Palladium(II) complexes bearing bidentate pyridyl-sulfonamide ligands: Synthesis and catalytic applications

Article abstract of DOI:10.1016/j.poly.2014.09.042

New palladium(II) complexes ([Pd(1-5)₂], 6-10, (1-5 = bidentate pyridyl-sulfonamide ligands)) were obtained from the reaction between Pd(OAc)₂ and bidentate pyridyl-sulfonamide ligands. The synthesized compounds were characterized by

Full text of DOI:10.1016/j.poly.2014.09.042

Accepted Manuscript
Palladium(II) complexes bearing bidentate pyridyl-sulfonamide ligands: Syn-
thesis and catalytic applications
Serkan Dayan, Ahmet Çetin, N. Burcu Arslan, Nilgün Kalaycıoğlu Özpozan,
Namık Özdemir, Osman Dayan
PII:
S0277-5387(14)00664-0
DOI:
http://dx.doi.org/10.1016/j.poly.2014.09.042
POLY 11015
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
3 September 2014
28 September 2014
Please cite this article as: S. Dayan, A. Çetin, N. Burcu Arslan, N.K. Özpozan, N. Özdemir, O. Dayan, Palladium(II)
complexes bearing bidentate pyridyl-sulfonamide ligands: Synthesis and catalytic applications, Polyhedron (2014),
doi: http://dx.doi.org/10.1016/j.poly.2014.09.042
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Palladium(II) complexes bearing bidentate pyridyl-sulfonamide ligands:
Synthesis and catalytic applications
Serkan Dayana, Ahmet Çetinb, N. Burcu Arslanc, Nilgün Kalaycıoğlu Özpozana, Namık
Özdemird,*, Osman Dayane,*
[a] Department of Chemistry, Faculty of Science, Erciyes University, 38039 Kayseri, Turkey
[b] Bingöl University, Faculty of Art and Sciences, Department of Chemistry, 12000- Bingöl, Turkey
[c] Department of Computer Education and Instructional Technology, Faculty of Education, Giresun University, 28100
Giresun, Turkey
[d],* Department of Physics, Faculty of Art and Sciences, Ondokuz Mayıs University, 55139 Samsun, Turkey
[e],* Laboratory of Inorganic Synthesis and Molecular Catalysis, Çanakkale Onsekiz Mart University, 17020 Çanakkale,
Turkey
Corresponding Authors
* Tel: +902862180018-1860; Fax: +902862180533 E-mail: osmandayan@comu.edu.tr (O.
Dayan)
# Tel: +903623121919-5256; Fax: +903624576081 E-mail: namiko@omu.edu.tr (N.
Özdemir)
Abstract
New palladium(II) complexes ([Pd(1-5)2], 6-10, (1-5 = bidentate pyridyl-sulfonamide
ligands)) were obtained from the reaction between Pd(OAc)2 and bidentate pyridyl-
sulfonamide ligands. The synthesized compounds were characterized by elemental analysis,
TG, NMR, IR and X-ray diffraction. The Pd(II) complexes 6-10 were investigated as catalysts
for the oxidation of benzyl alcohol to benzaldehyde in the presence of periodic acid as the
oxidant and acetonitrile as the solvent under reflux. All the complexes were moderately active
catalysts for the catalytic reaction (the oxidation of benzyl alcohol to benzaldehyde), with
good yields under mild conditions.
Keywords: Sulfonamides, Pd(II) complexes, pyridines, oxidation, benzyl alcohol,
benzaldehyde

