which
links the neighbouring chains in the bc‐plane (Figure 2a).
3.911(9) Å, θ = 162°: Cg is the centroid of C1–C6 ring)
are the driving force in extending the third dimension of
the crystal network. It is worth noting that the supramolecu-
lar association of C3 also includes two other interesting
interactions: C─H⋅⋅⋅Pd and S⋅⋅⋅Cl (3.385 Å) interactions
which link the neighbouring units into chains along the
b‐axis (Figure 3b).
From
another
perspective,
CH⋅⋅⋅π
(C8─H8⋅⋅⋅Cg,
FIGURE 1 Molecular structure of C1 (top) and C3 (bottom) with displacement ellipsoid at the 50% level
TABLE 3 Hydrogen bond data for solid‐state structures of C1 and C3
Compound
C1
D–H···A (°)
D···A (Å)
D–H (Å)
H···A (Å)
∠D–H···A (°)
Symmetry codes
N2–H2⋅⋅⋅Cl2
C5–H5⋅⋅⋅N2
C9–H9⋅⋅⋅Cl1
C9–H9⋅⋅⋅S1
C13–H13⋅⋅⋅Cl2
3.092(2)
3.008(3)
3.485(2)
3.678(2)
3.599(2)
0.88
0.95
0.95
0.95
0.95
2.22
2.56
2.69
2.96
2.80
171
109
142
133
142
−½ + x, ½ − y, −½ + z
Intra
Intra
½ + x, ½ − y, −½ + z
1 − x, −y, 1 – z
C3
N2–H2⋅⋅⋅Cl2
C2–H2A⋅⋅⋅Cl2
C10–H10⋅⋅⋅Cl1
C5–H5⋅⋅⋅Pd1
3.115(4)
3.386(5)
3.699(1)
3.608(1)
0.88
0.95
0.95
0.95
2.24
2.55
2.85
2.78
174
147
150
146
x, ½ − y, −½ + z
Intra
x, ½ + y, 3/2 − z
1 − x, ½ + y, 3/2 − z

GHOLIVAND ET AL.
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FIGURE 3 (a) a side view of the bc‐plane in C3, formed by NH...Cl,
CH...Cl H‐bonds, (b) CH...Pd and s...Cl interactions along the b‐axis
BCPs for the Pd─N and Pd─P bonds shows more covalent
property for the Pd─P interaction than the Pd─N one
(Table 4) Indeed, Pd─P charge densities are larger and
the related H(r) values are more negative than those at
Pd─N BCPs which correspond to stronger interactions in
the former.
FIGURE 2 Representation of (a) NH...Cl, CH...Cl linkages in the bc‐
plane and (b) CH...π and CH...S interactions between the NH...Cl
chains, creating (101) layers in C1
Also, the NBO analysis reveals an electronic delocaliza-
tion from the lone pair of the nitrogen donor, Lp(N), to the
acceptor orbitals LP*(Pd) and σ*(Pd─Cltrans‐to‐N). Stabiliza-
tion energies E2 of 55.86, 49.52 and 49.96 kcal mol−1 are
obtained for Lp(NP) ! LP*(Pd) and 22.55, 16.78 and
16.93 kcal mol−1 for the Lp(N) ! σ*(Pd─Cltrans‐to‐N) inter-
actions in C1, C2 and C3, respectively. However, for the case
of Pd─P interaction, NBO analysis suggests a covalent
characteristic with amounts of 1.80971, 1.80017 and
1.79881 electron density for C1, C2 and C3, respectively.
2.3 | NBO and AIM analysis of metal–ligand
interactions
Application of AIM to the title complexes allowed us to
find bond critical points (BCPs), and analyse their proper-
ties (electron density, ρ, its Laplacian, ∇2ρ, and total elec-
tronic energy density, H(r)). Generally, a large value of ρ
and ∇2ρ < 0 refers to a shared interaction or covalent
bond, while a small ρ value and ∇2ρ > 0 correspond to
closed‐shell interactions (e.g. ionic and hydrogen bonds
and van der Waals interactions). However, a clear distinc-
tion between closed‐shell and covalent‐type interactions is
impossible without determining H(r). Strong interactions
with (∇2ρ < 0 and H(r) < 0) indicate covalent character
and medium‐strength interactions with (∇2ρ > 0 and
H(r) < 0) indicate partial covalent character, whereas
weak interactions with (∇2ρ > 0 and H(r) > 0) are mainly
electrostatic. Thus, the magnitude of H(r) at a BCP,
instead of ∇2ρ, might be a more reliable index for charac-
terizing a weak interaction.[33–35] Analysing the obtained
TABLE 4 Calculated AIM parameters (electron density, ρ, its
Laplacian, ∇2ρ, and total electronic energy density, H(r)) at Pd–N and
Pd–P critical points of compounds C1–C3
Pd–N
∇2ρ
Pd–P
∇2ρ
Complex
ρ
H(r)
ρ
H(r)
C1
C2
C3
0.091 0.396 −0.022 0.103 0.141 −0.043
0.076 0.298 −0.016 0.104 0.137 −0.044
0.077 0.304 −0.017 0.105 0.136 −0.045

6 of 9
GHOLIVAND ET AL.
