Synthesis, structures and catalytic activity of Pd(II) saccharinate complexes with monophosphines in direct arylation of five-membered heteroarenes with aryl bromides

Article abstract of DOI:10.1016/j.ica.2019.119220

A number of new Pd(II) saccharinate (sac) complexes bearing a range of phenyl (Ph), cyclohexyl (Cy) and alkyl (Me and Et) substituted tertiary phosphine ligands with systematically changing electronic and steric properties, namely trans-[PdCl(sac)(L)₂] (L = PPh₃ (1); PPh₂Cy (3)), trans-[Pd(sac)₂(H₂O)(L)] (L = PPh₃ (2); PPh₂Cy (5)), trans-[Pd(sac)₂(L)₂] (L = PPh₂Cy (4); PPhCy₂ (6); PCy₃ (8)), [PdCl(sac)(PCy₃)(DMSO)] (7), trans-[Pd(sac)₂(PPh₂Me)(DMSO)] (9) and cis-[M(sac)₂(L)₂] (L = PPhMe₂ (10); PPh₂Et (11); PPhEt₂ (12)), were synthesized and structurally characterized. The Pd(II) complexes were applied for direct C2/C5 arylation of five-membered heteroarenes such as furan, thiophene and thiazole derivatives with aryl bromides. Notably, arylation products up to 99% yields were obtained in the presence of the Pd(II) complexes. The catalytic mechanism of the direct arylation was proposed to proceed via a Pd(0)/Pd(II) pathway, due to elimination of the sac ligand in the Pd(II) complexes during catalysis.

Full text of DOI:10.1016/j.ica.2019.119220

Journal Pre-proofs
Synthesis, structures and catalytic activity of Pd(II) saccharinate complexes with
monophosphines in direct arylation of five-membered heteroarenes with aryl
bromides
Veysel T. Yilmaz, Ceyda Icsel, Omer R. Turgut, Muhittin Aygun, Enes Evren,
Ismail Ozdemir
PII:
S0020-1693(19)31083-7
https://doi.org/10.1016/j.ica.2019.119220
ICA 119220
DOI:
Reference:
Inorganica Chimica Acta
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17 October 2019
Please cite this article as: V.T. Yilmaz, C. Icsel, O.R. Turgut, M. Aygun, E. Evren, I. Ozdemir, Synthesis, structures
and catalytic activity of Pd(II) saccharinate complexes with monophosphines in direct arylation of five-membered
heteroarenes with aryl bromides, Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.119220
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Synthesis, structures and catalytic activity of Pd(II) saccharinate
complexes with monophosphines in direct arylation of five-
membered heteroarenes with aryl bromides
Veysel T. Yilmaza,*, Ceyda Icsela, Omer R. Turguta, Muhittin Aygunb, Enes Evrenc, Ismail
Ozdemirc
aDepartment of Chemistry, Faculty of Arts and Sciences, Uludag University, 16059 Bursa,
Turkey
bDepartment of Physics, Faculty of Sciences, Dokuz Eylul University, 35210 Izmir, Turkey
cCatalysis Research and Application Center, Inonu University, 44280 Malatya, Turkey
ABSTRACT
A number of new Pd(II) saccharinate (sac) complexes bearing a range of phenyl (Ph),
cyclohexyl (Cy) and alkyl (Me and Et) substituted tertiary phosphine ligands with
systematically changing electronic and steric properties, namely trans-[PdCl(sac)(L)2] (L =
PPh3 (1); PPh2Cy (3)), trans-[Pd(sac)2(H2O)(L)] (L = PPh3 (2); PPh2Cy (5)),
trans-
[Pd(sac)2(L)2] (L = PPh2Cy (4), PPhCy2 (6); PCy3 (8)), [PdCl(sac)(PCy3)(DMSO)] (7), trans-
[Pd(sac)2(PPh2Me)(DMSO)] (9) and cis-[M(sac)2(L)2] (L = PPhMe2 (10); PPh2Et (11),
PPhEt2 (12), were synthesized and structurally characterized. The Pd(II) complexes were
applied for direct C2/C5 arylation of five-membered heteroarenes such as furan, thiophene
and thiazole derivatives with aryl bromides. Notably, arylation products up to 99% yields
were obtained in the presence of the Pd(II) complexes. The catalytic mechanism of the direct
arylation was proposed to proceed via a Pd(0)/Pd(II) pathway, due to elimination of the sac
ligand in the Pd(II) complexes during catalysis.
Keywords: Palladium(II); Saccharinate; Phosphine; Catalysis; Arylation; Heteroarenes
*Corresponding author.
E-mail address: vtyilmaz@uludag.edu.tr (V.T. Yilmaz).
1

1. Introduction
Saccharin (sacH, 1,1-dioxo-1,2-benzothiazol-3-one) is a worldwide artificial sweetener
and is used alone or as an ingredient of sweetener blends. The presence of carbonyl, sulfonyl
and imine groups makes sacH a potential ligand in coordination chemistry. In fact, sacH
readily deprotonates in solution, forming the corresponding anion (sac). This anion serves as a
versatile multifunctional ligand towards various metal ions and forms metal complexes from
mononuclear to coordination polymers [1].
After the first report by Henderson and co-workers on trans-[PdCl(sac)(PPh3)2] [2], the
Pd(II) complexes of sac have received significant attention. Their use in catalytic activity
studies is rare and only a few reports appeared in this field. The most predominant Pd(II) sac
complexes containing auxiliary phosphine ligands showed excellent catalytic efficiency in
several organic transformations via Suzuki–Miyaura, Heck and Sonogashira cross-couplings
[3–8]. In addition, a dinuclear palladium complex, [Pd2(μ-sac)2(bzq)2], where bzq is 7,8-
benzoquinolyl, was efficiently applied to the C–O bond activation and cross-coupling of 4-
coumaryltosylate with aryl boronic acids [9]. Furthermore, [Pd(sac)2(MeCN)2] and [Pd3(sac)6]
were used as catalysts for the regioselective difunctionalization of alkenes [10].
In the last two decades, direct arylation reactions have received great interest as possible
alternatives to the most employed cross-coupling reactions and there are many reports on the
Pd-catalysed direct arylation reactions of heteroaromatic compounds such as pyrroles, furans,
thiophenes, azoles, etc. with substituted aryl halides [11–14], but studies dealing with the
catalytic activity of Pd(II) complexes of sac in such reactions have not been reported yet. In
the present study, we report the synthesis of twelve new Pd(II) sac complexes bearing a wide
range of tertiary phosphines in which the Ph group is replaced with Cy, Me or Et groups.
Moreover, the newly synthesized Pd(II) complexes were tested as catalysts in the direct
C2/C5 arylation of a variety of five-membered heteroarenes such as furan, thiophene and
thiazole derivatives with a number aryl bromides bearing electron donating and electron
withdrawing groups. To the best of our knowledge, this is the first report, investigating Pd(II)-
sac-monophosphine complexes as catalysts for direct C–H bond arylation reactions.
2. Results and discussion
2.1. Synthesis and characterization
The Pd(II) sac complexes with the tertiary phosphines (1–12) were synthesized following
the procedure shown in Scheme 1. Bis(sac)palladium(II) complexes, (2, 4, 5, 6 and 8–12)
2