1. INTRODUCTION
Sulfonamides are well-documented compounds of synthetic importance which have been
widely used in chemistry, biology and medicine fields. The sulfonamides may be synthesized
by different techniques, such as the reaction of sulfonyl chlorides with excess ammonia in the
presence of a basic media or N-sulfonylation of amines in the presence of homogeneous and
heterogeneous catalytic systems [1-6].
The catalytic oxidation of alcohols to aldehydes is a fundamentally important process both in
the laboratory and on an industrial scale [7-8]. Especially, benzaldehyde is a significant fine
chemical, finding extensive uses in pharmaceuticals, dyestuff etc., and it is currently produced
by the liquid phase hydrolysis of benzyl chloride or by the selective oxidation of toluene;
however, the hazardous chemicals, complicated processes, Cl-contamination and low yields
for products are severe drawbacks for environmental effects and low cost manufacturing
steps. For these reasons, there is big research interest for innovative synthesis routes, mostly
based on the selective oxidation of benzyl alcohol [9-11].
Recently, palladium catalysts were synthesized and tested for the solvent-free selective
aerobic oxidation of toluene to obtain benzaldehyde [12]. With another method, a
Pd(OAc)2/pyridine/K2CO3 system selectively converted terpenic alcohols to aldehydes under
dioxygen [13]. More recently, Pd(II) complexes bearing sulfonamide ligands were reported
for the catalytic oxidation of benzyl alcohol to benzaldehyde in the presence of H5IO6 [14].
Another example for the oxidation of benzyl alcohol to benzaldehyde in heterogeneous
catalytic systems was reported by Hou and co-workers [15].
Herein, we report a simple synthesis and the structural characterization of Pd(II) complexes
bearing sulfonamido ligands by spectroscopic analyses. These Pd(II) complexes were
examined as catalysts for the oxidation of benzyl alcohol to benzaldehyde.
2. EXPERIMENTAL
2.1. Materials and methods
All chemicals were purchased from commercial suppliers and used as received. NMR spectra
were recorded at 297 K on a Bruker 400 NMR spectrometer at 400 MHz (1H) and 100.56
MHz (13C). The C, H and N analyses were performed using a Truspec MICRO (LECO)
instrument. FT-IR spectra were measured with a Perkin-Elmer Spectrum 400 FTIR system
and recorded using a universal ATR sampling accessory within the range 550-4000 cm-1. The

DTA and TG curves were obtained with a TG-DTA Perkin Elmer Diamond system apparatus.
The measurements were performed using a dynamic nitrogen atmosphere at a flow rate of 200
mL min-1 up to 1000 ºC. The heating rate was 10 °C min-1 and the sample sizes ranged in
mass from 8 to 10 mg, contained in a platinum crucible. A Younglin Acme 6100 GC
instrument for catalytic experiments was used with an FID and Optima 5MS capillary
column.
2.2. Synthesis of the compounds
2.2.1. General procedure for the synthesis of the ligands
1, 2 [16] and 5 [17] were synthesized according to the literature. For characterization data of
these compounds, please see supplementary materials. The other ligands were synthesized as
follows:
A THF solution (15 ml) of triethylamine (20 mmol) and 2-picoylamine (10 mmol) was slowly
added to another THF solution (10 ml) of the arylsulfonyl chlorides (10 mmol) and stirred for
24 h. At the end of this time, the mixture was filtered and the volatiles were removed in
vacuo. The residue was washed with H2O (3 x 20 ml) and recrystallized from CH2Cl2 (5
ml)/diethyl ether (20 ml) (Scheme 1).
2.2.1.1. Data for 4-n-propyl-butyl-N-(pyridine-2-ylmethyl)benzenesulfonamide, 3
1H NMR (CDCl3, δ ppm): 8.44 (1H, d, J = 8 Hz, -H1), 7.74 (2H, d, J = 8.0 Hz, -Ha), 7.61 (1H,
t, J = 8.0 Hz, -H3), 7.22 (2H, d, J = 8.0 Hz, -Hb), 7.20 (1H, d, J = 4.0 Hz, -H4), 7.15 (1H, t, J =
8.0 Hz, -H2), 6.32 (1H, t, J = 4 Hz, -NH-), 4.26 (2H, d, J =8 Hz, -H5), 2.60 (2H, t, J = 8.0 Hz,
-CH2CH2CH3), 1.63 (2H, m, -CH2CH2CH3), 0.92 (3H, t, J = 8.0 Hz, -CH2CH2CH3). 13C NMR
(CDCl3, ppm): 155.0 (-Ci1), 148.7 (-C1), 147.9 (-Cc), 137.1 (-Ci2), 136.9 (-C3), 129.0 (-Cb),
127.2 (-Ca), 122.7 (-C4), 122.2 (-C2), 47.4 (-CH2), 37.8 (-CH2CH2CH3), 24.2 (-CH2CH2CH3),
13.7 (-CH2CH2CH3). IR (cm-1): 3057 (-NH), 2959, 2929, 2861, 2807, 1596, 1570, 1483, 1462,
1438, 1409, 1310 (νas-SO2), 1187, 1160 (νs-SO2), 1147, 1093, 1070, 1053, 1018, 1006, 971,
905, 852, 829, 798, 767, 713, 672, 634, 617, 574, 559, 524, 498, 462. Anal. Calcd. For
[C16H20N2O2S]: C 62.04, H 6.25, N 9.65, O 11.02, S 11.04. Found: C 62.93, H 6.07, N 9.92,
S: 11.32%.
2.2.1.2. Data for 4-methoxy-butyl-N-(pyridine-2-ylmethyl)benzenesulfonamide, 4
1H NMR (CDCl3, δ ppm): 8.45 (1H, d, J = 8.0 Hz, -H1), 7.78 (2H, d, J = 8.0 Hz, -Ha), 7.68
(1H, t, J = 8.0 Hz, -H3), 7.23 (1H, d, J = 4.0 Hz, -H4), 7.19 (1H, t, J = 8.0 Hz, -H2), 6.90 (2H,