This result clarifies the greater strength of Pd─P bond (with
the covalent overlap) compared with the Pd─N interaction
which is mainly electrostatic in nature (donor–acceptor like).
The values for Wiberg bond indices (Table 5) further-
more confirm the more covalent character for the Pd─P bond
compared with the Pd─N interaction.
between iodobenzene and styrene was carried out in the
presence of complexes C1–C3. The addition of a large excess
of Hg(0) (300 equiv.) to the reaction mixture did quench the
catalytic activity of complexes (conversion =41, 55 and
49%, respectively, for C1, C2 and C3). Thus, the best interpre-
tation is that bare palladium (Pd(0)) is participating in the
catalytic cycle.
Also, the catalytic activity of the complexes presented in
this work is more favourable than that of previously reported
complexes containing (O, N)[3] or (P, P)[36,37] coordinated
ligands in terms of the reaction conditions; harsh reaction
conditions, such as using high reaction temperatures and long
reaction times, are not required.
2.4 | Heck coupling reactions
In order to compare catalytic activity of the title complexes
with the corresponding compounds, we used the same opti-
mization condition as in our previous work.[32] These com-
pounds were found to be efficient catalysts for the Heck
coupling reaction (Table 6). The coupling of aryl iodides
and bromides was superior and afforded the desired products
in good to excellent conversions (entries 1–13). Using 4‐
substituted aryl iodides led to excellent conversions of the
desired products (entries 4 and 5). Although, due to the
crowding effect of aryl halides substituted at the ortho posi-
tion, 2‐methoxyiodobenzene provided only low conversions
copared with the para derivative (entries 6 and 7). As
expected, for aryl bromides, the catalytic activity depended
on the halide and substituent of the electron‐withdrawing
groups on the aryl ring increased the reaction rate. However,
the Heck coupling of bromobenzene was rather difficult
under the same reaction conditions (entries 8–13). The
trans/cis product ratio for Heck coupling reactions of
iodobenzene/bromobenzene and styrene was about 94–98%,
but for all other substrates it was higher than 99%.
The results show that all three complexes C1–C3 are
almost equally effective in catalysing Heck coupling reactions
of olefins and aryl halides. The obtained conversions for five‐
membered ring Pd–P–N–C–N (entries 8, 9 and 13 with 91, 94
and 64%, respectively) were more than those of the same
reactions with bis(phosphino)amine Pd(II) complexes with
four‐membered ring Pd–P–N–P (61, 59, 13% for the same
entries) in our previous work. Moreover, Pd─P bond
distances in complexes C1 and C3 were about 0.02 Å shorter
than those of the mentioned complexes with the two phospho-
rus connected to the metal centre. These results confirm that
the presence of a hemilabile site could promote both the
stability and reactivity of the metal complex.[32] Indeed, high
catalytic reactivity of complexes C1–C3 can be related to the
lability of Pd─N bond and facile breaking of it during Heck
reactions.[18] The mercury poisoning test in Heck coupling
3 | EXPERIMENTAL
3.1 | Materials, methods and physical
techniques
All starting materials were commercially available and were
1
used without further purification. H NMR and 31P NMR
spectra were recorded with a Bruker Avance DRS 250 MHz
NMR spectrometer. IR spectra were recorded with a Nicolet
510P spectrophotometer using KBr discs. All reactions and
manipulations were performed under argon atmosphere
using standard Schlenk techniques unless otherwise stated.
Ph2PCl, 2‐aminothiazole, 2‐amino‐4‐methylthiazole and 2‐
aminobenzothiazole were purchased from Sigma‐Aldrich
and were used as received. The starting material
[MCl2(COD)] (M = Pd, COD =1,5‐cyclooctadiene) was
prepared according to literature procedures.[38] Solvents
were dried using the appropriate reagents. The electronic
properties and nature of the coordination interactions were
investigated through density functional theory calculations
using NBO[39] and AIM analyses at the B3LYP/LANL2DZ/
6–311 + G** level on the optimized structure at the same
level. The AIM analysis was performed by means of
Bader's quantum theory of AIM, with the help of AIM
2000 software.[34,35] All quantum chemical calculations
were carried out using the Gaussian 98 package.[40]
3.2 | General procedure for synthesis of L1–L3.