were obtained in a one-pot reaction by treating Pd(OAc)2 with sacH in the presence of the
corresponding phosphines. Although such palladium(II) complexes are conveniently prepared
by one-pot synthesis, molar ratio of phosphine:sacH has a significant impact upon the
structure of the complexes. The molar ratio of 1:1 yields bis(sac)bis(phos)palladium(II)
complexes (4, 6 and 8, 10–12), while changing the molar ratio to 1:2 results in
bis(sac)palladium(II) complexes bearing one phosphine ligand (2, 5 and 9). On the other
hand, using the Henderson’s method [2], trans-[PdCl2(L)2] (L = PPh3, PPh2Cy and PCy3)
reacted with Na(sac)·2H2O to give complexes with a sac ligand (1, 3 and 7). It is noteworthy
to emphasize that the addition of excess sac did not replace the second Cl ligand in these
complexes.
S
L
O
Cl
Cl
L
.
O
O
Pd
Na(sac) 2H2O
Pd
L
trans -[PdCl2(L)2]
N
S
N
S
L
CHCl3, MeOH
DMSO, 65 oC
O
O
O
O
7
= PCy3 ( )
1
L = PPh ( )
L
3
3
PPh2Cy ( )
O
S
N
O
S
O
O
O
i) 2 L
ii) 2 sacH
L
L
N
O
Pd
Pd(OAc)2
Pd
O
O
O
MeCN, H2O,
MeOH, r.t.
L
N
S
L
N
O
S
O
O
L
10
L = PPhMe2 (
)
L
4
L = PPh2Cy ( )
11
)
PPh2Et (
PPhEt2 (
6
PPhCy2 ( )
12
)
8
PCy3 ( )
O
O
O
S
N
O
S
N
i) L
ii) 2 sacH
L
L
O
Pd(OAc)2
O
Pd
L
Pd
L
H2O
O
O
MeCN, H2O
DMSO, MeOH, r.t.
OH2
N
S
N
S
O
S
O
O
O
O
2
L = PPh3 ( )
9
L = PPh2Me ( )
5
PPh2Cy ( )
Scheme 1. Synthetic routes of the palladium(II) complexes.
Steric effects associated with the phosphine ligands also have a greater impact on cis- and
trans-configuration of the present complexes and can quantitatively be described using the
Tolman’s cone angle concept [15]. The cone angles of the phosphines are in the order:
PPhMe2 (122°) < PPh2Me (136°) < PPhEt2 (136°) < PPh2Et (140°) < PPh3 (145°) < PPh2Cy
3

(153°) < PPhCy2 (162°) < PCy3 (170°), apparently becoming more bulky due to exchange of
Ph with the Cy group [15,16]. As a result, the palladium(II) complexes (1, 3, 4, 6 and 8) with
more bulky cyclohexylphenylphosphines preferentially have trans-configuration to reduce the
steric hindrance between the ligands, whereas the cis-configured palladium(II) complexes
(10–12) contain relatively less bulky alkylphenylphosphines.
All the Pd(II) complexes were obtained in good yields. They are air stable and are readily
soluble in common organic solvents such as MeOH, MeCN, CH2Cl2, CHCl3, DMSO and
DMF, but insoluble in water. Molar conductance values of the complexes in MeOH indicate
that all the complexes are nonelectrolytes.
Complexes 1–12 were characterised by elemental analysis, IR, NMR and ESI-MS
spectroscopy. The corresponding spectra are presented in Figs S1−S3. The OH stretch of the
coordinated water molecules of 2 and 5 appear at 3178 and 3229 cm−1, while the CH
vibrations of Ph and Cy groups are observed in the range of 3080 and 2850 cm−1. The IR
spectra display strong C=O stretching frequencies of sac between at 1684 and 1640 cm−1. The
asymmetric and symmetric stretchings of the sulfonyl group of sac occur as strong bands at
1305−1235 and 1173−1147 cm−1, respectively. Moreover, the strong absorption band at 989
cm−1 is assigned to the O-coordinated DMSO ligand in 7. The bands at 1030–999 and 521–
504 cm–1 are attributed to the symmetric and asymmetric vibrations of the P–C group in PR3,
respectively.
The NMR spectra of the complexes were measured in DMSO-d6 at room temperature (rt)
(see the data together with the corresponding assignments in the experimental section and Fig.
S2). The Ph protons of sac and phosphines in 1–6 overlap, while well-resolved Ph protons of
sac in the spectra of 7 and 8 occur as a multiplet in the range of 8.04–7.68 ppm. The protons
of the Cy group in 3–8 appear between 2.22 and 0.56 ppm as multiplets. The 13C NMR
spectra of the complexes display well-resolved signals. The carbonyl group of sac is observed
at ca. 166 ppm, while the C atom adjacent to the sulfonyl group resonances at ca. 142 ppm.
The signals of the Ph groups occur in the range of 135–120 ppm, whereas those of the Cy
group appear between 36–24 ppm. The signals of the C atoms in the phosphines can be
distinguished due to the P–C coupling. The resonance at ca. 40 ppm is assigned to the Me
groups of DMSO in 7. In addition, the Me signal in the spectra of 9 and 10 occurs at ca. 13
ppm, while those of Et in 11 and 12 are observed at ca. 20 and 8 ppm. These signals split into
1
doublets or triplets due to the coupling with the P nuclei with the JP–C coupling constants of
12-19 Hz. The 31P NMR spectra of the complexes show only a singlet. Complexes 10 and 11
4

feature notably line broadening of 31P NMR signals. Compared to those of free
monophosphines, the P nuclei in the coordinated ligands experience strong deshielding up to
53 ppm.
The complexes were also characterized by ESI-MS spectroscopy (Fig. S3). The
complexes form [M – Cl]+, [M – sac]+ and [M + Na]+ ions. Additional peaks correspond to
[Pd(sac)(H2O)(solvent)]+, [Pd(sac)(phos)(solvent)]+, [Pd(sac)]+, [Pd(sac)2(solvent) + Na]+,
[M(solvent) + Na]+, [Pd(sac)(phos)]+ [Pd(sac)(solvent)]+, [PdCl(phos)(solvent)]+ and
[PdCl(phos)2(solvent)]+ ions.
2.2. Solid-state structures
Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation
of concentrated solutions of complexes 1−5, 7 and 9−12. All the attempts for the
crystallization of 6 and 8 failed. The molecular structures of the complexes are shown in Fig.
1, and bond parameters are given in Table 1. Crystal data and refinement parameters for the
present structures are listed in Table S1.
The synthesis of 1 was reported previously [2], but its crystal and molecular structure has
been presented here. 2 and 3 contain two independent molecules in the asymmetric unit; both
of which have similar geometrical parameters. The Pd(II) ions in the complexes adopt a
distorted square-planar coordination geometry, mainly due to the steric effect of the present
phosphine ligands. As shown in Fig. 1, complexes 1−5 and 9 exhibit a trans configuration,
while 10−12 have a cis configuration. In addition, complex 7 presents four different ligands
such as aqua, chlorido and DMSO ligands. The Pd–P bond distances in the bis(phosphine)
complexes (1, 3, 4 and 10–12) compare well with those in the corresponding [PdCl2(phos)2]
complexes [17–19], but they are markedly longer than those in the rest of the complexes. It is
expected that M−P bonds are greatly affected by the electron donating ability and bulkiness of
the phosphine ligands as indexed as the cone angle [15]. However, it should be noted that the
differences in the Pd−P bond lengths listed in Table 1 do not necessarily truly reflect the steric
and electronic properties of the phosphine ligands. The sac ligand is N-coordinated and the
Pd–N bond distances are typical to the related Pd(II) complexes of sac with phosphine ligands
[20,21], but significantly shorter than the corresponding bonds in [Pd(py)(sac)(L)] (L = Phpy
or bzq) [7]. The Pd–Cl bonds in 1, 3 and 7 are trans to the Pd–N bonds and their distances
range from 2.276(3) to 2.302(1) Å. On the other hand, the Pd–O(aqua) and Pd–O(DMSO)
5

distances trans to the phosphines are in the same range with those in the aqua and DMSO
coordinated Pd(II) complexes [22,23].
The packing of molecules of the complexes is mainly achieved by a number of weak
intermolecular C–H···O hydrogen bonds involving the carbonyl and sulfonyl O atoms of sac
in the neighbouring molecules. In addition, the aqua ligands in 2 and 5, and the solvated
species in 4 form strong O–H···O(sulfonyl or carbonyl) hydrogen bonds between the adjacent
molecules, further stabilizing crystal packing.
Fig. 1. Solid-state molecular structures of complexes 1–5, 7 and 9–12. Ellipsoids are drawn at
the 40% probability level. The H atoms, except those of H2O and MeOH, are omitted and
highly disordered H2O in 1, DMF in 2 and DMSO in 12 was removed during the refinement
of the crystal data.
6