d, J = 8.0 Hz, -Hb), 6.23 (1H, t, J = 4.0 Hz, -NH-), 4.25 (2H, d, J = 8.0 Hz, -H5), 3.83 (3H, s, -
13
OCH3). C NMR (CDCl3, ppm): 162.8 (-Cc), 155.0 (-Ci1), 148.5 (-C1), 137.3 (-C3), 131.2 (-
Ci2), 129.3 (-Ca), 122.8 (-C4), 122.3 (-C2), 114.2 (-Cb), 55.6 (-OCH3), 47.3 (-CH2). IR (cm-1):
3270 (-NH), 3098, 3073, 3020, 2978, 2951, 1593, 1574, 1495, 1476, 1455, 1434, 1321 (νas-
SO2), 1300, 1260, 1143 (νs-SO2), 1111, 1091, 1072, 1016, 997, 860, 833, 801, 771, 751, 716,
667, 627, 603, 563, 538, 502, 463. Anal. Calcd. For [C13H14N2O3S]: C 56.10, H 5.07, N
10.06, O 17.25, S 11.52. Found: C 57.02, H 4.92, N 9.88, S 11.81%.
2.2.2. General procedure for the synthesis of Pd(II) complexes, 6-10
A mixture of Pd(OAc)2 (0.25 mmol) and the N-(pyridine-2-ylmethyl)benzenesulfonamides
o
(0.50 mmol) in DMSO (5 ml) was heated at 70 C for 72 hours. The solution was allowed to
cool to ambient temperature, then the solvent was removed under reduced pressure. The
residues were washed with diethyl ether (10 ml) and dried in vacuo (Scheme 1).
2.2.2.1.
Data
for
bis-[N-(pyridine-2-ylmethyl)-2,4,6-tri-methyl-
benzenesulfonamido]palladium(II), 6
1H NMR (CDCl3, δ ppm): 8.38-7.17 (8H, m, -H1-4), 6.95 (4H, s, -Hb), 4.07 (4H, d, J = 8.0 Hz,
13
-H5), 2.52 (12H, s, -2,6-(CH3)), 2.22 (6H, s, -4-(CH3)). C NMR (d6-DMSO, ppm): 157.8 (-
Ci1), 149.1 (-C1), 141.9 (-Cc), 138.7 (-Ca), 136.9 (-C3), 135.1 (-Ci2), 132.0 (-Cb), 122.7 (-C4),
121.9 (-C2), 47.7 (-CH2), 23.1 (-2,6-(CH3)), 20.8 (-4-(CH3)). IR (cm-1): 3032, 2967, 2934,
2910, 2840, 1606, 1563, 1470, 1454, 1445, 1402, 1376, 1339 (νas-SO2), 1277, 1246, 1217,
1184, 1159, 1128 (νs-SO2), 1116, 1056, 992, 977, 898, 862, 844, 830, 785, 770, 718, 666.
Anal. Calcd. For [C28H30N4O4PdS2]: C 51.18, H 4.60, N 8.53, S 9.76. Found: C 51.04, H 4.71,
N 8.48, S 9.91%.
2.2.2.2. Data for bis-[N-(pyridine-2-ylmethyl)-4-tert-butyl-benzenesulfonamido]palladium(II),
7
1H NMR (CDCl3, δ ppm): 8.69-7.00 (16H, m, Ar.H), 4.61 (4H, d, J = 8.0 Hz, -H5), 1.21 (18H,
s, -C(CH3)3). 13C NMR (CDCl3, ppm): 165.7 (-Cc), 154.2 (-Ci1), 152.8 (-C1), 139.7 (-Ci2),
138.3 (-C3), 127.4 (-Ca), 125.2 (-Cb), 121.9 (-C4), 119.7 (-C2), 58.1 (-CH2), 34.8 (-C(CH3)3),
31.09 (-C(CH3)3). IR (cm-1): 2963, 2929, 2903, 2870, 1609, 1594, 1473, 1438, 1399, 1363,
1335, 1300 (νas-SO2), 1283, 1251, 1208, 1185, 1143 (νs-SO2), 1104, 1083, 1050, 999, 894,
852, 831, 806, 776, 754, 733, 722, 652, 599, 564, 552, 525, 468. Anal. Calcd. For