An amount of 1.150
g
(5.056 mmol) of
chlorodiphenylphosphine (Ph2PCl) was added slowly into a
solution of amine (2‐aminothiazole (0.516 g, 5.050 mmol),
2‐amino‐4‐methylthiazole (0.589 g, 5.056 mmol) or 2‐
aminobenzothiazole (0.775 g, 5.056 mmol)) and
triethylamine(0.520 g, 5.087 mmol) in dichloromethane
(20 ml) at 0 °C. The resulting suspension was stirred for
2 h and then the solvent was removed by filtration through
a sintered Schlenk tube. The remaining solid was consecu-
tively washed with distilled water and ethanol, and then dried
TABLE 5 Calculated Wiberg bond indices for selected bonds at
B3LYP/LANL2DZ/6–311 + G**
Complex
Pd–P
Pd–N
Pd–Cltrans‐to‐P
Pd–Clcis‐to‐P
C1
C2
C3
0.6455
0.6421
0.6448
0.3788
0.3490
0.3498
0.6269
0.6233
0.6125
0.6661
0.6637
0.6630

GHOLIVAND ET AL.
7 of 9
TABLE 6 Heck reaction between aryl halides and olefins in presence of complexes C1, C2 and C3 as catalystsa
Conversion (%)b (TOF (h−1))c (trans/cis product ratio)
Entry
Ar–X
Olefins
C1
C2
C3
1
100 (50) (94)
100 (50) (94)
100 (50) (95)
2
3
100 (50)
100 (50)
100 (50)
100 (50)
100 (50)
100 (50)
4
5
100 (50)
100 (50)
100 (50)
100 (50)
100 (50)
100 (50)
6
7
93 (46.5)
92 (46)
91 (45.5)
92 (46)
93 (46.5)
93 (46.5)
8
9
91 (45.5)
94 (47)
89 (44.5)
88 (44)
89 (44.5)
95 (47.5)
10
91 (45.5)
90 (45)
92 (46)
11
12
63 (31.5) (97)
61 (60.5)
60 (30) (98)
58 (29)
60 (30) (98)
60 (30)
13
64 (32)
66 (33)
64 (32)
aReaction conditions: 1.0 mmol of aryl halides, 1.2 mmol of olefins, 2 mmol of K2CO3, 0.5 mol% complex, 3 ml of H2O–DMF, 4 h.
bGC conversion.
cTOF = (mmol of product/mmol of catalyst) per hour.
in vacuum to produce a white solid. Characterization data of
3.3 | General procedure for synthesis of C1–C3.
L1 and L3 have been reported previously.[19,20,23]
2‐(Diphenylphosphino)amino‐4‐methylthiazole
(L2).
A solution of [PdCl2(COD)] (0.029 g, 0.100 mmol) and
2‐(diphenylphosphino)aminothiazole (0.028 g, 0.100 mmol),
2‐(diphenylphosphino)amino‐4‐methylthiazole (0.003 g,
0.100 mmol) or 2‐(diphenylphosphino)aminobenzothiazole
(0.033 g, 0.100 mmol) in CH2Cl2 (10 ml) was stirred at
room temperature for 1 h. The volume of the solvent
was concentrated to 1–2 ml under reduced pressure and
Yield 1.210 g, 82%; m.p. 98–100 °C. 31P–{1H} NMR
1
(CDCl3, δ, ppm): 41.1 (s). H NMR (CDCl3, δ, ppm): 7.43
(m, 4H, Ph), 7.37 (m, 6H, Ph), 6.12 (s, 1H, thiazole), 2.06
(s, 3H, CH3). Selected IR data (KBr, cm−1): 3069, 1523
(C═N), 1432, 1387, 1297, 1231 (C─S), 1132, 986, 870
(P─N), 743, 695 s.

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GHOLIVAND ET AL.
addition of Et2O (15 ml) gave the palladium complexes
(C1–C3) as yellow solids which were isolated by filtration
and dried in vacuum.
3.5 | General procedure for heck reaction
A flask was charged with complex (0.5 mol%) along with an
appropriate amount of aryl halide (1.0 mmol), olefin
(1.2 mmol), K2CO3 (2.0 mmol) and H2O–DMF (3 ml) and
a magnetic stir bar. The mixture was heated to 100 °C with
stirring for a specified period of time. After the reaction mix-
ture was cooled to room temperature, hydrochloric acid (1 M,
6 ml) was added and the product was extracted with diethyl
ether (3 × 15 ml). The aqueous solution was separated from
the organic layer. The diethyl ether solution was washed with
water (3 × 15 ml), dried over MgSO4 and evaporated to
dryness under reduced pressure to afford the desired product,
which was then washed with hexane (3 × 5 ml). The purity of
the compounds was checked by GC and yields are based on
the aryl halide. Assignments of products were made by
comparison with authentic samples.