Table 1
Selected bond distances (Å) and angles (°) for complexes 1–5, 7 and 9–12.
1
2a
3a
4
5
7
9
10
11a
12
Pd1–N1
Pd1–N2
2.047(7) 2.021(6) 2.035(3) 2.030(9) 1.996(1 2.048(7)
1)
2.033(3)
2.086(6)
2.079(2)
2.086(4)
-
2.020(6)
-
2.033(9) 2.033(1
0)
-
2.038(3)
2.091(7)
-
-
2.107(4)
-
Pd1–Cl1
2.297(2)
-
2.302(1)
-
-
2.276(3)
-
-
Pd1–P1
2.340(2) 2.243(3) 2.341(1) 2.376(3) 2.256(4) 2.251(3)
2.240(2)
2.278(2)
2.2851(8) 2.296(2)
Pd1–P2
2.340(2)
-
2.334(1) 2.355(3)
-
-
-
2.267(2)
-
2.278(2)
Pd1–OW1
Pd1–O4
Pd1–O7
-
-
-
-
-
2.112(5)
-
-
173.4(3)
-
-
-
-
-
-
-
-
-
2.144(8) -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
2.125(7)
-
2.129(3)
176.4(2)
-
N1– Pd1–N2
N1– Pd1–N1i
N1– Pd1–P1
N1– Pd1–P2
P1– Pd1–P2
P1– Pd1–P1i
N2– Pd1–P1
N2– Pd1–P2
N1– Pd1–Cl1
P1– Pd1–Cl1
P2– Pd1–Cl1
N1– Pd1–OW1
N2– Pd1–OW1
P1– Pd1–OW1
P1–Pd1–O4
Cl1– Pd1–O4
N1−Pd1−O7
N2−Pd1−O7
P1−Pd1−O7
a
173.5(4) 171.9(4) -
-
86.9(3)
-
86.38(16)
-
-
-
87.33(14)
173.62(7) 176.56(12)
-
-
92.57(18) 91.9(2)
92.56(19)
173.60(9)
-
-
-
173.87(2)
89.48(9)
85.81(9)
-
-
-
-
-
94.35(9) 91.0(3)
94.31(9) 88.3(3)
165.73(3) 177.3(1)
-
-
94.3(3) 97.1(2)
90.64(11) 172.3(2)
-
-
-
-
-
-
-
-
-
-
-
-
-
90.12(19)
94.34(9)
-
89.64(12)
93.43(5)
-
90.60(12)
175.63(12)
-
-
-
-
-
-
-
-
-
-
-
93.96(4)
89.0(3)
91.3(3)
91.4(3)
-
92.94(11) 89.7(2)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
169.9(2)
172.59(9)
85.34(4)
87.53(4)
-
-
-
-
-
-
-
-
-
-
-
-
173.5(2)
-
-
-
-
-
-
-
88.64(10)
-
-
-
-
87.6(2)
88.2(2)
177.4(2)
-
-
-
-
-
-
-
-
-
-
-
-
-
87.7(4)
86.8(4)
177.6(3) -
-
-
-
-
-
177.4(2)
89.2(2)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
90.53(13)
85.87(14)
177.91(9)
Symmetry code (i) for 11: −x+1/2, y, −z+3/2. The crystals of 2, 3 and 11 contain two
independent molecules per unit cell and both molecules display the same bond parameters.
7

2.3. Catalytic studies
2.3.1. Direct arylation of 2-substituted furan and thiophene compounds
The catalytic performance of complexes 1−12 in intermolecular direct arylation reactions
between aryl bromides and substituted furan, thiophene and thiazole derivatives was explored.
To optimize reaction conditions, the direct arylation of 2-acetylfuran with 4-
bromoacetophenone in the presence of complex 1 was chosen as the test reaction. KOAc and
dimethylacetamide (DMAc) were used as the base and the solvent, respectively. As given in
Table 2 (entry 2), the best conversion was achieved using a 2 mol% catalyst loading and a
reaction time of 2 h at 120 °C. In the absence of 1, no desired product was observed in the
same conditions.
Table 2
Optimization of direct arylation reaction between 2-acetylfuran and 4-bromoacetylbenzene.a
O
O
O
O
O
O
1
Pd cat. ( )
Br
KOAc, DMAc
Entry
1
Time
Temperature
Conversion
(mol%)
-
2
1.5
1
(h)
2
2
2
2
(°C)
120
120
120
120
100
(%)
-
100
78
74
65
1
2
3
4
5
2
2
a Reaction conditions: 2-Furaldehyde (2.0 mmol), aryl halide (1.0 mmol), KOAc (2.0 mmol),
DMAc (2 mL). Conversions were estimated with respect to aryl halide from the results of GC.
All the complexes were tested as catalysts for the arylation of 2-acetylfuran and 2-
acetylthiophene with a range of para-substituted aryl bromides under the optimized
conditions (Table 3). Palladium-catalyzed of furan and thiophene compounds are strongly
favored in arylation at the C2 and C5 positions, but the substituents present on the heterocycle
greatly affect the regioselectivity of substrates [13,14]. Since the C2 position in the title furan
and thiophene compounds is blocked with an acetyl group, arylation then occurs at the C5
position (Table 3). Entries 1−10 indicate that low to excellent yields of the C5 arylated
products were obtained depending on the Pd(II) catalysts and the aryl bromides. The yields of
the arylated products are compatible with electronic properties of the substrates. For example,
the excellent yields of desired products were achieved with the aryl bromides containing
8

electron withdrawing CHO and COMe groups (Table 3 entries 2, 3, 7 and 8), whereas the aryl
bromides bearing electron donating groups gave considerably low yields. It should be noted
that the catalytic efficiency of all the complexes was much greater for the arylation of the
thiophene compound using the CHO and COMe derivatives of the aryl bromides (Table 3,
entries 7 and 8). Parallel findings were reported for the similar substrates employed in direct
arylation of furan and thiophenes with Pd(OAc)2, using relatively low catalyst loadings
(0.01−0.5 mol%) at 120 °C for 16
h
[24] and
0.5 mol% of {[2,6-
(iPr)2C6H3N=C(Ph)C(Ph)2OH]PdCl2} at 130 °C for 4 h [25]. On the other hand, N-
heterocyclic carbene (NHC) Pd(II) complexes permitted high yields of C5-arylation products
of 2-subtituted thiophenes and furans under higher catalyst loading (1 and 5 mol%), higher
reaction time (1, 12 and 20 h) and higher reaction temperature (120 and 150 °C) [26−28].
Among the present complexes, 1 seems to be the most efficient catalyst for the C5 arylation
reactions of the furan and thiophene compounds, being regardless of the electronic properties
of the aryl bromides. The yields obtained in the presence of 1 were comparable to those
effective Pd(II) catalysts used for the direct C5 arylation of furans and thiophenes in the
similar reaction conditions [24−28]. In addition, complex 2 also acts an effective catalyst to
afford the 5-arylated thiophenes with 65−98% yields (Table 3, entries 7−10).
PdCl2 was also tested in the same conditions for the selected arylation reactions to assess
the catalytic efficiency of the Pd(II) complexes. The reaction of the furan and thiophene
compounds with 4-bromoacetophenone in the presence of PdCl2 gave the final products with
comparatively low yields 18% and 16%, respectively, indicating excellent catalytic activity of
the title complexes.
9