[C30H34N4O4PdS2]: C 52.59, H 5.00, N 8.18, S 9.36. Found: C 52.71, H 5.11, N 8.03, S
9.17%.
2.2.2.3.
Data
for
bis-[N-(pyridine-2-ylmethyl)-4-n-propyl-butyl-
benzenesulfonamido]palladium(II), 8
1H NMR (CDCl3, δ ppm): 7.00-8.83 (16H, m, Ar.-H), 4.42 (4H, d, J = 8.0 Hz, -H5), 2.56 (4H,
t, J = 8.0 Hz, -CH2CH2CH3), 1.59 (4H, m, -CH2CH2CH3), 0.90 (6H, t, J = 8.0 Hz, -
13
CH2CH2CH3). C NMR (CDCl3, ppm): 150.5 (-Ci1), 138.9 (-C1), 129.0 (-Cc), 128.6 (-Ci2),
127.4 (-C3), 126.7 (-Cb), 126.4 (-Ca), 122.7 (-C4), 120.1 (-C2), 41.1 (-CH2), 37.8 (-
CH2CH2CH3), 24.3 (-CH2CH2CH3), 13.7 (-CH2CH2CH3). IR (cm-1): 2955, 2926, 2863, 1606,
1598, 1569, 1472, 1435, 1403, 1335, 1313 (νas-SO2), 1267, 1251, 1207, 1135, 1112 (νs-SO2),
1083, 1051, 997, 971, 953, 892, 841, 792, 773, 740, 719, 686, 639, 629, 617, 578, 546, 513,
465. Anal. Calcd. For [C28H30N4O4PdS2]: C 51.18, H 4.60, N 8.53, S 9.76. Found: C 51.29, H
4.49, N 8.43, S 9.67%.
2.2.2.4.
Data
for
bis-[N-(pyridine-2-ylmethyl)-4-methoxy-butyl-
benzenesulfonamido]palladium(II), 9
1H NMR (CDCl3, δ ppm): 8.84-6.60 (16H, m, Ar.H), 4.55 (4H, d, J = 8 Hz, -H5), 3.81 (6H, s,
13
-OCH3). C-NMR (CDCl3, ppm): 150.4 (-Cc), 138.6 (-Ci1), 129.6 (-C1), 128.7 (-C3), 123.7 (-
Ci2), 120.1 (-Ca), 114.1 (-C4), 113.6 (-C2), 113.4 (-Cb), 55.6 (-OCH3), 41.0 (-CH2). IR (cm-1):
3038, 2955, 2929, 2836, 1595, 1576, 1495, 1474, 1439, 1336, 1307 (νas-SO2), 1282, 1255,
1210, 1192, 1171, 1135 (νs-SO2), 1108, 1085, 1052, 1030, 999, 975, 893, 853, 828, 808, 797,
775, 723, 675, 635, 610, 564, 539, 486. Anal. Calcd. For [C24H22N4O6PdS2]: C 45.54, H 3.50,
N 8.85, S 10.13. Found: C 45.32, H 3.29, N 8.9, S 10.13%.
2.2.2.5. Data for bis-[N-(pyridine-2-ylmethyl)benzenesulfonamido]palladium(II), 10
1H NMR (DMSO, δ ppm): 8.68-7.23 (18H, m, Ar.H). 4.16 (d, 2H, J = 8.0 Hz, -H5). 13C NMR
(DMSO, ppm): 155.5 (-Ci1), 149.8 (-C1), 143.5 (-Ci2), 139.5 (-C3), 133.0 (-Cc), 129.7 (-Cb),
126.9 (-Ca), 123.7 (-C4), 123.2 (-C2), 47.3 (-CH2). IR (cm-1): 3104, 3057, 3028, 2954, 2902,
1608, 1573, 1481, 1447, 1418, 1356, 1316 (νas-SO2), 1283, 1255, 1228, 1167, 1148 (νs-SO2),
1118, 1087, 1073, 1061, 1038, 1001, 987, 959, 937, 896, 885, 860, 825, 802, 767, 750, 716,
691, 661, 635, 580, 531, 455, 419. Anal. Calcd. For [C22H18N4O4PdS2]: C 46.12, H 3.17, N
9.78, S 11.19. Found: C 46.30, H 3.02, N 9.59, S 11.30%.