3.3.1 | PdCl2[(Ph2P)HN(C3H2NS)] (C1)
Yield 0.039 g, 85%; m.p. (decomposed) 184–186 °C.
31P–{1H} NMR (CDCl3, δ, ppm): 77.48 (s). 1H NMR (CDCl3,
δ, ppm): 10.82 (1H, s, NH), 7.92 (m, 4H, Ph), 7.64 (m, 6H,
Ph), 6.85 (br, 1H, thiazole), 6.83 (br, 1H, thiazole). Selected
IR data (KBr, cm−1): 3432, 2929, 1557 (C═N), 1479, 1433
(C─S), 1311, 1159, 1104 (P─C), 933 (P─N), 836, 743, 694.
3.3.2 | PdCl2[(Ph2P)HN(C3H4NS)] (C2)
Yield 0.040 g, 85%; m.p. (decomposed) 180–182 °C.
31P–{1H} NMR (CDCl3, δ, ppm): 80.04 (s). 1H NMR (CDCl3,
δ, ppm): 10.50 (1H, br, NH), 7.89 (m, 4H, Ph), 7.39 (m, 6H,
Ph), 6.05 (s, 1H, thiazole), 2.37 (s, 3H, CH3). Selected IR
data (KBr, cm−1): 3054, 1552 (C═N), 1471, 1435, 1294,
1211, 1143 (C─S), 1103, 986 (P─N), 841, 743, 692 s.
4 | CONCLUSIONS
We have prepared and characterized Pd(II) complexes of
some aminothiazole‐based phosphine ligands. The crystal
structures of the new Pd(II) complexes reveal that the ligands
function in a chelating mode, coordinating through P and
Nendo atoms in square planar complexes [PdCl2L]. Structural
studies indicate a higher donating ability of the P rather than
Nendo towards Pd(II). Within the NBO framework, the Pd─N
interaction was found to be stabilizing donor–acceptor delo-
calization, while the Pd─P bonds in C1–C3 are covalent.
The stronger interaction of phosphorus with Pd than N‐donor
is also supported by the AIM analysis. Crystal packing of C1
and C3 is firstly driven by NH⋅⋅⋅Cl hydrogen bonds, followed
by weaker CH⋅⋅⋅Cl linkages and CH⋅⋅⋅π interactions. The
prepared complexes present high catalytic activity in the
Heck coupling reactions of aryl bromides and iodides with
various olefins. Indeed, the product conversions obtained
were more than those of the same reactions with
bis(phosphino)amine Pd(II) complexes, as the catalysts in
our previous work.[32]
3.3.3 | PdCl2[(Ph2P)HN(C7H4NS)] (C3)
Yield 0.046 g, 90%; m.p. 162–164 °C. 31P–{1H} NMR
(CDCl3, δ, ppm): 85.21 (s). 1H NMR (CDCl3, δ, ppm):
9.27 (1H, br, NH), 7.56–8.32 (m, 14H, Ar). Selected IR
data (KBr, cm−1): 3430, 2995, 1642 (C═N), 1460
(C─S), 1249, 1211, 1103 (P─C), 1025, 932 (P─N),
838, 749, 688.
3.4 | Crystal structure determination
Single‐crystal X‐ray diffraction data were collected for both
C1 and C3 using an Agilent Gemini Ultra diffractometer
equipped with an Eos CCD area detector and using either
Mo Kα radiation (λ = 0.71073 Å) or Cu Kα radiation
(λ = 1.5418 Å). The data were collected at 173 K using an
Oxford Cryosystems Cryostream 600. The data were
processed with CrysAlisPro.[41] Semi‐empirical absorption
corrections were carried out using the Multi‐Scan[42]
program. The structures were solved by direct methods using
SHELXT[43] and refined with full‐matrix least‐squares
refinement by SHELXL‐2013[44] within Olex2.[44] All non‐
hydrogen atoms were refined anisotropically. Hydrogen
atoms were added at calculated positions and refined using
a riding model based on the parent atom. The CIF files have
been deposited with the CCDC and have been given the
deposition numbers 1447821 and 1447820 for C1 and C3,
respectively.
ACKNOWLEDGMENT
Financial support of this work by Tarbiat Modares University
is gratefully acknowledged.
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How to cite this article: Gholivand K, Kahnouji M,
Mark Roe S, Gholami A, Fadaei FT. Palladium(II)
complexes of aminothiazole‐based phosphines:
Synthesis, structural characterization, density
functional theory calculations and catalytic application
in heck reaction. Appl Organometal Chem. 2017;
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