Table 3
Direct C5-arylation of 2-substituted furan and thiophene compounds by using aryl bromidesa
O
O
X
X
Pd cat. (2 mol%)
R
Br
R
KOAc, DMAc
120 C, 2 h
X = O or S
Pd catalyst (Yield%)
Entry Product
1
R
1
2
3
4
5
6
7
8
9
10 11 12
H
CHO
89 59 73 68 54 71 62 51 36 44 61 52
75 60 81 77 56 78 70 57 56 65 70 67
O
2
3
COMe 91 80 66 88 87 82 97 97 98 98 97 98
O
4
5
Me
OMe
74 51 60 52 36 44 49 45 25 22 43 34
64 40 49 16 29 20 37 16 28 18 11 40
R
6
7
H
CHO
67 65 64 81 59 69 70 46 54 26 72 50
98 96 87 81 93 90 95 93 87 94 94 80
O
8
COMe 99 87 85 82 82 87 86 84 93 93 93 91
S
9
10
Me
OMe
85 98 28 43 21 31 38 34 38 26 55 37
87 86 25 28 32 23 25 29 31 10 33 32
R
a
Reaction conditions: Pd catalyst (0.02 mmol), 2-acetylfuran or 2-acetylthiophene (2.0
mmol), aryl bromide (1.0 mmol), KOAc (2 mmol), DMAc (2 mL), 120 °C and 2 h. GC yields
were calculated with respect to aryl bromide from the results of GC.
2.3.2. Direct arylation of 4,5-dimethylthiazole
The scope of the direct arylation reaction was also extended to 4,5-dimethylthiazole using
the same substrates (Table 4). In the present case, only the C2 position is preferentially
appropriate for arylation of 4,5-dimethylthiazole. As presented in Table 4, direct C2 arylation
reactions resulted in low to high yields of desired coupling products. The reaction of 4,5-
dimethylthiazole with the electron withdrawing aryl bromide with the COMe group gave the
desired products in high yields (86−98%) in the presence of all the complexes (Table 4, entry
3). The product yields compare well with those obtained with Pd-NHC complexes for the C2
arylation of 4,5-dimethylthiazole in the following reaction conditions: 1 mol% Pd-NHC, 150
°C and 1 h [28,29]. Furthermore, 4-bromobenzaldehyde was also successfully coupled with
the thiazole compound to give C2 arylated products in moderate yields (54−91%) (Table 4,
entry 2). Relatively low yields were obtained for the coupling of the thiazole derivative with
bromobenzene, 4-bromotoluene and 4-bromoanisole (Table 4, entries 1, 4 and 5). Contrary to
the arylation reactions of the furan and thiophene derivatives, complex 1 induces only the
10

selective arylation of the thiazol compound with 4-bromoacetophenone. In addition, the Pd
sac complexes containing tertiary phosphine ligands with Me and Et groups display markedly
increased catalytic activity in the case of the aryl bromides bearing electron withdrawing
groups (Table 4, entries 2 and 3).
Table 4
Direct C2-arylation of 4,5-dimethylthiazole by using aryl bromidesa
S
S
Pd cat. (2 mol%)
R
Br
R
KOAc, DMAc
120 C, 2 h
N
N
Pd catalyst (Yield%)
Entry Product
1
R
1
2
3
4
5
6
7
8
9
10 11 12
H
CHO
49 41 43 41 26 63 28 12 27 10 10 84
61 66 60 64 72 74 63 54 86 73 89 91
S
2
R
3
4
COMe 91 89 86 94 93 95 92 95 96 98 97 95
Me
OMe
N
28 24 25 25 14 38 34 24 29 14 10 32
19 17 29 13 15 17 16 22 23 25
5
9
8
a
Reaction conditions: Pd catalyst (0.02 mmol), 2-acetylfuran or 2-acetylthiophene (2.0
mmol), aryl bromide (1.0 mmol), KOAc (2 mmol), DMAc (2 mL), 120 °C and 2 h. GC yields
were calculated with respect to aryl bromide from the results of GC.
2.3.3. Mechanistic aspects
In general, the electron-rich phosphines are expected to favour oxidative addition, while
their bulkiness enhances the reductive elimination in coupling reactions. From this point of
view, the reactivity of 7 and 8 containing PCy3 as a comparatively strong σ-donating and
bulky ligand is expected to be better than the rest of the complexes. However, the results of
the present study clearly indicate that the catalytic activity of the Pd(II) complexes bearing
various phosphine ligands does not differ considerably. Since complex 1 seems to be most
promising catalyst for the arylation of the furan and thiophene compounds with aryl bromides,
the mechanistic proposal for the C5 arylation of these compounds in the presence of 1 is
presented in Scheme 2. It is assumed that the C2 arylation of the thiazole compound follows
the same catalytic pathway.
11

Scheme 2. Proposed catalytic cycle of the direct arylation of 2-substituted furan and
thiophene compounds.
The dissociation of the two sac ligands in trans-[Pd(sac)2(PTA)2] (PTA = 1,3,5-triaza-7-
phosphaadamantane) employed in the arylation of nucleosides using Suzuki−Miyaura cross-
coupling was evidenced in situ during the catalytic reactions [6]. This observation offers the
possibility of Pd-catalyzed direct arylation through a Pd(0)/Pd(II) catalytic cycle [14,30]. The
first step involves the coordinatively unsaturated and reactive 14-electron Pd(0) intermediate
[Pd(PPh3)2] (I), formed due to both the reduction of Pd(II) and the elimination of chlorido and
sac ligands [31]. In the next steps, oxidative addition of aryl bromide to [Pd(PPh3)2] results in
the formation of a [Pd(Ar)Br(PPh3)2] intermediate (II), followed by exchange of the bromide
ligand with the base (KOAc) to give [Pd(2-AcO)(Ar)(PPh3)2] (III). The C–H activation
occurs in the next steps, in which III reacts with the 2-substituted furan or thiophene
nucleophiles (Nu), leading to the C−H bond cleavage and Pd−C bond formation via the
typical concerted metalation–deprotonation (CMD) transition states IV and V [25,32,33]. The
carboxylate anion plays an important role in the C−H cleavage process [32,34,35] and the
12

protonation of the 1 acetate-bound configuration eventually yields the intermediate
[Pd(Ar)(Nu)(PPh3)2] (VI). Finally, the reductive elimination of VI generates the C5 arylated
products of the furan or thiophene derivatives.
Complexes bearing two phosphine ligands (3, 4, 6, 8, 10–12) are most likely follow the
same catalytic cycle of 1. However, the aqua and DMSO ligands in complexes 2, 5, 7 and 9
are trans to phosphine. The significantly high trans influence of the phosphines makes these
ligands relatively labile, suggesting that they dissociate together with chloride and sac ligands
during catalysis. Therefore, complexes 2, 5, 7 and 9 may work by a different catalytic
mechanism presumably involving the monoligated [Pd(PR3)] species. It was suggested that
12-electron Pd(0) species bearing electron-rich and bulky phosphines favour the oxidative
addition of aryl halides onto the palladium(0) centre and act as catalytically active species in
cross-coupling reactions [36]. It is assumed that in the CMD pathway, a tri-coordinate
[Pd(PR3)(Ar)Br] intermediate forms and subsequently converts into a transition state of
[Pd(PR3)(Ar)(Nu)(OAc)]‡ [11,37,38].
3. Conclusions
In summary, twelve new Pd(II) sac complexes with tertiary phosphine ligands were
synthesized and fully characterized. Spectroscopic and X-ray crystallographic data confirmed
the molecular structures of all the complexes. The catalytic activities of the Pd(II) complexes
were investigated in the direct C2/C5-arylation of five-membered heteroarenes such as furan,
thiophene and thiazole derivatives. High yields of the arylated products were obtained. The
electronic and steric effects of the substituents on the tertiary phosphines did not have a
substantial effect on the overall catalytic performance of the Pd(II) complexes in the arylation
reactions. The sac ligand not only coordinates with Pd(II), but also directly participates in the
formation of the reactive Pd(0) complexes. Owing to the lability of aqua, DMSO, chloride and
sac ligands, the mechanism was proposed to proceed via a Pd(0)/Pd(II) pathway in the direct
arylation.
4. Experimental
4.1. Materials and measurements
All chemicals were purchased commercially and used as received. Elemental analysis
were performed on a Costech elemental analyser. IR spectra were recorded using a Perkin
Elmer Lambda 35 and a Perkin Elmer Spectrum Two FT-IR spectrophotometers, respectively.
13