2.3. Oxidation of benzyl alcohol
A test tube was filled with benzyl alcohol as the substrate, H5IO6 (periodic acid) as the
oxidant, Pd(II) complex as the catalyst and CH3CN (5 ml) as the solvent in a typical reaction.
This tube was heated under reflux conditions for the appropriate time. After this time, the
sample was treated with diethyl ether (10 ml) and filtered. The reactions were monitored by
gas chromatography.
2.4. X-ray analysis
Diffraction data of 6 were collected on a STOE IPDS II diffractometer at room
temperature (296 K) using graphite-monochromated Mo Kα radiation (λ=0.71073 Å) by
applying the ω-scan method. The structure was solved by direct methods using SHELXS-97
[18] and refined with full-matrix least-squares calculations on F2 using SHELXL-97 [18]
implemented in the WinGX [19] program suite. All H atoms were placed geometrically and
treated using a riding model, fixing the bond lengths at 0.93, 0.97 and 0.96 Å for CH, CH2 and
CH3 atoms, respectively. The displacement parameters of the H atoms were fixed at Uiso(H) =
1.2Ueq (1.5Ueq for methyl) of their parent atoms. Data collection: X-AREA [20], cell
refinement: X-AREA, data reduction: X-RED32 [20]. Crystal data, data collection and
structure refinement details are summarized in Table 1. The general-purpose crystallographic
tool PLATON [21] was used for the structure analysis and presentation of the results.
Molecular graphics were generated using ORTEP-3 [22].
Table 1. Crystal data and structure refinement parameters for 6.
CCDC depository
Color/shape
929522
Colorless/prism
[Pd(C15H34N2O2S)2]
685.13
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell parameters
a, b, c (Å)
296
0.71073 Mo Kα
Monoclinic
P21/c (No. 14)
15.4276(8), 8.8284(5), 11.2048(5)
α, β, γ (°)
90, 108.053(4), 90
1450.98(13)
2
1.568
0.827
Volume (Å3)
Z
Dcalc (g/cm3)
µ (mm−1)
Absorption correction
Tmin, Tmax
Integration
0.8834, 0.9607

F000
704
Crystal size (mm3)
0.19 × 0.12 × 0.05
Diffractometer/measurement method
Index ranges
STOE IPDS II/rotation (ω scan)
−
−
−18 ≤ h ≤ 18, 10 ≤ k ≤ 10, 13 ≤ l ≤ 13
θ range for data collection (°)
Reflections collected
Independent/observed reflections
Rint
2.69 ≤ θ ≤ 25.00
12817
2550/2075
0.093
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Full-matrix least-squares on F2
2550/0/190
1.07
R1 = 0.0525, wR2 = 0.1127
R1 = 0.0715, wR2 = 0.1211
0.74, −1.36
∆ρmax, ∆ρmin (e/Å3)
3. RESULT AND DISCUSSION
3.1. Synthesis
The synthesis of the N-(pyridine-2-ylmethyl)benzenesulfonamides (1-4) was performed with a
conventional method, by the reaction of 2-picoylamine and the commercially available
arylsulfonyl chlorides [16]. Additionally, the palladium(II) complexes (6-10) were also
synthesized from the reaction of Pd(OAc)2 and the appropriate ligands (1-5) (Scheme 1). All
1
the complex precursors and palladium complexes have been characterized by H and 13C
NMR, FT-IR, elemental and TG/DTA analyses. Furthermore, a single crystal-X-ray
diffraction study for 6 has been achieved.