1H, 13C and 31P NMR spectra were recorded on a Bruker Avance III (400.13 MHz 1H; 100.62
13
31
MHz C and 161.97 MHz P) NMR spectrometer in DMSO-d6 at rt. The ESI mass spectra
were obtained using a Bruker Daltonics Microtof II-ESI-TOF mass spectrometer. Catalytic
reactions were monitored on an Agilent 6890 N GC and Schimadzu 2010 Plus GC-MS system
by GC‐FID with an HP‐5 column of 30 m length, 0.32 mm diameter, and 0.25 μm film
thickness. The electrical conductivity measurements of the complexes in MeOH were carried
out with HANNA HI 5521 at rt. A BUCHI 560 instrument was used to determine melting
points of the complexes.
4.2. General procedure for the synthesis of Pd(II) complexes
Complexes 1, 3 and 7 were synthesized according to the Henderson’s method [2]. Trans-
[PdCl2(phos)2] prepared from the reaction of [PdCl2(COD)] with PPh3, PPh2Cy and PCy3 in
dichloromethane was mixed with the solid Na(sac)·2H2O in a 1:5 molar ratio. The solid
mixtures containing trans-[PdCl2(PPh3)2] and trans-[PdCl2(PPh2Cy)2] were dissolved in
MeOH (25 mL), while the mixture with trans-[PdCl2(PCy3)2] is soluble only in DMSO (25
mL). The resulting solutions were refluxed at 65 °C for 4 h. The addition of water (70 mL) to
these solutions resulted in the precipitation of 1 and 3, which were collected by filtration and
washed with water and ether. However, in the case of 7, no solid was observed after the
addition of water and this complex was obtained by removal of the solvents under reduced
pressure in a rotary evaporator.
Complexes 4, 6, 8 and 10–12 were prepared by the following method. SacH (0.5 mmol,
91.6 mg) in water (5 mL) was added to a solution of Pd(OAc)2 (0.25 mmol, 56.1 mg) in
MeCN (10 mL) and the solution was stirred for 30 min at rt. Then, the corresponding
phosphine (0.5 mmol) in MeOH (10 mL) was added to this solution and the resulting
solutions were refluxed over a day. Complexes 2, 5 and 9 were synthesized using the same
procedure, but the SacH/phosphine ratio was 2:1. In the case of 9, DMSO (10 mL) was added
to the reaction medium to dissolve the solid particles. The powders of these complexes were
obtained after removal of the solvents using a rotary evaporator.
The powders of the complexes were crystallized from mixtures of MeOH/H2O/DMF or
MeOH/H2O/DMSO. The saturated solutions were left to stand at rt and allowed to evaporate
slowly for crystallization. Single crystals suitable for X-ray diffraction were obtained for 1−5,
7 and 9−12 within 2 or 3 months. All characterization studies were performed using the bulk
products of the Pd(II) complexes.
14

trans-[PdCl(sac)(PPh3)2] (1). Yield: 161 mg (76%). Melting point: 210–211 °C
1
(decomp.). H NMR (400 MHz, DMSO-d6): δ (ppm) 7.85–7.19 (m, 30H, Ph protons and 4H-
sac). 13C NMR (101 MHz, DMSO-d6): δ (ppm) 165.0 (C7-sac), 142.7 (C1-sac), 134.9 (m,
3
Cipso-Ph), 132.5 (C3-sac), 132.0 (d, Cmeta-Ph, JPC = 9 Hz), 131.8 (C6-sac), 131.3 (C4-sac),
4
2
129.3 (d, Cpara-Ph, JPC = 3 Hz), 128.6 (dd, Cortho-Ph, JPC = 11 and 11 Hz), 123.5 (C5-sac),
31
120.0 (C2-sac). P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 25.55 (s). UV-vis (MeOH),
λmax/nm (max/M−1cm−1): 275 (20 803), 344 (19 426), 524 (288). Molar conductivity, ΛM
(MeOH, 298 K, 10–3 M) 5 S cm2 mol-1 (nonelectrolyte). ESI+–MS (m/z): 1334.1 (48%, calcd
1334.9)
[Pd2Cl2(sac)(PPh3)3(MeCN)2]+,
1313.9
(100%,
calcd
1314.3)
[Pd2Cl2(sac)(PPh3)3(MeCN)3/2]+, 1073.1 (21%, calcd 1072.6) [Pd2Cl2(sac)(PPh3)2(MeCN)2]+,
812.7 (35%, calcd 813.2) [M – Cl]+, 665.6 (31%, calcd 666.4) [M – sac]+, 350.8 (38%, calcd
350.2) [Pd(sac)(MeCN)3/2]+. IR (ν/cm–1): 3056, 1667, 1593, 1482, 1457, 1435, 1321, 1295,
1285, 1248, 1173, 1153, 1096, 1057, 999, 958, 794, 743, 707, 689, 674, 594, 561, 536, 506,
495. Anal. Calcd for C43H34ClNO3P2PdS (%): C, 60.86; H, 4.04; N, 1.65. Found: C, 59.83; H,
4.36; N, 1.49.
trans-[Pd(sac)2(H2O)(PPh3)] (2). Yield: 173 mg (92%). Melting point: 205–208 °C
(decomp.). 1H NMR (400 MHz, DMSO-d6): δ (ppm) 7.88–7.22 (m, 15H, Ph protons and 8H-
sac). 13C NMR (101 MHz, DMSO-d6): δ (ppm) 165.5 (C7-sac), 142.5 (C1-sac), 135.9 (m,
3
Cipso-Ph), 133.3 (d, Cmeta-Ph, JPC = 6 Hz), 131.8 (C3-sac), 130.2 (C6-sac), 129.2 (d, Cpara-Ph,
2
4JPC = 2 Hz), 128.1 (t, Cortho-Ph, JPC = 11 and 11 Hz), 127.4 (C4-sac), 123.4 (C5-sac), 120.1
31
(C2-sac). P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 26.41 (s). UV-vis (MeOH), λmax/nm
(max/M−1cm−1): 275 (21 662). Molar conductivity, ΛM (MeOH, 298 K, 10–3 M) 4 S cm2 mol-1
(nonelectrolyte). ESI+–MS (m/z): 591.4 (32%, calcd 591.9) [Pd(sac)(PPh3)(MeCN)]+, 550.4
(11%, calcd 550.9) [Pd(sac)(PPh3)]+, 339.1 (100%, calcd 338.7) [Pd(sac)(H2O)(MeOH)]+. IR
(ν/cm–1): 3179, 3061, 2930, 2852, 1662, 1640, 1590, 1459, 1435, 1322, 1311, 1296, 1257,
1169, 1154, 1099, 1056, 1002, 958, 789, 747, 692, 679, 591, 563, 535, 512, 494. Anal. Calcd
for C32H25N2O7PPdS2 (%): C, 51.17; H, 3.35; N, 3.73. Found: C, 50.95; H, 3.60; N, 3.92.
trans-[PdCl(sac)(PPh2Cy)2] (3). Yield: 86 mg (40%). Melting point: 228–234 °C
(decomp.). 1H NMR (400 MHz, DMSO-d6): δ (ppm) 7.99–7.03 (m, 20H, Ph protons and 4H-
13
sac), 2.11–0.59 (m, 22H, Cy protons). C NMR (101 MHz, DMSO-d6): δ (ppm) 162.8 (C7-
sac), 145.5 (C1-sac), 134.2 (m, Cipso-Ph), 133.7 (C3-sac), 131.8 (C6-sac), 131.6 (C4-sac),
131.1 (d, Cmeta-Ph, 3JPC = 9 Hz), 129.1 (t, Cortho-Ph, 2JPC = 12 and 12 Hz), 128.4 (m, Cpara-Ph),
123.1 (C5-sac), 120.2 (C2-sac), 36.3 (s, Cipso-Cy), 33.7 (s, Cortho-Cy), 29.1 (d, Cmeta-Cy, 3JPC =
15

4
31
6 Hz), 26.0 (d, Cpara-Cy, JPC = 3 Hz). P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 27.34
(s). UV-vis (MeOH), λmax/nm (max/M−1cm−1): 264 (21 635), 271 (21 055), 344 (18 581).
Molar conductivity, ΛM (MeOH, 298 K, 10–3 M) 5 S cm2 mol–1 (nonelectrolyte). ESI+–MS
(m/z): 883.5 (22%, calcd 883.7) [M
+
Na]+, 751.5 (23%, calcd 751.6)
[PdCl(PPh2Cy)2(MeOH)(MeCN)]+, 678.7 (100%, calcd 678.5) [M – sac]+, 593.0 (21%, calcd
593.4) [PdCl(sac)(PPh2Cy) + H]+ , 307.1 (35%, calcd 307.4) [K(PPh2Cy)]+. IR (ν/cm–1): 3056,
2929, 2852, 1681, 1592, 1487, 1433, 1324, 1293, 1283, 1244, 1169, 1147, 1117, 1099, 1001,
957, 791, 739, 693, 678, 595, 561, 529, 512, 473s. Anal. Calcd for C43H46ClNO3P2PdS (%):
C, 60.00; H, 5.39; N, 1.63. Found: C, 60.22; H, 5.57; N, 1.48.
trans-[Pd(sac)2(PPh2Cy)2] (4).Yield: 185 mg (74%). Melting point: 195–200 °C
1
(decomp.). HNMR (400 MHz, DMSO-d6): δ (ppm) 8.01–7.10 (m, 20H, Ph protons and 8H-
13
sac), 2.22–0.69 (m, 22H, Cy protons). C NMR (101 MHz, DMSO-d6): δ (ppm) 164.6 (C7-
1
sac), 141.7 (C1-sac), 132.8 (C3-sac), 132.2 (d, Cipso-Ph, JPC = 39 Hz), 131.8 (C6-sac), 130.7
(d, Cpara-Ph, 4JPC = 3 Hz), 130.0 (d, Cmeta-Ph, 3JPC = 8 Hz), 129.8 (C4-sac), 128.0 (d, Cortho-Ph,
2JPC = 10 Hz), 122.4 (C5-sac), 119.2 (C2-sac), 34.8 (s, Cipso-Cy), 34.1 (s, Cortho-Cy), 24.8 (d,
3
Cmeta-Cy, JPC = 12 Hz), 23.7 (s, Cpara-Cy). 31P{1H} NMR (162 MHz, DMSO-d6): δ (ppm)
32.54 (s). UV-vis (MeOH), λmax/nm (max/M−1cm−1): 265 (23 672), 272 (23 693). Molar
conductivity, ΛM (MeOH, 298 K, 10–3 M) 6 S cm2 mol–1 (nonelectrolyte). ESI+–MS (m/z):
1072.2 (56%, calcd 1071.5) [M(MeCN)
+
Na]+, 875.9 (38%, calcd 876.2)
589.6 (100%, calcd 589.0)
[Pd(sac)2(PPh2Cy)(MeCN)2(MeOH)
+
Na]+,
[Pd(sac)(PPh2Cy)(MeOH)]+, 307.1 (97%, calcd 307.4) [K(PPh2Cy)]+. IR (ν/cm–1): 3058,
2928, 2854, 1662, 1590, 1485, 1458, 1436, 1336, 1293, 1252, 1170, 1153, 1119, 1056, 1001,
953, 789, 747, 695, 678, 592, 561, 537, 517, 479. Anal. Calcd for C50H50N2O6P2PdS2 (%): C,
59.61; H, 5.00; N, 2.78. Found: C, 59.86; H, 5.21; N, 2.92.
trans-[Pd(sac)2(H2O)(PPh2Cy)] (5). Yield: 152 mg (80%). Melting point: 195–197 °C
1
(decomp.). H NMR (400 MHz, DMSO-d6): δ (ppm) 7.91–7.26 (m, 10H, Ph protons and 8H-
13
sac), 2.21–0.56 (m, 11H, Cy protons). C NMR (101 MHz, DMSO-d6): δ (ppm) 164.6 (C7-
sac), 141.6 (C1-sac), 132.5 (m, Cipso-Ph and C3-sac), 130.4 (s, Cortho-Ph), 129.8 (C6-sac), 127.3
(d, Cmeta-Ph, 3JPC = 10 Hz), 124.8 (s, Cpara-Ph), 124.2 (C4-sac), 122.4 (C5-sac), 119.3 (C2-sac),
3
34.6 (s, Cipso-Cy), 34.3 (s, Cortho-Cy), 25.6 (d, Cmeta-Cy, JPC = 12 Hz), 24.8 (s, Cpara-Cy).
31P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 32.45 (s). UV-vis (MeOH), λmax/nm
(max/M−1cm−1): 270 (21 423). Molar conductivity, ΛM (MeOH, 298 K, 10–3 M) 4 S cm2 mol–1
(nonelectrolyte). ESI+–MS (m/z): 597.6 (43%, calcd 597.9) [Pd(sac)(PPh2Cy)(MeCN)]+,
16

556.6 (98%, calcd 556.9) [Pd(sac)(PPh2Cy)]+, 452.5 (34%, calcd 452.8) [Pd(sac)(MeCN)4]+,
411.6 (28%, calcd 411.8) [Pd(sac)(MeCN)3]+, 373.0 (31%, calcd 373.7) [Pd(PPh2Cy) – H]+,
287.9 (100%, calcd 288.6) [Pd(sac)]+. IR (ν/cm–1): 3229, 3083, 2930, 2857, 1662, 1640, 1591,
1460, 1440, 1342, 1317, 1296, 1255, 1172, 1161, 1120, 1102, 1057, 1013, 973, 954, 790, 758,
745, 693, 680, 593, 564, 539, 518, 477. Anal. Calcd for C32H31N2O7PPdS2 (%): C, 50.76; H,
4.13; N, 3.70. Found: C, 50.92; H, 4.32; N, 3.59.
trans-[Pd(sac)2(PPhCy2)2] (6). Yield: 178 mg (70%). Melting point: 173–177 °C
(decomp.). 1H NMR (400 MHz, DMSO-d6): δ (ppm) 8.08–6.94 (m, 10H, Ph protons and 8H-
13
sac), 1.99–0.58 (m, 44H, Cy protons). C NMR (101 MHz, DMSO-d6): δ (ppm) 162.8 (C7-
3
sac), 142.8 (C1-sac), 133.5 (C3-sac), 133.1 (m, Cipso-Ph), 131.8 (d, Cmeta-Ph, JPC = 7 Hz),
2
130.9 (C6-sac), 130.5 (m, Cpara-Ph), 128.7 (d, Cortho-Ph, JPC = 10 Hz), 128.1 (C4-sac), 123.5
3
(C5-sac), 120.3 (C2-sac), 29.1 (m, Cipso-Cy), 27.0 (m, Cortho-Cy), 26.2 (d, Cmeta-Cy, JPC = 12
Hz), 24.8 (s, Cpara-Cy). 31P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 44.14 (s). UV-vis
(MeOH), λmax/nm (max/M−1cm−1): 264 (26 817), 271 (26 310). Molar conductivity, ΛM
(MeOH, 298 K, 10–3 M) 4 S cm2 mol–1 (nonelectrolyte). ESI+–MS (m/z): 1042.3 (13%, calcd
1042.5) [M + Na]+, 910.9 (20%, calcd 910.5) [Pd(sac)(PPhCy2)2(MeCN)(MeOH)]+, 878.1
(53%, calcd 878.4) [Pd(sac)(PPhCy2)2(MeCN)]+, 837.1 (100%, calcd 837.4) [M – sac]+,
654.9 (19%, calcd 654.2) [Pd(PPhCy2)2
–
H]+, 603.6 (14%, calcd 604.0)
[Pd(sac)(PPhCy2)(MeCN)]+, 313.6 (77%, calcd 313.5) [K(PPhCy2)]+. IR (ν/cm–1): 3062,
2927, 2852, 1674, 1604, 1546, 1450, 1435, 1336, 1305, 1245, 1170, 1155, 1121, 1055, 1002,
959, 850, 789, 747, 701, 678, 595, 561, 535, 518, 504. Anal. Calcd for C50H62N2O6P2PdS2
(%): C, 58.90; H, 6.13; N, 2.75. Found: C, 58.77; H, 6.26; N, 2.57.
[PdCl(sac)(PCy3)(DMSO)] (7). Yield: 102 mg (60%). Melting point: 151–155 °C
1
(decomp.). H NMR (400 MHz, DMSO-d6): δ (ppm) 8.04–7.68 (m, 4H-sac), 2.61–2.53 (s,
6H, CH3-dmso), 1.81–1.59 (m, 16H, Cy protons), 1.29–1.11 (m, 17H, Cy protons). 13C NMR
(101 MHz, DMSO-d6): δ (ppm) 166.2 (C7-sac), 142.0 (C1-sac), 133.1 (C3-sac), 132.7 (C6-
sac), 129.8 (C4-sac), 122.6 (C5-sac), 119.4 (C2-sac), 39.9 (DMSO), 34.2 (s, Cipso-Cy), 33.6 (s,
3
4
31
Cortho-Cy), 25.7 (d, Cmeta-Cy, JPC = 12 Hz), 25.2 (d, Cpara-Cy, JPC = 2 Hz). P{1H} NMR
(162 MHz, DMSO-d6): δ (ppm) 48.53 (s). UV-vis (MeOH), λmax/nm (max/M−1cm−1): 228 (48
649), 272 (13 140). Molar conductivity, ΛM (MeOH, 298 K, 10-3 M) 2 S cm2 mol–1
(nonelectrolyte). ESI+–MS (m/z): 1109.2 (18%, calcd 1108.9) [Pd2Cl2(sac)(PCy3)2(MeCN)2]+,
617.0 (100%, calcd 617.1) [Pd(sac)(POCy3)(MeOH)]+, 463.6 (20%, calcd 463.4)
[PdCl(PCy3)(MeCN)]+, 319.6 (36%, calcd 319.5) [K(PCy3)]+, 297.6 (12%, calcd 297.4)
17