Scheme 1 Synthesis and numbering scheme for the ligands (1-5) and Pd(II) complexes (6-10)
1
In the H NMR spectra of the N-(pyridine-2-ylmethyl)benzenesulfonamides (1-5), the -H5
proton was located between 4.06 and 4.31 ppm as a doublet. The -4-(CH3) (x), -2,6-(CH3) (y),
-C(CH3)3 (z), -CH2CH2CH3 (t, q, p) and -OCH3 (k) protons could be assigned as a singlet for
(x, y, z and k), triplet for (t and p), multiplet for (q) at δ 2.21 for (x), 2.52 for (y), 1.31 for (z),
2.60 for (t), 1.63 for (q), 0.92 for (p) and 3.83 for (k). Alike, in the 13C NMR spectra for 1-4,
the -CH2 carbon peak was assigned at around 47.0-48.4 ppm. The peaks of -4-(CH3) (x), -2,6-
(CH3) (y), -C(CH3)3 (z, v), -CH2CH2CH3 (t, q, p) and -OCH3 (k) carbons were observed at
20.4 for (x), 22.5 for (y), 35.1 for (z), 31.0 for (v), 37.8 for (t), 24.2 for (q), 13.7 for (p), 55.6
for (k). The peaks in the region 3270 to 3057 cm-1 are assigned to -NH vibrations in the FT-IR
spectra for the ligands (1-5).
1
While reviewing the H-NMR spectra of the Pd(II) complexes (6-10), the -H5 protons were
assigned between 4.07 and 4.61 ppm as an apparent doublet. In a similar way to the 1H NMR
spectra of the ligands, the -4-(CH3) (x), -2,6-(CH3) (y), -C(CH3)3 (z), -CH2CH2CH3 (t, q, p)
and -OCH3 (k) protons were observed at δ 2.22 for (x), 2.52 for (y), 1.21 for (z), 2.56 for (t),
1.59 for (q), 0.90 for (p) and 3.83 for (k), and in the 13C NMR spectra for 6-10, the -CH2 was

identified as being between 41.0 and 58.1 ppm. Additionally, N-H stretching frequency peaks
belonging to sulfonamide groups were not observed.
3.2. Description of the crystal structure of 6
The solid-state structure of 6 has been unambiguously confirmed by X-ray crystallography. A
perspective ORTEP-3 view of the complex with the atomic numbering scheme are depicted in
Fig. 1, while selected bond lengths and angles are given in Table 2. The complex crystallizes
in the monoclinic space group P21/c with two molecules in the unit cell.
Figure 1. A view of 6 showing the atom-numbering scheme. Displacement ellipsoids are
drawn at the 30% probability level. The dashed lines represent the intramolecular interactions
and only H atoms involved in the interactions are shown as small spheres of arbitrary radii.
Table 2. Selected geometric parameters for 6.
Bond lengths (Å)
Pd1—N1
2.015(4)
2.070(4)
1.429(4)
1.452(4)
1.618(4)
S1—C7
N1—C5
N1—C1
N2—C6
C5—C6
1.792(5)
1.346(6)
1.359(6)
1.472(6)
1.509(7)
Pd1—N2
S1—O1
S1—O2
S1—N2
Bond angles (°)
N1—Pd1—N1i
N1—Pd1—N2i
N1i—Pd1—N2i
N1—Pd1—N2
N1i—Pd1—N2
N2i—Pd1—N2
180.0
O2—S1—N2
O1—S1—C7
O2—S1—C7
N2—S1—C7
C5—N1—C1
112.3(2)
107.8(3)
107.1(2)
105.4(2)
119.4(4)
113.2(3)
98.28(16)
81.72(16)
81.72(16)
98.28(16)
180.000(1) C6—N2—S1