[POCy3 + H]+. IR (ν/cm–1): 2930, 2854, 1680, 1594, 1446, 1323, 1297, 1285, 1243, 1153,
1147, 1116, 1030, 989, 949, 926, 898, 790, 760, 680, 597, 559, 542, 521. Anal. Calcd for
C27H43ClNO4PPdS2 (%): C, 47.51; H, 6.35; N, 2.05. Found: C, 47.37; H, 6.17; N, 2.26.
trans-[Pd(sac)2(PCy3)2] (8). Yield: 211 mg (82%). Melting point: 173–175 °C (decomp.).
1H NMR (400 MHz, DMSO-d6): δ (ppm) 7.98–7.78 (m, 8H-sac), 2.14–0.79 (m, 66H, Cy
protons). 13C NMR (101 MHz, DMSO-d6): δ (ppm) 167.3 (C7-sac), 143.0 (C1-sac), 133.9 (C3-
sac), 133.7 (C6-sac), 130.9 (C4-sac), 123.6 (C5-sac), 120.5 (C2-sac), 35.3 (s, Cipso-Cy), 34.7 (s,
3
4
31
Cortho-Cy), 26.8 (d, Cmeta-Cy, JPC = 11 Hz), 26.3 (d, Cpara-Cy, JPC = 2 Hz). P{1H} NMR
(162 MHz, DMSO-d6,): δ (ppm) 48.49 (s). UV-vis (MeOH), λmax/nm (max/M−1cm−1): 224
(103 480), 266 (25 439). Molar conductivity, ΛM (MeOH, 298 K, 10–3 M) 7 S cm2 mol-1
(nonelectrolyte). ESI+–MS (m/z): 913.3 (16%, calcd 913.5) [M(MeCN) + Na]+, 616.8 (100%,
calcd 616.9) [Pd(sac)2(MeCN)3 + Na]+, 594.0 (48%, calcd 594.9) [Pd(sac)2(MeCN)3 + H]+,
319.6 (57%, calcd 319.5) [K(PCy3)]+, 297.4 (73%, calcd 297.4) [POCy3 + H]+. IR (ν/cm–1):
2927, 2851, 1684, 1593, 1447, 1325, 1294, 1235, 1170, 1154, 1124, 1058, 1005, 963, 849,
788, 754, 679, 596, 562, 537, 520, 494. Anal. Calcd for C50H74N2O6P2PdS2 (%): C, 58.21; H,
7.23; N, 2.72. Found: C, 58.04; H, 7.45; N, 2.89.
trans-[Pd(sac)2(PPh2Me)(DMSO)]·H2O (9). Yield: 155 mg (81%). Melting point: 174–
1
178 °C (decomp.). H NMR (400 MHz, DMSO-d6): δ (ppm) 7.87–7.56 (m, 4H, ortho-Ph
protons of PPh2Me and 8H, sac), 7.37–7.17 (m, 6H, meta and para-Ph protons of PPh2Me),
2.58–2.53 (s, 6H, CH3-dmso), 2.27–2.17 (d, 3H, CH3-PPh2Me, 2JHP = 12 Hz). 13C NMR (101
MHz, DMSO-d6): δ (ppm) 164.4 (C7-sac), 141.5 (C1-sac), 132.4 (s, Cipso-Ph), 132.3 (d, Cortho
-
Ph, 2JPC = 10 Hz), 130.5 (C3-sac), 129.6 (C6-sac), 129.0 (s, Cpara-Ph), 128.4 (C4-sac), 127.1 (d,
Cmeta-Ph, 3JPC = 12 Hz), 122.5 (C5-sac), 119.2 (C2-sac), 39.8 (DMSO), 12.2 (d, CH3-PPh2Me,
1JPC = 18 Hz). 31P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 18.66 (s). UV-vis (MeOH),
λmax/nm (max/M−1cm−1): 265 (26 741). Molar conductivity, ΛM (MeOH, 298 K, 10-3 M) 4 S
cm2 mol−1 (nonelectrolyte). ESI+–MS (m/z): 488.4 (67%, calcd 488.8) [Pd(sac)(PPh2Me)]+,
384.5 (100%, calcd 384.7) [Pd(sac)(DMSO)(H2O)]+. IR (ν/cm−1): 3545, 3465, 3063, 3018,
2925, 1672, 1594, 1461, 1439, 1327, 1306, 1285, 1248, 1171, 1155, 1123, 1105, 1056, 1030,
999, 973, 956, 890, 791, 752, 703, 677, 598, 562, 542, 519, 478, 464. Anal. Calcd for
C29H29N2O8PPdS3 (%): C, 45.40; H, 3.81; N, 3.65. Found: C, 45.22; H, 3.95; N, 3.90.
cis-[Pd(sac)2(PPhMe2)2] (10). Yield: 103 mg (55%). Melting point: 174–179 °C
1
(decomp.). H NMR (400 MHz, DMSO-d6): δ (ppm) 7.89–7.67 (m, 10H, Ph protons of
PPhMe2), 7.65–7.43 (m, 8H, sac), 1.54–1.42 (d, 12H, CH3-PPhMe2, 2JHP = 12 Hz). 13C NMR
18