O1—S1—O2
O1—S1—N2
116.4(3)
107.2(2)
N2—C6—C5
111.9(4)
Torsion angles (°)
O1—S1—N2—C6
O2—S1—N2—C6
C7—S1—N2—C6
S1—N2—C6—C5
N1—C5—C6—N2
C4—C5—C6—N2
172.0(3)
−58.9(4)
57.3(4)
84.1(4)
27.5(5)
O1—S1—C7—C12
O2—S1—C7—C12
O1—S1—C7—C8
O2—S1—C7—C8
N2—S1—C7—C12
N2—S1—C7—C8
−54.0(5)
−180.0(4)
122.7(5)
−3.3(5)
60.2(4)
−123.0(5)
−153.0(4)
Symmetry code: i −x + 1, −y + 1, −z + 1.
The molecule of
6
is composed of two 2,4,6-trimethyl-N-(pyridine-2-
ylmethyl)benzenesulfonamide ligands with a Pd(II) metal centre. The Pd(II) cation resides on
a crystallographic inversion center and the two benzenesulfonamide ligands are coordinated to
the palladium(II) center in a square-planar fashion via the pyridine and amine nitrogen atoms.
The Pd—N bond distances are slightly different, the Pd—Namine bond length [2.070(4) Å] is
longer than the Pd—Npyridine bond [2.015(4) Å] by 0.55 Å. The difference can be attributed to
the different hybridization of the Nsp2 and Nsp3 atoms. As can be seen from the cis angles,
which vary from 81.72(16) to 98.28(16)°, the coordination around the Pd(II) ion is rather
deformed. The square plane makes dihedral angles of 15.40(22) and 37.72(18)° with the
planes of the pyridine and trimethylbenzene rings, while the dihedral angle between the
pyridine and trimethylbenzene rings is 34.97(20)°. The pyridine and amine N-donor atoms
form a five-membered metallacycle (containing atoms Pd1/N1/C5/C6/N2), which has an
envelope conformation, with the atom N2 atom displaced from the Pd1—N1—C5—C6 mean
plane by 0.566(2) Å [puckering parameters: Q = 0.368(4) Å and φ = 323.11(15)°] [23]. In the
benzenesulfonamide ligand, the N2—C6 bond length of 1.472(6) Å confirms the single bond
character, and the S1—O1 and S1—O2 distances of 1.429(4) and 1.452(4) Å are consistent
with S=O double bonding. The atom S1 has a distorted tetrahedral configuration, which is
evident from the angles changing from 105.4(2) to 112.3(2)°.
In the molecular structure of the complex, there is an intramolecular interaction, C—
H···O, forming a six-membered ring with the graph-set descriptor S(6) [24]. In the crystal
structure, the molecules are packed into columns running along the b axis. The molecules in
each column are connected to one another via C—H···O hydrogen bonds and π—π stacking
interactions. In these C—H···O interactions, the pyridine carbon atom C3 in the molecule at
(x, y, z) acts as a hydrogen-bond donor, via atom H3, to the sulfonyl atom O1 in the molecule
at (x, y + 1, z). At the same time, the pyridine rings of the molecules at (x, y, z) and (x, y + 1,
z) are mutually parallel, with a distance of 3.619(4) Å between the ring centroids, and a

perpendicular distance of 3.371(5) Å between the rings. Together, these result in the
formation of molecular chains along the b axis (Fig. 2). Finally, the 21-screw symmetry-
related columns are connected to each other by means of other C—H···O interactions, in
which the pyridine carbon atom C2 in the molecule at (x, y, z) acts as a hydrogen-bond donor,
−
−
via atom H3, to the other sulfonyl atom O2 in the molecule at ( x + 1, y + 1/2, z + 3/2). Full
details of the hydrogen-bonding geometries are given in Table 3.
Figure 2. A partial cell packing diagram for 6 showing the C—H···O and π—π interactions
(dashed lines). For clarity, only H atoms involved in hydrogen bonding have been included.
Table 3. Hydrogen bonding geometry for 6.
D—H···A
D—H (Å)
H···A (Å)
D···A (Å)
D—H···A (°)
C15—H15A···O1
0.96
0.93
0.93
2.44
2.39
2.48
3.072(8)
3.242(7)
3.147(7)
123
152
128
C2—H2···O2ii
C3—H3···O1iii
Symmetry codes: ii −x + 1, y + 1/2, −z + 3/2; iii x, y + 1, z.

3.3. Thermal behavior of the Pd(II) complexes 6-10
The palladium(II) complexes (6-10) were thermally studied from ambient temperature to up
to 900 ºC under a nitrogen atmosphere. Typical thermal curves for 6-10 are reported in the
Supplementary Materials (Fig. S1). The thermal decomposition results of the complexes,
including initial and final temperatures and total mass loss for each decomposition step, are
summarized Table 4.
Table 4. TGA data of the synthesized complexes
First degradation temp. oC
Second degradation temp. oC
Char
Loss of
absorbed
solvent
%
at
900
oC
Comp.
Ton Tmax
Tend
Percentage
Ton Tmax Tend Percentage
%
of weight
of weight
loss
loss
6
7
267 271 1000
81.5
75.5
79.5
85
-
-
-
-
-
-
-
-
-
-
-
-
-
-
17
23
18
13
27
1.5
1.5
2.5
2
205 277
209 293
209 276
202 286
900
900
900
308
8
-
9
-
10
20
308 342 900
51
2
* Ton – thermal degradation onset temperature, Tmax – maximum weight loss temperature, Tend – final thermal
degradation temperature
The thermal curves of the Pd(II) complexes are similar, except for 10. The results show that
the samples decompose in one stage for complexes 6-9. On the other hand, for 10, two
decomposition stages are observed. From Table 4, the thermal stabilities of the Pd(II)
complexes increase as follows: 10 < 7 < 9 = 8 < 6.
3.4. Catalysis

In this study, we also investigated the synthesized Pd(II) complexes as catalysts for the
oxidation reaction of benzyl alcohol to benzaldehyde. For this purpose, identical conditions of
a published work [14] were chosen to allow a direct comparison of the results. In a typical
reaction, a test tube filled with an acetonitrile (5 ml) solution of benzyl alcohol (1 mmol),
H5IO6 (1mmol) and the Pd(II) complex (0.01 mmol) was heated at reflux under open air.
Under these conditions, benzaldehyde was formed as the only product, according to GC and
TLC results. As a result, the synthesized complexes are good catalysts for the oxidation of
benzyl alcohol to benzaldehyde (Table 5). The catalytic efficiency is easily affected by ligand
substitution. Electron donating groups increase the oxidation of benzyl alcohol to
benzaldehyde under the studied conditions. Moreover, a sterically hindered group (2,4,6-
trimethyl) decreases the catalytic activity of the catalyst.
Table 5. The oxidation of benzyl alcohol to benzaldehyde using the Pd(II) complexes as
catalysts
Yieldd [%]
Entry
Catalyst
TOFe (h-1)
a
b
C
1
2
3
4
5
73 79 87
78 86 93
75 82 88
83 95 100
65 76 81
146a
156a
150a
166a
130a
6
7
8
9
10
Absence of
catalyst
6
<3b
n.c.b
a : 30 minutes, b : 60 minutes, c : 120 minutes, d : GC yields, yields are based on benzaldehyde,
e: TOF= moles of product/(moles of catalyst) x (hour), n.c.= not calculated.
Reaction conditions: 1.0 mmol of benzyl alcohol, 1.0 mmol of H5IO6, 0.01 mmol of Pd(II)
complexes, CH3CN (5 mL), under reflux conditions.
4. CONCLUSION

In this work, we have synthesized a series of Pd(II) complexes bearing pyridyl-sulfonamide
ligands, and we have characterized them by different techniques. Also, the thermal behaviour
of the Pd(II) complexes was investigated. Thermal curves showed that these complexes are
thermally stable up to ca. 200 °C. Moreover, their catalytic efficiency was tested for the
oxidation reaction of benzyl alcohol to benzaldehyde. Catalytic experiments showed the
Pd(II) complexes 6-10 are good catalysts for the oxidation of benzyl alcohol to benzaldehyde.
The results indicate that their catalytic efficiency depends significantly on the ligand
properties. Electron donating groups increase the catalytic efficiency of the Pd(II) complexes
towards the oxidation of benzyl alcohol to benzaldehyde under the studied conditions.
Supplementary Information
CCDC 929522 contains the supplementary crystallographic data (excluding structure
factors) for compound 6 reported in this article. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
We acknowledge the Faculty of Arts and Sciences, Ondokuz Mayıs University, Turkey, for
the use of the STOE IPDS II diffractometer (purchased under grant No. F-279 of the
University Research Fund). We thank Prof. İsmet Kaya for thermal analyses.
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Scheme 1

Graphical Abstract
O
OH
1 mol% Pd(II) complex
H5IO6
CH3CN

Graphical abstract
New palladium(II) complexes have been synthesized from Pd(OAc)2 and bidentate pyridinyl-
sulfonamide ligands. The compounds were characterized by elemental analysis, TG, NMR, IR
and X-ray diffraction. Additionally, the synthesized Pd(II) complexes were tested as catalysts
for the oxidation of benzyl alcohol to benzaldehyde.