(101 MHz, DMSO-d6): δ (ppm) 165.6 (C7-sac), 142.6 (C1-sac), 132.2 (s, Cipso-Ph), 132.0 (C3-
2
sac), 131.2 (C6-sac), 130.8 (d, Cortho-Ph, JPC = 11 Hz), 130.0 (s, Cpara-Ph), 129.5 (C4-sac),
128.5 (d, Cmeta-Ph, 3JPC = 12 Hz), 122.7 (C5-sac), 119.2 (C2-sac), 12.8 (d, CH3-PPhMe2, 1JPC =
31
2
19 Hz). P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 6.86 (broad s), 2.96 (d, JPP = 21.1
2
Hz), −1.12 (t, JPP = 24.3 and 24.3 Hz). UV-vis (MeOH), λmax/nm (max/M−1cm−1): 266 (27
676). Molar conductivity, ΛM (MeOH, 298 K, 10-3 M) 6 S cm2 mol−1 (nonelectrolyte). ESI+–
MS (m/z, MeOH): 769.8 (4%, calcd 770.1) [M + Na]+, 564.5 (100%, calcd 564.9) [M – sac]+,
554.5 (22%, calcd 554.9) [Pd(sac)(PPhMe2)(MeOH)4]+, 427.4 (35%, calcd 426.8)
[Pd(sac)(PPhMe2)]+, 381.4 (32%, calcd 381.7) [Pd(PPhMe2)2 – H]+. IR (ν/cm−1): 3092, 3063,
3011, 2921, 1660, 1591, 1457, 1439, 1417, 1329, 1307, 1287, 1249, 1168, 1147, 1115, 1058,
999, 971, 950, 923, 912, 850, 839, 789, 765, 747, 717s, 697, 681, 651, 595, 556, 538, 522,
486. Anal. Calcd for C30H30N2O6P2PdS2 (%): C, 48.23; H, 4.05; N, 3.75. Found: C, 48.39; H,
4.20; N, 3.58.
cis-[Pd(sac)2(PPh2Et)2] (11). Yield: 148 mg (66%). Melting point: 187–189 °C (decomp.).
1H NMR (400 MHz, DMSO-d6): δ (ppm) 8.07–6.95 (m, 20H, Ph protons of PPh2Et and 8H,
sac), 2.45–1.94 (m, 4H, CH2-PPh2Et), 1.17–0.52 (m, 6H, CH3-PPh2Et). 13C NMR (101 MHz,
DMSO-d6): δ (ppm) 167.0 (C7-sac), 143.6 (C1-sac), 133.8 (m, Cipso-Ph and C3-sac), 132.0 (d,
Cortho-Ph, 2JPC = 11 Hz), 130.9 (m, Cpara-Ph and C6-sac), 128.9 (m, Cmeta-Ph and C4-sac), 123.7
1
2
(C5-sac), 120.2 (C2-sac), 21.2 (d, CH2-PPh2Et, JPC = 18 Hz), 9.0 (d, CH3-PPh2Et, JPC = 16
Hz). 31P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 22.76 (broad s). UV-vis (MeOH),
λmax/nm (max/M−1cm−1): 271 (30 411). Molar conductivity, ΛM (MeOH, 298 K, 10-3 M) 9 S
cm2 mol−1 (nonelectrolyte). ESI+–MS (m/z): 686.8 (100%, calcd 686.0) [Pd(sac)2(PPh2Et) +
H]+, 631.5 (80%, calcd 631.0) [Pd(sac)(PPh2Et)(MeOH)4]+, 567.4 (38%, calcd 566.9)
[Pd(sac)(PPh2Et)(MeOH)2]+. IR (ν/cm−1): 3072, 2992, 2938, 2876, 1662, 1594, 1487, 1479,
1460, 1440, 1335, 1306, 1288, 1248, 1170, 1152, 1127, 1101s, 1058, 1027, 1010, 1000, 964,
791, 770, 745, 693, 678, 654, 595, 559, 535, 518, 488. Anal. Calcd for C42H38N2O6P2PdS2
(%): C, 56.10; H, 4.26; N, 3.12. Found: C, 56.27; H, 4.32; N, 3.34.
cis-[Pd(sac)2(PPhEt2)2] (12). Yield: 171 mg (85%). Melting point: 205–208 °C (decomp.).
1H-NMR (400 MHz, DMSO-d6): δ (ppm) 8.17–7.19 (m, 10H, Ph protons of PPhEt2 and 8H,
sac), 2.64–1.67 (m, 8H, CH2-PPhEt2), 1.23–0.14 (m, 12H, CH3-PPhEt2). 13C NMR (101 MHz,
DMSO-d6): δ (ppm) 165.6 (C7-sac), 142.3 (C1-sac), 132.2 (s, Cipso-Ph), 132.0 (C3-sac), 131.2
(d, Cortho-Ph, 2JPC = 12 Hz), 130.7 (C6-sac), 130.2 (s, Cpara-Ph), 129.7 (C4-sac), 128.5 (t, Cmeta
-
3
Ph, JPC = 14 Hz), 122.7 (C5-sac), 119.0 (C2-sac), 20.5 (s, CH2-PphEt2), 6.8 (d, CH3-PphEt2,
19

2JPC = 21 Hz). 31P{1H} NMR (162 MHz, DMSO-d6): δ (ppm) 22.20 (s). UV-vis (MeOH),
λmax/nm (max/M−1cm−1): 258 (33 389). Molar conductivity, ΛM (MeOH, 298 K, 10-3 M) 4 S
cm2 mol−1 (nonelectrolyte). ESI+–MS (m/z): 826.0 (3%, calcd 826.2) [M + Na]+, 620.6 (56%,
calcd 621.0) [M – sac]+, 473.1 (100%, calcd 472.9) [Pd(sac)2 + H]+. IR (ν/cm−1): 3067, 2975,
2938, 2878, 1660, 1590, 1487, 1457, 1437, 1328, 1302, 1284, 1246, 1191, 1168, 1155, 1111,
1031, 1015, 997, 961, 782, 762, 752, 740, 724, 700, 678, 644, 591, 559, 540, 521, 509, 498,
471, 458. Anal. Calcd for C34H38N2O6P2PdS2 (%): C, 50.84; H, 4.77; N, 3.49. Found: C,
50.63; H, 4.90; N, 3.68.
4.3. X-ray structure determination
Diffraction data of complexes 1–5, 7 and 9–12 were collected on an Rigaku Xcalibur X-
ray diffractometer with EOS CCD detector using Mo-K radiation (0.71073 Å) with -scan
mode. The details of the data collection, cell refinement and data reduction are similar to
those for the previously reported Pd(II) and Pt(II) complexes [21]. All non-hydrogen atoms
were refined anisotropically, while all hydrogen atoms were located at calculated positions
and refined by using riding model. The electron densities of the highly disordered H2O in 1,
DMF in 2 and two DMSO molecules in 12 were removed using solvent mask procedure and
the hkl intensities were modified accordingly. The wR2 value higher than 0.25 is due to the
low crystal quality and highly disordered cyclohexane and phenyl rings of 5. Details of the
data collection and structure refinement are given in Table S1.
Crystallographic data for the structures reported in this paper were deposited in the
Cambridge Crystallographic Data Centre (CCDC) with the deposition numbers 1828361–
1828364, 1828369, 1828370 and 1915735–1915738.
4.4. The direct arylation of heteroaromatic compounds
In the catalysis studies, the bulk products of the Pd(II) complexes were used. An oven
dried 10 mL Schlenk tube was charged with the Pd(II) complex (0.02 mmol), heteroaromatic
compound derivative (2.0 mmol), aryl halide (1.0 mmol), KOAc (2.0 mmol), and DMAc
(dimethylacetamide, 2 mL) under argon. The Schlenk tube was placed in a preheated oil bath
at 100-120 °C, and the reaction mixture was stirred for 2h. After completion of the reaction,
the solvent was removed under vacuum and the residue was charged directly onto a micro
silica gel column. The products were eluted by using n-hexane/diethyl ether mixture (5:1,
20

v/v). GC yields were calculated with respect to aryl bromide from the results of GC
spectrometry with dodecane as internal standard.
Conflicts of interest
The authors declare no conflict of interest.
Acknowledgements
The authors gratefully acknowledge financial support from TUBITAK for the research
project 215Z230.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the online version, at
doi:https://doi.org….
21

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Graphical abstract
23

S
N
R
8 - 98 %
S
N
O
S
O
O
10 - 99 %
11 - 98 %
Br
R
O
S
s
o
ts
h
s
-p
ly
ta
c
a
-s
d
P
O
O
R
R
a
c
The palladium(II) complexes derived from saccharinate and tertiary phosphine ligands were
synthesized and structurally characterized. The complexes displayed efficient catalytic
performance in direct arylation of five-membered heteroarenes with aryl bromides.
Highlights
 Synthesis of Pd(II) saccharinate complexes with monophosphines as pre-catalysts.
 Direct arylation of substituted furan, thiophene and thiazoles with aryl bromides.
 Regioselective arylation of the five-membered heteroarenes.
 High catalytic efficiency with up to 99% yields of arylation products.
24

Conflicts of Interest
The authors declare no conflict of interest.
25